A multi-stage solar evaporator based on reverse distillation

Abstract

The application provides a multi-stage solar evaporator based on reverse distillation, which is characterized in that the multi-stage solar evaporator comprises a sunlight heat collection unit, a first-stage seawater evaporation unit, a rear-stage condensation unit and a fresh water collection unit, the first-stage seawater evaporation unit comprises a wick, the sunlight heat collection unit is thermally coupled to the wick, a water supply end of the wick is connected to seawater, the water supply end is higher than an inlet of an evaporation interface formed by thermal coupling of the wick and the sunlight heat collection unit, heat transferred from the sunlight heat collection unit to the wick evaporates part of the seawater flowing through the wick, the generated steam is condensed in the rear-stage condensation unit, and the condensed water is collected by the fresh water collection unit. Through the arrangement that the water supply end is higher than the inlet of the evaporation interface, the transport speed of salt ions in the hydrophilic material is strengthened to be greater than the aggregation speed of the salt ions, the salt ion deposition problem is relieved, meanwhile, the rear-stage condensation unit reduces the heat conduction loss of the seawater and improves the evaporation efficiency.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination technology, and in particular to a multi-stage solar evaporator based on reverse distillation. Background Technology

[0002] Solar-powered seawater desalination technology is an effective method to alleviate the global shortage of freshwater resources, and it also features zero energy consumption and low carbon emissions. Furthermore, its advantages such as low cost, high portability, and low equipment configuration complexity make it a promising application in remote and impoverished off-grid areas. Compared to traditional distillation technologies based on overall heating, solar-driven reverse distillation technology is considered a promising alternative. It not only eliminates the loss of light and heat conduction to the water source in traditional distillation modes (upward evaporation / condensation), but also achieves condensation heat recovery and expands the selection of materials by decoupling evaporator performance. However, hydrophilic materials transport water slowly through capillary action and have a very limited water carrying capacity. Under high-concentration seawater and intense sunlight, seawater evaporates rapidly, and salt ions quickly accumulate and crystallize at the evaporation interface. The formation of crystalline salts significantly reduces the evaporation performance and lifespan of the reverse distillation system, hindering long-term large-scale application.

[0003] Currently, researchers are mainly addressing the problem of salt deposition by focusing on material wettability and evaporator structural design.

[0004] (1) Salt precipitation design at specific locations: By optimizing the evaporator structure, the salt crystallization process is confined to specific locations (edges, ends, etc.) of the evaporator and collected.

[0005] (2) Shielding effect: Hydrophobic photothermal materials (fully hydrophobic structure, hydrophilic / hydrophobic bilayer Janus structure) or polyelectrolyte materials (Daunan effect) are used to confine salt ions to the region below the photothermal interface, thereby slowing down the deposition of salt ions at the photothermal interface;

[0006] (3) Potential field liquid flow driven: By improving the wettability of the material surface and optimizing the pore structure, under the driving force of concentration difference (nighttime self-dissolution, reverse self-diffusion), gravity (unidirectional liquid flow) and surface tension (Marangoni effect), the convective diffusion between the light absorber and the water body is enhanced, and the local enrichment of salt ions is avoided.

[0007] (4) Non-contact interface design: Separate the light absorber from the water body to completely avoid the problem of salt deposition on the light absorber.

[0008] Most of the strategies mentioned above were developed for traditional upward evaporation distillation systems. Strategies suitable for reverse distillation systems primarily utilize concentration gradients and surface tension to drive salt ions to spontaneously diffuse back into the water through hydrophilic materials from the evaporation interface. However, at high evaporation rates, the rate at which salt ions spontaneously diffuse away from the evaporation interface is far less than their accumulation rate, and the salt deposition problem remains unresolved. Furthermore, during evaporation, the diffusion of salt ions into the water increases heat transfer losses, thereby reducing evaporation efficiency.

[0009] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0010] The purpose of this invention is to provide a multi-stage solar evaporator based on reverse distillation, which can solve the problems of salt ion deposition at the evaporation interface and reduced evaporation efficiency.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] A multi-stage solar evaporator based on reverse distillation is provided, comprising a solar heat collection unit, a first-stage seawater evaporation unit, a subsequent condensation unit, and a freshwater collection unit. The first-stage seawater evaporation unit includes a liquid absorber core, and the solar heat collection unit is thermally coupled to the liquid absorber core. The water supply end of the liquid absorber core is connected to seawater, and the water supply end is higher than the inlet of the evaporation interface formed by the thermal coupling between the liquid absorber core and the solar heat collection unit. The heat transferred from the solar heat collection unit to the liquid absorber core evaporates part of the seawater flowing through the liquid absorber core. The generated steam is condensed in the subsequent condensation unit, and the condensate is collected by the freshwater collection unit.

[0013] In some embodiments of the present invention, the subsequent condensation unit includes one or more condensation / evaporation units and a final condensation unit. Each condensation / evaporation unit includes a condensing plate for receiving steam from the upper evaporation unit and a liquid-absorbing core attached to the condensing plate. The condensate generated by each condensing plate and the final condensation unit is collected by the freshwater collection unit. The liquid-absorbing core of the condensation / evaporation unit absorbs seawater by gravity or capillary action.

[0014] In some embodiments of the present invention, the first-stage seawater evaporation unit and the subsequent-stage condensation unit are vertical structures separated by a vertical air gap. The upper end of the liquid absorption core of the first-stage seawater evaporation unit is immersed in seawater, and the upper or lower end of the liquid absorption core of the subsequent-stage condensation unit is immersed in seawater.

[0015] In some embodiments of the present invention, the condenser plate of the last stage condensation unit is inserted into seawater.

[0016] In some embodiments of the present invention, the solar heat collection unit includes a parabolic concentrator and a heat absorber. The heat absorber extends vertically downward in contact with the liquid absorption core of the first-stage seawater evaporation unit. The parabolic concentrator is configured to reflect and concentrate sunlight onto the heat absorber. Preferably, it also includes a transparent glass plate installed above the parabolic concentrator.

[0017] In some embodiments of the present invention, the first-stage seawater evaporation unit and the subsequent-stage condensation unit are horizontal structures separated by a horizontal air gap. One end of the liquid absorption core of each of the first-stage seawater evaporation unit and the subsequent-stage condensation unit is immersed in seawater, and a hydrophobic membrane for preventing seawater from passing through is provided at the bottom of each liquid absorption core.

[0018] In some embodiments of the present invention, the solar heat collection unit includes a Fresnel lens and a heat absorber. The heat absorber is disposed above the liquid absorption core of the first-stage seawater evaporation unit, and the Fresnel lens is disposed above the heat absorber to concentrate sunlight onto the surface of the heat absorber. Preferably, it also includes a transparent glass plate mounted above the Fresnel lens.

[0019] In some embodiments of the present invention, the seawater flow rate is controlled by controlling the height difference between the water supply end and the evaporation interface inlet.

[0020] In some embodiments of the present invention, the flow rate of seawater at the inlet of the evaporation interface is adjusted by adjusting the contact area between the liquid absorption core of the first-stage seawater evaporation unit and the seawater.

[0021] In some embodiments of the present invention, the liquid-absorbing core extends to the height of the water supply end or is connected to the water supply end via an intermediate conduit.

[0022] The present invention has the following beneficial effects:

[0023] This invention incorporates a solar heat collection unit, a first-stage seawater evaporation unit, a subsequent condensation unit, and a freshwater collection unit. The solar heat collection unit is thermally coupled to the absorbent core of the first evaporation unit. The water supply end of the absorbent core is connected to seawater and is higher than the inlet of the evaporation interface formed by the thermal coupling between the absorbent core and the solar heat collection unit. The heat transferred from the solar heat collection unit to the absorbent core evaporates part of the seawater flowing through it. The resulting steam is condensed in the subsequent condensation unit. The height difference between the water supply end and the inlet of the evaporation interface enhances the transport rate of salt ions in the hydrophilic material of the absorbent core, making it greater than the salt ion aggregation rate, thus alleviating the salt ion deposition problem. It also reduces the heat conduction loss caused by the diffusion of salt ions into the water body during the evaporation process in the first evaporation unit, thereby improving the evaporation efficiency.

[0024] In some embodiments of the present invention, the seawater flow rate is controlled by controlling the height difference between the water supply end and the evaporation interface inlet, thereby adjusting the evaporation rate and seeking a balance between salt resistance and reducing heat conduction loss, thus achieving the effect of improving the evaporation efficiency of the multi-stage solar evaporator based on reverse distillation.

[0025] In some embodiments of the present invention, the flow rate of seawater at the evaporation interface inlet can be adjusted by adjusting the contact area between the liquid absorption core of the first-stage seawater evaporation unit and the seawater, thereby adjusting the evaporation rate and seeking a balance between salt resistance and reducing heat conduction loss, thereby improving the evaporation efficiency of the multi-stage solar evaporator based on reverse distillation.

[0026] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the vertical multi-stage solar evaporator with water supply from bottom to top in an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the vertical multi-stage solar evaporator with a water supply method from top to bottom in an embodiment of the present invention;

[0029] Figure 3 This is a schematic diagram of the structure of a horizontal multi-stage solar evaporator with a water supply method from bottom to top in an embodiment of the present invention;

[0030] Figure 4 This is a schematic diagram of the structure of a horizontal multi-stage solar evaporator with a water supply method from top to bottom in an embodiment of the present invention;

[0031] Figure 5 This is a detailed view of the height difference between the water supply end and the inlet of the vertical and horizontal multi-stage solar evaporators in this embodiment of the invention;

[0032] Figure 6This is a side view of the absorbent core with different soaking areas in an embodiment of the present invention.

[0033] Figure label:

[0034] 1. Insulation cotton, 2. Transparent glass plate, 3. Parabolic concentrator, 4. Absorber, 5. Liquid absorber core, 6. Condenser plate, 7. Seawater, 8. U-shaped tube, 9. Fresnel lens, 10. Hydrophobic film, 11. Fresh water, 12. Brine, 13. Acrylic plate, 14. Concentrating chamber, 51. Evaporation interface inlet, 52. Water supply end. Detailed Implementation

[0035] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0036] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for fixing, coupling, or communication.

[0037] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0039] Based on the aforementioned background problems, this invention proposes a multi-stage solar evaporator based on reverse distillation by optimizing the evaporator structure. The evaporator includes a solar heat collection unit, a first-stage seawater evaporation unit, a subsequent condensation unit, and a freshwater collection unit. The first-stage seawater evaporation unit includes a liquid absorber 5. The solar heat collection unit is thermally coupled to the liquid absorber 5. The water supply end 52 of the liquid absorber 5 is connected to seawater 7. The water supply end 52 is higher than the inlet of the evaporation interface formed by the thermal coupling between the liquid absorber 5 and the solar heat collection unit. The heat transferred from the solar heat collection unit to the liquid absorber 5 evaporates a portion of the seawater 7 flowing through the liquid absorber 5. The generated steam is condensed in the subsequent condensation unit, and the condensate is collected by the freshwater collection unit.

[0040] The liquid absorption core 5 of the first-stage seawater evaporation unit can extend to the height of the water supply end 52, or it can be connected to the water supply end 52 through a connecting pipe.

[0041] In this embodiment of the invention, the transport rate of salt ions in seawater 7 within the hydrophilic material of the absorbent core 5 is enhanced in the first-stage seawater evaporation unit, making it greater than the salt ion aggregation rate, thus alleviating the salt ion deposition problem. The remaining subsequent condensation units, due to limited energy input, have relatively slow evaporation rates, and salt crystallization is not significant. Therefore, the capillary force or gravity of the absorbent core 5 is still used to spontaneously and directionally transport seawater 7, and desalination occurs through nighttime self-dissolution. Simultaneously, by extending the evaporation interface formed by the thermal coupling between the absorbent core 5 and the solar heat collection unit in the first-stage seawater evaporation unit, the seawater 7 flowing out of the heating area of ​​the absorbent core 5 continues to evaporate, thereby reducing heat conduction losses during the diffusion of salt ions into the water body.

[0042] In different embodiments, the first-stage seawater evaporation unit and the subsequent condensation unit can be a vertical structure separated by a vertical air gap or a horizontal structure separated by a horizontal air gap, thereby forming two types of efficient salt removal multi-stage solar evaporation structures based on reverse distillation (vertical and horizontal), namely, a vertical multi-stage solar evaporator and a horizontal multi-stage solar evaporator.

[0043] Example 1

[0044] Vertical multi-stage solar evaporators (VMSS) come in two types: Figure 1 The water supply method uses a bottom-up vertical multi-stage solar evaporator, and Figure 2The water supply system utilizes a top-down vertical multi-stage solar evaporator, which includes a solar heat collection unit, a first-stage seawater evaporation unit, a subsequent condensation unit, and a freshwater collection unit. The solar heat collection unit comprises a parabolic concentrator 3 and an absorber 4. The parabolic concentrator 3 is covered with insulation cotton 1 to reduce heat loss through conduction to the environment, thereby increasing the temperature inside the concentrator chamber and the absorber temperature, and improving the system's water production rate. The parabolic concentrator 3 reflects sunlight onto the absorber 4 while maintaining the absorber 4 at a relatively high temperature. The absorber 4 extends vertically downwards, attached to the liquid absorption core 5. The parabolic concentrator 3 is designed to reflect and concentrate sunlight onto the absorber 4. The concentrator 3 is installed on the left side of the first-stage seawater evaporation unit, allowing it to receive incident light at any solar altitude angle. Preferably, in this embodiment of the invention, a transparent glass plate 2 is also installed above the parabolic concentrator 3 to prevent interference from the external environment inside the concentrator chamber. The parabolic concentrator 3, the transparent glass plate 2, and the upper end of the absorber together form a concentrator chamber 14. Without the transparent glass plate 2, the air inside the concentrator chamber 14 and the absorber 4 are in direct contact with the outside, resulting in significant heat loss and consequently, a low temperature inside the concentrator chamber 14 and a decrease in the system's water production rate. When the transparent glass plate 2 is installed, the heat loss of the hot air inside the concentrator chamber 14 to the outside is reduced, and the temperature inside the concentrator chamber 14 and the temperature of the absorber plate 4 are increased.

[0045] The intensity of solar radiation varies in different regions, allowing for flexible selection. Figure 1 or Figure 2 In a VMSS (Mean Seawater Sedimentation System), if the solar radiation intensity in the region is weak, the seawater supply to the first-stage evaporation unit is from top to bottom, while the seawater supply to the subsequent condensation unit is from bottom to top. Figure 1 The structure is such that if the solar radiation intensity in the region is strong, salt accumulation may still occur in the subsequent condensation unit. Therefore, the seawater supply for both the first-stage seawater evaporation unit and the subsequent condensation unit adopts a top-down structure. Figure 2 The structure.

[0046] In areas with weak solar radiation, adopt Figure 1The VMSS (Seawater Vapor Storage System) consists of multiple vertical units, including a first-stage seawater evaporation unit and a subsequent condensation unit. The first-stage seawater evaporation unit supplies seawater from top to bottom, while the subsequent condensation unit supplies seawater from bottom to top. The first-stage seawater evaporation unit includes a liquid absorber 5, to which a solar heat collection unit is thermally coupled. The water supply end 52 of the liquid absorber 5 is connected to seawater 7. The liquid absorber 5 extends to the height of the water supply end 52 or is connected to the water supply end 52 via an intermediate conduit. The water supply end 52 is higher than the liquid absorber 5 and thermally coupled to the solar heat collection unit. The inlet of the evaporation interface formed by the combination, the subsequent condensation unit includes one or more condensation / evaporation units and a final condensation unit. Each condensation / evaporation unit includes a condensing plate 6 for receiving steam from the upper evaporation unit and a liquid suction core 5 attached to the condensing plate 6. The liquid suction core 5 and the condensing plate 6 are parallel to each other and highly overlap. The condensate produced by each condensing plate 6 and the final condensation unit is collected by a freshwater collection unit, which is a U-shaped tube 8. The liquid suction core 5 of the condensation / evaporation unit absorbs seawater 7 from bottom to top by capillary action.

[0047] The first-stage seawater evaporation unit's absorbent core 5 and the subsequent condensation unit are vertically separated by a vertical air gap. The upper end of the absorbent core 5 in the first-stage seawater evaporation unit is immersed in seawater 7, and the lower end of the absorbent core 5 in the subsequent condensation unit is immersed in seawater 7. The absorbent core 5 is attached to one side of the absorber 4 in the first-stage seawater evaporation unit or the condenser plate 6 in the subsequent condensation unit, serving as the evaporation interface. The uncovered side of the condenser plate 6 serves as the condensation interface. The condenser plate 6 of the final condensation unit is inserted into the seawater 7 to increase the overall temperature difference of the system and improve evaporation efficiency. A U-shaped tube 8 is installed at the bottom of the condenser plate 6 to collect the obtained freshwater 11.

[0048] As the sun rises, the vertical multi-stage solar evaporator begins operation. Sunlight entering the parabolic concentrator 3, whether directly or reflected, converges onto the surface of the absorber 4, where photothermal conversion occurs. Heat transferred from the solar heat collection unit to the absorbing core 5 evaporates some of the seawater 7 within it. The seawater 7 in the absorbing core 5 is heated by the absorber 4 and generates steam. Driven by a temperature gradient, the steam passes through the narrow gaps of the subsequent condensation unit, reaches the condenser plate 6, and condenses. The condensate droplets, under gravity, converge into the U-shaped tube 8 of the freshwater collection unit, finally leaving the subsequent condensation unit and being collected. The latent heat released during condensation serves as the heat source for the next stage of evaporation / condensation, driving the evaporation and condensation process in that stage.

[0049] like Figure 5As shown in Figure a, the water supply end 52 is positioned higher than the inlet of the evaporation interface formed by the thermal coupling of the absorbent core 5 of the first-stage seawater evaporation unit and the solar heat collection unit. The seawater flow rate is controlled by adjusting the height difference between the water supply end 52 and the inlet of the evaporation interface, with the height difference being H1. Therefore, water pressure is generated at the inlet 51 of the evaporation interface. Under the combined action of water pressure, gravity, and the Marangoni effect, the seawater 7 continuously flows downward. In this embodiment of the invention, a beaker is used to collect the downward-flowing brine 12. This also significantly increases the downward diffusion rate of salt ions, which is greater than the aggregation rate caused by evaporation, thus preventing the formation of salt crystals. Furthermore, the downward extension of the absorber 4 and the absorbent core 5 ensures a continuous evaporation / condensation process, avoiding heat conduction losses caused by the rapid downward diffusion of seawater 7.

[0050] In areas with high solar radiation intensity, adopt Figure 2 The VMSS (Seawater Vapor Storage System) consists of multiple vertical units, including a first-stage seawater evaporation unit and a subsequent condensation unit. Both the first-stage and subsequent condensation units utilize a top-down seawater supply structure. The first-stage seawater evaporation unit includes a liquid absorber 5, to which a solar heat collection unit is thermally coupled. The supply end 52 of the liquid absorber 5 connects to seawater 7. The liquid absorber 5 extends to the height of the supply end 52 or is connected to the supply end 52 via an intermediate conduit. The supply end 52 is higher than the inlet of the evaporation interface formed by the thermal coupling of the liquid absorber 5 and the solar heat collection unit. The post-condensation unit includes one or more condensation / evaporation units and a final condensation unit. Each condensation / evaporation unit includes a condenser plate 6 for receiving steam from the upper evaporation unit and a liquid suction core 5 attached to the condenser plate 6. The liquid suction core 5 and the condenser plate 6 are parallel to each other and highly overlap. The condensate produced by each condenser plate 6 and the final condensation unit is collected by a freshwater collection unit. The freshwater collection unit is a U-shaped tube 8, which is installed at the bottom of the condenser plate 6 to collect freshwater 11. The liquid suction core 5 of the condensation / evaporation unit absorbs seawater 7 by gravity.

[0051] The first-stage seawater evaporation unit's absorbent core 5 and the subsequent condensation unit are vertically separated by a vertical air gap. The upper end of the absorbent core 5 in the first-stage seawater evaporation unit is immersed in seawater 7, and the upper end of the absorbent core 5 in the subsequent condensation unit is immersed in seawater 7. The absorbent core 5 is attached to one side of the absorber 4 in the first-stage seawater evaporation unit or the condenser plate 6 in the subsequent condensation unit, serving as the evaporation interface. Specifically, the upper ends of the absorbent cores 5 in the first-stage seawater evaporation unit and the subsequent condensation unit are immersed in seawater 7, while the lower ends of the absorbent cores 5 in the remaining subsequent condensation units are placed in the container collecting brine 12. The uncovered side of the condenser plate 6 serves as the condensation interface.

[0052] As the sun rises, the water supply system, operating from top to bottom via the VMSS (Vibration-to-Sun System), begins operation. Sunlight entering the parabolic concentrator 3, whether directly or reflected, converges onto the surface of the absorber 4, where photothermal conversion occurs. Heat transferred from the solar heat collection unit to the wick 5 evaporates some of the seawater 7 within it. The seawater 7 in the wick 5 is heated by the absorber 4, generating steam. Driven by a temperature gradient, this steam passes through the narrow gaps of the subsequent condensation unit, reaching the condenser plate 6 and condensing. The condensate droplets, under gravity, converge into the U-shaped tube 8 of the freshwater collection unit, finally leaving the subsequent condensation unit and being collected. The latent heat released during condensation serves as the heat source for the next stage of evaporation / condensation, driving the evaporation and condensation process in that stage.

[0053] like Figure 5 As shown in Figure a, the water supply end 52 is positioned higher than the inlet of the evaporation interface formed by the thermal coupling of the absorbent core 5 of the first-stage seawater evaporation unit and the solar heat collection unit. The seawater flow rate is controlled by adjusting the height difference between the water supply end 52 and the inlet of the evaporation interface, with the height difference being H1. Therefore, water pressure is generated at the inlet 51 of the evaporation interface. Under the combined action of water pressure, gravity, and the Marangoni effect, the seawater 7 continuously flows downward. In this embodiment of the invention, a beaker is used to collect the downward-flowing brine 12. This also significantly increases the downward diffusion rate of salt ions, which is greater than the aggregation rate caused by evaporation, thus preventing the formation of salt crystals. Furthermore, the downward extension of the absorber 4 and the absorbent core 5 ensures a continuous evaporation / condensation process, avoiding heat conduction losses caused by the rapid downward diffusion of seawater 7.

[0054] Example 2

[0055] Horizontal multi-stage solar stills (HMSS) come in two types: Figure 3 The water supply method is a bottom-up horizontal multi-stage solar evaporator, and Figure 4The water supply method is a horizontal multi-stage solar evaporator from top to bottom. Both are similar to VMSS in overall structure and operation principle, including a solar heat collection unit, a first-stage seawater evaporation unit, a subsequent condensation unit, and a freshwater collection unit. The main difference is that the solar heat collection unit includes a Fresnel lens 9 and a heat absorber 4. The heat absorber 4 is set above the liquid absorption core 5 of the first-stage seawater evaporation unit. The Fresnel lens 9 is set above the heat absorber 4 to concentrate sunlight on the surface of the heat absorber 4. An acrylic plate 13 is set below the Fresnel lens 9 to fix the Fresnel lens and reduce the area of ​​the solar collector. Preferably, it also includes a transparent glass plate 2 installed above the Fresnel lens 9. The Fresnel lens 9, the transparent glass plate 2, and the heat absorber 4 together form a concentrating chamber 14. Compared to the vertical structure of the first-stage seawater evaporation unit and the subsequent condensation unit in a vertical multi-stage solar evaporator, the embodiment of the present invention is a horizontal structure separated by horizontal air gaps. In the horizontal state, one end of the liquid absorption core 5 of the first-stage seawater evaporation unit and the subsequent condensation unit is immersed in seawater 7. A hydrophobic membrane 10 is provided at the bottom of each liquid absorption core 5 to support the liquid absorption core 5, prevent seawater 7 from passing through, and provide a water vapor passage channel. The rest of the structure is the same as VMSS.

[0056] The intensity of solar radiation varies in different regions, allowing for flexible selection. Figure 3 or Figure 4 In the HMSS (High-Minute Sun System), if the solar radiation intensity in the region is weak, the seawater supply to the first-stage seawater evaporation unit is from top to bottom, while the seawater supply to the subsequent condensation unit is from bottom to top. Figure 3 The structure; if the solar radiation intensity in the region is strong, salt accumulation may still occur in the subsequent condensation unit. Therefore, the seawater supply for both the first-stage seawater evaporation unit and the subsequent condensation unit adopts a top-down structure, i.e. Figure 4 The structure.

[0057] As the sun rises, the incident sunlight entering the Fresnel lens 9, whether directly or after reflection, converges on the surface of the absorber 4, where it undergoes photothermal conversion. The heat transferred from the solar heat collection unit to the wick 5 causes some of the seawater 7 flowing through it to evaporate. The seawater 7 in the wick 5 is then heated by the absorber 4 to produce steam. Driven by the temperature gradient, this steam passes through the narrow gaps of the subsequent condensation unit and reaches the condenser plate 6, where it condenses. The condensate droplets, under the influence of gravity, converge in the beaker of the freshwater collection unit, finally leaving the subsequent condensation unit and being collected. The latent heat released during condensation serves as the heat source for the next stage of evaporation / condensation, driving the evaporation and condensation process in that stage.

[0058] like Figure 5As shown in Figure b, the left end of the absorbent core 5 in the first-stage seawater evaporation unit is immersed in seawater 7. The absorbent core 5 extends to the height of the water supply end 52 or is connected to the water supply end 52 through an intermediate conduit. Its position is higher than the evaporation interface of the first-stage seawater evaporation unit, with a height difference of H2, thereby generating water pressure at the inlet 51 of the evaporation interface. As the evaporation process begins, the seawater 7 in the absorbent core 5 diffuses to the right-hand downstream condensation unit under the combined action of water pressure and the Marangoni effect (without gravity), preventing salt ions from accumulating locally and alleviating the salt crystallization problem. In this embodiment of the invention, a beaker is used to collect the brine 12 that flows downward after diffusion. At the same time, the downstream condensation unit extending to the right reduces the heat conduction loss of the seawater 7 and improves the evaporation efficiency. The freshwater 11 formed by condensation after evaporation is also collected by the beaker.

[0059] Seawater flow rate control

[0060] In the VMSS of Example 1, the transport of seawater 7 in the first-stage seawater evaporation unit is mainly affected by the combined influence of water pressure, gravity, and the Marangoni effect; in the HMSS of Example 2, the transport of seawater 7 in the first-stage seawater evaporation unit is affected by both water pressure and the Marangoni effect. Since the temperature and concentration gradients of seawater in the absorbent core 5 are influenced by both the system energy input and the evaporation process, and the system energy input is mainly affected by solar radiation intensity, controlling the temperature and concentration gradients of seawater in the absorbent core 5 is difficult to achieve. Therefore, the scheme of controlling the water flow velocity through the Marangoni effect is not feasible. The water pressure at the inlet 51 of the evaporation interface between the VMSS and HMSS is affected by the height differences H1 (VMSS) and H2 (HMSS) between the water supply end 52 and the inlet of the absorbent core 5. Figure 3 As shown, the seawater flow rate can be controlled by adjusting the height difference H between the water supply end 52 of the suction core 5 and the inlet 51 of the evaporation interface. Furthermore, the seawater flow rate at the inlet 51 of the evaporation interface can be adjusted by regulating the contact area between the suction core 5 of the first-stage seawater evaporation unit and the seawater 7, for example, by adjusting the soaking area to 1 / 4 of its original size. Figure 6 a), 1 / 2 ( Figure 6 (b), 3 / 4 Figure 6 c), 5 / 4 Figure 6 (e), 3 / 2 ( Figure 6 f) The immersion area and the area of ​​the absorbent core itself are the same. Figure 6 The flow rate of seawater at the evaporation interface inlet 51 can also be adjusted.

[0061] In summary, both the VMSS in Embodiment 1 and the HMSS in Embodiment 2 of the present invention can adjust the seawater flow rate into the evaporation system by controlling the height difference between the water supply end 52 and the evaporation interface inlet 51 or the contact area between the liquid suction core 5 and the water body, thereby seeking a balance between salt resistance and reducing heat conduction loss and improving the evaporation efficiency of the multi-stage solar evaporator based on reverse distillation.

[0062] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A multi-stage solar evaporator based on reverse distillation, characterized in that, The system includes a solar heat harvesting unit, a first-stage seawater evaporation unit, a subsequent condensation unit, and a freshwater collection unit. The first-stage seawater evaporation unit includes a liquid absorbent core. The solar heat harvesting unit is thermally coupled to the liquid absorbent core, and the water supply end of the liquid absorbent core is connected to seawater. The water supply end is higher than the inlet of the evaporation interface formed by the thermal coupling between the liquid absorbent core and the solar heat harvesting unit. The heat transferred from the solar heat harvesting unit to the liquid absorbent core evaporates part of the seawater flowing through the liquid absorbent core. The generated steam is condensed in the subsequent condensation unit, and the condensate is collected by the freshwater collection unit. The height difference formed between the water supply end of the liquid absorbent core and the inlet of the evaporation interface enhances the transport rate of salt ions in the seawater within the hydrophilic material of the liquid absorbent core, thereby alleviating the problem of salt ion deposition.

2. The multi-stage solar evaporator as described in claim 1, characterized in that, The subsequent condensation unit includes one or more condensation / evaporation units and a final condensation unit. Each condensation / evaporation unit includes a condensing plate for receiving steam from the previous evaporation unit and a liquid-absorbing core attached to the condensing plate. The condensate produced by each condensing plate and the final condensation unit is collected by the freshwater collection unit. The liquid-absorbing core of the condensation / evaporation unit absorbs seawater by gravity or capillary action.

3. The multi-stage solar evaporator as described in claim 2, characterized in that, The first-stage seawater evaporation unit and the subsequent-stage condensation unit are vertical structures separated by a vertical air gap. The upper end of the liquid absorption core of the first-stage seawater evaporation unit is immersed in seawater, and the upper or lower end of the liquid absorption core of the subsequent-stage condensation unit is immersed in seawater.

4. The multi-stage solar evaporator as described in claim 3, characterized in that, The condenser plate of the last stage condensation unit is inserted into seawater.

5. The multi-stage solar evaporator as described in claim 3, characterized in that, The solar heat collection unit includes a parabolic concentrator and a heat absorber. The heat absorber is attached to the liquid absorption core of the first-stage seawater evaporation unit and extends vertically downward. The parabolic concentrator is configured to reflect and concentrate sunlight onto the heat absorber.

6. The multi-stage solar evaporator as described in claim 5, characterized in that, It also includes a transparent glass plate mounted above the parabolic concentrator.

7. The multi-stage solar evaporator as described in claim 1 or 2, characterized in that, The first-stage seawater evaporation unit and the subsequent-stage condensation unit are horizontal structures separated by a horizontal air gap. One end of the liquid absorption core of each of the first-stage seawater evaporation unit and the subsequent-stage condensation unit is immersed in seawater, and a hydrophobic membrane is provided at the bottom of each liquid absorption core to prevent seawater from passing through.

8. The multi-stage solar evaporator as described in claim 3, characterized in that, The solar heat collection unit includes a Fresnel lens and a heat absorber. The heat absorber is positioned above the liquid absorption core of the first-stage seawater evaporation unit, and the Fresnel lens is positioned above the heat absorber to concentrate sunlight onto the surface of the heat absorber.

9. The multi-stage solar evaporator as described in claim 8, characterized in that, It also includes a transparent glass plate mounted above the Fresnel lens.

10. The multi-stage solar evaporator as described in any one of claims 1 to 2, characterized in that, The seawater flow rate is controlled by adjusting the height difference between the water supply end and the evaporation interface inlet.

11. The multi-stage solar evaporator as described in any one of claims 1 to 2, characterized in that, The flow rate of seawater at the inlet of the evaporation interface is adjusted by regulating the contact area between the liquid absorption core of the seawater evaporation unit and the seawater.

12. The multi-stage solar evaporator as described in any one of claims 1 to 2, characterized in that, The liquid-absorbing core extends to the height of the water supply end or is connected to the water supply end via an intermediate conduit.

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