Preparation and Application of Radial Heat Transfer Enhanced Ordered Array Electrothermal Conversion Shape-Stabilized Phase Change Material

Abstract

The preparation and application of a radially heat-transfer-enhanced ordered array electrothermal conversion shape-stabilized phase change material belongs to the field of phase change energy storage technology. A chemically cross-linked polymer with shape-stabilizing capabilities is selected as the phase change material, which is polymerized from a prepolymer under the action of an initiator. A polyacrylonitrile carbon fiber array connected to thermally conductive reinforcing fins is used as the support material to load the aforementioned polymeric phase change material, thus obtaining the electrothermal conversion shape-stabilized phase change material. This material establishes an axially electrically insulating and thermally conductive path for the ordered conductive array, achieving separation of the thermal and electrical conduction paths and constructing a radially heat-transfer-enhanced ordered array electrothermal conversion shape-stabilized phase change system. This phase change material has a phase change temperature of 41-45℃, a high phase change enthalpy, excellent electrical and thermal conductivity, no leakage during operation, and a long phase change process duration. The preparation method is simple, the raw materials are abundant, and it has good electrothermal conversion performance, making it suitable for a wide range of applications in fields such as human electrothermal therapy and heat dissipation in electronic devices.

Description

Technical Field

[0001] This invention relates to the preparation and application of a radially heat-transfer-enhanced ordered array electrothermal conversion shaped phase change material, which belongs to the field of phase change energy storage technology. Background Technology

[0002] Thermal energy, as one of the most abundant energy sources, is the foundation of industrial production in many countries, accounting for approximately 60-70% of the world's current energy consumption. However, thermal energy suffers from low utilization efficiency and spatiotemporal mismatch in practical applications, necessitating the development of new thermal energy storage technologies. Compared to other thermal storage methods, phase change thermal storage offers higher heat storage density, better stability, and controllability. It primarily utilizes phase change materials to store heat, achieving higher energy conversion efficiency. With the increasing severity of energy issues, finding clean, renewable, and non-toxic energy production and storage methods has become an urgent challenge for researchers. Solar energy, with its abundant, widespread, and clean characteristics, is considered one of the most promising sustainable energy sources, thus photothermal phase change materials have received extensive attention and exploration. However, the instability and spatiotemporal discontinuity of solar radiation intensity limit the practical application of photothermal phase change materials. Electrical energy, with its active, clean, and spatiotemporally unrestricted characteristics, makes electrothermal phase change an effective alternative to photothermal phase change.

[0003] Unlike inorganic phase change materials, which often exhibit phase separation and supercooling, organic phase change materials offer advantages such as controllable phase change temperature, good stability, and low cost, making them widely applicable in textiles, foams, fibers, and industrial thermal storage. However, their inherent low thermal and electrical conductivity severely limit their development.

[0004] The basic mechanism of electrothermal conversion involves the collision of moving electrons with other molecules or groups when an electric current flows through a conductive phase change material, generating Joule heat. The phase change material absorbs and releases this Joule heat, storing it as latent heat, thus completing the conversion and storage of electrical energy into thermal energy. From the perspective of electrical and thermal conductivity mechanisms, high electrical conductivity implies high thermal conductivity, but high thermal conductivity does not necessarily mean high electrical conductivity. Furthermore, the core challenge in preparing high-performance electrothermal conversion phase change materials lies in the fact that their thermal and electrical conduction pathways are the same, resulting in significant energy loss and low electrothermal conversion efficiency. Therefore, a method is needed to comprehensively improve the electrical and thermal conductivity of composite phase change materials. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a novel radially heat-transfer-enhanced ordered array electrothermal conversion shaping phase change material and its preparation method. Taking an axially efficient conductive path and a radially thermally enhanced ordered carbon fiber array as a breakthrough, an axially electrically insulating thermally conductive path is constructed for the ordered conductive array, achieving separation of the thermal and electrical conductive paths, thus building a radially heat-transfer-enhanced ordered array electrothermal conversion shaping phase change system. The radially heat-transfer-enhanced ordered array electrothermal conversion shaping phase change material prepared by this invention exhibits significantly improved thermal and electrical conductivity, a large phase change enthalpy, and excellent shaping effect, with no liquid leakage during operation. The synthesis process of this type of material is simple, and it has broad application prospects in fields such as human electrothermal therapy and heat dissipation for electronic devices.

[0006] The technical solution of the present invention is as follows: a radial heat transfer enhanced ordered array electrothermal conversion shaping phase change material, wherein the electrothermal conversion shaping phase change material uses a polyacrylonitrile carbon fiber array with excellent thermal and electrical conductivity as a supporting material, and connects a thermally conductive reinforcing agent and a chemically cross-linked polymer phase change material; the chemically cross-linked polymer phase change material is polymerized from a prepolymer under the action of an initiator.

[0007] The mass percentage of the components in the electrothermal conversion shape-stabilized phase change material is:

[0008] Chemically cross-linked polymer phase change materials: 60%-80%

[0009] Polyacrylonitrile carbon fiber: 20%-30%

[0010] Thermal conductivity enhancer: 0.1-1%.

[0011] The phase transition enthalpy of the electrothermal conversion shaping phase change material is 90-100 J / g, and the phase transition temperature is distributed between 41-45℃.

[0012] The prepolymer is at least one of methoxyethylene glycol methacrylate, ethylene, vinyl acetate, vinyl chloride, and styrene;

[0013] The initiator is one of azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, ammonium persulfate, azobisisoheptanenitrile, cumene hydroperoxide, dodecyl peroxide, and para-monane hydroperoxide.

[0014] The mass ratio of the prepolymer to the initiator is 1000:5-1000:10.

[0015] The thermal conductivity enhancer is one to three of the following: graphene, graphene oxide, single-arm carbon nanotubes, multi-walled carbon nanotubes, boron nitride nanoparticles, carbon black, expanded graphite, silver nanoparticles, copper nanoparticles, gold nanoparticles, aluminum, aluminum oxide, bismuth oxide, magnesium oxide, zinc oxide, aluminum nitride, and bismuth nitride.

[0016] A method for preparing a radially heat-transfer-enhanced ordered array electrothermal conversion shape-stabilized phase change material includes the following steps:

[0017] (1) Polyacrylonitrile fibers are placed in a tube furnace for high-temperature carbonization to obtain polyacrylonitrile carbon fibers;

[0018] (2) The thermally conductive reinforcing agent is mixed with the solvent to prepare a uniform solution with a mass fraction of 0.05%-5%. The thermally conductive reinforcing agent is attached to the carbon fiber surface as fins using the ice template method to obtain radially heat-conducting reinforced carbon fiber.

[0019] (3) After arranging the radial heat transfer reinforced carbon fiber array, add prepolymer and initiator, vacuum impregnate at 70-90℃ for 1-4h, and cool to room temperature to obtain radial heat transfer reinforced ordered array electrothermal conversion shape-stabilized phase change material.

[0020] In step (1), the first stage of carbonization is to raise the temperature of the carbonization furnace from 180℃ to 260℃ and circulate air; the second stage is to raise the temperature of the carbonization furnace from 260℃ to 600℃-900℃ under argon protection and keep it at that temperature for 1-4 hours.

[0021] The solvent mentioned in step (2) is one or two of the following: water, benzene, toluene, DMF, DMSO, tetrahydrofuran, methanol, ethanol, and acetone;

[0022] The particle size of the thermal conductivity enhancer is 10-30 micrometers.

[0023] Application of a radially heat-transfer-enhanced ordered array electrothermal conversion shaped phase change material, which is used in human body electrothermal therapy devices or heat dissipation devices for electronic devices.

[0024] Furthermore, the preparation method of radial heat transfer enhanced ordered array electrothermal conversion shape-stabilized phase change material includes the following steps:

[0025] Step 1: Preparation of polyacrylonitrile carbon fiber

[0026] Polyacrylonitrile fibers are placed in a tube furnace for carbonization. The first stage of carbonization is to raise the temperature of the carbonization furnace from 180℃ to 260℃ at a rate of 1℃ / min, while air is introduced. The second stage is to raise the temperature of the carbonization furnace from 260℃ to 600-900℃ (which can be 600℃, 700℃, 800℃, or 900℃) under argon protection at a rate of 10℃ / min, and hold at that temperature for 1-4 hours.

[0027] Step 2: Preparation of thermally conductive enhanced support material

[0028] A uniform solution with a mass fraction of 0.05%-5% was prepared by mixing the thermal conductivity enhancer with a solvent. The thermal conductivity enhancer was then attached to the carbon fiber surface in the form of fins using the ice template method to obtain radially heat-conducting reinforced carbon fiber.

[0029] Step 3: Preparation of composite shape-stabilized phase change materials

[0030] After arranging radially heat-transferring reinforced carbon fiber arrays, prepolymer and initiator (mass ratio of 1000:5-1000:10) are added, and the mixture is vacuum impregnated at 70-90℃ for 1-4 h, then cooled to room temperature to obtain radially heat-transferring reinforced ordered array electrothermal conversion shape-stabilized phase change material.

[0031] This phase change material is used in human electrothermal therapy devices or heat dissipation devices for electronic devices.

[0032] The beneficial effects of this invention are as follows: This invention provides a novel radially heat-transfer-enhanced ordered array electrothermal conversion shaping phase change material. It utilizes an axially efficient conductive path and a radially heat-conducting enhanced ordered carbon fiber array as a breakthrough point. An axially electrically insulating thermally conductive path is constructed for the ordered conductive array, achieving separation of the thermally and electrically conductive paths, thus building a radially heat-transfer-enhanced ordered array electrothermal conversion shaping phase change system. Compared to existing technologies, the fibers are arranged in an orderly manner along the current direction, exhibiting high axial (current direction) conductivity, enabling electrothermal conversion and heat energy storage under low pressure. The introduction of radial (current-perpendicular) thermally conductive fins forms an insulating, highly thermally conductive path, achieving separation of the conductive and thermally conductive paths. Simultaneously, combined with a comb-shaped shaping phase change material, it constructs an electrothermal conversion phase change system with high electrothermal conversion efficiency and low driving voltage.

[0033] This application selects a chemically cross-linked polymer with shape-stabilizing capabilities as the phase change material, which is polymerized from a prepolymer under the action of an initiator. A polyacrylonitrile carbon fiber array connected to thermally conductive reinforcing fins is used as the supporting material to load the aforementioned polymeric phase change material, resulting in a radially heat-transfer-enhanced ordered array electrothermal conversion shape-stabilized phase change material. The material prepared by this invention has a phase change temperature distribution of 41-45℃, a high phase change enthalpy, excellent electrical and thermal conductivity, no leakage during operation, and a long phase change process duration. The material preparation method is simple, the raw materials are abundant, and it has good electrothermal conversion performance, making it suitable for a wide range of applications in fields such as human electrothermal therapy and heat dissipation in electronic devices. Attached Figure Description

[0034] Figure 1 The image shown is a scanning electron microscope image of the carbon fiber in Example 1, where: a, carbon fiber, b, radially heat-conducting reinforced carbon fiber.

[0035] Figure 2 The infrared spectrum of the chemically cross-linked comb-like polymer phase change material in Example 1 is shown.

[0036] Figure 3 This is a diagram showing the shaping effect of the radial heat transfer enhanced ordered array electrothermal conversion shaping phase change material in Example 1.

[0037] Figure 4 The DSC curves are for the chemically cross-linked polymer phase change material and the radially heat-transfer-enhanced ordered array electrothermal conversion shaped phase change material in Example 1.

[0038] Figure 5 The temperature rise curves of the radial heat transfer enhanced ordered array electrothermal conversion shaped phase change material and the blank material without added thermal conductivity enhancer in Example 1 are shown under the same applied voltage.

[0039] Figure 6 The electrothermal conversion curves of the radial heat transfer enhanced ordered array electrothermal conversion shaped phase change material in Example 1 under different applied voltages are shown. Detailed Implementation

[0040] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way. Unless otherwise specified, the test methods described in the following embodiments are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Example

[0041] (1) Polyacrylonitrile fibers are carbonized in a tube furnace to obtain polyacrylonitrile carbon fibers. The first stage of carbonization is to raise the temperature of the carbonization furnace from 180℃ to 260℃ at a rate of 1℃ / min and to pass air. The second stage is to raise the temperature of the carbonization furnace from 260℃ to 900℃ under argon protection at a rate of 10℃ / min and to hold it for 2 hours.

[0042] (2) Polyacrylonitrile carbon fibers were added to a nano boron nitride aqueous dispersion (containing 1 g of boron nitride with a particle size of 10 micrometers and a mass fraction of 5% of nano boron nitride in the dispersion), and then freeze-dried to obtain radial heat transfer reinforced carbon fibers.

[0043] (3) After arranging 0.6g of radial heat transfer reinforced carbon fiber in the mold, add methoxyethylene glycol methacrylate and benzoyl peroxide (mass ratio 1000:9), 80 o Vacuum drying at C for 2 hours and cooling to room temperature yields a radially heat-transfer-enhanced ordered array electrothermal conversion shape-stabilized phase change material.

[0044] Figure 1These are electron microscope images of polyacrylonitrile (PA) carbon fibers and radially heat-conducting reinforced carbon fibers with boron nitride (BN) fins. 10-micron boron nitride nanoparticles are a better match for the size of PA carbon fibers. A 5% (w / w) boron nitride dispersion allows for grafting more thermally conductive reinforcing agent onto the carbon fibers, representing the optimal dispersion concentration.

[0045] Figure 2 This is a comparison of the infrared spectra of the chemically cross-linked polymer phase change material and the prepolymer in Example 1. As can be seen from the figure, the infrared peak of the chemically cross-linked polymer phase change material is significantly shorter than that of the prepolymer at 1637 cm⁻¹. -1 The disappearance of the stretching vibration peak belonging to the carbon-carbon double bond indicates that the prepolymer has undergone a polymerization reaction. The prepared composite phase change material exhibits excellent shape retention. When the prepolymer methoxyethylene glycol methacrylate and the composite phase change material are placed on a 70°C heating platform, the prepolymer partially melts after 4 minutes and completely melts after 10 minutes, losing its original shape. However, the composite phase change material shows no significant change in appearance or shape, maintaining its shape stability without leakage. Figure 3 ).

[0046] After being loaded onto a radially heat-transfer-reinforced carbon fiber array, the phase change material (PCM) exhibits excellent electrical and thermal conductivity. The phase change enthalpy of the polymer PCM is 121.40 J / g, while that of the composite PCM reaches 96.90 J / g, still exhibiting a high phase change enthalpy. The DSC curves of the obtained polymer PCM and the radially heat-transfer-reinforced ordered array electrothermal conversion shaped PCM are shown below. Figure 4 .

[0047] Figure 5 The figures show the temperature rise curves of the thermally enhanced composite phase change material and the blank material without added thermally enhanced agent in Example 1 at the same voltage (5V). It can be seen that the blank material without added boron nitride heats up to 70°C. o C takes 442 seconds, while the thermally enhanced composite phase change material with added boron nitride only takes 308 seconds, significantly improving thermal conductivity.

[0048] Figure 6 The heating curves of the radial heat transfer enhanced ordered array electrothermal conversion shaped phase change material in Example 1 under different voltages show that when a higher voltage is applied, the overall heat storage and release rate of the electrothermal conversion phase change material accelerates, and the energy conversion efficiency is improved.

[0049] Examples 2-5

[0050] The temperature of the second-stage carbonization tube furnace was increased from 260℃ to 600℃, 700℃, 800℃, and 1000℃ respectively to obtain the corresponding radially heat-transfer-enhanced ordered array electrothermal conversion shaped phase change materials. Other conditions were consistent with those in Example 1. The carbon fibers obtained at 600-800℃ had slightly poor electrical conductivity, while the carbon fibers obtained at 1000℃ were brittle and unsuitable for further research.

[0051] Examples 6-7

[0052] By changing the particle size of boron nitride nanoparticles to 30 micrometers and 50 micrometers, respectively, corresponding radial heat transfer enhanced ordered array electrothermal conversion shaped phase change materials were obtained, with other conditions consistent with the corresponding Example 1. The 50-micrometer boron nitride nanoparticle size is larger than the diameter of carbon fibers, making it difficult to attach to the fiber surface to form thermally conductive fins, resulting in minimal improvement in the system's thermal conductivity.

[0053] Examples 8-9

[0054] By changing the mass fraction of the boron nitride nano-dispersion to 0.5% and 0.05%, respectively, radially heat-transfer-enhanced ordered array electrothermal conversion shaped phase change materials were obtained, with other conditions consistent with the corresponding Example 1. In the 0.5% mass fraction boron nitride nano-dispersion, the effect of grafting boron nitride nano-carbon fiber onto the material was slightly worse; in the 0.05% mass fraction boron nitride nano-dispersion, the effect of grafting boron nitride nano-carbon fiber onto the material was poor, with only a small improvement in thermal conductivity. Example

[0055] By changing the mass of radially heat-transferring reinforced carbon fibers to 1g, a corresponding radially heat-transferring reinforced ordered array electrothermal conversion shaped phase change material was obtained, with other conditions consistent with the corresponding Example 1. Increasing the mass fraction of carbon fibers in the system reduced the electrothermal conversion efficiency of the phase change system.

[0056] Examples 11-18

[0057] Benzene, toluene, DMF, DMSO, tetrahydrofuran, methanol, ethanol, and acetone were used as solvents for thermal conductivity enhancement to obtain corresponding radially heat-transfer-enhanced ordered array electrothermal conversion shaped phase change materials, with other conditions consistent with those in Example 1. Among the solvents mentioned above, ethanol and tetrahydrofuran showed good dispersion effects on boron nitride nanoparticles, comparable to Example 1. Other dispersants showed slightly worse dispersion effects on boron nitride nanoparticles, and the effect of grafting boron nitride nanoparticles onto carbon fibers decreased accordingly.

[0058] Examples 19-34

[0059] Graphene, graphene oxide, single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon black, expanded graphite, nano-silver, nano-copper, nano-gold, aluminum, alumina, bismuth oxide, magnesium oxide, zinc oxide, aluminum nitride, and bismuth nitride were used as thermal conductivity enhancers to obtain corresponding radially heat-transfer-enhanced ordered array electrothermal conversion shaped phase change materials, with other conditions consistent with Example 1. The aforementioned thermal conductivity enhancers, nano-silver, nano-copper, nano-gold, aluminum, and alumina, can be attached to the carbon fiber surface using an ice-templating method to form thermally conductive fins, with effects comparable to Example 1; the affinity between the remaining thermal conductivity enhancers and carbon fibers is slightly weaker.

[0060] Examples 35-38

[0061] Ethylene, vinyl acetate, vinyl chloride, and styrene were used as prepolymers to obtain corresponding radially heat-transfer-enhanced ordered array electrothermal conversion shape-stabilizing phase change materials, with other conditions consistent with Example 1. Among the prepolymers, the polymer obtained from ethylene and styrene showed good shape-stabilizing effect comparable to that of Example 1, but its phase change enthalpy was lower. The shape-stabilizing effect of the prepolymers of vinyl acetate and vinyl chloride was slightly worse than that of the prepolymers of ethylene and styrene.

[0062] Examples 39-45

[0063] Azobisisobutyronitrile, potassium persulfate, ammonium persulfate, azobisisoheptanenitrile, cumene hydroperoxide, dodecyl peroxide, and p-menthol hydroperoxide were used as initiators to obtain corresponding radial heat transfer enhanced ordered array electrothermal conversion shape-stabilized phase change materials, with other conditions consistent with Example 1.

[0064] Examples 46-50

[0065] By changing the mass ratio of prepolymer to initiator to 1000:5, 1000:6, 1000:7, 1000:8, and 1000:10, respectively, corresponding radial heat transfer enhanced ordered array electrothermal conversion shape-stabilized phase change materials were obtained, with other conditions remaining consistent with Example 1. Among the above mass ratios, the 1000:8 and 1000:10 mass ratios could completely initiate the reaction, with effects comparable to Example 1. However, the 1000:5, 1000:6, and 1000:7 mass ratios could not completely initiate the reaction, resulting in a lower reaction yield compared to Example 1.

Claims

1. A radially heat-transfer-enhanced ordered array electrothermal conversion shape-stabilized phase change material, characterized in that: The electrothermal conversion shaping phase change material uses polyacrylonitrile carbon fiber as the supporting material, and connects a thermally conductive reinforcing agent and a chemically cross-linked polymeric phase change material; the chemically cross-linked polymeric phase change material is polymerized from a prepolymer under the action of an initiator. The prepolymer is at least one of methoxyethylene glycol methacrylate, ethylene, vinyl acetate, vinyl chloride, and styrene; the initiator is one of azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, ammonium persulfate, azobisisoheptanenitrile, cumene hydroperoxide, dodecyl peroxide, and para-monane hydroperoxide. The thermal conductivity enhancer is one to three of the following: graphene, graphene oxide, single-arm carbon nanotubes, multi-walled carbon nanotubes, boron nitride nanoparticles, carbon black, expanded graphite, silver nanoparticles, copper nanoparticles, gold nanoparticles, aluminum, aluminum oxide, bismuth oxide, magnesium oxide, zinc oxide, aluminum nitride, and bismuth nitride.

2. The radial heat transfer enhanced ordered array electrothermal conversion shape-stabilized phase change material according to claim 1, characterized in that: The mass percentage of the components in the electrothermal conversion shape-stabilized phase change material is: Chemically cross-linked polymer phase change materials: 60%-80% Polyacrylonitrile carbon fiber: 20%-30% Thermal conductivity enhancer: 0.1-1%.

3. The radial heat transfer enhanced ordered array electrothermal conversion shape-stabilized phase change material according to claim 1, characterized in that: The phase transition enthalpy of the electrothermal conversion shaping phase change material is 90-100 J / g, and the phase transition temperature is distributed between 41-45℃.

4. The radial heat transfer enhanced ordered array electrothermal conversion shape-stabilized phase change material according to claim 1, characterized in that: The mass ratio of the prepolymer to the initiator is 1000:5-1000:

10.

5. A method for preparing a radially heat-transfer-enhanced ordered array electrothermal conversion shape-stabilized phase change material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Polyacrylonitrile fibers are carbonized in a tube furnace to obtain polyacrylonitrile carbon fibers; (2) The thermal conductivity reinforcing agent is mixed with the solvent to prepare a uniform solution with a mass fraction of 0.05%-5%. The thermal conductivity reinforcing agent is attached to the surface of polyacrylonitrile carbon fiber as fins using the ice template method to obtain radially heat-transfer reinforcing carbon fiber. (3) After arranging the radial heat transfer reinforced carbon fiber array, add prepolymer and initiator, vacuum impregnate at 70-90℃ for 1-4h, and cool to room temperature to obtain radial heat transfer reinforced ordered array electrothermal conversion shape-stabilized phase change material.

6. The preparation method according to claim 5, characterized in that: In step (1), the first stage of carbonization is to raise the temperature of the carbonization furnace from 180℃ to 260℃ and circulate air; the second stage is to raise the temperature of the carbonization furnace from 260℃ to 600℃-900℃ under argon protection and keep it at that temperature for 1-4 hours.

7. The preparation method according to claim 5, characterized in that: The solvent mentioned in step (2) is one or two of water, benzene, toluene, DMF, DMSO, tetrahydrofuran, methanol, ethanol, and acetone; the particle size of the thermal conductivity enhancer is 10-30 micrometers.

8. The application of the radial heat transfer enhanced ordered array electrothermal conversion shaping phase change material according to any one of claims 1-4, characterized in that: This phase change material is used in human electrothermal therapy devices or heat dissipation devices for electronic devices.

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