Spherical sodium acetate trihydrate composite phase change material and microfluidic preparation method thereof

Abstract

This invention proposes a spherical sodium acetate trihydrate composite phase change material and its microfluidic preparation method. The method includes: mixing and melting sodium acetate trihydrate with a nucleating agent, a thickener, and a thermally conductive filler to form a homogeneous composite liquid; adding the composite liquid dropwise to a silicone oil medium of a specific viscosity using a microfluidic device, utilizing interfacial tension to shape the droplets into spherical shapes and complete controlled phase change solidification; finally, washing and drying to obtain the spherical product. A specific order is used: adding the nucleating agent first, then the thermally conductive filler, and finally the thickener. This invention, through the synergy of microfluidic technology and composite formulation, successfully prepares a composite phase change material with good sphericity and uniform particle size, effectively solving the problems of severe undercooling, easy phase separation, and the inability to controllably prepare spherical particles using traditional methods. The product exhibits low undercooling, high phase change enthalpy, and excellent cycling stability.

Description

Technical Field

[0001] This invention relates to the field of phase change material preparation technology, and in particular to a spherical sodium acetate trihydrate composite phase change material and its microfluidic preparation method. Background Technology

[0002] Sodium acetate trihydrate, as an inorganic hydrated salt phase change material, has broad application prospects in fields such as solar thermal storage, building energy conservation, and electronic thermal management due to its advantages such as large latent heat of phase change, suitable phase change temperature, low cost, and environmental friendliness. However, its practical application faces three inherent drawbacks: First, severe supercooling leads to delayed crystallization and untimely heat release; second, phase separation easily occurs during cycling, causing latent heat decay and performance failure; and third, products obtained by traditional preparation methods are mostly irregular blocks or powders, with problems such as uncontrollable morphology, uneven size, low bulk density, and poor flowability, which seriously limit its application in scenarios requiring precise filling or high-efficiency heat exchange.

[0003] To address the aforementioned issues, existing technologies typically modify sodium acetate trihydrate by introducing nucleating agents, thickeners, and thermally conductive fillers to improve its supercooling, phase separation, and thermal conductivity. However, in terms of specific preparation processes, most methods involve simple heating and mixing followed by natural cooling and molding, or granulation using mechanical granulation equipment. When using mechanical granulation, the material is subjected to mechanical shearing and collision during the granulation process, easily leading to particle breakage, irregular morphology, and a wide particle size distribution, making it difficult to obtain particles with uniform size and complete structure. On the other hand, simple cooling and molding methods make it difficult to effectively control the material morphology, resulting in materials that are mostly irregular blocky or sheet-like structures, unable to achieve spherical preparation. Furthermore, existing molding methods generally lack precise control over droplet formation and solidification processes, making it difficult to accurately control the particle morphology, size, and structure during the liquid-to-solid transition, thus failing to stably prepare spherical phase change materials with uniform particle size and regular morphology. This lack of precision in preparation severely limits the further application of sodium acetate trihydrate composite phase change materials in microscale energy storage devices, flexible thermal management systems, and high-performance temperature control.

[0004] Therefore, there is an urgent need to develop a new method that can achieve uniform mixing, stable modification, and controllable spheroidization of sodium acetate trihydrate composite phase change materials, in order to solve the problems of uncontrollable particle morphology, poor performance stability, and difficulty in precise control of the preparation process in the existing technology. Summary of the Invention

[0005] In view of this, the present invention proposes a spherical sodium acetate trihydrate composite phase change material and its microfluidic preparation method. It aims to solve a series of problems associated with traditional sodium acetate trihydrate phase change materials, including poor formability, inability to controllably prepare regular spherical structures, performance instability due to uneven mixing with additives, easy supercooling and phase separation, and insufficient control over the droplet solidification process and low preparation efficiency in existing methods.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a microfluidic preparation method for a spherical sodium acetate trihydrate composite phase change material, comprising the following steps: S1. Mix and melt sodium acetate trihydrate, nucleating agent, thermally conductive filler and thickener to form a uniform composite melt; S2. The composite melt obtained in step S1 is added dropwise to the silicone oil medium through a microfluidic device. The droplets are formed into spheres in the silicone oil and complete the phase change solidification to obtain spherical wet particles. S3. The spherical wet particles obtained in step S2 are washed and dried to obtain the spherical sodium acetate trihydrate composite phase change material.

[0007] Based on the above technical solution, preferably, in step S1, the nucleating agent includes sodium pyrophosphate decahydrate, disodium hydrogen phosphate dodecahydrate, and nano-SiO2; the thickener includes sodium carboxymethyl cellulose, sodium polyacrylate, and polyvinyl alcohol; and the thermally conductive filler includes nano-alumina, aluminum nitride, and graphene. Sodium pyrophosphate decahydrate, as a nucleating agent, effectively reduces material undercooling and promotes uniform nucleation; sodium carboxymethyl cellulose, as a stabilizer, inhibits phase separation and water separation by increasing the system viscosity and constructing a three-dimensional network structure; and nano-alumina, as a thermal conductivity enhancer, forms a thermally conductive network within the system, thereby improving the thermal response rate. The three components work synergistically to achieve comprehensive optimization of the material's nucleation behavior, structural stability, and thermal conductivity.

[0008] More preferably, in step S1, the addition amounts of the nucleating agent, thickener, and thermally conductive filler are 1%-5% of the mass of sodium acetate trihydrate. When the nucleating agent content is below 1%, nucleation is insufficient; when it is above 5%, excessive non-phase change components lead to a decrease in latent heat and uneven crystallization. When the stabilizer content is below 1%, the network structure is weak and the phase separation effect is limited; when it is above 5%, the system viscosity is too high, affecting droplet formation and heat transfer. When the thermally conductive filler content is below 1%, the effect is not obvious; when it is above 5%, it is prone to agglomeration, which is detrimental to heat conduction and further reduces latent heat.

[0009] In a further preferred embodiment, in step S1, the order of adding materials is as follows: after the sodium acetate trihydrate has completely melted, the nucleating agent is added first, and after it melts, the thermally conductive filler is added and dispersed evenly, and finally the thickener is added. Mechanical stirring is performed simultaneously during heating to promote the full dissolution and uniform dispersion of each component, thus constructing a homogeneous composite system.

[0010] More preferably, in step S1, the mixing and melting are carried out under heating and stirring conditions, with the heating temperature at 75℃-80℃ and the stirring speed at 400 rpm-800 rpm. The heating rate of sodium acetate trihydrate is controlled at 1-5℃ / min to avoid premature crystallization or uneven component distribution caused by local overheating.

[0011] Furthermore, the completely dissolved composite melt is kept at a constant temperature to prevent premature crystallization during subsequent operations, thereby constructing a metastable liquid phase system and providing a controllable phase transition window for subsequent droplet spheroidization.

[0012] More preferably, in step S2, the drop acceleration rate of the microfluidic device is 1 second / drop to 2 seconds / drop.

[0013] More preferably, in step S2, the viscosity of the silicone oil medium is 50-100 cSt.

[0014] More preferably, the temperature of the silicone oil medium is 15℃-25℃.

[0015] Based on the above technical solution, preferably, in step S2, the heat-insulated composite molten liquid is drawn into the syringe of the microfluidic device, and the syringe is controlled to drop the liquid into a container containing silicone oil at a rate of approximately 1.5 drops per second (drop height 5-10 cm). After entering the silicone oil, the droplet rapidly shrinks into a spherical shape under the action of interfacial tension, and maintains its shape stability through the viscous damping effect of the silicone oil. The droplet falls slowly in the silicone oil, and during this process, a temperature gradient is formed from the outside to the inside through heat exchange with the low-temperature silicone oil, inducing preferential crystallization on the outside and gradually advancing inward, realizing the simultaneous formation of phase change solidification and spherical structure. Within the confined space of the droplet, the solute is uniformly distributed, and combined with the action of the nucleating agent, it promotes uniform nucleation and controlled growth, ultimately obtaining dense, uniformly sized spherical wet sodium acetate trihydrate particles.

[0016] More preferably, in step S3, the spherical wet particles are washed with an organic solvent.

[0017] In a further preferred embodiment, after the droplets have completed spherical formation and phase change solidification in the silicone oil, solid-liquid separation is performed by filtration or centrifugation to collect the spherical particles. The particles are washed 2-3 times with anhydrous ethanol to remove surface silicone oil, and then dried at 20℃-40℃ for 12 hours. Afterwards, sieving can be performed to obtain a product with uniform particle size, and the separated silicone oil can be recycled and purified for reuse.

[0018] In a second aspect, the present invention provides a spherical sodium acetate trihydrate composite phase change material, which is prepared by the microfluidic preparation method described in any one of the first aspects above.

[0019] The present invention has the following advantages over the prior art: (1) By constructing a homogeneous composite precursor and performing microfluidic droplet control under metastable conditions, sodium acetate trihydrate was able to complete the coupling process of interface-induced spherical formation and phase change solidification in an immiscible continuous phase medium, successfully preparing spherical composite phase change material particles with uniform particle size and stable structure. The obtained particles have high sphericity and good size consistency, realizing controllable preparation under mold-free conditions.

[0020] (2) Compared with traditional blocky or irregular materials, the obtained spherical material has a larger specific surface area and a more uniform heat transfer interface. Combined with the built-in thermal conductivity enhancement components, the heat transfer efficiency and phase change response rate are significantly improved. The uniform distribution and restricted crystallization of multi-components achieved in the confined space of microdroplets effectively suppress phase separation and greatly reduce the supercooling of the system, thereby improving the stability, reversibility and cycle life of the phase change process.

[0021] (3) The droplets are simultaneously formed and cured during the falling of the silicone oil, requiring no complicated post-processing, resulting in a high yield and simple operation. By adjusting the amount of silicone oil and the dropping rate, it is easy to achieve batch and continuous preparation.

[0022] (4) The selected basic raw materials and additives are all common chemical products with low cost. The silicone oil medium can be recycled and reused, reducing material consumption and production costs. The overall process is green and efficient, and the resulting spherical particles have good flowability and excellent filling performance. They have great application potential in various heat storage and temperature control scenarios and have good prospects for industrial promotion. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a diagram illustrating the microfluidic droplet-controlled preparation method of spherical sodium acetate trihydrate according to the present invention; Figure 2 This is a SEM image of the spherical sodium acetate trihydrate composite phase change material prepared in Example 1 of this invention; Figure 3 The images show the sample of the spherical sodium acetate trihydrate composite phase change material prepared in Example 1 of this invention; where (a) and (b) are samples after microfluidic addition of silicone oil, (c) is the sample taken out before drying, and (d) is the sample after drying. Figure 4Comparison of the effects of different microfluidic drop acceleration rates on sphere formation: (a) Drop acceleration rate of 0.33 seconds / drop (Comparative Example 8), (b) Drop acceleration rate of 0.5 seconds / drop (Comparative Example 9), (c) Drop acceleration rate of 2.5 seconds / drop (Comparative Example 10), (d) Drop acceleration rate of 1.5 seconds / drop (Example 1). Figure 5 Comparison of the effect of silicone oil media with different viscosities on the balling effect: (a) 150 cSt viscosity (Comparative Example 13), (b) 200 cSt viscosity (Comparative Example 14), (c) 10 cSt viscosity (Comparative Example 11), (d) 20 cSt viscosity (Comparative Example 12). Figure 6 A comparison of the effects of different dispersion / coagulation media on pelletizing: (a) ether, (b) carbon tetrachloride; Figure 7 This is a comparison of the time-temperature cooling curves of different additive systems in this invention; Figure 8 Comparison of differential scanning calorimetry (DSC) curves of samples with different morphologies under the same formulation: (a) spherical sample prepared by microfluidic control (Example 1), (b) block sample prepared by conventional cooling (Comparative Example 1). Figure 9 Comparison of DSC curves for different binary additive composite systems: (a) sodium pyrophosphate decahydrate + sodium carboxymethyl cellulose (Comparative Example 2), (b) sodium pyrophosphate decahydrate + nano alumina (Comparative Example 4), (c) sodium carboxymethyl cellulose + nano alumina (Comparative Example 3), (d) pure sodium acetate trihydrate (Comparative Example 17). Figure 10 Comparison of DSC curves of samples with the same formulation after 50 thermal cycles: (a) spherical sample prepared by microfluidic control (Example 1), (b) block sample prepared by conventional cooling (Comparative Example 1). Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] All materials used in this invention were purchased from the market, specifically: sodium acetate trihydrate was purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium pyrophosphate decahydrate was purchased from Sinopharm Chemical Reagent Co., Ltd.; sodium carboxymethyl cellulose was purchased from Sinopharm Chemical Reagent Co., Ltd.; nano alumina was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; and 50cSt silicone oil was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0027] like Figure 1 As shown, the preparation process of the spherical sodium acetate trihydrate composite phase change material of the present invention is as follows: First, the sodium acetate trihydrate and various functional additives are weighed and proportioned; then, the mixed raw materials are placed in a heating and stirring device for heating and stirring to fully melt and uniformly disperse them to form a stable composite melt system; then, the molten droplets are slowly added to the 50 cSt silicone oil continuous phase using a microfluidic injection device, and the droplets gradually form spherical particles under the action of interfacial tension and cooling, and are uniformly dispersed in the silicone oil; finally, the obtained spherical particles are washed and dried to obtain the spherical sodium acetate trihydrate composite phase change material.

[0028] The thermophysical properties and stability of the spherical sodium acetate trihydrate composite phase change material prepared by this invention were tested using the following method: The phase change behavior of the sample was characterized using differential scanning calorimetry (DSC). The test was conducted according to GB / T 19466.3-2004 standard. A sample of 5-10 mg was placed in a sealed aluminum crucible and subjected to a nitrogen protective atmosphere (flow rate of 500 mg / L). The phase transition temperature and latent heat of the material were obtained by measuring the temperature at a rate of 10℃ / min (mL / min) and the heating and cooling rates were both set at 10℃ / min. The test temperature range was 20~80℃. The crystallization temperature of the material during cooling was recorded and compared with the melting temperature to calculate the supercooling. The thermal conductivity of the material was measured using the transient planar heat source method or a laser thermal conductivity meter, and the test temperature was controlled at room temperature. Cyclic stability was evaluated by measuring the latent heat of phase transition and the change in phase transition temperature after 50~100 heating-cooling cycles. The phase separation performance was assessed by observing the macroscopic morphology of the sample after multiple thermal cycles to determine whether there was stratification or water separation, thereby comprehensively evaluating the structural stability and application reliability of the material.

[0029] Example 1 S1. Take 30g of sodium acetate trihydrate as the matrix material, and add 1% (w / w) sodium pyrophosphate decahydrate (0.3g), 1% (w / w) sodium carboxymethyl cellulose (0.3g), and 1% (w / w) nano-alumina (0.3g). Place the above mixture in a magnetic stirring and heating device, and heat it at 75℃ and 400 rpm. A specific order of addition is used: after the sodium acetate trihydrate is completely melted, first add the sodium pyrophosphate decahydrate, and after it melts, add the nano-alumina and continue stirring for 20 minutes to disperse it evenly. Finally, add the sodium carboxymethyl cellulose in two batches. Continue stirring until a uniform, transparent composite melt is formed, and keep it at 75℃ for later use.

[0030] S2. Using a syringe pump (microfluidic device), the above-mentioned heat-insulated composite melt is dripped through a needle into a beaker containing silicone oil medium at 20°C and a viscosity of 50 cSt at a rate of 1.5 drops per second, with a drop height of approximately 8 cm. The droplets rapidly form spherical shapes in the silicone oil due to interfacial tension and complete phase transition solidification within 3-10 seconds.

[0031] S3. Collect the spherical wet particles in the silicone oil, wash them three times with anhydrous ethanol to remove the surface silicone oil, and then dry them at 25°C for 12 hours to obtain spherical sodium acetate trihydrate composite phase change material with uniform particle size.

[0032] like Figure 2 As shown: Under low magnification (×200), the spherical sodium acetate trihydrate composite phase change material prepared in this embodiment exhibits a dense and continuous overall structure with no obvious pores, cracks, or phase separation, and uniform grain distribution. Under medium magnification (×500), the matrix is ​​visible as a three-dimensional network structure formed by the interweaving of uniformly sized lamellar sodium acetate trihydrate grains of 1-5 μm, with additives uniformly dispersed at the grain boundaries. Under high magnification (×1000), the grains show intact crystal faces and tight interfacial bonding, forming a synergistic composite structure of "grain-binder phase-thermal conductive filler". This microstructure effectively solves the technical bottlenecks of traditional materials, such as large undercooling, poor cycle stability, and easy leakage, and achieves a comprehensive performance improvement in terms of low undercooling, high phase change enthalpy, and excellent thermal stability.

[0033] like Figure 3 As shown, the macroscopic morphology consists of regular spherical particles with uniform particle size and high sphericity, exhibiting no agglomeration, adhesion, or breakage. Even after washing and drying, the samples retain their intact spherical structure, demonstrating excellent dispersibility and enabling large-scale, standardized preparation. This regular spherical morphology effectively improves the material's dispersibility, heat transfer uniformity, and thermal cycling stability, providing a structural basis for its applications in energy storage, temperature control, and other fields.

[0034] Example 2 S1. Take 30g of sodium acetate trihydrate as the matrix material, and add 1% (w / w) sodium pyrophosphate decahydrate (0.3g), 3% (w / w) sodium carboxymethyl cellulose (0.9g), and 2% (w / w) nano-alumina (0.6g). Place the mixture in a magnetic stirring and heating device and heat at 80℃ and 600 rpm. A specific order of addition is used: after the sodium acetate trihydrate is completely melted, add the sodium pyrophosphate decahydrate first, and after it melts, add the nano-alumina and continue stirring for 20 minutes to ensure uniform dispersion. Finally, add the sodium carboxymethyl cellulose in two batches. Continue stirring until a uniform, transparent composite melt is formed, and keep it at 80℃ for later use.

[0035] S2. Using a syringe pump (microfluidic device), the above-mentioned heat-insulated composite melt is dripped through a needle at a rate of 1 drop per second into a beaker containing silicone oil medium at 15°C and a viscosity of 50 cSt, with a drop height of approximately 5 cm. The droplets rapidly form spherical shapes in the silicone oil due to interfacial tension and complete phase transition solidification within 3-10 seconds.

[0036] S3. Collect the spherical wet particles in the silicone oil, wash them three times with anhydrous ethanol to remove the surface silicone oil, and then dry them at 20°C for 12 hours to obtain spherical sodium acetate trihydrate composite phase change material with uniform particle size.

[0037] Example 3 S1. Take 30g of sodium acetate trihydrate as the matrix material, and add 5% sodium pyrophosphate decahydrate (1.5g), 5% sodium carboxymethyl cellulose (1.5g), and 5% nano-alumina (1.5g). Place the mixture in a magnetic stirring and heating device and heat at 800 rpm at 80°C. A specific order of addition is used: after the sodium acetate trihydrate is completely melted, add the sodium pyrophosphate decahydrate first, and after it melts, add the nano-alumina and continue stirring for 20 minutes to ensure uniform dispersion. Finally, add the sodium carboxymethyl cellulose in two batches. Continue stirring until a uniform, transparent composite melt is formed, and keep it at 80°C for later use.

[0038] S2. Using a syringe pump (microfluidic device), the above-mentioned heat-insulated composite melt is dripped through a needle into a beaker containing silicone oil medium at 25°C and a viscosity of 50 cSt at a rate of 2 drops per second, with a drop height of approximately 10 cm. The droplets rapidly form spherical shapes in the silicone oil due to interfacial tension and complete phase change solidification within 3-10 seconds.

[0039] S3. Collect the spherical wet particles in the silicone oil, wash them three times with anhydrous ethanol to remove the surface silicone oil, and then dry them at 40°C for 12 hours to obtain spherical sodium acetate trihydrate composite phase change material with uniform particle size.

[0040] Example 4 Unlike Example 1, silicone oil with a viscosity of 100 cSt was used in step S2. The remaining steps were the same as in Example 1 and will not be repeated here. After washing and drying, spherical sodium acetate trihydrate composite phase change material with uniform particle size was obtained.

[0041] Example 5 S1. Take 30g of sodium acetate trihydrate as the matrix material, and add 1% by mass of nano-SiO2 (0.3g), 1% by mass of sodium polyacrylate (0.3g), and 1% by mass of aluminum nitride (0.3g). Place the above mixture in a magnetic stirring and heating device, and heat it at 75°C and 400 rpm. A specific order of addition is used: after the sodium acetate trihydrate is completely melted, first add the nano-SiO2, and after it melts, add the aluminum nitride and continue stirring for 20 minutes to disperse it evenly. Finally, add the sodium polyacrylate in two batches. Continue stirring until a uniform and transparent composite melt is formed, and keep it at 75°C for later use.

[0042] The remaining steps are the same as in Example 1, and will not be repeated here. After washing and drying, spherical sodium acetate trihydrate composite phase change material with uniform particle size is obtained.

[0043] Example 6 S1. Take 30g of sodium acetate trihydrate as the matrix material, and add 1% (by mass) of disodium hydrogen phosphate dodecahydrate (0.3g), 1% (by mass) of polyvinyl alcohol (0.3g), and 1% (by mass) of graphene (0.3g). Place the mixture in a magnetic stirring and heating device and heat it at 75°C and 400 rpm. A specific order of addition is used: after the sodium acetate trihydrate is completely melted, first add disodium hydrogen phosphate dodecahydrate, and after it melts, add graphene and continue stirring for 20 minutes to ensure uniform dispersion. Finally, add polyvinyl alcohol in two batches. Continue stirring until a uniform, transparent composite melt is formed, and keep it at 75°C for later use.

[0044] The remaining steps are the same as in Example 1, and will not be repeated here. After washing and drying, spherical sodium acetate trihydrate composite phase change material with uniform particle size is obtained.

[0045] Comparative Example 1 Unlike Example 1, the mixture was melted and mixed evenly at 80°C and 600 rpm, then poured directly into a mold and allowed to cool and solidify naturally at room temperature to obtain a block sample. The remaining steps were the same as in Example 1 and will not be repeated here.

[0046] Comparing Example 1 with Comparative Example 1, such as... Figure 8 As shown: where Figure 8 (a) A spherical sample prepared by microfluidic method (Example 1) with a phase transition enthalpy of 251.3 J / g, an initial phase transition temperature of 61.9℃, a sharp peak shape, and sufficient latent heat release;Figure 8 (b) The bulk sample prepared by the conventional process (Comparative Example 1) has a phase transition enthalpy of 245 J / g, an initial phase transition temperature of 60.3℃, and exhibits peak broadening and reduced latent heat release efficiency. The results indicate that the microfluidic spheroidization process can significantly improve the crystallization integrity and phase transition enthalpy of the material, while optimizing the uniformity of the phase transition temperature, providing a core guarantee for the material's excellent thermal properties and cycling stability.

[0047] like Figure 10 As shown: DSC curves, used to characterize the effect of microfluidic spheroidization process on improving the long-term thermal cycling stability of materials. Figure 10 (a) The spherical sample prepared by microfluidic method (Example 1) still has a phase transition enthalpy of 220.1 J / g after 50 thermal cycles. The initial phase transition temperature is 59.5℃. The peak shape is sharp and symmetrical, and the latent heat release is concentrated. Compared with the initial enthalpy of 251.3 J / g, the enthalpy retention rate is as high as 87.6%, with only slight decay. This proves that the spherical structure can effectively suppress phase separation and leakage during the phase transition process, and ensure the structural stability and thermal performance of the material for long-term use. Figure 10 (b) The bulk sample prepared by the conventional process (Comparative Example 1) after 50 thermal cycles, the phase transition enthalpy value dropped significantly to 164 J / g, and the initial phase transition temperature was 57.1℃. Compared with the initial enthalpy value of 245 J / g, the enthalpy value retention rate was only 66.9%, the performance degradation was significant, and the peak shape broadened. This indicates that the bulk structure is prone to grain migration and structural collapse during repeated phase transitions, resulting in rapid loss of latent heat.

[0048] Comparative Example 2 Unlike Example 1, the composite melt in step S1 does not contain nano-alumina. The remaining steps are the same as in Example 1 and will not be repeated here.

[0049] Comparative Example 3 Unlike Example 1, sodium pyrophosphate decahydrate is not added to the composite melt in step S1. The remaining steps are the same as in Example 1 and will not be repeated here.

[0050] Comparative Example 4 Unlike Example 1, sodium carboxymethyl cellulose is not added to the composite melt in step S1. The remaining steps are the same as in Example 1, and will not be repeated here.

[0051] Comparative Example 5 Unlike Example 1, 30g of sodium acetate trihydrate was used as the matrix material, and only 0.5% sodium pyrophosphate decahydrate (0.15g), 0.5% sodium carboxymethyl cellulose (0.15g), and 0.5% nano-alumina (0.15g) were added. The remaining steps were the same as in Example 1, and will not be repeated here.

[0052] Comparative Example 6 Unlike Example 1, 30g of sodium acetate trihydrate was used as the matrix material, and 6% sodium pyrophosphate decahydrate (1.8g), 6% sodium carboxymethyl cellulose (1.8g), and 6% nano-alumina (1.8g) were added. The remaining steps were the same as in Example 1, and will not be repeated here.

[0053] As can be seen from the comparison of Example 1 with Comparative Examples 5 and 6: When the addition amounts of sodium pyrophosphate decahydrate, sodium carboxymethyl cellulose, and nano-alumina are all 0.5%, the low addition amounts of each functional component mean that their nucleation regulation, structural stability, and thermal conductivity enhancement effects on the sodium acetate trihydrate system cannot be fully utilized. This results in an insufficient number of heterogeneous nucleation sites in the composite system, limited viscosity regulation, and inadequate thermal network construction, which is detrimental to uniform heat transfer and controlled crystallization within the droplets. Ultimately, the resulting spherical sodium acetate trihydrate composite phase change material cannot achieve the optimized effects of Example 1 in terms of undercooling suppression, structural stability, and overall thermal performance.

[0054] When the addition amounts of sodium pyrophosphate decahydrate, sodium carboxymethyl cellulose, and nano alumina are all increased to 6%, although the content of auxiliary components in the composite system increases, the excessively high addition ratio will significantly reduce the proportion of the effective phase change component of sodium acetate trihydrate in the material. At the same time, it will cause a significant increase in the viscosity of the system and an increase in the particle dispersion resistance, which is not conducive to the uniform mixing of the composite melt and the stable spherical formation in the microfluidic droplet process. It is easy to cause problems such as unstable droplet formation, uneven particle size distribution, and a decrease in phase change enthalpy, thereby affecting the overall performance of the final product.

[0055] Comparative Example 7 Unlike Example 1, step S1 uses a different order of adding materials: after sodium acetate trihydrate is completely melted, sodium carboxymethyl cellulose is added first. After it dissolves and initially thickens, nano-alumina is added and stirred for 20 minutes. Finally, sodium pyrophosphate decahydrate is added.

[0056] Compared with Example 1, it can be seen that the excessively high viscosity of the system due to the premature addition of the thickener made subsequent dispersion of nanoparticles difficult, leading to agglomeration and making it difficult to uniformly disperse the nucleating agent. As a result, the sample supercooling increased to approximately 8-10°C (far higher than the 1.3°C in Example 1), and due to the deterioration of the system's rheological properties, the microfluidic sphericity was poor, and the sphericity and particle size uniformity of the particles decreased significantly. This result directly demonstrates the crucial role of a specific feeding sequence in obtaining high-performance spherical materials.

[0057] Comparative Examples 8-10 Unlike Example 1, the drop acceleration rates in step S2 are 0.33 seconds / drop, 0.5 seconds / drop, and 2.5 seconds / drop, respectively. The remaining steps are the same as in Example 1 and will not be repeated here.

[0058] Example 1 was compared with Comparative Examples 8-10, as follows: Figure 4 As shown: when the drop acceleration rate is 0.33 seconds / drop or 0.5 seconds / drop, the droplets are prone to collision and adhesion, forming agglomerates and irregular particles, resulting in poor spherical quality; when the drop acceleration rate is 2.5 seconds / drop, the droplets are prone to deformation and uneven size, resulting in low production efficiency; when the drop acceleration rate is 1.5 seconds / drop, the droplets can fully form spherical particles and cool and solidify, obtaining high-quality spherical samples with high sphericity, uniform particle size, and no adhesion, which is the optimal process parameter.

[0059] Comparative Examples 11-14 Unlike Example 1, in step S2, four types of silicone oil with viscosities of 10 cSt, 20 cSt, 150 cSt and 200 cSt are selected respectively. The remaining steps are the same as in Example 1, and will not be repeated here.

[0060] Example 1 was compared with Comparative Examples 11-14, as follows: Figure 5 As shown: low-viscosity (≤20 cSt) silicone oil cannot provide sufficient spherical shaping force, easily leading to droplet breakage and particle deformation; high-viscosity (≥150 cSt) silicone oil has excessive viscous resistance, limiting droplet formation and causing particle distortion and agglomeration. None of the above four viscosities can produce high-quality spherical particles. However, when using 50 cSt silicone oil, droplets can be fully formed and solidified under the action of interfacial tension and suitable resistance, ultimately yielding high-quality spherical sodium acetate trihydrate composite phase change material with high sphericity, uniform particle size, and no adhesion, which was determined to be the optimal process parameter.

[0061] Comparative Examples 15-16 Unlike Example 1, diethyl ether and carbon tetrachloride were used as dispersion media instead of silicone oil, respectively. The remaining steps were the same as in Example 1, and will not be repeated here.

[0062] Example 1 was compared with Comparative Examples 15-16, as follows: Figure 6 As shown: Diethyl ether, due to its high volatility and poor interfacial compatibility, causes droplets to break directly and cannot form complete particles; carbon tetrachloride has insufficient interfacial stability, causing droplets to easily adhere, aggregate, and deform, making it impossible to obtain spherical samples. Neither of these solvents can meet the requirements for spherical formation, while the 50 cSt silicone oil used in this invention can achieve efficient and stable droplet spherical formation, making it the optimal dispersion solvent.

[0063] Comparative Example 17 Unlike Example 1, only pure sodium acetate trihydrate (SAT) is used in step S1 without adding any other components. The remaining steps are the same as in Example 1 and will not be repeated here.

[0064] Comparing Example 1, Comparative Examples 2-4, and Comparative Example 17, as follows: Figure 7As shown, pure SAT exhibits severe supercooling, with no obvious exothermic crystallization plateau in the cooling curve, and the supercooling degree exceeds 40℃. While the supercooling degree is reduced compared to pure SAT when only binary components are added, it remains at a high level: the supercooling degree is 9.1℃ for the system without nano-alumina, 8.7℃ for the system without CMC, and a sharp increase to 16.9℃ for the system without sodium pyrophosphate decahydrate, all failing to meet the requirements for low supercooling applications. Example 1 of this invention uses a ternary compound system of 1% sodium pyrophosphate decahydrate + 1% CMC + 1% nano-alumina, combined with microfluidic pelletizing technology. The cooling curve shows a clear exothermic crystallization plateau, and the supercooling degree is significantly reduced to 1.3℃, greatly improving the supercooling problem of SAT and verifying the excellent effect of multi-component synergistic regulation.

[0065] like Figure 9 As shown: Figure 9 (a) is a binary system of 1% sodium pyrophosphate decahydrate (SPP・10H2O) + 1% sodium carboxymethyl cellulose (CMC), with a phase transition enthalpy of 241.9 J / g, an initial phase transition temperature of 59.7℃, a symmetrical peak shape, and concentrated latent heat release. The synergistic effect of nucleating agent and stabilizer effectively improved the crystallization performance of pure SAT. Although the enthalpy was lower than the theoretical value of pure SAT (284 J / g) due to the addition of non-phase change components, it still maintained a high latent heat level. However, due to the lack of nano-alumina thermally conductive filler, the heat transfer efficiency was insufficient, and there is still room for improvement in enthalpy and overall performance. Figure 9 (b) is a binary system of 1% SPP・10H2O + 1% nano alumina (Al2O3NPs), with a phase transition enthalpy of 236.3 J / g and an initial phase transition temperature of 61.2℃. The addition of nano alumina enhances the heat transfer efficiency and promotes the completeness of crystallization, resulting in a significantly higher enthalpy than the system without nucleating agents. However, the addition of non-phase change components leads to an enthalpy lower than the theoretical value of pure SAT. Furthermore, due to the lack of grain boundary stabilization effect of CMC, the long-term thermal cycling stability of the material is insufficient. Figure 9 (c) is a binary system of 1% CMC + 1% Al2O3NPs. Due to the lack of core nucleating agent SPP・10H2O, the nucleation ability is insufficient, resulting in incomplete crystallization. The phase transition enthalpy value drops to 225.1 J / g, the phase transition temperature range shifts, and the latent heat release efficiency decreases significantly. It is the worst performing binary system. Figure 9 (d) is the blank control group of pure SAT. Its theoretical phase transition enthalpy is about 284 J / g. However, due to severe supercooling and crystallization lag, the actual effective phase transition enthalpy is much lower than the theoretical value. The crystallization is incomplete and the latent heat release is seriously insufficient, which directly confirms the key role of additives in improving the phase transition performance of SAT.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A microfluidic preparation method for a spherical sodium acetate trihydrate composite phase change material, characterized in that, Includes the following steps: S1. Mix and melt sodium acetate trihydrate, nucleating agent, thermally conductive filler and thickener to form a uniform composite melt; S2. The composite melt obtained in step S1 is added dropwise to the silicone oil medium through a microfluidic device. The droplets are formed into spheres in the silicone oil and complete the phase change solidification to obtain spherical wet particles. S3. The spherical wet particles obtained in step S2 are washed and dried to obtain the spherical sodium acetate trihydrate composite phase change material. In step S1, the amounts of the nucleating agent, thickener, and thermally conductive filler added are 1%-5% of the mass of sodium acetate trihydrate, respectively. In step S2, the drop acceleration rate of the microfluidic device is 1 second / drop to 2 seconds / drop; In step S2, the viscosity of the silicone oil medium is 50-100 cSt.

2. The preparation method according to claim 1, characterized in that, In step S1, the nucleating agent includes sodium pyrophosphate decahydrate, disodium hydrogen phosphate dodecahydrate, and nano-SiO2; the thickener includes sodium carboxymethyl cellulose, sodium polyacrylate, and polyvinyl alcohol; and the thermally conductive filler includes nano-alumina, aluminum nitride, and graphene.

3. The preparation method according to claim 1, characterized in that, In step S1, the order of adding materials is as follows: after sodium acetate trihydrate has completely melted, nucleating agent is added first, and after it melts, thermally conductive filler is added and dispersed evenly, and finally thickener is added.

4. The preparation method according to claim 1, characterized in that, In step S1, the mixing and melting are carried out under heating and stirring conditions, with the heating temperature being 75℃-80℃ and the stirring speed being 400 rpm-800 rpm.

5. The preparation method according to claim 1, characterized in that, The temperature of the silicone oil medium is 15℃-25℃.

6. The preparation method according to claim 1, characterized in that, In step S3, the spherical wet particles are washed with an organic solvent.

7. A spherical sodium acetate trihydrate composite phase change material, characterized in that, The spherical sodium acetate trihydrate composite phase change material is prepared by the preparation method according to any one of claims 1-6.

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