Composite phase change material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of heat storage systems in solar heating systems, and particularly relates to a composite phase change material and a preparation method and application thereof. The composite phase change material is prepared from the following components in percentage by mass: 4% of expanded graphite, 1%-5% of modified expanded graphite and the balance of 1-octadecanol, totaling 100%, the modified expanded graphite is expanded graphite modified by an aluminate coupling agent. Through the synergistic effect of the modified expanded graphite and the expanded graphite, the heat transfer performance of the composite phase change material can be effectively improved; after 200 times of thermal cycles, the phase change temperature and phase change latent heat of the composite phase change material are almost unchanged, and the composite phase change material shows good thermal cycle stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat storage systems in solar heating systems, and in particular relates to a composite phase change material and a preparation method and application thereof. Background Art

[0002] As the connection point between solar thermal devices and end users, thermal storage systems play a prominent role in improving the spatial and temporal uneven distribution of energy supply. They also reduce environmental pollution caused by fossil fuel consumption, effectively alleviating the growing contradiction between energy supply and demand.

[0003] Currently, thermal storage technologies for thermal energy storage systems are primarily categorized into latent heat storage, sensible heat storage, and chemical energy storage. Compared to other energy storage methods, latent heat storage using phase change materials offers advantages such as ease of operation, low cost, high cost-performance ratio, stable phase change temperature, and high heat storage capacity. Phase change materials primarily include organic phase change materials, inorganic phase change materials, and eutectic phase change materials. Among these, organic phase change materials, represented by 1-octadecanol, have attracted considerable attention due to their stable physical and chemical properties, non-toxicity, low cost, low supercooling, and lack of phase separation.

[0004] However, the poor thermal conductivity of single organic phase change materials results in low energy efficiency in thermal storage systems. Most current research focuses on improving the overall thermal transfer performance of composite phase change materials by adding inorganic materials with high thermal conductivity to organic phase change materials. However, the poor compatibility of inorganic materials with organic phase change materials hinders their dispersion within the organic phase change material, resulting in a minimal effect of the inorganic materials on the thermal transfer performance of the organic composite phase change material. In fact, even after long-term cyclic use, the thermal storage performance is significantly reduced. Summary of the Invention

[0005] In order to solve the technical problem of poor compatibility between the above-mentioned inorganic materials and organic phase change materials, the present invention provides a composite phase change material and a preparation method and application thereof.

[0006] The first object of the present invention is to provide a composite phase change material, which is prepared from the following components by mass percentage: 4% expanded graphite, 1% to 5% modified expanded graphite, and the balance 1-octadecanol, totaling 100%.

[0007] The modified expanded graphite is expanded graphite modified with an aluminate coupling agent.

[0008] It should be noted that expanded graphite is a highly thermally conductive material, and its excellent thermal conductivity enables it to effectively transfer heat during heat conduction. However, using expanded graphite alone can lead to uneven dispersion of the expanded graphite in the phase change material, resulting in localized accumulation.

[0009] The present invention uses 1-octadecanol as a phase change material matrix, modified expanded graphite as a thermal conductive additive, and expanded graphite as a thermal conductive filler. A portion of the expanded graphite is modified using an aluminate coupling agent to obtain the modified expanded graphite. The modified expanded graphite is used to improve the compatibility of the expanded graphite with 1-octadecanol. Thus, the thermal conductivity of the phase change material is enhanced, thereby solving the technical problem of poor compatibility between inorganic materials and organic phase change materials.

[0010] Since expanded graphite has a stacked flaky structure, this unique structure enables it to form a good heat conduction channel in the phase change material. By adsorbing liquid 1-octadecyl alcohol phase change material, the thermal conductivity and structural stability of the composite phase change material are improved.

[0011] The present invention uses an aluminate coupling agent to surface-modify expanded graphite. The hydrophilic end of the aluminate coupling agent reacts with the hydroxyl groups on the surface of the expanded graphite to form a chemical bond, while the hydrophobic end bonds with the alkyl chain of 1-octadecanol via van der Waals forces, thereby helping to improve the interfacial compatibility between the expanded graphite and the organic phase change material. Simultaneously, the macromolecules in the aluminate coupling agent are adsorbed by the expanded graphite, effectively increasing the lipophilicity of the modified expanded graphite. The introduction of the aluminate coupling agent improves the dispersibility of the expanded graphite and the organic phase change material, thereby facilitating the integration of 1-octadecanol and the modified expanded graphite.

[0012] Preferably, the modified expanded graphite is prepared by the following method: Expanded graphite is dissolved in an aluminate coupling agent, and under the action of ultrasound, the expanded graphite obtains a lamellar structure, and molecular clusters of the aluminate coupling agent are attached to the lamellar structure to obtain modified expanded graphite.

[0013] It should be noted that before dissolving the expanded graphite in the aluminate coupling agent for modification, the expanded graphite is heated to remove moisture from the expanded graphite. The heated expanded graphite is then dissolved in the aluminate coupling agent and stirred to allow macromolecules in the aluminate coupling agent to be adsorbed by the expanded graphite, effectively improving the lipophilicity of the modified expanded graphite. Ultrasonic treatment is then performed to uniformly disperse the modified expanded graphite in the aluminate coupling agent. Furthermore, the ultrasonic treatment further enhances the lipophilicity of the expanded graphite.

[0014] Preferably, in the step of dissolving the expanded graphite in the aluminate coupling agent solution, the temperature is controlled to be 75° C. to 100° C. and the time is 20 min to 40 min.

[0015] The present invention uses surface modification treatment and ultrasonic cavitation to, on the one hand, break up the original worm-like morphology of expanded graphite, retain its unique lamellar structure, and increase the specific surface area of ​​the expanded graphite; on the other hand, through modification with an aluminate coupling agent, obtain modified expanded graphite, thereby enhancing the compatibility of the expanded graphite with 1-octadecanol.

[0016] Preferably, the ultrasonic temperature is 75° C. to 100° C. Preferably, the ultrasonic time is 4 h to 6 h.

[0017] Preferably, the usage ratio of expanded graphite and aluminate coupling agent is 1 g to 5 g: 0.02 mol.

[0018] Preferably, the particle size of the expanded graphite is 178 μm to 297 μm, and the expansion multiple is 100 mL / g to 425 mL / g.

[0019] A second object of the present invention is to provide a method for preparing a composite phase change material, characterized in that it comprises the following steps: Modified expanded graphite is added to molten 1-octadecanol. Under ultrasonic action, the molten 1-octadecanol and the modified expanded graphite are fused with each other. Then, expanded graphite is added, and the network structure formed in the 1-octadecanol matrix is ​​cross-linked to construct a heat conduction channel, which promotes the 1-octadecanol to penetrate into the pores of the expanded graphite to obtain a composite phase change material.

[0020] It should be noted that the present invention first adds modified expanded graphite to the molten 1-octadecanol, under the action of ultrasound, so that the modified expanded graphite is uniformly dispersed in the molten 1-octadecanol and merged with each other; then adding expanded graphite, the worm-like expanded graphite and the lamellar structure of the modified expanded graphite form a network structure in the 1-octadecanol matrix, and the network structure is cross-linked to construct a multiphase heat conduction channel, and heat is rapidly conducted along the heat conduction channel; at the same time, under the action of Brownian force, the modified expanded graphite undergoes micro-motion in the molten 1-octadecanol. This micro-motion enhances the micro-convection of the 1-octadecanol-based liquid, thereby improving thermal energy storage and release rate. Moreover, the modified expanded graphite has good adsorption properties to the 1-octadecanol that is also non-polar, so that the molten 1-octadecanol easily penetrates into the pores of the expanded graphite, thereby strengthening the thermal conductivity of the composite phase change material. In addition, the thermal conductivity of the expanded graphite is combined with the phase change characteristics of the 1-octadecanol to construct a composite material that comprehensively enhances overall thermal conductivity. The synergistic effect of this multiphase interface enables heat energy to be transferred more quickly and effectively during the melting and solidification process of 1-octadecanol.

[0021] Preferably, the molten 1-octadecanol is obtained by heating 1-octadecanol at 60° C. to 80° C.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses 1-octadecanol as a phase change material matrix, modified expanded graphite as a thermal conductive additive, and expanded graphite as a thermal conductive filler. A portion of the expanded graphite is modified using an aluminate coupling agent to obtain modified expanded graphite. The modified expanded graphite improves the compatibility of the expanded graphite with 1-octadecanol, which is conducive to the mutual fusion of 1-octadecanol and the modified expanded graphite. Thus, on the basis of enhancing the thermal conductivity of the phase change material, the technical problem of poor compatibility between inorganic materials and organic phase change materials is solved.

[0023] 2. The present invention uses an aluminate coupling agent to surface-modify expanded graphite. The hydrophilic end of the aluminate coupling agent reacts with the hydroxyl groups on the surface of the expanded graphite to form a chemical bond, while the hydrophobic end binds to the alkyl chain of 1-octadecanol via van der Waals forces, improving the interfacial compatibility between the expanded graphite and 1-octadecanol. Simultaneously, the macromolecules in the aluminate coupling agent are adsorbed by the expanded graphite, effectively increasing the lipophilicity of the modified expanded graphite. This, in turn, utilizes the introduction of the aluminate coupling agent to enhance the dispersibility of the expanded graphite with the organic phase change material.

[0024] 3. The present invention effectively improves the heat transfer performance of the composite phase change material through the synergistic effect of modified expanded graphite and expanded graphite; after 200 thermal cycles, the phase change temperature and phase change latent heat of the composite phase change material prepared by the present invention remain almost unchanged, showing good thermal cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 These are scanning electron microscope images of the expanded graphite prepared in Example 1 and the modified expanded graphite prepared in Comparative Example 1; wherein, (a) is a scanning electron microscope image of the expanded graphite at a magnification of 100 μm, (b) is a scanning electron microscope image of the expanded graphite at a magnification of 10 μm, (c) is a scanning electron microscope image of the modified expanded graphite at a magnification of 100 μm, and (d) is a scanning electron microscope image of the modified expanded graphite at a magnification of 10 μm.

[0026] Figure 2 The contact angle pictures of the modified expanded graphite prepared in Comparative Example 1 are shown; (a) is the water contact angle, and (b) is the oil contact angle.

[0027] Figure 3 N2 adsorption-desorption isotherm curves and pore size distribution curves of the expanded graphite prepared in Example 1 and the modified expanded graphite prepared in Comparative Example 1; wherein (a) is the N2 adsorption-desorption isotherm curve, and (b) is the pore size distribution curve.

[0028] Figure 4 These are the X-ray diffraction patterns of the expanded graphite prepared in Example 1 and the modified expanded graphite prepared in Comparative Example 1.

[0029] Figure 5The X-ray diffraction patterns of 1-octadecanol, the expanded graphite prepared in Example 1, and the composite phase change materials prepared in Example 1 and Comparative Examples 2 and 3 are shown.

[0030] Figure 6 The thermal conductivity and thermal diffusivity of the composite phase change materials prepared from 1-octadecanol and Examples 1 to 5.

[0031] Figure 7 These are the heat storage and heat release curves of the composite phase change material prepared by 1-octadecanol and Example 1.

[0032] Figure 8 This is the differential scanning calorimetry curve of the first cycle of the composite phase change materials prepared with 1-octadecanol and Examples 1, 3 and 5.

[0033] Figure 9 The differential scanning calorimetry curves of 1-octadecanol and the composite phase change materials prepared in Example 1, Example 3 and Example 5 after 200 cycles. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below with reference to specific embodiments and drawings.

[0035] In the description of the present invention, unless otherwise specified, all reagents used are commercially available and all methods used are conventional techniques in the art.

[0036] Example 1 This embodiment provides a composite phase change material.

[0037] The composite phase change material of this embodiment is prepared from the following components, calculated by mass percentage: 4% expanded graphite, 5% modified expanded graphite, and the balance 1-octadecanol, totaling 100%.

[0038] The English name of 1-octadecanol is 1-Octadecanol, abbreviated as OD.

[0039] The composite phase change material of this embodiment is prepared by the following method: S1. Add 2 g of expandable graphite with a particle size of 80 mesh and an expansion ratio of 425 mL / g to a 250 mL quartz beaker and place it in a digital display blower drying oven; wherein the digital display drying oven is set to 80°C and the drying time is 12 h.

[0040] S2. The dried expandable graphite was placed in a muffle furnace and heated at 900° C. for 1 min to obtain expanded graphite, which was recorded as EG. The expanded graphite was then placed in a glass container filled with alum for later use.

[0041] S3. Add 0.02 mol of an aluminate coupling agent to 1000 mL of anhydrous ethanol, and stir at a speed of 800 r / min for 30 min to obtain an aluminate coupling agent solution.

[0042] S4. Add 5 g of expanded graphite to the aluminate coupling agent solution, heat at 75°C, and stir at a speed of 800 r / min for 30 minutes to obtain a mixed solution; then place the mixed solution in an ultrasonic cleaning machine for ultrasonic oscillation for 5 hours; wherein, the ultrasonic frequency is 50 Hz, and the ultrasonic temperature is 75°C; after the ultrasonication, place the mixed solution on a magnetic stirrer and stir until it is naturally cooled, filter, and then place in a vacuum drying oven at 40°C for 24 hours to obtain modified expanded graphite.

[0043] S5. Place 91 g of 1-octadecanol in a 70°C water bath and heat until melted. Then add 5 g of modified expanded graphite to the molten 1-octadecanol, stir, and oscillate in an ultrasonic cleaner for 1 hour each, with the ultrasonic oscillation frequency being 50 Hz. Then, add 4 g of expanded graphite and stir at a speed of 800 r / min for 1 hour to obtain a composite phase change material, which is recorded as OD / EG4 / DEG5.

[0044] Example 2 This embodiment provides a composite phase change material.

[0045] The composite phase change material of this embodiment is prepared from the following components, calculated by mass percentage: 4% expanded graphite, 4% modified expanded graphite, and the balance 1-octadecanol, totaling 100%.

[0046] The preparation method of the composite phase change material of this embodiment refers to the preparation method of Example 1 to obtain a composite phase change material, which is recorded as OD / EG4 / DEG4.

[0047] Example 3 This embodiment provides a composite phase change material.

[0048] The composite phase change material of this embodiment is prepared from the following components, calculated by mass percentage: 4% expanded graphite, 3% modified expanded graphite, and the balance 1-octadecanol, totaling 100%.

[0049] The preparation method of the composite phase change material of this embodiment refers to the preparation method of Example 1 to obtain a composite phase change material, which is recorded as OD / EG4 / DEG3.

[0050] Example 4 This embodiment provides a composite phase change material.

[0051] The composite phase change material of this embodiment is prepared from the following components, calculated by mass percentage: 4% expanded graphite, 2% modified expanded graphite, and the balance 1-octadecanol, totaling 100%.

[0052] The preparation method of the composite phase change material of this embodiment refers to the preparation method of Example 1 to obtain a composite phase change material, which is recorded as OD / EG4 / DEG2.

[0053] Example 5 This embodiment provides a composite phase change material.

[0054] The composite phase change material of this embodiment is prepared from the following components, calculated by mass percentage: 4% expanded graphite, 1% modified expanded graphite, and the balance 1-octadecanol, totaling 100%.

[0055] The preparation method of the composite phase change material of this embodiment refers to the preparation method of Example 1 to obtain a composite phase change material, which is recorded as OD / EG4 / DEG1.

[0056] Comparative Example 1 This invention provides a method for preparing modified expanded graphite.

[0057] S1. Add 2 g of expandable graphite with a particle size of 80 mesh and an expansion ratio of 425 mL / g to a 250 mL quartz beaker and place it in a digital display blower drying oven; wherein the digital display drying oven is set to 80°C and the drying time is 12 h.

[0058] S2. Place the dried expandable graphite in a muffle furnace at 900° C. and heat it for 1 minute to obtain expanded graphite, which is then placed in a glass container filled with alum for later use.

[0059] S3. Add 0.02 mol of an aluminate coupling agent to 1000 mL of anhydrous ethanol, and stir at a speed of 800 r / min for 30 min to obtain an aluminate coupling agent solution.

[0060] S4. Add 5 g of expanded graphite to the aluminate coupling agent solution, heat at 75°C, and stir at a speed of 800 r / min for 30 minutes to obtain a mixed solution; then place the mixed solution in an ultrasonic cleaning machine for ultrasonic oscillation for 5 hours; wherein, the ultrasonic frequency is 50 Hz, and the ultrasonic temperature is 75°C; after the ultrasonication, place the mixed solution on a magnetic stirrer and stir until it is naturally cooled, filter, and then place in a vacuum drying oven at 40°C for 24 hours to obtain modified expanded graphite, recorded as DEG.

[0061] Comparative Example 2 This comparative example provides a composite phase change material.

[0062] The composite phase change material of this comparative example is composed of the following components, calculated by mass percentage: 4% expanded graphite and the balance 1-octadecanol, which together account for 100%.

[0063] The composite phase change material of this comparative example is prepared by the following steps: S1. Add 2 g of expandable graphite with a particle size of 80 mesh and an expansion ratio of 425 mL / g to a 250 mL quartz beaker and place it in a digital display blower drying oven; wherein the digital display drying oven is set to 80°C and the drying time is 12 h.

[0064] S2. Place the dried expandable graphite in a muffle furnace at 900° C. and heat it for 1 minute to obtain expanded graphite, which is then placed in a glass container filled with alum for later use.

[0065] S3. Heat 96 g of 1-octadecanol in a 70° C. water bath until melted, then add 4 g of expanded graphite to the melted 1-octadecanol, stir, and oscillate in an ultrasonic cleaner for 1 h each, with the ultrasonic oscillation frequency being 50 Hz, to obtain a composite phase change material, recorded as OD / EG.

[0066] The difference between this comparative example and Example 1 is: No modified expanded graphite is added to the composite phase change material of this comparative example.

[0067] Comparative Example 3 This comparative example provides a composite phase change material.

[0068] The composite phase change material of this comparative example is composed of the following components, calculated by mass percentage: 5% modified expanded graphite and the balance 1-octadecanol, which together total 100%.

[0069] The composite phase change material of this comparative example is prepared by the following steps: S1. Add 2 g of expandable graphite with a particle size of 80 mesh and an expansion ratio of 425 mL / g to a 250 mL quartz beaker and place it in a digital display blower drying oven; wherein the digital display drying oven is set to 80°C and the drying time is 12 h.

[0070] S2. Place the dried expandable graphite in a muffle furnace at 900° C. and heat it for 1 minute to obtain expanded graphite, which is then placed in a glass container filled with alum for later use.

[0071] S3. Add 0.02 mol of an aluminate coupling agent to 1000 mL of anhydrous ethanol, and stir at a speed of 800 r / min for 30 min to obtain an aluminate coupling agent solution.

[0072] S4. Add 5 g of expanded graphite to the aluminate coupling agent solution, heat at 75°C, and stir at a speed of 800 r / min for 30 minutes to obtain a mixed solution; then place the mixed solution in an ultrasonic cleaning machine for ultrasonic oscillation for 5 hours; wherein, the ultrasonic frequency is 50 Hz, and the ultrasonic temperature is 75°C; after the ultrasonication, place the mixed solution on a magnetic stirrer and stir until it is naturally cooled, filter, and then place in a vacuum drying oven at 40°C for 24 hours to obtain modified expanded graphite.

[0073] S5. Place 95 g of 1-octadecanol in a 70° C. water bath and heat until melted. Then add 5 g of modified expanded graphite to the molten 1-octadecanol, stir, and oscillate in an ultrasonic cleaner for 1 h each. The ultrasonic oscillation frequency is 50 Hz to obtain a composite phase change material, which is recorded as OD / DEG.

[0074] Experimental test: 1. Scanning electron microscopy characterization.

[0075] from Figure 1 As can be seen from (a) in the figure, the modified expanded graphite has a unique multilayer structure and crack-like pore structure; Figure 1 As can be seen in (b), the surface of the multilayer structure is covered with micron-scale honeycomb pore structures. This complex structure gives the expanded graphite a high specific surface area. At the same time, the surface active edges in the form of flakes give the expanded graphite a high adsorption capacity. Figure 1 (c) in Figure 3 shows that after surface treatment and ultrasonic cavitation, the modified expanded graphite obtained breaks up the original worm-like morphology of the expanded graphite, but retains its unique multilayer structure; Figure 1 As shown in (d), dispersed aluminate coupling agent molecular clusters were found on the graphite sheets, which improved the compatibility of expanded graphite and 1-octadecanol.

[0076] 2. Wettability test.

[0077] The modified expanded graphite prepared in Comparative Example 1 was tested for contact angle using a contact angle meter. 0.2 g of the modified expanded graphite was pressed into a 12 mm cylindrical sample at a pressure of 100 Pa. 2 μL of deionized water and oleic acid were added dropwise to the sample to assess its wettability with water and oil, respectively. The contact angle meter has a test range of 0° to 180° and an accuracy of ±0.1°.

[0078] from Figure 2 It can be seen that the contact angle between the modified expanded graphite and water is 127.87°, and the contact angle between the modified expanded graphite and oil is about 0°, indicating that the modified expanded graphite has excellent organophilic properties, which is more conducive to the mutual fusion of 1-octadecanol and the modified expanded graphite.

[0079] 3. N2 adsorption-desorption test.

[0080] The present invention uses a fully automatic surface area and porosity analyzer (ASAP2460, Micro-metrics, USA) to measure the specific surface area and pore size distribution of the expanded graphite prepared in Example 1 and the modified expanded graphite prepared in Comparative Example 1. Specific surface area tests were conducted at relative pressures P / P0 ranging from 0.01 to 0.12, 0.14 to 0.30, 0.10 to 0.20, 0.10 to 0.18, and 0.07 to 0.18, respectively. Pore size distribution tests were conducted on the isothermal adsorption branch. The total pore volume was calculated based on the N2 adsorption at a relative pressure P / P0 of 0.99. Relative pressure P / P0, where P refers to the nitrogen partial pressure and P0 refers to the saturated vapor pressure of the adsorbate gas at the adsorption temperature.

[0081] from Figure 3 It can be seen that the specific surface area of ​​modified expanded graphite increases from 24.87m 2 / g increased to 40.31m 2 / g, this is because the ultrasonic cavitation breaks some of the original existing pores, resulting in changes in the pore structure, making the modified expanded graphite have a smaller particle size, which helps to shorten the heat transfer path inside the material and reduce the thermal resistance.

[0082] 4. X-ray diffraction test.

[0083] like Figure 4 As shown, the diffraction peak at 26.5° corresponds to the (002) crystal plane of graphite crystal; the diffraction peak at 54.9° corresponds to the (004) crystal plane of graphite crystal.

[0084] Compared to Figure 4 The diffraction peaks of expanded graphite and modified expanded graphite, Figure 5 No new diffraction peaks appeared in the X-ray diffraction patterns of the composite phase-change materials. This was true regardless of whether the composite phase-change materials were formed from expanded graphite and 1-octadecanol, from modified expanded graphite and expanded graphite, or from expanded graphite, modified expanded graphite, and 1-octadecanol. This suggests that the modification of expanded graphite by the aluminate coupling agent is purely physical, not chemical, and that the composite phase-change materials were prepared through simple physical mixing.

[0085] 5. Thermal conductivity test.

[0086] from Figure 6It can be seen that the addition of modified expanded graphite can effectively improve the thermal transfer performance of the composite phase change material; as the proportion of modified expanded graphite in the composite phase change material increases, the thermal conductivity and thermal diffusivity of the composite phase change material also increase. Compared with the composite phase change material with only 4% modified expanded graphite added, when the mass fraction of modified expanded graphite is 5%, the thermal conductivity of the composite phase change material is 3.115W / (m·K), and the thermal conductivity is increased by 122.81%; the thermal diffusivity of the composite phase change material is 2.769mm 2 / s, and thermal diffusivity increased by 175.57%. When the mass fraction of modified expanded graphite was 5%, the thermal conductivity of the composite phase change material increased by 942.15% and the thermal diffusivity by 1202.44% compared to 1-octadecanol. This is primarily due to the three-dimensional pore structure and excellent adsorption properties of expanded and modified expanded graphite. The lamellae of worm-like expanded graphite and modified expanded graphite form a network structure within the 1-octadecanol matrix, which is cross-linked to form efficient heat conduction channels. The modified expanded graphite has excellent adsorption properties for 1-octadecanol, which is also non-polar, allowing liquid 1-octadecanol to easily penetrate the pores of the expanded graphite, thereby enhancing the thermal conductivity of the composite phase change material.

[0087] from Figure 7 As can be seen, the composite phase change material exhibits a 132.8% increase in heat storage rate and a 118.5% increase in heat release rate compared to 1-octadecanol. Pure 1-octadecanol has a low thermal conductivity and lacks effective heat transfer pathways during heat storage and release, resulting in slow heat storage and release rates. The addition of expanded graphite and modified expanded graphite allows for rapid heat transfer along these heat transfer pathways. Simultaneously, under the action of Brownian forces, the modified expanded graphite undergoes micromotion within the liquid 1-octadecanol. This micromotion enhances microconvection within the 1-octadecanol-based liquid, thereby increasing the rates of heat storage and release.

[0088] from Figure 8 As can be seen in the graph, only one peak is observed during the melting process, while during solidification, the solid 1-octadecanol exhibits supercooling during the transition from the γ phase to the α phase. The addition of expanded graphite and modified expanded graphite does not affect the phase transition behavior of 1-octadecanol. Due to their lack of participation in the phase transition of 1-octadecanol, the latent heat of the composite phase change material decreases. However, the composite still possesses a high latent heat value and a suitable phase transition temperature, suggesting great potential for use in thermal storage systems.

[0089] like Figure 9 As shown in FIG, after 200 thermal cycles, the slight changes in the phase change temperature and latent heat of the composite phase change material indicate that it has good thermal cycle stability.

[0090] It should be noted that when numerical ranges are mentioned in the present invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints may be selected. Since the steps and methods used are the same as those in the embodiments, the present invention describes preferred embodiments to avoid redundancy. Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they understand the basic inventive concepts, and such changes and modifications fall within the scope of the present invention.

[0091] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. If these modifications and variations of the present invention fall within the scope of the equivalent technology of the present invention, the present invention is also intended to include these modifications and variations.

Claims

1. A composite phase change material, characterized in that: The composite phase change material is prepared from the following components by mass percentage: 4% expanded graphite, 1% to 5% modified expanded graphite, and the balance 1-octadecanol, totaling 100%; The modified expanded graphite is expanded graphite modified with an aluminate coupling agent.

2. The composite phase change material according to claim 1, characterized in that: The composite phase change material is prepared by the following method: Modified expanded graphite is added to 1-octadecanol and dispersed uniformly, and then expanded graphite is added to obtain a composite phase change material.

3. The composite phase change material according to claim 1, characterized in that: Modified expanded graphite is prepared by the following method: Expanded graphite is dissolved in an aluminate coupling agent, and under the action of ultrasound, the expanded graphite obtains a lamellar structure, and aluminate coupling agent molecular groups are attached to the lamellar structure to obtain modified expanded graphite.

4. The composite phase change material according to claim 3, characterized in that: The usage ratio of the expanded graphite and the aluminate coupling agent is 1g~5g:0.02mol.

5. The composite phase change material according to claim 3, characterized in that: The temperature of the ultrasound is 75°C to 100°C.

6. The composite phase change material according to claim 1, characterized in that: The particle size of the expanded graphite is 178 μm to 297 μm, and the expansion multiple is 100 mL / g to 425 mL / g.

7. A method for preparing the composite phase change material according to any one of claims 1 to 6, characterized in that: The following steps are involved: Modified expanded graphite is added to molten 1-octadecanol to fuse the molten 1-octadecanol and the modified expanded graphite. Then, expanded graphite is added, and the network structure formed in the 1-octadecanol matrix is ​​cross-linked to construct a heat conduction channel, which promotes the 1-octadecanol to penetrate into the pores of the expanded graphite to obtain a composite phase change material.

8. The method for preparing a composite phase change material according to claim 7, characterized in that: The molten 1-octadecanol is obtained by heating 1-octadecanol at 60° C. to 80° C.

9. Use of the composite phase change material according to any one of claims 1 to 6 in a solar heating system.

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