Thermally induced phase change solar collector tube and coating method thereof

Abstract

The present invention provides a thermally induced phase change solar heat collector tube and its coating method. A vacuum interlayer is formed between the heat-absorbing section of the inner tube and the cover glass tube. The outer wall of the heat-absorbing section is coated with a selective absorption coating. The selective absorption coating comprises an infrared reflection layer, a low-resistance layer, a transition layer, a high-resistance layer, and an anti-reflection layer, sequentially formed on the outer wall of the heat-absorbing section. Furthermore, each of the low-resistance layer, transition layer, high-resistance layer, and anti-reflection layer is doped with vanadium dioxide at a molar ratio of 2% to 40% of the total amount. By employing a vanadium dioxide-doped selective absorption coating, the present invention achieves the desired performance of high absorption and low emission at low temperatures, which is beneficial for heat collection. Furthermore, the selective absorption coating achieves low absorption and high emission at high temperatures, effectively reducing the operating temperature of the heat collector tube when not in operation. This significantly improves the safety and reliability of the heat collector tube, particularly all-glass heat pipes.

Description

Technical Field

[0001] The invention relates to a thermally induced phase change solar heat collecting tube and a coating method thereof. Background Art

[0002] All-glass vacuum solar collector tubes have been developed for more than 30 years, forming the field of solar thermal utilization and are widely used in solar water heating applications.

[0003] With the launch of the Blue Sky Campaign and the rapid progress of coal-to-electricity and coal-to-gas projects, solar thermal technology has undergone necessary demonstration phases in the implementation of these projects. However, due to various factors, compared to widely adopted technologies such as conventional air-source heat pumps, off-peak electricity thermal storage, and gas-fired boiler heating, solar thermal utilization remains at the demonstration stage. A major factor is that existing solar thermal heating technologies still primarily utilize hot-water solar collectors, primarily all-glass vacuum tubes. This results in a collection temperature that cannot meet winter heating requirements. Furthermore, when the collection temperature reaches the designed heating supply temperature, the collection efficiency significantly decreases. Furthermore, the presence of water within the all-glass vacuum tubes can easily lead to scaling and icing, which can cause overheating, damage, breakage, and leaks. These factors contribute to the continued demonstration phase of solar thermal heating applications.

[0004] Because all-glass heat pipe solar collectors utilize phase-change heat transfer technology and are water-free, they address the issues of conventional all-glass vacuum collectors, which often result in slow startup, low thermal efficiency, and damage from scaling and icing. They are anti-scaling, anti-freezing, and anti-breakage and leak-proof, and are gradually gaining acceptance in the solar thermal heating market, with demonstration applications beginning to roll out.

[0005] However, the temperature inside the cavity of the current all-glass vacuum solar collector tube can reach up to 300°C under air-drying conditions, which has a certain impact on the vacuum degree and life of the collector tube.

[0006] When using the double-layer coaxial all-glass vacuum solar collector tube with water in the tube operation mode, once the water is added during the empty sun exposure, it is very easy to cause the high-temperature collector tube to encounter cold water and explode, causing damage to the collector tube.

[0007] When using all-glass heat pipe vacuum solar collectors, excessive pressure can occur in the tubes due to the low-temperature phase-change liquid working fluid inside the tubes, excessive workmanship caused by the process, and insufficient glass ring cutting grade. This can easily cause the tubes to explode and break under high temperature conditions. Therefore, for general all-glass heat pipe vacuum solar collectors, the workmanship is controlled to less than 1.5 thousandths of the volume to ensure safety. While this ensures the safety of the collector tubes under normal operating conditions, it significantly affects the heat transfer performance of the heat pipes, and thus the collection efficiency of the solar collector system.

[0008] All-glass vacuum solar collector tubes are generally suitable for domestic hot water and heating below 60°C. They are rarely used for heat above 100°C. Even when using CPC collectors, they are only suitable for high-temperature hot water below 100°C. Therefore, to address the temperature limitations of solar collector tubes and the problem of tube explosion at high temperatures, it is necessary to design and develop a solar collector tube that does not affect heat collection efficiency at low temperatures and can limit the maximum air temperature of the collector tube, thereby further improving the safety and reliability of the collector tube. Summary of the Invention

[0009] The purpose of the present invention is to provide a thermally induced phase change solar collector tube and its coating method, so that the solar collector tube does not affect the heat collection efficiency under low temperature conditions and can limit the maximum air exposure temperature of the collector tube, so as to further improve the safety and reliability of the collector tube.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] A thermally induced phase change solar heat collecting tube has a vacuum interlayer formed between the heat absorbing section of the inner tube and the cover glass tube. The outer wall of the heat absorbing section has a selective absorption coating. The selective absorption coating is composed of an infrared reflection layer, a low resistance layer, a transition layer, a high resistance layer and an anti-reflection layer formed in sequence on the outer wall of the heat absorbing section.

[0012] The invention is characterized in that the low resistance layer, the transition layer, the high resistance layer and the anti-reflection layer are doped with vanadium dioxide in a molar ratio of 2% to 40% of the total amount of each layer.

[0013] The thermally induced phase change solar heat collecting tube, wherein: the interior of the inner tube constitutes a working medium cavity, the working medium cavity is evacuated and liquid working medium is placed in it, and the volume ratio of the liquid working medium to the volume of the working medium cavity is 1.5% to 2%.

[0014] The thermally induced phase change solar heat collecting tube has a ratio of the volume of the liquid working medium to the volume of the working medium cavity of 0.3% to 0.6%.

[0015] The thermally induced phase change solar collector tube, wherein: the liquid working fluid is a high boiling point working fluid and a low boiling point working fluid, the volume of the high boiling point working fluid accounts for 20% to 50% of the total volume, and the rest is the low boiling point working fluid; the high boiling point working fluid refers to a liquid working fluid with a boiling point greater than or equal to the boiling point of water, and the low boiling point working fluid refers to a working fluid with a boiling point lower than the boiling point of water.

[0016] The thermotropic phase change solar collector tube comprises a low-resistance layer made of any one or a mixture of any number of metal aluminum, titanium, stainless steel, nickel, and their oxides as a matrix, doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 5%-20%, the coating thickness is 50-150nm, and the sheet resistance is 90-500 ohms.

[0017] The thermally induced phase change solar collector tube, wherein: the transition layer is based on any one of metal aluminum, titanium, stainless steel, nickel, silicon and their oxides or a mixture of any several of them, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 10% to 25%, the coating thickness is 50-150nm, and the square resistance is 500 to 2000 ohms.

[0018] The thermotropic phase change solar collector tube comprises a high resistance layer made of any one or a mixture of any number of metal aluminum, titanium, stainless steel, nickel, silicon and their oxides as a matrix, and doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 15% to 30%, the coating thickness is 50-150nm, and the sheet resistance is 1000 to 10000 ohms.

[0019] The thermotropic phase change solar collector tube has an anti-reflection layer based on any one of aluminum and silicon oxides or a mixture thereof, doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total is 30% to 50%, and the sheet resistance is greater than 50,000 ohms.

[0020] A coating method for a thermotropic phase change solar collector tube, characterized in that:

[0021] Target materials are sequentially sputtered on the outer wall of the heat absorption section of the inner tube to form an infrared reflection layer, a low resistance layer, a transition layer, a high resistance layer, and an anti-reflection layer; a certain proportion of vanadium dioxide is doped in the target materials of the low resistance layer, the transition layer, the high resistance layer, and the anti-reflection layer respectively;

[0022] The anti-reflection layer is subjected to high-temperature oxidation heat treatment to completely oxidize the metal vanadium into vanadium dioxide, and the low-resistance layer, transition layer, high-resistance layer and anti-reflection layer are doped with vanadium dioxide in a molar ratio of 2% to 40% of their total amount.

[0023] The present invention adopts a selective absorption coating doped with vanadium dioxide to achieve the performance requirements of high absorption and low emission of the selective absorption coating under low temperature conditions, which is beneficial to heat collection. At the same time, it achieves a state of low absorption and high emission under high temperature conditions, so as to effectively reduce the working temperature of the heat collection tube in the non-working state, and significantly improve the safety and reliability of the heat collection tube, especially the all-glass heat pipe heat collection tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural diagram of an all-glass heat pipe vacuum solar collector.

[0025] Figure 2 It is a structural diagram of the selective absorption coating.

[0026] Figure 3 It is a flow chart of the coating method provided by the present invention.

[0027] Explanation of the accompanying symbols: 1-condensation section; 2-heat absorption section; 3-selective absorption coating; 4-vacuum interlayer; 5-cover glass tube; 6-bracket; 7-adsorbent; 8-liquid working medium; A-coating process of the selective absorption coating; B-high-temperature oxidation heat treatment process of the selective absorption coating; C-exhaust process. DETAILED DESCRIPTION

[0028] like Figure 1 As shown, it is a structural schematic diagram of an all-glass heat pipe vacuum solar collector tube, which is mainly composed of an inner tube (including a condensing section 1 and a heat absorbing section 2, the diameter, wall thickness and other parameters of the condensing section 1 are the same as those of the heat absorbing section 2) and a cover glass tube 5. The round head of the heat absorbing section 2 is fixed to the cover glass tube 5 by a bracket 6, and a getter 7 is provided on the bracket 6. A vacuum interlayer 4 is provided between the heat absorbing section 2 and the cover glass tube 5, and the outer wall of the heat absorbing section 2 has a selective absorption coating 3. The interior of the heat absorbing section 2 and the condensing section 1 constitutes a working fluid cavity, which is evacuated and contains a liquid working fluid 8. The volume ratio of the liquid working fluid 8 to the volume of the working fluid cavity is 1.5 to 2% (preferably 3 to 6 thousandths).

[0029] The liquid working fluid is composed of two or more liquid working fluids with different boiling points, wherein the volume of the high-boiling-point working fluid accounts for 20% to 50% of the total volume, and the remainder is the low-boiling-point working fluid. The high-boiling-point working fluid refers to a liquid working fluid with a boiling point greater than or equal to the boiling point of water, including but not limited to ethylene glycol and propylene glycol. The low-boiling-point working fluid refers to a working fluid with a boiling point lower than the boiling point of water, including ethanol, acetone, etc.

[0030] like Figure 2As shown, the selective absorption coating comprises an infrared reflective layer 21, a low-resistance layer 22, a transition layer 23, a high-resistance layer 24, and an anti-reflection layer 25, which are sequentially formed on the outer wall of the heat absorption section 2. The present invention improves upon this by doping the low-resistance layer 22, the transition layer 23, the high-resistance layer 24, and the anti-reflection layer 25 with vanadium dioxide at a molar ratio of 2% to 40%.

[0031] Among them, the molar ratio of the main component, vanadium dioxide and coating thickness in each layer are:

[0032] The infrared reflection layer is made of pure metal such as aluminum or copper, does not contain vanadium dioxide, has a coating thickness of 60-120nm, and has a sheet resistance of 0 ohm.

[0033] The low resistance layer is based on any one or a mixture of any number of metal aluminum, titanium, stainless steel, nickel and their oxides, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 5%-20%, the coating thickness is 50-150nm, and the square resistance is 90-500 ohms.

[0034] The transition layer is based on any one or a mixture of any number of metal aluminum, titanium, stainless steel, nickel, silicon and their oxides, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 10% to 25%, the coating thickness is 50-150nm, and the square resistance is 500-2000 ohms.

[0035] The high resistance layer is based on any one or a mixture of any number of metal aluminum, titanium, stainless steel, nickel, silicon and their oxides, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 15% to 30%, the coating thickness is 50-150nm, and the square resistance is 1000 to 10000 ohms.

[0036] The anti-reflection layer is based on any one of aluminum and silicon oxides or a mixture thereof, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 30% to 50%, and the sheet resistance is greater than 50,000 ohms.

[0037] When a silicon-aluminum-vanadium target is used, the molar ratio of aluminum to the total amount is 10-20%, the molar ratio of vanadium to the total amount is 30-50%, and the remainder is silicon. When an aluminum-vanadium target is used, the molar ratio of aluminum to the total amount is 50-70%, and the remainder is vanadium.

[0038] By adopting the above-mentioned selective absorption coating structure, the present invention obtains a thermally induced phase change solar heat collecting tube. When the selective absorption coating is below 80°C, the heat absorption curve of the selective absorption coating shows the standard two interference peak characteristics, showing typical high absorption characteristics in the 300-2000nm band, and showing low absorption and low emission characteristics in the 10000nmd mid- and far-infrared band, thereby achieving high-efficiency heat collection performance of the heat collecting tube below 80°C; when the selective absorption coating of the heat collecting tube is above 80°C, the resistance characteristics of the low-resistance layer, transition layer, high-resistance layer and anti-reflection layer are changed by utilizing the property of vanadium dioxide changing from a semiconductor state to a metallic state at 68°C. , thereby changing the interference absorption curve into a non-interference curve, especially the metallization of vanadium dioxide in the anti-reflection layer, which leads to a significant reduction in the anti-reflection efficiency of the anti-reflection layer and a significant increase in the reflectivity, thereby significantly destroying the selective absorption characteristics of the selective absorption coating, significantly reducing the absorption characteristics of the 300-2000nm band, and at the same time significantly increasing the emission ratio of the mid- and far-infrared beyond 10000nm, which in turn significantly affects the heat collection performance of the heat collecting tube in the high temperature section, significantly reduces the air-exposure temperature of the heat collecting tube under air-exposure conditions, and effectively improves the safety and reliability of the heat collecting tube, especially for the all-glass heat pipe vacuum solar heat collecting tube, which has a more significant significance in improving the safety and reliability.

[0039] like Figure 3 As shown, the present invention provides a coating method for a thermotropic phase change solar collector tube, comprising the following steps:

[0040] Loading the inner tube into the vacuum chamber: This means loading the inner tube that has completed pre-treatment and is ready to be coated into the bracket in the vacuum chamber of the collector tube coating machine, and closing the vacuum chamber door.

[0041] Pumping high vacuum to background: This means turning on the vacuum unit and pumping the vacuum degree in the vacuum chamber to the background vacuum degree, which is generally required to be better than 8×10 -3 Pa.

[0042] Turn on the heater: when the vacuum is evacuated to 10Pa, turn on the heater in the vacuum chamber to make the temperature in the vacuum chamber reach between 100 and 200°C, and maintain it under the background vacuum condition for 10 to 30 minutes, generally about 15 minutes.

[0043] Open the stop valve: This means opening the stop valve at the vacuum port of the coating chamber to the set position to reduce the speed of gas extraction in the vacuum chamber.

[0044] Start the bracket rotation: This means starting the bracket on which the heat collector tube is mounted to rotate, so that the inner tube of the heat collector tube can rotate and revolve during the coating process. The rotation speed is 0.5 to 2 cycles per second, and the revolution speed is 0.5 to 5 cycles per second.

[0045] Filling the vacuum chamber with argon to a set vacuum level and maintaining it at 1 SCCM refers to the process of filling the vacuum coating chamber with high-purity argon gas via a mass flowmeter to achieve the set vacuum level. This is typically accomplished by setting the mass flowmeter flow rate based on empirical values ​​or by detecting the vacuum level signal via a vacuum gauge. This flow rate is then precisely controlled using a PID controller. The vacuum level in the vacuum coating chamber is generally required to be between 0.3 and 0.5 Pa. For example, the existing 850 conventional three-target coating machine uses a 100 SCCM mass flowmeter, controlling the flow rate to approximately 40-60 SCCM.

[0046] Turning on the Metal A target rotation: This means turning on the metal target to be coated with the infrared reflective layer, usually at a speed of 2-5 revolutions per minute. The target material used for the Metal A target is generally pure aluminum, pure copper, alloy aluminum, pure silver, etc.

[0047] Adjusting the current of metal target A to the set current: This means turning on the sputtering power supply for target A, gradually and automatically adjusting the current to the set current, and starting the sputtering infrared reflective coating mode. The target current is generally set to 40A. Depending on the target material and model, the target voltage is generally around 400-500V.

[0048] Sputtering infrared reflective coating: refers to the sputtering of metal infrared reflective coating under set target current, vacuum degree and argon flow conditions. The sputtering time is generally 10-30 minutes and the coating thickness is 60-120nm.

[0049] Turn off the metal target A and the rotating motor: This means that after the set infrared reflective coating is completed, the target A sputtering power supply is turned off first, and then the metal target A rotating motor is turned off to complete the target A sputtering work.

[0050] Fill with reactive gas oxygen or nitrogen-oxygen mixed gas SCCM2: generally control the flow rate to 15-30 SCCM. Control the vacuum degree to 0.4-0.6 Pa. When using nitrogen-oxygen mixed gas, the volume ratio of nitrogen to oxygen is 1:10 to 1:4.

[0051] Turning on the metal B and V targets: This means turning on the metal B and V target rotation motors, driving the metal B and V targets to rotate at a speed of 2-5 revolutions per minute. The B target can be a Ti or stainless steel target, and the V target can be a silicon-aluminum-vanadium or aluminum-vanadium target. When using a silicon-aluminum-vanadium target, the weight ratio of aluminum is 10-20%, the weight ratio of vanadium is 30-50%, and the balance is silicon. When using an aluminum-vanadium target, the weight ratio of aluminum is 10-20%, and the balance is vanadium.

[0052] Turn on the power supply of metal B target and V target: turns on the power supply of metal B target and V target sputtering, and starts the sputtering function of the sputtering target.

[0053] Adjusting the B target current AB2: refers to gradually adjusting the B target sputtering current to the set current, which is generally between 30-50A, with about 40A being the best.

[0054] Adjusting the V target current AV2: refers to gradually adjusting the V target sputtering current to the set current, which is generally between 30-50A, and is generally best at around 45A.

[0055] Sputtering a low-resistance layer: This involves sputtering a low-resistance layer using a metal B target, a V target, and an oxygen or nitrogen-oxygen mixture. The sputtering time is typically 10-20 minutes, typically 15 minutes. The resulting sputtered coating thickness is 60-120nm, preferably around 80nm, and the sheet resistance is 90-500 ohms, typically 100-150 ohms.

[0056] Completion of low-resistance layer sputtering: This means completing the sputtering of the low-resistance layer according to the low-resistance layer coating process and requirements. Prepare for transition layer sputtering.

[0057] Adjust the oxygen or nitrogen-oxygen mixture flow rate (sccm3): This refers to increasing the proportion of sputtering reaction gas by adjusting the oxygen or nitrogen-oxygen mixture flow rate. Typically, the flow rate is 40-60 sccm. The vacuum level is generally maintained at 0.5-0.7 Pa, with 0.6 Pa being the ideal value.

[0058] Adjusting the B target current AB3: refers to gradually adjusting the B target sputtering current to the set current, which is generally between 10-30A, with about 15A being the best.

[0059] Adjust the V target current AV3: This means gradually adjusting the V target sputtering current to the set current, generally between 30-50A, with 42A being the best. Start sputtering the high resistance layer.

[0060] Sputtering the high-resistance layer to a set time: This refers to sputtering the high-resistance layer using a metal B target, a V target, and an oxygen or nitrogen-oxygen mixture. The sputtering time is generally 10-30 minutes, with a sputtered coating thickness of 60nm-150nm, preferably around 120nm. The sheet resistance is 5000-50000 ohms, generally 20000 ohms.

[0061] Completion of high-resistance layer sputtering: This means completing the sputtering of the high-resistance layer according to the high-resistance coating process and requirements. Prepare for the anti-reflection layer sputtering.

[0062] Adjust the oxygen or nitrogen-oxygen mixture flow rate (sccm4): This refers to increasing the proportion of sputtering reaction gas by adjusting the oxygen or nitrogen-oxygen mixture flow rate. Typically, this is 60-100 sccm. The vacuum level is generally maintained at 0.5-0.7 Pa, with 0.65 Pa being the ideal value.

[0063] Adjust the B target current AB4, which is to gradually adjust the B target sputtering current to 0A, turn off the B target power supply and rotation, and stop the B target sputtering.

[0064] Adjust the V target current AV4: This means gradually adjusting the V target sputtering current to the set current, generally between 30-50A, with 40A being the best. Start the anti-reflection layer sputtering coating.

[0065] Sputtering the anti-reflection layer to the set time: This refers to sputtering the high-resistance layer using a V target and an oxygen or nitrogen-oxygen mixture. The sputtering time is generally 30-90 minutes, and the sputtering coating thickness is 60nm-150nm, preferably around 80nm, with a sheet resistance greater than 10 megohms.

[0066] Completing the sputtering of the anti-reflection layer: This means completing the sputtering of the anti-reflection layer according to the anti-reflection layer coating process and requirements. Prepare for the sputtering of the anti-reflection layer.

[0067] Turn off the sputtering power supply: After the sputtering of the anti-reflection layer is completed, turn off the sputtering power supply. Stop the sputtering of the anti-reflection layer.

[0068] Turn off the sputtering gas: refers to turning off the argon, oxygen or nitrogen-oxygen mixed gas.

[0069] Shut down the support rotation: refers to shutting down the revolution and rotation of the support with the inner tube of the heat collecting tube.

[0070] Close the high vacuum valve of the vacuum unit: This means closing the high vacuum valve between the vacuum unit and the coating chamber to isolate the connection between the vacuum chamber and the vacuum unit.

[0071] Filling the vacuum chamber with dry gas: This means filling the vacuum chamber with dry air or nitrogen through the inflation valve until the pressure difference between the inside and outside of the vacuum chamber is balanced.

[0072] Removing the coated glass inner tube: When the pressure difference between the inside and outside of the vacuum chamber is balanced, the vacuum chamber door is opened, the coated glass inner tube is removed, and the glass inner tube to be coated is replaced. The coating chamber enters the next coating cycle.

[0073] Completing the coating of the glass inner tube: refers to taking out the glass inner tube that has completed the coating process and completing the inner tube coating process.

[0074] Inner and outer tube assembly and sealing: This involves assembling the pre-prepared cover glass tube assembly and the coated glass inner tube, and then sealing the ring. For all-glass heat pipe vacuum solar collectors, this involves sealing the inner tube, cover glass tube, and condenser section.

[0075] The heat collecting tube assembly is loaded into the exhaust table: it means that the heat collecting tube assembly after the sealing work is completed is loaded into the vacuum exhaust table and prepared for exhaust work.

[0076] Evacuate to the set vacuum degree: This means using the exhaust table vacuum unit to evacuate the vacuum interlayer of the collector tube until the set vacuum degree is reached, which is generally better than 10Pa.

[0077] Heating to the set oxidation temperature: When the vacuum degree is better than 10Pa, continue to evacuate and turn on the heater to make the collector temperature reach the set oxidation temperature. Generally, the vacuum degree reaches 8×10 -3 Pa, the heating temperature reaches 400-480℃, generally around 460℃, but not lower than 450℃.

[0078] Closing the vacuum valve means closing the high valve of the vacuum unit on the exhaust platform and stopping the vacuum pumping of the vacuum interlayer of the collector tube.

[0079] Filling oxygen to the set pressure and maintaining it means filling high-purity oxygen into the vacuum interlayer of the collector tube through the bypass until it reaches and exceeds 0.1MPa.

[0080] High-temperature oxidation heat treatment time: This refers to the use of high-temperature oxygen at a constant temperature to further oxidize the selective absorption coating, particularly the metal ions within the anti-reflection layer, in order to convert the entire anti-reflection layer into metal oxides and completely oxidize the vanadium in the selective absorption coating, particularly the anti-reflection layer, into vanadium dioxide. High-temperature oxidation time generally ranges from 30 to 120 minutes, but for cost-effectiveness, 45 minutes is generally recommended.

[0081] Evacuate to the set background vacuum degree: After the selective absorption coating is oxidized at high temperature, close the oxygen inlet valve, open the high valve of the vacuum unit, and evacuate the vacuum interlayer of the vacuum collector tube until the set vacuum degree is generally better than 8×10 -3 Pa. Entering the vacuum interlayer exhaust process of the collector tube.

[0082] Evacuate to set time: This means that under set temperature conditions, the vacuum exhaust of the collector tube reaches the set time and the vacuum valve is closed. The setting time is generally 30-120 minutes, with 45 minutes at 450°C being the ideal time.

[0083] Tail pipe sealing: refers to the work of sealing the collector pipe and tail pipe after the vacuum interlayer of the vacuum collector pipe is dug and exhausted.

[0084] Completing the heat treatment and exhaust process: refers to taking the sealed heat collecting tube out of the exhaust platform, completing the exhaust process of the heat collecting tube, and the high-temperature oxidation process of the selective absorption coating.

[0085] Completion of the selective absorption coating process: means that after the exhaust gas sealing of the collector tube is completed, the entire process of the selective absorption coating is realized, including the coating and high-temperature oxidation process of the selective absorption coating.

[0086] The present invention utilizes the aforementioned coating method, employing a vanadium-doped metal target and oxygen-assisted sputtering to dope vanadium oxide into the low-resistance layer, transition layer, high-resistance layer, and anti-reflection layer of the interference-type selective absorption coating. High-temperature oxidation transforms the vanadium metal ion and vanadium oxide into vanadium dioxide. In particular, the efficient doping of vanadium dioxide in the anti-reflection layer achieves the modification of the high-temperature non-interference properties of the selective absorption coating while maintaining its low-temperature interference properties.

[0087] The coating method provided by the present invention, comprising a coating step A and a heat treatment step B, effectively ensures that the selective absorption coating maintains its selective absorption characteristics at low temperatures and its low absorption and high emission characteristics at high temperatures. This overcomes the single selectivity problem of conventional selective absorption coatings across the entire wavelength band and operating range.

[0088] The coating method provided by the present invention solves the problem of preparing the selective absorption coating doped with vanadium dioxide and can realize industrialization.

Claims

1. A thermally induced phase change solar collector tube, comprising a vacuum interlayer formed between the heat-absorbing section of the inner tube and the cover glass tube. The outer wall of the heat-absorbing section has a selective absorption coating. The selective absorption coating comprises an infrared reflection layer, a low-resistance layer, a transition layer, a high-resistance layer, and an anti-reflection layer, which are sequentially formed on the outer wall of the heat-absorbing section. Its characteristics are: The low resistance layer is based on any one of metal aluminum, titanium, stainless steel, nickel and their oxides or a mixture of any number of them, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 5%-20%, the coating thickness is 50-150nm, and the square resistance is 90-500 ohms; The transition layer is based on any one of metal aluminum, titanium, stainless steel, nickel, silicon and their oxides or a mixture of any number of them, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 10% to 25%, the coating thickness is 50-150nm, and the sheet resistance is 500-2000 ohms; The high resistance layer is based on any one of metal aluminum, titanium, stainless steel, nickel, silicon and their oxides or a mixture of any number of them, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 15% to 30%, the coating thickness is 50-150nm, and the square resistance is 1000 to 10000 ohms; The anti-reflection layer is based on any one of aluminum and silicon oxides or a mixture thereof, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 30% to 40%, and the sheet resistance is greater than 50,000 ohms.

2. The thermally induced phase change solar collector tube according to claim 1, characterized in that: The interior of the inner tube forms a working medium cavity, which is evacuated and contains liquid working medium. The volume ratio of the liquid working medium to the volume of the working medium cavity is 1.5 to 2%.

3. The thermally induced phase change solar collector tube according to claim 2, characterized in that: The volume ratio of the liquid working medium to the volume of the working medium cavity is 3 / 1000 to 6 / 1000.

4. The thermally induced phase change solar collector tube according to claim 2, characterized in that: The liquid working fluid comprises a high boiling point working fluid and a low boiling point working fluid, the volume of the high boiling point working fluid accounts for 20% to 50% of the total volume, and the rest is the low boiling point working fluid; the high boiling point working fluid refers to a liquid working fluid with a boiling point greater than or equal to the boiling point of water, and the low boiling point working fluid refers to a working fluid with a boiling point lower than the boiling point of water.

5. A coating method for a thermotropic phase change solar collector tube, characterized in that: Target materials are sequentially sputtered on the outer wall of the heat absorption section of the inner tube to form an infrared reflection layer, a low resistance layer, a transition layer, a high resistance layer, and an anti-reflection layer; a certain proportion of vanadium dioxide is doped in the target materials of the low resistance layer, the transition layer, the high resistance layer, and the anti-reflection layer respectively; The anti-reflection layer is subjected to a high-temperature oxidation heat treatment to completely oxidize the metal vanadium in the anti-reflection layer into vanadium dioxide, and the low-resistance layer, the transition layer, the high-resistance layer and the anti-reflection layer are doped with vanadium dioxide in a molar ratio of 2% to 40% of the total amount of each layer; The low-resistance layer is based on any one or a mixture of any number of metal aluminum, titanium, stainless steel, nickel and their oxides, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 5%-20%, the coating thickness is 50-150nm, and the sheet resistance is 90-500 ohms; The transition layer is based on any one or a mixture of any number of metal aluminum, titanium, stainless steel, nickel, silicon and their oxides, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 10% to 25%, the coating thickness is 50-150nm, and the sheet resistance is 500-2000 ohms; The high resistance layer is based on any one or a mixture of any number of metal aluminum, titanium, stainless steel, nickel, silicon and their oxides, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 15% to 30%, the coating thickness is 50-150nm, and the square resistance is 1000 to 10000 ohms; The anti-reflection layer is based on any one of aluminum and silicon oxides or a mixture thereof, and is doped with vanadium dioxide, wherein the molar ratio of vanadium dioxide to the total amount is 30% to 50%, and the sheet resistance is greater than 50,000 ohms.

Images