A dual-density matched particle thermocline heat storage and supply system and method

Abstract

This application relates to a dual-density matched particle thermocline thermal storage and heating system and method. The system includes a heat collection module, a thermocline thermal storage module, and a heating module; the hot water storage tank of the thermocline thermal storage module is filled with low-density particles and high-density particles, the low-density particles having a density of 962–970 kg / m³. 3 Slightly higher than the density of high-temperature water, the density of high-density particles is 990–995 kg / m³. 3 The density is slightly lower than that of low-temperature water. During operation, low-density particles naturally suspend above the thermocline, while high-density particles naturally settle below it, forming a symmetrical double-layer barrier structure. This physically blocks the convective mixing of hot and cold fluids and utilizes the low thermal conductivity of the particles to suppress vertical heat loss. The two types of particles adaptively and dynamically migrate along with the thermocline interface, maintaining stable sealing at all times. This application achieves precise stabilization and efficient thermal storage and heating of the thermocline, significantly improving thermal storage efficiency and heating stability.

Description

Technical Field

[0001] This application relates to the field of thermocline thermal storage technology, specifically to a dual-density matched particle thermocline thermal storage and heating system and method. Background Technology

[0002] With the global energy structure transformation, clean energy sources such as solar energy are widely used in the field of thermal utilization. However, solar energy is intermittent and fluctuates, requiring a thermal storage system to achieve continuous operation of "collection-storage-heating". Thermocline thermal storage technology has become the mainstream choice for solar thermal storage systems due to its advantages such as simple structure, low cost, and high thermal storage efficiency. The core principle of this technology is to utilize the density difference between hot and cold water to form a stable temperature stratification structure within the hot water storage tank: the upper layer is high-temperature hot water, the lower layer is low-temperature cold water, and the middle layer is a thermocline (also known as a sloping thermocline) with a rapidly changing temperature gradient. Through the vertical movement of the thermocline during the heat charging and releasing processes, the orderly storage and release of heat is achieved.

[0003] Existing thermocline thermal energy storage systems still have the following technical shortcomings in actual operation: 1. Thermocline Disruption and Severe Mixing of Hot and Cold Water: During the frequent switching between solar thermal charging and heating / discharging, disturbances caused by water injection and extraction disrupt the stability of the thermocline, leading to convective mixing of hot and cold water. This degrades the originally clear temperature stratification structure and expands the thermocline thickness. This reduces thermal storage efficiency (high-temperature heat is absorbed by the lower cold water) and causes large fluctuations in heating temperature, failing to meet the stable heating needs of terminal equipment. The thermocline degradation is more severe when the charging / discharging switching frequency is high.

[0004] 2. Lack of effective thermocline stabilization mechanisms: Existing technologies to alleviate thermocline disturbances mostly employ fluid dynamics methods such as optimizing water flow velocity, setting up flow guiding structures, or water distributors. These methods can only mitigate the effects of disturbances and cannot fundamentally suppress the direct contact and mixing of hot and cold water bodies. A few studies have proposed installing floating baffles (such as WO2010000892A2) in the thermal storage tank to physically separate the hot and cold fluids through a single layer of material. However, this baffle is a monolithic structure, which is prone to jamming or tilting in irregular water tanks or under complex water flow conditions. Furthermore, a single material can only provide single-layer isolation, and its ability to suppress heat conduction loss is limited.

[0005] 3. Packed bed technology suffers from fixed particles and lacks dynamic adaptability: Packed bed thermocline thermal storage technology (such as the Pack-bed system) uses solid particles such as quartz and ceramics randomly filled into the storage tank. While this can increase energy storage density, the particles remain stationary within the tank and cannot adapt to changes in the thermocline interface. During heat charging and discharging, the fixed particle bed cannot provide a continuous and effective physical barrier to the dynamically moving thermocline interface. Bypass flow easily occurs between the particle layer and the fluid interface, weakening the effect of stabilizing the thermocline.

[0006] 4. Low system integration and high heat loss: Existing solar thermal collectors and storage systems are mostly designed as separate units, with complex piping connections between the collector, storage, and heating units, resulting in significant heat loss during long-distance transmission. Furthermore, the hot water storage tank relies solely on its outer insulation layer to passively reduce heat dissipation, lacking active measures to mitigate heat loss within the tank caused by conduction and convection. Therefore, the overall energy efficiency ratio needs improvement.

[0007] Therefore, developing a thermal storage and heating system that can accurately stabilize the thermocline, suppress the mixing of hot and cold water, achieve dynamic adaptation between the particle layer and the thermocline, and has high integration and high operating efficiency has become an urgent technical problem to be solved in this field. Summary of the Invention

[0008] In view of this, embodiments of this application provide a dual-density matched particle thermocline thermal storage and heating system and method to solve the technical problems in existing thermocline thermal storage systems, such as easy thermocline disorder, severe mixing of hot and cold water, lack of effective dynamic stabilization mechanism, inability of fixed packed beds to adapt to thermocline interface movement, and low system integration leading to large heat loss.

[0009] This application proposes a dual-density matched particle thermocline thermal storage and heating system, including a heat collection module, a thermocline thermal storage module, and a heating module. The heat collection module is fluidly connected to the thermocline heat storage module and is used to collect heat from external heat sources and transport it to the thermocline heat storage module for layered storage; the external heat source includes any one or more of solar energy, industrial waste heat, air energy, and geothermal energy; the thermocline heat storage module is fluidly connected to the heating module and is used to release the stored heat to the heating module as needed to achieve end-point heating. The thermocline thermal storage module includes a hot water storage tank, which is a closed pressurized water tank; the hot water storage tank has a hot water inlet and outlet at the top and a cold water inlet and outlet at the bottom; the hot water storage tank is filled with low-density particles and high-density particles. The density of the low-density particles is higher than the density of the high-temperature water in the hot water storage tank under rated operating conditions but lower than the density of the low-temperature water; the density of the high-density particles is higher than the density of the high-temperature water but lower than the density of the low-temperature water, and the densities of both types of particles are between the densities of the high-temperature water and the low-temperature water. The densities of both the low-density particles and the high-density particles are between those of the high-temperature water and the low-temperature water, and the two types of particles form a symmetrical double-layer barrier structure on both sides of the thermocline interface; the thermal conductivity of both the low-density particles and the high-density particles is lower than that of water, and the particle surfaces are smooth and rounded. The "high-temperature water" mentioned above refers to the water in the upper hot water layer of the hot water storage tank, whose temperature is higher than the lower limit of the design operating temperature of the low-density particles. In typical thermal storage and heating applications, the temperature range of the high-temperature water is 60℃ to 100℃, corresponding to a water density range of approximately 958 to 983 kg / m³. 3 The term "low-temperature water" as used in this application refers to the water in the lower cold water layer of the hot water storage tank, whose temperature is lower than the upper limit of the design operating temperature of the high-density particles. In typical thermal storage and heating applications, the temperature range of the low-temperature water is 10℃ to 20℃, corresponding to a water density range of approximately 998 to 1000 kg / m³. 3 The temperature difference between the two is no less than 40℃ to ensure that the densities of the two types of particles are within a reasonable range matching the densities of their respective target water bodies.

[0010] Furthermore, both the low-density particles and the high-density particles are chemically inert, high-temperature resistant, insoluble in water, and have a smooth and rounded surface, and are solid particles with low thermal conductivity. The density of the low-density particles is 962–970 kg / m³. 3 The density of the high-density particles is 990–995 kg / m³. 3 The diameter of both the low-density particles and the high-density particles is 5-30 mm.

[0011] Furthermore, the high-density particles are selected from at least one of glass microspheres or high-temperature resistant ceramic particles; the low-density particles are selected from at least one of low thermal conductivity inert polymer particles or inorganic lightweight solid particles; the thermal conductivity of both types of particles is lower than that of water, and the particle surface is smooth and does not generate additional turbulence disturbance.

[0012] Furthermore, the thermocline thermal storage module also includes multiple temperature sensors, which are fixedly installed vertically at the top, middle and bottom of the hot water storage tank to detect the water temperature at different heights in the tank in real time, accurately obtain the height, thickness and offset of the thermocline, and realize real-time monitoring and control of the thermal storage status throughout the process.

[0013] Furthermore, the thermocline thermal storage module is also equipped with a suspended insulation plate; the suspended insulation plate is made of a lightweight insulation material with low thermal conductivity, high temperature resistance, waterproof and corrosion resistance; When the suspended heat insulation plate is used in conjunction with the dual-density particle barrier structure, the overall density of the suspended heat insulation plate is slightly lower than the density of the high-temperature water in the hot water storage tank. It floats adaptively above the liquid surface in the hot water storage tank and rises and falls with the liquid level. It isolates the liquid surface from the convective and radiative heat dissipation of the outside air, forming a dual heat insulation structure with the dual-density particle barrier structure, which provides heat insulation at the top liquid surface and internal interlayer barrier.

[0014] Furthermore, the solar collector module includes a solar collector, a first water pump, and a solar collector pipeline; the outlet of the solar collector is connected to the hot water inlet and outlet at the top of the hot water storage tank via the solar collector pipeline, and the inlet of the solar collector is connected to the cold water inlet and outlet at the bottom of the hot water storage tank via the solar collector pipeline; the first water pump is installed on the solar collector pipeline; during operation, the first water pump drives the low-temperature cold water at the bottom of the hot water storage tank to enter the solar collector to absorb heat and increase its temperature, and the heated high-temperature hot water flows back to the top of the hot water storage tank via the pipeline, continuously constructing a stratified water body with hot water at the top and cold water at the bottom in the water tank, completing the automatic solar collection and charging cycle of the system; the solar collector is a flat-plate solar collector or a vacuum tube solar collector, or any one of an industrial waste heat exchanger, an air source heat pump heat exchanger, or a geothermal heat exchanger.

[0015] Furthermore, the heating module includes a second water pump, a third water pump, several control valves, heating pipelines, and terminal heating equipment; the hot water inlet and outlet at the top of the hot water storage tank are connected to the inlet of the terminal heating equipment via the heating pipelines, and the outlet of the terminal heating equipment is connected to the cold water inlet and outlet at the bottom of the hot water storage tank via the heating pipelines; the terminal heating equipment is at least one of radiators, underfloor heating coils, or domestic hot water heat exchangers; the system has three operating modes: heat collection and storage, direct heat collection, and heat storage and supply, which can be switched on demand through the coordinated regulation of the control valves and water pumps.

[0016] A dual-density matched particle thermocline thermal storage and heating method, applied to any of the above-mentioned systems, the method comprising the following steps: Low-density particles and high-density particles are filled into the hot water storage tank. The two types of particles naturally stratify in the tank due to their density difference. The low-density particles are suspended at the bottom of the high-temperature water layer, and the high-density particles are settled at the top of the low-temperature water layer, forming a symmetrical double-layer particle barrier structure on both sides of the thermocline interface. Heat is charged into the hot water storage tank through the heat collection module. High-temperature hot water is injected from the top hot water inlet and outlet, and low-temperature cold water is discharged from the bottom cold water inlet and outlet. A stable stratified water body with hot water on top and cold water on the bottom is gradually formed in the water tank. The dual-density particles adaptively adjust their distribution according to the position of the thermocline interface, and continuously maintain the stability of the thermocline. The heating module is activated according to the heating demand, driving the high-temperature hot water at the top of the hot water storage tank to release heat through the terminal heating equipment. After the heat is released, the low-temperature return water returns from the bottom of the hot water storage tank. The granular double-layer barrier structure dynamically follows the displacement of the thermocline layer, suppressing the mixing of hot and cold fluids throughout the process and ensuring a stable output of hot water temperature. The temperature of each layer in the water tank is monitored in real time by temperature sensors. The pump speed and control valve opening are automatically adjusted according to the height, thickness and offset of the thermocline, so as to realize the closed-loop coordinated operation of the three modes of heat collection, heat storage and heat supply.

[0017] Furthermore, during the heat charging and storage process, the dynamic response of the particle layer is as follows: High-temperature hot water is injected from the top of the hot water storage tank, and the density of the water in the upper part of the tank decreases as the temperature rises; when the density of the upper hot water is lower than the density of the low-density particles, the relative density of the low-density particles increases, and they migrate downwards with the density difference, covering the interface between the hot and cold fluids; the high-density particles always settle stably at the top of the low-temperature cold water layer; the two types of particles together hold the hot and cold interface, constrain the thickness of the thermocline layer, and at the same time, the low thermal conductivity of the particles reduces the vertical heat conduction loss across the layers, inhibits the mixing and heat dissipation of water during the heat storage process, and ensures the stratified heat storage effect of the water tank.

[0018] Furthermore, during the heat release and heating process, the dynamic response of the particle layer is as follows: Low-temperature return water flows back into the water tank from the cold water inlet and outlet at the bottom of the hot water storage tank, the height of the cold water layer gradually increases, the thermocline interface moves upward accordingly, and the water temperature at the bottom of the tank remains low as the return water flows in, while the upper hot water layer continuously outputs heat to the terminal heating equipment; when the density of the upper water is higher than the density of the low-density particles, the low-density particles rise due to buoyancy and remain suspended above the interface between the cold and hot fluids; the high-density particles move upward synchronously with the top position of the cold water layer, working together with the low-density particles to maintain the double-layer barrier structure; the two types of particles jointly seal the cold and hot interface, preventing the upper cold water from intruding downward and the lower hot water from rising upward, while using the low thermal conductivity to reduce vertical heat loss, ensuring that the stored hot water releases heat in an orderly manner in layers, and improving the system's heating stability and thermal energy utilization rate.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention involves filling the hot water storage tank with a density of 962-970 kg / m³. 3 and 990~995kg / m 3The system utilizes both low-density and high-density particles, whose densities fall between those of high-temperature hot water and low-temperature cold water. During heat charging and discharging, these particles naturally suspend above and settle below the thermocline, respectively, forming a symmetrical double-layer physical barrier structure. Simultaneously, the two types of particles adaptively and dynamically migrate according to changes in their position at the thermocline interface, maintaining a dense isolation layer between the hot and cold fluids. This effectively blocks convective mixing paths, prevents thermocline expansion and degradation caused by water flow disturbances, and improves the stability of the thermocline and the continuity of the supplied hot water temperature.

[0020] 2. This invention employs low-density and high-density particles with thermal conductivity lower than that of water. This not only physically blocks convective mixing but also further suppresses vertical heat loss across the thermocline interface. Simultaneously, the smooth, rounded surfaces of both types of particles prevent additional turbulent disturbances during operation, avoiding secondary damage to the thermocline. This creates a dual insulation mechanism of "blocking convection + suppressing heat conduction," effectively reducing static and dynamic heat loss during thermal storage, extending storage time, and improving the overall energy efficiency ratio of the system.

[0021] 3. This invention designs low-density particles to be slightly higher than the density of high-temperature water and high-density particles to be slightly lower than the density of low-temperature water, limiting the particle diameter to 5-30mm. This allows the two types of particles to achieve natural stratification and dynamic following within the water tank entirely based on their density difference, without the need for external power. This solves the problems of easy jamming and tilting of the overall plate in existing floating baffle technology, and the shortcomings of fixed-bed technology where particles cannot adapt to the movement of the thermocline interface. It achieves adaptive matching for high-frequency charge-discharge switching (minute-level), improving the system's operational reliability under intermittent solar energy fluctuations.

[0022] 4. This invention integrates the heat collection module, the thermocline heat storage module, and the heating module into a single unit, forming three switchable operating modes: heat collection and storage, direct heat collection and supply, and heat storage and supply. Furthermore, temperature sensors arranged vertically along the water tank monitor the height, thickness, and offset of the thermocline in real time, automatically adjusting the water pump speed and control valve opening to achieve fully automatic closed-loop control of the system. This simplifies the system structure, reduces heat loss over long pipelines, and allows for flexible switching of operating modes based on heating demand and solar irradiance conditions, significantly improving the system's integration, adaptability, and energy efficiency.

[0023] 5. This invention utilizes a suspended insulation panel as a synergistic or alternative solution to the dual-density particle layer. The overall density of the suspended insulation panel lies between that of cold and hot water, allowing it to adaptively suspend at the thermocline position. Together with the dual-density particle layer, it forms a dual thermocline layer stabilization and heat preservation mechanism, or, under specific operating conditions, independently performs both thermocline layer stabilization and insulation functions. This enriches the system's application scenarios, allowing for flexible selection of particle structure, panel structure, or a combination of both based on cost and operating conditions, thus enhancing the scalability and market adaptability of the technical solution. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the overall structure of the dual-density matched particle thermocline thermal storage and heating system provided in an embodiment of the present invention; Figure 2 A schematic diagram of the circulation loop for the heat collection-storage mode (heat collection and storage mode) provided in an embodiment of the present invention; Figure 3 A schematic diagram of the circulation loop for the heat collection-heat supply mode (direct heat collection mode) provided in an embodiment of the present invention; Figure 4 A schematic diagram of the circulation loop for the thermal storage-heat supply mode (thermal storage-heat supply mode) provided in the embodiments of the present invention; Figure 5 This is a schematic diagram illustrating the thermal insulation effect of dual-density particles dynamically following the interface position of the thermocline layer during the heat charging and discharging process, as provided in an embodiment of the present invention.

[0026] Reference numerals: 1. Heat collection module; 2. Thermocline heat storage module; 2-1. Low-density particles; 2-2. High-density particles; 3. Heating module; P-1. First water pump; P-2. Second water pump; P-3. Third water pump; V-1, V-2, V-3, V-4, V-5: Control valves. Detailed Implementation

[0027] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0028] This application provides a dual-density matched particle thermocline thermal storage and heating system and method, which is mainly applied in the fields of solar thermal heating, industrial waste heat recovery and building heating. The method fills the hot water storage tank with low-density particles and high-density particles with precise density matching. The two types of particles naturally stratify due to the density difference and dynamically follow the position of the thermocline interface. During the heat charging and releasing process, a symmetrical double-layer physical barrier structure is formed, which replaces the traditional single floating partition or fixed filling bed method, and improves the stability of the thermocline and the thermal storage efficiency of the system.

[0029] In a typical thermocline thermal storage and heating scenario, the system integrates solar collector modules (such as flat-plate or vacuum tube collectors), thermocline thermal storage modules (including a hot water storage tank and an internal dual-density granular layer), and terminal heating modules (such as radiators, underfloor heating coils, or domestic hot water heat exchangers). When solar irradiance is sufficient, the collector modules inject the collected heat into the top of the hot water storage tank as high-temperature hot water. A stable stratified water body, with hotter water at the top and colder water at the bottom, gradually forms inside the tank, with a thermocline in the middle where the temperature gradient changes dramatically. When there is a heating demand, the high-temperature hot water at the top of the storage tank is extracted to the terminal heating equipment to release heat, and the low-temperature return water returns from the bottom of the tank. During frequent switching between charging and discharging, traditional methods lack an effective dynamic stabilization mechanism, making the thermocline susceptible to disturbances and diffusion caused by water flow, leading to mixing of hot and cold water and a decrease in thermal storage efficiency. This application, however, fundamentally solves the thermocline degradation problem through the adaptive dynamic barrier of the dual-density granular layer.

[0030] Example 1 like Figure 1 As shown in the figure, this embodiment provides a dual-density matched particle thermocline thermal storage and heating system. The system comprises three main functional units: a heat collection module 1, a thermocline thermal storage module 2, and a heating module 3. These three units are fluidly connected through pipelines and work together to complete the entire process of heat collection, stratified storage, and on-demand release. The following detailed description of the composition and operation of each module is provided in conjunction with the accompanying drawings: In the attached diagram, P-1 is the first water pump (hot water pump), installed on the heat collection pipeline, used to drive the heat collection circulation; P-2 is the second water pump (main hot water pump), installed on the heating pipeline, used to drive the heat storage and heating circulation; P-3 is the third water pump (auxiliary circulating water pump), installed on the heating return water pipeline, used to assist the return water circulation.

[0031] In this embodiment, "high-temperature water" specifically refers to the hot water layer in the upper part of the hot water storage tank, with a target operating temperature of 80℃~100℃; "low-temperature water" specifically refers to the cold water layer in the lower part of the hot water storage tank, with a target operating temperature of 10℃~20℃. Under these temperature conditions, the density of the low-density particles (2-1) is 962~970 kg / m³. 3 High-density particles (2-2) with a density of 990–995 kg / m³3 Both are between the densities of high-temperature water and low-temperature water, thus meeting the density matching requirements of this application.

[0032] In application, the dual-density matched particle thermocline thermal storage and heating system consists of three main functional units: a heat collection module 1, a thermocline thermal storage module 2, and a heating module 3. These three units are interconnected via pipelines, collaboratively completing the entire process of heat collection, stratified storage, and on-demand release. The heat collection module 1 is the system's heat source collection unit, its function being to convert usable heat from nature or industrial processes into thermal energy in the water body, and input it into the thermocline thermal storage module 2 as high-temperature hot water. The thermocline thermal storage module 2 is the core thermal storage unit of the system. Its internal hot water tank has hot water inlet and outlet at the top and cold water inlet and outlet at the bottom. During heat filling, hot water is injected from the top and cold water is discharged from the bottom. During heat release, high-temperature hot water is drawn out from the top and low-temperature return water flows back from the bottom. This unidirectional flow naturally creates a vertical stratified structure within the tank, with a high-temperature upper layer and a low-temperature lower layer. Heating module 3 is the system's heat consumption unit, responsible for transporting the high-temperature hot water stored in the hot water storage tank to terminal heating equipment such as radiators, underfloor heating coils, or domestic hot water heat exchangers, to complete the actual heat supply to the building or user.

[0033] The hot water storage tank is filled with two types of solid particles: low-density particles 2-1 and high-density particles 2-2. The densities of these two types of particles are precisely designed to fall between the densities of the high-temperature and low-temperature water within the tank. Since the density of water decreases as temperature increases, the density of high-temperature hot water is approximately 958–980 kg / m³. 3 The density of cold water at low temperatures is approximately 998–1000 kg / m³. 3 Therefore, the density of low-density particles 2-1 is slightly higher than that of the high-temperature water, allowing them to sink under gravity without floating in the hot water, while being supported by the greater buoyancy of the low-temperature cold water, thus naturally suspending them at the bottom of the high-temperature water layer above the interface between the hot and cold fluids. The density of high-density particles 2-2 is slightly lower than that of the low-temperature water, allowing them to sink in the low-temperature cold water, while not continuing to float through the hot water layer, thus naturally settling at the top of the low-temperature water layer below the interface between the hot and cold fluids.

[0034] Two types of particles form a symmetrical double-layer barrier structure on both sides of the thermocline interface. A 2-1 layer of low-density particles covers the upper part of the interface, while a 2-2 layer of high-density particles covers the lower part. Together, these two layers physically block the convection channels between the hot and cold water bodies, preventing mixing and temperature loss caused by the sinking of hot water and the rising of cold water. Figure 5As shown, during the heat charging process, low-density particles 2-1 and high-density particles 2-2 are suspended on the upper and lower sides of the thermocline, respectively. During the heat release process, both types of particles move upward synchronously with the interface displacement of the thermocline, maintaining a double-layer barrier structure to jointly block the convection channel between the hot and cold fluids. Both types of particles are chemically inert materials, do not react chemically with water, and are resistant to thermal aging within the system's operating temperature range. Their smooth and rounded surfaces reduce additional turbulence generated when water flows through them. At the same time, the thermal conductivity of the particles is lower than that of water, further suppressing vertical heat loss between the hot and cold layers on the basis of convection barrier.

[0035] Specifically, during actual operation, the solar collector module 1 draws low-temperature cold water from the bottom of the hot water storage tank and sends it to the solar collector for heating. The heated high-temperature hot water is then injected from the hot water inlet and outlet at the top of the tank, gradually establishing a stratified water body with hot water on top and cold water on the bottom. As the high-temperature hot water layer thickens, the hot and cold interface moves downwards. The low-density particles 2-1 are affected by the decrease in the density of the hot water above, and their buoyancy and gravity reach a new balance, keeping them suspended above the interface. The high-density particles 2-2, on the other hand, always sink to the top of the low-temperature water layer below the interface. The double-layer barrier structure dynamically moves downwards with the interface and adjusts synchronously, without any external drive or control, relying entirely on the density difference for automatic response. When the heating demand is activated, the second water pump (P-2) drives the high-temperature hot water at the top of the hot water storage tank to flow to the terminal heating equipment. The third water pump (P-3) assists in driving the return water circulation. The low-temperature return water after the terminal heat is released is pressurized by P-3 and returns from the bottom of the water tank. The hot and cold interface moves upward accordingly. The two types of particles move upward synchronously and maintain a double-layer sealing state, ensuring that the water tank does not mix hot and cold water during the entire heat release process, so that the output water temperature remains stable.

[0036] Among them, the low-density particles 2-1 can be low thermal conductivity inert polymer material particles with adjusted density, such as polypropylene microspheres or polyethylene microspheres with density controlled by a foaming process, or inorganic lightweight ceramic microspheres with sealed cavities inside, with the target density achieved by adjusting the cavity ratio. Among them, the high-density particles 2-2 can be solid glass microspheres, which have stable density, smooth surface, high temperature resistance, and good chemical inertness, or high temperature resistant dense ceramic particles, with the required density matching achieved by selecting different ceramic substrate formulations.

[0037] This system simultaneously arranges low-density particles 2-1 and high-density particles 2-2 within the hot water storage tank, forming a double-layer physical barrier on both sides of the thermocline interface in a completely passive, density-adaptive manner. This effectively suppresses the mixing of hot and cold water over the long term without the need for mechanical partitions or active control mechanisms, ensuring the hot water storage tank maintains a clear stratified structure throughout the dynamic processes of heat filling and releasing. Compared to traditional thermal storage methods that rely solely on natural water stratification, the double-layer particle barrier structure significantly reduces the thickness of the thermocline, decreases energy loss in the hot-cold transition zone, and improves the effective thermal storage capacity and the stability of the output water temperature, thereby enhancing the overall system's energy efficiency and heating reliability.

[0038] In an optional embodiment, the selection of the densities of low-density particles 2-1 and high-density particles 2-2, and the engineering considerations for particle diameters of 5–30 mm, are as follows: In this application, the embodiment specifies the density range and particle diameter of low-density particles 2-1 and high-density particles 2-2. The density of low-density particles 2-1 is set to 962–970 kg / m³. 3 The physical meaning of this density range is that the particle density is slightly higher than the density of the high-temperature hot water in the hot water storage tank under the system's design operating conditions. The density of high-temperature hot water at a typical operating temperature of 80–100℃ is approximately 958–972 kg / m³. 3 Therefore, the buoyancy experienced by low-density particles 2-1 in the hot water layer is slightly less than their own weight, allowing them to remain stably suspended at the bottom of the hot water layer without floating or dispersing. Simultaneously, because their density is much lower than that of the low-temperature cold water, they will not sink and cross the interface into the cold water layer. The density of high-density particles 2-2 is set at 990–995 kg / m³. 3 This density range results in a particle density slightly lower than that of cold water at low temperatures, which has a density of approximately 998–1000 kg / m³ at 10–20°C. 3 High-density particles 2-2 experience buoyancy slightly less than their own weight in the cold water layer, thus settling stably at the top of the cold water layer and not floating arbitrarily in the presence of hot and cold water. The diameter of both types of particles is set at 5–30 mm. This size range comprehensively considers the mechanical stability and packing characteristics of the particles. If the particle diameter is too small, the specific surface area is too large, increasing the water flow resistance between particles, and the particles are easily migrated with the liquid flow under water disturbance, making it difficult to remain stably in the interface region. If the particle diameter is too large, the particle layer thickness increases, reducing the tightness of the interface coverage, and local gaps appearing between particles, leading to the penetration of hot and cold water. The diameter range of 5–30 mm ensures that the particle layer has sufficient interface coverage density while maintaining stability, effectively blocking the convection channels in the interface region.

[0039] Specifically, under actual operating conditions of the hot water storage tank, when the temperature of the high-temperature water layer inside the tank is maintained between 80 and 100°C, the density is 962–970 kg / m³. 3 The low-density particles 2-1 remain stably suspended in the hot water layer, with a particle density slightly higher than that of the hot water, the density difference being approximately 4–12 kg / m³. 3 (The particle density is greater than that of water), creating a downward net gravitational force difference, which keeps the particles suspended above the interface and prevents them from settling due to hot water convection. Density is 990–995 kg / m³. 3 High-density particles 2-2 have a density of approximately 998–1000 kg / m³ 3 It maintains stable settling in cold water at low temperatures, with a density difference of approximately -4 to -9 kg / m³. 3 This creates a downward net gravitational force difference, causing the particles to settle stably on top of the cold water layer below the interface. The particle layer formed by particles with a diameter of 5–30 mm in the water tank is approximately 1–3 times the particle diameter thick, achieving complete coverage of the interface area without excessively increasing the effective heat storage volume occupied by the water tank.

[0040] The density of low-density particles 2-1 can be controlled using a precision foaming injection molding process. By adjusting the amount of foaming agent, the internal porosity of the polymer particles can be precisely controlled, thereby stabilizing the density at 962–970 kg / m³. 3 Within this range, hollow microsphere structures can also be used, and the overall density can be adjusted by changing the ratio of the shell thickness to the outer diameter, thus achieving precise customization of the density. The particle diameter range can be selected using standard industrial sieving processes to classify the produced particles, screening out particles in the 5–30 mm diameter range. Alternatively, a molding process can be used to directly produce standard spherical particles, precisely controlling particle size consistency by setting the mold diameter.

[0041] Precise definition of the particle density and diameter ranges ensures reliable self-positioning characteristics for both types of particles within the normal operating range of the system. This guarantees that regardless of minor temperature fluctuations in the water tank due to heat source variations or load changes, the particles remain stably positioned within their predetermined locations. The reasonable margin design within the density range allows the particles to tolerate a certain range of water temperature fluctuations without dislocation, thereby improving the system's adaptability to complex operating conditions, reducing reliance on precise water temperature control, and enhancing the system's operational robustness.

[0042] In an optional embodiment, the high-density particles 2-2 are selected from glass microspheres or high-temperature resistant ceramic particles, and the low-density particles 2-1 are selected from low thermal conductivity inert polymers or inorganic lightweight solid particles. The technical effects of the particles having a lower thermal conductivity than water and a smooth surface that does not generate turbulence are as follows: In this application, this embodiment specifies the material selection for the two types of particles and clarifies the surface characteristic requirements of the particles. High-density particles 2-2 are selected from at least one of glass microspheres or high-temperature resistant ceramic particles. Glass microspheres are solid spherical particles prepared from borosilicate glass or soda-lime glass through a high-temperature melting and spherical process. Their density is determined by the glass formulation, and they are chemically extremely stable. They do not dissolve, expand, or precipitate under long-term immersion in water, and their surface is extremely smooth, generating almost no additional turbulence. High-temperature resistant ceramic particles are sintered from heat-resistant ceramic matrix materials such as alumina, mullite, or cordierite. They can withstand temperatures up to several hundred degrees Celsius, fully meeting the temperature requirements of solar energy or industrial waste heat storage systems. Their chemical inertness ensures they have no risk of corrosion during long-term operation in water. The low-density particles 2-1 are selected from low-thermal-conductivity inert polymer or inorganic lightweight solid particles with matched density. Polymer materials include thermoplastics such as polypropylene and polyethylene. The density is precisely controlled within the target range through foaming and densification processes. Inorganic lightweight particles include density-matched hollow ceramic microspheres or expanded vermiculite particles, which possess excellent chemical stability. Both types of particles have lower thermal conductivity than water (approximately 0.6 W / (m·K)). The lower thermal conductivity of the particles means that even with contact between hot and cold water bodies, the overall heat transfer rate of the particle layer is lower than that of pure water, further reducing vertical heat loss at the interface region while physically blocking convection. The smooth particle surface prevents additional turbulence disturbance. This means that the outer surface of the particles is polished or spherical to achieve a low roughness, preventing local eddies induced by sharp edges or microscopic protrusions when water flows through the particle layer, thus avoiding additional mixing effects caused by particle surface characteristics.

[0043] Specifically, in the long-term operating environment of the system, the water temperature in the hot water storage tank cyclically changes between 10 and 80°C. The water may contain small amounts of minerals or additives. When glass microspheres are selected as high-density particles 2-2, their dense glass layer completely isolates ions in the water from contact with the particle matrix. The density and size of the particles remain unchanged after thousands of charge-discharge cycles. When polypropylene foam particles are selected as low-density particles 2-1, their closed honeycomb structure on the outer surface prevents water from penetrating into the particle interior and changing its density. At the same time, polypropylene has good chemical stability in water below 80°C and does not undergo oxidative degradation. Since the thermal conductivity of both types of particles is lower than that of water, the interface barrier layer formed by the double-layer stacking of particles has a better equivalent thermal conductivity than pure water. This can reduce the heat flux in the interface region, reduce the continuous diffusion of heat from the hot water layer to the cold water layer, and extend the heat storage and insulation time.

[0044] Among them, the high-density particles 2-2 can be made of soda-lime glass microspheres, formed in one step through melt-blowing process, resulting in a high surface finish. Alternatively, they can be made of alumina ceramic particles, which, after isostatic pressing and high-temperature sintering, achieve a dense surface that is wear-resistant and corrosion-resistant. The thermal conductivity of the low-density particles 2-1 can be controlled by using a closed-cell foam structure within the polymer particles. The air trapped within the micropores has a thermal conductivity as low as 0.025 W / (m·K), effectively reducing the equivalent thermal conductivity of the particles. Alternatively, a hollow inorganic microsphere structure can be used, where the static air layer within the hollow cavity significantly reduces the overall thermal conductivity of the particles while maintaining the structural strength of the particle shell.

[0045] By precisely selecting materials, both types of particles maintain density and dimensional stability throughout their entire life cycle, avoiding the risk of losing their positioning function due to particle density drift caused by material aging, water absorption and expansion, or chemical reactions. The introduction of low thermal conductivity materials enables the particle layer to have the dual functions of convection blocking and thermal conduction inhibition. Compared with the traditional solution that relies solely on the natural stratification of water, the effective heat preservation performance of the hot water storage tank is substantially improved, and the overall heat storage efficiency and heating stability of the system are thus significantly improved.

[0046] In one optional embodiment, multiple temperature sensors vertically installed at the top, middle, and bottom of the hot water storage tank, and methods for accurately acquiring the height, thickness, and offset of the thermocline by real-time detection of water temperature, thereby achieving real-time monitoring and control of the thermal storage status throughout the process, are as follows: In this application, the thermocline thermal storage module 2 is also equipped with multiple temperature sensors, which are vertically fixedly installed in the top, middle, and bottom areas of the hot water storage tank. Temperature sensors are temperature-sensing elements that convert water temperature into electrical signals. Common types include resistance temperature detectors (RTDs) and thermocouples. Fixed installation means that the sensors are embedded in the side wall or top and bottom plates of the tank through tubing, threaded interfaces, or welded fasteners, ensuring that the temperature-sensing elements are in direct contact with the water and are not subject to external interference. The vertical distribution of the sensors in the top, middle, and bottom areas means that there are at least three independent temperature-sensing nodes along the entire height of the tank. The top sensor reflects the temperature of the high-temperature hot water layer, the bottom sensor reflects the temperature of the low-temperature cold water layer, and the middle sensor directly senses the temperature changes in the area where the thermocline is located. By comparing the temperature values ​​at each node, the control system can calculate the current height position of the thermocline interface, i.e., determine the height of the top and bottom of the thermocline, and thus obtain the thickness of the thermocline, which is the vertical width of the hot-cold transition zone. The height of the thermocline reflects the proportion of the current heat storage to the total heat storage capacity, the thickness of the thermocline reflects the clarity of the hot and cold interface, and the offset state describes whether the thermocline interface has deviated from its normal position due to external disturbances. These three parameters together constitute a real-time characterization of the heat storage state throughout the entire process, providing direct data support for the formulation of system control strategies.

[0047] Specifically, during system operation, the controller continuously collects temperature readings from the top, middle, and bottom sensors. Taking a typical operating condition as an example, a top sensor reading of 75℃ indicates that the hot water layer fills the upper region; a bottom sensor reading of 15℃ indicates that the cold water layer still has sufficient volume; and a middle sensor reading of 40℃ indicates that the thermocline interface is currently located near the middle region. If the middle sensor temperature rapidly drops from 40℃ to 20℃, it indicates that the thermocline interface has shifted upwards, reducing the hot water storage. Based on this, the system determines whether to increase the heat collection power or reduce the heat output. If the temperature difference between the top and middle sensors decreases while the temperature difference between the middle and bottom sensors increases, it indicates that the thermocline has shifted downwards, the hot water layer has expanded, and the heat collection effect is good. The controller adjusts the speed of the first pump (P-1) and the second pump (P-2), as well as the opening of each control valve, in real time based on these temperature gradient data to achieve coordinated switching between the three modes of heat collection, heat storage, and heat supply.

[0048] The installation of temperature sensors can be achieved by uniformly distributing them at multiple points along the height of the water tank, for example, setting a temperature measurement node every 200-500 mm to obtain a more refined temperature distribution curve and achieve sub-layer precision positioning of the thermocline interface. Alternatively, distributed fiber optic temperature measurement technology can be used, with sensing fibers vertically deployed along the inner wall of the water tank to achieve continuous high-density temperature distribution acquisition and obtain a complete vertical temperature profile. The thickness of the thermocline can be determined using the adjacent sensor temperature difference threshold method; when the temperature difference between two adjacent sensors exceeds a set threshold, a thermocline is determined to exist in that interval. Another method is temperature gradient calculation, which performs differential calculations on the temperature data of each node, using the location of the maximum temperature gradient point to pinpoint the center of the thermocline interface.

[0049] The configuration of multiple temperature sensors enables the system to have real-time perception of the thermal storage status throughout the entire process. Compared with the traditional operation mode that relies on experience judgment or timed detection, closed-loop control supported by real-time monitoring data can significantly reduce heating interruptions or overheating problems caused by misjudgment of thermal storage. Precise temperature curve position perception also enables the system to adjust its operating strategy in a timely manner when the temperature curve thickens abnormally or its position drifts. This organically combines the protective effect of the granular double-layer barrier structure with precise operation control, maximizing the effective utilization rate of thermal energy storage.

[0050] In one optional embodiment, the material properties, density design, adaptive suspension principle, and implementation method of the suspended insulation panel, and its synergy with the dual-density particle layer to form a dual-stabilized heat insulation mechanism, are as follows: In applications, a suspended insulation panel can also be installed within the thermocline thermal storage module 2, serving as a synergistic reinforcing element or an independent alternative to the dual-density particle barrier structure. The suspended insulation panel is made of lightweight insulation material with low thermal conductivity, high temperature resistance, and waterproof and corrosion resistance. Low thermal conductivity means the material itself has weak heat transfer capacity, making it difficult for heat to be conducted from the hot water layer to the cold water layer. High temperature resistance means the material does not soften, deform, or degrade within the system's operating temperature range. Waterproof and corrosion-resistant means the material does not absorb water, swell, dissolve, or produce harmful precipitates in long-term water immersion. The overall density of the suspended insulation panel is between the density of the high-temperature water and the low-temperature water in the hot water storage tank. This density design allows the panel to maintain a neutral equilibrium state within the tank, neither sinking nor floating, adaptively suspending at the thermocline position where hot and cold fluids meet, without requiring a fixed support structure. The suspended insulation panel has a flat and airtight surface that completely covers the inner diameter of the water tank, thus physically separating the upper hot water layer from the lower cold water layer. This completely blocks cross-layer convective heat transfer, and the panel's low thermal conductivity further inhibits vertical heat conduction. When the suspended insulation panel works in conjunction with the dual-density particle barrier structure, the particle layer provides dispersed soft sealing on both sides of the thermocline interface, while the suspended insulation panel provides continuous planar rigid isolation. Together, they form a dual thermocline stabilization and heat preservation mechanism, complementing each other. Alternatively, when the system uses the suspended insulation panel instead of the dual-density particle layer alone, the panel independently handles the thermocline stabilization and insulation functions, making it suitable for applications requiring a simpler system structure.

[0051] Specifically, during system operation, the suspended insulation plate floats up and down dynamically according to the position of the thermocline interface. During heat charging, the hot water layer expands downward, the thermocline interface moves downward, and the suspended insulation plate sinks accordingly, always remaining close to the hot and cold interface to maintain physical isolation between the two water bodies. During heat release, the thermocline interface moves upward, and the suspended insulation plate floats upward, following the interface displacement throughout without any active driving. When working in conjunction with dual-density particles, low-density particles 2-1 are suspended at the bottom of the hot water layer above the insulation plate, while high-density particles 2-2 are deposited at the top of the cold water layer below the insulation plate. The particle layer fills any tiny gaps that may exist between the insulation plate and the inner wall of the water tank, enhancing the overall sealing effect. The three-layer structure together forms multiple layers of protection for the thermocline interface.

[0052] The suspended insulation panel can be made of closed-cell polyurethane foam board, with a thermal conductivity of approximately 0.02–0.04 W / (m·K), far lower than that of water. Its density can be precisely controlled within the target range by adjusting the foaming ratio. Alternatively, a hollow sandwich structure can be used, with a thin-walled, heat-resistant engineering plastic surface layer covering a low-density filler material. The surface layer provides waterproof sealing, while the inner layer provides low thermal conductivity and density regulation. The sealing between the suspended insulation panel and the inner wall of the water tank can employ flexible, elastic sealing strips fixed to the perimeter of the panel. These strips maintain elastic contact with the inner wall of the water tank during the panel's up-and-down movement, preventing water from seeping around the panel's edges. Alternatively, a labyrinthine gap structure can be used, with multi-level concave-convex fits between the panel's perimeter and the inner wall of the water tank, suppressing edge seepage through flow resistance.

[0053] The introduction of the suspended insulation panel adds a planar rigid insulation layer to the system, building upon the dual-density granular soft sealing. When these two mechanisms work together, the stability and insulation effect of the thermocline interface are superior to either method alone. The planar insulation eliminates the risk of localized seepage caused by interparticle gaps in the granular layer, while the granular layer compensates for potential bypass heat leakage when the insulation panel edges are not completely sealed. When the suspended insulation panel is used alone, the system structure is simplified, maintenance costs are reduced, and it is suitable for applications requiring high thermal storage capacity but allowing for slightly lower interface stability than optimal, demonstrating the flexibility and configurability of this system design.

[0054] In one optional embodiment, the connection relationship and working principle of the solar collector, the first water pump (P-1), and the solar collector piping, as well as various implementation methods for selecting flat-plate solar collectors, evacuated tube solar collectors, industrial waste heat exchangers, air source heat pump heat exchangers, or geothermal heat exchangers, are as follows: In application, the solar collector module 1 consists of three core components: a solar collector, a first water pump (P-1), and solar collector piping. The solar collector is a heat exchange device that converts external heat source energy into water heat energy. Its outlet is connected to the hot water inlet and outlet at the top of the hot water storage tank via solar collector piping, and its inlet is connected to the cold water inlet and outlet at the bottom of the hot water storage tank via solar collector piping. The first water pump (P-1) is installed on the solar collector piping, providing the driving force for fluid circulation. Connecting the solar collector's outlet to the top of the tank means that the high-temperature hot water generated after heating by the solar collector is directly injected into the hot water layer above the tank, merging with the stored high-temperature water without disturbing the lower cold water layer, conforming to the basic principle of stratified heat storage with hot water above and cold water below. Connecting the solar collector's inlet to the bottom of the tank means that the first water pump (P-1) draws low-temperature cold water from the bottom of the tank and sends it to the solar collector. The low-temperature water entering the solar collector has the greatest temperature difference driving force and the highest heat exchange efficiency. At the same time, drawing cold water from the bottom also avoids disturbing the hot water layer. The first water pump (P-1) controls the flow rate by adjusting its speed. A higher flow rate results in more heat injected per unit time but a smaller increase in water temperature; conversely, a lower flow rate results in a larger increase in water temperature but less heat injected. The control system dynamically adjusts the pump speed based on the relationship between the collector outlet temperature and the water tank top temperature to maintain optimal heat collection conditions. The types of collectors include flat-plate solar collectors, evacuated tube solar collectors, industrial waste heat exchangers, air-source heat pump heat exchangers, and geothermal heat exchangers. These five types cover four types of renewable or waste heat resources: solar energy, industrial waste heat, atmospheric heat energy, and geothermal energy, giving the system broad heat source adaptability.

[0055] Specifically, taking a flat-plate solar collector as an example, when the solar irradiance reaches the heat collection start-up threshold, the control system starts the first water pump (P-1). Low-temperature cold water at approximately 15°C at the bottom of the storage tank flows into the collector through the heat collection pipes. It is heated to 55-75°C within the collector's absorber core. The heated hot water then flows back through the heat collection pipes to the hot water inlet and outlet at the top of the storage tank. The hot water diffuses along the inner wall of the tank and floats above the existing hot water layer, gradually increasing the height of the hot water layer. The thermocline interface moves downwards accordingly, and the two types of particles dynamically adjust their positions to maintain the double-layer barrier structure, ensuring that newly injected hot water does not mix with the lower cold water during the heat collection process. When solar irradiance is insufficient or at night, the control system stops the first water pump (P-1), the heat collection cycle pauses, and the thermocline layer maintains stable insulation thanks to the double-layer barrier structure of the particles.

[0056] For the selection of collector type, flat-plate solar collectors can be used, which are simple in structure, easy to maintain, and moderately costly, making them suitable for rooftop installation. Vacuum tube solar collectors can also be used; the heat collection core tubes inside the vacuum insulated tubes reduce convection and heat conduction, maintaining high heat collection efficiency even under low solar irradiance and low ambient temperature conditions, making them suitable for high-latitude applications or applications with high winter heating demand. The flow control of the first water pump (P-1) can adopt a variable frequency drive, automatically adjusting the pump frequency by real-time detection of the temperature difference between the collector outlet temperature and the top temperature of the water tank. When the temperature difference is large, the flow rate is increased to fully utilize the heat collection capacity; when the temperature difference is small, the flow rate is reduced to avoid excessive circulation and a drop in hot water temperature. Alternatively, a timed intermittent operation mode can be used, setting the pump start-stop schedule based on solar radiation intensity data collected by the radiometer sensor, achieving simple and reliable heat collection control.

[0057] The connection between the collector module 1 and the hot water storage tank ensures a natural coordination between the heat collection process and the stratification of the water tank. The circulation path, from drawing cold water from the bottom to heating it in the collector and then injecting hot water from the top, always follows the natural stratification trend of the water body and does not disturb the thermocline interface. The interchangeability of various collector types allows this system to utilize the most abundant local heat resources according to local conditions, maximizing the system's economy and renewable energy utilization rate. At the same time, the unified hot water storage tank and stratification maintenance mechanism ensure that different heat sources can be stored and utilized with the same high efficiency.

[0058] In an optional embodiment, the circuit configuration and switching logic of the heat collection and storage mode, the direct heat collection mode, and the heat storage and heating mode, as well as the technical features of the low-density particles 2-1 and high-density particles 2-2 dynamically following the position of the thermocline interface and always maintaining the double-layer barrier structure in the heat storage and heating mode, are as follows: In the application, heating module 3 consists of a second water pump (P-2), a third water pump (P-3), heating pipelines, and terminal heating equipment. The hot water inlet and outlet at the top of the hot water storage tank are connected to the inlet of the terminal heating equipment via the heating pipelines, and the outlet of the terminal heating equipment is connected to the cold water inlet and outlet at the bottom of the hot water storage tank via the heating pipelines. The second water pump (P-2) is installed on the heating pipelines to provide driving force, and the third water pump (P-3) is installed on the heating return water pipelines to assist in return water circulation. The terminal heating equipment includes at least one of radiators, underfloor heating coils, and domestic hot water heat exchangers. Radiators radiate heat into the room through convection and radiation, underfloor heating coils provide uniform low-temperature heating to the floor through radiation, and domestic hot water heat exchangers convert the heat in the hot water storage tank into domestic hot water. The system operates in three modes: heat collection and storage mode, direct heat collection mode, and heat storage and supply mode.

[0059] like Figure 2As shown, in the heat collection and storage mode, the heat collection module 1 and the thermocline heat storage module 2 form a closed heat collection and storage loop. The hot water generated by the heat collector is continuously injected into the water tank to replenish the stored heat. The heating module 3 is disconnected from the loop, and the system focuses on maximizing the stored heat.

[0060] like Figure 3 As shown, in the direct heat collection mode, the heat collection module 1 and the heating module 3 are directly connected to form a heat collection and heating circulation loop. The hot water heated by the heat collector flows directly to the terminal heating equipment. This mode is suitable for situations where the heat collection power matches the current heating demand and there is no need for heat storage.

[0061] like Figure 4 As shown, in the thermal storage and heating mode, the thermocline thermal storage module 2 and the heating module 3 form a thermal storage and heating circulation loop. The second water pump (P-2) drives the high-temperature hot water at the top of the thermal storage tank to flow to the terminal heating equipment. The third water pump (P-3) assists in driving the return water circulation. The low-temperature return water after heat release is pressurized by P-3 and flows back from the bottom of the water tank. The thermocline interface gradually moves upward with the heat release process. The low-density particles 2-1 and high-density particles 2-2 dynamically follow the interface displacement, always maintaining the double-layer barrier structure, suppressing the mixing of hot and cold fluids and vertical heat conduction loss, and ensuring a stable and continuous output of hot water temperature.

[0062] The three operating modes can be switched on demand through the coordinated regulation of control valves and water pumps. The control valves are responsible for changing the pipeline connection relationship, and the first water pump (P-1), the second water pump (P-2), and the third water pump (P-3) are responsible for providing the fluid driving force in the corresponding mode. The three work together to enable the system to flexibly respond to different heating and heat collection needs without stopping the machine.

[0063] Among them, control valves V-1 to V-5 are all electric control valves: V-1 is installed on the inlet pipe of the solar collector to control the on / off of the solar collector circulation; V-2 is installed on the hot water outlet pipe at the top of the hot water storage tank to control the on / off of the heating water intake; V-3 is installed on the bypass pipe between the solar collector outlet and the heating module 3 to realize the switching of the direct solar collector supply mode; V-4 is installed on the heating return water pipe to regulate the return water flow; V-5 is installed on the solar collector circulation loop to cooperate with V-1 to complete the start and stop of the solar collector storage mode.

[0064] Specifically, in a typical winter heating daytime operation scenario, when solar radiation is sufficient during the day, the system operates in heat collection and storage mode. The first water pump (P-1) draws cold water from the bottom of the tank into the collector for heating and then pumps it back to the top of the tank, continuously increasing the stored heat. During the peak heating demand period at noon, the system switches to direct heat collection mode, where the hot water generated by the collector is directly driven into the radiator system, achieving immediate use and reducing heat storage loss. In the evening and at night, when solar energy is insufficient but heating demand still exists, the system switches to heat storage and supply mode. The second water pump (P-2) draws stored high-temperature hot water from the top of the tank and sends it to the underfloor heating coils. The third water pump (P-3) assists in the return water circulation. After heat release, the return water flows back from the bottom of the tank, and the thermocline in the tank gradually moves upward. The two types of particles maintain a double-layer barrier structure throughout the process, ensuring that the output water temperature remains stable throughout the heat release process until all the high-temperature hot water in the tank has been released.

[0065] The switching logic for the three operating modes can employ an automatic control strategy based on temperature sensor data. The controller continuously compares the collector outlet temperature, the water tank top temperature, and the terminal heating equipment inlet temperature, automatically triggering mode switching commands according to preset priority and threshold conditions. Alternatively, a combination of user-programmable timetables and automatic control can be used. Users can pre-set mode preferences for different time periods, and the controller executes mode switching according to the timetable when the set conditions are met. In case of abnormal states such as overheating or insufficient heating, the timetable is automatically overridden to perform protective switching. The terminal heating equipment can be configured using radiators and underfloor heating coils operating in parallel. By adjusting the balancing valves on each branch, flow distribution can be achieved to provide differentiated heating for different rooms or floors. Alternatively, a domestic hot water heat exchanger can be connected in series with the heating system. When the supplied hot water temperature meets domestic hot water demand, domestic hot water is prepared first, and the remaining heat is then used for heating, achieving tiered utilization.

[0066] The flexible switching between three operating modes allows the system to dynamically adjust its operating strategy based on real-time changes in heat source status, heat storage capacity, and end-user demand, avoiding energy waste or heating interruptions caused by operating in a single mode. In the thermal storage heating mode, the granular double-layer barrier structure dynamically maintains the thermocline, ensuring a clear stratification of the water tank throughout the long-term heat release process. This allows the end-user heating equipment to obtain a stable supply of hot water throughout the entire heat release cycle, avoiding the problem of sudden drops in hot water temperature caused by mixing of cold and hot water in the later stages of heat release, as is common in traditional thermal storage systems. This significantly improves the system's heating quality and user comfort.

[0067] Example 2 like Figures 1 to 4As shown, this embodiment provides a dual-density matched particle thermocline thermal storage and heating method. This method embodiment is based on the above system embodiment and includes four core steps: natural stratification of filling particles, heat collection module 1 charging, heat supply module 3 releasing heat, and closed-loop control by temperature sensors. Through the adaptive dynamic following characteristics of dual-density particles, the thermocline interface is stably sealed throughout the entire charging and releasing process. The operation process of each step is described in detail below with reference to the accompanying drawings: In application, filling the hot water storage tank with low-density particles 2-1 and high-density particles 2-2 is the first step in system initialization. This step is performed after the tank is first filled with water, or when the tank is put back into use after being emptied and repaired. The filling operation involves adding the two types of particles, prepared in advance according to the density matching principle, to the tank in batches according to the designed weight ratio. Due to the different densities of the two types of particles, low-density particles 2-1 will float on the water surface or at the bottom of the hot water layer, while high-density particles 2-2 will sink to the top of the cold water layer. In the initial water filling stage, the particle distribution is relatively random due to the uniform water temperature. However, as the tank gradually establishes a stratification of hot water on top and cold water on the bottom during the heating process, the two types of particles naturally migrate to their respective equilibrium positions based on their density difference with the hot and cold water bodies. Low-density particles 2-1 gather at the bottom of the high-temperature water layer, and high-density particles 2-2 are deposited at the top of the low-temperature water layer, automatically forming a symmetrical double-layer barrier structure without manual intervention. The completion of natural particle stratification is indicated by the temperature sensor showing a stable temperature gradient in the tank. At this point, the particle layer is in place and begins to perform its function of stabilizing the temperature gradient.

[0068] In application, charging the hot water storage tank with heat through the heat collection module 1 is the energy input step for system operation. Its purpose is to store the heat energy collected from external heat sources as high-temperature water in the upper hot water layer of the tank, gradually increasing the heat storage capacity of the hot water storage tank. During the charging process, high-temperature hot water is injected through the top hot water inlet and outlet, while low-temperature cold water is discharged through the bottom cold water inlet and outlet. The hot water injection at the top does not disturb the lower cold water layer, and the cold water discharge at the bottom does not disturb the upper hot water layer. The design of the two inlets located at the vertical ends of the tank ensures that the inflow and outflow of water minimizes disturbance to the stratified structure within the tank. The gradual formation of a stable stratified water body with hot water at the top and cold water at the bottom within the tank refers to the continuous increase in the height of the hot water layer and the steady downward movement of the thermocline interface as the charging time extends, transforming the overall tank from an initial uniform temperature state to a stratified heat storage state with a distinct temperature gradient. The adaptive distribution of dual-density particles with the position of the thermocline interface refers to the fact that the two types of particles do not require any external driving force, but rely solely on the dynamic balance of buoyancy and gravity to automatically follow the downward movement of the interface and redistribute themselves, always maintaining a double-layer sealing state in which low-density particles 2-1 cover the upper part of the interface and high-density particles 2-2 cover the lower part of the interface.

[0069] In application, activating heating module 3 according to heating demand is the execution step to release stored heat to the end-user heating equipment. Heating demand can come from a low room temperature signal fed back by an indoor temperature sensor, a user's manual start-up command for heating, or a preset heating time plan. After activation, the second water pump (P-2) drives the high-temperature hot water at the top of the hot water storage tank to release heat through the end-user heating equipment. The third water pump (P-3) assists in driving the return water circulation. When the hot water flows through radiators, underfloor heating coils, or domestic hot water heat exchangers, it releases heat energy into the indoor environment or water system. The return water, after its temperature drops, is pressurized by the third water pump (P-3) and returns to the water tank from the cold water inlet and outlet at the bottom of the hot water storage tank. The return water enters the lower cold water layer and mixes with the existing cold water, increasing the height of the cold water layer and causing the thermocline interface to move upward. The dynamic following of the thermocline displacement by the granular double-layer barrier structure means that as the interface moves upward, the high-density particles 2-2 and the low-density particles 2-1 move upward as a whole along with the upward movement of the equilibrium point of buoyancy and gravity. The two types of particles always stay close to and block the hot and cold interface, suppressing the mixing between the downward intrusion of cold return water and the upward surge of hot stored water throughout the process. This ensures that the temperature of the hot water drawn from the top of the water tank remains within a small fluctuation range throughout the entire heat release process, avoiding a rapid drop in the supply water temperature due to the mixing of hot and cold water.

[0070] In application, real-time monitoring of the temperature of each layer in the water tank using temperature sensors and adjusting the pump speed and control valve opening based on the monitoring results are the execution steps of the system's closed-loop control. This step is continuously executed throughout the system's operation, regardless of the current operating mode. Real-time monitoring means that the controller continuously reads the temperature sensor data of each layer at a sampling period of seconds or minutes, constructing a profile of the water tank's temperature distribution at the current moment. Automatically adjusting the pump speed and control valve opening based on the height, thickness, and offset of the thermocline means that if the thermocline height is too low, indicating insufficient heat storage, the controller increases the speed of the first pump (P-1) or triggers the start of the auxiliary heat source. If the thermocline thickness increases, indicating decreased stability of the particle layer or excessive flow velocity causing interface disturbance, the controller reduces the pump speed or adjusts the valve to slow the flow rate. If the thermocline offset indicates uneven distribution of heating or heat collection flow, the controller corrects this by adjusting the opening of the corresponding branch valves. The overall goal is the coordinated closed-loop operation of the three modes of heat collection, heat storage, and heat supply; all the above adjustments ultimately aim to ensure the system operates stably at maximum energy efficiency.

[0071] Specifically, in a complete cycle of heat storage and release, the system initially operates in heat collection and storage mode. The first pump (P-1) operates at a speed matched to the irradiance, injecting hot water heated by the solar collector into the tank from the top while simultaneously drawing out cold water from the bottom. The control system monitors the temperature at the top of the tank in real time. When the top temperature reaches the designed maximum heat storage temperature, it automatically reduces the speed of the first pump (P-1) or closes the control valve of the heat collection loop. When heating demand arises, the system switches to heat storage and supply mode. The second pump (P-2) starts drawing hot water from the top of the tank to supply the terminals, and the third pump (P-3) assists in the return water circulation. The control system monitors the inlet temperature of the terminal heating equipment. If this temperature is lower than the design heating temperature, it indicates that the effective hot water layer in the tank is nearly exhausted. The control system issues a low heat storage alarm and activates the auxiliary heat source in advance to ensure uninterrupted heating. Throughout the process, both types of particles automatically maintain a double-layer barrier structure without manual intervention. When the control system detects an abnormal increase in the thickness of the thermocline layer, it promptly reduces the pump flow rate to minimize interface disturbance.

[0072] The particle filling amount can be determined using theoretical calculations based on the water tank volume and design conditions. By calculating the movement range and interface area of ​​the thermocline interface throughout the entire heat charging and discharging process, the minimum particle filling amount that can fully cover the interface can be determined. Alternatively, a physical test calibration method can be used, observing the actual particle coverage effect during the water tank charging and discharging test, and adjusting the filling amount according to the test results until the interface coverage is uniform and without any exposed areas. The speed regulation of the second water pump (P-2) can employ a proportional-integral control algorithm based on the inlet temperature of the terminal heating equipment, adjusting the pump speed in real time according to the deviation between the inlet temperature and the set heating temperature. Alternatively, a fuzzy control algorithm based on indoor temperature feedback can be used, taking the room temperature deviation and the rate of room temperature change as inputs to comprehensively decide the pump speed and valve opening, achieving heating control prioritizing indoor thermal comfort.

[0073] This method organically links four steps—system initialization, thermal storage, heat release and supply, and closed-loop control—to form a complete adaptive thermal storage and supply operation process. Both types of particles respond automatically and passively to changes in the thermocline position throughout all steps, requiring no additional drive devices or complex particle management operations, resulting in extremely low operation and maintenance workload. The closed-loop control step directly correlates temperature sensor data with pump and valve actions, enabling the system to make rapid and accurate adaptive responses to heat source fluctuations, load changes, and ambient temperature variations. It maintains the quality of thermal storage stratification and the stability of the supplied water temperature under various operating conditions, demonstrating the comprehensive advantages of this method in terms of engineering practicality and energy efficiency.

[0074] In an optional embodiment, during the thermal storage process, after the injection of high-temperature hot water, the density of the upper water body decreases, the relative density of low-density particles 2-1 increases and migrates downward to cover the interface between the hot and cold fluids, and the high-density particles 2-2 always settle stably at the top of the low-temperature cold water layer. The dynamic response processes in which the two types of particles jointly hold the hot and cold interface, constrain the thickness of the thermocline layer, and suppress vertical heat conduction loss are as follows: In applications, the dynamic response of the particle layer during thermal charging and storage describes how two types of particles adaptively redistribute upon injection of high-temperature hot water, maintaining continuous sealing of the thermocline interface. After high-temperature hot water is injected from the top of the storage tank, the water temperature near the injection point increases, and the water density in the corresponding area decreases, with the hot water density decreasing from approximately 999 kg / m³ at room temperature. 3 Decreased to approximately 970 kg / m 3 If the density of low-density particles 2-1 is set to 962-970 kg / m³ 3 Within this range, when the density of the upper hot water decreases to a critical point close to or even slightly below the particle density, the buoyancy of the particles is less than their weight, and the net density of the particles relative to the hot water increases, causing them to tend to sink. Driven by this density difference, the particles migrate downwards and cover the interface between the hot and cold fluids. The physical essence of this process is that the particle density remains constant, while the density of the surrounding hot water dynamically decreases due to temperature increases. The change in the density relationship between the two determines the direction of particle movement, thus enabling the particles to passively follow the interface position. The density of the high-density particles 2-2 is 990–995 kg / m³ throughout the entire heating process. 3 It is consistently higher than the minimum density value of approximately 998 kg / m³ in the low-temperature cold water density range. 3 In other words, the buoyancy of high-density particles 2-2 in cold water is always less than their weight, so they always settle stably at the top of the low-temperature cold water layer and their position does not change due to the expansion of the hot water layer, unless the overall position of the hot and cold interface shifts downward, causing the position of the particles to switch from the cold water region to the transition region. The two types of particles jointly holding the hot and cold interface means that low-density particles 2-1 cover the interface from above, while high-density particles 2-2 support the interface from below. The two layers of particles hold the thermocline interface in the middle, creating obstacles to the lateral and longitudinal movement of the hot and cold fluids within the interface region. The low thermal conductivity of the particles reduces vertical heat loss across layers. This means that the presence of the particle layer reduces the equivalent thermal conductivity of the interface region. Even with a vertical temperature gradient, the heat flow through the interface region is less than that in pure water, thus slowing down the rate of heat leakage from the hot water layer to the cold water layer.

[0075] Specifically, in a typical operating condition of a thermal charging and storage process, the initial temperature of the water tank is 20℃, and the water density is approximately 998 kg / m³. 3Both types of particles either settle at the bottom of the tank or remain suspended in the middle. After the collector begins supplying 90°C hot water, the water temperature in the upper part of the tank rapidly rises to approximately 90°C, and the density decreases to approximately 965 kg / m³. 3 At this point, the density of low-density particles 2-1 is 962–970 kg / m³. 3 Slightly lower than the density of the surrounding hot water (particle density close to but slightly lower than water density, experiencing greater upward net buoyancy in the low-temperature cold water zone, and hovering with a density close to water in the high-temperature hot water zone), these particles aggregate at the bottom of the hot water layer and above the hot and cold water interface. As the thickness of the hot water layer increases, the interface continues to move downwards, and the low-density particles 2-1 move downwards accordingly, while the high-density particles 2-2 remain in a settled state at the top of the cold water layer. The double-layer covering structure above and below the interface automatically reconstructs, constraining the thickness of the thermocline layer to not exceed 2 to 3 times the particle diameter, significantly reducing heat loss due to mixing of hot and cold water during the heating process.

[0076] During the heating process, the downward migration rate of low-density particles 2-1 can be controlled by combining particle size and density difference. When the particle diameter is larger, the Stokes settling velocity is faster, enabling a rapid response to interface displacement. Alternatively, a flow straightening and guiding device can be installed at the water inlet at the top of the tank to reduce local impact disturbances during hot water injection, preventing the disturbance velocity from exceeding the particle settling velocity and dislodging the particles from the interface. The thickness of the thermocline layer during heating can be constrained by controlling the flow rate of the first water pump (P-1). Reducing the flow rate of hot water injected per unit time reduces the convection intensity within the tank, minimizing disturbance to the particle layer. Furthermore, a porous distribution plate can be installed at the hot water inlet at the top of the tank to disperse the hot water inflow into a low-velocity, uniform flow, reducing the impact of local flow velocities on the stability of the particle layer.

[0077] The adaptive dynamic response of the particle layer during the heat charging and storage process enables the system to maintain the sealing state of the thermocline interface without any mechanical drive or control signal throughout the entire heat charging process. The interface thickness is constrained by the particle layer, and the expansion of the hot and cold transition zone is effectively suppressed. Compared with traditional hot water storage tanks without particles, the thickness of the thermocline layer is significantly reduced, and the effective heat storage volume is thus increased. After the heat charging is completed, the temperature uniformity of the high-temperature hot water layer in the tank is better, which creates conditions for the subsequent output of higher quality hot water.

[0078] In an optional embodiment, during the heat release and heating process, after the low-temperature return water is injected, the density of the upper water increases, the low-density particles 2-1 rise due to buoyancy and remain suspended above the interface between the cold and hot fluids, and the high-density particles 2-2 move upward synchronously with the top of the cold water layer. The two types of particles work together to maintain the double-layer barrier structure, preventing the upper cold water from intruding downwards and the lower hot water from rising upwards. At the same time, the dynamic response process of reducing vertical heat loss by utilizing the low thermal conductivity is as follows: In application, the dynamic response of the particle layer during exothermic heating describes how two types of particles adaptively move upward as low-temperature return water enters the water tank, maintaining continuous sealing of the thermocline interface. Low-temperature return water enters the water tank through the cold water inlet and outlet at the bottom of the hot water storage tank. After entering, it mixes with the existing cold water layer, increasing the height of the cold water layer and causing the thermocline interface to move upward. If the return water temperature from the terminal equipment in the heating system is significantly lower than the temperature of the high-temperature hot water layer, a large amount of return water from the bottom will cause the top surface of the cold water layer to rise, directly pushing the thermocline interface upward. As the interface moves upward, the water surrounding the low-density particles 2-1 gradually changes from higher-temperature hot water to lower-temperature water. The density of the surrounding water increases as the temperature decreases. When the water density rises to a level comparable to that of the low-density particles 2-1, the buoyancy and gravity of the particles reach equilibrium again. If the water density further increases beyond the particle density, the particles experience an upward net buoyancy force, causing them to float upward and remain suspended above the interface between the hot and cold fluids. The physical nature of this process is the opposite of the heat-filling stage. During the heat-filling stage, the particles sink due to the increased relative density caused by the decrease in hot water density. During the heat-release stage, the particles float upwards from the bottom of the hot water layer due to the increased density of cold water. In both processes, the particles automatically adjust their position according to the interface without external intervention. The synchronous upward movement of high-density particles 2-2 with the top of the cold water layer means that high-density particles 2-2 remain stably settled at the top of the cold water layer throughout the entire heat-release process. The top of the cold water layer moves upwards as a whole with the interface, and the high-density particle 2-2 group moves upwards accordingly, maintaining a cooperative relationship with the low-density particle 2-1 layer. The description of the two types of particles jointly sealing the hot and cold interface describes the dual-layer particle structure working together to prevent the downward intrusion of cold water from the upper layer and the upward surge of hot water from the lower layer. The low-density particle 2-1 layer prevents the downward seepage of cold water from the upper layer, while the high-density particle 2-2 layer prevents the upward surge of hot water from the lower layer. The two layers of particles form a complementary bidirectional sealing effect. The low thermal conductivity reduces vertical heat loss and also plays a role in the heat release stage. The thermal conductivity of the particle layer is lower than that of the water body, which reduces the heat conduction rate in the interface area, delays the process of heat penetrating from the hot water layer to the cold water layer, and ensures the temperature maintenance time of the hot water layer and the continuous stability of the heat output.

[0079] Specifically, during the heat release and heating process, it is assumed that the initial state of the water tank consists of an upper 75°C hot water layer and a lower 15°C cold water layer, with both types of particles in their respective equilibrium positions. As the second water pump (P-2) extracts hot water from the top, and the third water pump (P-3) assists in the return water circulation, the return water at the end flows back from the bottom at a temperature of approximately 35-45°C, and the height of the cold water layer gradually increases. The rate of interface upward movement is proportional to the heating flow rate. When the interface moves upward by approximately 100mm, the high-density particle layer 2-2, which was originally located below the interface, moves upward by 100mm along with the top of the cold water layer. The low-density particle layer 2-1, driven by the density change of the water in the transition zone between the rising hot and cold water, also floats upward by 100mm. Both particle layers move synchronously with the interface displacement, and the interface blockage is maintained throughout the process. Throughout the heat release process, the reading of the hot water temperature sensor at the top of the water tank remained within the range of 70-75℃, indicating that the particle barrier structure effectively prevented the mixing of hot and cold water, and the output water temperature remained stable until the height of the hot water layer dropped to the minimum design water level before the water temperature began to decline.

[0080] During the heat release phase, the upward movement response of the particle layer can be accelerated by reducing the density difference between the particles and the water. The smaller the density difference, the more sensitive the particles are to changes in buoyancy and the faster they respond to interface displacement. Alternatively, particle inertia can be reduced by controlling the particle diameter within a smaller range, allowing the particles to achieve rapid displacement response with a lower density difference driving force. To suppress the impact disturbance caused by return water entering the tank from the bottom during the heating process, low-speed distribution baffles can be installed at the cold water inlet and outlet to disperse the return water inflow velocity across the entire cross-section, reducing the impact of local flow velocity on the particle layer. Variable frequency pumps can also be used to control the heating flow rate, appropriately reducing the heating flow rate during the rapid upward movement phase of the interface to slow down the interface displacement velocity, allowing the particle layer sufficient time to adjust its position.

[0081] The dynamic adaptive following characteristics of the granular layer during the heat release and heating phase ensure that the hot water storage tank maintains a clear stratification throughout the entire heat release process. The temperature and volume of the effective hot water layer are fully protected. Compared with traditional hot water storage tanks without granular layer protection, the effective heat release is significantly improved, and the stable duration of the heating output water temperature is significantly extended. This avoids the phenomenon of sudden drop in hot water temperature caused by the mixing of hot and cold water in the later stages of heat release in traditional systems, fundamentally improving the energy utilization rate and user-end thermal comfort guarantee capability of the thermal storage and heating system.

[0082] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A dual-density matched particle thermocline thermal storage and heating system, characterized in that, It includes a heat collection module (1), a thermocline heat storage module (2), and a heating module (3); The heat collection module (1) is fluidly connected to the thermocline heat storage module (2) and is used to collect heat from external heat sources and transport it to the thermocline heat storage module (2) for layered storage; the external heat sources include any one or more of solar energy, industrial waste heat, air energy, and geothermal energy; the thermocline heat storage module (2) is fluidly connected to the heating module (3) and is used to release the stored heat to the heating module (3) as needed to achieve end-point heating; The thermocline thermal storage module (2) includes a hot water storage tank, which is a closed pressurized water tank; the hot water storage tank is provided with a hot water inlet and outlet at the top and a cold water inlet and outlet at the bottom; the hot water storage tank is filled with low-density particles (2-1) and high-density particles (2-2). The density of the low-density particles (2-1) is higher than the density of the high-temperature water in the hot water storage tank under rated operating conditions and lower than the density of the low-temperature water; the density of the high-density particles (2-2) is higher than the density of the high-temperature water and lower than the density of the low-temperature water, and the densities of both types of particles are between the densities of the high-temperature water and the low-temperature water. The densities of the low-density particles (2-1) and the high-density particles (2-2) are both between the densities of the high-temperature water and the low-temperature water. The two types of particles form a symmetrical double-layer barrier structure on the upper and lower sides of the thermocline interface. The thermal conductivity of the low-density particles (2-1) and the high-density particles (2-2) is lower than that of water, and the particle surfaces are smooth and round.

2. The dual-density matched particle thermocline thermal storage and heating system according to claim 1, characterized in that, Both the low-density particles (2-1) and the high-density particles (2-2) are chemically inert, high-temperature resistant, water-insoluble, and have a smooth and rounded surface with low thermal conductivity. The density of the low-density particles (2-1) is 962-970 kg / m³. 3 The density of the high-density particles (2-2) is 990-995 kg / m³. 3 The diameter of both the low-density particles (2-1) and the high-density particles (2-2) is 5-30 mm.

3. The dual-density matched particle thermocline thermal storage and heating system according to claim 1, characterized in that, The high-density particles (2-2) are selected from at least one of glass microspheres or high-temperature resistant ceramic particles; the low-density particles (2-1) are selected from at least one of low thermal conductivity inert polymer particles or inorganic lightweight solid particles; the thermal conductivity of both types of particles is lower than that of water, and the particle surface is smooth and does not generate additional turbulence disturbance.

4. The dual-density matched particle thermocline thermal storage and heating system according to claim 1, characterized in that, The thermocline thermal storage module (2) also includes multiple temperature sensors, which are fixedly installed vertically in the top, middle and bottom areas of the hot water storage tank to detect the water temperature at different heights in the tank in real time, accurately obtain the height, thickness and offset of the thermocline, and realize real-time monitoring and control of the thermal storage status throughout the process.

5. The dual-density matched particle thermocline thermal storage and heating system according to claim 1, characterized in that, The thermocline thermal storage module (2) is also equipped with a suspended thermal insulation plate; the suspended thermal insulation plate is made of lightweight thermal insulation material with low thermal conductivity, high temperature resistance, waterproof and corrosion resistance; When the suspended heat insulation plate is used in conjunction with the dual-density particle barrier structure, the overall density of the suspended heat insulation plate is slightly lower than the density of the high-temperature water in the hot water storage tank. It floats adaptively above the liquid surface in the hot water storage tank and rises and falls with the liquid level. It isolates the liquid surface from the convective and radiative heat dissipation of the outside air, forming a dual heat insulation structure with the dual-density particle barrier structure, which provides heat insulation at the top liquid surface and internal interlayer barrier.

6. The dual-density matched particle thermocline thermal storage and heating system according to claim 1, characterized in that, The heat collection module (1) includes a heat collector, a first water pump (P-1), and a heat collection pipeline. The outlet of the heat collector is connected to the hot water inlet and outlet at the top of the hot water storage tank via the heat collection pipeline, and the inlet of the heat collector is connected to the cold water inlet and outlet at the bottom of the hot water storage tank via the heat collection pipeline. The first water pump (P-1) is installed on the heat collection pipeline. During operation, the first water pump (P-1) drives the low-temperature cold water at the bottom of the hot water storage tank to enter the heat collector to absorb heat and raise its temperature. The high-temperature hot water after being raised flows back to the top of the hot water storage tank via the pipeline, continuously constructing a layered water body with hot water at the top and cold water at the bottom in the water tank, completing the automatic heat collection and charging cycle of the system. The heat collector is a flat-plate solar collector or a vacuum tube solar collector, or any one of an industrial waste heat exchanger, an air source heat pump heat exchanger, or a geothermal heat exchanger.

7. The dual-density matched particle thermocline thermal storage and heating system according to claim 1, characterized in that, The heating module (3) includes a second water pump (P-2), a third water pump (P-3), several control valves, heating pipelines, and terminal heating equipment; the hot water inlet and outlet at the top of the hot water storage tank are connected to the inlet of the terminal heating equipment via the heating pipeline, and the outlet of the terminal heating equipment is connected to the cold water inlet and outlet at the bottom of the hot water storage tank via the heating pipeline; the terminal heating equipment is at least one of radiators, floor heating coils, or domestic hot water heat exchangers; the system has three operating modes: heat collection and storage, direct heat collection and supply, and heat storage and supply, which can be switched on demand through the coordinated regulation of the control valves and water pumps.

8. A dual-density matched particle thermocline thermal storage and heating method, applied to the system according to any one of claims 1 to 7, characterized in that, The method includes the following steps: Low-density particles (2-1) and high-density particles (2-2) are filled into the hot water storage tank. The two types of particles naturally stratify in the tank due to their density difference. The low-density particles (2-1) are suspended at the bottom of the high-temperature water layer, and the high-density particles (2-2) are settled at the top of the low-temperature water layer, forming a symmetrical double-layer particle barrier structure on both sides of the thermocline interface. Heat is charged into the hot water storage tank through the heat collection module (1). High-temperature hot water is injected from the top hot water inlet and outlet, and low-temperature cold water is discharged from the bottom cold water inlet and outlet. A stable layered water body with hot water on top and cold water on the bottom is gradually formed in the water tank. The dual-density particles are adaptively adjusted according to the position of the thermocline interface to continuously maintain the stability of the thermocline. The heating module (3) is activated according to the heating demand, and the high-temperature hot water at the top of the hot water storage tank is driven to release heat through the terminal heating equipment. After the heat is released, the low-temperature return water returns from the bottom of the hot water storage tank. The granular double-layer barrier structure dynamically follows the displacement of the temperature jump layer, suppressing the mixing of hot and cold fluids throughout the process and ensuring stable output of hot water temperature. The temperature of each layer in the water tank is monitored in real time by temperature sensors. The pump speed and control valve opening are automatically adjusted according to the height, thickness and offset of the thermocline, so as to realize the closed-loop coordinated operation of the three modes of heat collection, heat storage and heat supply.

9. The dual-density matched particle thermocline thermal storage and heating method according to claim 8, characterized in that, During the heat storage process, the dynamic response of the particle layer is as follows: High-temperature hot water is injected from the top of the hot water tank, and the density of the water in the upper part of the tank decreases as the temperature rises; when the density of the hot water in the upper part is lower than the density of the low-density particles (2-1), the relative density of the low-density particles (2-1) increases, and they migrate downwards with the density difference, covering the interface between the hot and cold fluids; the high-density particles (2-2) always settle stably at the top of the low-temperature cold water layer; the two types of particles together hold the hot and cold interface, constrain the thickness of the thermocline layer, and at the same time, the low thermal conductivity of the particles weakens the vertical heat conduction loss across the layers, inhibits the heat dissipation of water mixing during the heat storage process, and ensures the layered heat storage effect of the water tank.

10. The dual-density matched particle thermocline thermal storage and heating method according to claim 8, characterized in that, During the heat release and heating process, the dynamic response of the particle layer is as follows: Low-temperature return water flows back into the water tank from the cold water inlet and outlet at the bottom of the hot water storage tank. The height of the cold water layer gradually increases, and the thermocline interface moves upward accordingly. The water temperature at the bottom of the water tank remains low as the return water flows in, while the upper hot water layer continuously outputs heat to the terminal heating equipment. When the density of the upper water is higher than the density of the low-density particles (2-1), the low-density particles (2-1) rise due to buoyancy and remain suspended above the interface between the cold and hot fluids. The high-density particles (2-2) move upward synchronously with the top position of the cold water layer and work together with the low-density particles (2-1) to maintain the double-layer barrier structure. The two types of particles jointly block the cold and hot interface, preventing the upper cold water from intruding downward and the lower hot water from rising upward. At the same time, the low thermal conductivity reduces vertical heat loss, ensuring that the stored hot water releases heat in an orderly manner in layers, and improving the system's heating stability and thermal energy utilization rate.

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