Silica gel-based composite phase change heat storage material and preparation method thereof

Abstract

This invention relates to the field of phase change thermal energy storage materials, and particularly to a composite phase change thermal energy storage material based on silica gel and its preparation method. The preparation method includes: mixing and stirring tetraethoxysilane, ethanol, and deionized water, and adding ammonia dropwise to form a homogeneous precursor solution; sealing and heating to obtain a silica nucleating agent; determining the nucleation site characterization value based on the transmittance and blue light intensity of the nucleating agent, and adjusting the ammonia dropwise acceleration rate for subsequent nucleating agent preparation accordingly; mixing and heating urea, erythritol, and deionized water, adding a dispersant, and then adding the nucleating agent dropwise, dynamically adjusting the stirring speed by real-time monitoring of the transmittance change rate to obtain a eutectic phase change solution; and finally drying and shaping. This invention significantly reduces material supercooling and improves thermal cycling stability through closed-loop control of nucleating agent activity characterization and dispersion process, solving the core problem of low nucleation efficiency in organic phase change thermal energy storage materials.

Description

Technical Field

[0001] This invention relates to the field of phase change thermal energy storage materials, and in particular to a composite phase change thermal energy storage material based on silica gel and its preparation method. Background Technology

[0002] Over the past 20 years, the development model of centralized heating systems in northern cities has undergone a significant transformation: from an extensive, incremental model relying on regionally built boiler rooms and experience-based adjustments, to a refined, unmanned, and improved model. Nevertheless, current energy consumption for heating in northern cities still reaches 217 million tons of standard coal, accounting for nearly a quarter of the nation's building operation energy consumption, making energy conservation and emission reduction in heating imperative. Therefore, promoting the widespread adoption of new energy and renewable clean energy in the centralized heating sector is essential. However, typical clean energy sources such as solar and wind power are limited by natural conditions, resulting in large fluctuations in output and making it difficult to match energy demand in real time. Large-scale energy storage is therefore necessary to "smooth out peak flows and fill valleys."

[0003] Traditional water tanks rely solely on the specific heat capacity of water for sensible heat storage. To obtain the same amount of heat, tens to hundreds of cubic meters of water are required, resulting in a large footprint, a corresponding increase in the heat dissipation area of ​​the insulation layer, and persistently high system heat loss. This is no longer sufficient to meet the demands of distributed, compact, and modular modern energy systems, necessitating higher energy density heat storage solutions. Phase change thermal storage materials utilize the latent heat of solid-liquid phase change, offering advantages such as reversible circulation, high energy density, small system size, and a narrow and constant operating temperature range. They can simultaneously reduce the heat dissipation area and insulation load, and can be flexibly embedded into the user side or heat source side in modular units, achieving high-density on-site heat storage and precise on-demand heat release, effectively overcoming the bottlenecks of traditional water tanks in terms of space, heat loss, and scalability.

[0004] Organic phase change materials (PCMs) possess high latent heat, capable of absorbing and releasing significant amounts of heat during solid-liquid phase transitions without phase separation, and their heat storage performance remains virtually unchanged after multiple cycles. Simultaneously, they exhibit outstanding chemical inertness, showing extremely low corrosivity to copper, aluminum, stainless steel, and commonly used polymer pipes, eliminating the need for linings or corrosion inhibitors, thus reducing initial system investment and maintenance costs. Erythritol is a typical example, with a melting point of approximately 118℃, a phase change enthalpy of approximately 310 kJ / kg, and high heat storage density, making it a candidate material for building heating and domestic hot water systems. However, its melting point is higher than the temperature of conventional centralized heating networks and its supercooling is significant, requiring the addition of nucleating agents to trigger crystallization and heat release; otherwise, the heat release temperature lags behind, making direct coupling with existing centralized heating systems difficult.

[0005] Chinese Patent Publication No. CN114561191A discloses a shaped phase change material for long-term energy storage across seasons, its preparation, and its application. This method uses erythritol as the heat storage unit and a cross-linked network of polyacrylamide and water-soluble phenolic resin as the supporting material to prepare the shaped phase change material for long-term energy storage across seasons. The shaped phase change material prepared by this method has advantages such as high latent heat of phase change, good energy storage stability, good thermal stability, simple operation, and low cost, making it easy to apply in solar thermal energy storage, waste heat recovery, and other fields. However, the shaped phase change material for long-term energy storage across seasons and its preparation and application have the following problems: its preparation process requires multiple organic synthesis steps and nitrogen protection, making the process complex and energy-intensive; simultaneously, although the cross-linked network suppresses supercooling, it sacrifices the phase change enthalpy, resulting in a final product phase change temperature as high as 97℃, which is unsuitable for medium- and low-temperature thermal storage scenarios, limiting its practical application. Summary of the Invention

[0006] Therefore, this invention provides a composite phase change thermal storage material based on silica gel and its preparation method, in order to overcome the problems of high supercooling and poor thermal cycling stability of existing low-temperature organic phase change thermal storage materials.

[0007] To achieve the above objectives, the present invention provides a composite phase change thermal storage material based on silica gel and a method for preparing the same, comprising:

[0008] Step S1: Tetraethoxysilane, anhydrous ethanol and deionized water are mixed and mechanically stirred at 25°C at the first stirring speed. During continuous stirring, ammonia water is added dropwise at a constant rate of the first drop acceleration to obtain a homogeneous precursor solution.

[0009] Step S2: Seal the homogeneous precursor liquid and heat it in a water bath to 50°C, then mechanically stir it at a first stirring speed to obtain a silica nucleating agent.

[0010] Step S3: Detect the silica nucleating agent to obtain nucleation site characterization values, which are determined based on the first transmittance of the nucleating agent and the blue light intensity.

[0011] Step S4: Determine whether the difference between the nucleation site characterization value and the ideal nucleation site characterization value is greater than a preset threshold. If the difference is greater than or equal to the preset threshold, adjust the first drop acceleration rate of ammonia in the subsequent preparation of silica nucleating agent.

[0012] Step S5: Weigh urea and erythritol, mix them, add deionized water, heat in a water bath to 40°C, and mechanically stir at the second stirring speed. During continuous stirring, add a dispersant and add the silica nucleating agent dropwise at a constant rate with a second drop acceleration rate to obtain an organic-organic eutectic phase change solution. The second drop acceleration rate is determined based on the nucleation site characterization value.

[0013] Step S6: The organic-organic eutectic phase change material solution is transferred to an electric heating oven and statically dried at 60°C to obtain the composite phase change thermal storage material.

[0014] Further, step S5 includes:

[0015] Step S51: Weigh urea and erythritol, mix them, add deionized water, and heat in a water bath to 40°C.

[0016] Step S52: Add dispersant, mechanically stir at the second basic stirring speed, and detect the rate of change of the system's transmittance.

[0017] Step S53: When the rate of change of transmittance is less than or equal to the threshold of influence of the dispersant, the silica nucleating agent is added dropwise at a constant rate of the second drop acceleration, and mechanical stirring is continued to obtain the organic-organic eutectic phase change solution.

[0018] Furthermore, in step S52, the basic second stirring speed is determined based on the nucleation site characterization value.

[0019] Further, step S53 includes:

[0020] Step S531: After the silica nucleating agent is added dropwise, the transmittance change rate of the system is continuously monitored. If the transmittance change rate is less than or equal to the transmittance change rate threshold, it is determined that the basic second stirring speed should be adjusted.

[0021] Step S532: Determine the basic stirring rate adjustment amount based on the difference between the transmittance change rate and the transmittance change rate threshold.

[0022] Step S533: Correct the basic stirring rate adjustment amount based on the nucleation site characterization value to obtain the corrected stirring rate adjustment amount;

[0023] Step S534: Adjust the basic second stirring speed according to the modified stirring rate adjustment amount to obtain a second stirring speed, and perform continuous mechanical stirring at the second stirring speed.

[0024] Furthermore, in step 53, the acceleration rate of the second drop is negatively correlated with the nucleation site characterization value.

[0025] Furthermore, in step S4, the adjustment amount of the first drop acceleration rate is positively correlated with the difference between the nucleation site characterization value and the ideal nucleation site characterization value.

[0026] Furthermore, the nucleation site characterization value is positively correlated with the first transmittance, and the nucleation site characterization value is negatively correlated with the blue light intensity.

[0027] Furthermore, the first stirring speed is 200 rpm to 300 rpm.

[0028] On the other hand, the present invention also provides a composite phase change thermal storage material based on silica gel, wherein the raw materials of the composite phase change thermal storage material, by weight, include:

[0029] Erythritol 50-60 parts, urea 40-50 parts, deionized water 1800-2200 parts, silica nucleating agent 12-24 parts, and dispersant 0.5 parts;

[0030] The silica nucleating agent is a silica gel with a solid content of 8% to 12%, which is prepared by mixing ethanol, tetraethoxysilane, deionized water and ammonia in a volume ratio of 30:5:1.12:0.32.

[0031] The dispersant is sodium alginate.

[0032] Furthermore, the phase change temperature of the composite phase change thermal storage material is 76℃~80℃, and the subcooling degree is 12℃~15℃.

[0033] Compared with existing technologies, the beneficial effects of this invention are that it effectively solves the key problems of high supercooling and poor thermal cycling stability caused by low nucleation efficiency in medium- and low-temperature organic phase change thermal storage materials by establishing a closed-loop control mechanism for the characterization and dispersion process of silica nucleating agents. Based on the dynamic optimization of the nucleating agent synthesis process using nucleation site characterization values, and combined with real-time feedback of transmittance to adjust the dispersion intensity of the eutectic system, uniform dispersion of nano-nucleating agents in the phase change matrix and maximum utilization of active sites are achieved. This significantly reduces material supercooling and improves long-term cycling reliability, making it suitable for phase change energy storage technologies in the fields of energy conservation and energy storage. Especially in centralized heating systems, it can achieve high-density on-site heat storage and precise on-demand heat release, effectively overcoming the bottlenecks of traditional water tanks in terms of space, heat loss, and expandability.

[0034] Furthermore, this invention quantifies the nucleation site characterization values ​​by coupling transmittance and blue light intensity, accurately reflecting the size distribution and surface activity state of silica nanoparticles. Based on these characterization values, the ammonia droplet acceleration rate is dynamically adjusted to effectively suppress excessive particle growth or aggregation during the nucleating agent preparation process, ensuring the acquisition of highly active, monodisperse nanonucleation templates.

[0035] Furthermore, this invention captures the evolution of the dispersion state during the addition of the nucleating agent by real-time monitoring of the transmittance change rate of the eutectic system. When the transmittance change rate is lower than a threshold, the stirring shear force is dynamically increased based on the activity characteristics of the nucleating agent to promptly disrupt the van der Waals forces between particles and avoid the failure of nucleation sites caused by local agglomeration.

[0036] Furthermore, this invention parametrically correlates the activity state of the nucleating agent with the dropping rate and stirring intensity. For highly active nanoparticles, the dropping rate is reduced while the shear force is increased; for less active particles, the dropping rate is moderately increased. This achieves a dynamic match between the nucleating agent introduction rate and the dispersion capability of the eutectic solution, avoiding irreversible aggregation caused by concentration gradients.

[0037] Furthermore, this invention maintains the monodisperse state of the nanonucleating agent in the phase change matrix, ensuring that the heterogeneous nucleation sites retain structural integrity during multiple solid-liquid phase change cycles. This effectively suppresses the attenuation of nucleation efficiency caused by nucleating agent agglomeration, coarsening, or interfacial detachment, significantly extending the material's lifespan.

[0038] Furthermore, the control mechanism described in this invention is based on online optical signal feedback, which eliminates the need for complex external equipment and can be directly embedded into existing phase change material production lines. Through the standardized mapping relationship between nucleation site characterization values ​​and process parameters, it is applicable to composite phase change material preparation systems of different compositions and scales. Attached Figure Description

[0039] Figure 1 This is a flowchart of the preparation method of the composite phase change thermal storage material based on silica gel according to the present invention;

[0040] Figure 2 This is a flowchart of step S5 in the preparation method of the composite phase change thermal storage material based on silica gel of the present invention;

[0041] Figure 3 This is a flowchart of step S53 of the preparation method of the composite phase change thermal storage material based on silica gel according to the present invention;

[0042] Figure 4 The DSC curve (a) of the erythritol / urea eutectic obtained in an embodiment of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention is shown.

[0043] Figure 5 The DSC curve (b) of the erythritol / urea eutectic obtained in an embodiment of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention is shown.

[0044] Figure 6The image shows the XRD pattern of the erythritol / urea eutectic obtained in an embodiment of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention.

[0045] Figure 7 This is a step cooling curve of the composite phase change thermal storage material prepared in an embodiment of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention.

[0046] Figure 8 This is a step cooling curve of the composite phase change thermal storage material prepared in an embodiment of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention after 20 high and low temperature cycles. Detailed Implementation

[0047] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0048] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0049] This invention provides a composite phase change thermal storage material based on silica gel. The raw materials of the composite phase change thermal storage material, by weight, include:

[0050] Erythritol 50-60 parts, urea 40-50 parts, deionized water 1800-2200 parts, silica nucleating agent 12-24 parts, and dispersant 0.5 parts;

[0051] The silica nucleating agent is a silica gel with a solid content of 8% to 12%, which is prepared by mixing ethanol, tetraethoxysilane, deionized water and ammonia in a volume ratio of 30:5:1.12:0.32.

[0052] Specifically, the dispersant is sodium alginate.

[0053] Specifically, the phase change temperature of the composite phase change thermal storage material is 76℃~80℃, and the subcooling degree is 12℃~15℃.

[0054] Please see Figure 1 The diagram shows a flowchart of the preparation method of the composite phase change thermal storage material based on silica gel according to the present invention; an embodiment of the present invention provides a preparation method of a composite phase change thermal storage material based on silica gel, comprising:

[0055] Step S1: Tetraethoxysilane, anhydrous ethanol and deionized water are mixed and mechanically stirred at 25°C at the first stirring speed. During continuous stirring, ammonia water is added dropwise at a constant rate of the first drop acceleration to obtain a homogeneous precursor solution.

[0056] Specifically, the first stirring speed is 200 rpm to 300 rpm.

[0057] In this embodiment of the invention, anhydrous ethanol, tetraethoxysilane, and deionized water were added to a reaction flask in a volume ratio of 30:5:1.12 and mixed. The mixture was mechanically stirred at 200 rpm to 300 rpm (i.e., the first stirring speed) at 25°C for 60 min. Ammonia was added dropwise at a constant rate of 0.32 under continuous stirring to form a homogeneous precursor solution. The volume ratio of ammonia was 0.32, and the first drop rate was 0.3 ml / min.

[0058] Step S2: Seal the homogeneous precursor liquid and heat it in a water bath to 50°C, then mechanically stir it at a first stirring speed to obtain a silica nucleating agent.

[0059] In this embodiment of the invention, the homogeneous precursor liquid obtained in step S1 is transferred to a stainless steel high-pressure reactor, with the liquid level ≤ 70% of the container volume (to allow for expansion space); a flange and a polytetrafluoroethylene gasket are used for sealing (bolts are tightened diagonally); the reaction flask is fixed to the water bath support so that the liquid level is completely submerged; the water bath is started and the temperature is increased to 50°C at a rate of 2°C / min to 5°C / min; the temperature is maintained at 50°C ± 0.5°C, and the mixture is continuously mechanically stirred at the first stirring speed (200 to 300 rpm) for 24 hours, finally yielding a silica nucleating agent that is nearly transparent and slightly bluish in appearance.

[0060] Understandably, sealing is to prevent the evaporation of anhydrous ethanol from causing an imbalance in the component ratio, and to prevent the leakage of ammonia water, which would cause the pH to drop and affect the rate of hydrolysis and condensation.

[0061] Step S3: Detect the silica nucleating agent to obtain nucleation site characterization values, which are determined based on the first transmittance of the nucleating agent and the blue light intensity.

[0062] Specifically, the nucleation site characterization value is positively correlated with the first transmittance, and the nucleation site characterization value is negatively correlated with the blue light intensity.

[0063] In this embodiment of the invention, an online transmittance sensor with a blue light source is used to simultaneously measure:

[0064] First transmittance T: the ratio of transmitted light intensity at a wavelength of 660nm (unit: %, accuracy: ±0.5%).

[0065] Blue light intensity B: Backscattered light intensity at 450nm wavelength (unit: mV, corresponding to μW / cm² after calibration).

[0066] The specific formula for calculating the nucleation site characterization value is as follows:

[0067] ,

[0068] Wherein, N is the nucleation site characterization value, dimensionless; T is the first transmittance, the unit is converted from a percentage to a decimal; B is the blue light intensity, the unit is mV; B0 is the reference scattering intensity, which is the scattering value of pure ethanol at 450nm, B0 is taken as 15mV; k is the blue light intensity normalization coefficient, the value range is 0.8 to 0.9, preferably, k is taken as 0.85.

[0069] Understandably, the core principle of nucleation site characterization is the application of light scattering theory to sol-gel systems. Transmittance directly reflects the dispersion state of silica nanoparticles: when particle size is small and uniformly distributed, light scattering weakens, and transmittance increases, indicating a high density and strong activity of nucleation sites. Blue light intensity, based on Rayleigh scattering, is proportional to particle diameter and is extremely sensitive to agglomerates. By coupling these two factors in calculation, this characterization value simultaneously captures two key characteristics of nucleating agents: the dispersion and size distribution of nanoparticles, thus quantitatively reflecting their effectiveness as heterogeneous nucleation templates. High nucleation site characterization values ​​correspond to small-particle-size, monodisperse, active nucleating agents, which can significantly reduce the supercooling of phase change materials; low nucleation site characterization values ​​indicate agglomeration or excessively large particle size, requiring adjustment of the ammonia droplet rate to optimize the process.

[0070] Step S4: Determine whether the difference between the nucleation site characterization value and the ideal nucleation site characterization value is greater than a preset threshold. If the difference is greater than or equal to the preset threshold, adjust the first drop acceleration rate of ammonia in the subsequent preparation of silica nucleating agent.

[0071] In this embodiment of the invention, the difference between the nucleation site characterization value and the ideal nucleation site characterization value is specifically as follows:

[0072] ,

[0073] Wherein, N0 is the ideal nucleation site characterization value, which is dimensionless. N0 is 0.8, which is the optimal value of the nucleation site characterization value, calibrated according to several historical experiments, which will not be elaborated here; ΔN is the difference between the nucleation site characterization value and the ideal nucleation site characterization value, which is dimensionless.

[0074] The specific judgment logic is as follows:

[0075] ,

[0076] Wherein, d is a preset threshold, which is 0.05 and is calibrated based on several historical experiments, which will not be elaborated here.

[0077] Specifically, in step S4, the adjustment amount of the first drop acceleration rate is positively correlated with the difference between the nucleation site characterization value and the ideal nucleation site characterization value.

[0078] In this embodiment of the invention, the formula for calculating the adjustment amount of the first drop acceleration rate is as follows:

[0079] ,

[0080] Wherein, Δr is the adjustment amount of the acceleration rate of the first drop, in ml / min; k1 is the adjustment coefficient of the acceleration rate of the first drop, with a value range of -1.6 ml / min to -1.4 ml / min, preferably -1.5 ml / min.

[0081] Specifically, the minimum value of the first drop acceleration rate is 0.2 ml / min, and the maximum value is 0.6 ml / min, to prevent the ammonia water from dripping too fast or too slow.

[0082] Understandably, a nucleation site characterization value greater than the ideal value indicates that the silica nanoparticles are too small or too dispersed. This is due to excessively rapid ammonia dripping, leading to vigorous hydrolysis and the generation of excessive nucleation centers. In this case, the dripping rate needs to be reduced to inhibit excessive nucleation. Conversely, when the characterization value is less than the ideal value, it indicates insufficient ammonia addition, causing particle growth to dominate and forming large aggregates. In this case, the dripping rate needs to be increased to promote nucleation. The adjustment coefficient k is negative to achieve this reverse control logic: when the characterization value is too high, the dripping rate is adjusted downwards; when it is too low, it is adjusted upwards.

[0083] Step S5: Weigh urea and erythritol, mix them, add deionized water, heat in a water bath to 40°C, and mechanically stir at the second stirring speed. During continuous stirring, add a dispersant and add the silica nucleating agent dropwise at a constant rate with a second drop acceleration rate to obtain an organic-organic eutectic phase change solution. The second drop acceleration rate is determined based on the nucleation site characterization value.

[0084] Please continue reading. Figure 2 and Figure 3 The flowcharts shown are respectively the flowcharts of step S5 and step S53 of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention.

[0085] Specifically, step S5 includes:

[0086] Step S51: Weigh urea and erythritol, mix them, add deionized water, and heat in a water bath to 40°C.

[0087] Step S52: Add dispersant, mechanically stir at the second basic stirring speed, and detect the rate of change of the system's transmittance.

[0088] Specifically, in step S52, the basic second stirring speed is determined based on the nucleation site characterization value.

[0089] In this embodiment of the invention, the calculation formula for the basic second stirring speed is specifically as follows:

[0090] ,

[0091] Among them, V 2b The second basic stirring speed is expressed in rpm; α is the basic speed constant, ranging from 180 rpm to 220 rpm, preferably 200 rpm; β is the speed adjustment coefficient, ranging from 200 rpm to 300 rpm, preferably 200 rpm.

[0092] It is understandable that the basic second stirring speed increases with the increase of the nucleation site characterization value, because a high nucleation site characterization value corresponds to a small particle size and a highly active nucleating agent, which requires a stronger fluid shear force to prevent agglomeration during subsequent drop addition.

[0093] Step S53: When the rate of change of transmittance is less than or equal to the threshold of influence of the dispersant, the silica nucleating agent is added dropwise at a constant rate of the second drop acceleration, and mechanical stirring is continued to obtain the organic-organic eutectic phase change solution.

[0094] In this embodiment of the invention, an online transmittance sensor (wavelength 660nm) is used to collect the transmittance data of the system every 1 minute, and the transmittance change rate is calculated; the transmittance change rate is denoted as u, and the unit is % / min.

[0095] In this embodiment of the invention, the influence threshold of the dispersant is 0.8% / min.

[0096] It is understandable that sodium alginate, a dispersant, is a white powder. When added to the system formed by urea and erythritol, it will cause changes in the transmittance of the system, interfering with the subsequent detection of transmittance change rate. When the transmittance change rate is less than or equal to the threshold of influence of the dispersant, it indicates that the system tends to be stable (sodium alginate molecules are fully dispersed in the system). Then, silica nucleating agent is added dropwise from the starting point to reduce the transmittance interference of the dispersant.

[0097] Specifically, in step 53, the acceleration rate of the second drop is negatively correlated with the nucleation site characterization value.

[0098] In this embodiment of the invention, the formula for calculating the acceleration rate of the second drop is as follows:

[0099] ,

[0100] Among them, R 2b Based on the second drop acceleration, the unit is ml / min, preferably, R 2b Take 1.2 ml / min; R2 is the acceleration rate of the second drop, in ml / min; m is the correction coefficient for the acceleration rate of the second drop, in ml / min, preferably m is 0.5 ml / min.

[0101] Understandably, the core of this step lies in coordinating the dynamic balance between nucleating agent activity and dispersion rate. A high nucleation site characterization value indicates small silica nanoparticle size, large specific surface area, and high surface energy; this highly active state makes them prone to aggregation during the dropping process. By reducing the dropping rate, the contact time between the particles and the eutectic solution is prolonged. Conversely, when the characterization value is low, the particles are larger and less active; appropriately increasing the dropping rate can prevent degradation of the eutectic components due to prolonged heat exposure. This dropping rate regulation based on nucleating activity essentially quantitatively correlates the microscopic interfacial behavior of the sol-gel with macroscopic process parameters, solving the problem of uncontrolled aggregation in highly active nanoparticle systems using traditional fixed dropping rate methods.

[0102] Specifically, step S53 includes:

[0103] Step S531: After the silica nucleating agent is added dropwise, the transmittance change rate of the system is continuously monitored. If the transmittance change rate is less than or equal to the transmittance change rate threshold, it is determined that the basic second stirring speed should be adjusted.

[0104] In this embodiment of the invention, the transmittance change rate threshold is 1.2% / min, which is based on several sets of pre-experiment calibrations. When u≤1.2% / min, it indicates that the nucleating agent dispersion is close to equilibrium, and the shear force needs to be enhanced to prevent aggregation.

[0105] Step S532: Determine the basic stirring rate adjustment amount based on the difference between the transmittance change rate and the transmittance change rate threshold.

[0106] In this embodiment of the invention, the calculation formula for the basic stirring rate adjustment is as follows:

[0107] ,

[0108] Where, ΔV 2bk1 is the basic stirring rate adjustment amount, in rpm; k2 is the adjustment sensitivity coefficient, in rpm·min / %, with a value range of 15 rpm·min / % to 25 rpm·min / %, preferably 20 rpm·min / %. The value range of the adjustment sensitivity coefficient k2 is calibrated through fluid dynamics simulation and emulsion stability experiments, and will not be elaborated here; u th The transmittance change rate threshold is set to 1.2% / min.

[0109] Step S533: Correct the basic stirring rate adjustment amount based on the nucleation site characterization value to obtain the corrected stirring rate adjustment amount;

[0110] In this embodiment of the invention, the calculation formula for the adjusted stirring rate is specifically as follows:

[0111] ,

[0112] Wherein, ΔV2 is the adjustment amount of the stirring rate, in rpm; γ is the correction coefficient of the stirring rate adjustment, dimensionless, with a value range of 0.3 to 0.5, preferably γ is 0.4.

[0113] Understandably, the essence of this correction mechanism is to couple the inherent characteristics of the nucleating agent with its real-time dispersion state. When N > N0, it indicates that the nucleating agent has a small particle size and a large specific surface area, requiring stronger shear force to suppress agglomeration caused by van der Waals forces, hence the adjustment amount is increased; when N < N0, the nucleating agent has a large particle size, so the adjustment amount is appropriately reduced to avoid excessive energy consumption.

[0114] Step S534: Adjust the basic second stirring speed according to the modified stirring rate adjustment amount to obtain a second stirring speed, and perform continuous mechanical stirring at the second stirring speed.

[0115] In this embodiment of the invention, the second stirring speed is the sum of the base second stirring speed and the adjustment amount of the modified stirring rate. Continuous mechanical stirring at the second stirring speed for 60 minutes yields an organic-organic eutectic phase change solution.

[0116] Understandably, the core principle of this implementation lies in establishing a closed-loop control mechanism of "optical signal-fluid dynamics-nucleation characteristics". The transmittance change rate directly reflects the dispersion kinetics of the silica nucleating agent in the eutectic solution. When the transmittance change rate is consistently below the threshold, it indicates that the Brownian motion of the particles is weakening and there is a tendency for aggregation. At this time, increasing the stirring speed to enhance the fluid shear force can break the adsorption energy barrier between particles. The correction based on the nucleation site characterization value is essentially introducing feedback from the intrinsic properties of the nucleating agent. High nucleation site characterization values ​​correspond to small-diameter, high-surface-energy particles, which are more prone to heterogeneous aggregation and require a more intense shear field; low nucleation site characterization values ​​have a lower tendency for particle aggregation, and excessive shearing leads to energy waste. This dynamic optimization ensures that the nano-nucleating agent remains monodisperse in the phase change matrix. The uniformly dispersed nucleation sites significantly reduce the crystallization energy barrier, significantly reduce the supercooling phenomenon, improve the immediacy of heat release, and the optimized interfacial bonding strength effectively resists thermal cycling stress, maintaining the stability of long-term nucleation efficiency, ultimately maximizing nucleation efficiency and minimizing supercooling.

[0117] Step S6: The organic-organic eutectic phase change material solution is transferred to an electric heating oven and statically dried at 60°C to obtain the composite phase change thermal storage material.

[0118] Example 1:

[0119] Ingredients: 90g erythritol, 10g urea, 2000ml deionized water, 200ml silica nucleating agent (10% solid content), 0.5g sodium alginate.

[0120] Preparation method:

[0121] 1. Preparation of silica nucleating agent:

[0122] Mix 300 ml of anhydrous ethanol, 50 ml of tetraethoxysilane, and 11.2 ml of deionized water, and stir at 250 rpm for 60 min at 25°C.

[0123] Add 3.2 ml of ammonia water dropwise at a rate of 0.3 ml / min to form a homogeneous precursor solution.

[0124] After sealing, the water bath temperature was raised to 50°C, and the mixture was stirred at 250 rpm for 24 hours to obtain a light blue silica gel.

[0125] The nucleation site characterization value N was detected and calculated to be 0.88; the dropping rate was adjusted to 0.2 ml / min for the next preparation of silica nucleating agent.

[0126] 2. Preparation of eutectic solution:

[0127] 60g erythritol, 40g urea, and 2000ml deionized water are heated in a 40℃ water bath.

[0128] Based on the nucleation site characterization value N=0.88, the basic second stirring speed was determined to be 216 rpm.

[0129] Add 0.5g of sodium alginate and stir at 216rpm until the transmittance change rate is ≤0.5% / min.

[0130] Based on the nucleation site characterization value N=0.88, the acceleration rate of the second drop was determined to be 1.16 ml / min;

[0131] The silica nucleating agent was added dropwise at a rate of 1.16 ml / min, and the second stirring speed was dynamically adjusted according to the rate of change in transmittance, with the final stirring speed being 224 rpm.

[0132] 3. Drying and shaping:

[0133] The composite phase change material was obtained by placing it in an electric heating oven and statically drying it at 60°C for 24 hours, and then grinding it.

[0134] Example 2

[0135] Erythritol 80g, urea 20g, the rest are exactly the same as in Example 1.

[0136] Example 3

[0137] Erythritol 70g, urea 30g, the rest are exactly the same as in Example 1.

[0138] Example 4

[0139] Erythritol 60g, urea 40g, the rest are exactly the same as in Example 1.

[0140] Example 5

[0141] Erythritol 50g, urea 50g, the rest are exactly the same as in Example 1.

[0142] Example 6

[0143] Erythritol 40g, urea 60g, the rest are exactly the same as in Example 1.

[0144] Example 7

[0145] Erythritol 30g, urea 70g, the rest are exactly the same as in Example 1.

[0146] Example 8

[0147] Erythritol 50g, urea 50g, the rest are exactly the same as in Example 5.

[0148] Example 9

[0149] 20 ml of silica nucleating agent, the rest is exactly the same as in Example 5.

[0150] Example 10

[0151] 15 ml of silica nucleating agent, the rest is exactly the same as in Example 5.

[0152] Example 11

[0153] 10 ml of silica nucleating agent, the rest is exactly the same as in Example 5.

[0154] Example 12

[0155] The rate of change in transmittance was not monitored when adding the silica nucleating agent. The stirring speed was kept constant at 200 rpm throughout the process, and everything else was exactly the same as in Example 9.

[0156] Example 13

[0157] The acceleration rate for the second drop was not adjusted based on the nucleation site characterization value and was fixed at 1.2 ml / min; otherwise, it was exactly the same as in Example 9.

[0158] Please see Figure 4 and Figure 5 As shown, these are DSC curves (a) and (b) of the erythritol / urea eutectic obtained in the examples of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention, respectively; specifically, they are the DSC test results of Examples 1 to 8, based on... Figure 4 and Figure 5 It can be seen that the melting peaks of the erythritol / urea organic-organic phase change thermal storage materials prepared in Examples 1 to 3 and Examples 6 to 8 all showed separation, indicating that erythritol and urea could not form a eutectic when their mass ratios were 90:10, 80:20, 70:30, 40:60, 30:70, and 20:80. In contrast, the erythritol / urea organic-organic eutectic phase change thermal storage materials in Examples 4 and 5 only showed a single melting peak. Therefore, 50% to 60% erythritol and 40% to 50% urea can form an organic-organic binary eutectic with a phase change temperature of 76°C to 80°C.

[0159] Please continue reading. Figure 6 As shown, it is the XRD pattern of the erythritol / urea eutectic obtained in an embodiment of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention; according to Figure 2The XRD test results show that the X-ray diffraction peaks of the prepared erythritol / urea organic-organic phase change thermal storage material are the same as those of the raw materials (erythritol and urea), and no other new peaks are generated. This confirms that the eutectic phase change material is a simple physical mixture between erythritol and urea, and no chemical reaction has occurred.

[0160] Please continue reading. Figure 7 and Figure 8 As shown, these are, respectively, the cooling curves of the composite phase change thermal storage material prepared in the embodiment of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention, and the cooling curves of the composite phase change thermal storage material prepared in the embodiment of the preparation method of the composite phase change thermal storage material based on silica gel of the present invention after 20 high and low temperature cycles. Figure 4 The cooling curves of composite phase change thermal storage materials with added silica gel nucleating agents of different volumes are shown.

[0161] from Figure 7 As can be seen, the supercooling of Example 9 is approximately 13°C, that of Example 10 is approximately 16°C, and that of Example 11 is approximately 22°C. Compared with the eutectic phase change material without nucleating agent, the supercooling of the composite phase change thermal storage material with 20 ml of silica gel as a nucleating agent is significantly reduced, decreasing by approximately 35°C. This indicates that the amount of silica gel nucleating agent added has a significant impact on the supercooling of the composite phase change material. Appropriately increasing the amount of nucleating agent can effectively reduce the supercooling, thereby improving the thermal performance of the material.

[0162] from Figure 8 As can be seen, after 20 cycles, the supercooling of the composite phase change thermal storage materials with different volumes of silica gel nucleating agents was approximately 23°C in Example 9, approximately 23°C in Example 10, and approximately 31°C in Example 11. Compared with before cycling, the increase in supercooling of each example was less than 10°C. This indicates that even after multiple cycles, the supercooling of the composite phase change material changed little, demonstrating good cycling stability.

[0163] Please refer to Table 1, which is a performance comparison table for Examples 12 and 13.

[0164] Table 1 Performance Comparison of Examples 12 and 13

[0165] Initial subcooling 13℃ 18℃ 16℃ Subcooling after 20 cycles 23℃ 28℃ 25℃ Phase transition temperature stability 78±0.5℃ 78±1.2℃ 78±0.8℃ Thermal cycle decay rate 0.087 0.154 0.125

[0166] As shown in Table 1, both Examples 12 and 13 exhibited a certain degree of performance degradation. It is understandable that this performance degradation stemmed from the lack of key process control steps, leading to a deterioration in the dispersion state of the nanonucleating agent. In Example 12, due to the absence of transmittance change rate monitoring, the real-time changes in the system's dispersion state during nucleating agent addition could not be captured. In particular, when the transmittance change rate fell below a threshold, the stirring speed was not increased in time, resulting in insufficient fluid shear force. This lack of shear force caused the high surface energy silica nanoparticles to locally agglomerate in the eutectic solution, forming excessively large agglomerates. This reduced the effective nucleation site density, decreased heterogeneous nucleation efficiency, and ultimately manifested as increased supercooling and greater fluctuations in phase transition temperature. In Example 13, although the stirring speed adjustment mechanism was maintained, the fixed dropping rate of 1.2 ml / min did not account for differences in the nucleating agent's active state (nucleation site characterization value N=0.82). For highly active nanoparticles (N > 0.8), excessively rapid dropping rates lead to an excessively high particle concentration introduced per unit time, exceeding the instantaneous dispersion capacity of the eutectic solution. This triggers a local concentration gradient, causing irreversible agglomeration of particles due to van der Waals forces before diffusion is complete. These agglomerates further coarsen during thermal cycling, reducing not only the initial nucleation efficiency but also accelerating performance degradation during cycling. Both failure modes demonstrate that transmittance feedback and synergistic regulation of nucleation activity are the core guarantees for achieving stable dispersion of nanonucleating agents; the absence of either link will disrupt the optimal balance between particle dispersion and nucleation efficiency.

[0167] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite phase change thermal storage material based on silica gel, characterized in that, include: Step S1: Tetraethoxysilane, anhydrous ethanol and deionized water are mixed and mechanically stirred at 25°C at the first stirring speed. During continuous stirring, ammonia water is added dropwise at a constant rate of the first drop acceleration to obtain a homogeneous precursor solution. Step S2: Seal the homogeneous precursor liquid and heat it in a water bath to 50°C, then mechanically stir it at a first stirring speed to obtain a silica nucleating agent. Step S3: Detect the silica nucleating agent to obtain nucleation site characterization values, which are determined based on the first transmittance of the nucleating agent and the blue light intensity. Step S4: Determine whether the difference between the nucleation site characterization value and the ideal nucleation site characterization value is greater than a preset threshold. If the difference is greater than or equal to the preset threshold, adjust the first drop acceleration rate of ammonia in the subsequent preparation of silica nucleating agent. Step S5: Weigh urea and erythritol, mix them, add deionized water, heat in a water bath to 40°C, and mechanically stir at the second stirring speed. During continuous stirring, add a dispersant and add the silica nucleating agent dropwise at a constant rate with a second drop acceleration rate to obtain an organic-organic eutectic phase change solution. The second drop acceleration rate is determined based on the nucleation site characterization value. Step S5 includes: Step S51: Weigh urea and erythritol, mix them, add deionized water, and heat in a water bath to 40°C. Step S52: Add dispersant, mechanically stir at the second basic stirring speed, and detect the rate of change of the system's transmittance. Step S53: When the transmittance change rate is less than or equal to the dispersant influence threshold, the silica nucleating agent is added dropwise at a constant rate with a second drop acceleration, and mechanical stirring is continued to obtain the organic-organic eutectic phase change solution. Step S53 includes: In step S531, after the silica nucleating agent is started to be added, the transmittance change rate of the system is continuously monitored. If the transmittance change rate is less than or equal to the transmittance change rate threshold, it is determined that the basic second stirring speed is adjusted. In step S52, the basic second stirring speed is determined based on the nucleation site characterization value. Step S532: Determine the basic stirring rate adjustment amount based on the difference between the transmittance change rate and the transmittance change rate threshold. Step S533: Correct the basic stirring rate adjustment amount based on the nucleation site characterization value to obtain the corrected stirring rate adjustment amount; Step S534: Adjust the basic second stirring speed according to the modified stirring rate adjustment amount to obtain the second stirring speed, and perform continuous mechanical stirring at the second stirring speed; The raw materials of the composite phase change thermal storage material, by weight, include: Erythritol 50-60 parts, urea 40-50 parts, deionized water 1800-2200 parts, silica nucleating agent 12-24 parts, and dispersant 0.5 parts; The silica nucleating agent is a silica gel with a solid content of 8% to 12%, which is prepared by mixing ethanol, tetraethoxysilane, deionized water and ammonia in a volume ratio of 30:5:1.12:0.

32. The dispersant is sodium alginate; Step S6: The organic-organic eutectic phase change material solution is transferred to an electric heating oven and statically dried at 60°C to obtain the composite phase change thermal storage material.

2. The preparation method of the composite phase change thermal storage material based on silica gel according to claim 1, characterized in that, In step 53, the acceleration rate of the second drop is negatively correlated with the nucleation site characterization value.

3. The preparation method of the composite phase change thermal storage material based on silica gel according to claim 1, characterized in that, In step S4, the adjustment amount of the first drop acceleration rate is positively correlated with the difference between the nucleation site characterization value and the ideal nucleation site characterization value.

4. The method for preparing composite phase change thermal storage material based on silica gel according to claim 1, characterized in that, The nucleation site characterization value is positively correlated with the first transmittance, and the nucleation site characterization value is negatively correlated with the blue light intensity.

5. The method for preparing composite phase change thermal storage material based on silica gel according to claim 1, characterized in that, The first stirring speed is 200 rpm to 300 rpm.

6. A composite phase change thermal storage material based on silica gel, manufactured using the preparation method of the composite phase change thermal storage material based on silica gel according to any one of claims 1-5, characterized in that, The raw materials of the composite phase change thermal storage material, by weight, include: Erythritol 50-60 parts, urea 40-50 parts, deionized water 1800-2200 parts, silica nucleating agent 12-24 parts, and dispersant 0.5 parts; The silica nucleating agent is a silica gel with a solid content of 8% to 12%, which is prepared by mixing ethanol, tetraethoxysilane, deionized water and ammonia in a volume ratio of 30:5:1.12:0.32, and the dispersant is sodium alginate. The phase change temperature of the composite phase change thermal storage material is 76℃~80℃, and the subcooling degree is 12℃~15℃.

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