A -15~-20℃ eutectic salt low-temperature phase change cold storage material and its preparation method

Abstract

This invention discloses a -15~-20℃ eutectic salt low-temperature phase change cold storage material and its preparation method, belonging to the technical field of phase change cold storage materials. The key technical point is that the -15~-20℃ eutectic salt low-temperature phase change cold storage material comprises the following components by weight percentage: sodium chloride 3.0-16.5%, ammonium chloride 5.5-15.0%, nucleating agent 0.75-1.5%, corrosion inhibitor 0.3-0.8%, and the balance being deionized water. By optimizing the addition ratio of sodium chloride and ammonium chloride and the selection of the nucleating agent, the phase change temperature of the phase change material is effectively stabilized within the -15~-20℃ range. Furthermore, after 50 cycles of use, the phase change temperature variation is ≤0.5℃, the latent heat decay rate is ≤3%, there is no obvious phase separation or crystallization precipitation, and the service life is long.

Description

Technical Field

[0001] This invention relates to the field of phase change cold storage materials, and in particular to a -15~-20℃ eutectic salt low-temperature phase change cold storage material and its preparation method. Background Technology

[0002] Phase change energy storage materials absorb or release large amounts of latent heat through a phase change process, achieving energy storage and release. Due to their high energy density and stable temperature during the phase change process, they have been widely used in frozen food transportation, cryogenic medical device preservation, and cold chain logistics. With the continuous development of these fields, the performance requirements for phase change energy storage materials are becoming increasingly stringent. Their performance directly affects the quality of related products and transportation efficiency; therefore, the development of high-performance phase change energy storage materials has become an important research direction in this field.

[0003] Currently, low-temperature phase change energy storage materials are mainly divided into organic and inorganic types. Organic phase change materials are often used in applications requiring high corrosion resistance. Inorganic phase change materials, primarily salt solutions or eutectic salts, have attracted significant attention in the field of low-temperature energy storage due to their excellent thermal conductivity, high latent heat of phase change, readily available raw materials, and low cost. Among these, chloride salt systems are frequently used to prepare energy storage materials for different temperature ranges due to their wide adjustable phase change temperature range; for example, low-temperature energy storage materials have already been prepared using chloride salts such as sodium chloride and ammonium chloride.

[0004] However, existing technologies have many drawbacks. Most low-temperature cold storage materials prepared using chloride salts suffer from phase transition temperatures deviating from the target temperature range. Some chloride eutectic systems have phase transition temperatures higher than the target range, failing to meet the requirements for deep cryogenic storage and transportation. While some systems can achieve lower phase transition temperatures, they require the addition of large amounts of toxic and harmful components, limiting their application in food, pharmaceutical, and other fields. Furthermore, traditional chloride salt cold storage materials are prone to supercooling during phase transitions, and after repeated use, they are susceptible to salt crystallization and solid-liquid stratification, leading to a significant decrease in cold storage performance and a shortened service life. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a -15~-20℃ eutectic salt low-temperature phase change cold storage material and its preparation method. By optimizing the addition ratio of sodium chloride and ammonium chloride and the selection of nucleating agent, the phase change temperature of the phase change material is effectively stabilized within the range of -15~-20℃. After 50 cycles of use, the phase change temperature variation is ≤0.5℃, the latent heat decay rate of phase change is ≤3%, there is no obvious phase separation or crystal precipitation, and the service life is long.

[0006] The first aspect of this invention is to provide a -15~-20℃ eutectic salt low-temperature phase change cold storage material, which adopts the following technical solution: A -15~-20℃ eutectic salt low-temperature phase change cold storage material, by weight percentage, comprises the following components: sodium chloride 3.0-16.5%, ammonium chloride 5.5-15.0%, nucleating agent 0.75-1.5%, corrosion inhibitor 0.3-0.8%, and the balance being deionized water.

[0007] In a preferred embodiment, the low-temperature phase change cold storage material comprises the following components by weight percentage: 5-13% sodium chloride, 8-12% ammonium chloride, 0.9-1.2% nucleating agent, 0.3-0.8% corrosion inhibitor, and the balance being deionized water.

[0008] By adopting the above technical solution, sodium chloride and ammonium chloride, within a specific ratio (sodium chloride 3.0-16.5%, ammonium chloride 5.5-15.0%), interact to form a eutectic system. Due to the wide adjustable range of the phase transition temperature of the chloride salt system, this ratio ensures that the phase transition temperature of the eutectic system remains stable within the target temperature range of -15 to -20℃, meeting the requirements for cryogenic storage and transportation. Simultaneously, the nucleating agent (0.75-1.5%) effectively reduces the supercooling during the material's phase transition process, minimizing the occurrence of supercooling and inhibiting salt crystallization; the corrosion inhibitor (0.3-0.8%) prevents the material from corroding the container, avoiding problems such as solid-liquid stratification caused by corrosion. Therefore, after 50 freeze-thaw cycles, the phase transition temperature variation is ≤0.5℃, the latent heat of phase transition decay rate is ≤3%, there is no significant phase separation or crystallization, and the material has a long service life.

[0009] In a preferred embodiment, the nucleating agent is sodium borate decahydrate.

[0010] By adopting the above technical solution, when the nucleating agent is sodium borate decahydrate, the supercooling of the phase change cold storage material can be effectively reduced, the phase change process can be promoted smoothly, and the material can be crystallized and released in time at the target temperature, avoiding the problem of delayed cold release caused by supercooling.

[0011] In a preferred embodiment, the corrosion inhibitor is a mixture of sodium benzoate and sodium molybdate.

[0012] By adopting the above technical solution, when the corrosion inhibitor is a mixture of sodium benzoate and sodium molybdate, a protective film can be formed on the inner wall of the container, which can significantly reduce the corrosive effect of chloride solution on metal containers, extend the service life of containers, and at the same time, it will not have an adverse effect on the phase transformation properties of materials.

[0013] In a preferred embodiment, the weight ratio of sodium benzoate to sodium molybdate is (1.5-2.5):1.

[0014] In a preferred embodiment, the phase change cold storage material has a phase change temperature of -15.1 to -20.5°C and a latent heat of phase change of ≥240 kJ / kg.

[0015] A second aspect of the present invention is to provide a method for preparing the -15~-20℃ eutectic salt low-temperature phase change cold storage material, comprising the following steps: S1. Add sodium chloride and ammonium chloride to deionized water and stir under a constant temperature water bath until the salts are completely dissolved to obtain a mixed salt solution; S2. Add the nucleating agent to the mixed salt solution and stir until completely dissolved; S3. Add corrosion inhibitor to step S2 and stir to disperse evenly. After cooling to room temperature, pre-cool at -25℃ for 1-2 hours to obtain eutectic salt low-temperature phase change cold storage material at -15~-20℃.

[0016] In a preferred embodiment, the temperature of the constant temperature water bath in steps S1-S3 is 30-40°C.

[0017] In a preferred embodiment, the stirring rate in steps S1-S3 is 250-500 r / min.

[0018] In summary, the present invention has the following beneficial effects: 1. This invention stabilizes the phase transition temperature of the eutectic system within the temperature range of -15 to -20°C by precisely controlling the addition ratio of sodium chloride and ammonium chloride, which can accurately match the temperature control requirements of scenarios such as frozen food transportation and low-temperature biological reagent storage.

[0019] 2. The phase change cold storage material obtained by the formulation of the present invention has a latent heat of phase change ≥240kJ / kg, high energy storage density, excellent cold storage release efficiency, and can achieve stable cooling for a long time.

[0020] 3. By adding the nucleating agent sodium borate decahydrate, this invention effectively reduces the supercooling of the material and avoids the phenomenon of delayed crystallization during the phase change process. At the same time, after 50 freeze-thaw cycles, the phase change temperature change range of the phase change cold storage material is ≤0.5℃, the phase change latent heat decay rate is ≤3%, there is no obvious phase separation and crystal precipitation phenomenon, and it has good stability and long service life.

[0021] 4. The corrosion inhibitor composed of sodium benzoate and sodium molybdate effectively reduces the corrosive effect of chloride salt solutions on metal containers. Tests show that the corrosion rate on 304 stainless steel is ≤0.02mm / a, thus expanding the application range of the material.

[0022] 5. The raw materials used in this invention are all common inorganic compounds, which are widely available, inexpensive, and free of toxic or harmful components. The preparation process is simple, energy-efficient, and easy to industrialize. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to embodiments. All details not specifically stated herein are based on conventional conditions or conditions recommended by the manufacturer. All reagents and instruments, unless otherwise stated below, are commercially available conventional reagent products. Example 1

[0024] A method for preparing a -15~-20℃ eutectic salt low-temperature phase change cold storage material includes the following steps: S1. Add 16.5g sodium chloride and 5.5g ammonium chloride to 76.95g deionized water, and stir at 300r / min for 20min in a constant temperature water bath at 35℃ until the salts are completely dissolved to obtain a mixed salt solution. S2. While maintaining the water temperature and stirring rate of step S1, add 0.75g of sodium borate decahydrate to the mixed salt solution and stir for 30 minutes until completely dissolved. S3. Add 0.3g of corrosion inhibitor (0.2g of sodium benzoate and 0.1g of sodium molybdate) to step S2, stir for 15min, stop stirring and heating, let it cool naturally to room temperature, and then pre-cool at -25℃ for 80min to obtain a eutectic salt low-temperature phase change cold storage material at -15~-20℃. Example 2

[0025] A method for preparing a -15~-20℃ eutectic salt low-temperature phase change cold storage material includes the following steps: S1. Add 6g of sodium chloride and 15g of ammonium chloride to 77.4g of deionized water, and stir at 280r / min for 25min in a constant temperature water bath at 30℃ until the salts are completely dissolved to obtain a mixed salt solution. S2. While maintaining the water temperature and stirring rate of step S1, add 1g of sodium borate decahydrate to the mixed salt solution and stir for 35min until completely dissolved. S3. Add 0.6g of corrosion inhibitor (0.4g of sodium benzoate and 0.2g of sodium molybdate) to step S2, stir for 20min, stop stirring and heating, let it cool naturally to room temperature, and then pre-cool it at -25℃ for 70min to obtain a eutectic salt low-temperature phase change cold storage material at -15~-20℃. Example 3

[0026] A method for preparing a -15~-20℃ eutectic salt low-temperature phase change cold storage material includes the following steps: S1. Add 3g sodium chloride and 15g ammonium chloride to 79.75g deionized water, and stir at 400r / min for 10min in a constant temperature water bath at 40℃ until the salts are completely dissolved to obtain a mixed salt solution. S2. While maintaining the water temperature and stirring rate of step S1, add 1.5g of sodium borate decahydrate to the mixed salt solution and stir for 30 minutes until completely dissolved. S3. Add 0.75g of corrosion inhibitor (0.5g of sodium benzoate and 0.25g of sodium molybdate) to step S2, stir for 10 minutes, then stop stirring and heating, let it cool naturally to room temperature, and then pre-cool it at -25℃ for 60 minutes to obtain a eutectic salt low-temperature phase change cold storage material at -15~-20℃. Example 4

[0027] A method for preparing a -15~-20℃ eutectic salt low-temperature phase change cold storage material includes the following steps: S1. Add 13g sodium chloride and 8g ammonium chloride to 77.2g deionized water, and stir at 300r / min for 20min in a constant temperature water bath at 35℃ until the salts are completely dissolved to obtain a mixed salt solution. S2. While maintaining the water temperature and stirring rate of step S1, add 1.2g of sodium borate decahydrate to the mixed salt solution and stir for 30min until completely dissolved. S3. Add 0.6g of corrosion inhibitor (0.43g sodium benzoate and 0.17g sodium molybdate) to step S2, stir for 15min, stop stirring and heating, let it cool naturally to room temperature, and then pre-cool at -25℃ for 80min to obtain a eutectic salt low-temperature phase change cold storage material at -15~-20℃. Example 5

[0028] A method for preparing a -15~-20℃ eutectic salt low-temperature phase change cold storage material includes the following steps: S1. Add 6g of sodium chloride and 12g of ammonium chloride to 80.5g of deionized water, and stir at 300r / min for 20min in a constant temperature water bath at 35℃ until the salts are completely dissolved to obtain a mixed salt solution. S2. While maintaining the water temperature and stirring rate of step S1, add 0.9g of sodium borate decahydrate to the mixed salt solution and stir for 30 minutes until completely dissolved. S3. Add 0.6g of corrosion inhibitor (0.36g of sodium benzoate and 0.24g of sodium molybdate) to step S2, stir for 15min, stop stirring and heating, let it cool naturally to room temperature, and then pre-cool at -25℃ for 80min to obtain a eutectic salt low-temperature phase change cold storage material at -15~-20℃.

[0029] A method for preparing a phase change cold storage material differs from Example 3 in that no nucleating agent is added, while the remaining components and preparation method are the same as in Example 3.

[0030] A method for preparing a phase change cold storage material differs from Example 3 in that only sodium benzoate is used as the corrosion inhibitor, while all other aspects are the same as in Example 3.

[0031] A method for preparing a phase change cold storage material differs from Example 3 in that only sodium molybdate is used as the corrosion inhibitor, while all other aspects are the same as in Example 3.

[0032] A method for preparing a phase change cold storage material differs from Example 3 in that an equal amount of benzotriazole is used instead of the composite corrosion inhibitor, while all other aspects are the same as in Example 3.

[0033] A method for preparing a phase change cold storage material differs from Example 3 in that the amount of sodium chloride used is 2g, the amount of ammonium chloride used is 17g, and the amount of water used is 78.75g, while the remaining components and preparation method are the same as in Example 3.

[0034] A method for preparing a phase change cold storage material differs from Example 3 in that an equal amount of aluminum chloride is used to replace sodium borate decahydrate, while all other aspects are the same as in Example 3.

[0035] A method for preparing a phase change cold storage material differs from Example 3 in that an equal amount of potassium chloride is used instead of sodium chloride, while all other aspects are the same as in Example 3.

[0036] The phase change cold storage materials obtained in the above embodiments and comparative examples were tested for phase change temperature, subcooling, latent heat of phase change, and phase change temperature, subcooling, and latent heat of phase change after freeze-thaw cycles. At the same time, the corrosion performance of the phase change cold storage materials on stainless steel was tested. The test results are shown in the table below.

[0037] Testing Procedure: The thermophysical properties (phase transition temperature and latent heat of phase transition) of the sample were determined using DSC. Under a nitrogen atmosphere, a heating-cooling cycle test was conducted at a scan rate of 10℃ / min. The sample, with a mass of 6-10 mg, was encapsulated in an aluminum crucible. The temperature range was -60 to 20℃, and the accuracy of temperature and heat measurement was ±2.0%. To remove the thermal history of the sample, the first heating cycle was ignored. The phase transition temperature and latent heat of phase transition were obtained from the heat flow curve. A temperature recorder probe was inserted into a test tube containing the sample. After setting the parameters, the tube was placed in a -40℃ cryogenic storage chamber for cooling. After complete solidification, the tube was removed and placed in an intelligent artificial climate chamber to be heated to 20℃. Temperature recording curves for cooling and heating were obtained.

[0038] The phase change cold storage material was placed in an environment of -40℃ for cooling. After it was completely solidified, it was taken out and placed in an intelligent artificial climate chamber and heated to 20℃. The phase separation test was carried out by 50 cycles of freeze-thaw. The thermal performance changes of the sample after thermal cycling were measured by DSC.

[0039] Supercooling refers to the temperature difference between the actual temperature at which a substance begins to crystallize and its equilibrium melting point (melting temperature) during the cooling process. Using a differential scanning calorimeter (DSC), the equilibrium melting onset temperature and the actual crystallization onset temperature of a sample are measured through programmed heating and cooling. The difference between these two temperatures is the supercooling.

[0040] Corrosion rate The formula for calculating (mm / a) is as follows:

[0041] in: Δm: Mass loss of the metal sample (g); S: Surface area of ​​the test piece (cm²), the surface area of ​​the test piece in this experiment is 28 cm²; t: soaking time (h), the soaking time in this experiment was 720h; ρ: Density of the metal (g / cm³), the density of 304 stainless steel is 7.93.

[0042] Table 1. Performance Test Results of Phase Change Cold Storage Materials Based on the test results in Table 1: The phase change temperature of the phase change cold storage materials obtained in Examples 1-5 of this application is stable in the range of -15 to -20°C, and the initial supercooling is less than 1.5°C. They have good phase change stability and controllability. After 50 cycles of use, the phase change temperature is also basically stable in the range of -15 to -20°C and the supercooling is <2°C, which can achieve long-term cooling.

[0043] Compared with Example 3, when the nucleating agent was missing, the supercooling of Comparative Example 1 was >2℃, the latent heat of phase change was also reduced, and phase separation occurred after 5 cycles. The phase change temperature was -13.1℃, the latent heat of phase change was 220kJ / kg, and the supercooling was 4.1℃. It can be seen that when the nucleating agent was missing, the phase change stability of the phase change material was reduced, and long-term cooling could not be achieved.

[0044] Compared with Example 3, Comparative Examples 2-4 showed that when only sodium benzoate, sodium molybdate, or benzotriazole was used as the corrosion inhibitor, the corrosion rate of 304 stainless steel was increased compared with Example 3.

[0045] Compared with Example 3, when the amount of sodium chloride was lower than that specified in this application and the amount of ammonium chloride exceeded that specified in this application, the phase change temperature of the phase change cold storage material obtained in Comparative Example 5 increased and the latent heat of phase change decreased. After 5 cycles, the phase change temperature was -9.3℃, the supercooling was 4.9℃, and the latent heat of phase change was 200kJ / kg, which was far from meeting the requirement of the range of -15~-20℃. Moreover, the phase separation phenomenon was serious and the solution was unstable.

[0046] Compared with Example 3, Comparative Example 6 showed a greater degree of supercooling and unstable solution when aluminum chloride nucleating agent was used. In particular, when an equal amount of titanium dioxide was used as nucleating agent, the titanium dioxide would settle after being placed in the laboratory for 72 hours, and the desired effect could not be achieved.

[0047] Compared with Example 3, Comparative Example 7, when potassium chloride was used instead of sodium chloride, could not reach the required relative temperature of -15 to -20°C.

[0048] The embodiments described herein are merely illustrative of preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A low-temperature phase change cold storage material of eutectic salt at -15~-20℃, characterized in that: The low-temperature phase change cold storage material comprises the following components by weight percentage: sodium chloride 3.0-16.5%, ammonium chloride 5.5-15.0%, nucleating agent 0.75-1.5%, corrosion inhibitor 0.3-0.8%, and the balance being deionized water.

2. The -15~-20℃ eutectic salt low-temperature phase change cold storage material according to claim 1, characterized in that: according to By weight percentage, the low-temperature phase change cold storage material comprises the following components: 6-13% sodium chloride, 8-12% ammonium chloride, 0.9-1.2% nucleating agent, 0.3-0.8% corrosion inhibitor, and the balance being deionized water.

3. The -15~-20℃ eutectic salt low-temperature phase change cold storage material according to claim 1, characterized in that: Place The nucleating agent is sodium borate decahydrate.

4. The -15~-20℃ eutectic salt low-temperature phase change cold storage material according to claim 1, characterized in that: The corrosion inhibitor is a mixture of sodium benzoate and sodium molybdate.

5. The -15~-20℃ eutectic salt low-temperature phase change cold storage material according to claim 1, characterized in that: The weight ratio of sodium benzoate to sodium molybdate is (1.5-2.5):

1.

6. The -15~-20℃ eutectic salt low-temperature phase change cold storage material according to claim 1, characterized in that: The phase change cold storage material has a phase change temperature of -15.1~-20.5℃ and a latent heat of phase change ≥240kJ / kg.

7. A method for preparing a -15~-20℃ eutectic salt low-temperature phase change cold storage material according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Add sodium chloride and ammonium chloride to deionized water and stir under a constant temperature water bath until the salts are completely dissolved to obtain a mixed salt solution; S2. Add the nucleating agent to the mixed salt solution and stir until completely dissolved; S3. Add corrosion inhibitor to step S2 and stir to disperse evenly. After cooling to room temperature, pre-cool at -25℃ for 1-2 hours to obtain eutectic salt low-temperature phase change cold storage material at -15~-20℃.

8. The method for preparing a -15~-20℃ eutectic salt low-temperature phase change cold storage material according to claim 7, characterized in that: The constant temperature water bath temperature in steps S1-S3 is 30-40℃.

9. The method for preparing a -15~-20℃ eutectic salt low-temperature phase change cold storage material according to claim 7, characterized in that: The stirring rate in steps S1-S3 is 250-500 r / min.

Images