A method for thermal rectification control of graphene composite braided structure

Abstract

This invention discloses a method for controlling the thermal rectification of a graphene composite braided structure, relating to the field of micro-nano-scale thermal rectification control. The method includes: braiding several graphene strips to obtain a graphene composite braided structure with a gradient change in thermal conductivity along the heat transfer direction; analyzing the relationship between the thermal rectification coefficient of the graphene composite braided structure and temperature, and analyzing the relationship between the thermal rectification coefficient and structural dimensions; and designing a graphene composite braided structure with the optimal thermal rectification coefficient based on these two relationships. This method, by changing the temperature environment and structural dimensions of the graphene composite braided structure, seeks the variation law of the thermal rectification coefficient with temperature and dimensions, and achieves control over the thermal rectification of the graphene composite braided structure from the variation law, thereby solving the problem of heat dissipation in micro-nano-scale electronic devices.

Description

Technical Field

[0001] This invention relates to the field of thermal rectification control at the micro-nano scale, and in particular to a method for thermal rectification control of a graphene composite braided structure. Background Technology

[0002] With the increasing integration and miniaturization of electronic devices, the efficiency of high-density additional energy transfer generated during device operation at the nanoscale will significantly affect their operational stability. Therefore, thermal control at the micro- and nano-scale should receive widespread attention from the engineering and academic communities. Graphene, a two-dimensional nanofilm material, is widely used in the design of thermal rectifiers, thermal transistors, thermal logic gates, and other devices to control the transfer of high-density additional heat due to its excellent thermal properties.

[0003] Weaving is one of the oldest human crafts, allowing strips to be interwoven or hooked together to form composite structures, either strip-shaped or block-shaped. The properties and strength of woven materials are significantly improved. Therefore, this application considers forming a novel two-dimensional material with a novel structure by weaving graphene strips and proposes a method for thermal rectification and control to address the heat dissipation problem in micro / nano-scale electronic devices. Summary of the Invention

[0004] To address the problem of high-density additional energy transfer in electronic devices, this invention proposes a thermal rectification control method for a graphene composite braided structure. The technical solution of this invention is as follows:

[0005] A method for controlling the thermal rectification of a graphene composite braided structure includes the following steps:

[0006] Several graphene strips are woven together to obtain a graphene composite woven structure with a gradient change in thermal conductivity along the heat transfer direction.

[0007] The relationship between the thermal rectification coefficient of the graphene composite braided structure and temperature was analyzed, as well as the relationship between the thermal rectification coefficient and structural dimensions of the graphene composite braided structure.

[0008] Based on two variation relationships, a graphene composite braided structure with the optimal thermal rectification coefficient was designed.

[0009] A further technical solution involves weaving several graphene strips together, including:

[0010] N graphene strips are taken as latitude lines and M graphene strips are taken as longitude lines, with the heat transfer direction defined as the extension direction of the latitude lines.

[0011] The weft threads are arranged at intervals along the orthogonal direction of heat transfer, and the warp threads are arranged at intervals along the direction of heat transfer. The area where the warp threads are located is divided into multiple weaving areas along the direction of heat transfer.

[0012] The weft threads are sequentially woven with the warp threads of each weaving area, and the weaving constraints of each weaving area increase or decrease linearly according to the area order. The weaving constraint refers to the number of weft threads that change the direction of overlap when weaving with the warp threads.

[0013] A further technical solution involves a method whereby, as the weaving constraints of each weaving area increase linearly according to the area sequence, the weft threads are sequentially woven with the warp threads of each weaving area.

[0014] Let the weaving constraint of weaving region I be i. Starting from weaving region I, the weft threads on each warp in the region are woven in sequence in the manner of i consecutive threads overlapping on one side of the warp thread, and then i consecutive threads overlapping on the other side of the warp thread, so as to obtain the graphene weaving structure of the region. Let i = i + j as the weaving constraint of the next weaving region, until all weaving regions are completed, where i and j are both positive integers.

[0015] A further technical solution involves a method where, as the weaving constraints of each weaving area decrease linearly according to the area sequence, the weft threads are sequentially woven with the warp threads of each weaving area.

[0016] Let the weaving constraint of weaving region I be i, where i is a positive integer greater than 1. Starting from weaving region I, the weft threads on each warp in the region are woven sequentially in the manner of i consecutive threads overlapping on one side of the warp thread, followed by i consecutive threads overlapping on the other side of the warp thread, to obtain the graphene weaving structure of the region. Let i = ij as the weaving constraint of the next weaving region, until all weaving regions are completed, where j is a positive integer less than i.

[0017] A further technical solution is that when the weaving constraints of each weaving region increase linearly according to the region order, the weaving density of the graphene composite weaving structure in each weaving region changes from dense to sparse, and the thermal conductivity of the graphene composite weaving structure in each weaving region gradually increases.

[0018] When the weaving constraints of each weaving region decrease linearly according to the region order, the weaving density of the graphene composite weaving structure in each weaving region changes from sparse to dense, and the thermal conductivity of the graphene composite weaving structure in each weaving region gradually decreases.

[0019] A further technical solution is that, when i = N, in the weaving area, all the weft threads on each warp overlap on one side of the warp, or all the weft threads overlap on the other side of the warp.

[0020] A further technical solution involves analyzing the relationship between the thermal rectification coefficient of graphene composite braided structures and temperature, including:

[0021] The thermal rectification coefficient of the graphene composite braided structure was obtained under different temperature conditions. The relationship curve of the thermal rectification coefficient of the graphene composite braided structure with temperature was fitted, and it was found that: within the set temperature range, as the temperature gradually increases, the thermal rectification coefficient of the graphene composite braided structure gradually decreases and tends to stabilize.

[0022] A further technical solution involves analyzing the relationship between the thermal rectification coefficient and the structural dimensions of graphene composite braided structures, including:

[0023] By changing the dimensions of the graphene composite braided structure along the heat transfer direction, with the dimension being the length of the graphene composite braided structure, the thermal rectification coefficient of the graphene composite braided structure at different lengths was obtained. The relationship curve of the thermal rectification coefficient of the graphene composite braided structure with the length was fitted, and it was found that: within the set size range, as the length of the graphene composite braided structure gradually increases, the thermal rectification coefficient of the graphene composite braided structure gradually decreases.

[0024] A further technical solution involves designing a graphene composite braided structure with the optimal thermal rectification coefficient based on two variation relationships, including:

[0025] The dimensions of the graphene composite braided structure along the heat transfer direction are designed to be the minimum values ​​within a specified size range in the size variation relationship;

[0026] The ambient temperature of the graphene composite braided structure after the design size change is the lowest temperature within the set temperature range in the temperature change relationship, thereby obtaining the graphene composite braided structure with the best thermal rectification coefficient.

[0027] The beneficial technical effects of this invention are:

[0028] Using single-layer graphene strips as raw materials, different weaving methods are employed to weave the graphene strips, forming a graphene composite woven structure with a gradient change in thermal conductivity along the heat transfer direction. By changing the temperature environment and structural dimensions of the graphene composite woven structure, the variation law of the thermal rectification coefficient with temperature and size of the graphene composite woven structure is sought. From the variation law, the thermal rectification of the graphene composite woven structure can be controlled, thereby determining the temperature and size parameters of the graphene composite woven structure with the optimal thermal rectification coefficient. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of one weaving method for the woven graphene strips provided in this application.

[0030] Figure 2This is a schematic diagram of another weaving method for the woven graphene strips provided in this application.

[0031] Figure 3 This is a schematic diagram of another weaving method for the woven graphene strips provided in this application.

[0032] Figure 4 This is a schematic diagram of the graphene composite braided structure provided in this application.

[0033] Figure 5 This is the correlation curve between the reciprocal of the thermal conductivity and the reciprocal of the size of the single-layer graphene strip provided in this application.

[0034] Figure 6 This is the full atomic diagram of the graphene composite braided structure model provided in this application.

[0035] Figure 7 This is a curve showing the relationship between the thermal conductivity k of the graphene composite braided structure provided in this application and temperature.

[0036] Figure 8 This is a curve showing the relationship between the thermal rectification coefficient μ of the graphene composite braided structure provided in this application and temperature.

[0037] Figure 9 This is a curve showing the relationship between the thermal conductivity k of the graphene composite braided structure provided in this application and its size.

[0038] Figure 10 This is a curve showing the relationship between the thermal rectification coefficient μ of the graphene composite braided structure provided in this application and its size. Detailed Implementation

[0039] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0040] This embodiment provides a method for controlling the thermal rectification of a graphene composite braided structure, the method comprising the following steps:

[0041] Step 1: Take several graphene strips and weave them together to obtain a graphene composite woven structure with a gradient of thermal conductivity along the heat transfer direction. This step specifically includes the following sub-steps:

[0042] Step 1-1: Take N graphene strips with complete structure, width W1 = 10nm and length L1 = 140nm as weft lines, and arrange them in an orderly manner along the Y direction with an interval d1 = 5nm between the weft lines.

[0043] Step 1-2: Take M graphene strips with complete structure, width W2 = 10nm and length L2 = 95nm as warp lines, and arrange them in an orderly manner along the X direction with an interval d2 = 5nm between the warp lines.

[0044] Combination Figure 1-4 As shown, in this embodiment, N=6 and M=9, and the X direction is defined as the heat transfer direction.

[0045] Steps 1-3: Divide the area where the warp is located into multiple weaving areas along the heat transfer direction, and let the weft threads weave with the warp threads of each weaving area in turn. The weaving constraints of each weaving area increase or decrease linearly according to the area order.

[0046] like Figure 4 As shown, this embodiment divides the area containing the warp threads into three weaving regions: Weaving Region I, Weaving Region II, and Weaving Region III, along the heat transfer direction. The specific weaving methods of Weaving Regions I, II, and III are explained using the example of weaving constraints increasing linearly according to the region order (assuming j=1). Here, weaving constraint refers to the number of weft threads that change their overlapping direction when weaving with the warp threads.

[0047] In weaving region I, assuming weaving constraint i = 1, the weft threads 12 on each warp 11 are woven sequentially, with one overlapping on one side of the warp 11 and the other overlapping on the other side, resulting in a graphene woven structure as shown below. Figure 1 As shown in the diagram, the overlap on one side and the other side of meridian 11 can be understood as latitude 12 overlapping above or below meridian 11.

[0048] In weaving region II, the weaving constraint i = 2. The weft threads 22 on each warp 21 are woven sequentially in a pattern where two consecutive threads overlap on one side of the warp 21, followed by two consecutive threads overlapping on the other side. The resulting graphene woven structure is as follows: Figure 2 As shown.

[0049] In weaving region III, the weaving constraint i = 3. The weft threads 32 on each warp 31 are woven sequentially in a pattern where three consecutive threads overlap on one side of the warp 31, followed by three consecutive threads overlapping on the other side. The resulting graphene woven structure is as follows: Figure 3 As shown.

[0050] In actual weaving, each weaving area is woven continuously and without interruption, ultimately resulting in a graphene composite woven structure as shown below. Figure 4As shown, the first three rows of graphene braided structures are the densest, significantly suppressing out-of-plane phonon vibrations. Since most of the thermal conductivity of graphene is contributed by out-of-plane phonons, this region has the lowest thermal conductivity. Similarly, the middle three rows of graphene braided structures have higher thermal conductivity than the first three rows, while the bottom three rows have the highest thermal conductivity. Therefore, we can conclude that: when the braiding constraint in each braided region increases linearly according to the region order, the braiding density of the graphene braided structure in each braided region changes from dense to sparse, and the thermal conductivity of the graphene braided structure in each braided region gradually increases. Conversely, when the braiding constraint in each braided region decreases linearly according to the region order, the braiding density of the graphene braided structure in each braided region changes from sparse to dense, and the thermal conductivity of the graphene braided structure in each braided region gradually decreases.

[0051] It should be noted that the weaving constraints of each weaving area decrease linearly according to the area order, which is the reverse of the linearly increasing weaving method mentioned above. The warp and weft weaving situation of each weaving area will not be described again here.

[0052] As the number of levels along the heat transfer direction in the graphene composite braided structure increases, so does its size. Graphene is a low-dimensional material, and the thermal conductivity of low-dimensional materials depends on size. Furthermore, as the size increases, the number of interlacing lines in the warp and weft directions of the graphene gradually decreases. If the size along the heat transfer direction is infinitely large, i.e., when i = N, in this braided region, all weft threads on each warp overlap on one side of the warp, or all weft threads overlap on the other side of the warp. Then the thermal conductivity of this region tends to be similar to that of a single-layer graphene strip. Calculating the relationship between the thermal conductivity k of a single-layer graphene strip and its size L, it was observed that within 750 nm, the reciprocal of the thermal conductivity k of the single-layer graphene strip is linearly correlated with the reciprocal of the size L, as shown below. Figure 5 As shown, the relationship is:

[0053]

[0054] Step 2: As Figure 6 As shown, the graphene composite braided structure was realized through molecular dynamics simulation, and the thermal conductivity was obtained using a reverse nonequilibrium molecular dynamics method. The Tersoff potential was used to describe the interactions within the graphene strips, and the LJ potential was used to describe the interactions between the warp and weft graphene strips. The specific calculation method included fixing two endpoints as the cold and hot ends, and applying cold and heat sources respectively. Along the heat transfer direction, the graphene composite braided structure was divided into several equal-length blocks. After a stable temperature gradient was formed, the heat flux density J and temperature gradient of the composite braided structure were obtained. The structural thermal conductivity is calculated using equation (2). The heat and cold sources are then exchanged, and the structural thermal conductivity is calculated again for subsequent calculations to obtain the thermal rectification coefficient. The formula for calculating thermal conductivity is:

[0055]

[0056] In the formula, A is the cross-sectional area, which can be regarded as the cross-sectional area at the intersection of the warp and weft graphene strips.

[0057] The formula for calculating the thermal rectification coefficient is:

[0058]

[0059] In the formula, k 上→下 The thermal conductivity of the composite braided structure is represented by k when heat is transferred from top to bottom. 下→上 This indicates the thermal conductivity of the composite braided structure when heat is transferred from bottom to top.

[0060] Step 3: Analyze the relationship between the thermal rectification coefficient of the graphene composite braided structure and temperature. Specifically, this includes: obtaining the thermal conductivity and thermal rectification coefficient of the graphene composite braided structure under different temperature conditions based on the method in Step 2, and fitting the curve of the thermal conductivity k of the graphene composite braided structure as a function of temperature, such as... Figure 7 As shown, the relationship between the thermal rectification coefficient μ of the fitted graphene composite braided structure and temperature is illustrated in the figure. Figure 8 As shown in the figure, this example selects a temperature environment variation between 300K and 500K. It can be seen from the figure that the thermal conductivity k initially increases with increasing temperature, then decreases again around 400K with further temperature increases. Ultimately, it can be concluded that within the set temperature range, as the temperature gradually increases, the thermal rectification coefficient μ of the graphene composite braided structure gradually decreases (observing the absolute value change) and tends to stabilize.

[0061] Step 4: Analyze the relationship between the thermal rectification coefficient and the structural dimensions of the graphene composite braided structure. Specifically, this includes changing the dimensions of the graphene composite braided structure along the heat transfer direction, where the dimension is the length of the graphene composite braided structure. Based on the method in Step 2, obtain the thermal conductivity and thermal rectification coefficient of the graphene composite braided structure at different lengths, and fit the curve of the thermal conductivity k of the graphene composite braided structure as a function of length, such as... Figure 9 As shown, the relationship between the thermal rectification coefficient μ of the fitted graphene composite braided structure and its length is illustrated in the figure. Figure 10 As shown in the figure, this example selects a length variation between 140nm and 260nm. It can be seen from the figure that the thermal conductivity k increases with increasing length. Ultimately, it can be concluded that within a set size range, as the length of the graphene composite braided structure gradually increases, the thermal rectification coefficient μ of the graphene composite braided structure gradually decreases (observing the absolute value change).

[0062] Step 5: Design the graphene composite braided structure with the optimal thermal rectification coefficient based on two variation relationships. Specifically, this includes: designing the dimension of the graphene composite braided structure along the heat transfer direction to be the minimum value within the set dimension range in the dimension variation relationship; and designing the ambient temperature of the graphene composite braided structure after the dimension change to be the lowest temperature within the set temperature range in the temperature variation relationship, thus obtaining the graphene braided structure with the optimal thermal rectification coefficient. In this example, the dimension of the graphene composite braided structure along the heat transfer direction is designed to be 140 nm, and the ambient temperature is 300 K, at which point the calculated thermal rectification coefficient is optimal.

[0063] The above descriptions are merely preferred embodiments of this application, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for controlling the thermal rectification of a graphene composite braided structure, characterized in that, The method includes: Several graphene strips are woven together to obtain a graphene composite woven structure with a gradient change in thermal conductivity along the heat transfer direction. The relationship between the thermal rectification coefficient of the graphene composite braided structure and temperature was analyzed, as well as the relationship between the thermal rectification coefficient and structural dimensions of the graphene composite braided structure. Based on two variation relationships, a graphene composite braided structure with the optimal thermal rectification coefficient was designed, including: The dimensions of the graphene composite braided structure along the heat transfer direction are designed to be the minimum values ​​within a set size range in the size variation relationship; The ambient temperature of the graphene composite braided structure after the design size change is the lowest temperature within the set temperature range in the temperature change relationship. The graphene composite braided structure has the best thermal rectification coefficient at the minimum size and lowest temperature.

2. The thermal rectification and control method for the graphene composite braided structure according to claim 1, characterized in that, Methods for weaving together several graphene strips include: N graphene strips are taken as weft lines, and M graphene strips are taken as warp lines, with the heat transfer direction defined as the extension direction of the weft lines. The weft threads are arranged at intervals along the orthogonal direction of the heat transfer direction, and the warp threads are arranged at intervals along the heat transfer direction. The area where the warp threads are located is divided into multiple weaving areas along the heat transfer direction. The weft threads are sequentially woven with the warp threads of each weaving area, and the weaving constraints of each weaving area increase or decrease linearly according to the area order. The weaving constraint refers to the number of weft threads that change the overlapping direction when weaving with the warp threads.

3. The thermal rectification and control method for the graphene composite braided structure according to claim 2, characterized in that, When the weaving constraints of each weaving region increase linearly according to the region order, the method of weaving the weft threads sequentially with the warp threads of each weaving region includes: Let the weaving constraint of weaving region I be i. Starting from weaving region I, the weft threads on each warp in the region are woven sequentially in the manner of i consecutive overlapping on one side of the warp thread, followed by i consecutive overlapping on the other side of the warp thread, to obtain the graphene weaving structure of the region. Let i = i + j as the weaving constraint of the next weaving region, until all weaving regions are completed, where i and j are both positive integers.

4. The method for controlling the thermal rectification of the graphene composite braided structure according to claim 2, characterized in that, When the weaving constraints of each weaving region decrease linearly according to the region order, the method for sequentially weaving the weft threads with the warp threads of each weaving region includes: Let the weaving constraint of weaving region I be i, where i is a positive integer greater than 1. Starting from weaving region I, the weft threads on each warp in the region are woven sequentially in such a way that i consecutive threads overlap on one side of the warp thread, and then i consecutive threads overlap on the other side of the warp thread, to obtain the graphene weaving structure of the region. Let i = ij as the weaving constraint of the next weaving region, until all weaving regions are completed, where j is a positive integer less than i.

5. The method for controlling the thermal rectification of the graphene composite braided structure according to claim 2, characterized in that, When the weaving constraints of each weaving region increase linearly according to the region order, the weaving density of the graphene composite weaving structure in each weaving region changes from dense to sparse, and the thermal conductivity of the graphene composite weaving structure in each weaving region gradually increases. When the weaving constraints of each weaving region decrease linearly according to the region order, the weaving density of the graphene composite weaving structure in each weaving region changes from sparse to dense, and the thermal conductivity of the graphene composite weaving structure in each weaving region gradually decreases.

6. The method for thermal rectification and control of the graphene composite braided structure according to claim 3 or 4, characterized in that, When i=N, in this weaving area, all the weft threads on each warp overlap on one side of the warp, or all the weft threads overlap on the other side of the warp.

7. The thermal rectification and control method for the graphene composite braided structure according to claim 1, characterized in that, The methods for analyzing the relationship between the thermal rectification coefficient and temperature of the graphene composite braided structure include: The thermal rectification coefficient of the graphene composite braided structure was obtained under different temperature conditions. The relationship curve of the thermal rectification coefficient of the graphene composite braided structure with temperature was fitted, and it was found that: within the set temperature range, as the temperature gradually increases, the thermal rectification coefficient of the graphene composite braided structure gradually decreases and tends to stabilize.

8. The thermal rectification and control method for the graphene composite braided structure according to claim 1, characterized in that, The methods for analyzing the relationship between the thermal rectification coefficient and the structural dimensions of the graphene composite braided structure include: By changing the dimensions of the graphene composite braided structure along the heat transfer direction, where the dimension is the length of the graphene composite braided structure, the thermal rectification coefficient of the graphene composite braided structure at different lengths is obtained. The relationship curve of the thermal rectification coefficient of the graphene composite braided structure with the length is fitted, and it is found that: within a set size range, as the length of the graphene composite braided structure gradually increases, the thermal rectification coefficient of the graphene composite braided structure gradually decreases.

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