CN114318468B - Graphene surface enhanced heat transfer composite material and preparation method thereof - Google Patents
Graphene surface enhanced heat transfer composite material and preparation method thereof Download PDFInfo
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Abstract
The invention provides a graphene surface enhanced heat transfer composite material and a preparation method thereof, wherein the preparation method comprises the following steps: uniformly mixing a graphene material with isopropanol to form a negatively charged graphene solution; adding magnesium salt into the graphene solution to prepare a mixed solution, wherein the weight ratio of the graphene material to the magnesium salt is 1:5-3:1; and taking the conductive material as a cathode, and performing electrophoretic deposition in the mixed solution to obtain the graphene surface enhanced heat transfer composite material. According to the invention, the graphene material and the conductive material are stably connected together through the magnesium hydroxide and the ester group formed in the electrophoretic deposition process, and the graphene material and the conductive material are used as the surface enhanced heat transfer composite material, so that the phase change heat transfer performance can be improved; the graphene material in the surface enhanced heat transfer composite material obtained by the method is connected to the surface of the conductive material in a vertical orientation mode, and the vertically oriented connected graphene material can reduce the superheat degree required by the initial nucleate boiling of phase change heat transfer and obviously improve the phase change heat transfer rate.
Description
Technical Field
The invention relates to the technical field of phase change heat transfer, in particular to a graphene surface enhanced heat transfer composite material and a preparation method thereof.
Background
With the rapid development of the aerospace technology, new generation of spacecrafts such as satellites are developed in the directions of high resolution, high precision and microminiaturization, the effective load of devices is increased due to the high integration of an electronic system, the heat flux density in a limited space is also increased sharply, the local temperature of the spacecrafts is easy to be overhigh, and the thermal control technology of the spacecrafts also faces greater challenges. In order to improve reliability, stability and service life of the spacecraft, the problem of micro thermal control of high heat flux components and parts in a narrow space needs to be solved, so that the highest temperature of the equipment is kept at an acceptable limit condition, and the temperature uniformity of the whole equipment is improved.
Phase change heat transfer refers to a convective heat transfer process in which heat is transferred from a wall to a liquid, causing the liquid to boil and vaporize. The phase change heat transfer can obtain a great heat transfer coefficient under a smaller superheat degree, so that the phase change heat transfer becomes a research hot spot. The phase change heat transfer performance can be further improved through the graphene coating, and the methods for enhancing the aluminum metal phase change heat transfer performance through graphene in the prior art include a self-assembly method, a spraying method and the like. However, due to strong pi-pi bond and van der Waals force interaction between graphene sheets, irreversible agglomeration or overlapping is easy to form on the graphene sheets, and the graphene nano sheets are horizontally oriented on the aluminum surface, so that the phase change heat transfer performance is affected.
Disclosure of Invention
The invention solves the problem that graphene nano sheets in the prior art are horizontally oriented and distributed on the surface of aluminum, and irreversible agglomeration or overlapping is easy to form among graphene sheets, so that the phase change heat transfer performance is affected.
In order to solve at least one aspect of the above problems, the present invention provides a method for preparing a graphene surface-enhanced heat transfer composite material, comprising the steps of:
step S1, uniformly mixing a graphene material with isopropanol to form a negatively charged graphene material solution;
s2, adding magnesium salt into the graphene material solution to prepare a mixed solution, wherein the weight ratio of the graphene material to the magnesium salt is 1:5-3:1;
and S3, taking the conductive material as a cathode, and performing electrophoretic deposition in the mixed solution to obtain the graphene surface enhanced heat transfer composite material.
Preferably, in the step S1, the graphene material is added into the isopropanol, and is ultrasonically dispersed for 1h, so as to form a uniform graphene solution.
Preferably, the graphene material comprises graphene oxide or reduced graphene oxide.
Preferably, the magnesium salt comprises magnesium nitrate, magnesium carbonate or magnesium sulfate.
Preferably, in the step S2, the weight ratio of the graphene material to the magnesium salt is 1:1.
Preferably, in the step S3, a platinum sheet is used as an anode during the electrophoretic deposition.
Preferably, in the step S3, the reaction voltage during the electrophoretic deposition is 220V, and the reaction time is 2min.
Preferably, the conductive material comprises aluminum sheet, copper sheet, carbon cloth or carbon fiber.
According to the invention, the graphene material and the magnesium salt are prepared into the mixed solution, as the surface of the graphene material has a negatively charged functional group, and magnesium ions have positive charges, under the attraction of the positive charges and the negative charges, the magnesium ions can be adsorbed on the surface of the graphene material, when the conductive material is used as a cathode to carry out electrophoretic deposition in the mixed solution, under the action of an electric field, particles mixed into the solution undergo oxidation-reduction reaction on an anode and the cathode, and the magnesium ions adsorbed on the surface of the graphene material react with hydroxyl groups on the surface of the conductive material to generate magnesium hydroxide, so that the graphene material is connected with the conductive material through the bridge action of the magnesium hydroxide; in addition, functional groups such as carboxyl on the surface of the graphene material can react with hydroxyl on the surface of the conductive material to generate ester groups, so that the connection stability of the graphene material and the conductive material can be further improved; the graphene material and the conductive material are stably connected together through the magnesium hydroxide and the ester group formed in the electrophoretic deposition process, and the graphene material is used as a graphene surface enhanced heat transfer composite material, so that the phase change heat transfer performance can be improved; the graphene materials in the surface enhanced heat transfer composite material obtained by the method are connected to the conductive material in a vertical orientation mode, the vertically oriented connected graphene materials can increase active sites and reduce the superheat degree required for the initiation of phase change heat transfer nucleate boiling, and the vertically oriented graphene material structure has the effect of inhibiting the growth of bubbles, so that the bubbles are separated in a small-size state, and the phase change heat transfer rate can be remarkably improved.
The invention also aims to provide a graphene surface enhanced heat transfer composite material, which is prepared by the preparation method of the graphene surface enhanced heat transfer composite material.
Preferably, the conductive material and the graphene material adsorbed on the conductive material are included, and the graphene material is connected to the conductive material in a vertical orientation manner.
The beneficial effects of the graphene surface enhanced heat transfer composite material provided by the invention are the same as those of the graphene surface enhanced heat transfer composite material preparation method, and are not repeated here.
Drawings
FIG. 1 is a flow chart of a preparation method of a graphene surface enhanced heat transfer composite material in an embodiment of the present invention;
FIG. 2 is a schematic diagram of the mechanism of redox reactions during electrophoretic deposition;
FIG. 3 is a top view of an SEM of a surface graphene reinforced heat transfer composite in accordance with an embodiment of the present invention;
FIG. 4 is a SEM side view of a graphene surface-enhanced heat transfer composite in accordance with an embodiment of the present invention;
FIG. 5 is a schematic diagram of a thermal flow density measurement device;
FIG. 6 is a graph showing the comparison of heat flux density curves of different materials according to an embodiment of the present invention.
Detailed Description
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of embodiments of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
It should be noted that, without conflict, features in the embodiments of the present invention may be combined with each other. The terms "comprising," "including," "containing," and "having" are intended to be non-limiting, as other steps and other ingredients not affecting the result may be added. The above terms encompass the terms "consisting of … …" and "consisting essentially of … …". Materials, equipment, reagents are commercially available unless otherwise specified.
The embodiment of the invention provides a preparation method of a graphene surface enhanced heat transfer composite material, which is shown in fig. 1 and comprises the following steps:
step S1, uniformly mixing a graphene material with isopropanol to form a negatively charged graphene material solution;
s2, adding magnesium salt into the graphene material solution to prepare a mixed solution, wherein the weight ratio of the graphene material to the magnesium salt is 1:5-3:1;
and S3, taking the conductive material as a cathode, and performing electrophoretic deposition in the mixed solution to obtain the graphene surface enhanced heat transfer composite material.
In the step S1, graphene materials are added into isopropanol, and are subjected to ultrasonic dispersion for 1h to form a uniform graphene solution. Wherein the graphene material comprises Graphene Oxide (GO) or reduced graphene oxide (rGO). The graphene materials such as GO and rGO have strong hydrophilicity and exhaust property, can promote the circulating flow of liquid between dry and wet areas, and can accelerate the cooling rate and improve the heat transfer effect by connecting the graphene materials on the surface of the heat conducting substrate. The graphene material can be fully dispersed in isopropanol in an ultrasonic dispersion mode, so that a uniform graphene solution is obtained.
In the step S2, adding magnesium salt into the graphene solution to prepare a mixed solution, wherein the weight ratio of the graphene material to the magnesium salt is 1:5-3:1. Wherein the magnesium salt is magnesium nitrate, magnesium carbonate or magnesium sulfate. Magnesium ions are contained in the magnesium salt, the magnesium ions have positive charges, a large number of functional groups with negative charges are distributed on the surface of the graphene material, and a large number of magnesium ions can be adsorbed on the surface of the graphene material through the attraction effect of the positive charges and the negative charges. The weight ratio of graphene material to magnesium salt is preferably set to 1:1.
In the step S3, the platinum sheet is used as an anode, the conductive material is used as a cathode, the electrophoretic deposition is carried out in the mixed solution, the reflection voltage in the electrophoretic deposition process is set to 220V, and the reaction time is 2min. Wherein the conductive material comprises aluminum sheet, copper sheet, carbon cloth or carbon fiber.
As shown in fig. 2, in the electrophoretic deposition process, particles in the mixed solution undergo oxidation-reduction reaction on the positive and negative electrode materials due to the presence of a strong electric field, wherein the anode undergoes the following reaction:
4OH - -4e - →2H 2 O+O 2
and the cathode reacts as follows:
O 2 +2H 2 O+4e - →4OH -
NO 3 - +H 2 O+2e - →NO 2 - +2OH -
Mg 2+ +2OH - →Mg(OH) 2
the magnesium ions in the solution react with hydroxyl groups on the cathode conductive material to generate magnesium hydroxide, and the magnesium ions are connected with the graphene material on one hand and connected with the cathode conductive material through the hydroxyl groups on the other hand, so that the graphene material and the conductive material can be connected through the bridge effect of the magnesium hydroxide to form a composite material, and the graphene materials can be prevented from being mutually stacked due to repulsive force existing between the magnesium ions, so that the graphene materials are connected to the conductive material in a vertical orientation mode, the vertically-oriented connected graphene materials can increase active sites, the overheat degree required for starting phase-change heat transfer nucleate boiling is reduced, and the vertically-oriented structure of the graphene materials has the effect of inhibiting bubble growth, so that bubbles are promoted to be separated in a small-size state, and the phase-change heat transfer rate can be remarkably improved.
In addition, a large number of carboxyl groups and other groups are distributed on the graphene material and can react with hydroxyl groups on the conductive material to form ester groups, and the ester groups are in strong chemical bond connection, so that the quantity of the ester groups is increased along with the temperature rise in the phase change heat transfer process, and the connection stability of the graphene material and the conductive material can be further enhanced.
The graphene surface enhanced heat transfer composite material comprises a conductive material and a graphene material adsorbed on the conductive material, wherein the graphene material is connected to the conductive material in a vertical orientation mode.
The preparation method of the graphene surface-enhanced heat transfer composite material is described below with reference to specific examples:
example 1
1.1, adding reduced graphene oxide (rGO) into isopropanol, and performing ultrasonic dispersion for 1h to obtain a GO solution with uniform dispersion;
1.2, adding magnesium nitrate into the rGO solution, and uniformly mixing to obtain a mixed solution of rGO and magnesium nitrate, wherein the mass ratio of the rGO to the magnesium nitrate is 1:1;
1.3, taking a platinum sheet as an anode, taking an aluminum sheet as a cathode, wherein the reaction voltage is 220V, the reaction time is 2min, and enabling particles in the mixed solution to undergo oxidation-reduction reaction on the anode and the cathode, so that rGO is adsorbed on the aluminum sheet and connected with the aluminum sheet in a vertical orientation mode, thereby obtaining the graphene surface enhanced heat transfer composite material.
Example 2
2.1, adding Graphene Oxide (GO) into isopropanol, and performing ultrasonic dispersion for 1h to obtain a GO solution with uniform dispersion;
2.2, adding magnesium sulfate into the GO solution, and uniformly mixing to obtain a mixed solution of GO and magnesium sulfate, wherein the mass ratio of GO to magnesium sulfate is 1:3;
2.3, taking a platinum sheet as an anode, and a copper sheet as a cathode, wherein the reaction voltage is 220V, the reaction time is 2min, and enabling particles in the mixed solution to undergo oxidation-reduction reaction on the anode and the cathode, so that GO is adsorbed on the copper sheet, and is connected with the copper sheet in a vertical orientation mode, thereby obtaining the graphene surface enhanced heat transfer composite material.
Example 3
3.1, adding reduced graphene oxide (rGO) into isopropanol, and performing ultrasonic dispersion for 1h to obtain a GO solution with uniform dispersion;
3.2, adding magnesium carbonate into the rGO solution, and uniformly mixing to obtain a mixed solution of rGO and magnesium carbonate, wherein the mass ratio of the rGO to the magnesium carbonate is 1:5;
3.3, taking a platinum sheet as an anode, taking an aluminum sheet as a cathode, wherein the reaction voltage is 220V, the reaction time is 2min, and enabling particles in the mixed solution to undergo oxidation-reduction reaction on the anode and the cathode, so that rGO is adsorbed on the aluminum sheet and connected with the aluminum sheet in a vertical orientation mode, thereby obtaining the graphene surface enhanced heat transfer composite material.
Experimental example 1
The composite material formed by the reduced graphene oxide and the aluminum sheet prepared in example 1 was observed under SEM electron microscope.
Fig. 3 and 4 are top and side views of the composite material under SEM electron microscope, respectively, and it can be seen from fig. 3 and 4 that rGO is attached to the surface of the aluminum sheet by means of vertical orientation and has less overlapping each other. The method is mainly characterized in that in the electrophoretic deposition process, oxidation-reduction reaction is carried out on an anode and a cathode, magnesium ions in the mixed solution are firstly combined with rGO to change electronegativity of the mixed solution, magnesium hydroxide is generated through the oxidation-reduction reaction of the cathode, and the magnesium hydroxide can serve as a bridge to connect the rGO with an aluminum sheet; meanwhile, due to repulsive force between magnesium ions, stacking between rGO sheets can be prevented, and rGO can be connected to the aluminum sheets in a vertically oriented manner.
Experimental example 2
The heat flux density curves of pure aluminum and the Al/rGO pool boiling heat transfer material prepared in example 1 were tested separately in the following manner:
the pure aluminum and the Al/rGO pool boiling heat transfer material prepared in the example 1 are respectively used as samples to be tested, and the heat flux density of the materials is tested by a self-made measuring device which consists of a heating system, a sealing system and a data acquisition system, as shown in figure 5. The heating system is formed by connecting a copper heating block and a sample to be measured through processing threads, and the thread size is as follows
The length is 7mm. The copper heating block and the sample to be tested are provided with +.>
The hole, 9mm deep, represents the position of a type K thermocouple (+ -0.2K). The interval between each thermocouple in the copper block was 5mm for measuring the temperature gradient (T 1 、T 2 、T 3 ). Furthermore, a thermocouple inside the sample to be measured is used to measure the wall temperature (T w ). Ceramic fiber (k < 0.14W m) -1 k -1 ) The copper heating block is wrapped and a waterproof sealant is coated around the aluminum sample to reduce heat loss from the device to the surrounding environment. A data acquisition system (HIOKI LR8450, japan) was used to monitor the temperature change of the thermocouple. In addition, the movement of the underwater vapor bubble was observed by a high-speed camera (fascam Mini UX100, japan).
The water in the vessel is first heated to boiling and maintained for half an hour to remove insoluble gases from the water. Surface temperature T of sample to be measured w Starting the test after reaching 100deg.C, increasing the initial power of the heating rod by 5W, and waiting until T 1 ，T 2 ，T 3 The temperature is not changing and reaches steady state, at which point the relevant temperature data is recorded. And (5) increasing the power of the heating rod by 5W again, repeating the steps, and finally obtaining the critical heat flux density (the critical heat flux density refers to the maximum heat flux density obtained in the test process). By measuring T 1 And T 2 、T 2 And T 3 、T 1 And T 3 The temperature difference between the two is combined with the known heat conductivity of the copper block, and the heat flow density q' is calculated according to the Fourier heat conduction law:
wherein k is Cu Is the heat conductivity coefficient of the copper block, the value is 401W m -1 K -1 Δx is thermocouple T 1 And T 2 The interval between them. Wall superheat delta T w The calculation can be performed by the following formula:
ΔT w ＝T w -T sat
wherein T is w Is the wall temperature of the sample to be measured, T sat Is a water saturation boiling temperature of 100 ℃.
In FIG. 6, the abscissa indicates the wall superheat DeltaT w The ordinate indicates heat flux q ", al represents pure aluminum, al/rGO represents the graphene surface enhanced heat transfer composite material prepared in example 1, and as can be seen from fig. 6, the graphene surface enhanced heat transfer composite material prepared in example 1 has a greater critical heat flux density (CHF) and a smaller nucleation boiling superheat (ONB) for phase transition heat transfer than pure aluminum, wherein CHF is improved by 95%, indicating that the graphene surface enhanced heat transfer composite material prepared in the example of the present invention significantly improves phase transition heat transfer performance compared to pure aluminum.
Although the present disclosure is described above, the scope of protection of the present disclosure is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the disclosure, and these changes and modifications will fall within the scope of the invention.
Claims (6)
1. The preparation method of the graphene surface enhanced heat transfer composite material is characterized by comprising the following steps of:
step S1, uniformly mixing a graphene material with isopropanol to form a negatively charged graphene material solution;
s2, adding magnesium salt into the graphene solution to prepare a mixed solution, wherein the weight ratio of the graphene material to the magnesium salt is 1:1;
s3, taking the conductive material as a cathode, and performing electrophoretic deposition in the mixed solution to obtain the graphene surface enhanced heat transfer composite material;
in the step S1, adding the graphene material into the isopropanol, and performing ultrasonic dispersion for 1h to form a uniform graphene solution;
in the step S3, the reaction voltage is 220V and the reaction time is 2min in the electrophoretic deposition process;
the conductive material is aluminum sheet or copper sheet.
2. The method of preparing a surface enhanced heat transfer composite according to claim 1, wherein the graphene material comprises graphene oxide or reduced graphene oxide.
3. The method of preparing a surface enhanced heat transfer composite according to claim 1, wherein the magnesium salt comprises magnesium nitrate, magnesium carbonate or magnesium sulfate.
4. The method for preparing a surface enhanced heat transfer composite according to claim 1, wherein in the step S3, a platinum sheet is used as an anode during the electrophoretic deposition.
5. A surface enhanced heat transfer composite prepared by the method of any one of claims 1-4.
6. The surface enhanced heat transfer composite of claim 5, comprising a conductive material and a graphene material adsorbed on the conductive material, wherein the graphene material is attached to the conductive material by a vertical orientation.
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