A daytime water collection device based on passive radiative cooling and hydrophobic effect

Abstract

This invention discloses a daytime water collection device based on passive radiative cooling and hydrophobic effects, relating to the field of water vapor collection technology. First, by utilizing the high emission characteristics of biopolymer materials, the high thermal conductivity of inorganic fillers, and the hydrophobicity of silane coatings, a metal condenser plate with passive radiative cooling and hydrophobic effects is prepared and applied to a daytime water collection device for freshwater collection. The excellent hydrophobicity is beneficial for water vapor to form droplet condensation on the surface, making it easier to drip and thus accelerating the water collection rate and improving the efficiency of steam condensation.

Description

Technical Field

[0001] This invention relates to the field of water vapor collection technology, specifically to a daytime water collection device based on passive radiative cooling and hydrophobic effects. Background Technology

[0002] Drought is a widespread problem globally, particularly in arid regions covering over 38% of the world's land area. Therefore, seeking technological solutions to water scarcity is crucial. Solar desalination, utilizing sunlight to desalinate water, has been extensively studied. Solar desalination systems typically include a water evaporation system and a water vapor collection system. Traditional water vapor collection systems often use energy-intensive condensers, unsuitable for condensation at room temperature. Developing an energy-efficient condenser with strong cooling effect and high condensation capacity for water vapor collection systems is essential. Currently, dew collection devices based on radiative cooling are in use at night; however, these devices struggle to operate under sunlight. Developing an energy-efficient condenser that can operate during the day while enhancing cooling performance is critical. Passive radiative cooling refers to the phenomenon where a surface reflects sunlight (0.3–2.5 μm) and radiates heat into outer space through an atmospheric transmission window (8–13 μm). Under direct sunlight during the day, passive radiative cooling can lower the condenser's surface temperature below ambient temperature, thereby collecting water vapor.

[0003] In recent years, the development of metamaterials has expanded their application in passive radiative cooling freshwater collection. Zhou et al. constructed a bilayer structure with passive radiative cooling function on the surface of a condenser using polydimethylsiloxane and silver. The passive radiative cooling condenser can reduce the surface temperature by about 8°C and collect water throughout the day. However, the thermal conductivity of the radiative cooling coating was neglected. Thermal conductivity is crucial, as it is the primary means of rapidly transferring latent heat to the surface of the radiative cooling coating and then further transferring it from the surface to the external environment. An ideal passive cooling condenser should possess both passive radiative cooling effect and suitable thermal conductivity. Furthermore, the required raw materials should be inexpensive and suitable for large-scale application. Summary of the Invention

[0004] To address the problems of existing technologies, the present invention aims to overcome the shortcomings of existing technologies and provide a metal condenser plate with passive radiative cooling and hydrophobic effect, as well as its preparation method. The preparation method has low raw material and process costs, simple and controllable steps, and the prepared metal condenser plate has excellent cooling effect. When applied to daytime water collection devices, it effectively solves the problems of poor heat conduction, low condensation rate, and high raw material prices of traditional water collection devices.

[0005] One of the objectives of this invention is to provide a metal condenser plate, the technical solution of which is as follows:

[0006] A metal condenser plate consists of three layers, from top to bottom: a heat exchange layer, a metal layer, and a hydrophobic layer. The heat exchange layer is a composite coating composed of highly thermally conductive nano-inorganic materials and biopolymer materials, and the hydrophobic layer is a silane coating.

[0007] Preferably, the nano-inorganic material is aluminum oxide, magnesium oxide, or boron nitride.

[0008] Preferably, the biopolymer material is at least one selected from acetylcellulose, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, ethylcellulose, cyanoethylcellulose, hydroxypropylcellulose, and hydroxymethylcellulose.

[0009] The second objective of this invention is to provide a method for preparing the aforementioned metal condenser plate, the technical solution of which is as follows:

[0010] A method for preparing a metal condenser plate includes the following two steps:

[0011] The first step is to perform a modification and cleaning treatment on the metal sheet to obtain a modified and cleaned metal sheet;

[0012] The second step involves spraying silane onto one side of the modified clean metal plate and then heating and drying it to coat one side of the modified metal plate with a hydrophobic layer. A precursor solution is then coated onto the other side of the modified metal plate and allowed to air dry naturally, resulting in a heat exchange layer on the other side of the modified metal plate, thus obtaining the metal condenser plate. The precursor solution contains a mixed solution of highly thermally conductive nano-inorganic materials and biopolymer materials dispersed in an organic solvent.

[0013] Preferably, the modified cleaning treatment involves sandblasting the metal plate, then cleaning it with an organic cleaning agent, and finally immersing it in a neutral saline solution with a concentration of 0.225±wt% at 55℃±10℃ for 17.5±2.5 minutes.

[0014] Preferably, the silane is a silane with a mass ratio of 4 to 6 wt%.

[0015] Preferably, the temperature of the heating and drying treatment is 130℃±10℃, and the time is 0.75h±0.25h.

[0016] Preferably, the nano-inorganic material is aluminum oxide, magnesium oxide, or boron nitride.

[0017] Preferably, the biopolymer material is at least one of the following biopolymer materials: acetyl cellulose, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose, and hydroxymethyl cellulose.

[0018] The third objective of this invention is to provide a daytime water collection device based on passive radiative cooling and hydrophobic effect, prepared using a metal condenser plate. The technical solution is as follows:

[0019] A daytime water collection device based on passive radiative cooling and hydrophobic effect includes a water collection tank with one end open and a metal condenser plate. The metal condenser plate covers the opening of the water collection tank, and the outer layer of the water collection tank is covered with a low emissivity metal thin film material. Steam inlets and gas outlets are provided on the two side chambers of the water collection tank.

[0020] Compared with the prior art, the beneficial effects of the present invention are:

[0021] This invention provides a method for preparing a metal condenser plate. By modifying the surface of the metal plate, silane is used to change the surface of the metal plate from hydrophilic to hydrophobic, with a water contact angle greater than 142°. A heat exchange layer with passive radiative cooling properties is prepared by using a composite coating of biopolymer materials and highly thermally conductive inorganic nanomaterials. The cooling effect and cooling efficiency of the prepared metal condenser plate are superior to those of untreated metal plates and commonly used sub-environmental radiation emitters. This method is simple and easy to implement, requires low-cost raw materials and process steps, and allows for easy control of various technical parameters, resulting in high cooling efficiency.

[0022] The metal condenser plate prepared by this invention has excellent cooling effect and cooling efficiency. When applied to a daytime water collection device based on passive radiation cooling and hydrophobic effect, it can generate fresh water from steam under direct sunlight without active energy consumption. It has a high water collection speed and a high condensation rate, mainly because it has a heat exchange layer with high thermal conductivity, which can enhance the loss of latent heat of condensation.

[0023] The present invention provides a daytime water collection device based on passive radiative cooling and hydrophobic effect. The excellent hydrophobicity of the metal condenser plate is beneficial for water vapor to form droplets on the surface, making it easier to drip and accelerating the water collection rate. It exhibits good water collection capacity under direct sunlight and does not require additional energy consumption. It can be integrated with other solar water purification systems to achieve freshwater collection. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a metal condenser plate provided in this invention;

[0025] Figure 2 for Figure 1 A magnified view of part A in the middle;

[0026] Figure 3 This is a high-magnification scanning electron microscope image of the heat exchange layer of the metal condenser plate prepared in Example 1 of this invention;

[0027] Figure 4 This is a hydrophobicity test diagram of the hydrophobic layer of the metal condenser plate prepared in Example 1 of this invention;

[0028] Figure 5 A temperature comparison test diagram of the hydrophobic layer of the untreated metal plate board-0 and the metal condensation plate board-1 prepared in Example 1 under solar irradiation;

[0029] Figure 6 This is a schematic diagram of the daytime water collection device based on passive radiative cooling and hydrophobic effect provided by the present invention.

[0030] Figure 7 for Figure 6 A magnified view of part B in the middle section;

[0031] Figure 8 This is a comparison chart of the condensation rates of the insulating condensers made from the board-0 and board-1 metal plates tested in this invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] like Figure 1 and Figure 2 As shown, a metal condenser plate 1 is divided into three layers, from top to bottom: heat exchange layer 11, metal layer 12 and hydrophobic layer 13.

[0034] Furthermore, the heat exchange layer 11 is a composite coating composed of inorganic materials and cellulose materials.

[0035] Specifically, the inorganic materials are aluminum oxide, magnesium oxide, or boron nitride.

[0036] Specifically, the cellulose material is at least one of the following biopolymers: acetyl cellulose, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose, and hydroxymethyl cellulose.

[0037] Furthermore, the hydrophobic layer 13 is a silane coating.

[0038] Specifically, the silane is 1H,1H,2H,2H-perfluorodecyltriethoxysilane.

[0039] The following is an example of a method for preparing a metal condenser plate, using an aluminum plate as an example.

[0040] Example 1

[0041] S1. The aluminum plate is sandblasted using a sandblasting machine, cleaned with an organic cleaning agent, and then immersed in a 0.225±wt% NaCl aqueous solution at 55℃±10℃ for 17.5±2.5 minutes to obtain a modified clean metal plate.

[0042] S2. Spray 1H,1H,2H,2H-perfluorodecyltriethoxysilane onto one side of the modified clean metal plate, and then keep it at 130℃±10℃ for 0.75h±0.25h to coat one side of the modified clean metal plate with a hydrophobic layer.

[0043] S3. Disperse 3g of nano-alumina in a mixed solution of 20mL acetone and 20mL anhydrous ethanol, add 6.5g of acetylcellulose to dissolve, and sonicate for 10min to make the solution uniformly mixed to obtain the precursor solution.

[0044] S4. The precursor solution is coated on the other side of the modified clean metal plate. The wet film thickness is 400 μm. The plate is then air-dried to obtain a metal condensation plate, labeled as board-1.

[0045] Example 2

[0046] The steps in this embodiment are basically the same as those in Embodiment 1, except that in step S3, 6.5g of acetylated cellulose is replaced with 6.5g of hydroxyethyl cellulose, and the resulting metal condenser plate is labeled as board-2.

[0047] Example 3

[0048] The steps in this embodiment are basically the same as those in Embodiment 2, except that in step S3, 3g of nano aluminum oxide is replaced with 3g of nano magnesium oxide, and the resulting metal condenser plate is marked as board-3.

[0049] Example 4

[0050] The steps in this embodiment are basically the same as those in Embodiment 1, except that in step S3, 3g of nano aluminum oxide is replaced with 3g of nano magnesium oxide, and the resulting metal condenser plate is marked as board-4.

[0051] Example 5

[0052] The steps in this embodiment are basically the same as those in Embodiment 2, except that in step S3, 3g of nano aluminum oxide is replaced with 3g of nano boron nitride, and the resulting condenser plate is marked as board-5.

[0053] The NaCl aqueous solution in the above five examples can also be replaced with other neutral salt aqueous solutions, such as KCl solution.

[0054] In the above five embodiments, the 1H,1H,2H,2H-perfluorodecyltriethoxysilane spraying can also be replaced with other silanes that can make the metal surface hydrophobic, such as silanes with a mass ratio of 4 to 6 wt%.

[0055] It should be noted that the amount of 1H,1H,2H,2H-perfluorodecyltriethoxysilane sprayed onto one side surface of the modified clean metal plate as described in the above five embodiments is approximately 11.25 cm. 2 / mL, and in actual implementation, the thickness of the hydrophobic layer can be adjusted according to the actual situation.

[0056] In the above five embodiments, the hydroxyethyl cellulose and acetyl cellulose used are, in actual implementation, they can also be replaced by at least one of methyl cellulose, carboxymethyl cellulose, ethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose and hydroxymethyl cellulose.

[0057] In the above five embodiments, the organic cleaning agent used is ethanol or trichloroethylene.

[0058] The high-magnification scanning electron microscope image of the heat exchange layer of the metal condenser plate in Embodiment 1 above is shown below. Figure 3 As shown, the biopolymer-high thermal conductivity condensate coated on the aluminum plate is uniformly distributed; after testing, the heat exchange layer has a high thermal emissivity ≥0.95 and a solar irradiance reflectivity ≥0.94.

[0059] The hydrophobicity test of the hydrophobic layer of the metal condenser plate in Example 1 above is as follows: Figure 4 As shown, the hydrophobic layer exhibits significant hydrophobicity, with a water contact angle >142°.

[0060] The cooling performance of the metal condenser plates prepared in the above five embodiments was tested in a real environment:

[0061] An untreated metal plate (aluminum plate, denoted as board-0) and an existing sub-environmental radiation emitter (denoted as SRE) were used as comparative examples. These were compared with the metal condensation plates prepared in the five embodiments described above. Temperature difference tests were conducted on the surface of the hydrophobic layer. Figure 5As shown, this is a comparison of the temperatures of the lower surfaces of board-1 (hydrophobic layer facing down) (test data corresponds to the radiation-cooled sample line in the figure) and board-0 (test data corresponds to the pure aluminum line in the figure) under the same solar irradiance. Here, Ambient represents the ambient temperature.

[0062] Using formula

[0063]

[0064] ΔT2=T board-0 -T board-i and

[0065] ΔT3=T SRE -T board-i

[0066] The temperature difference between the lower surfaces was calculated separately, where T represents the lower surface temperature, and i = 1, 2, 3, 4, or 5. The results are shown in Table 1. It can be seen that the lower surface of the metal condenser plate has a lower temperature.

[0067] Furthermore, a daytime water collection device based on passive radiative cooling and hydrophobic effect was constructed by using the condensing metal plates in the five embodiments, such as... Figure 6 and Figure 7 As shown, it includes a water collection tank 2 with one end open and a metal condenser plate 1 located at the opening of the water collection tank. The metal condenser plate 1 can cover the opening of the water collection tank 2. The water collection tank 2 has a humidifier spray inlet and a gas flow outlet (not shown in the figure) on both sides respectively.

[0068] The metal condenser plate 1 is divided into three layers, from top to bottom: heat exchange layer 11, metal layer 12 and hydrophobic layer 13, with the hydrophobic layer facing the inside of the water collection tank 2.

[0069] In this specific embodiment, the water collection tank 2 uses a foam box as the inner layer 21, and is covered with a layer of low emissivity metal thin film material 22 on the outside to block all radiative heat exchange channels and reduce the evaporation of fresh water.

[0070] board-0 and the same water collection tank 2 as described above constitute a common water collection device, which serves as a comparative test example.

[0071] All metal plates are 5cm x 5cm in size. The air temperature is 27℃, and the distance between the humidifier spray nozzle and the metal plate is 15cm. As shown in Table 1, the water collection efficiency of the metal condenser plate is much higher than that of the untreated metal plate. The degree of improvement in water collection efficiency is... The letter E indicates the water collection efficiency of the corresponding metal plate.

[0072] In addition, all dimensions are 112.5cm. 2 Comparative examples, board-0 and board-1, have their metal condenser plates placed in insulating boxes of the same size as the aforementioned water collection tank, forming two insulating condensers. Under ambient air temperature of 30℃±5℃ and relative humidity of 92.5%±2.5%, they produce a flow rate of not less than 0.7 L·h. -1 Humidified air was pumped into two insulated condensers at a constant rate, and the condensation rate of the insulated condensers was tested. The results are as follows: Figure 8 As shown, the condensation rate of the metal condenser plate board-1 (test data corresponds to the Hydrohobic modified radiant cooling condenser in the figure) is approximately twice that of the condensation rate of the plate-0 (test data corresponds to the Common radiant cooling condenser in the figure).

[0073] <![CDATA[ΔT1]]> <![CDATA[ΔT2]]> <![CDATA[ΔT3]]> P board-0 / / / / board-1 2 7 2 333％ board-2 1.8 5 1.2 300％ board-3 1.8 7 1.5 325％ board-4 1.5 6 1.7 330％ board-5 1.8 8 2 317％

[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended embodiments and their equivalents.

Claims

1. A method for preparing a metal condenser plate, characterized in that, It includes the following two steps: The first step is to perform a modification and cleaning treatment on the metal sheet to obtain a modified and cleaned metal sheet; The second step involves spraying silane onto one side of the modified cleaning metal plate and then heating and drying it to coat one side of the modified cleaning metal plate with a hydrophobic layer. A precursor solution is then coated onto the other side of the modified cleaning metal plate and allowed to air dry naturally, resulting in a heat exchange layer on the other side of the modified cleaning metal plate, thus obtaining the metal condenser plate. The precursor solution contains a mixed solution of highly thermally conductive nano-inorganic materials and biopolymer materials dispersed in an organic solvent. The nano-inorganic material is aluminum oxide, magnesium oxide, or boron nitride. The biopolymer material is at least one of the following: acetylcellulose, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, ethylcellulose, cyanoethylcellulose, hydroxypropylcellulose, and hydroxymethylcellulose.

2. The method for preparing a metal condenser plate according to claim 1, characterized in that, The modified cleaning treatment involves sandblasting the metal plate, then cleaning it with an organic cleaning agent, and finally immersing it in a neutral saline solution with a concentration of 0.225±wt% at 55℃±10℃ for 17.5±2.5 minutes.

3. The method for preparing a metal condenser plate according to claim 1, characterized in that, The silane is a silane with a mass ratio of 4 to 6 wt%.

4. The method for preparing a metal condenser plate according to claim 1, characterized in that, The heating and drying process is carried out at a temperature of 130℃±10℃ for a time of 0.75h±0.25h.

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