Preparation of capsule-type composite phase change materials

Abstract

This invention discloses a method for preparing a capsule-type composite phase change material, belonging to the field of heat transfer and thermal storage technology. The capsule-type composite phase change material of this invention consists of a phase change material core and a graphite-modified polytetrafluoroethylene (PTFE) wall material coating the outer layer of the phase change material core. This invention uses graphite-modified PTFE, which is resistant to high temperatures and corrosion and has good thermal conductivity, as a carrier. By utilizing the microstructure characteristics of graphite-modified PTFE to encapsulate the phase change material, a composite phase change thermal storage material with high thermal storage capacity, good thermal shock resistance, high thermal conductivity, and low reversible corrosion during heat charging / discharging is prepared. Furthermore, it is low in cost, easy to mass-produce, and has significant application value. Graphite modification of PTFE improves the thermal conductivity and mechanical properties of the composite material.

Description

Technical Field

[0001] This invention relates to the field of heat transfer and heat storage technology, and in particular to a method for preparing a capsule-type composite phase change material. Background Technology

[0002] Phase change materials (PCMs) play a crucial role in the field of phase change thermal storage due to their advantages such as high thermal efficiency, stable chemical properties, and low cost. Currently, the phase change temperatures of various PCMs are generally below 150℃ or above 220℃. However, the temperatures of industrial heating and distributed solar organic Rankine cycles are mostly concentrated in the 150-220℃ temperature range, and existing PCMs cannot yet adequately cover this range, requiring further research.

[0003] To address the lack of high-performance phase change thermal storage materials in the 150-220℃ range, molten salt composite thermal storage materials represent one research direction. Molten salt composite thermal storage materials utilize the phase change properties of molten salt to store and release heat. Molten salt, formed by the melting of salts, is an ionic melt composed of cations and anions, possessing advantages such as high thermal density, low viscosity, low cost, long lifespan, and high efficiency, making it suitable for heat transfer and storage applications. Molten salt composite thermal storage materials can be fabricated into phase change capsule structures using solar salt, Hitec salt, or modified solar salt as the core material and polytetrafluoroethylene (PTFE) or silica as the wall material. However, existing molten salt composite thermal storage materials with phase change capsule structures typically suffer from low shell thermal conductivity and poor thermal properties, limiting their application in heat recovery. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a capsule-type composite phase change material to solve the aforementioned problems in the background art. This invention uses graphite-modified polytetrafluoroethylene (PTFE), which is resistant to high temperatures and corrosion and has good thermal conductivity, as a carrier. The microstructure characteristics of graphite-modified PTFE are utilized to encapsulate the phase change material, thereby preparing a composite phase change thermal storage material with high heat storage capacity, good thermal shock resistance, high thermal conductivity, and low reversible corrosion during heat charging / discharging. Furthermore, it is low-cost, easy to mass-produce, and has significant application value. Graphite modification of PTFE improves the thermal conductivity and mechanical properties of the composite material.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] One of the technical solutions of the present invention is to provide a capsule-type composite phase change material, which is composed of a phase change material core and a graphite-modified polytetrafluoroethylene wall material covering the outer layer of the phase change material core.

[0007] The second technical solution of the present invention provides a method for preparing the above-mentioned capsule-type composite phase change material, comprising the following steps:

[0008] (1) Take phase change material powder, press it into shape, and obtain phase change material core material;

[0009] Polytetrafluoroethylene powder and graphite powder are mixed to obtain modified polytetrafluoroethylene powder.

[0010] (2) Wrap the modified polytetrafluoroethylene powder around the surface of the phase change material core and compact it to obtain a phase change capsule embryo;

[0011] (3) The phase change capsule embryo is subjected to thermoforming treatment to obtain the capsule-type composite phase change material.

[0012] Preferably, the phase change material powder is a mixed nitrate powder with a melting point of 150-220℃.

[0013] Preferably, the mold used for pressing is a spherical mold cavity or a cylindrical mold cavity.

[0014] Preferably, the pressing pressure is 1200N, and the density of the resulting phase change material core is 1809-1949 kg / m³. 3 .

[0015] More preferably, the method for preparing the mixed nitrate powder with a melting point of 150-220℃ is as follows: heating the mixed nitrate powder to a molten state, cooling it, then taking it out and pulverizing it to an average particle size of 75μm to obtain the mixed nitrate powder with a melting point of 150-220℃.

[0016] More preferably, the mixed nitrate powder contains two or more of KNO3, NaNO3, NaNO2 and Ca(NO3)2.

[0017] Preferably, the mass ratio of the polytetrafluoroethylene powder to the graphite powder is 10:1.

[0018] Preferably, the mass ratio of the phase change material core to the modified polytetrafluoroethylene powder is 6.5-7:2.5-3.

[0019] Preferably, the compaction pressure is 1200N, and the density of the resulting phase change capsule embryo is 1988-2385 kg / m³. 3 .

[0020] Preferably, the thermoforming process is as follows: heating the phase change capsule embryo at 350°C for 15 minutes, then heating it at 450°C for 15 minutes, and finally cooling it down to 350°C and heating it for 15 minutes.

[0021] In the thermoforming process of this invention, the outermost layer of polytetrafluoroethylene (PTFE) of the phase change capsule preform first softens and partially melts at 350°C, which helps in subsequent molding. After the temperature is raised to 450°C, the melting and flow of PTFE can be further promoted, allowing it to be better filled. At the stage of cooling down to 350°C, the cooling process of the reaction system can be controlled, allowing the molten PTFE to gradually solidify and stabilize, and also helps to eliminate the internal stress of the product and improve the crystallinity of the product.

[0022] The third technical solution of the present invention provides an application of the above-mentioned capsule-type composite phase change material in the field of phase change thermal storage.

[0023] This invention involves pressing phase change material powder into shape, and then pressing a layer of modified polytetrafluoroethylene (PTFE) powder onto it to obtain the final product. When the capsule-type composite phase change material is heated, the air inside the capsule is discharged through the micropores on the surface of the PTFE shell, and the volume expansion of the phase change material causes the PTFE to expand synchronously. Furthermore, the solidification of the molten PCM begins from the wall surface. The PTFE shell is supported by the pre-solidified PCM and can maintain a constant volume. As the PCM solidifies, its volume decreases, thus forming a cavity of a certain volume inside the capsule. This can optimize heat transfer, control the temperature distribution of the phase change material, and improve the overall efficiency and performance of the phase change capsule.

[0024] The beneficial technical effects of the present invention are as follows:

[0025] This invention uses graphite-modified polytetrafluoroethylene (PTFE), a material known for its high temperature and corrosion resistance and excellent thermal conductivity, as a carrier. By utilizing the microstructure of graphite-modified PTFE to encapsulate phase change materials, a composite phase change thermal storage material with high heat storage capacity, good thermal shock resistance, high thermal conductivity, and low reversible corrosion during heat charging / discharging is prepared. Furthermore, it is low-cost, easy to mass-produce, and has significant application value. Graphite modification of PTFE improves the thermal conductivity and mechanical properties of the composite material. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The results show the thermophysical properties of different types of phase change material cores in Example 1. (a) represents melting point, (b) latent heat of fusion, (c) specific heat capacity, (d) thermal conductivity, (e) density, and (f) viscosity.

[0028] Figure 2 The results show the decomposition point measurements of different types of phase change material cores in Example 1.

[0029] Figure 3 The images show the microstructures of the products from Example 1 and Comparative Examples 1-2. In the images, (a) is PTFE, (b) is graphite-PTFE, (c) is polystyrene-PTFE, (d) is carbon fiber-PTFE, (e) is copper powder-PTFE, and (f) is molybdenum disulfide-PTFE.

[0030] Figure 4 Infrared spectra of PTFE, graphite-PTFE, and polystyrene-PTFE.

[0031] Figure 5 Infrared spectra of carbon fiber-PTFE, copper powder-PTFE, and molybdenum disulfide-PTFE.

[0032] Figure 6 XRD patterns of PTFE, graphite-PTFE, and polystyrene-PTFE.

[0033] Figure 7 XRD patterns of carbon fiber-PTFE, copper powder-PTFE, and molybdenum disulfide-PTFE. Detailed Implementation

[0034] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0035] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0036] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0037] The terms “comprising,” “including,” “having,” “containing,” etc., used in this invention are all open-ended terms, meaning that they include but are not limited to.

[0038] Unless otherwise specified, "room temperature" in this invention refers to 10-30°C.

[0039] The raw material composition and proportion of the phase change material powders (1S, 2S, 3S, 1H, 2H, and solar salt) used in the following embodiments and comparative examples of the present invention are shown in Table 1. The preparation method of the phase change material powders is as follows: the mixed nitrate powders are heated to a molten state, cooled, and then taken out and pulverized to an average particle size of 75 μm to obtain the phase change material powders.

[0040] Table 1. Raw material composition and proportion

[0041]

[0042]

[0043] The graphite powder, polystyrene powder, carbon fiber, copper powder, and molybdenum disulfide powder used in this invention have an average particle size of 10 μm, 10 μm, 10 μm, and 10 μm, respectively. All raw materials used in the following embodiments and comparative examples of this invention are commercially available products.

[0044] Example 1

[0045] Capsule-type composite phase change materials were prepared using 1S, 2S, 3S, 1H, 2H, or solar salt as phase change material powders, respectively, following these steps:

[0046] (1) Take phase change material powder, put it into a spherical mold cavity with a diameter of 19 mm, and press it into shape using a hydraulic press to obtain phase change material core material (pressure of 1200 N, density of phase change material core material of 1925 kg / m³). 3 );

[0047] Polytetrafluoroethylene powder and graphite powder were mixed at a mass ratio of 10:1 to obtain modified polytetrafluoroethylene powder.

[0048] (2) Prepare phase change material core material and modified polytetrafluoroethylene powder at a mass ratio of 5.875:2.44. Evenly coat the surface of the phase change material core material with the modified polytetrafluoroethylene powder, place it into a spherical mold cavity, and compact it using a hydraulic press to obtain a phase change capsule preform (pressure 1200 N, density of the phase change capsule preform 2150 kg / m³). 3 );

[0049] (3) The phase change capsule preform is thermoformed; the phase change capsule preform is first heated at 350℃ for 15 min, then heated at 450℃ for 15 min, and finally cooled to 350℃ and heated for 15 min, and then naturally cooled to room temperature to obtain capsule-type composite phase change material (the product made with 3s as phase change material powder is called graphite-PTFE).

[0050] Example 2

[0051] The only difference from graphite-PTFE is that the mold shape used for hydraulic pressing is modified to a cylindrical cavity with a diameter of 15m.

[0052] Comparative Example 1

[0053] The only difference from graphite-PTFE is that the graphite powder in step (1) is replaced with an equal mass of polystyrene powder, carbon fiber, copper powder or molybdenum disulfide powder, and the resulting products are denoted as polystyrene-PTFE, carbon fiber-PTFE, copper powder-PTFE, and molybdenum disulfide-PTFE.

[0054] Comparative Example 2

[0055] The only difference from Example 1 is that the addition of graphite powder in step (1) is omitted, and the resulting product is denoted as PTFE.

[0056] Effect verification

[0057] Thermophysical parameters of different types of phase change material cores prepared in Example 1 were tested. The test results are as follows: Figure 1-2 As shown in Table 2-3.

[0058] Table 2 Thermophysical properties

[0059] Thermal property parameters Sun Salt <![CDATA[Density (kg / m 3 )]]> 1925 Latent heat (J / kg) 96060 Specific heat capacity (J / (kg·K)) 1520 Thermal conductivity (W / (m·K)) 0.45(l)0.75(s) Dynamic viscosity (Pa·s) 0.00693 Coefficient of thermal expansion (1 / K) 0.000375 Solid temperature (K) 493.35 Liquid phase temperature (K) 518.45

[0060] Table 3 Thermophysical properties

[0061]

[0062]

[0063] Figure 1 The results show the thermophysical properties of different types of phase change material cores in Example 1. (a) represents melting point, (b) latent heat of fusion, (c) specific heat capacity, (d) thermal conductivity, (e) density, and (f) viscosity.

[0064] Figure 1 The terms "solar salt," "1s," "2s," "3s," "1h," and "2h" refer to the relevant data of phase change material core materials obtained using solar salt, "1s," "2s," "3s," "1h," and "2h" as raw materials.

[0065] Figure 2 The results show the decomposition point measurements of different types of phase change material cores in Example 1.

[0066] Figure 2The terms 1S, 2S, 3S, 1H, and 2H refer to the relevant data of the phase change material core material obtained using 1S, 2S, 3S, 1H, and 2H as raw materials.

[0067] Figure 3 The images show the microstructures of the products from Example 1 and Comparative Examples 1-2. In the images, (a) is PTFE, (b) is graphite-PTFE, (c) is polystyrene-PTFE, (d) is carbon fiber-PTFE, (e) is copper powder-PTFE, and (f) is molybdenum disulfide-PTFE.

[0068] Infrared spectral data are generated, and information on chemical bonds and functional groups in the experimental sample is analyzed based on the infrared spectra. By comparing the infrared spectra with those of samples with known structures, the chemical structure and identification of the experimental sample can be determined. Test results are as follows: Figure 4-5 As shown.

[0069] Figure 4 Infrared spectra of PTFE, graphite-PTFE, and polystyrene-PTFE.

[0070] Figure 5 Infrared spectra of carbon fiber-PTFE, copper powder-PTFE, and molybdenum disulfide-PTFE.

[0071] Figure 6 XRD patterns of PTFE, graphite-PTFE, and polystyrene-PTFE.

[0072] Figure 7 XRD patterns of carbon fiber-PTFE, copper powder-PTFE, and molybdenum disulfide-PTFE.

[0073] Table 4 Thermophysical properties

[0074]

[0075]

[0076] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A capsule-type composite phase change material, characterized by, The capsule type composite phase change material is composed of a phase change material core and a graphite modified polytetrafluoroethylene wall material coated on the outer layer of the phase change material core. The preparation method of the capsule type composite phase change material comprises the following steps: (1) taking phase change material powder, compression molding to obtain a phase change material core; polytetrafluoroethylene powder and graphite powder are mixed to obtain modified polytetrafluoroethylene powder; (2) the modified polytetrafluoroethylene powder is wrapped on the surface of the phase change material core, and is compacted to obtain a phase change capsule embryo; (3) the phase change capsule embryo is subjected to heat forming treatment to obtain the capsule type composite phase change material; the mass ratio of the polytetrafluoroethylene powder and the graphite powder is 10:1; the mass ratio of the phase change material core and the modified polytetrafluoroethylene powder is 6.5-7:2.5-3.

2. The encapsulated composite phase change material of claim 1, wherein, the phase change material powder is mixed nitrate powder with a melting point of 150-220℃.

3. The encapsulated composite phase change material of claim 1, wherein, The pressure of the press molding is 1200N, and the density of the phase change material core material obtained is 1809-1949 kg / m 3 .

4. The encapsulated composite phase change material of claim 1, wherein, The compaction pressure is 1200 N, and the density of the phase change capsule obtained is 1988-2385 kg / m 3 .

5. The encapsulated composite phase change material of claim 1, wherein, the heat forming treatment is: the phase change capsule embryo is heated at 350℃ for 15 min, then heated at 450℃ for 15 min, finally cooled to 350℃ and heated for 15 min.

6. Application of the capsule type composite phase change material of claim 1 in the field of phase change heat storage.

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