Daytime water collecting device based on passive radiation refrigeration and hydrophobic effect

Abstract

The invention discloses a daytime water collection device based on passive radiation refrigeration and a hydrophobic effect, and relates to the technical field of water vapor collection. The metal condensation plate with passive radiation refrigeration and the hydrophobic effect is prepared, the metal condensation plate is applied to a daytime water collection device and used for fresh water collection, the excellent hydrophobicity is beneficial for water vapor to form dropwise condensation on the surface, water vapor drips more easily, the water collection rate is increased, and the steam condensation efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of water vapor collection, and in particular to a daytime water collection device based on passive radiation cooling and hydrophobic effect. Background Art

[0002] Drought is a common problem all over the world, especially in arid regions around the world, which account for more than 38% of the world's land area. Therefore, it is very important to find technical solutions to water shortages. Solar desalination, that is, the use of sunlight to desalinate water, has been widely studied. Solar desalination systems usually include a water evaporation system and a water vapor collection system. The condensers used in traditional water vapor collection systems usually consume a lot of energy and are not suitable for condensation at room temperature. It is very important to develop a non-energy condenser with strong cooling effect and high condensation capacity for water vapor collection systems. At present, night dew collection devices based on the radiation cooling phenomenon have been put into use. However, these devices are difficult to work under sunlight. It is very important to develop a non-energy condenser that can work during the day and enhance the cooling effect. Passive radiation cooling refers to the phenomenon that the surface reflects sunlight (0.3-2.5 μm) and radiates heat to outer space through the atmospheric transmission window (8-13 μm). In the case of direct sunlight during the day, the surface temperature of the condenser can be reduced to below the ambient temperature through passive radiation cooling, thereby collecting water vapor.

[0003] In recent years, the development of metamaterials has expanded their applications in freshwater collection by passive radiative cooling. Zhou et al. constructed a double-layer structure with passive radiative cooling function on the condenser surface using polydimethylsiloxane and silver. The passive radiative cooling condenser can reduce the surface temperature by about 8 °C and collect water all day long. However, the thermal conduction of the radiative cooling coating has been neglected. Thermal conduction is very important and is the main means to quickly transfer latent heat to the surface of the radiative cooling coating and then further transfer it from the surface of the radiative cooling coating to the external environment. An ideal passive cooling condenser should have both passive radiative cooling effect and suitable thermal conductivity. In addition, the required raw materials should be cheap for large-scale application. Summary of the invention

[0004] In order to solve the problems of the prior art, the purpose of the present invention is to overcome the shortcomings of the existing technology and provide a metal condensation plate with passive radiation refrigeration and hydrophobic effect and a preparation method thereof. The preparation method has low costs for raw materials and processes, and the steps are simple and controllable. The prepared metal condensation plate has excellent refrigeration effect. It is applied to a daytime water collection device to effectively solve the problems of poor thermal conductivity, low condensation rate, and expensive raw materials of traditional water collection devices.

[0005] One of the purposes of the present invention is to provide a metal condensation plate, the technical solution of which is as follows:

[0006] A metal condensation plate is divided into 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 a high thermal conductivity nano inorganic material and a biopolymer material, 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 of acetyl cellulose, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose and hydroxymethyl cellulose.

[0009] The second object of the present invention is to provide a method for preparing the above-mentioned metal condensation plate, and the technical scheme is as follows:

[0010] A method for preparing a metal condensation plate comprises the following two steps:

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

[0012] The second step is to spray silane on one side of the modified clean metal plate, and then heat and dry it so that one side of the modified metal plate is covered with a hydrophobic layer; a layer of precursor solution is coated on the other side of the modified metal plate, and it is naturally dried so that the other side of the modified metal plate is covered with a heat exchange layer to obtain the metal condensation plate, wherein 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 is to sandblast the metal plate, then clean it with an organic cleaning agent, and then soak it in a neutral salt solution with a concentration of 0.225±wt% at 55°C±10°C for 17.5±2.5 minutes.

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

[0015] Preferably, the temperature of the heating and drying treatment is 130°C±10°C, 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 biopolymer materials such as acetyl cellulose, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose and hydroxymethyl cellulose.

[0018] The third object of the present invention is to provide a daytime water collection device based on passive radiation cooling and hydrophobic effect prepared by using a metal condensation plate, and the technical scheme is as follows:

[0019] A daytime water collection device based on passive radiation cooling and hydrophobic effect, comprising a water collection trough with an opening at one end and a metal condensation plate, wherein the metal condensation plate covers the opening of the water collection trough, and the outer layer of the water collection trough is coated with a low-emissivity metal film material; steam inlets and gas outlets are provided on the two side boxes of the water collection trough.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a method for preparing a metal condensation plate. The surface of the metal plate is modified by using silane to change the surface of the metal plate from hydrophilic to hydrophobic, with a water contact angle greater than 142°. A biopolymer material and a high thermal conductivity inorganic nanomaterial composite coating are used to prepare a heat exchange layer with passive radiation cooling properties. The refrigeration effect and refrigeration efficiency of the prepared metal condensation plate are better than those of an untreated metal plate and a currently commonly used sub-ambient radiation emitter. The method is simple and easy to implement, the required raw materials and process steps are low in cost, various technical parameters are easy to control, and the refrigeration efficiency is high.

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

[0023] The present invention prepares a daytime water collection device based on passive radiation cooling and hydrophobic effect. The excellent hydrophobicity of the metal condensation plate is beneficial to the formation of droplet-like condensation of water vapor on the surface, which is easier to drip and is beneficial to the acceleration of water collection rate. It shows good water collection ability under direct sunlight and does not require additional energy consumption. It can be integrated with other solar water purification systems to realize the collection of fresh water. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 for Figure 1 A partial enlarged view of part A;

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

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

[0028] Figure 5 This is a temperature comparison test diagram of the hydrophobic layer of the untreated metal plate board-0 in the present invention and the metal condensation plate board-1 prepared in Example 1 under solar radiation;

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

[0030] Figure 7 for Figure 6 A partial enlarged view of part B;

[0031] Figure 8 This is a comparison chart of the condensation rates of the insulating condensers prepared with the board-0 and board-1 metal plates tested in the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

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

[0035] Specifically, the inorganic material is aluminum oxide, magnesium oxide or boron nitride.

[0036] Specifically, the cellulose material is at least one of biopolymer materials such as 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] An embodiment of a method for preparing a metal condensation plate is introduced below by taking an aluminum plate as an example.

[0040] Example 1

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

[0042] S2. Spray 1H,1H,2H,2H-perfluorodecyltriethoxysilane on one side of the modified clean metal plate, and then maintain at 130°C±10°C for 0.75h±0.25h to coat a hydrophobic layer on one side of the modified clean metal plate;

[0043] S3, dispersing 3 g of nano-aluminum oxide in a mixed solution of 20 mL of acetone and 20 mL of anhydrous ethanol, adding 6.5 g of acetyl cellulose to dissolve, and ultrasonically dispersing for 10 min to mix the solution evenly to obtain a precursor solution;

[0044] S4. Coat the precursor solution on the other side of the modified clean metal plate, with a wet film thickness of 400 μm, and dry it naturally to obtain a metal condensation plate, which is marked as board-1.

[0045] Example 2

[0046] The steps of this embodiment are basically the same as those of the first embodiment, except that in step S3, 6.5 g of acetyl cellulose is replaced with 6.5 g of hydroxyethyl cellulose, and the prepared metal condensation plate is marked as board-2.

[0047] Example 3

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

[0049] Example 4

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

[0051] Example 5

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

[0053] The NaCl aqueous solution in the above five embodiments may also be replaced by other neutral salt solution, such as KCl solution.

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

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

[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 of the heat exchange layer of the metal condensation plate of Example 1 is as follows Figure 3 As shown, it can be seen that the biopolymer-high thermal conductivity material condensation polymer coated on the aluminum plate is evenly distributed; after testing, the high thermal emissivity of the heat exchange layer is ≧0.95, and the solar irradiance reflectivity is ≧0.94.

[0059] The hydrophobic test of the hydrophobic layer of the metal condensation plate of Example 1 is as follows Figure 4 As shown, it can be seen that the hydrophobic layer has obvious hydrophobicity, and the water contact angle is greater than 142°.

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

[0061] An untreated metal plate (aluminum plate, indicated as board-0) and an existing sub-ambient radiation emitter (indicated as SRE) were used as comparative examples and compared with the metal condensation plates prepared in the above five embodiments. The hydrophobic layer surface temperature difference test was performed. Figure 5As shown, the temperature comparison diagram of the tested lower surface of board-1 (hydrophobic layer facing downwards) (the test data corresponds to the radiation cooled sample line in the figure) and board-0 (the test data corresponds to the pure aluminium line in the figure) under the same solar irradiance, where 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 lower surface temperature difference is calculated respectively, where T represents the lower surface temperature, i=1, 2, 3, 4, or 5, and the results are shown in Table 1. It can be seen that the lower surface of the metal condensation plate has a lower temperature.

[0067] In addition, a daytime water collection device based on passive radiation 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 collecting tank 2 with an opening at one end and a metal condensation plate 1 arranged at the opening of the water collecting tank, and the metal condensation plate 1 can cover the notch of the water collecting tank 2. The two sides of the water collecting tank 2 are respectively provided with a humidifier spray inlet and a gas flow outlet (not shown in the figure);

[0068] The metal condensation plate 1 is divided into three layers, from top to bottom: a heat exchange layer 11 , a metal layer 12 and a hydrophobic layer 13 , and the hydrophobic layer faces 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 coated on the outer side with a layer of low-emissivity metal film material layer 22 to block all radiation heat exchange channels and reduce the evaporation of fresh water.

[0070] Board-0 and the same water collection tank 2 as above constitute a common water collection device as a comparative test example.

[0071] The size of all metal plates is 5 cm × 5 cm, the air temperature is 27 ° C, and the distance between the humidifier spray port and the metal plate is 15 cm. As shown in Table 1, the water collection efficiency of the metal condensation plate is much higher than that of the untreated metal plate. The letter E represents the water collection efficiency of the corresponding metal plate.

[0072] In addition, the size is 112.5cm 2 The metal condensation plates of board-0 and board-1 of the comparative example are placed in insulating boxes with the same size as the above-mentioned water collection tank to form two insulating condensers. Under the ambient air temperature of 30℃±5℃ and relative humidity of 92.5%±2.5%, the condensation rate is not less than 0.7L·h -1 The 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 shown in Figure 8 As shown, the condensation rate corresponding to the metal condensation board board-1 (Hydrophobic modified radiant cooling condenser in the test data corresponding figure) is about twice the condensation rate corresponding to board-0 (Common radiant cooling condenser in the test data corresponding 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 present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is limited by the attached embodiments and their equivalents.

Claims

1. A metal condensation plate, characterized in that: The structure of the metal condensation plate is divided into 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 high thermal conductivity nano-inorganic materials and biopolymer materials, and the hydrophobic layer is a silane coating.

2. A metal condensation plate according to claim 1, characterized in that: The nano inorganic material is aluminum oxide, magnesium oxide or boron nitride.

3. A metal condensation plate according to claim 1, characterized in that: The biopolymer material is at least one of acetyl cellulose, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose and hydroxymethyl cellulose.

4. A method for preparing a metal condensation plate, characterized in that: It includes the following two steps: The first step is to perform a modification and cleaning treatment on the metal plate to obtain a modified and cleaned metal plate; The second step is to spray silane on one side of the surface of the modified clean metal plate, and then perform a heating and drying treatment so that one side of the modified metal plate is coated with a hydrophobic layer; A layer of precursor solution is coated on the other side of the modified metal plate and dried naturally so that the other side of the modified metal plate is covered with a heat exchange layer to obtain the metal condensation plate. The precursor solution contains a mixed solution of highly thermally conductive nano-inorganic materials and biopolymer materials dispersed in an organic solvent.

5. The method for preparing a metal condensation plate according to claim 4, characterized in that: The modified cleaning treatment is to perform sandblasting on the metal plate, then perform cleaning with an organic cleaning agent, and then soak the metal plate in a neutral salt solution with a concentration of 0.225±wt% and a temperature of 55°C±10°C for 17.5±2.5 minutes.

6. The method for preparing a metal condensation plate according to claim 4, characterized in that: The silane has a mass ratio of 4 to 6 wt %.

7. The method for preparing a metal condensation plate according to claim 4, characterized in that: The temperature of the heating and drying treatment is 130°C±10°C, and the time is 0.75h±0.25h.

8. The method for preparing a metal condensation plate according to claim 4, characterized in that: The nano inorganic material is aluminum oxide, magnesium oxide or boron nitride.

9. The method for preparing a metal condensation plate according to claim 4, characterized in that: The biopolymer material is at least one of biopolymer materials such as acetyl cellulose, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, ethyl cellulose, cyanoethyl cellulose, hydroxypropyl cellulose and hydroxymethyl cellulose. The third object of the present invention is to provide a daytime water collection device based on passive radiation cooling and hydrophobic effect, which is prepared by using a metal condensation plate. The technical solution is as follows.

10. A daytime water collection device based on passive radiation cooling and hydrophobic effect, characterized in that: It comprises a water collecting tank with an opening at one end and a metal condensation plate, wherein the metal condensation plate covers the opening of the water collecting tank, and the outer layer of the water collecting tank is coated with a low-emissivity metal film material; steam inlets and gas outlets are arranged on the boxes on both sides of the water collecting tank.

Images