CN117625139A - Anisotropic flexible composite phase change material and preparation method thereof - Google Patents
Anisotropic flexible composite phase change material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses an anisotropic flexible phase change material, which comprises a phase change matrix material, a supporting material and a heat conduction reinforcing agent, wherein the mass ratio of the phase change matrix material to the supporting material to the heat conduction reinforcing agent is (55-65): (30-35): (5-10), the phase change matrix adopts paraffin, the flexible support carrier adopts hydroxy cellulose nano fiber, and the heat conduction enhancer is expanded graphite. And (3) completely melting paraffin wax, adding the paraffin wax into the expanded graphite, adsorbing liquid paraffin wax in a porous structure of the expanded graphite, and adding the hydroxycellulose nanofiber to prepare the anisotropic flexible heat-conducting composite phase change material. According to the invention, a specific directional freezing device is adopted, so that the high consistency of the orientation of the expanded graphite in the phase change material after directional freezing is ensured, the prepared anisotropic flexible composite phase change material product has flexibility and anisotropy, the anisotropic distribution of the thermal conductivity of the phase change material can be realized, the unidirectional heat transmission rate is obviously improved, and the thermal control performance of a local heat source is greatly improved.
Description
Technical Field
The invention relates to an anisotropic flexible phase change material and a preparation method thereof, belonging to the technical field of preparation of characteristic phase change materials.
Background
In the prior art, the heat conduction enhancement of the phase change material mainly stays at an isotropic layer, so that the heat conduction is extremely limited, and the heat conduction is far less than 10W/(mK) order, so that the rapid heat absorption and the rapid temperature reduction of a local heat source cannot be realized. The anisotropic heat conduction of the phase change material is enhanced by using a carbon-based framework with high anisotropy as a support carrier, and the unidirectional heat conduction can be realized as high as 30W/(mK). Therefore, the research and development of the anisotropic phase change material can pertinently solve the current heat dissipation problem. However, the existing anisotropic phase change material is fragile and brittle, cannot be applied to a compact local heat source, and has a molecular structure of a carbon-based skeleton of a carrier material and a molecular structure of a flexible carrier which are different, so that the two materials are difficult to melt and blend in a phase change matrix material at the same time, and the composite material prepared at present is difficult to have the common characteristics of flexibility and anisotropy. Therefore, it is imperative to study the physical compatibility method of the anisotropic carrier and the flexible carrier in the phase change matrix material melt.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the anisotropic flexible composite phase change material and the preparation method thereof are provided, the high consistency of the orientation of the heat conduction reinforcing agent in the phase change material is maintained, the obtained product has flexibility and anisotropy, the anisotropic distribution of the heat conductivity of the phase change material can be realized, the unidirectional heat transmission rate is obviously improved, and the heat control performance of a local heat source is greatly improved.
The technical scheme adopted by the invention for solving the technical problems is as follows:
the anisotropic flexible composite phase change material comprises a phase change matrix material, a supporting material and a heat conduction reinforcing agent, wherein the mass ratio of the phase change matrix material to the supporting material to the heat conduction reinforcing agent is (55-65): (30-35): (5-10).
The phase change matrix material is one or more of paraffin, alkane, fatty acid and alcohol; the supporting material is one or more of hydroxy cellulose nanofiber, polyurethane nanofiber and cellulose; the heat conduction enhancer is any one of graphite, expanded graphite and graphene.
The alkane is any one of hexadecane, heptadecane, octadecane and tetracosane; the paraffin is any one of 52#, 58#, 72#, 77# solid paraffin; the fatty acid is any one of lauric acid, stearic acid, palmitic acid and sebacic acid; the alcohol is any one of n-dodecanol and lauryl alcohol.
Preferably, the phase change matrix material is paraffin, the support material is hydroxycellulose nanofiber, and the heat conduction enhancer is expanded graphite.
The preparation method of the anisotropic flexible composite phase change material comprises the following preparation steps:
A. taking the obvious pore structure and higher adsorptivity of the expanded graphite into consideration, performing oscillation diffusion on the expanded graphite by adopting an ultrasonic dispersion instrument to form a carbon-based suspension serving as a precursor of anisotropic carbon aerogel;
B. adding a metal ion solution into the carbon-based suspension to strengthen the skeleton supporting strength and the cross-linking property of the carbon substrate layer;
C. adopting a directional freezing device, and utilizing ice crystals to grow directionally along the direction of a set temperature gradient to realize the arrangement of pores of the carbon-based material along the direction of the ice crystals;
D. drying the directionally frozen expanded graphite in a vacuum drying oven to remove ice crystals to obtain carbon aerogel with high anisotropy and high adsorptivity, wherein the drying temperature is 75-85 ℃ and the pressure is 0.9MPa;
E. placing paraffin into a constant-temperature reaction container, wherein the temperature in the reaction container is set to be 10-20 ℃ higher than the melting point of the phase-change matrix material, and heating and melting the paraffin at the temperature until the paraffin is completely melted;
F. adding the prepared carbon aerogel serving as a heat conduction enhancer of the phase change matrix material into paraffin in a molten state, and stirring to realize preliminary adsorption of the paraffin melt under the stirring action, wherein the preliminary adsorption is uniformly stirred;
G. placing the uniformly stirred mixture in a vacuum drying oven, heating for about 1h, circularly stirring the mixture for multiple times, so that liquid paraffin can be fully injected into pores of the carbon aerogel matrix, and enough uniformity and saturation are achieved, and a fluffy phase change material is formed by virtue of capillary force of the carbon aerogel pores;
H. taking out the phase change material, and then carrying out directional hot pressing to obtain the anisotropic shape-stabilized phase change material;
I. raising the temperature of the reaction vessel to 170-190 ℃ and keeping the temperature constant, adding the hydroxycellulose nanofiber serving as a flexible support carrier into the reaction vessel, and heating to fully melt;
J. adding the fused flexible support carrier into the anisotropic phase-change material, and stirring by using a stirrer to ensure that the anisotropic phase-change material and the flexible support carrier are fully fused and uniformly stirred;
K. after being stirred uniformly, the temperature of the reactor is kept unchanged, and the reactor is kept stand for 30 to 60 minutes, so that each component is in a loose state;
l, introducing the loose composite phase-change material into a die, and properly compressing the loose composite phase-change material under the action of a tablet press until the required thickness is obtained;
m, cooling the mold to room temperature, and completely solidifying the composite phase change material in a high-temperature state, thereby obtaining the anisotropic flexible composite phase change material with preset density and mass fraction;
and N, opening the mold cover when the mold is cooled to the room temperature environment, and taking out the solidified material to obtain the solidified anisotropic flexible composite phase change material.
Preferably, in the step B, the metal ion solution is Ca 2+ 、Na + And after oscillation, the expanded graphite is combined with metal ions to form a cementing material.
Preferably, in step N, the anisotropic flexible composite phase change material may be processed into powder, plate, or coil.
Preferably, in the step C, the directional freezing device comprises an upper sample container bin and a lower freezing bin, a partition plate is arranged between the upper sample container bin and the lower freezing bin, the lower freezing bin comprises a bin body shell and a heat transfer copper column, and liquid nitrogen is filled between the bin body shell and the heat transfer copper column.
A polyurethane foam layer is arranged outside the bin body shell, and a baffle protection layer is arranged on the baffle; a supporting frame is arranged between the bottom of the heat transfer copper column and the shell of the bin body, so that liquid nitrogen with different temperatures is uniformly mixed through heat exchange; the upper part of the upper sample container bin is provided with a heat-preservation sealing cover, so that the sample can be conveniently taken out and put in; the central position on the heat preservation sealing cover is provided with a handle.
The position of the partition plate contacted with the upper sample container bin is processed by high-heat-conductivity materials.
In the invention, the paraffin wax has poor thermal conductivity, but the thermal conductivity is rapidly increased after the expanded graphite is added; and then the hydroxyl cellulose nanofiber is added, so that the sample has stronger anisotropy and good flexibility.
The anisotropic distribution of the thermal conductivity of the anisotropic flexible composite phase change material remarkably improves the unidirectional heat transmission rate, is beneficial to greatly improving the heat control performance of local heat sources, and has flexibility.
The anisotropic flexible composite phase change material is prepared based on the polymer organic matters as the supporting materials, the supporting materials adopted by the invention are the polymer organic matters, the strength and toughness of the materials are higher, the shaped phase change material particles prepared by wrapping the phase change matrix materials are prepared, and the strength and toughness of the shaped phase change material particles are effectively improved while the leak-free property is ensured.
The anisotropic composite phase change material prepared by the invention can obviously improve the unidirectional thermal conductivity of the material on the premise of not improving the thickness of the material; however, conventional phase change materials have limited thermal conductivity due to isotropic thermal conductivity, and in order to further improve the thermal conduction effect, a thermal conduction enhancer needs to be greatly added, so that the material cost is greatly increased.
The high consistency of the orientation of the heat conduction reinforcing agent in the phase change material is maintained by adopting a certain method, the anisotropic distribution of the heat conductivity of the phase change material can be realized, the unidirectional heat transmission rate is obviously improved, and the heat control performance of a local heat source is greatly improved. The three-dimensional structure of the macromolecule support carrier has better shaping effect than porous materials adsorbed by capillary force, and further reduces leakage of the phase change matrix; the addition of the polymeric material enhances the processability.
The research test of the anisotropy and flexibility of the phase change material is as follows:
the paraffin is adsorbed into the pores of the expanded graphite due to the action of capillary force. After melting and solidification setting, the lamellar structure gradually appears, and the expanded graphite lamellar layers show regular parallel arrangement, so that heat flow is transmitted in the radial surface layer inside the sample and along the lamellar thickness direction. There is a significant difference in the speed of heat flow transfer in the radial and thickness directions, thus exhibiting anisotropy.
Anisotropic thermal conductivity of the material is tested by using a anisotropic thermal conductivity testing module in a Hot Disk thermophysical analyzerThermal conductivity. The anisotropic composite phase change material prepared by the invention has anisotropic flexible heat conductivity related to the content and material density of the expanded graphite. When the content of the expanded graphite is unchanged, the density and the anisotropic heat conductivity of the material are obviously changed when the material is increased. The content of the expanded graphite is 8 percent, and the density is 680kg/m 3 The phase change material (C) has an axial thermal conductivity of 3.5W/(m.k), a radial thermal conductivity of 3.0W/(m.k), and a small difference in thermal conductivity in both directions, and is considered to be isotropic. The content of the expanded graphite was 8%, and the density was increased to 750kg/m 3 The axial thermal conductivity increases to 3.7W/(m.k) and the radial thermal conductivity increases to 4.1W/(m.k). It can be seen that the thermal conductivity in the two directions differ little, but increasing the compaction density increases the radial thermal conductivity significantly, and the material exhibits anisotropy. The content of the expanded graphite was 860kg/m 3 As can be seen from the thermal conductivity of the phase change material of (a), the anisotropy of the material increases significantly with increasing compaction density (see fig. 2).
The phase change material has anisotropy at low density, when the content of the expanded graphite is 13%, the density is 680kg/m 3 The phase change material has an axial thermal conductivity of 4.6W/(m.k), a radial thermal conductivity of 5.7W/(m.k), and a thermal conductivity difference in both directions of 1.1W/(m.k). The density is increased to 750kg/m 3 The axial thermal conductivity is increased to 3.9W/(m.k), the radial thermal conductivity is increased to 6.8W/(m.k), and the thermal conductivity in both directions is different by 1.1W/(m.k). The density is increased to 860kg/m 3 The axial thermal conductivity is increased to 3.4W/(m.k), the radial thermal conductivity is increased to 8.1W/(m.k), and the radial thermal conductivity is 2.34 times the axial thermal conductivity. The material samples were analyzed for anisotropic thermal conductivity as above, with both axial and radial thermal conductivities of the samples increasing with increasing expanded graphite content (see fig. 3). And at the same compaction density, the content of the expanded graphite is increased, and the anisotropy of the sample shows a more obvious degree of anisotropy.
In order to better verify the flexibility of the anisotropic flexible composite phase change material prepared by the invention, a group of samples with the magnitude of 2mm are respectively prepared, and under the same force, a flexible bending test is carried out, and the result is as follows:
FIG. 4 shows the flexibility of a sample obtained after melt molding of pure paraffin, after bending test;
FIG. 5 is the flexibility of a sample obtained by bending test with carbon aerogel (expanded graphite) added after melting of pure paraffin;
FIG. 6 shows the flexibility of a sample obtained from the anisotropic flexible composite phase change material prepared by the present invention, which is tested by bending.
The sample of figure 4 was tested to be inflexible; the sample obtained in fig. 5 is not flexible due to brittle fracture (broken); the bending of fig. 6 has better flexibility.
In addition, the prepared phase change material is used for bending test, and the fact that certain flexibility is gradually shown along with the increase of the base cellulose nanofiber is found, so that the flexibility of the composite phase change material is obtained mainly by virtue of the function of the elastic support material, namely the hydroxy cellulose nanofiber.
From the above experiments, it can be seen that: the anisotropic flexible composite phase change material prepared by the invention has good anisotropic characteristics and good flexibility. At present, the research on the anisotropy and the research on the flexibility are carried out, but the research on the good anisotropy and the good flexibility prepared by combining the two has not been carried out yet, the anisotropic distribution of the heat conductivity of the phase change material can be realized, the unidirectional heat transmission rate is obviously improved, and the heat control performance of a local heat source is greatly improved.
According to the invention, paraffin is completely melted and added into the expanded graphite, so that liquid paraffin is adsorbed in the porous structure of the expanded graphite, the heat conduction of the phase change material is opposite, and the hydroxy cellulose nanofiber is added, so that the phase change material is flexible, and the opposite flexible heat conduction composite phase change material is prepared. The anisotropic flexible phase change material consists of a phase change matrix, a flexible support carrier and a heat conduction reinforcing agent. The phase change matrix adopts paraffin wax, the flexible support carrier adopts hydroxy cellulose nano fiber, and the heat conduction enhancer is expanded graphite. The anisotropic flexible phase change material prepared by the method disclosed by the invention maintains the high consistency of the orientation of the heat conduction reinforcing agent in the phase change material by adopting a certain method, can realize the anisotropic distribution of the heat conductivity of the phase change material, obviously improves the unidirectional heat transmission rate, and is favorable for greatly improving the heat control performance of a local heat source.
Because the anisotropic carrier material is mostly a brittle carbon-based framework material, the encapsulation of the phase change matrix material is mainly realized by virtue of an internal three-dimensional porous structure, so that the prepared anisotropic material is brittle. The flexible carrier material is used for packaging and shaping the phase-change matrix material, and mainly utilizes the similar hydrocarbon linear chain molecular structure between the high polymer material and the phase-change matrix material and the van der Waals intermolecular force generated by hydrocarbon atoms. The two carriers and the phase change matrix material have different physical mechanisms, so that when the two carriers are mixed with the phase change matrix material through melt stirring, the two carriers are difficult to coexist, and mutual repulsion and precipitation are easy to occur. Therefore, the preparation method of the invention perfectly solves the technical problem, and adopts the physical compatibility and adsorption mixing method of the anisotropic carrier material and the flexible carrier material in the phase change matrix material melt mixed liquid, so that the prepared anisotropic flexible composite phase change material has good anisotropic characteristics and good flexible characteristics.
According to the invention, a specific directional freezing device is adopted, so that the high consistency of the orientation of the expanded graphite in the phase change material after directional freezing is ensured, the prepared anisotropic flexible composite phase change material product has flexibility and anisotropy, the anisotropic distribution of the thermal conductivity of the phase change material can be realized, the unidirectional heat transmission rate is obviously improved, and the thermal control performance of a local heat source is greatly improved.
Drawings
FIG. 1 is a schematic view of a directional freezer in accordance with the present invention;
FIG. 2 shows the expanded graphite content of 8% and the density of 680kg/m in the test according to the invention 3 When the phase change material is used, the axial and radial distribution of the heat conductivity of the phase change material is schematically shown;
FIG. 3 shows the expanded graphite content of 13% and the density of 680kg/m in the test according to the invention 3 When the phase change material is used, the axial and radial distribution of the heat conductivity of the phase change material is schematically shown;
FIG. 4 shows the flexibility of a sample obtained after melt molding of pure paraffin, after bending test;
FIG. 5 is the flexibility of a sample obtained by bending test with carbon aerogel (expanded graphite) added after melting of pure paraffin;
FIG. 6 shows the flexibility of a sample obtained from the anisotropic flexible composite phase change material prepared by the present invention, which is tested by bending.
Detailed Description
The invention is further illustrated and described below with reference to the accompanying drawings and specific examples:
examples: the anisotropic flexible composite phase change material comprises a phase change matrix material, a supporting material and a heat conduction reinforcing agent, wherein the mass ratio of the phase change matrix material to the supporting material to the heat conduction reinforcing agent is 60:30:10. the phase change matrix material is paraffin, the supporting material is hydroxycellulose nanofiber, and the heat conduction enhancer is expanded graphite.
The preparation method of the anisotropic flexible composite phase change material comprises the following preparation steps:
A. taking the obvious pore structure and higher adsorptivity of the expanded graphite into consideration, performing oscillation diffusion on the expanded graphite by adopting an ultrasonic dispersion instrument to form a carbon-based suspension serving as a precursor of anisotropic carbon aerogel;
B. adding a metal ion solution into the carbon-based suspension to strengthen the skeleton supporting strength and the cross-linking property of the carbon substrate layer;
C. adopting a directional freezing device, and utilizing ice crystals to grow directionally along the direction of a set temperature gradient to realize the arrangement of pores of the carbon-based material along the direction of the ice crystals;
D. drying the directionally frozen expanded graphite in a vacuum drying oven to remove ice crystals to obtain carbon aerogel with high anisotropy and high adsorptivity, wherein the drying temperature is 75-85 ℃ and the pressure is 0.9MPa;
E. placing paraffin into a constant-temperature reaction container, wherein the temperature in the reaction container is set to be 10-20 ℃ higher than the melting point of the phase-change matrix material, and heating and melting the paraffin at the temperature until the paraffin is completely melted;
F. adding the prepared carbon aerogel serving as a heat conduction enhancer of the phase change matrix material into paraffin in a molten state, and stirring to realize preliminary adsorption of the paraffin melt under the stirring action, wherein the preliminary adsorption is uniformly stirred;
G. placing the uniformly stirred mixture in a vacuum drying oven, heating for about 1h, circularly stirring the mixture for multiple times, so that liquid paraffin can be fully injected into pores of the carbon aerogel matrix, and enough uniformity and saturation are achieved, and a fluffy phase change material is formed by virtue of capillary force of the carbon aerogel pores;
H. taking out the phase change material, and then carrying out directional hot pressing to obtain the anisotropic shape-stabilized phase change material;
I. raising the temperature of the reaction vessel to 170-190 ℃ and keeping the temperature constant, adding the hydroxycellulose nanofiber serving as a flexible support carrier into the reaction vessel, and heating to fully melt;
J. adding the fused flexible support carrier into the anisotropic phase-change material, and stirring by using a stirrer to ensure that the anisotropic phase-change material and the flexible support carrier are fully fused and uniformly stirred;
K. after being stirred uniformly, the temperature of the reactor is kept unchanged, and the reactor is kept stand for 30 to 60 minutes, so that each component is in a loose state;
l, introducing the loose composite phase-change material into a die, and properly compressing the loose composite phase-change material under the action of a tablet press until the required thickness is obtained;
m, cooling the mold to room temperature, and completely solidifying the composite phase change material in a high-temperature state, thereby obtaining the anisotropic flexible composite phase change material with preset density and mass fraction;
and N, opening the mold cover when the mold is cooled to the room temperature environment, and taking out the solidified material to obtain the solidified anisotropic flexible composite phase change material.
In the step B, the metal ion solution is Ca 2+ And after oscillation, the expanded graphite is combined with metal ions to form a cementing material.
In the step N, the anisotropic flexible composite phase change material is processed into a plate shape.
In step C, the directional freezing device comprises an upper sample container bin 7 and a lower freezing bin 11, a partition plate 3 is arranged between the upper sample container bin 7 and the lower freezing bin 11, the lower freezing bin comprises a bin body shell 1 and a heat transfer copper column 5, and liquid nitrogen is filled between the bin body shell 1 and the heat transfer copper column 5.
A polyurethane foam layer 2 is arranged outside the bin body shell 1, and a baffle protection layer 8 is arranged on the baffle 3; a supporting frame 6 is arranged between the bottom of the heat transfer copper column 5 and the bin body shell 1, so that liquid nitrogen with different temperatures can be uniformly mixed through heat exchange; a heat-preservation sealing cover 9 is arranged at the upper part of the upper sample container bin 7, so that the sample can be conveniently taken out and put in; a handle 10 is arranged at the center of the heat-preserving sealing cover 9.
The partition 3 is machined from a highly thermally conductive material 4 at the point of contact with the upper sample container compartment 7.
According to the invention, paraffin is completely melted and added into the expanded graphite, so that liquid paraffin is adsorbed in the porous structure of the expanded graphite, the heat conduction of the phase change material is opposite, and the hydroxy cellulose nanofiber is added, so that the phase change material is flexible, and the opposite flexible heat conduction composite phase change material is prepared. The anisotropic flexible phase change material consists of a phase change matrix, a flexible support carrier and a heat conduction reinforcing agent. The phase change matrix adopts paraffin wax, the flexible support carrier adopts hydroxy cellulose nano fiber, and the heat conduction enhancer is expanded graphite. The anisotropic flexible phase change material prepared by the invention adopts a specific directional freezing device to ensure the high consistency of the orientation of the expanded graphite in the phase change material after directional freezing, so that the prepared anisotropic flexible composite phase change material product has flexibility and anisotropy, can realize anisotropic distribution of the thermal conductivity of the phase change material, remarkably improves the unidirectional heat transmission rate, and is favorable for greatly improving the thermal control performance of local heat sources.
In the present invention, various embodiments can be formed according to the different selected raw material components or types and different set process parameters, and any modification of the present invention according to the spirit or the essential content of the present invention is within the scope of the present invention.
Claims (10)
1. An anisotropic flexible composite phase change material, which is characterized in that: the anisotropic flexible composite phase change material comprises a phase change matrix material, a supporting material and a heat conduction reinforcing agent, wherein the mass ratio of the phase change matrix material to the supporting material to the heat conduction reinforcing agent is (55-65): (30-35): (5-10).
2. The anisotropic flexible composite phase change material of claim 1, wherein: the phase change matrix material is one or more of paraffin, alkane, fatty acid and alcohol; the supporting material is one or more of hydroxy cellulose nanofiber, polyurethane nanofiber and cellulose; the heat conduction enhancer is any one of graphite, expanded graphite and graphene.
3. The anisotropic flexible composite phase change material of claim 2, wherein: the alkane is any one of hexadecane, heptadecane, octadecane and tetracosane; the paraffin is any one of 52#, 58#, 72#, 77# solid paraffin; the fatty acid is any one of lauric acid, stearic acid, palmitic acid and sebacic acid; the alcohol is any one of n-dodecanol and lauryl alcohol.
4. The anisotropic flexible composite phase change material of claim 3, wherein: the phase change matrix material is paraffin, the supporting material is hydroxycellulose nanofiber, and the heat conduction enhancer is expanded graphite.
5. The preparation method of the anisotropic flexible composite phase change material as claimed in claim 4, comprising the following preparation steps:
A. taking the obvious pore structure and higher adsorptivity of the expanded graphite into consideration, performing oscillation diffusion on the expanded graphite by adopting an ultrasonic dispersion instrument to form a carbon-based suspension serving as a precursor of anisotropic carbon aerogel;
B. adding a metal ion solution into the carbon-based suspension to strengthen the skeleton supporting strength and the cross-linking property of the carbon substrate layer;
C. adopting a directional freezing device, and utilizing ice crystals to grow directionally along the direction of a set temperature gradient to realize the arrangement of pores of the carbon-based material along the direction of the ice crystals;
D. drying the directionally frozen expanded graphite in a vacuum drying oven to remove ice crystals to obtain carbon aerogel with high anisotropy and high adsorptivity, wherein the drying temperature is 75-85 ℃ and the pressure is 0.9MPa;
E. placing paraffin into a constant-temperature reaction container, wherein the temperature in the reaction container is set to be 10-20 ℃ higher than the melting point of the phase-change matrix material, and heating and melting the paraffin at the temperature until the paraffin is completely melted;
F. adding the prepared carbon aerogel serving as a heat conduction enhancer of the phase change matrix material into paraffin in a molten state, and stirring to realize preliminary adsorption of the paraffin melt under the stirring action, wherein the preliminary adsorption is uniformly stirred;
G. placing the uniformly stirred mixture in a vacuum drying oven, heating for about 1h, circularly stirring the mixture for multiple times, so that liquid paraffin can be fully injected into pores of the carbon aerogel matrix, and enough uniformity and saturation are achieved, and a fluffy phase change material is formed by virtue of capillary force of the carbon aerogel pores;
H. taking out the phase change material, and then carrying out directional hot pressing to obtain the anisotropic shape-stabilized phase change material;
I. raising the temperature of the reaction vessel to 170-190 ℃ and keeping the temperature constant, adding the hydroxycellulose nanofiber serving as a flexible support carrier into the reaction vessel, and heating to fully melt;
J. adding the fused flexible support carrier into the anisotropic phase-change material, and stirring by using a stirrer to ensure that the anisotropic phase-change material and the flexible support carrier are fully fused and uniformly stirred;
K. after being stirred uniformly, the temperature of the reactor is kept unchanged, and the reactor is kept stand for 30 to 60 minutes, so that each component is in a loose state;
l, introducing the loose composite phase-change material into a die, and properly compressing the loose composite phase-change material under the action of a tablet press until the required thickness is obtained;
m, cooling the die to room temperature, and completely solidifying the composite phase change material in a high-temperature state, thereby obtaining the anisotropic flexible composite phase change material with preset density and mass fraction;
and N, opening the mold cover when the mold is cooled to the room temperature environment, and taking out the solidified material to obtain the solidified anisotropic flexible composite phase change material.
6. The method for preparing the anisotropic flexible composite phase change material according to claim 5, wherein the method comprises the following steps: in the step B, the metal ion solution is Ca 2+ 、Na + And after oscillation, the expanded graphite is combined with metal ions to form a cementing material.
7. The method for preparing the anisotropic flexible composite phase change material according to claim 5, wherein the method comprises the following steps: in step N, the anisotropic flexible composite phase change material may be processed into powder, plate, or coil.
8. The directional freezer as recited in claim 5, wherein: the directional freezing device comprises an upper sample container bin (7) and a lower freezing bin (11), a partition plate (3) is arranged between the upper sample container bin (7) and the lower freezing bin (11), the lower freezing bin comprises a bin body shell (1) and a heat transfer copper column (5), and liquid nitrogen is filled between the bin body shell (1) and the heat transfer copper column (5).
9. The directional freezer of claim 8, wherein: a polyurethane foam layer (2) is arranged outside the bin body shell (1), and a baffle protection layer (8) is arranged on the baffle plate (3); a supporting frame (6) is arranged between the bottom of the heat transfer copper column (5) and the bin body shell (1), so that liquid nitrogen with different temperatures can be uniformly mixed through heat exchange; the upper part of the upper sample container bin (7) is provided with a heat-preservation sealing cover (9), so that the sample can be conveniently taken out and put in; a handle (10) is arranged at the center position on the heat-preservation sealing cover (9).
10. The directional freezer of claim 8, wherein: the position of the partition plate (3) contacted with the upper sample container bin (7) is processed by a high-heat-conductivity material (4).
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