High-efficiency heat storage and exchange composite phase change material and preparation method thereof

Abstract

The application relates to the technical field of phase change heat storage materials, and specifically discloses a high-efficiency heat storage and heat exchange composite phase change material and a preparation method thereof. The composite phase change material comprises a rare earth doped sodium-potassium eutectic material and a nano silicon dioxide coating layer for wrapping the rare earth doped sodium-potassium eutectic material, and the rare earth doped sodium-potassium eutectic material comprises the following raw materials in parts by weight: 45-55 parts of sodium nitrate, 30-40 parts of potassium nitrate, 1-3 parts of lanthanum oxide, 8-12 parts of a heat conducting material, 3-5 parts of polytetrafluoroethylene micro powder, 2-4 parts of a corrosion-resistant slow-release agent, and 5-10 parts of a polyimide solution with a solid content of 30%-60%. The composite phase change material has a phase change temperature of 220-250 DEG C, has a high-efficiency heat storage and heat exchange effect, and can reduce the corrosion of the inner wall of a steam boiler.

Description

Technical Field

[0001] This invention relates to the technical field of phase change thermal energy storage materials, and in particular to a high-efficiency composite phase change material for thermal energy storage and exchange and its preparation method. Background Technology

[0002] Phase change materials (PCMs) have significant application value in the fields of heat storage and heat exchange due to their ability to efficiently absorb, store, and release large amounts of latent heat during phase change processes, such as solar thermal utilization, industrial waste heat recovery, building energy-saving temperature control, and thermal management of electronic equipment.

[0003] In related technologies, a uniformly fused composite phase change material and its preparation method are disclosed, belonging to the technical field of phase change energy storage materials. The uniformly fused composite phase change material includes a phase change material and a thermally conductive material. The phase change material includes a primary phase change material and a secondary phase change material; wherein, the primary phase change material is magnesium nitrate hexahydrate, with a content of 60-70 mol%; the secondary phase change material is lithium nitrate, with a content of 30-40 mol%; and the thermally conductive material has a content of 0-5 wt% of the sum of the primary and secondary phase change materials, and its content is not zero.

[0004] However, the phase change temperature of magnesium nitrate hexahydrate is approximately 89-90℃, and that of lithium nitrate is approximately 255℃. Mixing them may form a composite phase change material with a phase change temperature of approximately 100-150℃. In contrast, the steam generation temperature of an electric steam boiler under high pressure is approximately 250℃. Therefore, when this composite phase change material is applied to an electric steam boiler, its phase change temperature is far lower than the steam generation temperature, making it difficult to achieve efficient heat storage and exchange. Summary of the Invention

[0005] To improve the heat storage and heat exchange performance of composite phase change materials when applied to electric steam boilers, this application provides a high-efficiency composite phase change material for heat storage and heat exchange and its preparation method.

[0006] In the first aspect, this application provides a high-efficiency thermal storage and heat exchange composite phase change material, which adopts the following technical solution: A high-efficiency thermal storage and heat exchange composite phase change material includes a rare earth-doped sodium-potassium eutectic material and a nano-silica coating layer for encapsulating the rare earth-doped sodium-potassium eutectic material. The rare earth-doped sodium-potassium eutectic material comprises the following raw materials in parts by weight: 45-55 parts sodium nitrate, 30-40 parts potassium nitrate, 1-3 parts lanthanum oxide, 8-12 parts thermally conductive material, 3-5 parts polytetrafluoroethylene micropowder, 2-4 parts corrosion-resistant slow-release agent, and 5-10 parts polyimide solution with a solid content of 30%-60%.

[0007] By employing the above technical solution and using the specified proportions of sodium nitrate, potassium nitrate, and lanthanum oxide, lanthanum oxide acts as a nucleating agent to reduce supercooling and induces ordered crystallization of nitrates through lattice matching, thereby increasing the thermal decomposition temperature and inhibiting phase separation during heat storage and heat exchange in the composite phase change material. The lubricity of polytetrafluoroethylene (PTFE) allows for micro-slippage during phase change expansion, preventing skeletal cracking during heat storage and heat exchange. A polyimide solution with a solid content of 30%-60% helps form a porous structure within the composite phase change material, while the thermally conductive material improves its thermal conductivity, thus synergistically enhancing its heat storage density and rapid heat transfer capability. A corrosion-resistant slow-release agent passivates the metal surface, and the nano-silica coating inhibits nitrate decomposition at high temperatures, thereby helping to reduce corrosion of the boiler inner wall by the composite phase change material during operation. Therefore, by using the above raw material ratio, a composite phase change material that is more suitable for the steam generation temperature of electric steam boilers can be prepared. The phase change temperature is 220-250℃. When the electric steam boiler is working, it has a high efficiency of heat storage and heat exchange effect, and can reduce the corrosion of the inner wall of the steam boiler.

[0008] In one specific implementation, the thermally conductive material is a carbon nanotube, graphene, or boron nitride nanotube.

[0009] By employing the above technical solution, carbon nanotubes can be loaded with lanthanum oxide, and through La... 3+ Coordination bonds with molten salt reduce interfacial thermal resistance, contributing to improved thermal conductivity and impact resistance of composite phase change materials. Graphene's high infrared emissivity enhances radiative heat transfer efficiency between molten salt and boiler walls, increasing the heat release rate. Boron nitride nanotubes not only improve the thermal conductivity of composite phase change materials but also exhibit greater stability in nitrate melts, failing to react with NaNO3 / KNO3 eutectic salts, thus extending the cycle life of composite phase change materials.

[0010] In one specific implementation, the corrosion-resistant slow-release agent comprises at least one of sodium molybdate or zirconium phosphate.

[0011] By employing the above technical solution, sodium molybdate is ionized in molten salt to generate MoO4. 2- It reacts with the boiler's metal wall to form a dense passivation film of ferric molybdate or chromium molybdate, blocking the contact between the molten salt and the metal. Furthermore, Mo... 6+ It can capture free radicals generated by the high-temperature decomposition of molten salt, which helps to increase the thermal decomposition temperature of nitrates, thereby inhibiting phase separation of composite phase change materials during heat storage and heat exchange. Zirconium phosphate does not undergo a phase change below 400℃, and the interlayer hydroxyl groups react with La in the molten salt. 3+ By using coordinate bonds to enhance interfacial bonding, it helps to suppress phase separation in composite phase change materials during heat storage and heat exchange.

[0012] In one specific implementation, the corrosion-resistant slow-release agent comprises sodium molybdate or zirconium phosphate in a mass ratio of 1:(0.8-1.2).

[0013] By adopting the above technical solution, MoO4 2- A passivation film is rapidly formed to resist high-pressure steam erosion, while ZrP nanosheets reduce stress corrosion caused by molten salt penetration. This application finds that using corrosion-resistant inhibitors within the above-mentioned proportion range helps to inhibit corrosion, improve thermal stability, and enhance thermal conductivity.

[0014] In one specific embodiment, the invention further includes a titanate-gadolinium complex comprising tetrabutyl titanate and gadolinium oxide in a mass ratio of (2.8-3.4):1.

[0015] By adopting the above technical solution, TBT hydrolysis generates Ti-O-Ti network-encapsulated Gd. 3+ This forms a "rigid-rare earth" synergistic structure, suppressing molten salt leakage, Gd 3+ The magnetocaloric effect can assist external magnetic fields in regulating the heat storage / release rate, thereby further improving the thermal conductivity and heat exchange efficiency of composite phase change materials.

[0016] In one specific implementation, silicon carbide nanowires are also included.

[0017] By adopting the above technical solution, silicon carbide nanowires can form a three-dimensional interpenetrating network in molten salt, which helps to improve the thermal conductivity and heat transfer efficiency of composite phase change materials.

[0018] Secondly, this application provides a method for preparing a high-efficiency thermal storage and heat exchange composite phase change material, which adopts the following technical solution: A method for preparing a high-efficiency thermal storage and heat exchange composite phase change material includes the following steps: S1. Mix sodium nitrate and potassium nitrate in proportion, heat to 300-320℃ to melt, and obtain molten material; S2. Add lanthanum oxide, thermally conductive material, polytetrafluoroethylene micro powder and corrosion-resistant slow-release agent to the molten material, and perform shear emulsification at 280-320℃ to obtain the molten composite. S3. Cool the molten composite to 200-220℃, add a polyimide solution with a solid content of 30%-60%, degas under vacuum, and solidify at 150-300℃ to obtain a rare earth-doped sodium-potassium eutectic material. S4. Spray silica sol onto the surface of rare earth-doped sodium-potassium eutectic material and heat-treat it at 150-180℃. The silica sol forms a nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0019] By adopting the above technical solution, step S1, through high-temperature melting, can form a sodium nitrate-potassium nitrate eutectic system. This not only locks the phase transition temperature within the range of 220-250℃, but also, the high temperature promotes the expansion of the nitrate lattice, which is beneficial for the subsequent insertion of lanthanum oxide into the grain boundaries. Through shearing, the raw materials and molten material are homogeneously composited. In step S3, when the temperature is lowered to 200-220℃, the molten composite remains in a molten state, allowing the polyimide solution to fully wet the pores. After solidification, it exhibits high porosity, which helps improve the heat storage density and thermal conductivity of the composite phase change material. Finally, after spraying silica sol and heat treatment, a nano-silica coating layer is formed, which helps prevent molten salt leakage and high-temperature oxidation.

[0020] In one specific feasible implementation, in step S3, the molten composite is cooled to 200-220°C, a titanate-gadolinium composite and a polyimide solution with a solid content of 30%-60% are added, vacuum degassing is performed, and curing is carried out at 150-300°C to obtain a rare earth-doped sodium-potassium eutectic material.

[0021] In one specific feasible implementation, in step S2, lanthanum oxide, thermally conductive material, polytetrafluoroethylene micro powder, corrosion-resistant slow-release agent and silicon carbide nanowires are added to the molten material, and shear emulsification is carried out at 280-320°C to obtain a molten composite.

[0022] In summary, this application has the following beneficial effects: 1. This application utilizes a specific ratio of sodium nitrate, potassium nitrate, lanthanum oxide, polytetrafluoroethylene micro powder, corrosion-resistant slow-release agent, and a polyimide solution with a solid content of 30%-60% to prepare rare earth-doped sodium-potassium eutectic materials. After coating the surface of the rare earth-doped sodium-potassium eutectic materials with a nano-silica coating layer, a composite phase change material more suitable for the steam generation temperature of electric steam boilers is obtained. The phase change temperature is 220-250℃, which has a high-efficiency heat storage and heat exchange effect when the electric steam boiler is working, and can also reduce the corrosion of the inner wall of the steam boiler.

[0023] 2. In this application, titanate-gadolinium composite and silicon carbide nanowires are preferred, which can further improve the thermal conductivity and heat exchange efficiency of the composite phase change material. Detailed Implementation

[0024] Unless otherwise specified, all raw materials used in this application were commercially available. The polytetrafluoroethylene (PTFE) micropowder is grade L-2. The polyimide solution was purchased from Shandong Jinye Guangcheng Chemical Co., Ltd., and conforms to national standards. The carbon nanotubes are TF-1000. The graphene was purchased from Zhongke Leiming (Beijing) Technology Co., Ltd., with a diameter of 0.5-3 μm. The boron nitride nanotubes are grade SP10. The silicon carbide nanowires are grade XBY-SiC.

[0025] The present application will be further described in detail below with reference to embodiments and comparative examples.

[0026] Example Example 1

[0027] This embodiment provides a high-efficiency thermal storage and heat exchange composite phase change material, including a rare earth-doped sodium-potassium eutectic material and a nano-silica coating layer, wherein the nano-silica coating layer is wrapped around the outer surface of the rare earth-doped sodium-potassium eutectic material.

[0028] The rare earth-doped sodium-potassium eutectic material includes the following raw materials: 50 kg sodium nitrate, 35 kg potassium nitrate, 2 kg lanthanum oxide, 10 kg graphene, 4 kg polytetrafluoroethylene micro powder, 3 kg sodium molybdate, and 7 kg polyimide solution with a solid content of 45%.

[0029] The preparation method of high-efficiency thermal storage and heat exchange composite phase change materials adopts the following steps: S1. Mix sodium nitrate and potassium nitrate according to the above proportions, heat to 310°C to melt, and obtain molten material after complete melting.

[0030] S2. Lanthanum oxide, graphene, polytetrafluoroethylene micro powder and sodium molybdate are added to the molten material. Shear emulsification is carried out at a constant temperature of 300℃ for 30 minutes at a speed of 12000 rpm to obtain the molten composite.

[0031] S3. Cool the molten composite to 210℃, add a polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain a rare earth-doped sodium-potassium eutectic material.

[0032] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 165℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0033] Example 2

[0034] The only difference between this embodiment and Embodiment 1 is that the rare earth-doped sodium-potassium eutectic material includes the following raw materials: 45 kg of sodium nitrate, 40 kg of potassium nitrate, 1 kg of lanthanum oxide, 8 kg of graphene, 3 kg of polytetrafluoroethylene micro powder, 2 kg of sodium molybdate, and 5 kg of polyimide solution with a solid content of 45%.

[0035] Example 3

[0036] The only difference between this embodiment and Embodiment 1 is that the rare earth-doped sodium-potassium eutectic material includes the following raw materials: 55 kg of sodium nitrate, 30 kg of potassium nitrate, 3 kg of lanthanum oxide, 12 kg of graphene, 5 kg of polytetrafluoroethylene micro powder, 4 kg of sodium molybdate, and 10 kg of polyimide solution with a solid content of 45%.

[0037] Example 4

[0038] The only difference between this embodiment and Embodiment 1 is that an equal amount of polyimide solution with a solid content of 30% is used instead of a polyimide solution with a solid content of 45%.

[0039] Example 5

[0040] The only difference between this embodiment and Embodiment 1 is that an equal amount of polyimide solution with a solid content of 60% is used instead of a polyimide solution with a solid content of 45%.

[0041] Example 6

[0042] The only difference between this embodiment and Embodiment 1 is that graphene is replaced with an equal amount of carbon nanotubes.

[0043] Example 7

[0044] The only difference between this embodiment and Embodiment 1 is that graphene is replaced with an equal amount of boron nitride nanotubes.

[0045] Example 8

[0046] The only difference between this embodiment and Embodiment 1 is that an equal amount of zirconium phosphate is used to replace sodium molybdate.

[0047] Example 9

[0048] The only difference between this embodiment and Embodiment 1 is that sodium molybdate is replaced with an equal amount of corrosion-resistant slow-release agent, which includes sodium molybdate or zirconium phosphate in a mass ratio of 1:0.6.

[0049] Example 10

[0050] The only difference between this embodiment and Embodiment 1 is that sodium molybdate is replaced with an equal amount of corrosion-resistant slow-release agent, which includes sodium molybdate or zirconium phosphate in a mass ratio of 1:0.8.

[0051] Example 11

[0052] The only difference between this embodiment and Embodiment 1 is that sodium molybdate is replaced with an equal amount of corrosion-resistant slow-release agent, which includes sodium molybdate or zirconium phosphate in a mass ratio of 1:1.

[0053] Example 12

[0054] The only difference between this embodiment and Embodiment 1 is that sodium molybdate is replaced with an equal amount of corrosion-resistant slow-release agent, which includes sodium molybdate or zirconium phosphate in a mass ratio of 1:1.2.

[0055] Example 13

[0056] The only difference between this embodiment and Embodiment 1 is that sodium molybdate is replaced with an equal amount of corrosion-resistant slow-release agent, which includes sodium molybdate or zirconium phosphate in a mass ratio of 1:1.4.

[0057] Example 14

[0058] The only difference between this embodiment and Embodiment 1 is the method for preparing the composite phase change material with high efficiency in heat storage and heat exchange: S1. Mix sodium nitrate and potassium nitrate according to the above ratio, heat to 300°C to melt, and obtain molten material after complete melting.

[0059] S2. Lanthanum oxide, graphene, polytetrafluoroethylene micro powder and sodium molybdate are added to the molten material, and shear emulsification is carried out at a constant temperature of 280℃. After shear emulsification at a speed of 12000 rpm for 30 minutes, the molten composite is obtained.

[0060] S3. Cool the molten composite to 200℃, add a polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain a rare earth-doped sodium-potassium eutectic material.

[0061] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 150℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0062] Example 15

[0063] The only difference between this embodiment and Embodiment 1 is the method for preparing the composite phase change material with high efficiency in heat storage and heat exchange: S1. Mix sodium nitrate and potassium nitrate according to the above ratio, heat to 320°C to melt, and obtain molten material after complete melting.

[0064] S2. Lanthanum oxide, graphene, polytetrafluoroethylene powder and sodium molybdate are added to the molten material, and shear emulsification is carried out at a constant temperature of 320℃. After shear emulsification at a speed of 12000 rpm for 30 minutes, the molten composite is obtained.

[0065] S3. Cool the molten composite to 220℃, add a polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain a rare earth-doped sodium-potassium eutectic material.

[0066] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 180℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0067] Example 16

[0068] The only difference between this embodiment and Embodiment 1 is that the rare earth-doped sodium-potassium eutectic material comprises the following raw materials: 50 kg sodium nitrate, 35 kg potassium nitrate, 2 kg lanthanum oxide, 10 kg graphene, 4 kg polytetrafluoroethylene micropowder, 3 kg sodium molybdate, 7 kg polyimide solution with a solid content of 45%, and 1.5 kg titanate-gadolinium composite. The titanate-gadolinium composite comprises tetrabutyl titanate and gadolinium oxide in a mass ratio of 2.8:1.

[0069] The preparation method of high-efficiency thermal storage and heat exchange composite phase change materials adopts the following steps: S1. Mix sodium nitrate and potassium nitrate according to the above ratio, heat to 310°C to melt, and obtain molten material after complete melting.

[0070] S2. Lanthanum oxide, graphene, polytetrafluoroethylene micro powder and sodium molybdate are added to the molten material. Shear emulsification is carried out at a constant temperature of 300℃ for 30 minutes at a speed of 12000 rpm to obtain the molten composite.

[0071] S3. Cool the molten composite to 210℃, add titanate-gadolinium composite and polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Then cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain rare earth doped sodium-potassium eutectic material.

[0072] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 165℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0073] Example 17

[0074] The only difference between this embodiment and Embodiment 1 is that the rare earth-doped sodium-potassium eutectic material comprises the following raw materials: 50 kg sodium nitrate, 35 kg potassium nitrate, 2 kg lanthanum oxide, 10 kg graphene, 4 kg polytetrafluoroethylene micropowder, 3 kg sodium molybdate, 7 kg polyimide solution with a solid content of 45%, and 1.5 kg titanate-gadolinium composite. The titanate-gadolinium composite comprises tetrabutyl titanate and gadolinium oxide in a mass ratio of 3:1.

[0075] The preparation method of high-efficiency thermal storage and heat exchange composite phase change materials adopts the following steps: S1. Mix sodium nitrate and potassium nitrate according to the above ratio, heat to 310°C to melt, and obtain molten material after complete melting.

[0076] S2. Lanthanum oxide, graphene, polytetrafluoroethylene micro powder and sodium molybdate are added to the molten material. Shear emulsification is carried out at a constant temperature of 300℃ for 30 minutes at a speed of 12000 rpm to obtain the molten composite.

[0077] S3. Cool the molten composite to 210℃, add titanate-gadolinium composite and polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Then cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain rare earth doped sodium-potassium eutectic material.

[0078] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 165℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0079] Example 18

[0080] The only difference between this embodiment and Embodiment 1 is that the rare earth-doped sodium-potassium eutectic material comprises the following raw materials: 50 kg sodium nitrate, 35 kg potassium nitrate, 2 kg lanthanum oxide, 10 kg graphene, 4 kg polytetrafluoroethylene micropowder, 3 kg sodium molybdate, 7 kg polyimide solution with a solid content of 45%, and 1.5 kg titanate-gadolinium composite. The titanate-gadolinium composite comprises tetrabutyl titanate and gadolinium oxide in a mass ratio of 3.2:1.

[0081] The preparation method of high-efficiency thermal storage and heat exchange composite phase change materials adopts the following steps: S1. Mix sodium nitrate and potassium nitrate according to the above ratio, heat to 310°C to melt, and obtain molten material after complete melting.

[0082] S2. Lanthanum oxide, graphene, polytetrafluoroethylene micro powder and sodium molybdate are added to the molten material. Shear emulsification is carried out at a constant temperature of 300℃ for 30 minutes at a speed of 12000 rpm to obtain the molten composite.

[0083] S3. Cool the molten composite to 210℃, add titanate-gadolinium composite and polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Then cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain rare earth doped sodium-potassium eutectic material.

[0084] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 165℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0085] Example 19

[0086] The only difference between this embodiment and Embodiment 1 is that the rare earth-doped sodium-potassium eutectic material comprises the following raw materials: 50 kg sodium nitrate, 35 kg potassium nitrate, 2 kg lanthanum oxide, 10 kg graphene, 4 kg polytetrafluoroethylene micropowder, 3 kg sodium molybdate, 7 kg polyimide solution with a solid content of 45%, and 1.5 kg titanate-gadolinium composite. The titanate-gadolinium composite comprises tetrabutyl titanate and gadolinium oxide in a mass ratio of 3.4:1.

[0087] The preparation method of high-efficiency thermal storage and heat exchange composite phase change materials adopts the following steps: S1. Mix sodium nitrate and potassium nitrate according to the above ratio, heat to 310°C to melt, and obtain molten material after complete melting.

[0088] S2. Lanthanum oxide, graphene, polytetrafluoroethylene micro powder and sodium molybdate are added to the molten material. Shear emulsification is carried out at a constant temperature of 300℃ for 30 minutes at a speed of 12000 rpm to obtain the molten composite.

[0089] S3. Cool the molten composite to 210℃, add titanate-gadolinium composite and polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Then cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain rare earth doped sodium-potassium eutectic material.

[0090] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 165℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0091] Example 20

[0092] The only difference between this embodiment and Embodiment 1 is that the rare earth-doped sodium-potassium eutectic material includes the following raw materials: 50 kg of sodium nitrate, 35 kg of potassium nitrate, 2 kg of lanthanum oxide, 10 kg of graphene, 4 kg of polytetrafluoroethylene micro powder, 3 kg of sodium molybdate, 7 kg of polyimide solution with a solid content of 45%, and 1 kg of silicon carbide nanowires.

[0093] The preparation method of high-efficiency thermal storage and heat exchange composite phase change materials adopts the following steps: S1. Mix sodium nitrate and potassium nitrate according to the above ratio, heat to 310°C to melt, and obtain molten material after complete melting.

[0094] S2. Lanthanum oxide, graphene, polytetrafluoroethylene micro powder, sodium molybdate and silicon carbide nanowires are added to the molten material. Shear emulsification is carried out at a constant temperature of 300℃ for 30 minutes at a speed of 12000 rpm to obtain the molten composite.

[0095] S3. Cool the molten composite to 210℃, add a polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain a rare earth-doped sodium-potassium eutectic material.

[0096] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 165℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0097] Example 21

[0098] The only difference between this embodiment and Embodiment 1 is that the rare earth-doped sodium-potassium eutectic material comprises the following raw materials: 50 kg sodium nitrate, 35 kg potassium nitrate, 2 kg lanthanum oxide, 10 kg graphene, 4 kg polytetrafluoroethylene micropowder, 3 kg sodium molybdate, 7 kg polyimide solution with a solid content of 45%, 1.5 kg titanate-gadolinium composite, and 1 kg silicon carbide nanowires. The titanate-gadolinium composite comprises tetrabutyl titanate and gadolinium oxide in a mass ratio of 3:1.

[0099] The preparation method of high-efficiency thermal storage and heat exchange composite phase change materials adopts the following steps: S1. Mix sodium nitrate and potassium nitrate according to the above ratio, heat to 310°C to melt, and obtain molten material after complete melting.

[0100] S2. Lanthanum oxide, graphene, polytetrafluoroethylene micro powder, sodium molybdate and silicon carbide nanowires are added to the molten material. Shear emulsification is carried out at a constant temperature of 300℃ for 30 minutes at a speed of 12000 rpm to obtain the molten composite.

[0101] S3. Cool the molten composite to 210℃, add titanate-gadolinium composite and polyimide solution with a solid content of 40%, then perform vacuum degassing, and then inject it into the mold. Then cure it sequentially at a temperature range of 150-200℃ for 2 hours, at a temperature range of 200-250℃ for 3 hours, and at a temperature range of 250-300℃ for 1 hour to obtain rare earth doped sodium-potassium eutectic material.

[0102] S4. Spray silica sol (Kening, HG / T2521-2022) onto the surface of rare earth-doped sodium-potassium eutectic material, and heat-treat it at 165℃. The silica sol forms a 5nm thick nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

[0103] Comparative Example Comparative Example 1 The only difference between this comparative example and Example 1 is that an equal amount of potassium nitrate is used instead of sodium nitrate.

[0104] Comparative Example 2 The only difference between this comparative example and Example 1 is that potassium nitrate is replaced with an equal amount of sodium nitrate.

[0105] Comparative Example 3 The only difference between this comparative example and Example 1 is that lanthanum oxide is replaced with an equal amount of graphene.

[0106] Comparative Example 4 The only difference between this comparative example and Example 1 is that an equal amount of graphene is used to replace the polytetrafluoroethylene micropowder.

[0107] Comparative Example 5 The only difference between this comparative example and Example 1 is that sodium molybdate is replaced with an equal amount of polyimide solution with a solid content of 40%.

[0108] Comparative Example 6 The only difference between this comparative example and Example 1 is that an equal amount of sodium molybdate is used to replace the polyimide solution with a solid content of 40%.

[0109] Performance testing The following performance tests were conducted on Examples 1-21 and Comparative Examples 1-6: According to ISO 11357-1, the phase change temperature range (T0 to T10) of the high-efficiency heat storage and heat exchange composite phase change materials prepared in each embodiment and comparative example was tested using a differential scanning calorimeter (DSC 214 Polyma). e ) and mass storage density (J / g).

[0110] The thermal conductivity (W / m·K) of the high-efficiency heat storage and heat exchange composite phase change materials prepared in each embodiment and comparative example was tested using a laser thermal conductivity meter (LFA 467 HyperFlash) in accordance with ASTM E1461.

[0111] A 50×25×2 mm 304 stainless steel specimen was cleaned with acetone, dried, and weighed. It was then completely embedded in molten phase change material and placed in a high-temperature furnace. After standing at 250℃ for 500 hours, the 304 stainless steel specimen was removed, cleaned with acetone, dried, and weighed again. The mass loss rate (%) was calculated. Mass loss rate = (weight of specimen before heating - weight of specimen after 500 hours of heating) ÷ weight of specimen before heating × 100%.

[0112] The test results are shown in Table 1.

[0113] Table 1

[0114] Combining Example 1 and Comparative Examples 1-6 with Table 1, it can be seen that compared to Example 1, the phase change temperature range of Comparative Examples 1-4 is significantly increased and exceeds 250℃. The mass storage density and thermal conductivity are significantly reduced. The mass loss rate of the 304 stainless steel specimens in Comparative Examples 5-6 is significantly increased. This indicates that by using the raw material ratios and preparation methods of Example 1, composite phase change materials with a phase change temperature of around 250℃ can be prepared. Furthermore, the mass storage density and thermal conductivity of the composite phase change material can be improved, thereby increasing its heat storage and heat exchange efficiency and reducing its corrosiveness to the boiler's metal inner wall, making it more suitable for electric steam boilers.

[0115] As can be seen from Examples 1-21 and Table 1, the phase change temperature range of Examples 1-21 is all within 220-250℃, the mass storage energy density is all greater than 170 J / g, and the thermal conductivity is all greater than 4.0 W / m·K. Furthermore, the mass loss rate of the 304 stainless steel specimens is less than 23%. This indicates that using the raw material ratios and preparation methods within the range of Examples 1-21 can improve the heat storage and heat transfer efficiency of the composite phase change material and reduce its corrosiveness to the boiler's metal inner wall.

[0116] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A high-efficiency composite phase change material for heat storage and exchange, characterized in that, The invention includes a rare-earth-doped sodium-potassium eutectic material and a nano-silica coating layer for encapsulating the rare-earth-doped sodium-potassium eutectic material. The rare-earth-doped sodium-potassium eutectic material comprises the following raw materials in parts by weight: 45-55 parts sodium nitrate, 30-40 parts potassium nitrate, 1-3 parts lanthanum oxide, 8-12 parts thermally conductive material, 3-5 parts polytetrafluoroethylene micropowder, 2-4 parts corrosion-resistant slow-release agent, and 5-10 parts polyimide solution with a solid content of 30%-60%. The corrosion-resistant slow-release agent includes at least one of sodium molybdate or zirconium phosphate.

2. The high-efficiency thermal storage and heat exchange composite phase change material according to claim 1, characterized in that, The thermally conductive material is carbon nanotubes, graphene, or boron nitride nanotubes.

3. The high-efficiency thermal storage and heat exchange composite phase change material according to claim 1, characterized in that, The corrosion-resistant slow-release agent comprises sodium molybdate and zirconium phosphate in a mass ratio of 1:(0.8-1.2).

4. The high-efficiency thermal storage and heat exchange composite phase change material according to claim 1, characterized in that, It also includes a titanate-gadolinium complex, which comprises tetrabutyl titanate and gadolinium oxide in a mass ratio of (2.8-3.4):

1.

5. The high-efficiency thermal storage and heat exchange composite phase change material according to claim 4, characterized in that, It also includes silicon carbide nanowires.

6. A method for preparing a high-efficiency thermal storage and heat exchange composite phase change material according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Mix sodium nitrate and potassium nitrate in proportion, heat to 300-320℃ to melt, and obtain molten material; S2. Add lanthanum oxide, thermally conductive material, polytetrafluoroethylene micro powder and corrosion-resistant slow-release agent to the molten material, and perform shear emulsification at 280-320℃ to obtain the molten composite. S3. Cool the molten composite to 200-220℃, add a polyimide solution with a solid content of 30%-60%, degas under vacuum, and solidify at 150-300℃ to obtain a rare earth-doped sodium-potassium eutectic material. S4. Spray silica sol onto the surface of rare earth-doped sodium-potassium eutectic material and heat-treat it at 150-180℃. The silica sol forms a nano-silica coating layer that encapsulates the rare earth-doped sodium-potassium eutectic material, thus obtaining a composite phase change material with high efficiency in heat storage and heat exchange.

7. The method for preparing the high-efficiency thermal storage and heat exchange composite phase change material according to claim 6, characterized in that, In step S3, the molten composite is cooled to 200-220℃, and a titanate-gadolinium composite and a polyimide solution with a solid content of 30%-60% are added. The mixture is then degassed under vacuum and cured at 150-300℃ to obtain a rare earth-doped sodium-potassium eutectic material.

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