Electrolyte for micro-arc oxidation and method for preparing micro-arc oxidation ceramic coating and radiation cooling device

Abstract

An electrolyte for micro-arc oxidation, comprising: a main salt with a concentration of 5-50 g / L, a pH regulator with a concentration of 1-10 g / L, and characterized by further comprising an electrolyte functional salt or particle with a concentration of 0.1-1 g / L, the electrolyte functional salt or particle being one or a mixture of several of (NH4)2ZrF6, ZnH2PO4, ZnO, ZrO2, and TiO2 reagents or particles. A method for preparing a micro-arc oxidation ceramic coating, comprising the following steps: placing an aluminum alloy coil pipe as an anode and a stainless steel as a cathode in an electrolytic cell, and using an electrolyte for micro-arc oxidation in the electrolytic cell; and performing micro-arc oxidation surface treatment on the aluminum alloy coil pipe to obtain a micro-arc oxidation ceramic coating on the surface of the aluminum alloy coil pipe. A radiation cooling device characterized by welding and connecting in series and parallel the aluminum alloy coil pipe with the micro-arc oxidation ceramic coating to serve as the radiation cooling device.

Description

TECHNICAL FIELD

[0001] The application provides an electrolyte for micro-arc oxidation and a preparation method of a micro-arc oxidation ceramic coating and a radiative cooling device. BACKGROUND

[0002] The global environment continues to deteriorate, causing a general rise in global temperature, especially in summer. Due to environmental warming, the summer temperature in most areas of the world has risen, and in some areas, the surface temperature has even reached more than 50℃, and the duration is long. In the face of such a trend of rapid warming, countries around the world are introducing measures to cope with it. In addition to developing long-term carbon emission reduction and carbon peak environmental improvement plans, to cope with the sustained rise in summer temperature in a short period of time, large cooling devices such as central air conditioning systems and fresh air systems have become effective cooling measures.

[0003] However, in the face of the increasingly tense global energy crisis, active cooling devices and measures need to consume a large amount of fossil energy and other energy. For non-recyclable fossil energy, a large amount of greenhouse gases is also generated during use, further deteriorating the natural environment, and thus entering a vicious cycle of environmental destruction. The use of clean energy such as solar energy and wind energy solves the problem of environmental destruction. However, due to the limitations of regional applicability and power generation efficiency, clean energy such as solar energy and wind energy accounts for a very small proportion, and cannot meet the demand for summer peak electricity consumption.

[0004] Passive refrigeration device or material refrigeration process, such as radiation cooling, is a new type of non-energy consumption cooling device that has emerged in recent years. It has been applied to the cooling of key components of satellites, LED devices, and other fields. Radiation cooling is a passive cooling method that achieves heat dissipation to the external space without using energy. The principle of radiation cooling is to release heat to the atmospheric environment in the 8-14 μm infrared band with high transmittance, thereby achieving the cooling effect of the body. Previously, there have been several developments and applications of radiation cooling devices. For example, patent 202210114761.4 mentions a radiation cooler made of polyester resin and incompatible resin mixed and stretched into a film, and patent 201821379433.2 mentions a radiation cooling film device for vehicle surfaces made of a scratch-resistant coating, a radiation refrigeration layer, a metal layer, an adhesive layer, a transparent polyester PET layer, a mounting adhesive, and a release protection film. However, due to the high cost of polymer film radiation cooling materials and device preparation, their application in civilian fields is still limited. In addition, since most radiation cooling films are not white or light-colored films, they have poor radiation and refraction effects under strong sunlight, which means they have poor blocking effects on external heat. Therefore, the radiation cooling effect is generally low. The visible light radiation energy of the sun can account for nearly 50% of the total radiation energy, which is the main cause of the temperature rise of the surface and interior of an object. Light-colored, especially white, barrier layers can reflect most of the visible light, thereby avoiding or reducing the temperature rise caused by the absorption of visible light by the surface of an object.

[0005] Centralized cooling in summer is a new type of cooling measure that has emerged in China. By using facilities for winter heating, cooling water is circulated to supply large centralized communities or environments, achieving good cooling effect and reducing the consumption of large amounts of electricity during the summer peak period.

[0006] Therefore, developing a cheap white radiation cooling material with good visible light reflection, achieving low absorption of sunlight and high emission of environmental heat, and applying it to summer cooling devices is one of the preferred ways to achieve energy saving, emission reduction, carbon neutrality, and carbon peak, and to solve the problem of centralized cooling in summer.

[0007] Generally, the micro-arc oxidation process can be used to prepare coatings with good corrosion resistance, but it is less used for light-colored or white coatings for radiation cooling. The main method for preparing a coating with good reflection of sunlight is coating, which is brushing a light-colored or white metal oxide coating on the surface of the substrate. However, this coating is prone to peeling off the surface of the substrate, and as the oxide carrier ages, the color becomes darker, the reflection of sunlight decreases, and the long-term effectiveness cannot be maintained.

[0008] The micro-arc oxidation process can realize the ceramicization of the surface of a substrate, and an Al2O3-based ceramic coating is formed on the aluminum alloy during the micro-arc oxidation process, but if the selected functional substance does not match, a light color or white micro-arc oxidation ceramic coating cannot be formed. SUMMARY

[0009] The application provides an electrolyte for micro-arc oxidation and a preparation method of a micro-arc oxidation ceramic coating and a radiation cooling device, and solves the problem of high energy consumption of indoor cooling in summer.

[0010] To achieve the above-mentioned purposes, the application adopts the technical scheme including: an electrolyte for micro-arc oxidation, which comprises: a main salt solution with a concentration of 5-50 g / L, a pH regulator with a concentration of 1-10 g / L, and an electrolyte functional salt or particle with a concentration of 0.1-1 g / L. The electrolyte functional salt or particle is one or a mixture of several of (NH4)2ZrF6, ZnH2PO4, ZnO, ZrO2 and TiO2.

[0011] The main salt comprises one or a mixture of several of Na2SiO3, Na3PO4, Na2HPO4 and (NaPO3)6.

[0012] The water is distilled water, ultrapure water or deionized water.

[0013] The pH regulator is one or a mixture of two of KOH and NaOH.

[0014] The application further provides a preparation method of a micro-arc oxidation ceramic coating, which comprises the following steps:

[0015] The aforementioned micro-arc oxidation electrolyte is added into an electrolytic cell, an aluminum alloy coil pipe is used as an anode, stainless steel is used as a cathode, and the two are placed in the electrolytic cell. The micro-arc oxidation surface treatment of the aluminum alloy coil pipe can obtain a micro-arc oxidation ceramic coating on the surface of the aluminum alloy coil pipe.

[0016] The power supply parameters are set as follows: the anode and the cathode end, the input current density is 2-10 A / dm 2 , the output voltage is 400-600 V, the duty cycle is 45%, the anode / cathode pulse number ratio is 1:1, the power supply frequency is set to 50 Hz, and the oxidation time is 30-120 min. The electrolyte temperature is maintained below 30 DEG C through the cooling circulating water of a low-temperature constant-temperature tank, the operating power supply is connected to the anode and the cathode, the micro-arc oxidation surface treatment of the aluminum alloy coil pipe is carried out, after the reaction is completed, the aluminum alloy coil pipe is rinsed with distilled water and dried, and a micro-arc oxidation ceramic coating is obtained on the surface of the aluminum alloy coil pipe.

[0017] The electrolyte for micro-arc oxidation comprises: a main salt at a concentration of 5-50 g / L, a pH adjuster at a concentration of 1-10 g / L, and electrolyte functional salts or particles at a concentration of 0.1-1 g / L. The electrolyte functional salts or particles are one or a mixture of several of (NH4)2ZrF6, ZnH2PO4, ZnO, ZrO2, and TiO2.

[0018] The main salt includes one or a mixture of several of Na2SiO3, Na3PO4, Na2HPO4, and (NaPO3)6.

[0019] The water mentioned is distilled water, ultrapure water, or deionized water.

[0020] pH adjusters are one or a mixture of two of KOH and NaOH.

[0021] The present invention also provides a radiation cooling device, which uses the aforementioned aluminum alloy coil with a micro-arc oxidation ceramic coating as the radiation cooling device.

[0022] The inner diameter of the aluminum alloy tube used is 5-10mm, and the inner diameter of the coil is 5cm-10cm.

[0023] Aluminum alloy coils with micro-arc anodized ceramic coatings are welded together in series and parallel to form a radiant cooling device. This device maintains the low temperature of cooling water during the summer cooling process, which is used in winter heating systems.

[0024] This invention provides a method for preparing an electrolyte and a micro-arc oxidation ceramic coating for micro-arc oxidation, as well as a radiative cooling device, which has low maintenance costs under stable and safe operating conditions. The micro-arc oxidation ceramic coating obtained on the surface of an aluminum alloy coil exhibits an absorption rate of up to 0.28 and an infrared emissivity of up to 0.97, effectively reflecting sunlight while dissipating heat from the cooling water. This invention uses a micro-arc oxidation process to select specific functional salts or particles in the electrolyte to form a white micro-arc oxidation ceramic coating on the surface of the aluminum alloy coil. This coating not only reflects most visible, ultraviolet, and near-ultraviolet light but also radiates infrared heat into the environment, providing radiative cooling. Cooling is achieved even when the ambient temperature is higher than the fluid level in the coil, without requiring additional energy. Compared to existing active cooling technologies, the advantages of this invention include: the micro-arc oxidation ceramic coating obtained on the surface of the aluminum alloy coil provided by this invention is a passive water cooling material that achieves water cooling without the need for energy, thus reducing energy consumption. The micro-arc oxidation ceramic coating on the surface of an aluminum alloy coil provided by this invention can maintain the low-temperature characteristics of cold water during circulation and significantly reduce the energy consumption for recooling the cold water. The micro-arc oxidation ceramic coating process provided by this invention does not use expensive organic polymer materials, and can fully realize the blackbody radiation efficiency of the material while reducing or maintaining the water temperature, thereby reducing equipment maintenance and operating costs. Detailed Implementation

[0025] Example 1: The electrolyte for micro-arc oxidation was prepared with the following concentrations: main salt (NaPO3) 6 at 50 g / L, pH adjuster KOH at 1.5 g / L, and functional particles TiO2 at 1 g / L. The preparation method for the micro-arc oxidation ceramic coating used constant current mode, with an anolyte / cathode current density of 8 A / dm³. 2 The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0026] The radiant cooling device uses an aluminum alloy tube with an inner diameter of 5mm, which is coiled into an aluminum alloy coil with an inner diameter of 5cm. After micro-arc oxidation, the aluminum alloy coil is coated with a micro-arc oxidation ceramic coating. After fusion welding, it is connected in series.

[0027] Each section of the series-connected micro-arc oxidation ceramic aluminum alloy coil is 1 meter long, with 5 coils in each series circuit and 5 parallel series circuits, serving as a radiant cooling device. Test conditions were: cooling water inlet temperature of 15℃, 20℃, and 25℃; cooling water flow rate of 0.5 m³ / h; room temperature of 30℃; and measurement of the outlet temperature.

[0028] The following embodiments use the same series and parallel connection conditions and test conditions for the radiation cooling devices as described above.

[0029] Testing revealed that the radiative coating on the coil had an absorptivity of 0.28 and an emissivity of 0.97. With inlet temperatures of 15℃, 20℃, and 25℃, the outlet temperatures were 13.2℃, 17.8℃, and 21.3℃, respectively. The radiative coating exhibits low absorptivity for solar radiation and high emissivity for radiation into space, resulting in a significant cooling effect on the cooling water.

[0030] Example 2: The similarities to Example 1 will not be repeated here. The difference lies in the use of an aluminum alloy tube with an inner diameter of 5mm, coiled into a coil with an inner diameter of 8cm. The electrolyte is prepared with a concentration of 10g / L for the main salt (NaPO3), 6g / L for the pH adjuster (KOH), and 0.1g / L for the functional particles (TiO2). The electrical parameters are constant current mode, with an anode / cathode current density of 10A / dm³. 2 The output voltage is 560V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0031] Tests showed that the radiation coating on the coil had an absorptivity of 0.29 and an emissivity of 0.97. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.3℃, ​​17.8℃, and 21.4℃, respectively.

[0032] Example 3: The similarities to Example 1 will not be repeated here. The difference lies in the use of an 8mm inner diameter aluminum alloy tube coiled into a 10cm inner diameter coil. The electrolyte is prepared with a concentration of 25g / L for the main salt (NaPO3), 10g / L for the pH adjuster (KOH), and 0.5g / L for the functional particles (TiO2). The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2The output voltage is 540V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 100min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0033] Tests showed that the radiation coating on the coil had an absorptivity of 0.28 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.3℃, ​​17.8℃, and 21.3℃, respectively.

[0034] Example 4: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts Na3PO4 and Na2HPO4 are prepared at a 1:1 mass ratio of 30g / L, the pH adjuster KOH is at 5g / L, and the electrolyte functional salt (NH4)2ZrF6 and granular ZnO are prepared at a 1:1 mass ratio of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 10A / dm³. 2 The output voltage is 560V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 30 minutes. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0035] Tests showed that the radiation coating on the coil had an absorptivity of 0.30 and an emissivity of 0.95. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.6℃, ​​18.1℃, and 22.4℃, respectively.

[0036] Example 5: The similarities to Example 1 are not repeated here. The difference is that an aluminum alloy tube with an inner diameter of 5mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na3PO4 and Na2HPO4 are prepared at a mass ratio of 2:1 at 5g / L, the pH adjuster KOH at 6g / L, and the electrolyte functional salt (NH4)2ZrF6 and granular ZnO at a mass ratio of 1:2 at a concentration of 1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 5A / dm³. 2The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0037] Tests showed that the radiation coating on the coil had an absorptivity of 0.29 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.4℃, 18.0℃, and 21.9℃, respectively.

[0038] Example 6: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 5mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts Na3PO4 and Na2HPO4 are prepared at a mass ratio of 1:2 at 50g / L, the pH adjuster KOH is at 4g / L, and the electrolyte functional salt (NH4)2ZrF6 and granular ZnO are prepared at a mass ratio of 2:1 at a concentration of 1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2 The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0039] Tests showed that the radiation coating on the coil had an absorptivity of 0.28 and an emissivity of 0.94. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.5℃, 18.2℃, and 22.1℃, respectively.

[0040] Example 7: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 8cm. The main salts Na3PO4 and Na2HPO4 are prepared at a mass ratio of 2:1 at 25g / L, the pH adjuster KOH at 6g / L, and the electrolyte functional salt (NH4)2ZrF6 and granular ZnO at a mass ratio of 2:1 at a concentration of 0.1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 6A / dm³. 2The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0041] Tests showed that the radiation coating on the coil had an absorptivity of 0.31 and an emissivity of 0.97. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.6℃, ​​17.9℃, and 22.0℃, respectively.

[0042] Example 8: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 5mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts Na3PO4 and Na2HPO4 are prepared at a mass ratio of 1:2 at 5g / L, the pH adjuster KOH at 8g / L, and the electrolyte functional salt (NH4)2ZrF6 and granular ZnO at a mass ratio of 1:2 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2 The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0043] Tests showed that the radiation coating on the coil had an absorptivity of 0.31 and an emissivity of 0.95. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.9℃, 18.1℃, and 22.2℃, respectively.

[0044] Example 9: The similarities between this example and Example 1 will not be repeated. The difference is that an aluminum alloy tube with an inner diameter of 10mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts are Na3PO4 and Na2HPO4. 4 The electrolyte was prepared by using (NaPO3)6 at a mass ratio of 1:1:2 at 40 g / L, NaOH as a pH adjuster at 2 g / L, and functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZrO2 at a mass ratio of 1:1:1 at a concentration of 1 g / L. The electrolyte was prepared in constant current mode, with an anode / cathode current density of 5 A / dm³. 2The output voltage is 450V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 60min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0045] Tests showed that the radiation coating on the coil had an absorptivity of 0.31 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.7℃, 18.1℃, and 21.9℃, respectively.

[0046] Example 10: The similarities between this example and Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 10mm is selected and coiled into a coil with an inner diameter of 8cm. The main salts are Na3PO4 and Na2HPO4. 4 The electrolyte was prepared by mixing (NaPO3)6 at a mass ratio of 1:1:1 (5 g / L), NaOH (pH adjuster) at 2 g / L, and functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZrO2 at a mass ratio of 1:2:1 (0.1 g / L). The electrolyte was prepared in constant current mode with an anode / cathode current density of 5 A / dm³. 2 The output voltage is 450V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0047] Tests showed that the radiation coating on the coil had an absorptivity of 0.30 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.6℃, ​​18.0℃, and 21.7℃, respectively.

[0048] Example 11: The similarities between this example and Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 5mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts are Na3PO4 and Na2HPO4. 4 The electrolyte was prepared by using (NaPO3)6 at a mass ratio of 1:2:1 at 25 g / L, NaOH as a pH adjuster at 6 g / L, and functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZrO2 at a mass ratio of 2:1:1 at a concentration of 0.5 g / L. The electrical parameters were constant current mode, with an anode / cathode current density of 8 A / dm³. 2The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0049] Tests showed that the radiation coating on the coil had an absorptivity of 0.31 and an emissivity of 0.95. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.8℃, 18.2℃, and 22.1℃, respectively.

[0050] Example 12: The similarities between this example and Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts are Na3PO4 and Na2HPO4. 4 The electrolyte was prepared by using (NaPO3)6 at a mass ratio of 2:1:1 (50 g / L), NaOH as a pH adjuster at 6 g / L, and functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZrO2 at a mass ratio of 1:1:1 (0.8 g / L). The electrolyte was prepared in constant current mode with an anode / cathode current density of 5 A / dm³. 2 The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 100min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the surface of the aluminum alloy.

[0051] Tests showed that the radiation coating on the coil had an absorptivity of 0.32 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.8℃, 18.1℃, and 22.0℃, respectively.

[0052] Example 13: The similarities between this example and Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 10mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts are Na3PO4 and Na2HPO4. 4 The electrolyte was prepared by mixing (NaPO3)6 at a mass ratio of 1:1:1 (5 g / L), NaOH (6 g / L) as a pH adjuster, and functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZrO2 at a mass ratio of 1:1:1 (0.5 g / L). The electrolyte was set to constant current mode, with an anode / cathode current density of 8 A / dm³. 2The output voltage is 560V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 100min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0053] Tests showed that the radiation coating on the coil had an absorptivity of 0.31 and an emissivity of 0.97. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.6℃, ​​17.8℃, and 21.7℃, respectively.

[0054] Example 14: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na2HPO4 and (NaPO3)6 are prepared at a mass ratio of 1:1 at 5g / L, the pH adjuster NaOH is at 4g / L, and the electrolyte functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZnO are prepared at a mass ratio of 1:2:1 at a concentration of 0.1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2 The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 30 minutes. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0055] Tests showed that the radiation coating on the coil had an absorptivity of 0.32 and an emissivity of 0.93. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.1℃, 18.3℃, and 22.7℃, respectively.

[0056] Example 15: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts Na2HPO4 and (NaPO3)6 are prepared at a mass ratio of 2:1 at 50g / L, the pH adjuster KOH is at 6g / L, and the electrolyte functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZnO are prepared at a mass ratio of 1:1:1 at a concentration of 1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 5A / dm³. 2The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0057] Tests showed that the radiation coating on the coil had an absorptivity of 0.32 and an emissivity of 0.94. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.0℃, 18.2℃, and 22.7℃, respectively.

[0058] Example 16: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 6mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na2HPO4 and (NaPO3)6 are prepared at a mass ratio of 2:1 at 50g / L, the pH adjuster NaOH is at 6g / L, and the electrolyte functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZnO are prepared at a mass ratio of 2:1:1 at a concentration of 1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 5A / dm³. 2 The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 60min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0059] Tests showed that the radiation coating on the coil had an absorptivity of 0.31 and an emissivity of 0.93. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.0℃, 18.1℃, and 22.6℃, respectively.

[0060] Example 17: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 6mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na2HPO4 and (NaPO3)6 are prepared at a mass ratio of 2:1 at 25g / L, the pH adjuster KOH is at 4g / L, and the electrolyte functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZnO are prepared at a mass ratio of 1:2:1 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 10A / dm³. 2The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 30 minutes. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0061] Tests showed that the radiation coating on the coil had an absorptivity of 0.32 and an emissivity of 0.95. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.8℃, 17.8℃, and 22.4℃, respectively.

[0062] Example 18: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na2HPO4 and (NaPO3)6 are prepared at a mass ratio of 2:1 at 10g / L, the pH adjuster NaOH is at 8g / L, and the electrolyte functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZnO are prepared at a mass ratio of 1:1:2 at a concentration of 0.1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 5A / dm³. 2 The output voltage is 480V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 60min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0063] Tests showed that the radiation coating on the coil had an absorptivity of 0.31 and an emissivity of 0.94. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.9℃, 18.0℃, and 22.5℃, respectively.

[0064] Example 19: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 10mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na2HPO4 and (NaPO3)6 are prepared at a mass ratio of 1:2 at 25g / L, the pH adjuster NaOH is at 6g / L, and the electrolyte functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZnO are prepared at a mass ratio of 2:1:1 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 5A / dm³. 2The output voltage is 480V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0065] Tests showed that the radiation coating on the coil had an absorptivity of 0.33 and an emissivity of 0.95. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.9℃, 17.9℃, and 22.5℃, respectively.

[0066] Example 20: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na2HPO4 and (NaPO3)6 are prepared at a mass ratio of 1:2 at 10g / L, the pH adjuster NaOH is at 6g / L, and the electrolyte functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZnO are prepared at a mass ratio of 1:2:1 at a concentration of 0.1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 2A / dm³. 2 The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 100min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0067] Tests showed that the radiation coating on the coil had an absorptivity of 0.30 and an emissivity of 0.94. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.8℃, 17.9℃, and 22.4℃, respectively.

[0068] Example 21: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na2HPO4 and (NaPO3)6 are prepared at a mass ratio of 1:2 at 30g / L, the pH adjuster NaOH is at 8g / L, and the electrolyte functional salts (NH4)2ZrF6, ZnH2PO4, and granular ZnO are prepared at a mass ratio of 1:1:2 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 10A / dm³. 2The output voltage is 540V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0069] Tests showed that the radiation coating on the coil had an absorptivity of 0.30 and an emissivity of 0.93. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.8℃, 18.0℃, and 22.5℃, respectively.

[0070] Example 22: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 5mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts Na2SiO3, Na3PO4, and Na2HPO4 are prepared at a mass ratio of 1:2:1 at 50g / L, the pH adjuster NaOH is at 2g / L, and the electrolyte functional salts (NH4)2ZrF6 and ZnH2PO4 are prepared at a mass ratio of 1:1 at a concentration of 1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 10A / dm³. 2 The output voltage is 550V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0071] Tests showed that the radiation coating on the coil had an absorptivity of 0.30 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.6℃, ​​17.9℃, and 21.6℃, respectively.

[0072] Example 23: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts Na2SiO3, Na3PO4, and Na2HPO4 are prepared at a mass ratio of 2:1:1 at 5g / L, the pH adjuster NaOH at 6g / L, and the electrolyte functional salts (NH4)2ZrF6 and ZnH2PO4 at a mass ratio of 1:1 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2The output voltage is 550V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0073] Tests showed that the radiation coating on the coil had an absorptivity of 0.30 and an emissivity of 0.95. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.7℃, 18.0℃, and 21.7℃, respectively.

[0074] Example 24: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na2SiO3, Na3PO4, and Na2HPO4 are prepared at a mass ratio of 1:1:2 at 25g / L, the pH adjuster KOH is at 6g / L, and the electrolyte functional salts (NH4)2ZrF6 and ZnH2PO4 are prepared at a mass ratio of 1:1 at a concentration of 0.1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 5A / dm³. 2 The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0075] Tests showed that the radiation coating on the coil had an absorptivity of 0.32 and an emissivity of 0.95. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.9℃, 18.3℃, and 21.9℃, respectively.

[0076] Example 25: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts Na2SiO3, Na3PO4, and Na2HPO4 are prepared at a mass ratio of 1:1:1 at 25g / L, the pH adjuster NaOH is at 6g / L, and the electrolyte functional salts (NH4)2ZrF6 and ZnH2PO4 are prepared at a mass ratio of 2:1 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 60min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0077] Tests showed that the radiation coating on the coil had an absorptivity of 0.31 and an emissivity of 0.93. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.9℃, 18.3℃, and 22.0℃, respectively.

[0078] Example 26: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 5mm is selected and coiled into a coil with an inner diameter of 10cm. The main salts Na2SiO3, Na3PO4, and Na2HPO4 are prepared at a mass ratio of 1:1:1 at 10g / L, the pH adjuster NaOH is at 2g / L, and the electrolyte functional salts (NH4)2ZrF6 and ZnH2PO4 are prepared at a mass ratio of 1:2 at a concentration of 0.1g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 10A / dm³. 2 The output voltage is 550V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0079] Tests showed that the radiation coating on the coil had an absorptivity of 0.32 and an emissivity of 0.97. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.6℃, ​​18.1℃, and 21.7℃, respectively.

[0080] Example 27: This example is similar to Example 1 and will not be repeated. The difference is that an aluminum alloy tube with an inner diameter of 10mm is selected and coiled into a coil with an inner diameter of 5cm. The main salts Na3PO4 and Na2HPO4 are prepared at a mass ratio of 1:1 at 20g / L, the pH adjuster KOH is at 2g / L, and the electrolyte functional salts ZnH2PO4 and granular ZrO2 are prepared at a mass ratio of 1:1 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2The output voltage is 480V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0081] Tests showed that the radiation coating on the coil had an absorptivity of 0.29 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.2℃, 17.7℃, and 22.1℃, respectively.

[0082] Example 28: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 8cm. The electrolyte is prepared by using the main salts Na3PO4 and Na2HPO4 at a mass ratio of 2:1 at 50g / L, the pH adjuster KOH at 6g / L, and the electrolyte functional salts ZnH2PO4 and granular ZrO2 at a mass ratio of 2:1 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 5A / dm³. 2 The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 100min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0083] Tests showed that the radiation coating on the coil had an absorptivity of 0.28 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.1℃, 17.5℃, and 22.0℃, respectively.

[0084] Example 29: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8mm is selected and coiled into a coil with an inner diameter of 5cm. The electrolyte is prepared by using the main salts Na3PO4 and Na2HPO4 at a mass ratio of 2:1 (5g / L), the pH adjuster KOH at 8g / L, and the electrolyte functional salts ZnH2PO4 and granular ZrO2 at a mass ratio of 1:2 (1g / L). The electrical parameters are constant current mode, with an anode / cathode current density of 5A / dm³. 2The output voltage is 480V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0085] Tests showed that the radiation coating on the coil had an absorptivity of 0.30 and an emissivity of 0.96. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.3℃, ​​17.6℃, and 22.1℃, respectively.

[0086] Example 30: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 10 mm is selected and coiled into a coil with an inner diameter of 5 cm. The main salts Na3PO4 and Na2HPO4 are prepared at a mass ratio of 1:2 at 50 g / L, the pH adjuster KOH is at 10 g / L, and the electrolyte functional salts ZnH2PO4 and granular ZrO2 are prepared at a mass ratio of 2:1 at a concentration of 0.1 g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8 A / dm³. 2 The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0087] Tests showed that the radiation coating on the coil had an absorptivity of 0.29 and an emissivity of 0.95. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.3℃, ​​17.8℃, and 22.2℃, respectively.

[0088] Example 31: The similarities to Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 10mm is selected and coiled into a coil with an inner diameter of 5cm. The electrolyte is prepared by using the main salts Na3PO4 and Na2HPO4 at a mass ratio of 1:2 at 25g / L, the pH adjuster KOH at 8g / L, and the electrolyte functional salts ZnH2PO4 and granular ZrO2 at a mass ratio of 1:2 at a concentration of 0.5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 6A / dm³. 2The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 60min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a porous white micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0089] Tests showed that the radiation coating on the coil had an absorptivity of 0.30 and an emissivity of 0.94. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 13.5℃, 18.1℃, and 22.2℃, respectively.

[0090] Comparative Example 1: Preparation method of micro-arc oxidation ceramic coating. The electrolyte for micro-arc oxidation includes 50 g / L of main salt (NaPO3)6 and 1.5 g / L of pH adjuster KOH. The electrical parameters are constant current mode, and the anodic / cathode current density is 8 A / dm³. 2 The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90 minutes. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy coil; after the reaction, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface. The radiation cooling device uses an aluminum alloy tube with an inner diameter of 5mm, which is coiled into a coil with an inner diameter of 5cm and a micro-arc oxidation ceramic coating.

[0091] Each section of the series-connected micro-arc oxidation ceramic aluminum alloy coil is 1 meter long, with 5 coils in each series circuit and 5 parallel series circuits, serving as a radiant cooling device. Test conditions were: cooling water inlet temperature of 15℃, 20℃, and 25℃; cooling water flow rate of 0.5 m³ / h; room temperature of 30℃; and measurement of the outlet temperature.

[0092] The following comparative radiative cooling devices have the same series and parallel connection conditions and test conditions as described above.

[0093] Tests showed that the radiation coating on the coil had an absorptivity of 0.39 and an emissivity of 0.89. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.8℃, 19.8℃, and 24.7℃, respectively.

[0094] Comparative Example 2: Similarities to Comparative Example 1 will not be repeated here. The difference lies in the selection of an 8mm inner diameter aluminum alloy tube, coiled into a 10cm inner diameter coil. The main salts Na3PO4 and Na2HPO4 are used at a 1:1 mass ratio of 30g / L, and the pH adjuster KOH is used at 5g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 10A / dm³. 2The output voltage is 560V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 30 minutes. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0095] Tests showed that the radiation coating on the coil had an absorptivity of 0.40 and an emissivity of 0.87. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.9℃, 19.9℃, and 24.9℃, respectively.

[0096] Comparative Example 3: Similarities to Comparative Example 1 will not be repeated here. The difference lies in the selection of an aluminum alloy tube with an inner diameter of 10 mm, coiled into a coil with an inner diameter of 10 cm. The main salts Na3PO4, Na2HPO4, and (NaPO3)6 are in a 1:1:2 mass ratio at 40 g / L, and the pH adjuster NaOH is at 2 g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 5 A / dm³. 2 The output voltage is 450V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 60min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0097] Tests showed that the radiation coating on the coil had an absorptivity of 0.45 and an emissivity of 0.85. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 15.0℃, 20.1℃, and 25.0℃, respectively.

[0098] Comparative Example 4: Similarities to Comparative Example 1 will not be repeated here. The difference lies in the selection of an 8mm inner diameter aluminum alloy tube, coiled into a 5cm inner diameter coil. The main salts Na₂HPO₄ and (NaPO₃)₆ are used at a 1:1 mass ratio of 5g / L, and the pH adjuster NaOH is used at 4g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2 The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 30 minutes. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0099] Tests showed that the radiation coating on the coil had an absorptivity of 0.42 and an emissivity of 0.86. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.9℃, 20.0℃, and 24.9℃, respectively.

[0100] Comparative Example 5: Similarities to Comparative Example 1 will not be repeated here. The difference lies in the selection of an aluminum alloy tube with an inner diameter of 5mm, coiled into a coil with an inner diameter of 10cm. The main salts Na2SiO3, Na3PO4, and Na2HPO4 are in a 1:2:1 mass ratio at 50g / L, and the pH adjuster NaOH is at 2g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 10A / dm³. 2 The output voltage is 550V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0101] Tests showed that the radiation coating on the coil had an absorptivity of 0.41 and an emissivity of 0.88. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.8℃, 19.7℃, and 24.8℃, respectively.

[0102] Comparative Example 6: Similarities to Comparative Example 1 will not be repeated here. The difference lies in the selection of an aluminum alloy tube with an inner diameter of 10 mm, coiled into a coil with an inner diameter of 5 cm. The main salts Na3PO4 and Na2HPO4 are used at a 1:1 mass ratio of 20 g / L, and the pH adjuster KOH is used at 2 g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8 A / dm³. 2 The output voltage is 480V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0103] Tests showed that the radiation coating on the coil had an absorptivity of 0.37 and an emissivity of 0.86. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.9℃, 19.9℃, and 24.8℃, respectively.

[0104] Comparative Example 7: Similarities to Comparative Example 1 will not be repeated here. The difference lies in the following: an aluminum alloy tube with an inner diameter of 5mm was selected and coiled into a coil with an inner diameter of 10cm. The main salt Na₂SiO₃ was used at 60g / L, and the pH adjuster NaOH was used at 10g / L. The electrical parameters were constant current mode, with an anode / cathode current density of 15A / dm², an output voltage of 580V, and an anode / cathode pulse ratio of 1:1. The power supply frequency was set to 50Hz, and the oxidation time was 20min. The electrolyte temperature was maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The power supply was connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy. After the reaction, the surface was rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0105] Tests showed that the radiation coating on the coil had an absorptivity of 0.46 and an emissivity of 0.83. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 15.1℃, 19.6℃, and 24.8℃, respectively.

[0106] Comparative Example 8: The similarities between this comparative example and Comparative Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 10 mm was selected and coiled into a coil with an inner diameter of 5 cm. The main salts Na3PO4 and Na2HPO4 were used at a mass ratio of 5:1 at 5 g / L, and the pH adjuster NaOH was used at 0.5 g / L. The electrical parameters were constant current mode, with an anode / cathode current density of 1 A / dm³. 2 The output voltage is 400V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 120min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0107] Tests showed that the radiation coating on the coil had an absorptivity of 0.42 and an emissivity of 0.85. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.8℃, 19.7℃, and 24.7℃, respectively.

[0108] Comparative Example 9: Similarities to Comparative Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 5mm was selected and coiled into a coil with an inner diameter of 5cm. The main salt (NaPO3)6 was prepared at 50g / L, the pH adjuster KOH at 2g / L, and the electrolyte was prepared with functional salts NaAlO2 and granular MgO at a mass ratio of 1:2 and a concentration of 1g / L. The electrolyte parameters were constant current mode, with an anode / cathode current density of 8A / dm³. 2The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0109] Tests showed that the radiation coating on the coil had an absorptivity of 0.37 and an emissivity of 0.90. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.5℃, 19.3℃, and 24.4℃, respectively.

[0110] Comparative Example 10: Similarities to Comparative Example 1 will not be repeated here. The difference is that an aluminum alloy tube with an inner diameter of 8 mm was selected and coiled into a coil with an inner diameter of 10 cm. The main salts Na3PO4 and Na2HPO4 were prepared at a mass ratio of 1:1 at 30 g / L, the pH adjuster KOH at 5 g / L, and the electrolyte functional salts MgSiF6, Ca(H2PO2)2, and granular Al2O3 were prepared at a mass ratio of 1:1:2 at a concentration of 1 g / L. The electrolyte was prepared in constant current mode, with an anode / cathode current density of 10 A / dm³. 2 The output voltage is 560V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 30 minutes. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0111] Tests showed that the radiation coating on the coil had an absorptivity of 0.40 and an emissivity of 0.90. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.6℃, 19.5℃, and 24.6℃, respectively.

[0112] Comparative Example 11: Following the method of patent CN103194780A, an aluminum alloy tube with an inner diameter of 5mm was selected and coiled into a coil with an inner diameter of 5cm. The main salt Na2SiO3 was 5g / L, the auxiliary salt Na3PO4 was 5g / L, the electrolyte pH was 10, and a pulsed micro-arc oxidation power supply was used with a current density of 10A / dm³. 2 Under the conditions of a forward voltage of 400V, a power supply frequency of 100Hz, a duty cycle of 20%, and an electrolyte temperature of 30℃, a micro-arc oxidation reaction was carried out for 20 minutes to grow a ceramic coating in situ on the aluminum alloy surface.

[0113] Tests showed that the radiation coating on the coil had an absorptivity of 0.39 and an emissivity of 0.89. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.4℃, 18.9℃, and 23.5℃, respectively.

[0114] Comparative Example 12: Similarities to Comparative Example 1 will not be repeated here. The difference lies in the selection of an aluminum alloy tube with an inner diameter of 5 mm, coiled into a coil with an inner diameter of 5 cm. The electrolyte was prepared with a concentration of 50 g / L for the main salt (NaPO3)6, 1.5 g / L for the pH adjuster KOH, and 8 g / L for the functional particles TiO2. The preparation method for the micro-arc oxidation ceramic coating used constant current mode, with an anodic / cathode current density of 8 A / dm³. 2 The output voltage is 520V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 90min. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0115] Tests showed that the radiation coating on the coil had an absorptivity of 0.41 and an emissivity of 0.89. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.7℃, 18.9℃, and 24.1℃, respectively.

[0116] Comparative Example 13: The similarities between this example and Example 1 will not be repeated. The difference lies in the use of an 8mm inner diameter aluminum alloy tube coiled into a 5cm inner diameter coil. The main salts Na₂HPO₄ and (NaPO₃)₆ are prepared at a 1:1 mass ratio of 5g / L, the pH adjuster NaOH is at 4g / L, and the electrolyte functional salts (NH₄)₂ZrF₆, ZnH₂PO₄, and granular ZnO are prepared at a 1:5:1 mass ratio of 7g / L. The electrical parameters are constant current mode, with an anode / cathode current density of 8A / dm³. 2 The output voltage is 500V, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, and the oxidation time is 30 minutes. The electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low-temperature constant temperature bath. The operating power supply is connected to the anode and cathode to perform micro-arc oxidation surface treatment on the aluminum alloy; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the aluminum alloy surface.

[0117] Tests showed that the radiation coating on the coil had an absorptivity of 0.40 and an emissivity of 0.90. When the inlet temperature of the device was 15℃, 20℃, and 25℃, the outlet temperatures were 14.8℃, 19.1℃, and 24.3℃, respectively.

[0118] The above tests show that the embodiment exhibits a significant temperature reduction after the cooling water passes through the radiation-cooled micro-arc anodizing aluminum alloy coil. The temperature reduction ranges as follows: at an inlet temperature of 15°C, the lowest outlet temperature drops to 13.1°C, and the highest outlet temperature is 14.1°C; at an inlet temperature of 20°C, the lowest outlet temperature drops to 17.5°C, and the highest outlet temperature is 18.3°C; at an inlet temperature of 25°C, the lowest outlet temperature drops to 21.3°C, and the highest outlet temperature is 22.9°C. The temperature reductions at inlet temperatures of 15°C, 20°C, and 25°C reach a maximum of 1.9°C, 2.5°C, and 3.7°C, respectively, indicating that the radiation-cooled micro-arc anodizing aluminum alloy device has a good cooling effect. In contrast, micro-arc anodizing coatings prepared according to other patents and other component ratios show inferior cooling effects compared to the embodiment. The temperature reduction range is as follows: when the inlet temperature is 15℃, the lowest outlet temperature is 14.4℃ and the highest outlet temperature is 15.1℃; when the inlet temperature is 20℃, the lowest outlet temperature is 18.9℃ and the highest outlet temperature is 20.1℃; when the inlet temperature is 25℃, the lowest outlet temperature is 23.5℃ and the highest outlet temperature is 25.0℃. The temperature reduction at inlet temperatures of 15℃, 20℃, and 25℃ is only a maximum of 0.6℃, 1.1℃, and 1.5℃, respectively. This is also confirmed by the solar absorption rate and the emissivity of the micro-arc oxidation coating. In the example, the micro-arc oxidation coating has a solar absorption rate ranging from a minimum of 0.28 to a maximum of 0.33, and an emissivity ranging from a minimum of 0.93 to a maximum of 0.97; while in the comparative example, the solar absorption rate ranges from a minimum of 0.35 to a maximum of 0.46, and the emissivity ranges from a minimum of 0.83 to a maximum of 0.91. For passive radiation cooling technology and processes, the radiation-cooled micro-arc oxidation coating obtained in the examples has a significant improvement in reducing the absorption rate of sunlight or increasing the emissivity of external radiation.

Claims

1. A method for preparing a micro-arc oxidation ceramic coating, characterized in that: It includes the following steps: The electrolyte for micro-arc oxidation in the electrolytic cell uses an aluminum alloy coil as the anode and stainless steel as the cathode, and both are placed in the electrolytic cell. Micro-arc oxidation surface treatment can be applied to aluminum alloy coils to obtain a micro-arc oxidation ceramic coating on the surface of the aluminum alloy coils. The electrolyte for micro-arc oxidation includes: a solution of a main salt with a concentration of 5-50 g / L, a pH adjuster with a concentration of 1-10 g / L, and a solution of electrolyte functional salts or particles with a concentration of 0.1-1 g / L. The electrolyte functional salts or particles are one or a mixture of several of (NH4)2ZrF6, Zn(H2PO4)2, ZnO, ZrO2, and TiO2. The main salt includes one or a mixture of several of Na2SiO3, Na3PO4, Na2HPO4, and (NaPO3)6. The pH adjuster is one or a mixture of two of KOH and NaOH. The power supply parameters are set as follows: the input current density at both the anode and cathode ends is 2-10 A / dm³. 2 The output voltage is 400-600V, the duty cycle is 45%, the anode / cathode pulse ratio is 1:1, the power frequency is set to 50Hz, the oxidation time is 30-120min, the electrolyte temperature is maintained below 30℃ by the cooling circulating water of the low temperature constant temperature bath, the operating power supply is connected to the anode and cathode, and the aluminum alloy coil is subjected to micro-arc oxidation surface treatment; after the reaction is completed, it is rinsed with distilled water and dried to obtain a micro-arc oxidation ceramic coating on the surface of the aluminum alloy coil.

2. A radiation cooling device, characterized in that: The aluminum alloy coil with a micro-arc oxidation ceramic coating on its surface, as described in claim 1, is used as a radiation cooling device.

3. The radiation cooling device according to claim 2, characterized in that: The inner diameter of the aluminum alloy tube used is 5-10mm, and the inner diameter of the aluminum alloy coil is 5cm-10cm.

4. The radiative cooling device according to claim 2, characterized in that: Aluminum alloy coils with micro-arc oxidation ceramic coatings are connected in series and parallel after being welded together to form a radiant cooling device.