Heat-conducting phase-change material based on plate-nail type composite structure framework

Abstract

The invention provides a heat-conducting phase-change material based on a plate-nail type composite structure framework, relates to the technical field of material science and engineering, and aims to solve the scientific problem that an existing composite material is not easy to realize out-of-plane ordered intercommunication framework construction. Multi-scale structure design is carried out by means of electric field induction, a one-dimensional strengthening path perpendicular to the framework sheet layer direction is constructed, and the characteristic of high phase change latent heat of the composite PCM is still kept while high out-of-plane heat conduction, high phase change efficiency and shape stability of the composite PCM are achieved. Heat can be quickly stored in a high-phase-change latent heat form through the synergistic effect between the plate and nail structures, a double-lock fixing effect can be achieved on the fused PCM, the shape stability of the composite PCM is improved, a small amount of one-dimensional micron-sized carbon fiber reinforcing materials are introduced through vacuum-assisted impregnation of the PCM, self-assembly is induced by means of the capillary adsorption effect-electric field, and the composite PCM is prepared. And arranging the carbon fibers among the diamond hole wall layers along the horizontal direction.

Description

Technical Field

[0001] The present invention belongs to the field of material science and engineering technology, and more specifically, particularly relates to a heat-conducting phase change material based on a "plate-nail type" composite structural skeleton. Background Art

[0002] Energy is the foundation for human survival and development and the lifeblood of the national economy. However, with the increasing depletion of non-renewable energy such as fossil fuels, the energy crisis is becoming more and more serious. Improving energy utilization efficiency, reducing energy use costs, and reducing environmental pollution emissions have become the inevitable choice to solve the energy and environmental problems faced by human society in the process of development. In recent years, with the development of the energy storage industry, a variety of new energy storage technologies have made continuous breakthroughs. Phase change energy storage technology uses the phase change material (PCM) to absorb or release a large amount of heat during the phase change process to achieve energy storage and release. With the advantages of high heat storage density, stable working temperature, low large-scale cost, and environmental friendliness, it has shown great application potential in the fields of industrial waste heat recovery, renewable energy utilization, low-carbon buildings, and thermal management of electronic devices. Among many PCMs, organic solid-liquid PCM has the advantages of large phase change latent heat, wide phase change temperature range, not easy to appear supercooling and phase separation, non-toxic and non-corrosive, and low cost, which has attracted great attention. However, solid-liquid PCM generally has the problems of melting leakage during the phase change process and low inherent thermal conductivity (generally between 0.15-0.35 Wm -1 K -1 ), which has led to a significant reduction in the thermal storage efficiency of PCMs, seriously restricting their development and application in the fields of energy storage and temperature control. Therefore, the packaging shaping and thermal conductivity enhancement of PCMs have become the current research focus.

[0003] The current mainstream solution is to prevent leakage and improve the thermal conductivity of composite PCM by doping high thermal conductivity fillers into PCM. But generally speaking, the introduction of fillers will have an adverse effect on the thermal storage performance of composite PCM. Researchers have proposed that constructing a large-scale oriented aerogel skeleton inside the composite PCM is expected to further improve thermal conductivity while maintaining high energy storage density. The oriented aerogel skeleton can effectively interconnect the thermally conductive fillers, reduce the number of filler-filler nodes and the filler-PCM interface area, avoid redundant thermal resistance, and maximize the heat transfer along the high-speed channel composed of the filler, thereby achieving a synergistic improvement in thermal conductivity and thermal storage performance at a low filling amount. However, due to the lack of an effective through-surface assembly strategy, the out-of-plane thermal conductivity of the composite PCM in the vertical direction is generally low (generally <5 W m -1 K -1 ), resulting in the inability to quickly remove hot spots, causing problems such as overheating of the material surface and severe energy loss, limiting the demand for longitudinal heat conduction in areas such as solar absorbers and electronic device heat dissipation.

[0004] In addition, the ordered layered structure prepared by the existing technology can solve the game effect between thermal conductivity and heat storage performance to a certain extent, as well as the problem of easy leakage of solid-liquid PCM, but there are still key difficulties that need to be solved: (1) Blindly improving the orientation of the thermal conductive skeleton in the vertical direction to enhance the directional heat transfer effect is not conducive to the phase change efficiency of PCM, because there is a large temperature difference between the PCM close to the skeleton layered wall and the distant part; (2) In addition to thermal conductivity and energy storage properties, mechanical properties are also key properties of composite PCM, which will have a direct impact on the shape stability and service life of composite PCM. Therefore, on the basis of directional assembly of sheets, how to improve the temperature response speed from the support body to the inside of PCM, improve the phase change efficiency, and at the same time enhance the in-plane mechanical properties of composite PCM to enable it to have excellent shape stability, is a great technical challenge.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a thermally conductive phase change material based on a "plate-nail type" composite structural skeleton to solve the above problems.

[0007] Based on the thermal conductive phase change material of the "plate-nail" composite structure skeleton, a three-dimensional directional connected skeleton is constructed by the bidirectional freezing method. At the same time, multi-scale structural design is carried out with the help of electric field induction to construct a one-dimensional reinforcement path perpendicular to the direction of the skeleton layer. Zero-dimensional nanoscale diamond is selected as the thermal conductive material, and a layered aerogel skeleton in the vertical direction is prefabricated based on ice crystal induced self-assembly as a support.

[0008] Preferably, a small amount (1-3wt%) of one-dimensional micron-sized carbon fiber reinforcement is introduced into PCM by vacuum-assisted impregnation, and the carbon fibers are horizontally oriented and arranged between the diamond pore wall layers by means of capillary adsorption effect-electric field induced self-assembly, forming a "plate-nail" composite structure PCM with both a longitudinally layered connected thermal conductive body and a transversely linear connected reinforcement body.

[0009] Preferably, a collaborative design of freezing and electric field orientation methods is adopted to influence the growth direction and morphology of ice crystals through temperature gradient to achieve microstructural regulation of the composite skeleton.

[0010] Preferably, the "plate-nail" composite structure comprises a diamond "plate" and carbon fiber "nail".

[0011] Preferably, diamond "plates" are located within the composite structure.

[0012] Preferably, carbon fiber "spikes" are located in the composite structure.

[0013] Preferably, a "plate-nail type" composite structure PCM.

[0014] Preferably, the preparation method of PCM comprises the following steps: S1: Preparation of vertically oriented layered aerogel skeletons; S2: Preparation of “plate-nail” composite structure skeleton.

[0015] Preferably, S1 comprises the following steps: S11: Diamond (20-500 mg / mL) was ultrasonically dispersed in a polyvinyl alcohol (PVA) aqueous solution (2 wt%) to prepare slurries with different solid contents; S12: using a cell disruptor to ultrasonically treat the slurry liquid at 30% of the rated power for 30-60 minutes, and then vacuum degassing for 2-3 hours for standby use; S13: pouring the slurry into a custom square polytetrafluoroethylene mold (30 mm×30 mm×20 mm), the bottom of the mold is provided with a polydimethylsiloxane wedge structure with an inclination angle of 15°; S14: A solid copper cylinder is placed vertically in the center of the Dewar flask as a refrigerant transmission body, a mold containing the slurry is placed on the upper surface of the copper cylinder, and then a freezing medium (liquid nitrogen) is added to immerse the copper cylinder therein, and the refrigerant is transferred to the bottom of the mold through the copper cylinder to cause the aqueous slurry to begin to freeze; S15: Under the induction of temperature gradients in the x and z directions, ice crystals grow along these two directions into ice sheets parallel to the xz plane, while squeezing and displacing diamonds to form diamond "plates" with a layered structure; S16: The frozen sample is placed in a freeze dryer and de-iced at a set temperature (-50°C) and vacuum degree (<10Pa) to obtain a vertically oriented layered diamond aerogel skeleton.

[0016] Preferably, S2 comprises the following steps: S21: First, polyethylene glycol (PEG, molecular weight 2000-16000) was heated to 90°C and maintained for 0.5 h to melt it into a transparent liquid; S22: Add (5-100 mg / mL) carbon fiber (CF) and mix well; S23: impregnating the mixed solution into the diamond aerogel at 90 °C by vacuum assistance, and then applying a high voltage electric field horizontally parallel to the y-axis direction of the aerogel; S24: With the help of aerogel capillary adsorption effect - electric field induced self-assembly, the conductive CF tends to be oriented horizontally in the diamond pore wall layer, thereby self-assembling to obtain a diamond / carbon fiber skeleton with a dual-oriented composite structure. The high insulation performance of diamond makes the aerogel structure completely unaffected by the electric field and still maintains a vertical high orientation; S25: Finally, the sample was cooled and solidified at room temperature. The high voltage electric field was maintained during this process. The obtained composite PCM was named DD / CF / PEG.

[0017] Compared with the prior art, the present invention has the following beneficial effects: In the present invention, ice crystals formed during the freezing process of water are used as templates, and a layered aerogel skeleton in the vertical direction is prefabricated based on ice crystal-induced self-assembly to obtain a longitudinally layered interconnected heat-conducting body, thereby ensuring directional and rapid heat transmission.

[0018] In the present invention, a small amount of one-dimensional micron-sized carbon fiber reinforcement material is introduced into PCM through vacuum-assisted impregnation, and the carbon fibers are oriented and arranged horizontally between the diamond pore wall layers by means of the capillary adsorption effect-electric field induced self-assembly, thereby obtaining a carbon fiber "nail" that connects the reinforcement in a transverse linear manner, thereby accelerating the phase change efficiency of PCM and enhancing the mechanical strength in the y-axis direction.

[0019] In the present invention, the synergistic effect between the "plate" and "nail" structures can quickly store heat in the form of high phase change latent heat, and can play a "double lock" fixing role on the molten PCM, effectively improving the shape stability of the composite PCM. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a SEM image of the "plate-nail type" dual-oriented composite structure PCM in the present invention; Figure 2 is the out-of-plane thermal conductivity of the composite PCM with different contents in the present invention; Figure 3 is the DSC graph of the composite PCM with different contents in the present invention; Figure 4 The present invention compares the anti-leakage and mechanical properties of PEG and the prepared composite PCM during the heating process. DETAILED DESCRIPTION

[0021] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0022] See also Figure 1-Figure 4 The present invention provides a thermally conductive phase change material based on a "plate-nail" composite structural skeleton. Aiming at the scientific problem that it is difficult for existing composite materials to realize out-of-plane orderly interconnected skeleton construction, the present invention uses a two-way freezing method to construct a three-dimensional directional interconnected skeleton. At the same time, it proposes to use electric field induction to perform multi-scale structural design and construct a one-dimensional reinforcement path perpendicular to the skeleton layer direction, so as to achieve high out-of-plane thermal conductivity, high phase change efficiency and shape stability of the composite PCM while still maintaining its high phase change latent heat characteristics; Zero-dimensional nano-diamond was selected as the thermal conductive material, and a layered aerogel skeleton in the vertical direction was prefabricated based on ice crystal induced self-assembly as the support. A small amount (1-3 wt%) of one-dimensional micron-sized carbon fiber reinforcement was introduced into PCM by vacuum-assisted impregnation. With the help of capillary adsorption effect-electric field induced self-assembly, the carbon fibers were oriented and arranged in the horizontal direction between the diamond pore walls, and a "plate-nail" composite structure PCM with both longitudinal layered connected thermal conductive body and transverse linear connection reinforcement was obtained. The microstructure of the composite skeleton was regulated by using the collaborative design of freezing and electric field orientation methods, and the growth direction and morphology of ice crystals were affected by temperature gradient. On the one hand, the diamond "plate" in the "plate-nail" composite structure can ensure the directional and rapid transmission of heat energy inside PCCs, while the carbon fiber "nail" can accelerate the phase change efficiency of PCM and enhance the mechanical strength in the direction perpendicular to the skeleton layer; on the other hand, the synergistic effect between the "plate" and "nail" structures can enable the heat to be quickly stored in the form of high phase change latent heat, and can play a "double lock" fixing role on the molten PCM, effectively improving the shape stability of the composite PCM.

[0023] The preparation steps of PCM are as follows: S1: Preparation of vertically oriented layered aerogel skeletons; S2: Preparation of “plate-nail” composite structure skeleton.

[0024] The specific steps of S1 are: Diamond (20-500 mg / mL) was ultrasonically dispersed in a polyvinyl alcohol (PVA) aqueous solution (2 wt%) to prepare slurries with different solid contents. The slurries were ultrasonically treated for 30-60 min at a rated power of 30% using a cell disruptor, and then vacuum degassed for 2-3 h for use. The slurry was poured into a custom square polytetrafluoroethylene mold (30 mm × 30 mm × 20 mm), and a polydimethylsiloxane wedge structure with an inclination angle of 15° was provided at the bottom of the mold. A solid copper cylinder was placed vertically in the center of the Dewar flask as a refrigerant transmission body, and the mold containing the slurry was placed on the upper surface of the copper cylinder. Then, a freezing medium (liquid nitrogen) was added to immerse the copper cylinder in it. The refrigerant was transferred to the bottom of the mold through the copper cylinder to cause the aqueous slurry to begin to freeze. Under the induction of temperature gradients in the x and z directions, ice crystals grew along these two directions into ice crystals parallel to the xz plane, while squeezing and displacing diamonds to form a diamond "plate" with a layered structure ( Figure 1 The frozen sample was placed in a freeze dryer and de-iced at a set temperature (-50 °C) and vacuum (<10 Pa) to obtain a vertically oriented layered diamond aerogel skeleton.

[0025] The specific steps of S2 are: First, polyethylene glycol (PEG, molecular weight 2000-16000) was heated to 90 °C and kept for 0.5 h to melt it into a transparent liquid, and carbon fiber (CF) (5-100 mg / mL) was added and mixed evenly. Secondly, the mixed liquid was impregnated into the diamond aerogel at 90 °C with vacuum assistance, and then a high voltage electric field ( Figure 1 ). With the help of aerogel capillary adsorption effect-electric field induced self-assembly, the conductive CF tends to be oriented horizontally in the diamond pore wall layer, thereby self-assembling to obtain a diamond / carbon fiber skeleton with a dual-oriented composite structure. The high insulation performance of diamond makes the aerogel structure completely unaffected by the electric field and still maintains a vertical high orientation. Finally, the sample is cooled and solidified at room temperature, and this process maintains the high voltage electric field. The obtained composite PCM is named DD / CF / PEG.

[0026] A multifunctional composite PCM was developed based on a new strategy of bidirectional ice template method coupled with electric field induced dual assembly. Nano-diamond was used as the thermal conductivity reinforcement material, and a vertically oriented diamond layered thermal conductive skeleton support was prefabricated based on ice crystal induced self-assembly. A small amount of micron-sized carbon fiber reinforcement was introduced by vacuum-assisted impregnation PEG. The external electric field was used to induce the horizontal orientation of the carbon fibers and make them evenly distributed between the diamond pore wall layers, thereby obtaining a "plate-nail-type" dual-oriented composite structural skeleton with both a longitudinally layered connected thermal conductive body and a transverse linear connecting reinforcement. The dual-oriented composite structural skeleton has a vertically oriented high-speed phonon transmission channel and a horizontally oriented efficient enhanced transmission path, which can achieve high out-of-plane thermal conductivity, high phase change latent heat, shape stability and excellent mechanical strength.

[0027] In view of the scientific difficulty of existing composite PCM in realizing out-of-plane orderly interconnected skeleton construction, it is proposed to use ice crystals formed by water in the freezing process as a template to prefabricate a layered aerogel skeleton in the vertical direction based on ice crystal induced self-assembly, thereby obtaining a longitudinally layered interconnected heat-conducting body to ensure the directional and rapid transmission of heat. In order to improve the temperature response speed of the support body to the inside of the PCM and enhance the mechanical strength in the y-axis direction, a small amount of one-dimensional micron-sized carbon fiber reinforcement material was introduced into the PCM through vacuum-assisted impregnation. With the help of capillary adsorption effect-electric field-induced self-assembly, the carbon fibers were oriented and arranged horizontally between the diamond pore wall layers to obtain a carbon fiber "nail" that connects the reinforcement body in a transverse linear manner, which accelerates the phase change efficiency of the PCM and enhances the mechanical strength in the y-axis direction. The synergistic effect between the "plate" and "nail" structures enables rapid storage of heat in the form of high phase change latent heat, and can play a "double lock" role in fixing the molten PCM, effectively improving the shape stability of the composite PCM.

[0028] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

Claims

1. Thermally conductive phase change material based on a "plate-nail" composite structural skeleton, characterized by: A three-dimensional directional connected skeleton was constructed using the bidirectional freezing method, and multi-scale structural design was carried out with the help of electric field induction. A one-dimensional reinforcement path perpendicular to the direction of the skeleton layer was constructed. Zero-dimensional nanoscale diamond was selected as the thermal conductive material, and a layered aerogel skeleton in the vertical direction was prefabricated based on ice crystal induced self-assembly as a support.

2. The thermally conductive phase change material based on the "plate-nail type" composite structural skeleton as claimed in claim 1, characterized in that: A small amount (1-3wt%) of one-dimensional micron-sized carbon fiber reinforcement is introduced into PCM through vacuum-assisted impregnation. With the help of capillary adsorption effect-electric field induced self-assembly, the carbon fibers are oriented and arranged horizontally between the diamond pore wall layers, forming a "plate-nail" composite structure PCM with both a longitudinal layered connected heat-conducting body and a transverse linear connection reinforcement body.

3. The thermally conductive phase change material based on the "plate-nail" composite structural skeleton as claimed in claim 2, characterized in that: By adopting the collaborative design of freezing and electric field orientation methods, the growth direction and morphology of ice crystals are affected by temperature gradient to achieve microstructural regulation of the composite skeleton.

4. The thermally conductive phase change material based on the "plate-nail type" composite structural skeleton as claimed in claim 3, characterized in that: The "plate-nail" composite structure consists of diamond "plates" and carbon fiber "nails".

5. The thermally conductive phase change material based on the "plate-nail type" composite structural skeleton as claimed in claim 4, characterized in that: Diamond "plates" are located within the composite structure.

6. The thermally conductive phase change material based on the "plate-nail" composite structural skeleton as claimed in claim 5, characterized in that: Carbon fiber "spikes" are located in the composite structure.

7. The thermally conductive phase change material based on the "plate-nail" composite structural skeleton as claimed in claim 6, characterized in that: "Board-nail" composite structure PCM.

8. The thermally conductive phase change material based on the "plate-nail" composite structural skeleton as claimed in claim 7, characterized in that: The preparation steps of PCM are as follows: S1: Preparation of vertically oriented layered aerogel skeletons; S2: Preparation of "plate-nail" composite structure skeleton.

9. The thermally conductive phase change material based on the "plate-nail type" composite structural skeleton as claimed in claim 8, characterized in that: S1 includes the following steps: S11: Diamond (20-500 mg / mL) was ultrasonically dispersed in a polyvinyl alcohol (PVA) aqueous solution (2 wt%) to prepare slurries with different solid contents; S12: using a cell disruptor to ultrasonically treat the slurry liquid at 30% of the rated power for 30-60 minutes, and then vacuum degassing for 2-3 hours for standby use; S13: pouring the slurry into a custom square polytetrafluoroethylene mold (30 mm×30 mm×20 mm), the bottom of the mold is provided with a polydimethylsiloxane wedge structure with an inclination angle of 15°; S14: A solid copper cylinder is placed vertically in the center of the Dewar flask as a refrigerant transmission body, a mold containing the slurry is placed on the upper surface of the copper cylinder, and then a freezing medium (liquid nitrogen) is added to immerse the copper cylinder therein, and the refrigerant is transferred to the bottom of the mold through the copper cylinder to cause the aqueous slurry to begin to freeze; S15: Under the induction of temperature gradients in the x and z directions, ice crystals grow along these two directions into ice sheets parallel to the xz plane, while squeezing and displacing diamonds to form diamond "plates" with a layered structure; S16: The frozen sample is placed in a freeze dryer and de-iced at a set temperature (-50°C) and vacuum degree (<10Pa) to obtain a vertically oriented layered diamond aerogel skeleton.

10. The thermally conductive phase change material based on the "plate-nail" composite structural skeleton as claimed in claim 9, characterized in that: S2 includes the following steps: S21: First, polyethylene glycol (PEG, molecular weight 2000-16000) was heated to 90°C and maintained for 0.5 h to melt it into a transparent liquid; S22: Add (5-100 mg / mL) carbon fiber (CF) and mix well; S23: impregnating the mixed solution into the diamond aerogel at 90 °C by vacuum assistance, and then applying a high voltage electric field horizontally parallel to the y-axis direction of the aerogel; S24: With the help of aerogel capillary adsorption effect - electric field induced self-assembly, the conductive CF tends to be oriented horizontally in the diamond pore wall layer, thereby self-assembling to obtain a diamond / carbon fiber skeleton with a dual-oriented composite structure. The high insulation performance of diamond makes the aerogel structure completely unaffected by the electric field and still maintains a vertical high orientation; S25: Finally, the sample was cooled and solidified at room temperature. The high voltage electric field was maintained during this process. The obtained composite PCM was named DD / CF / PEG.

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