Laponite-paraffin microcapsule latent heat fluid and preparation method thereof

Abstract

This invention relates to a lithium saponite@paraffin microcapsule latent heat fluid and its preparation method. The latent heat fluid comprises a lithium saponite@paraffin microcapsule phase change material and a solvent, wherein the mass fraction of the lithium saponite@paraffin microcapsule phase change material does not exceed 50%. The first step involves dispersing lithium saponite in a solvent and exfoliating it into lithium saponite nanosheets, then adding a cationic modifier for modification, resulting in a modified lithium saponite nanosheet suspension. The second step involves mixing the phase change material, an anionic modifier, and solvents such as water to obtain a modified phase change material emulsion. The third step involves adding the modified lithium saponite nanosheet suspension to the modified phase change material emulsion and mixing thoroughly to obtain an initial latent heat fluid solution. This solution is then diluted, concentrated, dried, and redispersed to finally obtain the target latent heat fluid. The latent heat fluid provided by this invention exhibits good thermal conductivity and storage capacity, suspension stability, and low viscosity, showing promising application prospects in heating and heat exchange.

Description

Technical Field

[0001] This invention relates to the field of phase change materials and fluid technology, specifically to a lithium saponite@paraffin microcapsule latent heat fluid and its preparation method. Background Technology

[0002] Latent heat fluid is a novel working medium that integrates heat storage and enhanced heat transfer. It is formed by dispersing phase change material particles into a single-phase heat transfer fluid. Due to its superior thermal properties, latent heat fluid has broad application prospects in building heating, air conditioning systems, and heat exchangers.

[0003] Generally speaking, the performance of latent heat fluids is mainly determined by the properties of the phase change material particles dispersed within them. Due to the density difference between the phase change material particles and the dispersion medium, and the fact that the surface of most phase change material particles is organic, their compatibility with water is poor, thus easily leading to problems such as stratification, agglomeration of phase change material particles, and poor thermal conductivity. In addition, the phase change material particles in the latent heat fluid cause an increase in the viscosity of the suspension and a decrease in its fluidity, which can easily lead to pipe blockage and also increase the power of the pump. The emulsion prepared by Zhao Zhennan et al. (Zhao Zhennan, Wu Ting, Shi Yuquan et al. Study on the rheological and heat transfer properties of phase change emulsions [J]. Journal of Engineering Thermophysics, 2001, 22(5): 589) had a tetradecane content of 0.163, a viscosity of 16 times that of water at 278.15 K, and the emulsion exhibited obvious non-Newtonian fluid characteristics and was not easy to flow. Zhang et al. (Xu H, Yang R, Zhang YP, et al. Thermal physical properties and key influence factors of phase change emulsion[J]. Chinese Sci Bull, 2005, 50(1): 88) prepared an emulsion with a viscosity 5 times that of water, but the thermal conductivity of the emulsion was very small, about 0.1-0.2 W / (m·K), while the thermal conductivity of water was about 0.6 W / (m·K).

[0004] Lithium saponite has naturally superior dispersion and thermal conductivity in water. By adjusting the proportion of lithium saponite in microcapsule phase change materials, microcapsule phase change materials with the same density as the water phase can be obtained without adding thickeners, so that they can be stably suspended and dispersed in water, thereby obtaining high-performance latent heat fluids. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of poor dispersion, high viscosity and low thermal conductivity that are common in existing latent heat fluids, and to provide a novel latent heat fluid. The components of this latent heat fluid include lithium saponite@paraffin microcapsules and a solvent, wherein the lithium saponite@paraffin microcapsules have a core-shell structure, with paraffin as the core and lithium saponite nanosheets as the shell.

[0006] Furthermore, the solvent is selected from at least one of water, alcohol, and oil, preferably water.

[0007] Furthermore, the mass fraction of lithium saponite@paraffin microcapsules in the latent heat fluid does not exceed 50%, preferably 5%-10%.

[0008] The second objective of this invention is to provide a method for preparing the aforementioned latent heat fluid, which includes the following steps: (a) dispersing lithium saponite in a solvent such as ultrapure water and exfoliating it into lithium saponite nanosheets, then adding a cationic modifier for modification to obtain a modified lithium saponite nanosheet suspension; (b) mixing a phase change material, an anionic modifier, and water or other solvent for modification to obtain a modified phase change material emulsion; (c) adding the modified lithium saponite nanosheet suspension obtained in step (a) to the modified phase change material emulsion, mixing evenly to obtain an initial latent heat fluid liquid, and diluting, concentrating, or drying the initial latent heat fluid liquid and redispersing it to obtain the target latent heat fluid.

[0009] Further, in step (a), lithium saponite is added to a solvent and stirred at 200-1500 rpm for 3-24 hours. Then, lithium saponite is exfoliated into nanosheets by first ultrasonication and then high-speed shearing. The ultrasonic power is 100-500W and the ultrasonic time is 5-20 minutes. The high-speed shearing speed is 2000-15000 rpm and the high-speed shearing time is 5-20 minutes. After adding a cationic modifier, the modification is carried out at 200-1500 rpm for 3-24 hours.

[0010] Furthermore, in step (a), the amount of lithium saponite and cationic modifier added is equivalent to 0.1%-6% of the mass of the suspension, and the cationic modifier is selected from at least one of hexadecyltrimethylammonium bromide, octadecyldimethylbenzylammonium chloride, octadecyltrimethylammonium chloride, and dodecyltrimethylammonium chloride.

[0011] Furthermore, in step (b), the phase change material, anionic modifier, and solvent are mixed and stirred thoroughly at 200-1500 rpm and 55-75°C. Then, the rotation speed is increased and sheared at 2000-15000 rpm for 5-20 minutes to complete the modification.

[0012] Furthermore, in step (b), the emulsion contains 1%-30% by mass of phase change material and 0.1%-5% by mass of anionic modifier, and the phase change material is specifically paraffin wax, and the anionic modifier is selected from at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzenesulfonate, and sodium benzenesulfonate.

[0013] Furthermore, in step (c), after the modified phase change material emulsion is cooled to room temperature, the modified lithium saponite nanosheet suspension is added, and then the mixture is stirred at 200-1500 rpm for 3-24 hours at room temperature to obtain the initial liquid of latent heat fluid.

[0014] The third objective of this invention is to provide applications of the aforementioned latent heat fluid in heating, heat exchange, and other fields.

[0015] Compared with existing similar products, the improvement of the present invention is mainly reflected in the following aspects: (1) The present invention uses lithium saponite@paraffin microcapsule phase change material as the dispersion medium, which greatly improves the thermal conductivity and heat storage capacity of the latent heat fluid. By adjusting its content, latent heat fluids with different heat storage capacities can be obtained; (2) Compared with various phase change particles or microcapsule phase change particles commonly used in the past, the lithium saponite@paraffin microcapsule phase change material selected in the present invention greatly improves the suspension stability of the latent heat fluid; (3) Compared with the traditional method of achieving suspension stability by adding thickeners, the latent heat fluid of the present invention can achieve long-term suspension stability without adding thickeners, and reduces the viscosity of the latent heat fluid. Attached Figure Description

[0016] Figure 1 This is a comparison of the stability of the latent heat fluids prepared in Examples 1-2 after being left to stand for different times;

[0017] Figure 2 A schematic diagram of the heat dissipation performance testing equipment for various fluid samples;

[0018] Figure 3 This is a comparison chart showing the heat dissipation performance test results of the latent heat fluids and pure water prepared in Examples 1-3. Detailed Implementation

[0019] 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.

[0020] Example 1

[0021] 1.8 g of lithium saponite was mixed with 180 g of ultrapure water, and the resulting mixture was stirred at 500 rpm for 24 h to obtain a lithium saponite suspension. The lithium saponite suspension was transferred to an ultrasonic disruptor and sonicated at 300 W for 10 min for the first exfoliation. After sonication, the mixture was transferred to a high-speed shear mixer and sheared at 7500 rpm for 10 min for further exfoliation to obtain a lithium saponite nanosheet suspension. 1.8 g of hexadecyltrimethylammonium bromide was added to the lithium saponite nanosheet suspension at 500 rpm, and the surface of the lithium saponite nanosheets was modified by hexadecyltrimethylammonium bromide for 12 h to finally obtain a modified lithium saponite suspension.

[0022] 0.6g sodium dodecyl sulfate was mixed with 60g ultrapure water, and then 9g paraffin was added. The resulting mixture was stirred at 500rpm and 65℃ until the paraffin was completely melted. Then, the mixture was stirred and sheared at 7500rpm for 5min to obtain the modified paraffin emulsion.

[0023] The modified paraffin emulsion was cooled to room temperature by maintaining a rotation speed of 500 rpm, and then all the modified lithium saponite suspension was added. The resulting mixture was stirred at 500 rpm for 6 hours at room temperature to obtain the initial liquid of the latent heat fluid. The pure water in the initial liquid was evaporated by heating to obtain a latent heat fluid with a lithium saponite@paraffin microcapsule mass fraction of 5%.

[0024] Example 2

[0025] 1.8 g of lithium saponite was mixed with 180 g of ultrapure water, and the resulting mixture was stirred at 500 rpm for 24 h to obtain a lithium saponite suspension. The lithium saponite suspension was transferred to an ultrasonic disruptor and sonicated at 300 W for 10 min for the first exfoliation. After sonication, the mixture was transferred to a high-speed shear mixer and sheared at 7500 rpm for 10 min for further exfoliation to obtain a lithium saponite nanosheet suspension. 1.8 g of hexadecyltrimethylammonium bromide was added to the lithium saponite nanosheet suspension at 500 rpm, and the surface of the lithium saponite nanosheets was modified by hexadecyltrimethylammonium bromide for 12 h to finally obtain a modified lithium saponite suspension.

[0026] 0.6g sodium dodecyl sulfate was mixed with 60g ultrapure water, and then 9g paraffin was added. The resulting mixture was stirred at 500rpm and 65℃ until the paraffin was completely melted. Then, the mixture was stirred and sheared at 7500rpm for 5min to obtain the modified paraffin emulsion.

[0027] The modified paraffin emulsion was cooled to room temperature by maintaining a rotation speed of 500 rpm, and then all the modified lithium saponite suspension was added. The resulting mixture was stirred at 500 rpm for 6 hours at room temperature to obtain the initial liquid of the latent heat fluid. The pure water in the initial liquid was evaporated by heating to obtain a latent heat fluid with a lithium saponite@paraffin microcapsule mass fraction of 8%.

[0028] Example 3

[0029] 1.8 g of lithium saponite was mixed with 180 g of ultrapure water, and the resulting mixture was stirred at 500 rpm for 24 h to obtain a lithium saponite suspension. The lithium saponite suspension was transferred to an ultrasonic disruptor and sonicated at 300 W for 10 min for the first exfoliation. After sonication, the mixture was transferred to a high-speed shear mixer and sheared at 7500 rpm for 10 min for further exfoliation to obtain a lithium saponite nanosheet suspension. 1.8 g of hexadecyltrimethylammonium bromide was added to the lithium saponite nanosheet suspension at 500 rpm, and the surface of the lithium saponite nanosheets was modified by hexadecyltrimethylammonium bromide for 12 h to finally obtain a modified lithium saponite suspension.

[0030] 0.6g sodium dodecyl sulfate was mixed with 60g ultrapure water, and then 9g paraffin was added. The resulting mixture was stirred at 500rpm and 65℃ until the paraffin was completely melted. Then, the mixture was stirred and sheared at 7500rpm for 5min to obtain the modified paraffin emulsion.

[0031] The modified paraffin emulsion was cooled to room temperature by maintaining a rotation speed of 500 rpm, and then all the modified lithium saponite suspension was added. The resulting mixture was stirred at 500 rpm for 6 hours at room temperature to obtain the initial liquid of the latent heat fluid. The pure water in the initial liquid was evaporated by heating to obtain a latent heat fluid with a lithium saponite@paraffin microcapsule mass fraction of 10%.

[0032] Example 4

[0033] This embodiment is basically the same as Embodiment 1, except that the modifiers hexadecyltrimethylammonium bromide and sodium dodecyl sulfate are replaced with equal masses of octadecyldimethylbenzylammonium chloride and sodium benzenesulfonate, respectively, and the mass fraction of the latent heat fluid is controlled at 15%.

[0034] Example 5

[0035] This embodiment is basically the same as Example 1, except that the modifiers hexadecyltrimethylammonium bromide and sodium dodecyl sulfate are replaced with equal masses of sodium dodecyltrimethylammonium chloride and sodium dodecyl sulfonate, respectively, and the mass fraction of latent heat fluid is controlled at 50%.

[0036] Example 6

[0037] This embodiment is basically the same as Example 1, except that the modifiers hexadecyltrimethylammonium bromide and sodium dodecyl sulfate are replaced with equal masses of octadecyltrimethylammonium chloride and sodium dodecylbenzenesulfonate, respectively, and the mass fraction of the latent heat fluid is controlled at 30%.

[0038] To fully understand the product performance, a comparative test of the heat dissipation performance was conducted on the latent heat fluids prepared in Examples 1-3 and pure water. The experimental setup for the heat dissipation performance test is as follows: Figure 2As shown, an MCH ceramic heating element was used as the heat source, and a brass water-cooling head with an internal M-shaped channel was used as the heat sink. The ceramic heating element was placed on the upper surface of the heat sink, and the temperature of the upper surface of the ceramic heating element was detected by an infrared thermal imager. When the ceramic heating element was powered on and heating up, pure water and the latent heat fluid prepared in Examples 1-3 were introduced into the heat sink at a volume flow rate of Q = 7 mL / min. The heat dissipation of the ceramic heating element was tested and the heat dissipation performance of each fluid sample was obtained. The relevant test results are shown in Table 1.

[0039] Table 1. Performance Comparison of Latent Heat Fluids Prepared in Examples 1-3

[0040] Example 1 Example 2 Example 3 Enthalpy of microcapsules (J / g) 144.20 144.20 144.20 Microcapsule particle size (µm) 2.5-105 2.5-105 2.5-105 <![CDATA[Density (10 3 × kg / m 3 )]]> 0.995 0.997 0.998 <![CDATA[Dynamic viscosity (10 -3 ×Pa·s)]]> 3.16 4.90 6.73 <![CDATA[Kinematic viscosity (10 -6 ×m 2 / s)]]> 3.18 4.91 6.74 pH 8.23 7.75 7.44 Surface temperature of the heating element (°C) after 20 minutes 87.7 86.2 84.4 Heat dissipation effect compared to pure water (%) 6.4 8.0 9.9

[0041] Generally, the properties of latent heat fluids are largely determined by the phase change material dispersed within them. As shown in Table 1, the latent heat value of the microcapsule phase change material prepared in Example 1 is as high as 144.20 J / g, thus it can significantly improve the heat storage capacity of latent heat fluids. The dynamic viscosity of pure water at 30°C is approximately 0.8 × 10⁻⁶. -3 As shown in Table 1, the viscosity of the sample in Example 1 is 4 times that of pure water, the viscosity of the sample in Example 2 is 6 times that of pure water, and the viscosity of the sample in Example 3 is 8 times that of pure water. This indicates that all samples have good flowability. The pH data in Table 1 shows that the pH values ​​of the latent heat fluid samples in Examples 1-3 are close to neutral, indicating that the latent heat fluid is not corrosive to acids or alkalis during application. The density data in Table 1 shows that the density of the latent heat fluid after adding the microencapsulated phase change material is similar to the density of pure water (the density of pure water at 30°C is approximately 0.995 × 10⁻⁶). 3 kg / m 3 The density difference between the dispersed phase and the dispersant in this latent heat fluid is almost the same, which indicates that the small density difference between the dispersed phase and the dispersant is more conducive to suspension stability.

[0042] The heat dissipation performance test results of the latent heat fluids and pure water prepared in Examples 1-3 are as follows: Figure 3 As shown. By Figure 3The test results show that after 20 minutes, the surface temperature of the heating element was 93.7℃ when using pure water as the heat dissipation medium; 87.7℃ when using the latent heat fluid prepared in Example 1 as the heat dissipation medium; 86.2℃ when using the latent heat fluid prepared in Example 2 as the heat dissipation medium; and 84.4℃ when using the latent heat fluid prepared in Example 3 as the heat dissipation medium. Compared with the heat dissipation of pure water, the latent heat fluids prepared in Examples 1-3 improved the heat dissipation effect of the heating element by 6.4%, 8.0%, and 9.9%, respectively. This indicates that due to the presence of lithium saponite@paraffin microcapsule phase change material, the latent heat fluid has a stronger heat storage capacity than water and exhibits better heat dissipation performance than pure water in the heat dissipation test. Under the same volumetric flow rate, the heat dissipation effect increases with the increase of the mass fraction of lithium saponite@paraffin microcapsule phase change material in the latent heat fluid.

[0043] The suspension stability test of the latent heat fluids prepared in Examples 1-2 is as follows: Figure 1 As shown in the figure, after 30 days of settling, no stratification or agglomeration was observed in any of the latent heat fluid samples, which proves that the microcapsule phase change material in the latent heat fluid is uniformly dispersed and has excellent suspension stability.

Claims

1. A latent heat fluid, characterized in that: The latent heat fluid comprises lithium saponite@paraffin microcapsules and a solvent, wherein the lithium saponite@paraffin microcapsules have a core-shell structure with paraffin as the core and lithium saponite nanosheets as the shell; the solvent is selected from at least one of water, alcohol, and oil.

2. The latent heat fluid as described in claim 1, characterized in that: The mass fraction of lithium saponite@paraffin microcapsules in the latent heat fluid does not exceed 50%.

3. The latent heat fluid as described in claim 2, characterized in that: The mass fraction of lithium saponite@paraffin microcapsules in the latent heat fluid is 5%-10%.

4. The method for preparing the latent heat fluid according to any one of claims 1-3, characterized in that... The method includes the following steps: (a) exfoliating lithium saponite into lithium saponite nanosheets, and then modifying them with a cationic modifier to obtain a modified lithium saponite nanosheet suspension, wherein the cationic modifier is selected from at least one of hexadecyltrimethylammonium bromide, octadecyldimethylbenzylammonium chloride, octadecyltrimethylammonium chloride, and dodecyltrimethylammonium chloride; (b) mixing paraffin wax, anionic modifier and solvent to obtain a modified paraffin wax emulsion, wherein the anionic modifier is selected from at least one of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzenesulfonate and sodium benzenesulfonate; (c) adding the modified lithium saponite nanosheet suspension obtained in step (a) to the modified paraffin wax emulsion, mixing evenly to obtain a latent heat fluid initial liquid, and then diluting, concentrating or drying and redispersing the latent heat fluid initial liquid.

5. The method as described in claim 4, characterized in that: Step (a) Lithium saponite is added to a solvent and stirred thoroughly at 200-1500 rpm for 3-24 hours. Then, lithium saponite is exfoliated into nanosheets by first ultrasonication and then high-speed shearing. Next, a cationic modifier is added and modified at 200-1500 rpm for 3-24 hours.

6. The method as described in claim 5, characterized in that: The ultrasonic power is 100-500W, the ultrasonic time is 5-20min, the high-speed shearing speed is 2000-15000rpm, and the high-speed shearing time is 5-20min.

7. The method as described in claim 4, characterized in that: In step (a), the amount of lithium saponite and cationic modifier added is equivalent to 0.1%-6% of the mass of the suspension.

8. The method as described in claim 4, characterized in that: In step (b), paraffin, anionic modifier, and solvent are mixed and stirred thoroughly at 200-1500 rpm and 55-75 ℃. Then, the rotation speed is increased and sheared at 2000-15000 rpm for 5-20 minutes to complete the modification.

9. The method as described in claim 4, characterized in that: The mass percentage of paraffin in the emulsion described in step (b) is 1%-30%, and the mass percentage of the anionic modifier is 0.1%-5%.

10. The method as described in claim 4, characterized in that: In step (c), after the modified paraffin emulsion is cooled to room temperature, the modified lithium saponite nanosheet suspension is added, and then the mixture is stirred at 200-1500 rpm for 3-24 hours at room temperature to obtain the initial latent heat fluid.

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