Solar cascade-driven thermal-membrane-interface evaporation coupled brackish water desalination system and method

Abstract

The application discloses a solar step-by-step driving heat-film-interface evaporation coupling brackish water desalination system and method, and belongs to the field of solar brackish water desalination. The system comprises a CPC light-concentrating heat-collecting-gradient foam metal heat and mass transfer heat method desalination subsystem, a heat-film-natural interface evaporation coupling desalination subsystem, a spraying interface evaporation desalination subsystem and a power supply and control subsystem. The CPC light-concentrating heat-collecting subsystem converts solar radiation energy into high-temperature steam, the condensation heat released by steam condensation heats brackish water in a film hot side heat recovery tank, and drives membrane distillation and natural interface evaporation; the sensible heat released by condensation fresh water cooling is preheated for aeration air after being recovered by a phase change heat storage unit; the spraying interface evaporation desalination subsystem is intermittently operated during the day, and desalination brackish water with residual heat is carried out after sunset. Through light-heat-electricity-cold multi-energy field collaborative conversion and step-by-step utilization, solar independent efficient driving brackish water desalination, zero fossil energy consumption and high-yield operation are realized.

Description

Technical Field

[0001] This invention relates to the field of solar-powered brackish water desalination technology, specifically to a system and method that couples four desalination methods—solar thermal method, membrane distillation, natural interfacial evaporation, and spray interfacial evaporation—in a cascade manner. Background Technology

[0002] Solar-powered brackish water desalination technology is an important approach to solving the problem of freshwater shortage in areas with abundant brackish water and solar energy resources. It mainly includes three forms: thermal methods, membrane distillation, and interfacial evaporation, but all have drawbacks. (1) Although thermal desalination (such as CPC concentrator-vacuum tube evaporation) can produce high-temperature and high-pressure steam, it still has the following shortcomings: the heat of condensation of high-temperature and high-pressure steam cannot be recovered and utilized in a high proportion in traditional systems; at the same time, vaporization is limited to the two-dimensional surface of the smooth tube wall, the heat transfer efficiency is limited, and the bubble nucleation rate is low. (2) Although membrane distillation can operate at lower temperatures, the transmembrane temperature difference driving force is low and unstable, and membrane fouling is a prominent problem, both of which can lead to a decrease in membrane flux. In addition, the heat source on the membrane heat side usually relies on traditional energy supply or auxiliary, which limits its independent application in solar-driven scenarios; (3) Although the interface evaporation has a simple structure, it has problems such as steam condensation affecting light transmission and salt crystallization easily occurring at the evaporation interface, making it difficult to operate continuously and stably.

[0003] To address the aforementioned issues, researchers have explored multi-form coupled desalination. Patent application CN202010989399.6 discloses a solar thermal film coupled multi-effect desalination device and method, coupling CPC concentrated solar evaporation with membrane distillation, which features condensation heat recovery. However, it only involves two forms: thermal and membrane distillation, neglecting natural interface evaporation and spray interface evaporation, as well as the recovery and utilization of sensible heat from condensate, and methods to enhance heat and mass transfer such as gradient foam metal, aeration, semiconductor thermal migration cooling, and three-stage preheating of aeration air. Furthermore, existing research has explored desalination technologies coupled with thermoelectric cooling and membrane distillation, and membrane distillation and interface evaporation, but these are all limited to simple combinations of two or three desalination forms, failing to form a complete energy cascade utilization chain and the synergistic conversion of light-heat-electricity-cooling multi-energy fields.

[0004] Therefore, existing technologies have not yet disclosed a technical solution for integrating four desalination methods—solar thermal method, membrane distillation, natural interface evaporation, and spray interface evaporation—into the same system, and for using enhanced heat and mass transfer, synergistic conversion of light-heat-electricity-cooling multi-energy fields, and energy cascade utilization to achieve independent and efficient solar-driven brackish water desalination. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a solar-driven cascade-driven thermal-membrane-interface evaporation coupled brackish water desalination system and method. The core concept is to achieve all-weather, high-efficiency water production under zero fossil fuel replenishment conditions by using a multi-energy field synergistic conversion design of light, heat, electricity, and cold, following a thermal energy grade decreasing path of "high temperature-medium temperature-low temperature".

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A solar-driven cascaded thermal-film-interface evaporation coupled brackish water desalination system is provided, comprising a CPC concentrating solar collector-gradient foam metal heat and mass transfer thermal desalination subsystem, a thermal-film-natural interface evaporation coupled desalination subsystem, a spray interface evaporation desalination subsystem, and a power supply and control subsystem. The steam output end of the CPC concentrating heat collection-gradient foam metal heat and mass transfer desalination subsystem is connected to the inlet of the spiral condensation-heat recovery copper pipe in the heat-film-natural interface evaporation coupling desalination subsystem through a high-temperature and high-pressure steam discharge main pipe. The outlet of the spiral condensation-heat recovery copper pipe is connected to the inlet of the sensible heat recovery channel in the center of the condensation waste heat recovery-air reheat phase change thermal storage unit. The outlet of the sensible heat recovery channel is connected to the heat-film-natural interface evaporation coupling freshwater tank through a thermal water production recovery branch pipe. The brackish water manifold of the CPC concentrating heat collection-gradient foam metal heat and mass transfer desalination subsystem is connected to the side outlet of the liquid level control storage tank and the spray main of the spray interface evaporation desalination subsystem via a brackish water electric three-way valve, forming an automatically switchable water replenishment path and spray water supply path. The thermal-membrane-natural interface evaporation coupled desalination subsystem includes a membrane thermal side heat recovery tank and a natural interface evaporation forced condensation-preheating chamber located above it. The bottom outlet of the membrane thermal side heat recovery tank is connected to the spray main pipe via an electric two-way valve. A hydrophobic ceramic membrane is embedded in the vertical wall of the membrane thermal side heat recovery tank facing due south. A membrane cold side semiconductor refrigeration condensation-aeration enhancement air preheating integrated unit is attached to the cold side of the hydrophobic ceramic membrane. The bottom of the membrane distillation cold chamber in the membrane cold side semiconductor refrigeration condensation-aeration enhancement air preheating integrated unit is connected to the thermal-membrane-natural interface evaporation coupled desalination tank via a membrane permeate recovery branch pipe. The air outlet of the natural interface evaporation forced condensation-preheating chamber is connected to the air inlet of the semiconductor refrigeration heat recovery chamber in the integrated unit for air preheating for aeration enhancement in the membrane cold side semiconductor refrigeration condensation-aeration enhancement. The air outlet of the semiconductor refrigeration heat recovery chamber is connected in sequence to the inlet of the spiral blade guide-enhanced heat transfer type air reheating channel, the secondary flow fan and the gas-liquid mixing pipe of the condensation waste heat recovery-air reheating phase change heat storage unit. The spray interface evaporation desalination subsystem's spray interface evaporation desalination water collection pipe is connected to the spray interface evaporation desalination water tank, and the bottom return water outlet is connected to the brackish water pool. Both the heat-film-nature interface evaporation coupling freshwater tank and the spray interface evaporation freshwater tank are equipped with an atmospheric connection and a water intake pipe with a water intake pump. The power supply and control subsystem is electrically connected to each power component, electric valve and sensor through power cables, and communicates with each component through signal cables, and supplies power to each electrical component.

[0007] Furthermore, the CPC concentrating solar collector-gradient foam metal heat and mass transfer desalination subsystem includes: CPC condenser lens has a transparent white glass cover with a self-cleaning coating on its light-receiving surface. A glass-metal vacuum tube, located at the focal line of the CPC condenser lens, is divided into an evaporation zone and a brackish water zone along its length. The steam outlet of the glass-metal vacuum tube is connected to the high-temperature and high-pressure steam discharge main pipe via a high-temperature and high-pressure steam manifold. The brackish water inlet / outlet is connected to a brackish water electric three-way valve via the brackish water manifold. The brackish water electric three-way valve is a three-position three-way reversing valve, which connects the water level control storage tank to the water supply level of the glass-metal vacuum tube, the water level control storage tank to the spray main pipe, and the vacuum tube to the spray main pipe. A gradient foam metal heat and mass transfer core is disposed inside the glass-metal vacuum tube; The liquid level control water storage tank has one side outlet that goes through a check valve and a brackish water electric three-way valve to the bottom of the glass-metal vacuum tube via a brackish water manifold, and another outlet that goes through a liquid level control pipeline check valve and an electric two-way valve to the membrane thermal side heat recovery tank, which is used to simultaneously replenish water to the glass-metal vacuum tube and the membrane thermal side heat recovery tank.

[0008] Furthermore, the gradient foam metal heat and mass transfer core is an integrated foam metal structure, with its outer wall surface in close contact with the inner wall surface of the glass-metal vacuum tube. From the outer wall surface radially inward from the center, there are brackish water supply layer, phase change backbone layer and steam escape layer. The pore size and porosity of the three layers increase sequentially, and the thickness of the phase change backbone layer is greater than the thickness of the steam escape layer, and the thickness of the steam escape layer is greater than the thickness of the brackish water supply layer. The end of the gradient foam metal heat and mass transfer inner core is provided with a connection-positioning metal head that is threadedly connected to a glass-metal vacuum tube.

[0009] Furthermore, the integrated air preheating unit for membrane cold-side semiconductor refrigeration condensation-aeration enhancement includes, from the membrane cold side outwards: The membrane distillation cold chamber has inclined cooling and condensation fins arranged inside the semiconductor refrigeration chip on the cold side of the membrane. The bottom surface of the membrane distillation cold chamber is an inclined flow guide wall, and the center of the lowest edge of the inclined flow guide wall is connected to the membrane permeate recovery branch pipe. Film cold-side semiconductor refrigeration chip; The semiconductor cooling heat recovery chamber is equipped with a heat-side enhanced heat recovery fan and an air preheating vertical pipe for enhanced aeration. The outer surface of the vertical pipe is provided with downward-sloping porous fins for enhanced air preheating and heat transfer. The gas-liquid mixing pipe is provided with enhanced heat transfer aeration holes and enhanced mass transfer aeration holes. The enhanced heat transfer aeration holes are located at the spiral center of the spiral condensation-heat recovery copper pipe, and the enhanced mass transfer aeration holes are located near the hot side of the hydrophobic ceramic film. The outlet of the secondary flow fan is connected to the air inlet of the throat of the Venturi pressure reducing pipe via a pipeline. The heated brackish water flows in from the inlet of the Venturi pressure reducing pipe. When it flows through its throat, the flow velocity increases, forming a low-pressure zone. It draws in the reheated air flowing in through the air inlet and increases its speed. After the gas and liquid phases are mixed, they enter the gas-liquid mixing pipe. The gas-liquid two-phase flow output from the enhanced heat transfer aeration holes and enhanced mass transfer aeration holes simultaneously enhances the condensation heat transfer and membrane distillation mass transfer performance, and suppresses membrane fouling.

[0010] Furthermore, the condensation waste heat recovery-air reheat phase change thermal storage unit is a cylindrical tank, and its interior is arranged radially from the center outwards as follows: The sensible heat waste heat recovery channel is equipped with downwardly inclined and staggered flow damping type enhanced heat transfer ribs inside, which are used to receive and cool the condensed fresh water from the spiral condensation-heat recovery copper tube. The phase change thermal storage material filling area is fitted outside the sensible heat waste heat recovery channel. Its inner and outer walls are provided with horizontally staggered reinforced heat transfer porous fins for storing phase change thermal storage material. The spiral-bladed air reheating channel with enhanced heat transfer is fitted outside the phase change thermal storage material filling area and has spiral-shaped guide vanes inside, which are used to reheat the aeration air flowing through it using the heat released by the phase change thermal storage material.

[0011] Furthermore, the spray interface evaporation desalination subsystem also includes: A spray booster pump is located upstream of the main spray pipe; The spray interface evaporation chamber is equipped with a spray branch pipe group, an inclined photothermal-photovoltaic integrated spray evaporation interface located below the spray branch pipe group, and a spray interface evaporation waste water recovery port located downstream of the lowest point of the inclined photothermal-photovoltaic integrated spray evaporation interface; the top of the spray interface evaporation chamber is equipped with a spray interface evaporation forced convection heat exchange channel. The bottom surface of the inclined photothermal-photoelectric integrated spray evaporation interface is also provided with a spray interface evaporation electric heating plate, a lower ultrasonic transducer, and an upper ultrasonic transducer.

[0012] Furthermore, the power supply and control subsystem includes: Off-grid photovoltaic power generation system, which includes photovoltaic array, energy storage battery pack and charge / discharge control-inverter integrated unit; Power supply and control integrated unit; Sensors, including temperature sensors, flow sensors, and level sensors; The temperature sensors include a temperature sensor in the membrane thermal side heat recovery tank, an ambient temperature sensor, a temperature sensor for the tilted cooling condenser fins, and a temperature sensor for the tilted photothermal-photoelectric integrated spray evaporation interface; the flow sensors include a flow sensor for the reheated air diversion branch and a flow sensor for the heated brackish water diversion branch; the liquid level sensors include a lower limit liquid level sensor and an upper limit liquid level sensor, which are respectively installed at the lower limit liquid level and the upper limit liquid level on the inner wall of the liquid level control storage tank.

[0013] Furthermore, the system also utilizes the heat of evaporation and condensation at the natural interface, the waste heat on the hot side of the semiconductor refrigeration chip, and phase change heat storage to form a three-stage preheating chain for the air used for aeration: The primary preheating path is as follows: ambient air is introduced into the natural interface evaporation forced condensation preheating chamber through the forced condensation preheating fan, and then flows out through the natural interface evaporation preheating air duct to complete the primary preheating of the air for aeration. The secondary preheating path is as follows: the air preheated in the primary stage flows through the aeration enhancement air preheating vertical pipe in the semiconductor cooling heat recovery chamber to complete the secondary preheating of the aeration air; The three-stage reheating path is as follows: the air preheated in the second stage flows through the spiral blade guide of the condensation waste heat recovery-air reheat phase change heat storage unit-enhanced heat transfer type air reheating channel to complete the three-stage reheating of the aeration air. The aeration air preheated in the three stages is finally delivered to the gas-liquid mixing pipe after being accelerated by the secondary flow fan.

[0014] A solar-driven, cascade-driven, heat-film-interface evaporation coupled brackish water desalination method, implemented through any of the aforementioned systems, divides the system operation into four standard modes: M1 mode is the stage with sufficient condensation heat recovery; M2 mode is the stage with insufficient condensation heat recovery; M3 mode is the stage of low-temperature waste heat spray evaporation; and M4 mode is the standby stage with minimum power consumption. The method includes the following steps: S1: After sunrise, when the output voltage of the photovoltaic array reaches the start-up threshold, the power supply and control subsystem sends a system wake-up signal, the water replenishment pump is powered on, the brackish water electric three-way valve switches to the water replenishment path, the electric two-way valve between the liquid level control water storage tank and the membrane thermal side heat recovery tank is opened, and the brackish water enters the glass-metal vacuum tube and the membrane thermal side heat recovery tank respectively until the liquid levels at both places reach the upper limit liquid level, and the initial liquid level is established. S2: CPC concentrator focuses solar radiation energy. The brackish water in the glass-metal vacuum tube continuously absorbs heat and heats up to generate high-temperature steam. After the steam accumulation pressure reaches the preset external delivery pressure threshold, the high-temperature and high-pressure steam flows spontaneously through the high-temperature and high-pressure steam manifold and the high-temperature and high-pressure steam discharge main pipe in sequence, and is transported to the spiral condensation-heat recovery copper tube to complete the condensation and heat release. The latent heat of condensation is simultaneously transferred to the brackish water in the membrane heat recovery pool. S3: When the average temperature of the brackish water in the membrane heat recovery tank continuously rises to 55℃, the system enters the M2 mode. In this mode, the power supply and control subsystem controls the step-by-step activation of the brine circulation pump, forced condensation-preheating fan, heat-side enhanced heat recovery fan and secondary drainage fan, and adjusts the flow distribution deviation of each branch to less than 1%. The heat-membrane-natural interface evaporation coupling desalination operates efficiently, while the spray interface evaporation desalination subsystem operates intermittently. S4: The power supply and control subsystem continuously monitors the liquid level in the liquid level control storage tank. When the lower limit liquid level sensor is triggered, the water supply pump is powered on, and the brackish water electric three-way valve switches to the water supply path. The brackish water enters the glass-metal vacuum tube and the membrane heat recovery pool through the liquid level control storage tank. When the upper limit liquid level sensor is triggered, the water supply pump is powered off, and the brackish water electric three-way valve switches to the spray path on the liquid level control storage tank side. The liquid level drops due to the consumption of thermal desalination, spray interface evaporation, membrane distillation and natural interface evaporation. After dropping to the lower limit liquid level, the brackish water electric three-way valve switches back to the water supply path, and the liquid level oscillates between the upper and lower limit liquid levels. S5: When the average temperature of the brackish water in the membrane thermal side heat recovery tank further increases to 65°C or above, it indicates that the condensation recovery heat is sufficient, and the system naturally transitions to the M1 mode. In this mode, the pipeline-type saline electric heater is kept off, the brackish water electric three-way valve alternately switches between the water supply passage and the spray passage on the liquid level control water storage tank side, the electric two-way valve between the liquid level control water storage tank and the membrane thermal side heat recovery tank is kept open to maintain the water supply passage on this side, the thermal-membrane-natural interface evaporation coupling desalination operates efficiently, and the spray interface evaporation desalination subsystem operates intermittently. S6: As the solar radiation energy input to the system decreases, the amount of condensation heat supply to the system also decreases. When the average temperature of the brackish water in the membrane heat recovery tank drops below 65°C, the system naturally transitions to mode M2. In this mode, the equipment already in operation in mode M1 remains powered on. When the average temperature of the brackish water in the tank is above 55°C, the pipeline-type brine electric heater remains powered off. When the average temperature of the brackish water in the tank drops to 55°C, the pipeline-type brine electric heater is powered on. When the tank temperature rises back to above 65°C, the system naturally transitions to mode M1. S7: When the output voltage of the photovoltaic array is lower than the shutdown threshold, the average temperature of the membrane thermal side heat recovery pool drops to 45℃ and the state of charge of the energy storage battery pack is greater than 30%, the power supply and control subsystem performs an active switch from M2 to M3, de-energizing the membrane cold side semiconductor refrigeration chip, the thermal side enhanced heat recovery fan, the secondary flow fan, and the brine circulation pump, and delaying the de-energizing of the forced condensation-preheating fan, closing the electric double-way valve between the liquid level control water tank and the membrane thermal side heat recovery pool, switching the brackish water electric three-way valve to the vacuum tube side spray passage, opening the electric double-way valve at the bottom of the membrane thermal side heat recovery pool, and sequentially energizing and putting into operation the spray pressurization pump, electric heating plate, lower ultrasonic transducer, upper ultrasonic transducer, and forced convection drive fan of the spray interface evaporation desalination condensation link, so as to introduce the brackish water with residual heat from the glass-metal vacuum tube and the membrane thermal side heat recovery pool into the spray interface evaporation chamber for desalination; S8: If there is residual brackish water with residual heat in the heat recovery tank of the glass-metal vacuum tube or membrane heat side, or if the automatic cleaning process of the gradient foam metal heat and mass transfer core has not been completed, but the state of charge of the energy storage battery pack is less than 30%, the lower ultrasonic transducer, the upper ultrasonic transducer, the forced convection drive fan of the spray interface evaporation desalination and condensation link will be turned off, while the spray pressurization pump and the spray interface evaporation electric heating plate will remain on. The system will operate inefficiently in M3 mode. S9: When all the brackish water with residual heat in the glass-metal vacuum tube and the membrane thermal side heat recovery tank is exhausted and the glass-metal vacuum tube is cleaned, or when the state of charge of the energy storage battery pack drops to 20%, the power supply and control subsystem will de-energize the spray pressurization pump, electric heating plate, lower ultrasonic transducer, upper ultrasonic transducer and forced convection drive fan of the spray interface evaporation desalination and condensation link, switch the brackish water electric three-way valve to the water replenishment channel, close the electric two-way valve at the bottom of the membrane thermal side heat recovery tank, and switch the system from M3 mode to M4 mode, waiting for the wake-up signal the next day.

[0015] Furthermore, during the initial startup of the M3 mode, the automatic cleaning of the gradient foam metal heat and mass transfer core is performed simultaneously. The cleaning return water enters the spray main pipe and participates in the spray interface evaporation and desalination process together with the water from the vacuum tube and the membrane heat recovery tank, so as to recover and utilize the waste heat carried by the cleaning wastewater. Cleaning water supply path: The water supply pump draws water from the brackish water tank, and delivers it through the cleaning check valve and the cleaning water supply pipe to the cleaning pipeline connection port of the connecting-positioning metal head, rinsing the gradient foam metal heat and mass transfer inner core from top to bottom. Cleaning drainage path: The cleaning return water flows out from the bottom of the glass-metal vacuum tube, passes through the brackish water manifold and the vacuum tube side spray passage of the brackish water electric three-way valve, enters the spray main pipe, and is then sprayed to the evaporation interface of the spray interface evaporation chamber.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By constructing a CPC concentrator-vacuum tube thermal distillation, membrane distillation, natural interface evaporation, and spray interface evaporation coupled desalination system, a solar-powered cascaded high-efficiency brackish water desalination system is achieved. After sunlight is focused by the CPC concentrator, it undergoes photothermal conversion at the heat-absorbing surface of the glass-metal vacuum tube, driving the production of high-temperature steam (high-temperature thermal energy utilization). The latent heat of condensation of the high-temperature steam drives membrane distillation and natural interface evaporation desalination (medium-temperature thermal energy utilization). The natural interface evaporation condensation recovers heat, waste heat from the hot side of the semiconductor refrigeration chip, and sensible heat from the condensed freshwater for three-stage preheating and aeration enhancement of air (low-temperature thermal energy utilization). The brackish water with residual heat generated from membrane distillation, thermal desalination, and core cleaning is used for spray interface evaporation (low-temperature thermal energy utilization). The entire energy utilization chain is matched step by step from high temperature to low temperature, with no step waste, and the solar energy utilization rate is significantly improved compared to single technologies. 2. The gradient foam metal heat and mass transfer core features a three-layer gradient pore structure: a supply layer for strong gripping, a main layer for efficient vaporization and low-resistance transport, and an escape layer for smooth exhaust. This structure expands the phase change space from a two-dimensional interface to a three-dimensional porous interface. Heat is rapidly transferred along the three-dimensional network through the high thermal conductivity foam metal skeleton, resulting in a significant improvement in effective heat exchange area and evaporation intensity per unit volume compared to traditional structures. The three-layer gradient pore design overcomes the technical contradiction of traditional foam metals in balancing capillary pumping liquid supply and smooth vapor escape, ensuring that the vaporization surface is always covered by liquid under high heat flux density, eliminating problems such as local drying, burning, and "vapor lock". 3. A membrane distillation system with enhanced aeration and semiconductor refrigeration was constructed. By arranging enhanced heat transfer aeration holes and enhanced mass transfer aeration holes in separate zones, on the one hand, semiconductor refrigeration actively reduces the temperature on the cold side of the membrane to increase the driving force of the transmembrane temperature difference; on the other hand, aeration disturbance on the hot side of the membrane suppresses membrane fouling. The membrane flux is improved simultaneously from two dimensions: driving force and membrane fouling control, resulting in a significant improvement in membrane distillation efficiency. At the same time, the waste heat on the hot side of the semiconductor refrigeration chip is recovered through the preheating riser in the heat recovery chamber and used for secondary preheating of the aeration air, realizing a positive cycle of "refrigeration power consumption - increased transmembrane temperature difference - waste heat recovery and preheating of aeration air - further improvement in membrane flux". 4. A three-stage preheating chain for aeration air was established, connecting the evaporation and condensation heat of the natural interface, the waste heat on the hot side of the semiconductor refrigeration chip, and the phase change heat storage into a unidirectional energy transfer chain. This allows the aeration inlet temperature to be gradually increased from the ambient temperature to above 50℃ (first-stage preheating 30-40℃, second-stage preheating 40-50℃, and third-stage reheating above 50℃). This effectively reduces the negative impact of low-temperature aeration on the temperature of brackish water in the membrane heat recovery tank, while also improving the mass transfer efficiency of the membrane distillation process. 5. The switching logic between water replenishment in metal-glass vacuum tubes and desalination through spray interface evaporation, as well as the dual-mode operation strategy of daytime photovoltaic-thermal complementary drive for spray interface evaporation and nighttime energy storage battery group drive for spray interface evaporation with waste heat brackish water, have further improved the utilization rate of solar energy and the overall water production. Attached Figure Description

[0017] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 (a) is a schematic diagram of the CPC concentrating solar collector-gradient foam metal heat and mass transfer structure. Figure 2 (b) is a sectional view at point AA; Figure 3 This is a schematic diagram of a local structure of thermal-film-nature interface evaporation coupling; Figure 4 Schematic diagram of a phase change thermal energy storage unit for condensation waste heat recovery and air reheating; Figure 5 This is a schematic diagram of the spray interface evaporation desalination subsystem. Figure 6 This is a schematic diagram of the power supply and control subsystem.

[0018] In the diagram: Ⅰ-CPC concentrating solar collector-gradient foam metal heat and mass transfer desalination subsystem, Ⅱ-thermal-film-natural interface evaporation coupled desalination subsystem, Ⅲ-spray interface evaporation desalination subsystem, Ⅳ-power supply and control subsystem; 101-CPC Condenser Lens, 102-Transparent White Glass Cover Plate, 103-Glass-Metal Vacuum Tube, 104-Gradient Foam Metal Heat and Mass Transfer Core, 1041-Connecting and Positioning Metal Head, 1042-Steam Channel, 1043-Steam Escape Layer, 1044-Phase Change Main Layer, 1045-Brackish Water Replenishment Layer, 105-High Temperature and High Pressure Steam Manifold, 106-High Temperature and High Pressure Steam Exhaust Main Pipe, 107-Brackish Water Manifold, 1 08-Brackish water electric three-way valve, 109-Level control water storage tank, 110-Level control pipeline check valve, 111-Water supply pipe, 112-Water supply pump, 113-Overflow pipe, 114-Upper limit level sensor, 115-Lower limit level sensor, 116-Upper limit level, 117-Lower limit level, 118-Electric shut-off valve for cleaning, 119-Check valve for cleaning, 120-Water supply pipe for cleaning, 121-Cleaning manhole; 201- Spiral condenser-heat recovery copper tube; 202- Hydrophobic ceramic membrane; 203- Membrane distillation cold chamber; 204- Inclined cooling condenser fins; 205- Inclined flow guide wall; 206- Membrane cold-side semiconductor refrigeration chip; 207- Semiconductor refrigeration heat recovery chamber; 208- Hot-side enhanced heat recovery fan; 209- Air preheating enhanced heat transfer porous fins; 210- Membrane-based product water recovery branch pipe; 211- Membrane-natural interface evaporation product water recovery branch pipe; 212- Heat-membrane-natural interface evaporation product water recovery main pipe; 213- 214-Condensation waste heat recovery-air reheat phase change thermal storage unit; 215-Spiral finned flow guide-enhanced heat transfer type air reheat channel; 216-Phase change thermal storage material filling area; 217-Flow damping type enhanced heat transfer inclined fins; 218-Staggered arrangement type enhanced heat transfer porous fins; 219-Gas-liquid mixing pipe; 220-Enhanced heat transfer aeration hole; 221-Enhanced mass transfer aeration hole; 222-Secondary drainage fan; 223-Venturi pressure reducing pipe; 224-Air two-way electric valve; 225-Including... Brine circulation pump; 226-Brackish water double-way electric valve; 227-Pipeline brine electric heater; 228-Natural interface evaporation condensation - translucent white glass; 229-Natural interface evaporation translucent white glass; 230-Natural interface evaporation forced condensation - preheating chamber; 231-Natural interface evaporation preheating air duct; 232-Forced condensation - preheating fan; 233-Natural interface evaporation freshwater collection tank; 234-Natural interface evaporation freshwater recovery branch pipe; 235-Pipeline air heater; 236-Phase change material exhaust fan. 237-Hot air electric three-way valve, 238-Phase change material discharge pipe, 239-Insulation layer with electric heat tracing, 240-Liquid phase change thermal storage material injection pipe, 241-Funnel-shaped phase change thermal storage material electric heating plate, 242-Phase change thermal storage material melting-filling tank, 243-Solid phase change thermal storage material injection port, 244-Lower limit liquid level on the membrane thermal side, 245-Upper limit liquid level on the membrane thermal side, 246-Atmospheric connection and water intake pipe, 247-Membrane thermal side heat recovery tank, 248-Heat-membrane-natural interface evaporation coupling freshwater tank; 301-Spray pressurization pump, 302-Spray main pipe, 303-Spray branch pipe, 304-Spray nozzle, 305-Inclined integrated photothermal and photoelectric spray evaporation interface, 306-Spray interface evaporation electric heating plate, 307-Lower ultrasonic transducer, 308-Upper ultrasonic transducer, 309-Spray interface evaporation forced convection heat exchange channel, 310-Spray interface evaporation translucent-condensing double-layer white glass top cover, 311-Spray interface evaporation freshwater collection tank, 312-Spray interface evaporator Freshwater collection pipe; 313-Spray interface evaporation and condensation air inlet; 314-Spray interface evaporation desalination and condensation forced convection drive fan; 315-Spray interface evaporation maintenance door; 316-Electromagnetic self-priming lock; 317-Maintenance door opening and closing rotary motor; 318-Horizontal maintenance door limiter; 319-Replaceable spray interface evaporation return water filter; 320-Drain pipe; 321-Spray interface evaporation chamber; 322-Brackish water tank; 323-Spray interface evaporation freshwater tank. 401-Photovoltaic array, 402-Energy storage battery pack, 403-Charging and discharging control-inverter integrated machine. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] I. Subsystem Implementation Details and Operation Process like Figure 1 As shown, this embodiment provides a solar-driven cascaded thermal-film-interface evaporation coupled brackish water desalination system, including a CPC concentrating and collecting heat-gradient foam metal heat and mass transfer thermal desalination subsystem I, a thermal-film-natural interface evaporation coupled desalination subsystem II, a spray interface evaporation desalination subsystem III, and a power supply and control subsystem IV. It utilizes the synergistic conversion of light-heat-electricity-cooling multi-energy fields to achieve diversified utilization of solar energy. The solar energy is utilized in a cascaded manner through CPC concentrating, glass-metal vacuum tube photothermal conversion, gradient foam metal high-efficiency thermal desalination (high-temperature thermal energy utilization), hydrophobic ceramic membrane 202 distillation desalination (medium-temperature thermal energy utilization), natural interface evaporation desalination (medium-low temperature thermal energy utilization), and spray interface evaporation desalination (low-temperature thermal energy utilization).

[0022] Specifically, the steam output end of subsystem I is connected to the inlet end of the spiral condenser-heat recovery copper pipe 201 via the discharge main pipe 106, the outlet end of the spiral condenser-heat recovery copper pipe 201 is connected to the inlet of the sensible heat recovery channel in the center of the condenser waste heat recovery-air reheat phase change heat storage unit 214, and the outlet of the sensible heat recovery channel is connected to the thermal-film-natural interface evaporation coupling freshwater tank 248 via the thermal water production recovery branch pipe 213.

[0023] The brackish water manifold 107 of CPC concentrating solar collector-gradient foam metal heat and mass transfer desalination subsystem I is connected to the side outlet of the liquid level control storage tank 109 and the spray main pipe 302 of the spray interface evaporation desalination subsystem III via a brackish water electric three-way valve 108, forming an automatically switchable water replenishment path and spray path.

[0024] The thermal-membrane-natural interface evaporation coupled desalination subsystem II includes a membrane thermal side heat recovery tank 247 and a natural interface evaporation forced condensation-preheating chamber 230 located above it. The bottom outlet of the membrane thermal side heat recovery tank 247 is connected to the spray main pipe 302 via an electric two-way valve. A hydrophobic ceramic membrane 202 is embedded in the vertical wall of the membrane thermal side heat recovery tank 247 facing due south. A membrane cold side semiconductor refrigeration condensation-aeration enhancement air preheating integrated unit is attached to the cold side of the hydrophobic ceramic membrane 202. The bottom of the membrane distillation cold chamber 203 in this integrated unit is connected to the thermal-membrane-natural interface evaporation coupled desalination tank 248 via a membrane permeate recovery branch pipe 210.

[0025] The natural interface evaporation forced condensation-preheating chamber 230 is located at the top of the membrane heat recovery pool 247. Its air outlet is connected to the air inlet of the semiconductor refrigeration heat recovery chamber 207 via the natural interface evaporation preheating air duct 231. The air outlet of the semiconductor refrigeration heat recovery chamber 207 is connected to the inlet of the spiral blade guide-enhanced heat transfer type air reheating channel 215 of the condensation waste heat recovery-air reheating phase change heat storage unit 214 via a pipeline, and is connected in sequence to the secondary induced flow fan 222 and the gas-liquid mixing pipe 219. The spray interface evaporation freshwater collection pipe 312 is connected to the spray interface evaporation freshwater tank 323, and the bottom return water outlet of the spray interface evaporation chamber 321 is connected to the brackish water pool 322.

[0026] The power supply and control subsystem IV is electrically connected to each power component, electric valve and sensor through power cables, and is also connected for communication through signal cables, and supplies power to each electrical component.

[0027] The specific implementation methods of each subsystem are described below.

[0028] 1. CPC Concentrating Solar Collector-Gradient Foam Metal Heat and Mass Transfer Desalination Subsystem I This subsystem realizes solar concentrating photothermal conversion and three-dimensional efficient heat and mass transfer. It inputs solar radiation energy and normal temperature brackish water, and outputs thermal water production, high temperature and high pressure steam condensation heat recovery, brackish water with waste heat and washing return water. It belongs to the highest temperature energy utilization level of solar cascade driven brackish water desalination.

[0029] like Figure 1 and 2 As shown, the subsystem includes a CPC condenser lens 101, a glass-metal vacuum tube 103 with an internally threaded head, a gradient foam metal heat and mass transfer core 104, and a liquid level control water storage tank 109, etc. Specific implementation details are as follows: (1) Implementation details of each component of Subsystem I In this embodiment, the CPC concentrator 101 is a tracking-free solar concentrator that faces due south and is installed at an angle to the local latitude. Preferably, its concentration ratio is 4 to 8, and a transparent white glass cover plate 102 with a self-cleaning coating is provided at the opening of the light-receiving surface to prevent dust accumulation on the reflector and reduce heat loss.

[0030] A glass-metal vacuum tube 103 with an internally threaded head is positioned at the focal line of the CPC condenser lens 101. Its steam outlet is connected to the high-temperature, high-pressure steam discharge main pipe 106 via a high-temperature, high-pressure steam manifold 105. The brackish water inlet / outlet at its lower part is connected to a brackish water electric three-way valve 108 via a brackish water manifold 107. The glass-metal vacuum tube 103 is divided into two functional zones along its length: an evaporation zone and a brackish water zone. The interface is the dynamic liquid level within the level control zone between the upper limit liquid level 116 and the lower limit liquid level 117. The evaporation zone is located above the dynamic liquid level, accounting for 60-70% of the total length of the glass-metal vacuum tube 103, and belongs to the main evaporation and vaporization zone of brackish water. The brackish water zone is located below the dynamic liquid level, accounting for 30-40% of the total length of the glass-metal vacuum tube 103, and is used for preheating, liquid storage, and salt buffering. The level control zone accounts for 10% of the total length of the glass-metal vacuum tube 103.

[0031] The gradient foam metal heat and mass transfer core 104 is an integrated structure comprising a threaded connecting and positioning metal head 1041, a steam channel 1042, a steam escape layer 1043, a phase change main layer 1044, and a brackish water supply layer 1045. From the outer wall surface along the center radially inward, the brackish water supply layer 1045, the phase change main layer 1044, and the steam escape layer 1043 are arranged in sequence. The pore size and porosity of the three layers increase sequentially, and the thickness of the phase change main layer 1044 is greater than the thickness of the steam escape layer 1043, and the thickness of the steam escape layer 1043 is greater than the thickness of the brackish water supply layer 1045. The high thermal conductivity of its foam metal skeleton (preferably copper-based or aluminum-based alloy) (the thermal conductivity of copper-based alloy is 200~300 W / (m•K)) enables heat to be transferred rapidly along the three-dimensional network, and the effective heat exchange area is increased by 15~20 times compared with smooth tubes. Preferably, the brackish water supply layer 1045 has a pore size range of 20~100μm, a thickness of 1.5mm, and a porosity of 55%, actively pumping brackish water upwards using strong capillary force; the phase change backbone layer 1044 has a pore size range of 150~250μm, a thickness of 6mm, and a porosity of 75%, providing a large liquid-vapor phase change area to significantly improve the vaporization rate of brackish water; the steam escape layer 1043 has a pore size range of 500~800μm, a thickness of 4mm, and a porosity of 85%, used for low-resistance discharge of high-temperature steam. A cleaning pipeline connection port and a cleaning electric shut-off valve 118 are provided between the threaded connection-positioning metal head 1041 and the high-temperature, high-pressure steam manifold 105 to limit the flow direction of the cleaning brackish water during the periodic cleaning process of the gradient foam metal heat and mass transfer inner core 104. The cleaning pipeline includes a water supply pump 112, a cleaning check valve 119, and a cleaning water supply pipe 120. After cleaning, the wastewater is discharged through a brackish water electric three-way valve 108 to the spray interface evaporation desalination subsystem III for interface evaporation desalination. The unevaporated residual water is eventually returned to the brackish water tank 322.

[0032] The bottom of the level control water storage tank 109 is connected to the brackish water tank 322 via a water supply pipe 111 and a water supply pump 112. One side outlet of the level control water storage tank 109 is connected to the brackish water zone of the glass-metal vacuum tube 103 via a water supply passage through a check valve and a brackish water electric three-way valve 108, and another outlet is connected to the membrane thermal side heat recovery tank 247 via a level control pipeline check valve 110 and an electric two-way valve, for synchronous water supply to the glass-metal vacuum tube 103 and the membrane thermal side heat recovery tank 247. An overflow port is provided on the side of the level control water storage tank 109 at the same height as the upper limit liquid level 116, and is connected to the overflow pipe 113 to the brackish water tank 322 to assist the upper limit liquid level sensor 115 in accurately controlling the upper limit liquid level 116. An upper limit level sensor 114 is installed on the inner wall of the level control water storage tank 109 at the same height as the upper limit level 116. This sensor provides a water replenishment stop signal to the power supply and control subsystem IV. A lower limit level sensor 115 is installed at the same height as the lower limit level 117. This sensor provides a water replenishment start signal to the power supply and control subsystem IV. The dynamic brackish water level in the glass-metal vacuum tube 103 and the membrane thermal side heat recovery tank 247 is maintained within the level control range between the upper limit level 116 and the lower limit level 117. One-way valves are installed in the pipelines connecting the level control water storage tank 109 to the brackish water manifold 107 and the membrane thermal side heat recovery tank 247 to prevent backflow of high-temperature brackish water from both sides. The top of the level control water storage tank 109 is equipped with an end cap with a cleaning manhole 121 for periodically cleaning sediment inside the tank. The working principle of the level control water storage tank 109 is as follows: when the lower limit level sensor 115 detects that the dynamic brackish water level coincides with the lower limit level 117, the power supply and control subsystem IV coordinates the brackish water electric three-way valve 108 and the water replenishment pump 112 to open the water replenishment channel and replenish water to the level control water storage tank 109; when the upper limit level sensor 114 detects that the dynamic brackish water level coincides with the upper limit level 116, the water replenishment channel is closed and water replenishment stops.

[0033] (2) Operation process of subsystem I From sunrise to sunset, sunlight enters through the light-receiving surface of the CPC condenser 101 and is reflected by the composite parabolic mirror before converging onto the outer surface of the metal tube (with a selective absorption coating) of the glass-metal vacuum tube 103 to complete photothermal conversion. Most of the heat generated after conversion is transferred sequentially to the inner surface of the metal tube, the brackish water supply layer 1045, and the phase change backbone layer 1044 via thermal conductivity. Simultaneously, when the dynamic brackish water level is higher than the lower limit level 117, the fine pores of the brackish water supply layer 1045 generate strong capillary forces (capillary head 5-8). (kPa) Liquid brackish water is actively drawn from the brackish water region to the entire three-dimensional porous heating surface. Combined with the large pore channels of the phase change main layer 1044, a synergistic liquid supply mode of "strong gripping of the replenishment layer, efficient vaporization of the main layer, and low-resistance transport" is formed. This ensures that the inner surface of the metal pipe, the brackish water replenishment layer 1045, and the phase change main layer 1044 are always covered by liquid under high heat flux density, ensuring efficient evaporation and vaporization of the brackish water and fundamentally eliminating the risk of local drying and burnout. After high-temperature steam is generated in the phase change main layer 1044, it immediately enters the large-pore steam escape layer 1043. The porosity is about 1.5 times higher than that of the replenishment layer, and the steam flow resistance is extremely low, allowing the vapor and liquid phases to flow separately, completely eliminating the "steam lock" problem of steam retention and blockage of liquid replenishment in traditional structures; the steam escape layer 1043 continuously supplies high-temperature steam to the steam channel 1042. When the high-temperature steam accumulation pressure reaches the preset external delivery pressure threshold, it is automatically transported to the high-temperature and high-pressure steam manifold 105, and flows through the high-temperature and high-pressure steam discharge main pipe 106 to the spiral condenser-heat recovery copper pipe 201 for condensation, while simultaneously transferring the latent heat of steam condensation to the brackish water in the membrane heat recovery pool 247.

[0034] After sunset, the power supply and control subsystem IV coordinates and regulates the electric double-way valve at the bottom of the membrane heat recovery tank, the water replenishment pump 112, the brackish water electric three-way valve 108, and the spray interface evaporation desalination subsystem III, etc., to start the synchronous operation mode of cleaning the gradient foam metal heat and mass transfer inner core 104 and spray interface evaporation desalination, so as to complete the inner core cleaning and low-temperature waste heat reuse.

[0035] 2. Thermal-film-natural interface evaporation coupled desalination subsystem II This subsystem employs aeration-enhanced heat and mass transfer and semiconductor refrigeration-induced thermal migration technology to achieve efficient recovery of heat from high-temperature, high-pressure steam condensation and promote efficient mass transfer in membrane distillation. The efficient recovery of heat from high-temperature, high-pressure steam condensation is achieved through aeration disturbance on the outer wall of the spiral condensation-heat recovery copper tube 201 and turbulent flow created by gas-liquid two-phase flow. The efficient mass transfer in membrane distillation is achieved through three enhancement methods: aeration disturbance on the hot side of the hydrophobic ceramic membrane 202 to enhance mass transfer / inhibit membrane fouling; semiconductor refrigeration on the cold side of the hydrophobic ceramic membrane 202 to increase the transmembrane temperature difference; and three-stage preheating of the aeration air to indirectly stabilize the hot-side temperature of the membrane. The subsystem inputs high-temperature, high-pressure steam condensation heat, photovoltaic power, ambient temperature brackish water, and ambient cold air; and outputs membrane-natural interface evaporation product water and brackish water with residual heat. It belongs to the low-to-medium temperature energy utilization stage of solar-driven brackish water desalination.

[0036] like Figure 3 and 4 As shown, the subsystem includes a membrane heat recovery tank 247, a spiral condensation-heat recovery copper tube 201, a hydrophobic ceramic membrane array 202, a membrane cold-side semiconductor refrigeration condensation-aeration enhancement air preheating integrated unit array, a natural interface evaporation forced condensation-preheating chamber 230, a condensation waste heat recovery-air reheating phase change thermal storage unit 214, an aeration enhancement heat and mass transfer unit, and a heat-membrane-natural interface evaporation coupled freshwater tank 248, etc. Specific implementation details are as follows: (1) Implementation details of each component of subsystem II The membrane heat recovery tank 247 is a rectangular tank that holds brackish water, which serves as the heat transfer medium for membrane distillation / natural interface evaporation and for high-temperature, high-pressure steam condensation heat recovery. The brackish water level is controlled within the level control zone. Temperature sensors are installed at high, medium, and low positions within the tank to monitor the average temperature of the brackish water.

[0037] A spiral condenser-heat recovery copper tube 201 is installed inside the membrane heating side heat recovery tank 247. High-temperature and high-pressure steam condenses and releases heat inside the tube, and the heat is transferred to the brackish water in the tank through the tube wall. The outlet of the spiral condenser-heat recovery copper tube 201 is connected to the inlet of the sensible heat recovery channel in the center of the condensation waste heat recovery-air reheat phase change thermal energy storage unit 214.

[0038] The hydrophobic ceramic membrane 202 array includes at least one sealed, embedded hydrophobic ceramic membrane 202 on the south-facing wall of the membrane hot-side heat recovery pool 247. The membrane is circular, with a diameter of 100-200 mm and a thickness of 3-5 mm.

[0039] The integrated unit for membrane-side semiconductor refrigeration condensation and aeration enhancement air preheating consists of, from the membrane cold side outwards, a membrane distillation cold chamber 203, a membrane cold-side semiconductor refrigeration chip 206, and a semiconductor refrigeration heat recovery chamber 207. Inclined cooling and condensing fins 204 are installed in the membrane distillation cold chamber 203, closely attached to the cold surface of the membrane cold-side semiconductor refrigeration chip 206. The bottom surface of the membrane distillation cold chamber 203 is an inclined guide wall 205, with the lower edge of the inclined guide wall 205 connected to the membrane permeate recovery branch pipe 210. The semiconductor refrigeration heat recovery chamber 207 houses a heat-side enhanced heat recovery fan 208 and an aeration enhancement air preheating vertical pipe. The outer surface of the vertical pipe has downward-sloping porous fins 209 for enhanced air preheating and heat transfer.

[0040] The natural interface evaporation forced condensation-preheating chamber 230 is located at the top of the membrane thermal side heat recovery tank 247 and is enclosed by natural interface evaporation condensation-transparent white glass 228 and natural interface evaporation transparent white glass 229. The bottom of the natural interface evaporation condensation-transparent white glass 228 is equipped with a natural interface evaporation desalination water collection tank 233, which passively collects the natural interface evaporation desalination product water under the combined action of gravity, surface tension, and adhesion, and flows into the natural interface evaporation desalination water recovery branch pipe 234. The natural interface evaporation desalination water recovery branch pipe 234 is connected to the membrane-natural interface evaporation product water recovery branch pipe 211, which is further connected to the thermal-membrane-natural interface evaporation product water recovery main pipe 212, ultimately flowing into the thermal-membrane-natural interface evaporation coupled desalination tank 248. The outlet of the natural interface evaporation forced condensation-preheating chamber 230 is connected to the inlet of the semiconductor refrigeration heat recovery chamber 207 via the natural interface evaporation preheating air duct 231.

[0041] The condensation waste heat recovery-air reheat phase change thermal energy storage unit 214 is a cylindrical tank. Its interior, arranged radially from the center outwards, includes a sensible heat recovery channel (circular horizontal cross-section), a phase change thermal energy storage material filling area 216 (annular horizontal cross-section), a spiral-bladed flow-enhanced heat transfer air reheat channel 215 (annular horizontal cross-section), and an external insulation wall. The sensible heat recovery channel contains downwardly inclined and staggered flow-damping enhanced heat transfer fins 217 to enhance heat transfer performance. The inner and outer walls of the phase change thermal energy storage material filling area 216 are equipped with horizontally arranged and vertically staggered porous fins 218, which not only enhance heat transfer performance but also ensure rapid downward flow of the liquid phase change thermal energy storage material, ultimately filling the phase change thermal energy storage material filling area 216. In this embodiment, the phase change thermal storage material filling area 216 is filled with paraffin-based phase change thermal storage material (preferably, industrial 52# paraffin with a melting point of 52-54°C and a latent heat of 180-220 J / g). The condensate temperature at the outlet of the spiral condensation-heat recovery copper pipe (201) is 55-65°C, which is higher than the melting point of paraffin, allowing the phase change material to fully absorb the sensible heat of the condensate and undergo solid-liquid phase change thermal storage during the day; after sunset or when solar radiation weakens, the phase change material solidifies and releases heat (the solidification point is slightly lower than the melting point), releasing the stored heat for the third-stage reheating of the aeration air (target temperature above 50°C). The spiral-bladed flow-enhanced heat transfer type air reheat channel 215 is equipped with spiral-bladed flow guides for flow guidance and uniform and efficient heat exchange. The top of the condensation waste heat recovery-air reheat phase change thermal energy storage unit 214 is connected to the phase change thermal energy storage material melting-filling tank 242 via a liquid phase change thermal energy storage material injection pipe 240. The liquid phase change thermal energy storage material injection pipe 240 is wrapped with an electrically heated insulation layer 239. The top of the phase change thermal energy storage material melting-filling tank 242 is provided with a solid phase change thermal energy storage material injection port 243 for filling solid phase change thermal energy. The bottom of the phase change thermal energy storage material melting-filling tank 242 is provided with a funnel-shaped phase change thermal energy storage material electric heating plate 241 for melting the phase change thermal energy storage material, ensuring that the phase change thermal energy storage material can be smoothly injected into the phase change thermal energy storage material filling area 216. The bottom of the condensation waste heat recovery-air reheat phase change thermal energy storage unit 214 is provided with a phase change material discharge port, which is connected to a phase change material electric double-way valve via a phase change material discharge pipe 238, and finally leads to the phase change thermal energy storage material recovery pool. The hot air electric three-way valve 237 is used to switch between the phase change thermal storage material discharge path and the aeration air path. During the phase change thermal storage material discharge stage, the hot air electric three-way valve 237 switches to the phase change thermal storage material discharge path. The phase change material discharge fan 236 (only activated during regular maintenance and linked with the hot air electric three-way valve 237) drives the air flow. The pipeline air heater 235 (not activated during the three-stage reheating stage of the aeration air) is energized to heat the air. The hot air flows in through the spiral vane guide-enhanced heat transfer type air reheating channel 215, so that the phase change thermal storage material in the phase change thermal storage material filling area 216 is completely melted and then discharged.During the aeration-enhanced heat and mass transfer stage, the hot air electric three-way valve 237 switches to the aeration air passage, and the condensation waste heat recovery-air reheat phase change heat storage unit 214 supplies the aeration-enhanced heat and mass transfer unit with three-stage reheated air.

[0042] The aeration-enhanced heat and mass transfer unit includes a secondary induced draft fan 222, an air dual-way electric valve 224, a Venturi pressure reducing pipe 223, a pipeline-type brine electric heater 227, a brine circulation pump 225, a brackish water dual-way electric valve 226, and a gas-liquid mixing pipe 219. The tertiary reheated air, after being accelerated by the secondary induced draft fan 222, is evenly distributed through the air dual-way electric valve 224 before flowing into the throat of the Venturi pressure reducing pipe 223. The brine circulation pump 225 drives the brackish water in the membrane heat recovery tank 247 to flow out from the outlet slightly below the lower limit liquid level 117. After being heated as needed by the pipeline-type brine electric heater 227, it enters the brackish water dual-way electric valve 226 for even distribution before flowing in from the inlet of the Venturi pressure reducing pipe 223. The number of branch lines for the third-stage reheated air and the heated brackish water is the same as that for the hydrophobic ceramic membrane 202, and the outlet of each branch line is located 2 mm below the lowest point of the corresponding hydrophobic ceramic membrane 202. When the heated brackish water flows to the throat of the Venturi pressure reducing pipe 223, the flow velocity increases, resulting in a low-pressure zone, which accelerates the flow of the third-stage reheated air and facilitates gas-liquid mixing. The gas-liquid two-phase flow exits the Venturi pressure reducing pipe 223 and enters the gas-liquid mixing pipe 219. The gas-liquid mixing pipe 219 has enhanced heat transfer aeration holes 220 and enhanced mass transfer aeration holes 221. The enhanced heat transfer aeration holes 220 are located at the spiral center of the spiral condenser-heat recovery copper pipe 201, and the enhanced mass transfer aeration holes 221 are located near the hot side of the hydrophobic ceramic membrane 202. The number of aeration holes should ensure that the aeration disturbance can cover the entire hot side interface of the membrane and the heat exchange surface of the spiral condenser-heat recovery copper pipe 201. The air used for aeration is pretreated using the following three-stage preheating process: The primary preheating path is as follows: ambient air is introduced into the natural interface evaporation forced condensation-preheating chamber 230 via the forced condensation-preheating fan 232, and then flows out through the natural interface evaporation preheating duct 231, thus completing the primary preheating of the air for aeration. The secondary preheating path is as follows: the air preheated in the primary stage flows through the aeration enhancement air preheating vertical pipe in the semiconductor cooling heat recovery chamber 207 to complete the secondary preheating of the aeration air; The three-stage reheating path is as follows: the air preheated in the second stage flows through the spiral blade guide of the condensation waste heat recovery-air reheating phase change heat storage unit 214 and the enhanced heat transfer type air reheating channel 215 to complete the three-stage reheating of the air for aeration.

[0043] After the above three-stage preheating process, the temperature of the aeration air increases progressively: after the first stage of preheating, the air temperature rises to 30–40°C; after the second stage, it rises to 40–50°C; and after the third stage of reheating, it can be further increased to over 50°C. The medium-temperature air after the third stage of reheating is accelerated by the secondary flow fan 222 and then transported to the gas-liquid mixing pipe 219, and finally enters the membrane heat recovery tank 247 to participate in the aeration-enhanced heat and mass transfer process.

[0044] Specifically, the forced condensing-preheating fan 232 draws in ambient air, causing it to sweep across the natural interface evaporation forced condensing-preheating chamber 230 at a high flow rate. This increases the condensation rate of the natural interface evaporation desalination steam and preheats the aeration air to 30-40°C. The preheated aeration air (30-40°C) flows out from the bottom of the natural interface evaporation forced condensing-preheating chamber 230 and sequentially flows through the forced condensing-preheating fan 232 and the aeration enhancement air in the semiconductor refrigeration heat recovery chamber 207. The preheating riser completes secondary preheating (heating to 40-50℃) under the heating of waste heat from the hot side of the semiconductor refrigeration chip; the aeration air after secondary preheating flows through the spiral blade guide of the condensation waste heat recovery-air reheat phase change heat storage unit 214-enhanced heat transfer type air reheat channel 215, absorbs the heat released by the phase change heat storage material and completes tertiary reheating (further temperature rise to above 50℃), and finally is transported to the aeration enhanced heat and mass transfer unit after being accelerated by the secondary flow fan 222 and the Venturi pressure reducing pipe 223.

[0045] The top of the thermal-film-natural interface evaporation coupling freshwater tank 248 is provided with an inlet that is connected to the thermal-film-natural interface evaporation product water recovery main pipe 212. It is also provided with an atmospheric connection and a water intake pipe 246 with a water intake pump. The water intake pump is located on the bottom surface of the thermal-film-natural interface evaporation coupling freshwater tank 248.

[0046] (2) Operation process of subsystem II At sunrise, the power supply and control subsystem IV controls the opening of the electric double-way valve between the liquid level control storage tank 109 and the membrane thermal side heat recovery tank 247, injecting brackish water into the membrane thermal side heat recovery tank 247 until the natural liquid level in the tank reaches the upper limit liquid level 116, after which it enters the liquid level control zone for dynamic adjustment. The brackish water in the membrane thermal side heat recovery tank 247 recovers the latent heat of condensation of high-temperature and high-pressure steam through the spiral condensation-heat recovery copper pipe 201. The phase change thermal storage material in the phase change thermal storage material filling area 216 further recovers the sensible heat carried by the condensate through the sensible heat recovery channel in the center of the condensation waste heat recovery-air reheat phase change thermal storage unit 214. The lower limit liquid level 244 of the membrane thermal side heat recovery tank 247 is at the same height as the lower limit liquid level sensor 115 in the liquid level control storage tank, and the upper limit liquid level 245 is at the same height as the upper limit liquid level sensor 114 in the liquid level control storage tank, so as to ensure that the natural liquid level of the membrane thermal side heat recovery tank 247 is located in the liquid level control zone between the upper limit liquid level and the lower limit liquid level.

[0047] After the system is replenished with water, the power supply and control subsystem IV collects the system operating parameters in real time. When the average temperature of the brackish water in the membrane thermal side heat recovery tank 247 continuously rises to 55℃, the system controls and starts the membrane cold side semiconductor cooling chip 206, the thermal side enhanced heat recovery fan 208, the forced condensation-preheating fan 232, the secondary drainage fan 222, and the brine circulation pump 225. At this time, thermal distillation, membrane distillation, and natural interface evaporation begin to couple desalination synchronously. The permeate from each part flows through the desalination recovery pipe to the thermal-membrane-natural interface evaporation coupling desalination tank 248. When the power supply and control subsystem IV detects that the flow distribution deviation of the reheated air and the warmed brackish water branch is greater than 5%, it dynamically adjusts the air dual-way electric valve 224 and the brackish water dual-way electric valve 226 through PID control based on the feedback signal from the flow sensor, so that the flow distribution deviation of each branch is less than 1%. After the flow distribution is balanced, the enhanced heat transfer aeration holes 220 and enhanced mass transfer aeration holes 221 continuously / intermittently output high-speed gas-liquid two-phase flow upwards. The aerated brackish water in the membrane heat recovery tank 247 is in a dynamic flow and violently turbulent state. The flow and turbulence at the spiral center of the spiral condenser-heat recovery copper tube 201 can effectively enhance the condensation rate and heat recovery rate of high-temperature and high-pressure steam. Based on the large temperature difference driving mass transfer on both sides of the hydrophobic ceramic membrane 202, the flow and turbulence of the gas-liquid two-phase flow on the membrane heat side can further improve the mass transfer coefficient and anti-membrane fouling ability of the membrane distillation process. The violent turbulence of the natural liquid surface in the membrane heat recovery tank 247 can effectively enhance the evaporation rate of the natural interface evaporation stage. At the same time, the ambient air flows through the natural interface evaporation forced condensation-preheating chamber 230 at a high flow rate under the drive of the forced condensation-preheating fan 232, realizing the forced condensation of the natural interface evaporation steam and the primary preheating of the aeration air. The upper and lower enclosures of the natural interface evaporation forced condensation-preheating chamber 230 are both inclined, translucent white glass facing due south, allowing sunlight to pass through and enhancing the evaporation rate of brackish water at the free liquid surface in the membrane heat recovery pool 247 using solar radiation. When the temperature of the inclined cooling condenser fins 204 is detected to drop to a preset low temperature threshold (e.g., 15°C), the thermoelectric cooler 206 and its heat-side enhanced heat recovery fan 208 are turned off (the fan is turned off after a 2-minute delay), and the thermoelectric cooler stops thermal migration and cooling. When the temperature of the inclined cooling condenser fins 204 is detected to rise back to a preset opening threshold (e.g., 22°C), the membrane cold-side thermoelectric cooler 206 and its heat-side enhanced heat recovery fan 208 are simultaneously turned on, and the thermoelectric cooler begins thermal migration and cooling. When the temperature of the inclined cooling condenser fins 204 drops rapidly to the preset low temperature threshold, the thermoelectric cooler 206 and its heat-side enhanced heat recovery fan 208 are turned off sequentially. This process is repeated cyclically. The purpose of setting the temperature hysteresis range (15℃~22℃) is to prevent frequent start-ups and shutdowns of the cooling element and ensure stable system operation. During the period when the semiconductor thermal migration cooling on the membrane cold side is activated, the air used for enhanced aeration will complete the three-stage preheating in an orderly manner.During the cooling and shutdown period of the semiconductor thermal migration on the cold side of the membrane, the air used for aeration enhancement only completes the first and third stages of preheating. The third-stage reheated air eventually flows into the membrane thermal side heat recovery tank 247, which not only further improves the system-level solar energy utilization rate, but also indirectly reduces the negative impact of the aeration enhancement process on the temperature of the brackish water in the membrane thermal side heat recovery tank 247. When the solar radiation energy input to the system continuously decreases, and the average temperature of the brackish water in the membrane thermal side heat recovery tank 247 is continuously reduced to 55°C, the pipeline brine electric heater 227 is turned on, and the brine temperature at its outlet is controlled at 65°C to maintain the high-yield state of the thermal-membrane-natural interface evaporation coupling desalination process.

[0048] After sunset, the thermal-membrane-natural interface evaporation coupling desalination process stops. The power supply and control subsystem IV regulates and closes the brackish water electric double-way valve between the liquid level control water storage tank 109 and the membrane thermal side heat recovery tank 247, and opens the brackish water electric double-way valve connecting the membrane thermal side heat recovery tank 247 and the spray interface evaporation desalination subsystem III. Then, the brackish water with residual heat in the membrane thermal side heat recovery tank 247 is introduced into the spray interface evaporation desalination subsystem III for spray interface evaporation desalination, so as to further improve the system-level solar energy utilization rate and the overall water production.

[0049] In summary, this subsystem achieves coupled operation of three desalination methods—thermal method, membrane distillation, and natural interface evaporation—and cascade utilization of solar energy.

[0050] 3. Spray Interface Evaporation Desalination Subsystem III During sunrise and sunset, this subsystem is driven by a combination of solar radiation and photovoltaic power from the double-layered white glass top cover 310 that allows light to pass through the spray interface and evaporate through the condensation. It uses room-temperature brackish water in the level-controlled storage tank 109 for intermittent spray interface evaporation and desalination. After sunset, the subsystem is driven by the energy storage battery pack 402, utilizing the residual heat from the brackish water in the glass-metal vacuum tube 103 and the membrane thermal recovery tank 247, as well as the cleaning return water from the gradient foam metal heat and mass transfer core 104, for spray interface evaporation and desalination. This subsystem utilizes liquid brackish water spray atomization and ultrasonic oscillation excitation to enhance the interface evaporation intensity. The tilted photothermal-photovoltaic integrated spray evaporation interface 305 can be indirectly heated by the photovoltaic power-driven spray interface evaporation electric heating plate 306 (all-day heating), or directly heated by sunlight transmitted through the double-layered white glass top cover 310 via photothermal conversion (during periods of sunshine). The subsystem takes in ambient temperature / residual heat brackish water, photovoltaic power, solar radiation and ambient cold air, and outputs water produced by spray interface evaporation, salt scale and brackish water return. It belongs to the low-temperature energy utilization level of solar cascade driven brackish water desalination.

[0051] like Figure 5As shown, the subsystem includes a spray pressurization pump 301, a spray interface evaporation chamber 321, a forced convection drive fan 314 for the spray interface evaporation desalination condensation stage, a brackish water tank 322, and a spray interface evaporation desalination tank 323, etc. Specific implementation details are as follows: (1) Implementation details of each component of subsystem III A spray pressurization pump 301 is located upstream of the spray main pipe 302 and is used for pressurizing the brackish water spray. A forced convection heat exchange channel 309 for spray interface evaporation is located at the top of the spray interface evaporation chamber 321. This channel faces due south and is installed at an angle relative to the local latitude. It consists of a double-layered white glass top cover 310 for light transmission and condensation of the spray interface evaporation and a freshwater collection tank 311 for spray interface evaporation. It is used for forced condensation of the desalination steam from the spray interface evaporation and for direct heating of the inclined photothermal-photovoltaic integrated spray evaporation interface by transmitted sunlight. The highest point of the forced convection heat exchange channel 309 is the condensation air inlet 313. Ambient air, under the suction of the forced convection drive fan 314 in the spray interface evaporation desalination condensation stage, enters the forced convection heat exchange channel 309 through the condensation air inlet 313, forming forced convection at the lower glass layer of the double-layered white glass top cover 310 to enhance steam condensation efficiency. The spray interface evaporation freshwater collection tank 311 is located at the lowest position inside the top cover and is connected to the spray interface evaporation freshwater tank 323 through the spray interface evaporation freshwater collection pipe 312 to collect and store the spray interface evaporation product water.

[0052] The spray interface evaporation chamber 321 contains a spray branch pipe assembly, an inclined photovoltaic-thermal integrated spray evaporation interface 305 located below the spray branch pipe assembly, and a spray interface evaporation waste water recovery port located downstream of the lowest point of the inclined photovoltaic-thermal integrated spray evaporation interface 305. The spray branch pipe assembly consists of at least two spray branch pipes 303 evenly intersecting at circumferential angles, with spray nozzles 304 of 0.5mm diameter spaced 5mm apart at each spray branch pipe 303. The bottom surface of the inclined photovoltaic-thermal integrated spray evaporation interface 305 also includes a spray interface evaporation electric heating plate 306, a lower ultrasonic transducer 307, and an upper ultrasonic transducer 308. The spray interface evaporation electric heating plate 306 is located in the middle of the bottom surface of the inclined photovoltaic-thermal integrated spray evaporation interface 305 and is driven by photovoltaic power to heat the spray evaporation interface. The lower ultrasonic transducer 307 and the upper ultrasonic transducer 308 are installed on the bottom surface of the inclined photothermal-photoelectric integrated spray evaporation interface 305, located on the upper and lower sides of the spray interface evaporation electric heating plate 306, respectively, to simultaneously improve the evaporation intensity and the uniformity of the temperature field of the spray interface. The spray interface evaporation waste water recovery port is connected to the brackish water tank 322 to divert the waste water from the spray interface evaporation to the brackish water tank 322 for reuse.

[0053] (2) Operation process of subsystem III From sunrise to sunset, the thermal-film-natural interface evaporation desalination process operates in a coupled manner. When the liquid level in the glass-metal vacuum tube 103 is higher than the lower limit liquid level 117, the brackish water electric three-way valve 108 switches to the spray passage on the liquid level control storage tank side. The spray interface evaporation desalination subsystem is driven by photovoltaic power and solar radiation energy through the evaporation-condensation double-layer white glass top cover 310 of the spray interface. When the liquid level in the glass-metal vacuum tube 103 equals the lower limit level 117, the brackish water electric three-way valve 108 switches to the water replenishment path, and the spray interface evaporation desalination subsystem III stops operating. Water is then replenished to the glass-metal vacuum tube 103 from the level-controlled storage tank 109 using the principle of communicating vessels, until the liquid level in the glass-metal vacuum tube 103 equals the upper limit level 116. At this point, the brackish water electric three-way valve 108 switches to the spray path on the level-controlled storage tank side, and the spray interface evaporation desalination subsystem is again driven by a combination of photovoltaic power and solar radiation from the double-layered white glass top cover 310 that allows for evaporation and condensation at the spray interface. This process can be repeated during periods of sunshine.

[0054] After sunset, the thermal-film-natural interface evaporation coupling desalination process stops. The electric double-way valve for brackish water between the liquid level control storage tank 109 and the membrane thermal side heat recovery tank 247 is closed. The electric double-way valve for brackish water between the spray main pipe 302 and the membrane thermal side heat recovery tank 247 is opened. The electric three-way valve for brackish water 108 is switched to the vacuum tube side spray passage. The spray pressurization pump 301 introduces the brackish water with residual heat from the membrane thermal side heat recovery tank 247, the glass-metal vacuum tube 103, and the cleaning return water from the gradient foam metal heat and mass transfer inner core 104 into the spray main pipe 302. Then, the brackish water is sprayed onto the inclined photothermal-photovoltaic integrated spray evaporation interface 305 through the spray nozzles 304. The spray interface evaporation electric heating plate 306 heats the evaporation interface. The lower ultrasonic transducer 307 and the upper ultrasonic transducer 308 are activated to enhance the interface evaporation intensity and homogenize the temperature field of the evaporation interface through ultrasonic oscillation excitation. Water vapor generated by the spray interface evaporation rises and accumulates on the bottom surface of the double-layered white glass top cover 310 for light transmission and condensation at the spray interface evaporation. The forced convection drive fan 314 of the spray interface evaporation desalination and condensation stage is activated, introducing ambient temperature air into the forced convection heat exchange channel 309. Forced convection promotes efficient condensation of the water vapor at the bottom surface. The condensed desalinated water flows downwards under the combined action of gravity, surface tension, and adhesion, collecting in the spray interface evaporation desalinated water collection tank 311, and then flowing into the spray interface evaporation desalinated water tank 323 via the spray interface evaporation desalinated water collection pipe 312. Unevaporated brackish water flows downwards along the inclined integrated photothermal-photovoltaic spray evaporation interface 305 and flows back to the brackish water pool 322 via the spray interface evaporation waste water recovery port.

[0055] In summary, this subsystem achieves dual-mode operation: photovoltaic-thermal complementary drive for spray interface evaporation when there is sunshine, and energy storage battery pack drive spray interface evaporation using waste heat brackish water when there is no sunshine.

[0056] 4. Power Supply and Control Subsystem IV This subsystem serves as the power source and collaborative control center for all desalination subsystems, enabling efficient photovoltaic-electric conversion, energy storage, DC-AC inversion, energy output, temperature / flow / level signal acquisition, and start / stop control of various power components. It inputs solar radiation energy and temperature / flow / level signals, and outputs AC / DC power and control signals.

[0057] like Figure 6 As shown, this subsystem consists of an off-grid photovoltaic power generation system, an integrated power supply and control unit, and various sensors. The off-grid photovoltaic power generation system includes a photovoltaic array 401, an energy storage battery pack 402, and a charge / discharge control-inverter integrated unit 403, etc. Specific implementation details are as follows: (1) Implementation details of each component of subsystem IV The photovoltaic array 401 consists of polycrystalline or monocrystalline silicon photovoltaic modules connected in series and parallel, and can be used as a rooftop (installed according to the actual orientation and slope of the roof) or ground-mounted (facing due south, with the installation tilt angle based on the local latitude) photovoltaic power generation system. The energy storage battery pack 402 consists of lithium-ion batteries connected in series and parallel, housed in a fireproof, sun-proof, and weatherproof energy storage cabinet. The charge / discharge control-inverter integrated unit 403 features maximum power point tracking and AC-DC inverter functions.

[0058] The integrated power supply and control unit has a DC power supply port, an AC power supply port, a temperature / flow / level signal acquisition port, a control signal output port, and a control strategy actuator.

[0059] The sensors include temperature, flow rate, and liquid level sensors. The temperature sensors include the upper, middle, and lower sets of temperature sensors in the membrane thermal side heat recovery tank 247, the ambient temperature sensor, the temperature sensor of the inclined cooling condensation fins 204, and the temperature sensor of the inclined photothermal-photoelectric integrated spray evaporation interface 305; the flow rate sensors include the flow rate sensor of the reheated air diversion branch and the flow rate sensor of the heated brackish water diversion branch; the liquid level sensors include the lower limit liquid level sensor 115 and the upper limit liquid level sensor 114, which are respectively installed at the lower limit liquid level 117 and the upper limit liquid level 116 on the inner wall of the liquid level control storage tank 109.

[0060] (2) Operation process of subsystem IV Subsystem IV operates on the same power generation principle as traditional off-grid photovoltaic power generation systems. During charging, the charge / discharge control-inverter integrated unit 403 improves the photovoltaic-to-electricity conversion efficiency through a maximum power point tracking strategy. During discharging, the charge / discharge control-inverter integrated unit 403 and the power supply and control integrated unit work together to intelligently switch between AC / DC output, direct photovoltaic power supply, and power supply modes via the energy storage battery pack 402. Specifically: when solar radiation is sufficient, the photovoltaic system directly drives each desalination subsystem, and excess electricity is stored in the energy storage battery pack 402; when solar radiation supply and demand are balanced, the photovoltaic system directly drives each desalination subsystem, with no excess electricity; when solar radiation is insufficient, direct photovoltaic power supply to each desalination subsystem is prioritized, and the remaining energy is supplied by the energy storage battery pack 402; during periods without sunshine, the energy storage battery pack 402 independently drives each desalination subsystem.

[0061] The energy storage battery pack 402 implements the following four-level state of charge protection strategy: normal operation zone (state of charge greater than 50%): no restrictions; power warning zone (state of charge 30%~50%): reduce the priority of non-critical loads; power alert zone (state of charge 20%~30%): only necessary drive equipment is kept running, and enhanced equipment is shut down; over-discharge danger zone (state of charge less than 20%): cut off all AC / DC outputs.

[0062] II. Control of Coupled System Operation Process The operation of the coupled system is divided into four standard modes: M1 mode (sufficient condensation heat recovery stage), M2 mode (insufficient condensation heat recovery stage), M3 mode (low-temperature waste heat spray evaporation stage), and M4 mode (lowest power consumption standby stage). The control method for the operation of the coupled system is as follows: After sunrise, the output voltage of the photovoltaic array 401 reaches the start-up threshold, the power supply and control subsystem IV is activated, the water pump 112 is powered on, and the initial liquid level is established. The CPC concentrator 101 gathers solar radiation energy to produce high-temperature steam. After the steam accumulation pressure reaches the preset external delivery pressure threshold, it is automatically transported to the spiral condenser-heat recovery copper pipe 201.

[0063] When the average temperature of the brackish water in the membrane heat recovery tank 247 continuously rises to 55°C, the brine circulation pump 225, the forced condensing-preheating fan 232, the heat-side enhanced heat recovery fan 208, and the secondary diversion fan 222 are sequentially powered on and put into operation, adjusting the flow distribution deviation of each branch to within 1%. The heat-membrane-natural interface evaporation coupling desalination operates efficiently, while the spray interface evaporation desalination subsystem operates intermittently, and the system enters the M2 mode.

[0064] When the average temperature of the brackish water in the membrane heat recovery tank 247 rises to 65°C or above, it is considered that the condensation recovery heat supply is sufficient, and the system naturally transitions to mode M1. In this mode, the pipeline-type saline electric heater 227 remains de-energized, the brackish water electric three-way valve 108 alternately switches between the water supply path and the spray path on the liquid level control storage tank side, the heat-membrane-natural interface evaporation desalination coupling operates efficiently, and the spray interface evaporation desalination subsystem operates intermittently.

[0065] As the solar radiation energy input to the system continuously decreases, the amount of condensation heat supply to the system also begins to decline, causing the average temperature of the brackish water in the membrane heat recovery tank 247 to drop below 65°C. This is considered insufficient condensation heat supply, and the system naturally transitions to mode M2. In this mode, all auxiliary equipment that was energized in mode M1 remains powered on. When the average temperature of the brackish water in the membrane heat recovery tank 247 is between 55°C and 65°C, although the transmembrane temperature difference driving force and the intensity of natural interface evaporation are somewhat weakened compared to mode M1, they still remain at a relatively strong level. The membrane distillation and natural interface evaporation desalination processes can still be maintained by condensation heat recovery, and the spray interface evaporation desalination subsystem operates intermittently without the need for electrical assistance. When the average temperature of the brackish water in the pool drops to 55℃, the heat recovery from condensation becomes insufficient to maintain a strong transmembrane temperature difference driving force and natural interface evaporation intensity. The pipeline-type brine electric heater 227 is then energized, and its outlet temperature is controlled at 65℃ to ensure efficient operation of the heat-membrane-natural interface evaporation coupled desalination system. The spray interface evaporation desalination subsystem operates intermittently. When the average temperature of the brackish water in the membrane heat recovery pool 247 rises to 65℃, the system naturally transitions from mode M2 ​​to mode M1. Therefore, the switching between modes M1 and M2 is caused by changes in solar radiation intensity and does not require active switching.

[0066] After sunset, when the output voltage of the photovoltaic array 401 reaches the shutdown threshold, the average temperature of the brackish water in the membrane thermal side heat recovery tank 247 drops to 45°C, and the state of charge of the energy storage battery pack is greater than 30%, the membrane cold side semiconductor refrigeration chip 206, the thermal side enhanced heat recovery fan 208, the secondary drainage fan 222, and the brine circulation pump 225 are de-energized, and the forced condensation-preheating fan 232 is de-energized after a 2-minute delay; the electric double-way valve between the level control water storage tank 109 and the membrane thermal side heat recovery tank 247 is closed; and the brackish water electric three-way valve 108 is switched to... The vacuum tube side spray passage is opened; the bottom electric double-way valve of the membrane thermal side heat recovery tank 247 is opened; the spray pressurization pump 301, the spray interface evaporation electric heating plate 306, the lower ultrasonic transducer 307, the upper ultrasonic transducer 308, and the forced convection drive fan 314 of the spray interface evaporation desalination condensation link are sequentially powered on and put into operation. The brackish water with residual heat in the glass-metal vacuum tube 103 and the membrane thermal side heat recovery tank 247 is introduced into the spray interface evaporation chamber 321 by the spray pressurization pump 301 for spray interface evaporation, and the system switches from M2 mode to M3 mode. In the initial stage of M3 mode operation, the gradient foam metal heat and mass transfer inner core 104 is cleaned simultaneously, and the cleaning return water enters the spray main pipe 302, which, together with the water from the glass-metal vacuum tube 103 and the membrane thermal side heat recovery tank 247, participates in the spray interface evaporation desalination, realizing the recycling and reuse of cleaning wastewater.

[0067] When brackish water with residual heat remains in the glass-metal vacuum tube 103 or the membrane thermal side heat recovery pool 247, or when the automatic cleaning process of the gradient foam metal heat and mass transfer core 104 has not been completed, but the state of charge of the energy storage battery pack is below 30%, the lower ultrasonic transducer 307, the upper ultrasonic transducer 308 and the forced convection drive fan 314 of the spray interface evaporation desalination and condensation link are turned off, while the spray pressurization pump 301 and the spray interface evaporation electric heating plate 306 remain on, and the system operates inefficiently in M3 mode.

[0068] When the brackish water with residual heat in the glass-metal vacuum tube 103 and the membrane thermal side heat recovery tank 247 is depleted and the glass-metal vacuum tube 103 is cleaned, or when the state of charge of the energy storage battery pack drops to 20%, the spray pressurization pump 301, the spray interface evaporation electric heating plate 306, the lower ultrasonic transducer 307, the upper ultrasonic transducer 308, and the forced convection drive fan 314 of the spray interface evaporation desalination and condensation link are shut off. The brackish water electric three-way valve 108 is switched to the water replenishment path, the electric two-way valve at the bottom of the membrane thermal side heat recovery tank 247 is closed, and the electric two-way valve between the liquid level control water tank 109 and the membrane thermal side heat recovery tank 247 is closed. Only the sensor monitoring circuit and the clock circuit are powered at low power, and the system switches from mode M3 to mode M4. At this time, if the state of charge of the energy storage battery pack is still greater than 30%, cleaning and maintenance work can be carried out. After completion, the system waits for wake-up the next day in mode M4.

[0069] III. Cleaning and Maintenance Process 1. Cleaning of the gradient foam metal heat and mass transfer core 104 At the initial stage of daily M3 mode startup, the cleaning of the gradient foam metal heat and mass transfer core 104 is automatically performed. A 15-minute enhanced cleaning is triggered every 3 days, and a standard 5-minute cleaning is triggered daily thereafter. Before cleaning, the electric shut-off valve 118 for cleaning is automatically closed and reopened the following day upon system startup to prevent the brackish water used for cleaning from entering the downstream steam pipeline and causing contamination.

[0070] Cleaning water supply path: The water supply pump 112 draws water from the brackish water tank 322, and after passing through the cleaning check valve 119 and the cleaning water supply pipe 120, it is delivered to the cleaning pipeline connection port of the connection-positioning metal head 1041. The gradient foam metal heat and mass transfer core 104 is flushed from top to bottom to remove the scale and impurities deposited on various parts of the gradient foam metal heat and mass transfer core 104.

[0071] Cleaning drainage path: Cleaning return water flows out from the bottom of the glass-metal vacuum tube 103, enters the spray main 302 through the vacuum tube side spray passage of the brackish water manifold 107 and the brackish water electric three-way valve 108, and participates in the spray interface evaporation desalination process together with the water from the glass-metal vacuum tube 103 and the membrane heat recovery tank 247. The unevaporated residual water is finally returned to the brackish water tank 322 through the residual water recovery port.

[0072] 2. Regular maintenance of the spray interface evaporation chamber 321 Every week of system operation, a maintenance prompt is issued by the human-machine interface in M4 mode. After manual confirmation, maintenance work is performed on the spray interface evaporation chamber 321. First, the power supply and control subsystem IV sends an unlocking command to the electromagnetic self-priming lock 316 with limit function, and after a 3-second delay, outputs a forward rotation command to the maintenance door opening and closing rotary motor 317. The spray interface evaporation maintenance door 315 rotates to a horizontal position under the limit of the horizontal maintenance door limiter 318. Second, the descaling and cleaning of the inclined photothermal-photovoltaic integrated spray evaporation interface 305 and the replacement of the replaceable spray interface evaporation return water filter 319 are carried out. Finally, after maintenance is completed, the power supply and control subsystem IV sends a reverse rotation command to the maintenance door opening and closing rotary motor 317. The maintenance door resets and automatically locks, and the system returns to M4 mode.

[0073] 3. Regular cleaning of the water level control storage tank 109 Every year during system operation, the internal cleaning of the level control water storage tank 109 is carried out in M4 mode. The electric three-way valve at the water supply pipe 111 is switched to the drain passage. After all the brackish water in the level control water storage tank 109 is drained into the brackish water pool 322 through the drain pipe 320, the internal cleaning of the level control water storage tank 109 is carried out. After cleaning is completed, the electric three-way valve is switched back to the water supply passage.

[0074] 4. Regular maintenance of the condensation waste heat recovery-air reheat phase change thermal storage unit Every 3 years, maintenance work is carried out on the condensation waste heat recovery-air reheat phase change thermal storage unit 214 under M4 mode. First, switch the hot air electric three-way valve 237 to the phase change thermal storage material discharge passage; second, after turning on the phase change material discharge fan 236 and the duct air heater 235, adjust the power supply to control the air temperature at the outlet of the duct air heater 235 to 120°C, and let it flow into the spiral vane guide-enhanced heat transfer type air reheat passage 215, thereby completely melting the phase change thermal storage material in the phase change thermal storage material filling area 216; third, open the phase change thermal storage material electric two-way valve at the phase change material discharge pipe 238 to discharge all the liquid phase change thermal storage material to the phase change material recovery tank; fourth, test the heat storage / release characteristics of the phase change material. If it is qualified, re-inject it into the phase change thermal storage material filling area 216; otherwise, replace it with new material and inject it into the phase change thermal storage material filling area 216; finally, switch the hot air electric three-way valve 237 to the aeration passage.

[0075] Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-mentioned technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by substituting the above-mentioned features with technical features disclosed in this application (but not limited to) that have similar functions.

Claims

1. A solar-powered cascade-driven thermal-film-interface evaporation coupled brackish water desalination system, characterized in that, It includes a CPC concentrating heat collection-gradient foam metal heat and mass transfer desalination subsystem (Ⅰ), a heat-film-natural interface evaporation coupled desalination subsystem (Ⅱ), a spray interface evaporation desalination subsystem (Ⅲ), and a power supply and control subsystem (Ⅳ). The steam output end of the CPC concentrating heat collection-gradient foam metal heat and mass transfer desalination subsystem (I) is connected to the inlet of the spiral condensing-heat recovery copper pipe (201) in the heat-film-natural interface evaporation coupling desalination subsystem (II) through a high temperature and high pressure steam discharge main pipe (106). The outlet of the spiral condensing-heat recovery copper pipe (201) is connected to the inlet of the sensible heat recovery channel in the center of the condensing waste heat recovery-air reheat phase change heat storage unit (214). The outlet of the sensible heat recovery channel is connected to the heat-film-natural interface evaporation coupling freshwater tank (248) through a thermal water recovery branch pipe (213). The brackish water manifold (107) of the CPC concentrating heat collection-gradient foam metal heat transfer and mass transfer desalination subsystem (Ⅰ) is connected to the side outlet of the liquid level control storage tank (109) and the spray main pipe (302) of the spray interface evaporation desalination subsystem (Ⅲ) via the brackish water electric three-way valve (108), forming an automatically switchable water replenishment path and spray water supply path. The thermal-membrane-natural interface evaporation coupled desalination subsystem (II) includes a membrane thermal side heat recovery tank (247) and a natural interface evaporation forced condensation-preheating chamber (230) located above it. The bottom outlet of the membrane thermal side heat recovery tank (247) is connected to the spray main pipe (302) via an electric double-way valve. A hydrophobic ceramic membrane (202) is embedded in the vertical wall of the membrane thermal side heat recovery tank (247) facing due south. A membrane cold side semiconductor refrigeration condensation-aeration enhancement air preheating integrated unit is attached to the cold side of the hydrophobic ceramic membrane (202). The bottom of the membrane distillation cold chamber (203) in the membrane cold side semiconductor refrigeration condensation-aeration enhancement air preheating integrated unit is connected to the thermal-membrane-natural interface evaporation coupled desalination tank (248) via a membrane permeate recovery branch pipe (210). The air outlet of the natural interface evaporation forced condensation-preheating chamber (230) is connected to the air inlet of the semiconductor refrigeration heat recovery chamber (207) in the integrated unit for air preheating for semiconductor refrigeration condensation-aeration enhancement on the membrane cold side via the natural interface evaporation preheating air duct (231). The air outlet of the semiconductor refrigeration heat recovery chamber (207) is connected in sequence via pipeline to the inlet of the spiral blade guide-enhanced heat transfer type air reheating channel (215) of the condensation waste heat recovery-air reheating phase change heat storage unit (214), the secondary flow fan (222), and the gas-liquid mixing pipe (219). The spray interface evaporation desalination subsystem (Ⅲ) has a spray interface evaporation desalination water collection pipe (312) connected to a spray interface evaporation desalination water tank (323), and a bottom return water outlet connected to a brackish water pool (322). Both the heat-film-natural interface evaporation coupling freshwater tank (248) and the spray interface evaporation freshwater tank (323) are equipped with an atmospheric connection and a water intake pipe (246) with a water intake pump. The power supply and control subsystem (Ⅳ) is electrically connected to each power element, electric valve and sensor through power cables, and is also connected for communication through signal cables, and supplies power to each electrical component.

2. The brackish water desalination system according to claim 1, characterized in that, The CPC concentrating solar collector-gradient foam metal heat and mass transfer desalination subsystem (Ⅰ) includes: CPC condenser lens (101) has a light-transmitting white glass cover (102) with a self-cleaning coating on its light-receiving surface. A glass-metal vacuum tube (103) is located at the focal line of the CPC condenser lens (101) and is divided into an evaporation zone and a brackish water zone along its length. The steam outlet of the glass-metal vacuum tube (103) is connected to the high-temperature and high-pressure steam discharge main pipe (106) via a high-temperature and high-pressure steam manifold (105), and the brackish water inlet / outlet is connected to the brackish water electric three-way valve (108) via the brackish water manifold (107). The brackish water electric three-way valve (108) is a three-position three-way reversing valve, which connects the water level control storage tank (109) and the glass-metal vacuum tube (103) to the water supply level, the water level control storage tank (109) and the spray main pipe (302) to the water tank spray position, and the glass-metal vacuum tube (103) and the spray main pipe (302) to the vacuum tube spray position. A gradient foam metal heat and mass transfer core (104) is disposed inside the glass-metal vacuum tube (103); The liquid level control water storage tank (109) has one side outlet that goes through a check valve and a brackish water electric three-way valve (108) and then through a brackish water manifold (107) to the bottom of the glass-metal vacuum tube (103). The other outlet goes through a liquid level control pipeline check valve (110) and an electric two-way valve and then to the membrane thermal side heat recovery tank (247) for synchronously replenishing water to the glass-metal vacuum tube (103) and the membrane thermal side heat recovery tank (247).

3. The brackish water desalination system according to claim 2, characterized in that, The gradient foam metal heat and mass transfer core (104) is an integrated foam metal structure. Its outer wall surface is in close contact with the inner wall surface of the glass-metal vacuum tube (103). From the outer wall surface, radially inward from the center, there are brackish water supply layer (1045), phase change main layer (1044) and steam escape layer (1043). The pore size and porosity of the three increase in sequence. The thickness of the phase change main layer (1044) is greater than the thickness of the steam escape layer (1043), and the thickness of the steam escape layer (1043) is greater than the thickness of the brackish water supply layer (1045). The end of the gradient foam metal heat and mass transfer inner core (104) is provided with a connection-positioning metal head (1041) that is threadedly connected to the glass-metal vacuum tube (103).

4. The brackish water desalination system according to claim 1, characterized in that, The integrated air preheating unit for semiconductor refrigeration and condensation-aeration enhancement on the membrane cold side comprises, from the membrane cold side outwards: The membrane distillation cold chamber (203) has inclined cooling and condensing fins (204) arranged on the cold side of the membrane cold side semiconductor refrigeration chip (206) closely attached inside. The bottom surface of the membrane distillation cold chamber (203) is an inclined flow guide wall (205), and the lowest side center of the inclined flow guide wall (205) is connected to the membrane permeate recovery branch pipe (210). Film cold-side semiconductor refrigeration chip (206); The semiconductor cooling heat recovery chamber (207) is equipped with a heat-side enhanced heat recovery fan (208) and an air preheating vertical pipe for enhanced aeration. The outer surface of the vertical pipe is provided with downward-sloping porous fins for enhanced air preheating and heat transfer (209). The gas-liquid mixing pipe (219) is provided with enhanced heat transfer aeration holes (220) and enhanced mass transfer aeration holes (221). The enhanced heat transfer aeration holes (220) are located at the spiral center of the spiral condensation-heat recovery copper pipe (201), and the enhanced mass transfer aeration holes (221) are located near the hot side of the hydrophobic ceramic membrane (202). The outlet of the secondary flow fan (222) is connected to the air inlet at the throat of the Venturi pressure reducing pipe (223) via a pipeline. The heated brackish water flows in from the inlet of the Venturi pressure reducing pipe (223). When it flows through its throat, the flow velocity increases, forming a low-pressure zone. It draws in the reheated air flowing in through the air inlet and increases its speed. After the gas and liquid phases are mixed, they enter the gas-liquid mixing pipe (219). The gas-liquid two-phase flow output from the enhanced heat transfer aeration holes (220) and enhanced mass transfer aeration holes (221) simultaneously enhances the condensation heat transfer and membrane distillation mass transfer performance, and suppresses membrane fouling.

5. The brackish water desalination system according to claim 1, characterized in that, The condensation waste heat recovery-air reheat phase change thermal storage unit (214) is a cylindrical tank, and its interior is arranged radially from the center outwards as follows: The sensible heat waste heat recovery channel is provided with downwardly inclined and staggered flow damping type enhanced heat transfer fins (217) inside, which are used to receive and cool the condensed fresh water from the spiral condensation-heat recovery copper tube (201). The phase change thermal storage material filling area (216) is fitted outside the sensible heat waste heat recovery channel, and its inner and outer walls are provided with horizontally staggered heat transfer reinforced porous fins (218) for storing phase change thermal storage material. Spiral blade flow guide-enhanced heat transfer type air reheating channel (215) is sleeved outside the phase change heat storage material filling area (216), and has spiral blades inside for reheating the aeration air flowing through it by using the heat released by the phase change heat storage material. The top of the condensation waste heat recovery-air reheat phase change thermal energy storage unit (214) is connected to the phase change thermal energy storage material melting-filling tank (242) through a liquid phase change thermal energy storage material injection pipe (240). The liquid phase change thermal energy storage material injection pipe (240) is wrapped with an electrically heated insulation layer (239). The bottom of the phase change thermal energy storage material melting-filling tank (242) is provided with a funnel-shaped phase change thermal energy storage material electric heating plate (241). The bottom of the condensation waste heat recovery-air reheat phase change thermal energy storage unit (214) is provided with a phase change material discharge port, and is connected to a phase change material electric double-way valve through a phase change material discharge pipe (238).

6. The brackish water desalination system according to claim 1, characterized in that, The spray interface evaporation desalination subsystem (Ⅲ) also includes: A spray booster pump (301) is located upstream of the spray main pipe (302); The spray interface evaporation chamber (321) is provided with a spray branch pipe group, an inclined photothermal-photovoltaic integrated spray evaporation interface (305) located below the spray branch pipe group, and a spray interface evaporation waste water recovery port located downstream of the lowest point of the inclined photothermal-photovoltaic integrated spray evaporation interface (305); the top of the spray interface evaporation chamber (321) is provided with a spray interface evaporation forced convection heat exchange channel (309). The bottom surface of the inclined photothermal-photoelectric integrated spray evaporation interface (305) is also provided with a spray interface evaporation electric heating plate (306), a lower ultrasonic transducer (307) and an upper ultrasonic transducer (308).

7. The brackish water desalination system according to claim 1, characterized in that, The power supply and control subsystem (Ⅳ) includes: An off-grid photovoltaic power generation system, comprising a photovoltaic array (401), an energy storage battery pack (402), and a charge / discharge control-inverter integrated unit (403). Power supply and control integrated unit; Sensors, including temperature sensors, flow sensors, and level sensors; The temperature sensors include a temperature sensor in the membrane heat recovery tank (247), an ambient temperature sensor, a temperature sensor for the inclined cooling condensation fins (204), and a temperature sensor for the inclined photothermal-photoelectric integrated spray evaporation interface (305); the flow sensors include a flow sensor for the reheat air diversion branch and a flow sensor for the heating brackish water diversion branch; the liquid level sensors include a lower limit liquid level sensor (115) and an upper limit liquid level sensor (114), which are respectively installed at the lower limit liquid level (117) and the upper limit liquid level (116) on the inner wall of the liquid level control storage tank (109).

8. The brackish water desalination system according to claim 1, characterized in that, The system utilizes the heat of evaporation and condensation at the natural interface, the waste heat from the hot side of the semiconductor refrigeration chip, and phase change heat storage to form a three-stage preheating chain for the air used for aeration: The primary preheating path is as follows: ambient air is introduced into the natural interface evaporation forced condensation preheating chamber (230) via the forced condensation-preheating fan (232), and then flows out through the natural interface evaporation preheating air duct (231) to complete the primary preheating of the aeration air; The secondary preheating path is as follows: the air preheated by the primary stage flows through the aeration enhancement air preheating vertical pipe in the semiconductor refrigeration heat recovery chamber (207) to complete the secondary preheating of the aeration air; The three-stage reheating path is as follows: the air preheated in the second stage flows through the spiral blade guide-enhanced heat transfer type air reheating channel (215) of the condensation waste heat recovery-air reheating phase change heat storage unit (214) to complete the three-stage reheating of the aeration air. The aeration air preheated in the three stages is finally accelerated by the secondary induced flow fan (222) and then transported to the gas-liquid mixing pipe (219).

9. A solar-driven, cascade-driven, heat-film-interface evaporation coupled brackish water desalination method, characterized in that, The system operation process described in any one of claims 1 to 8 is divided into four standard modes: mode M1 is the stage with sufficient condensation heat recovery; mode M2 ​​is the stage with insufficient condensation heat recovery; mode M3 is the stage of low-temperature waste heat spray evaporation; and mode M4 is the stage of standby with the lowest power consumption. The method includes the following steps: S1: After sunrise each day, when the output voltage of the photovoltaic array (401) reaches the start-up threshold, the power supply and control subsystem (Ⅳ) sends a system wake-up signal, the water replenishment pump (112) is powered on, the brackish water electric three-way valve (108) is switched to the water replenishment path, the electric double-way valve between the liquid level control storage tank (109) and the membrane thermal side heat recovery pool (247) is opened, and the brackish water enters the glass-metal vacuum tube (103) and the membrane thermal side heat recovery pool (247) respectively, until the liquid levels at both places reach the upper limit liquid level (116), and the initial liquid level establishment is completed; S2: CPC condenser (101) gathers solar radiation energy. The brackish water in the glass-metal vacuum tube (103) continuously absorbs heat and heats up to generate high-temperature steam. After the steam accumulation pressure reaches the preset external delivery pressure threshold, the high-temperature and high-pressure steam flows spontaneously through the high-temperature and high-pressure steam manifold (105) and the high-temperature and high-pressure steam discharge main pipe (106) in sequence, and is transported to the spiral condensation-heat recovery copper tube (201) to complete condensation and heat release. The latent heat of condensation is simultaneously transferred to the brackish water in the membrane heat recovery pool (247). S3: When the average temperature of brackish water in the membrane heat recovery tank (247) continuously rises to 55°C, the system enters the M2 mode. In this mode, the power supply and control subsystem (Ⅳ) controls the step-by-step activation of the brine circulation pump (225), the forced condensing-preheating fan (232), the heat-side enhanced heat recovery fan (208), and the secondary diversion fan (222), adjusting the flow distribution deviation of each branch to less than 1%. The heat-membrane-natural interface evaporation coupling desalination operates efficiently, while the spray interface evaporation desalination subsystem operates intermittently. S4: The power supply and control subsystem (Ⅳ) continuously monitors the liquid level in the liquid level control storage tank (109). When the lower limit liquid level sensor (115) is triggered, the water supply pump (112) is powered on, and the brackish water electric three-way valve (108) switches to the water supply path. The brackish water enters the glass-metal vacuum tube (103) and the membrane heat recovery pool (247) through the liquid level control storage tank (109). When the upper limit liquid level sensor (114) is triggered, the water supply pump (112) is powered off, and the brackish water electric three-way valve (108) switches to the spray path on the liquid level control storage tank side. The liquid level drops due to the consumption of thermal desalination, spray interface evaporation, membrane distillation and natural interface evaporation. After it drops to the lower limit liquid level (117), the brackish water electric three-way valve (108) switches to the water supply mode again. The liquid level oscillates between the upper and lower limit liquid levels. S5: When the average temperature of the brackish water in the membrane thermal side heat recovery tank (247) further increases to 65°C or above, it indicates that the condensation recovery heat is sufficient and the system naturally transitions to the M1 mode. In this mode, the pipeline-type saline electric heater (227) is kept off, the brackish water electric three-way valve (108) alternately switches between the water supply passage and the spray passage on the liquid level control storage tank side, the electric double-way valve between the liquid level control storage tank (109) and the membrane thermal side heat recovery tank (247) remains open to maintain the water supply passage on this side, the heat-membrane-natural interface evaporation coupling desalination operates efficiently, and the spray interface evaporation desalination subsystem operates intermittently. S6: When the solar radiation energy input to the system decreases, the amount of condensation heat supply to the system also decreases. When the average temperature of the brackish water in the membrane heat recovery tank (247) drops below 65°C, the system naturally transitions to the M2 mode. In this mode, the equipment that has been powered on in the M1 mode remains powered on. When the average temperature of the brackish water in the tank is higher than 55°C, the pipeline-type saline electric heater (227) remains powered off. When the average temperature of the brackish water in the tank drops to 55°C, the pipeline-type saline electric heater (227) is powered on. When the tank temperature rises back to above 65°C, the system naturally transitions to the M1 mode. S7: When the output voltage of the photovoltaic array (401) is lower than the shutdown threshold, the average temperature of the membrane thermal side heat recovery tank (247) drops to 45°C, and the state of charge of the energy storage battery pack is greater than 30%, the power supply and control subsystem (Ⅳ) performs an active switch from M2 to M3, de-energizing the membrane cold side semiconductor refrigeration chip (206), the thermal side enhanced heat recovery fan (208), the secondary drainage fan (222), and the brine circulation pump (225), and de-energizing the forced condensing-preheating fan (232) after a delay, and shutting down the liquid level control water tank (109) and the membrane thermal side heat recovery tank (247). The electric double-way valve between the glass-metal vacuum tube (103) and the electric three-way valve (108) of the brackish water is switched to the vacuum tube side spray passage. The electric double-way valve at the bottom of the membrane heat recovery tank (247) is opened. The spray pressurization pump (301), electric heating plate (306), lower ultrasonic transducer (307), upper ultrasonic transducer (308), and forced convection drive fan (314) of the spray interface evaporation desalination condensation link are powered on in sequence to introduce the brackish water with residual heat in the glass-metal vacuum tube (103) and the membrane heat recovery tank (247) into the spray interface evaporation chamber (321) for desalination. S8: There is residual brackish water with residual heat in the glass-metal vacuum tube (103) or the membrane thermal side heat recovery pool (247), or the automatic cleaning process of the gradient foam metal heat and mass transfer core (104) has not been completed. However, when the state of charge of the energy storage battery pack is less than 30%, the lower ultrasonic transducer (307), the upper ultrasonic transducer (308), and the forced convection drive fan (314) of the spray interface evaporation desalination and condensation link are turned off, while the spray pressurization pump (301) and the spray interface evaporation electric heating plate (306) remain on. The system operates inefficiently in M3 mode. S9: When all the brackish water with residual heat in the glass-metal vacuum tube (103) and the membrane thermal side heat recovery tank (247) is exhausted and the glass-metal vacuum tube (103) is cleaned, or when the state of charge of the energy storage battery pack is reduced to 20%, the power supply and control subsystem (Ⅳ) will de-energize the spray pressurization pump (301), electric heating plate (306), lower ultrasonic transducer (307), upper ultrasonic transducer (308) and forced convection drive fan (314) of the spray interface evaporation desalination condensation link, switch the brackish water electric three-way valve (108) to the water replenishment channel, close the electric two-way valve at the bottom of the membrane thermal side heat recovery tank (247), and switch the system from M3 mode to M4 mode, waiting for the wake-up signal the next day.

10. The method according to claim 9, characterized in that, In the initial stage of M3 mode startup, the gradient foam metal heat and mass transfer core (104) is automatically cleaned simultaneously. The cleaning return water enters the spray main pipe (302) and participates in the spray interface evaporation and desalination process together with the water from the glass-metal vacuum tube (103) and the membrane heat recovery tank (247) to recover and utilize the residual heat carried by the cleaning wastewater. Cleaning water supply path: The water supply pump (112) draws water from the brackish water tank (322), and delivers it to the cleaning pipeline connection port of the connection-positioning metal head (1041) through the cleaning check valve (119) and the cleaning water supply pipe (120) to flush the gradient foam metal heat and mass transfer core (104) from top to bottom. Cleaning drainage path: The cleaning return water flows out from the bottom of the glass-metal vacuum tube (103), enters the spray main pipe (302) through the vacuum tube side spray passage of the brackish water manifold (107) and the brackish water electric three-way valve (108), and then sprays to the evaporation interface of the spray interface evaporation chamber (321).

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