High latent heat composite low temperature phase change cold accumulator and preparation method thereof

Abstract

The application relates to a high latent heat composite low-temperature phase change cold accumulator and a preparation method thereof. The phase change cold accumulator is composed of sodium chloride, polyacrylamide, hectorite, water and other solvents; during preparation, the sodium chloride is first mixed with water and stirred uniformly, then the hectorite is slowly added and fully stirred to be uniformly dispersed, and finally the polyacrylamide is quickly and uniformly added and stirred uniformly. The latent heat of the phase change cold accumulator is up to 230 J / g, the phase change temperature is 0 DEG C to -25 DEG C, and the performance can be flexibly and simply adjusted by regulating the content of the sodium chloride, so as to adapt to different application scenes and purposes. The application simultaneously solves the problems of easy leakage, phase separation and short service life of the current inorganic phase change cold accumulator, and the prepared phase change cold accumulator product has a good application prospect in cold chain transportation, peak shifting and valley filling of power supply and the like.

Description

Technical Field

[0001] This invention relates to the field of phase change materials technology, specifically to a high latent heat composite low-temperature phase change coolant, its preparation method, and its application. Background Technology

[0002] With rapid economic development, my country's demand for cold chain transportation is constantly growing, and the requirements for the freshness of products during transportation are becoming increasingly stringent.

[0003] Peak shaving and valley filling refer to storing energy during periods of low electricity demand and releasing it during peak demand periods. This effectively addresses the problems of electricity waste and supply-demand imbalance. Cold storage technology, as an effective means of peak shaving and valley filling, has attracted widespread attention from researchers, and its application is increasingly widespread. Therefore, developing efficient cold storage technology is of great significance for reducing economic losses in cold chain transportation and solving the problem of power supply imbalance.

[0004] Cold storage technology refers to the technology of using electric cooling during off-peak electricity hours at night. It utilizes the sensible or latent heat properties of energy storage materials to convert electricity into cooling energy, which is then stored in a cold storage medium. This cooling energy is released during peak electricity demand periods in the daytime. It not only serves as a peak-shifting mechanism for electricity consumption but also plays an important role in fields such as refrigeration, chemicals, pharmaceuticals, and food processing.

[0005] Currently known cold storage technologies include water cold storage, ice cold storage, and phase change cold storage. Water cold storage essentially uses the sensible heat of water to store cold energy, releasing it when needed. Due to water's low specific heat capacity, large quantities of water are typically required to store cold energy, leading to limitations such as poor storage effect, low storage density, low efficiency, large footprint, and significant cold energy loss. Ice cold storage primarily stores cold energy through the latent heat of phase change of ice, releasing it as the ice melts. At normal pressure, the latent heat of phase change of ice at 0°C is as high as 333.7 J / g, far exceeding the sensible heat of water. Therefore, a unit volume of ice stores significantly more cold energy than a unit volume of water. While ice cold storage has a high latent heat, it is prone to leakage, and the phase change temperature of ice (0°C) cannot meet the requirements of cold chain transportation and cold storage with high temperature requirements. Phase change energy storage (PCE) refers to the use of phase change materials as a cold storage medium, storing cold energy through their latent heat of phase change, and then releasing the cold energy when needed. For the same volume, PCE has an energy storage density 5-14 times that of sensible heat energy storage. It boasts advantages such as small temperature variations, high storage efficiency, minimal volume changes, lightweight, diverse types, and a wide storage temperature range, making it a crucial technology in the cold storage field. Compared to water and ice cold storage technologies, PCE also offers advantages such as lower storage temperatures, higher cold energy storage density, and greater versatility. Therefore, developing PCE-based cold storage technology is of great significance in addressing issues such as cold chain transportation losses and power supply imbalances.

[0006] Phase change refrigerants primarily utilize phase change materials for heat storage. Phase change materials are substances that, under constant temperature, exhibit heat absorption and release during phase change. During this phase change, the material releases or absorbs a significant amount of heat; this heat is called the latent heat of phase change, and the temperature at which the phase change occurs is called the phase change temperature. Heat storage primarily involves the transfer of energy from one phase state of the material to another. For example, when sodium chloride is kept at a constant temperature, it absorbs heat and changes from a solid to a liquid state. In this process, the sodium chloride's temperature does not change; only the phase changes. Therefore, sodium chloride can be considered a phase change material, and the heat absorbed during the change from solid to liquid is called the latent heat of phase change.

[0007] Phase change refrigerants can be classified into three categories according to their chemical composition: inorganic phase change refrigerants, organic phase change refrigerants, and composite phase change refrigerants. Among them, organic phase change refrigerants have advantages such as high latent heat, small supercooling, phase separation, and rich variety, as seen in publications such as: 1 (Zhou Sunxi, Zhang Xuelai, Liu Sheng. Preparation and performance of tetradecane-n-octanoic acid organic composite phase change materials [J]. Energy Storage Science and Technology, 2018, 7(04): 692-697) and 2 (Fang Guiyin, Xing Lin, Yang Fan, et al. Preparation and thermal performance study of phase change refrigerants [J]. Low Temperature and Superconductivity, 2006(01): 68-70). Although organic phase change refrigerants have many advantages, they also have some problems, such as inherent low thermal conductivity, poor flame retardancy, and poor thermal stability, which greatly limit their application.

[0008] In contrast, inorganic phase change refrigerants have a wider range of application prospects and represent the main development direction of cold storage technology. Inorganic phase change refrigerants possess a series of advantages, including odorlessness, high latent heat, high thermal conductivity, small volume change, environmental friendliness, and low cost. However, they also have some problems (i.e., supercooling and phase separation), and are prone to leakage and pollution during solid-liquid phase transitions. Leakage is a major challenge for liquid-solid inorganic phase change refrigerants. Phase separation refers to the phenomenon where, after multiple freeze-thaw cycles, some solute (salts) precipitates and settles at the bottom, resulting in solute-solvent stratification. Phase separation not only disrupts the homogeneity of the phase change refrigerant but also severely affects the phase change temperature and latent heat of the phase change material, leading to reduced stability and a shorter lifespan. Furthermore, as the number of freeze-thaw cycles increases, the precipitation of inorganic salts in the solution becomes more severe, and the phase separation becomes more pronounced, resulting in increasingly poor cold storage performance of the phase change material. Therefore, solving the problems of supercooling and phase separation has become the main task in the research and development of new inorganic phase change refrigerants.

[0009] Sodium chloride is the most common inorganic salt, with advantages such as abundant reserves and low price, giving it a significant cost advantage in the production of phase change cold storage agents. However, sodium chloride solutions are prone to leakage during solid-liquid phase transitions, and there are also problems of overcooling and phase separation. In published literature 3 (Ban Chaofang, Lu Lixin, Pan Liao. Preparation and performance evaluation of cryogenic composite phase change cold storage materials [J]. New Chemical Materials, 2019, 47(05): 218-221, 226.), Ban Chaofang et al. developed a new type of composite phase change cold storage agent by using NaCl as the main energy storage agent and adding sodium carboxymethyl cellulose (CMC) as a thickener. However, CMC has poor salt resistance and thickening effect, resulting in high fluidity of the cold storage agent, which poses a risk of leakage and pollution, and may have certain limitations in practical applications. In published literature 4 (Wu Tong. Preparation and performance study of magnesium-based inorganic salt low-temperature phase change materials [D]. South China University of Technology, 2020. DOI:10.27151 / d.cnki.ghnlu.2020.003553.), Wu Tong et al. developed a novel composite phase change cold storage agent using 23wt% MgCl2 solution as the main energy storage material, 1wt% CaCl2 and 0.25wt% Ca(OH)2 as nucleating agents, and 0.5wt% xanthan gum as a thickener. The literature indicates that this composite phase change cold storage agent has a low latent heat of only 139.8 J / g, suggesting low efficiency in storing cold energy. In published paper 5 (HAN B, CHOl JH, DANTZlG JA, et al. A quanttative analysis on latent heat of anaqueous binary mixture [J]. Cryobiology 2006, 52(1): 146-151), HAN et al. prepared five different concentrations of salt-water binary inorganic phase change materials. Through DSC technology, they found that the phase change temperature of one of the inorganic phase change materials was -22℃, but its latent heat of phase change was low, only 115 J / g.

[0010] To address the issues of leakage and phase separation, we employed a synergistic thickening process using polyacrylamide and lithium saponite. Polyacrylamide is a commonly used organic thickener, while lithium saponite is a highly efficient inorganic thickener. Furthermore, the two can cross-link in aqueous solution through hydrogen bonding and electrostatic interactions, further thickening the solution and effectively reducing its fluidity. In addition, lithium saponite can act as a nucleating agent, effectively reducing the supercooling of the sodium chloride phase change refrigerant. The resulting composite phase change refrigerant exhibits advantages such as high viscosity, strong cycle stability, large latent heat of phase change, and no phase separation or leakage. Summary of the Invention

[0011] The main objective of this invention is to address the common problems of leakage, phase separation, and short service life in existing inorganic phase change cold storage agents. Addressing the weak thickening effects of common crosslinking agents and thickeners, this invention proposes a synergistic thickening process using polyacrylamide and lithium saponite through crosslinking. Furthermore, lithium saponite also has the function of inhibiting supercooling. By adjusting the proportion of sodium chloride solution, different phase change temperature points can be flexibly controlled, thus adapting to the food preservation needs under different transportation environments. This not only saves transportation and preservation costs but also reduces environmental pollution. Experimental results also show that the composite low-temperature phase change cold storage agent provided by this invention has excellent cycling performance; even after multiple cycles, its thermal properties do not change significantly.

[0012] This invention provides a high latent heat composite low-temperature phase change refrigerant, which is composed of sodium chloride, polyacrylamide, lithium saponite, and a solvent, with sodium chloride, polyacrylamide, and lithium saponite all uniformly dispersed in the solvent. Sodium chloride solution serves as the primary energy storage substance; polyacrylamide and lithium saponite act as thickeners to increase the solution viscosity and prevent leakage and phase separation; lithium saponite has dual functions as a thickener and nucleating agent, further increasing the solution viscosity while effectively inhibiting supercooling.

[0013] In one embodiment, the mass fractions of the components in the composite low-temperature phase change refrigerant are as follows: sodium chloride ≥ polyacrylamide ≥ lithium saponite. When the mass fraction of polyacrylamide is less than 5%, the solution viscosity is too low to form a viscous gel, making leakage and phase separation likely. Therefore, the mass fraction of polyacrylamide should be greater than 5%. Sodium chloride solution is the main energy storage material. Changes in sodium chloride concentration affect the phase change temperature and latent heat of phase change; higher sodium chloride concentrations result in lower phase change temperatures and reduced latent heat of phase change. Lithium saponite primarily serves a dual purpose: reducing supercooling and thickening.

[0014] In another embodiment, the composite low-temperature phase change cold storage agent is composed of the following components by mass fraction: sodium chloride not exceeding 26.5%, polyacrylamide not exceeding 15%, lithium saponite not exceeding 10%, and the remainder being solvent.

[0015] In a preferred embodiment, the composite low-temperature phase change refrigerant comprises, by weight fraction: 5%-10% sodium chloride, 5%-7% polyacrylamide, 3%-4% lithium saponite, with the remainder being solvent.

[0016] In one embodiment, the solvent is specifically deionized water.

[0017] In one embodiment, the latent heat of the composite low-temperature phase change refrigerant is 0-230 J / g, preferably 200-230 J / g, and the phase change temperature is 0°C to -25°C, preferably -6°C to -25°C.

[0018] This invention also provides a method for preparing a high latent heat composite low-temperature phase change refrigerant, specifically including the following steps: first, prepare materials according to a ratio; then, mix sodium chloride with a solvent and stir evenly; next, slowly add lithium saponite and stir to disperse it evenly; finally, quickly and evenly add polyacrylamide and stir evenly. The reason this invention requires preparing a sodium chloride solution of a certain concentration first is that the sodium chloride solution can reduce the viscosity of lithium saponite or polyacrylamide. For example, a simple 3wt% lithium saponite or polyacrylamide solution already has a very high viscosity, almost no fluidity. If lithium saponite or polyacrylamide is added first, the solution has already formed a gel and cannot be stirred. Adding sodium chloride then will only cause it to float on top of the gel and cannot dissolve, thus failing to prepare a uniformly dispersed solution. Therefore, lithium saponite can only be added after sodium chloride, because lithium saponite has little effect on the viscosity of the sodium chloride solution, and the mixed solution can still be stirred normally after adding lithium saponite. If polyacrylamide is added first after sodium chloride, the solution viscosity may be too high to stir, making it difficult to dissolve lithium saponite later. The reason why this invention requires the rapid and uniform addition of polyacrylamide is mainly to prevent its agglomeration and the resulting uneven dispersion.

[0019] In one approach, the stirring speed when adding sodium chloride is less than or equal to the stirring speed when adding lithium soapstone, which in turn is less than the stirring speed before adding polyacrylamide, which is less than the stirring speed after adding polyacrylamide. Lithium soapstone has little effect on the viscosity of the sodium chloride solution, so the stirring speed does not need to be changed after adding it. Increasing the stirring speed after adding polyacrylamide is to accelerate its dissolution and uniform dispersion. Increasing the speed again after adding polyacrylamide is because the gradual dissolution of polyacrylamide increases the solution viscosity and stirring resistance, requiring an increased speed to ensure rapid and uniform mixing.

[0020] In another scheme, the stirring speed is 300-800 r / min when adding sodium chloride, 600-800 r / min when adding lithium saponite, 800-1000 r / min before adding polyacrylamide, and 1000-2300 r / min after adding polyacrylamide.

[0021] In one of the schemes, the stirring time when adding polyacrylamide is less than the stirring time after adding sodium chloride, which is less than the stirring time after adding lithium soapstone.

[0022] In another scheme, the stirring time is 5-20 seconds when polyacrylamide is added, 5-20 minutes after adding sodium chloride, 10-30 minutes after adding lithium soapstone, and 150-300 minutes after adding polyacrylamide.

[0023] This invention also provides an application of a high latent heat composite low-temperature phase change cold storage agent in cold chain transportation, peak power shifting, and other applications.

[0024] This invention aims to provide a novel high latent heat composite low-temperature phase change refrigerant, successfully solving the common problems and defects of current inorganic phase change refrigerants, such as easy leakage, phase separation, and short service life. This invention utilizes polyacrylamide and lithium saponite as synergistic thickeners to simultaneously suppress supercooling. By optimizing the proportion of sodium chloride, the phase change temperature of the refrigerant can be easily and flexibly controlled to adapt to different application requirements. When the sodium chloride concentration is 5%, the melting temperature of the refrigerant is -6.768℃; when the sodium chloride concentration is 15%, the melting temperature decreases to -21.77℃. Experimental test results show that this composite low-temperature phase change refrigerant has excellent cycling performance; even after multiple cycles (more than 20 freeze-thaw cycles), the thermal properties do not change significantly. This composite low-temperature phase change refrigerant has high viscosity and therefore low flowability; even when placed upside down in an open container, it will not leak, effectively preventing leakage accidents and the resulting environmental pollution.

[0025] Compared with the aforementioned similar products, the advantages of this invention are reflected in the following aspects: (1) The composite low-temperature phase change cold storage agent provided by the present invention has a high latent heat, with a phase change latent heat as high as 224.71 J / g, while the phase change latent heat of conventional composite inorganic phase change cold storage agents is usually at the level of 160 J / g. From this indicator, the present invention has obvious advantages. (2) The composite low-temperature phase change cold storage agent provided by the present invention has excellent cycle performance. After more than 20 freeze-thaw cycles, its thermal properties remain almost unchanged, so it has a good service life and a low overall cost. (3) The composite low-temperature phase change cold storage agent provided by the present invention has good temperature controllability. By simply changing the amount of sodium chloride added during the preparation process, composite low-temperature phase change cold storage agents with different phase change temperatures can be easily synthesized. Moreover, the phase change temperature range is wide and can be flexibly adjusted between 0℃ and -25℃, which is conducive to expanding its application fields and application scenarios. (4) The composite low-temperature phase change cold storage agent provided by the present invention has very high viscosity and poor fluidity, which effectively solves the long-standing problems of easy leakage and phase separation of inorganic cold storage agents, so there is no need to worry about pollution caused by leakage. (5) The composite low-temperature phase change cold storage agent provided by the present invention uses sodium chloride solution as the main energy storage substance. Sodium chloride has many advantages such as low price, wide availability, stable properties and high cost performance. Therefore, the cold storage agent can be produced in batches at low cost. Attached Figure Description

[0026] Figure 1 Photographs showing the flow properties of the composite low-temperature phase change refrigerant prepared in Examples 1-3; Figure 2 The DSC curve of the composite low-temperature phase change refrigerant prepared in Example 1 is shown below. Figure 3 The DSC curve of the composite low-temperature phase change refrigerant prepared in Example 2 is shown below. Figure 4 The DSC curve of the composite low-temperature phase change refrigerant prepared in Example 3 is shown below. Figure 5 The image shows the DSC curve of the heat absorption / exothermic cycle test of the composite low-temperature phase change refrigerant prepared in Example 2. Figure 6 Cooling curves of composite low-temperature phase change refrigerants prepared at different lithium saponite concentrations; Figure 7 The graph shows a comparison of the cooling effects of the composite low-temperature phase change refrigerant prepared in Examples 1-3 with those of air and water. Detailed Implementation

[0027] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the following description is provided in conjunction with specific embodiments and accompanying drawings.

[0028] Example 1 A high latent heat composite low-temperature phase change cold storage agent, the mass percentage composition of which is: 5% sodium chloride, 5% polyacrylamide, 4% lithium saponite, and the remainder is deionized water.

[0029] The preparation process of this high latent heat composite low-temperature phase change refrigerant is as follows: Weigh 5g of sodium chloride and pour it into a beaker, then add 86mL of deionized water. Stir magnetically at 500r / min for 10min to completely dissolve the sodium chloride in the water and mix it evenly to obtain a sodium chloride solution. Weigh 4g of lithium saponite and slowly add it to the above sodium chloride solution. Stir magnetically at 600r / min for more than 15min to evenly disperse the lithium saponite in the sodium chloride solution. Increase the speed of the magnetic stirrer appropriately to 800-1000r / min, and then add 5g of polyacrylamide quickly and evenly to the mixed solution. Increase the speed of the magnetic stirrer again to 1000-2300r / min to ensure that the solution is stirred evenly for 180min until it is uniformly stirred, thus obtaining the sodium chloride / polyacrylamide / lithium saponite composite phase change refrigerant.

[0030] Example 2 A high latent heat composite low-temperature phase change cold storage agent, the mass percentage composition of which is: sodium chloride 10%, polyacrylamide 5%, lithium saponite 4%, and the remainder is deionized water.

[0031] The preparation process of this high latent heat composite low-temperature phase change refrigerant is as follows: Weigh 10g of sodium chloride and pour it into a beaker, then add 81mL of deionized water. Stir magnetically at 600r / min for 10min to completely dissolve the sodium chloride in the water and mix it evenly to obtain a sodium chloride solution. Weigh 4g of lithium saponite and slowly add it to the above sodium chloride solution. Stir magnetically at 700r / min for more than 20min to evenly disperse the lithium saponite in the sodium chloride solution. Appropriately increase the speed of the magnetic stirrer to more than 800-1000r / min, and then quickly and evenly add 5g of polyacrylamide to the mixed solution. Increase the speed of the magnetic stirrer again to 1000-2300r / min and ensure that the solution is stirred evenly for 220min until it is uniformly stirred, thereby obtaining the sodium chloride / polyacrylamide / lithium saponite composite phase change refrigerant.

[0032] Example 3 A high latent heat composite low-temperature phase change cold storage agent, the mass percentage composition of which is: sodium chloride 15%, polyacrylamide 5%, lithium saponite 4%, and the remainder is deionized water.

[0033] The preparation process of this high latent heat composite low-temperature phase change refrigerant is as follows: Weigh 15g of sodium chloride and pour it into a beaker, then add 76mL of deionized water. Stir magnetically at 700r / min for 15min to completely dissolve the sodium chloride in the water and mix it evenly to obtain a sodium chloride solution. Weigh 4g of lithium saponite and slowly add it to the above sodium chloride solution. Stir magnetically at 750r / min for more than 20min to evenly disperse the lithium saponite in the sodium chloride solution. Appropriately increase the speed of the magnetic stirrer to more than 800-1000r / min, and then quickly and evenly add 5g of polyacrylamide to the mixed solution. Increase the speed of the magnetic stirrer again to 1000-2300r / min to ensure that the solution is stirred evenly for 240min until it is uniformly stirred, thus obtaining the sodium chloride / polyacrylamide / lithium saponite composite phase change refrigerant.

[0034] Example 4 A high latent heat composite low-temperature phase change cold storage agent, the mass percentage composition of which is: sodium chloride 10%, polyacrylamide 7%, lithium saponite 4%, and the remainder is deionized water.

[0035] The preparation process of this high latent heat composite low-temperature phase change refrigerant is as follows: Weigh 10g of sodium chloride and pour it into a beaker, then add 79mL of deionized water. Stir magnetically at 600r / min for 10min to completely dissolve the sodium chloride in the water and mix it evenly to obtain a sodium chloride solution. Weigh 4g of lithium saponite and slowly add it to the above sodium chloride solution. Stir magnetically at 700r / min for more than 20min to evenly disperse the lithium saponite in the sodium chloride solution. Appropriately increase the speed of the magnetic stirrer to more than 800-1000r / min, and then quickly and evenly add 7g of polyacrylamide to the mixed solution. Increase the speed of the magnetic stirrer again to 1000-2300r / min to ensure that the solution is stirred evenly for 250min until it is uniformly stirred, thereby obtaining the sodium chloride / polyacrylamide / lithium saponite composite phase change refrigerant.

[0036] Example 5 A high latent heat composite low-temperature phase change cold storage agent, the mass percentage composition of which is: sodium chloride 15%, polyacrylamide 7%, lithium saponite 3%, and the remainder is deionized water.

[0037] The preparation process of this high latent heat composite low-temperature phase change refrigerant is as follows: Weigh 15g of sodium chloride and pour it into a beaker, then add 75mL of deionized water. Stir magnetically at 700r / min for 15min to completely dissolve the sodium chloride in the water and mix it evenly to obtain a sodium chloride solution. Weigh 3g of lithium saponite and slowly add it to the above sodium chloride solution. Stir magnetically at 750r / min for more than 20min to evenly disperse the lithium saponite in the sodium chloride solution. Increase the speed of the magnetic stirrer appropriately to 800-1000r / min, and then add 7g of polyacrylamide quickly and evenly to the mixed solution. Increase the speed of the magnetic stirrer again to 1000-2300r / min to ensure that the solution is stirred evenly for 280min until it is uniformly stirred, thus obtaining the sodium chloride / polyacrylamide / lithium saponite composite phase change refrigerant.

[0038] To fully understand the performance of each of the refrigerants prepared according to the present invention, tests were conducted on them respectively.

[0039] (1) Liquidity test The experimental procedure is as follows: 50g of coolant was added to different beakers and left to stand for 60 minutes. Then, one beaker was placed upside down while the other was placed normally. After standing for another 5 minutes, the coolant was observed to see if it dripped or flowed.

[0040] Flowability test photos of the composite phase change refrigerants prepared in Examples 1-3 are shown below. Figure 1 As shown, the top row (a) consists of samples in a normal static state, while the bottom row (b) consists of samples in an inverted static state. From left to right, the top and bottom rows represent the refrigerant samples from Examples 1-3. Figure 1 It can be seen that the composite phase change refrigerants prepared in Examples 1-3 all have high viscosity. Even when placed upside down, they will not drip or flow under the influence of gravity. This indicates that the refrigerants have very poor fluidity and there is no need to worry about leakage and pollution during use.

[0041] (2) DSC test The DSC test results of the composite phase change refrigerants prepared in Examples 1-3 are as follows: Figure 2-4 As shown in the figure, the latent heats of the composite phase change refrigerants in Examples 1-3 are 224.72 J / g, 210.47 J / g, and 208.72 J / g, respectively, and the phase change temperatures are -6.768℃, -8.833℃, and -21.77℃, respectively. This indicates that the prepared composite phase change refrigerants all have high latent heats and low phase change temperatures, and these temperatures decrease with increasing sodium chloride content. Therefore, the performance of the composite phase change refrigerants can be flexibly adjusted by controlling the sodium chloride content.

[0042] (3) Endothermic / Exothermic Cycle Test The experimental procedure is as follows: 20g of composite low-temperature phase change refrigerant was placed in a beaker, sealed with plastic wrap, and then placed in a refrigerator (-25℃) for 6 hours to ensure that it was completely frozen. After removing the beaker, it was placed in a room temperature environment to allow it to naturally rise to room temperature. This freezing-thawing cycle was repeated 20 times. Samples of the composite low-temperature phase change refrigerant from the first and 20th cycles were taken for DSC analysis.

[0043] The endothermic / exothermic cycling test results of the composite low-temperature phase change refrigerant prepared in Example 2 are as follows: Figure 5 As shown in the figure, the subcooling of this refrigerant is relatively small, only 0.8℃. After 20 freeze-thaw cycles, its latent heat of phase change remains unchanged at 210.47 J / g. This indicates that the refrigerant has excellent cycle performance and a long service life, which not only saves production and usage costs but also reduces environmental pollution.

[0044] (4) Cooling test at different lithium saponite concentrations Taking Example 2 as an example, while keeping other conditions unchanged, only the amount of lithium saponite was varied to prepare phase change refrigerants with lithium saponite contents of 0%, 2%, 3%, and 4%. The composite low-temperature phase change refrigerants with different lithium saponite concentrations were placed in plastic beakers and placed inside a refrigerator. The temperature probe of a Jingchuang GSP-6 smart thermometer was inserted into the interior of these composite low-temperature phase change refrigerants, and the temperature recording switch was turned on, recording the temperature change every 10 seconds. Because the bottom temperature of the refrigerator (set temperature -25℃) was too low, a layer of foam board was placed under the beakers to prevent the composite low-temperature phase change refrigerant from directly contacting the bottom of the refrigerator, thus ensuring a uniform temperature around the composite low-temperature phase change refrigerant. The temperature changes of the three refrigerants during the phase change process were monitored and recorded in real time. Finally, the data were analyzed and calculated to obtain the supercooling degree, and the results are as follows. Figure 6 As shown.

[0045] Depend on Figure 6 It can be seen that the composite low-temperature phase change refrigerant with 0% lithium saponite content exhibits higher undercooling, while the composite low-temperature phase change refrigerant with 4% lithium saponite content shows lower undercooling and the best effect. As the lithium saponite content increases, the undercooling of the samples gradually decreases, indicating that lithium saponite plays a role in improving the undercooling phenomenon of the composite phase change refrigerant. In summary, in addition to adjusting the viscosity of the refrigerant, lithium saponite can significantly reduce undercooling, effectively improving the practical application effect of the refrigerant, and its role is crucial.

[0046] (5) Cold storage effect test Using the composite low-temperature phase change refrigerant prepared in Examples 1-3, along with air and water, as raw materials, four samples were placed in beakers and then frozen thoroughly in a refrigerator. Five identical insulated boxes were placed on a table, and a Jingchuang GSP-6 temperature probe was inserted into each box. The thermometer was turned on to record temperature changes. The four frozen samples were added to four of the insulated boxes, with the remaining box used as a blank control. Temperature changes inside the box at room temperature were recorded. The experimental data were plotted and calculated, and the results are shown below. Figure 7 As shown.

[0047] Depend on Figure 7 It can be seen that all three composite low-temperature phase change refrigerants with different ratios have good cold storage effects and can maintain a low temperature for a long time, with better results than water. The experiment also found that composite low-temperature phase change refrigerants with sodium chloride contents of 10% and 15% can maintain even lower temperatures, and the cold storage effect gradually increases with increasing sodium chloride content, maintaining the low temperature for a longer period. Therefore, composite low-temperature phase change refrigerants with different sodium chloride contents can be selected according to different practical requirements.

Claims

1. A high latent heat composite low-temperature phase change refrigerant, characterized in that: The cold storage agent is composed of the following components by mass fraction: 5%-10% sodium chloride, 5%-7% polyacrylamide, 3%-4% lithium saponite, and the remainder is solvent, specifically deionized water. The sodium chloride, polyacrylamide, and lithium saponite are uniformly dispersed in the solvent, and the mass fraction of sodium chloride is greater than or equal to the mass fraction of polyacrylamide and greater than the mass fraction of lithium saponite. The preparation method of the cold storage agent includes: first, preparing materials according to the specified proportions; then, mixing sodium chloride with the solvent and stirring until homogeneous; then, slowly adding lithium saponite and stirring until homogeneous; finally, quickly and uniformly adding polyacrylamide and stirring until homogeneous. The stirring speed when adding sodium chloride is less than the stirring speed when adding lithium saponite, less than the stirring speed before adding polyacrylamide, and the stirring time when adding polyacrylamide is less than the stirring time after adding sodium chloride, less than the stirring time after adding lithium saponite, and less than the stirring time after adding polyacrylamide.

2. The high latent heat composite low-temperature phase change refrigerant as described in claim 1, characterized in that: The stirring speed is 300-800 r / min when adding sodium chloride, 600-800 r / min when adding lithium soapstone, 800-1000 r / min before adding polyacrylamide, and 1000-2300 r / min after adding polyacrylamide.

3. The high latent heat composite low-temperature phase change refrigerant as described in claim 1, characterized in that: The stirring time is 5-20 seconds when adding polyacrylamide, 5-20 minutes after adding sodium chloride, 10-30 minutes after adding lithium soapstone, and 150-300 minutes after adding polyacrylamide.

4. The application of the high latent heat composite low temperature phase change cold storage agent as described in claim 1 in cold chain transportation and peak power shifting.

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