A method for preparing composite phase change thermal storage material

Abstract

The present invention is applicable to the field of heat storage technology, and is a method for preparing a composite phase-change heat storage material: it comprises the following steps: mixing the phase-change material powder and the modified expanded graphite in a mass ratio of 7-7.5:1, and then heating, mixing, vacuum drying and briquetting to obtain a composite phase-change heat storage material block; wherein the method for preparing the modified expanded graphite comprises the following steps: (1) pretreatment; (2) mixing; (3) crushing and cooling; (4) filtration and drying. Beneficial effects: The present invention discloses a method for preparing a composite phase-change heat storage material, which has good dispersion stability and strong lipophilicity, effectively improves the thermal conductivity of the modified expanded graphite, and has excellent heat transfer, thermal stability and anti-leakage performance.

Description

Technical Field

[0001] The invention relates to the field of heat storage technology, and more specifically, to a method for preparing a composite phase-change heat storage material. Background Art

[0002] Solar radiation can be stored in the heat storage device through phase change thermal storage technology, i.e., phase change material (PCM), which undergoes phase change in the heat storage device, thus solving the intermittent and unstable problems of solar energy. In solar phase change energy storage materials, organic matter usually increases with the increase of carbon atom number, and the phase change latent heat and phase change temperature will increase. According to this principle, fatty acids often become one of the preferred materials for phase change thermal storage, as a typical solid-liquid organic PCM, which has stable physical and chemical properties and good solid formability. Compared with other organic PCMs, fatty acids and their derivatives have a unique eutectic effect. Melting and mixing different fatty acids to form a eutectic mixture can effectively reduce the phase change temperature of the mixture, thereby broadening the phase change temperature range of fatty acid PCMs. Among them, polyethylene glycol stearic acid (PGSA), soft fatty acid (SFA), lauric acid, capric acid, etc. are the most potential phase change thermal storage materials in fatty acids. Since the phase transition temperature of PGSA or SFA is relatively high, the preparation of binary or polybasic fatty acid eutectic mixtures through the eutectic effect can effectively solve the disadvantage of fixed phase transition temperature of single fatty acid and expand the phase transition temperature range of fatty acids to meet the needs of practical applications. However, the eutectic mixture is prone to liquid phase leakage and low thermal conductivity during phase change. Direct application of it in solar heating systems requires additional container packaging, which not only increases the thermal resistance of the system but also increases the application cost.

[0003] Therefore, application number 201110175057.1 discloses a composite phase-change thermal storage material with enhanced thermal conductivity and a preparation method thereof, which discloses that polyethylene glycol stearic acid and palmitic acid are mixed, heated to complete melting, and then stirred to form a eutectic mixture, and then the eutectic mixture is compounded with expanded graphite to improve the thermal conductivity and thermal stability of the thermal storage material; at the same time, application number 201410220101.X discloses a composite phase-change energy storage material and a preparation method thereof, which discloses that the material is compounded from a phase-change energy storage material and a supporting material; the phase-change energy storage material is formed by melting and mixing polyethylene glycol stearic acid and palmitic acid, and the supporting material is expanded graphite. The expanded graphite improves the thermal conductivity of the phase-change material on the one hand, and acts as a supporting material to shape and prevent leakage of the phase-change material on the other hand. Although expanded graphite (EG) is an ideal porous support material due to its high thermal conductivity and large pore volume, the mineralization degree of the EG surface is very high. It is neither a lipophilic substance nor a hydrophilic substance. Due to the strong intrinsic van der Waals attraction between the sheets and its high specific surface area, it is difficult for EG to be stably dispersed in the above-mentioned mixed organic phase change material of polyethylene glycol stearic acid and palmitic acid. Therefore, the thermal conductivity and thermal stability of the composite phase change thermal storage material disclosed in the above-mentioned document have certain limitations, so its surface must be modified to solve the compatibility problem between EG and other components. Summary of the invention

[0004] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for preparing a composite phase change thermal storage material which has improved thermal conductivity of modified expanded graphite and has excellent heat transfer, thermal stability and anti-leakage performance.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a composite phase-change thermal storage material, comprising the following steps: mixing phase-change material powder and modified expanded graphite uniformly at a mass ratio of 7-7.5:1, and then heating, mixing, vacuum drying and briquetting to obtain a composite phase-change thermal storage material block;

[0006] Wherein, the preparation method of the modified expanded graphite comprises the following steps:

[0007] (1) Pretreatment: Place the expanded graphite powder in a vacuum drying oven at 80-90°C and dry for 12-15 hours; then place it in a furnace at 800-900°C and bake it for 50-60 seconds to obtain pretreated expanded graphite;

[0008] (2) Mixing: placing the expanded graphite in step (1) in a 0.02 mol / L tetradecanoic acid ethanol (TAE) solution, wherein the mass ratio of the expanded graphite to the tetradecanoic acid ethanol solution is 1-1.5:7.5; then stirring for 18.5-20 min at a temperature of 48.2-50.3° C. to obtain a mixture;

[0009] (3) Crushing and cooling: placing the mixture in step (2) in an environment at a temperature of 38.5-40° C. for ultrasonic crushing for 5.8-6.2 h, and then stirring and cooling the mixture to room temperature;

[0010] (4) Filtration and drying: The mixture cooled to room temperature in step (3) is filtered, and the filtered solid is dried to obtain modified expanded graphite with a particle size of 60-80 μm.

[0011] Furthermore, the stirring speed in step (2) is 850-900 r / min.

[0012] Furthermore, the ultrasonic power in step (3) is 120-150W.

[0013] Furthermore, the drying conditions in step (4) are a drying temperature of 75-82° C. and a drying time of 10-10.5 h.

[0014] Furthermore, the preparation method of the phase change material powder includes the following steps: according to the weight fraction, 70-76 parts of polyethylene glycol stearate and 13-16 parts of palmitic acid are stirred for 8-8.5 hours in a water bath at a temperature of 80-84°C to mix them evenly, wherein the stirring speed is 875-900r / min, and then naturally cooled to room temperature to solidify, and finally ground into a powder with a particle size of 130-150μm, and sealed for storage.

[0015] Furthermore, the preparation method of the phase change material powder also includes the following steps: according to the weight fraction, 10-12 parts of magnesium oxide, 70-76 parts of polyethylene glycol stearate and 13-16 parts of palmitic acid are heated in a water bath at a temperature of 78-82°C, stirred for 7.5-8h to mix them evenly, wherein the stirring speed is 875-925r / min, then naturally cooled to room temperature to solidify, and finally ground into a powder with a particle size of 220-280μm, and sealed for storage.

[0016] Furthermore, the heating and mixing is specifically as follows: placing the uniformly mixed materials in a water bath heating environment at a temperature of 80-85° C. and stirring once every 1 hour for 9.5-10 hours to obtain a mixed material.

[0017] Furthermore, each stirring time is 5-8 minutes, and the stirring speed is 800-850 r / min.

[0018] Furthermore, the mixed material is placed in a vacuum drying oven, heated and dried for 15-15.5 hours at a temperature of 80-85° C. and a vacuum degree of 8106-12159 Pa, and then naturally cooled to room temperature to obtain a composite phase change thermal storage material.

[0019] Furthermore, the briquetting is specifically: the composite phase change thermal storage material is briquetting at 8.5-9.2Mpa using a tablet press to obtain a density of 790-812kg / m 3 The composite phase change thermal storage material block.

[0020] The advantages of the present invention are:

[0021] 1. The present invention discloses a method for preparing a composite phase-change thermal storage material, wherein the original worm-like structure is destroyed by surface modification and ultrasonic crushing of expanded graphite, and the lamellar graphite is broken up, so that its particle size tends to be micron-level, thereby reducing the strong van der Waals attraction between the original expanded graphite lamellar layers, making it easier to disperse in the organic phase change material, with good dispersion stability and strong lipophilicity; at the same time, the tetradecanoic acid molecular group is uniformly attached to the lamellar structure of the modified expanded graphite by physical adsorption, which effectively improves the thermal conductivity of the modified expanded graphite.

[0022] 2. The present invention discloses a method for preparing a composite phase change thermal storage material, which uses modified expanded graphite as a matrix, adsorbs phase change material powder, and finally forms a block with a density of 790-812 kg / m 3 The composite phase change thermal storage material block has excellent heat transfer, thermal stability and anti-leakage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a flow chart of preparing phase change material powder in Example 1 of the present invention.

[0024] Figure 2 This is a flow chart of preparing modified expanded graphite in Example 1 of the present invention.

[0025] Figure 3 This is a flow chart of preparing a composite phase-change thermal storage material block according to Example 1 of the present invention.

[0026] Figure 4 These are actual photos of pretreated expanded graphite (EG) and modified expanded graphite (CEG).

[0027] Figure 5 Contact diagrams of EG and CEG sheets with water and oil, respectively.

[0028] Figure 6 This is the XRD pattern of modified expanded graphite.

[0029] Figure 7 This is the FT-IR graph of modified expanded graphite.

[0030] Figure 8 These are appearance photos of composite phase change thermal storage material blocks of different densities after 50 cycles of heat storage and release.

[0031] Fig. 9 This is a SEM scanning electron microscope image.

[0032] Fig.10 It is a heat storage and release curve.

[0033] Fig.11 Thermogravimetric curve. DETAILED DESCRIPTION

[0034] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0035] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs.

[0036] In the present invention, unless otherwise specified, the directions used, such as "up" and "down", usually refer to the directions shown in the drawings, or to the vertical, perpendicular or gravity directions; similarly, for ease of understanding and description, "left" and "right" usually refer to the left and right shown in the drawings; "inside" and "outside" refer to the inside and outside relative to the outline of each component itself, but the above-mentioned directions are not used to limit the present invention.

[0037] Embodiment 1: A method for preparing a composite phase change thermal storage material, comprising the following steps:

[0038] like Figure 1 As shown, the preparation method of phase change material powder includes the following steps: 105g magnesium oxide (MgO), 700g polyethylene glycol stearate (PGSA) and 130g palmitic acid (SFA) are stirred for 8h in a water bath at 80°C to mix them evenly, wherein the stirring speed is 900r / min, then naturally cooled to room temperature to solidify, and finally ground into powder with a particle size of 220-280μm, and sealed for storage.

[0039] like Figure 2 As shown, the preparation method of modified expanded graphite comprises the following steps:

[0040] (1) Pretreatment: Place the expanded graphite powder in a vacuum drying oven at 80-82°C for 12 hours; then place it in a furnace at 800°C for calcination and expansion for 50-52 seconds to obtain pretreated expanded graphite (EG);

[0041] (2) Mixing: placing 100 g of the expanded graphite in step (1) in 750 g of a 0.02 mol / L tetradecanoic acid ethanol (TAE) solution; stirring the mixture at a temperature of 50° C. for 20 min at a stirring speed of 870 r / min to obtain a mixture;

[0042] (3) Crushing and cooling: placing the mixture in step (2) in an environment at a temperature of 40° C. and subjecting it to ultrasonic crushing for 6 h, wherein the ultrasonic power is 130 W, and then stirring the mixture and cooling it to room temperature;

[0043] (4) Filtration and drying: The mixture cooled to room temperature in step (3) is filtered, and the filtered solid is dried at a drying temperature of 80° C. for 10 h to obtain modified expanded graphite (CEG) with a particle size of 60-80 μm.

[0044] like Figure 3 As shown, the preparation method of the composite phase change thermal storage material block (PCM) includes the following steps: 100g of the above phase change material powder and 14.3g of the above modified expanded graphite are stirred and mixed evenly, and then the mixed materials are placed in a water bath heating environment at a temperature of 80°C and stirred once every 1h, wherein each stirring time is 6min, the stirring speed is 830r / min, and the stirring time is 9.7h to obtain a mixed material; then the mixed material is placed in a vacuum drying oven, heated and dried at a temperature of 83°C and a vacuum degree of 10050Pa for 15.3h, and then naturally cooled to room temperature to obtain a composite phase change thermal storage material; finally, the composite phase change thermal storage material is pressed into a block at 8.5-9.2Mpa using a tablet press to obtain a density of 790-812kg / m 3 The composite phase change thermal storage material block.

[0045] The actual photos of pre-treated expanded graphite (EG) and modified expanded graphite (CEG) are shown in Figure 4 The dispersibility of modified expanded graphite (CEG) is better than that of pretreated expanded graphite (EG); and the wettability of pretreated expanded graphite (EG) and modified expanded graphite (CEG) is studied by compressing EG and CEG into sheets with a diameter of 10 mm and a height of 1 mm under a pressure of 7 MPa, and then testing the contact angles of EG and CEG sheets with water and oil (OA), such as Figure 5 As shown, from Figure 5 (a) and Figure 5As can be seen from (b), the contact angle between EG and water is 62.8°, while the contact angle between CEG and water is 116.4°, indicating that the hydrophobicity of CEG has been improved. Figure 5 (c) and Figure 5 As can be seen from (d), the contact angle between EG and OA is 46.8°, while the contact angle between CEG and OA is about 1°, which indicates that the lipophilicity of CEG has been significantly improved. Obviously, the hydrophobicity and lipophilicity of CEG have been significantly improved, and the phase separation phenomenon of PCM after synthesis has been reduced. In this embodiment, the surface of expanded graphite (EG) is modified and ultrasonically crushed to destroy the original worm-like microstructure, break the lamellar structure, make the particles tend to micronized, improve its dispersibility, and make it easier to disperse in organic solvents.

[0046] The modified expanded graphite (CEG) was tested by XRD and FT-IR spectra. The test results show that: Figure 6 As shown in the figure, the main characteristic diffraction peaks of TAE are located at 2θ=21.3º and 2θ=24.2º. The characteristic diffraction peaks of TAE were also detected in CEG, although the TAE adsorbed on the CEG surface was relatively less in mass, so the characteristic peaks were not obvious, and no new diffraction peaks were found. This shows that CEG is formed by physical adsorption of TAE without involving chemical reaction. Figure 7 As shown in Figure 2, it can be observed that CEG and TAE have similar infrared absorption characteristics; the main characteristic peak is located at 2916 cm -1 、2847cm -1 、1697cm -1 and 1473cm -1 At, respectively represent-CH3 and-CH2 functional group stretching vibration, C=O stretching vibration and-CH2 bending vibration. These peak positions correspond to each other, but the relative intensity is different, and no new absorption peak appears, indicating that TAE is physically adsorbed on the CEG sheet, and no chemical reaction occurs during the modification process. And then show that the tetradecanoic acid molecular group of the present embodiment is uniformly attached to the lamellar structure of the modified expanded graphite in the form of physical adsorption, effectively improving the thermal conductivity of the modified expanded graphite.

[0047] Embodiment 2: A method for preparing a composite phase change thermal storage material, comprising the following steps:

[0048] The preparation method of phase change material powder includes the following steps: 110g of magnesium oxide, 720g of polyethylene glycol stearate and 140g of palmitic acid are stirred for 7.5h in a water bath at 78°C to mix them evenly, wherein the stirring speed is 875r / min, then naturally cooled to room temperature to solidify, and finally ground into powder with a particle size of 220-280μm and sealed for storage.

[0049] The preparation method of modified expanded graphite comprises the following steps:

[0050] (1) Pretreatment: Place the expanded graphite powder in a vacuum drying oven at 82-84°C and dry for 13 hours; then place it in a furnace at 820°C for calcination and expansion for 53 seconds to obtain pretreated expanded graphite;

[0051] (2) Mixing: placing 115 g of the expanded graphite in step (1) in 750 g of a 0.02 mol / L tetradecanoic acid ethanol solution; stirring the mixture for 18.5 min at a temperature of 48.2° C. and a stirring speed of 850 r / min to obtain a mixture;

[0052] (3) Crushing and cooling: placing the mixture in step (2) in an environment at a temperature of 38.5° C. and subjecting it to ultrasonic crushing for 6.2 h, wherein the ultrasonic power is 120 W, and then stirring the mixture and cooling it to room temperature;

[0053] (4) Filtration and drying: The mixture cooled to room temperature in step (3) is filtered, and the filtered solid is dried at a drying temperature of 75° C. for 10.5 h to obtain modified expanded graphite with a particle size of 60-80 μm.

[0054] The preparation method of the composite phase change thermal storage material block comprises the following steps: 100g of the above phase change material powder and 13.9g of the above modified expanded graphite are stirred and mixed evenly, and then the mixed materials are placed in a water bath heating environment at a temperature of 85°C and stirred once every 1h, wherein each stirring time is 5min, the stirring speed is 850r / min, and the stirring time is continued for 9.5h to obtain a mixed material; then the mixed material is placed in a vacuum drying oven, heated and dried at a temperature of 80°C and a vacuum degree of 8106Pa for 15.5h, and then naturally cooled to room temperature to obtain a composite phase change thermal storage material; finally, the composite phase change thermal storage material is pressed into a block at 8.5-9.2Mpa using a tablet press to obtain a density of 790-812kg / m 3 The composite phase change thermal storage material block.

[0055] Embodiment 3: A method for preparing a composite phase change thermal storage material, comprising the following steps:

[0056] The preparation method of phase change material powder includes the following steps: 115g of magnesium oxide, 740g of polyethylene glycol stearate and 150g of palmitic acid are stirred for 7.8h in a water bath at 82°C to mix them evenly, wherein the stirring speed is 925r / min, and then naturally cooled to room temperature to solidify, and finally ground into powder with a particle size of 220-280μm and sealed for storage.

[0057] The preparation method of modified expanded graphite comprises the following steps:

[0058] (1) Pretreatment: Place the expanded graphite powder in a vacuum drying oven at 85-87°C and dry for 14 hours; then place it in a furnace at 840°C for calcination and expansion for 55 seconds to obtain pretreated expanded graphite;

[0059] (2) Mixing: placing 130 g of the expanded graphite in step (1) in 750 g of a 0.02 mol / L tetradecanoic acid ethanol solution; stirring the mixture at a temperature of 50.3° C. for 19 min at a stirring speed of 900 r / min to obtain a mixture;

[0060] (3) Crushing and cooling: placing the mixture in step (2) in an environment at a temperature of 39° C. and subjecting it to ultrasonic crushing for 5.8 h, wherein the ultrasonic power is 150 W, and then stirring the mixture and cooling it to room temperature;

[0061] (4) Filtration and drying: The mixture cooled to room temperature in step (3) is filtered, and the filtered solid is dried at a drying temperature of 82° C. and a drying time of 10.2 h to obtain modified expanded graphite with a particle size of 60-80 μm.

[0062] The preparation method of the composite phase change thermal storage material block comprises the following steps: 100g of the above-mentioned phase change material powder and 13.6g of the above-mentioned modified expanded graphite are stirred and mixed evenly, and then the mixed materials are placed in a water bath heating environment at a temperature of 80°C and stirred once every 1h, wherein each stirring time is 8min, the stirring speed is 800r / min, and the stirring time is continued for 10h to obtain a mixed material; then the mixed material is placed in a vacuum drying oven, heated and dried for 15h at a temperature of 80°C and a vacuum degree of 12159Pa, and then naturally cooled to room temperature to obtain a composite phase change thermal storage material; finally, the composite phase change thermal storage material is pressed into a block at 8.5-9.2Mpa using a tablet press to obtain a density of 790-812kg / m 3 The composite phase change thermal storage material block.

[0063] Example 4: The overall method is the same as that of Example 1, except that the preparation method of phase change material powder includes the following steps: 760g of polyethylene glycol stearate and 160g of palmitic acid are stirred for 8h in a water bath at 80°C to mix them evenly, wherein the stirring speed is 900r / min, and then naturally cooled to room temperature to solidify, and finally ground into powder with a particle size of 130-150μm and sealed for storage.

[0064] Comparative Example 1: The overall method is the same as that of Example 1, except that only the pretreatment in step (1) is performed, and the pretreated expanded graphite obtained in step (1) is directly mixed with the phase change material powder.

[0065] Experiment 1:

[0066] The thermal stability test was conducted on 10 composite phase change thermal storage material blocks prepared in Example 1 with different densities (specific densities are shown in Table 1), that is, the composite phase change thermal storage material blocks prepared in Example 1 with different densities were placed in a water bath and heated from 20 to 80° C. When the temperature reached 80° C., the water bath was controlled to cool down, and the water bath program was set to automatically store and release heat 50 times in a cycle, and then photographed to obtain appearance photos of 10 composite phase change thermal storage material blocks with different densities, as shown in FIG. Figure 8 shown.

[0067] Table 1 Density values ​​of composite phase change thermal storage material blocks

[0068]

[0069] from Figure 8 It can be seen that the density is 534kg / m 3 Up to 781kg / m 3 Cracks appeared in the composite phase change thermal storage material blocks within the range, and the degree of cracks decreased with the increase of block density. This is because when the block density is low, the bonding force between the materials is weak, resulting in thermal expansion and contraction during the solid-liquid conversion of PCM. When the block density exceeds 821kg / m 3 When the density of the briquette was 790kg / m 3 Up to 812kg / m 3 When the composite phase change thermal storage material block is basically unchanged, the density of the block formed after pressing is 790-812kg / m 3 The composite phase change thermal storage material block has excellent thermal stability and anti-leakage performance.

[0070] Experiment 2: The composite phase-change thermal storage material blocks prepared in Example 1 and Comparative Example 1 were subjected to DSC testing by differential scanning calorimetry (DSC), wherein the temperature parameter range of the DSC equipment was set to 20-80°C, and the results are shown in Table 2. As can be seen from Table 2, the thermal conductivity of the MgO-PGSA-SFA / CEG prepared in Example 1 reached 8.93W / (m∙K), which is 35.5 times that of the MgO-PGSA-SFA / EG prepared in Comparative Example 1. It is obvious that the composite phase-change thermal storage material block prepared in Example 1 of the present invention has better heat transfer performance. The thermal diffusivity of the MgO-PGSA-SFA / CEG prepared in Example 1 is 26.5 times that of the MgO-PGSA-SFA / EG prepared in Comparative Example 1, and the thermal storage coefficient of the MgO-PGSA-SFA / CEG prepared in Example 1 is 5 times that of the MgO-PGSA-SFA / EG prepared in Comparative Example 1, indicating that the thermal stability of the composite phase-change thermal storage material block prepared in Example 1 of the present invention has been significantly improved.

[0071] Table 2 Comprehensive thermal coefficients of MgO-PGSA-SFA / EG and MgO-PGSA-SFA / CEG

[0072]

[0073] Experiment 3: The microstructures of EG in Comparative Example 1, MgO-PGSA-SFA / EG in Comparative Example 1, CEG in Example 1, and MgO-PGSA-SFA / CEG in Example 1 were observed by scanning electron microscopy (SEM). Fig. 9 ,in Fig. 9 (a) is the SEM image of EG. Fig. 9 (b) is the SEM image of MgO-PGSA-SFA / EG. Fig. 9 (c) is the SEM image of MgO-PGSA-SFA / CEG. Fig. 9 (d) is the SEM image of CEG. Fig. 9 (a) It can be observed that the EG surface presents crack-like pore structure and micrometer-scale honeycomb pore structure. Fig. 9 (b) It can be seen that MgO-PGSA-SFA is uniformly adsorbed in the crack-like and honeycomb-like pore structures of EG. Fig. 9 (c) shows that its structure is clearly layered, and MgO-PGSA-SFA is evenly attached to the CEG layer, increasing the contact area between MgO-PGSA-SFA and CEG, thereby further improving the thermal conductivity of MgO-PGSA-SFA / CEG. Fig. 9(d) It can be seen that the modified CEG breaks the crack pore lamellar structure. From the enlarged image, it can be seen that the degree of pore dispersion is significantly weakened. This result can significantly improve the fusion and polymerization of CEG in MgO-PGSA-SFA.

[0074] Experiment 4: The composite phase-change thermal storage material blocks prepared in Example 1 and Comparative Example 1 were subjected to heat storage and heat release tests. Temperature sensing probes were placed in the centers of the two composite phase-change thermal storage material blocks, and the temperature change curves during the heat storage and release process were collected by a data acquisition instrument. First, the two composite phase-change thermal storage material blocks were placed in a water bath with an initial temperature of 20°C at the same time. When the probe temperatures were both 20°C, the water bath began to heat up until the heating stopped at 80°C, and the heat storage curves of the two composite phase-change thermal storage material blocks were collected. When the probe temperature stabilized at 80°C, the water bath began to cool down until it stopped at 20°C, and the heat storage and release curves of the two composite phase-change thermal storage material blocks were recorded. The test results are as follows: Fig.10 As shown, Fig.10 (a) is the heat storage temperature curve, Fig.10 (b) is the exothermic temperature curve; Fig.10 (a) It can be seen that it takes 1185s for MgO-PGSA-SFA / EG to complete the entire thermal storage process, while MgO-PGSA-SFA / CEG only takes 485s, and the thermal storage efficiency is increased by 144%. Fig.10 (b) It can be observed that the heat release process of MgO-PGSA-SFA / EG takes 3080s, while that of MgO-PGSA-SFA / CEG only takes 710s, and the heat release efficiency is increased by 334%. These results show that the composite phase change thermal storage material block prepared in Example 1 of the present invention has excellent heat storage / release characteristics.

[0075] Experiment 5: The composite phase change thermal storage material blocks prepared in Example 1 and Comparative Example 1 were placed in a water bath and heated from 20 to 80°C. When the temperature reached 80°C, the water bath was controlled to cool down. After setting the water bath program, 0, 200, 400, 600, 800 and 1000 cycles of thermal storage were performed. Then, the material blocks after thermal storage were subjected to DSC tests. The specific test results are shown in Tables 3 and 4. It can be seen from Tables 3 and 4 that the melting temperature of MgO-PGSA-SFA / CEG after 1000 cycles of thermal storage was only reduced by 0.03 compared with the melting temperature of MgO-PGSA-SFA / CEG after 0 cycles. ℃, the latent heat of melting only decreased by 3J / g, the solidification temperature only decreased by 0.03℃, and the latent heat of solidification only decreased by 2.85J / g; and the melting temperature of MgO-PGSA-SFA / EG after 1000 cycles of heat storage and release was 4.03℃ lower than that of MgO-PGSA-SFA / EG with 0 cycles, the latent heat of melting decreased by 6J / g, the solidification temperature decreased by 3.49℃, and the latent heat of solidification decreased by 6J / g; compared with MgO-PGSA-SFA / EG, the phase change temperature and latent heat of phase change of MgO-PGSA-SFA / CEG remained almost unchanged after 1000 cycles of heat storage and release, and it has good thermal stability.

[0076] Table 3 Thermal properties of MgO-PGSA-SFA / CEG prepared in Example 1 at different cycle times

[0077]

[0078] Table 4 Thermal properties of MgO-PGSA-SFA / EG prepared in Comparative Example 1 at different cycle times

[0079]

[0080] In addition, the MgO-PGSA-SFA / EG prepared in Comparative Example 1 and the MgO-PGSA-SFA / CEG prepared in Example 1 after 1000 thermal cycles were subjected to thermogravimetric testing by a thermogravimetric analyzer (TGA) device, wherein nitrogen was used as the atmosphere to avoid experimental errors due to oxidation; the temperature range was set to 0-500°C and the heating rate was 10°C / min, and the results were as follows: Fig.11 ;like Fig.11As shown, the mass of the two materials hardly changes with increasing temperature in the range of 0-145℃. In the range of 145-212℃, the mass begins to decrease gently with increasing temperature. When the temperature reaches 212-271℃, the mass drops precipitously with increasing temperature. However, the lower limit of the mass of MgO-PGSA-SFA / CEG is improved compared with that of MgO-PGSA-SFA / EG, and the rate of decrease is slow. In the range of 271-500℃, the mass hardly decreases with increasing temperature and reaches a steady-state zone. This proves that the thermal decomposition stability of MgO-PGSA-SFA / CEG in the range of 145-271℃ is improved compared with MgO-PGSA-SFA / EG.

[0081] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a composite phase change thermal storage material, characterized in that: It includes the following steps: The phase change material powder and the modified expanded graphite are stirred and mixed evenly in a mass ratio of 7-7.5:1, and then heated, mixed, vacuum dried and pressed into blocks to obtain a composite phase change thermal storage material block; Wherein, the preparation method of the modified expanded graphite comprises the following steps: (1) Pretreatment: Place the expanded graphite powder in a vacuum drying oven at 80-90°C and dry for 12-15 hours; then place it in a furnace at 800-900°C and bake it for 50-60 seconds to obtain pretreated expanded graphite; (2) Mixing: placing the expanded graphite in step (1) in a 0.02 mol / L tetradecanoic acid ethanol solution, wherein the mass ratio of the expanded graphite to the tetradecanoic acid ethanol solution is 1-1.5:7.5; then stirring at a temperature of 48.2-50.3° C. for 18.5-20 min to obtain a mixture; (3) Crushing and cooling: placing the mixture in step (2) in an environment at a temperature of 38.5-40° C. for ultrasonic crushing for 5.8-6.2 h, and then stirring and cooling the mixture to room temperature; (4) Filtration and drying: Filtration is performed on the mixture cooled to room temperature in step (3), and the filtered solid is dried to obtain modified expanded graphite with a particle size of 60-80 μm; The preparation method of the phase change material powder comprises the following steps: according to the weight fraction, 70-76 parts of polyethylene glycol stearate and 13-16 parts of palmitic acid are stirred for 8-8.5 hours in a water bath at a temperature of 80-84° C. to make them uniformly mixed, wherein the stirring speed is 875-900 r / min, then naturally cooled to room temperature to solidify, and finally ground into powder with a particle size of 130-150 μm, and sealed for storage; Alternatively, the preparation method of the phase change material powder comprises the following steps: according to weight fractions, 10-12 parts of magnesium oxide, 70-76 parts of polyethylene glycol stearate and 13-16 parts of palmitic acid are stirred for 7.5-8 hours in a water bath at a temperature of 78-82° C. to mix them evenly, wherein the stirring speed is 875-925 r / min, then naturally cooled to room temperature to solidify, and finally ground into powder with a particle size of 220-280 μm, and sealed for storage.

2. The method for preparing a composite phase change thermal storage material according to claim 1, characterized in that: The stirring speed in step (2) is 850-900 r / min.

3. The method for preparing a composite phase change thermal storage material according to claim 1, characterized in that: The ultrasonic power in step (3) is 120-150W.

4. The method for preparing a composite phase change thermal storage material according to claim 1, characterized in that: The drying conditions in step (4) are a drying temperature of 75-82° C. and a drying time of 10-10.5 h.

5. The method for preparing a composite phase change thermal storage material according to claim 1, characterized in that: The heating and mixing is specifically as follows: placing the uniformly mixed materials in a water bath heating environment at a temperature of 80-85° C. and stirring once every 1 hour for 9.5-10 hours to obtain a mixed material.

6. The method for preparing a composite phase change thermal storage material according to claim 5, characterized in that: Each stirring time is 5-8 minutes, and the stirring speed is 800-850r / min.

7. The method for preparing a composite phase change thermal storage material according to claim 5, characterized in that: The vacuum drying is specifically as follows: placing the mixed material in a vacuum drying oven, heating and drying at a temperature of 80-85° C. and a vacuum degree of 8106-12159 Pa for 15-15.5 hours, and then naturally cooling to room temperature to obtain a composite phase change thermal storage material.

8. The method for preparing a composite phase-change thermal storage material according to claim 7, characterized in that: The briquetting is specifically: the composite phase change thermal storage material is briquetting by a tabletting machine at 8.5-9.2Mpa to obtain a density of 790-812kg / m 3 The composite phase change thermal storage material block.

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