An isothermal microchannel device and method of making the same

Abstract

The application discloses a kind of equal-temperature microchannel devices and preparation method thereof, equal-temperature microchannel device includes: main body, the material of the main body is composite material, multiple microchannels are set in the main body, the microchannel is used to supply the flow of liquid working substance, the composite material is composed of metal matrix and reinforcing body, the reinforcing body is set in the metal matrix, the volume fraction of the reinforcing body in the composite material gradient changes along the extension direction of the microchannel, to make the thermal conductivity of the microchannel gradient increases along the flow direction of the liquid working substance.This application is by using segmented design, so that the thermal conductivity of microchannel can constantly increase, can make the heat transfer efficiency in the whole heat dissipation process tend to be consistent, improve the equal-temperature and improve the heat conduction effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of microchannels, and particularly relates to a uniform-temperature microchannel device and a preparation method thereof. BACKGROUND

[0002] With the development of micro-nano processing technology and new generation semiconductor materials, the development of chips also presents new characteristics. According to the international semiconductor technology, the power density of integrated circuits (IC) will increase to 1 MW / m 2 or even higher, and the high heat flow problem will seriously affect the performance and reliability of the device. For chips with different characteristics, thermal management is always the key to restricting their working performance and stability, and is also the bottleneck restricting their performance improvement. At present, microchannel heat sinks (MCHS) are attracting much attention due to their small size and strong heat dissipation capacity, and are an excellent means to replace traditional air cooling. Although the traditional microchannel heat sink can effectively reduce the temperature of the chip to a certain extent, it still faces the problem of uneven temperature distribution, which may cause overheating in some chip areas and limit the performance of the chip. SUMMARY

[0003] Therefore, it is necessary to provide a uniform-temperature microchannel device with good heat conduction performance and strong uniformity.

[0004] A uniform-temperature microchannel device comprises:

[0005] A main body made of a composite material, a plurality of microchannels are formed in the main body, the microchannels are used for the flow of liquid working medium, the composite material is composed of a metal matrix and a reinforcing body, the reinforcing body is arranged in the metal matrix, the volume fraction of the reinforcing body in the composite material changes along the extension direction of the microchannels, so that the thermal conductivity of the microchannels increases along the flow direction of the liquid working medium.

[0006] Optionally, the microchannel has a liquid inlet and a liquid outlet, the liquid working medium enters the microchannel through the liquid inlet and then flows out from the liquid outlet, the volume fraction of the reinforcing body in the composite material increases along the direction from the liquid inlet to the liquid outlet, and the thermal conductivity of the microchannel increases along the direction from the liquid inlet to the liquid outlet.

[0007] A preparation method of a uniform-temperature microchannel device comprises the following steps:

[0008] Preparation of the composite material: the types of the metal matrix and the reinforcing body are preset, the reinforcing body is pretreated, and then the reinforcing body and the metal matrix are mixed uniformly at different proportions to obtain a mixture with different proportions, and the mixture with different proportions is assembled in a mold to make the volume fraction of the reinforcing body in the composite material change in a gradient manner, thereby producing a segmented effect, and finally, hot-pressing sintering is performed to obtain the composite material, wherein the volume fraction of the reinforcing body changes according to a preset rule;

[0009] Processing of the micro-channel: a femtosecond laser processing technology is used to process a plurality of micro-channels in the composite material.

[0010] Optionally, the metal matrix is copper powder with a purity greater than 99.99%, and the reinforcing body is diamond.

[0011] Optionally, the volume fraction of the reinforcing body changes according to a preset rule, including:

[0012] The volume fraction of the reinforcing body changes according to a preset rule, including:

[0013] The thermal conductivity coefficient of the composite material at the initial liquid inlet and the liquid outlet is set as a first thermal conductivity coefficient K1, and the composite heat transfer coefficient at the initial liquid outlet is calculated according to the first thermal conductivity coefficient according to formula (1);

[0014] The thermal conductivity coefficient of the composite material at the initial liquid inlet and the liquid outlet is set as a first thermal conductivity coefficient K1, and the composite heat transfer coefficient at the initial liquid outlet is calculated according to the first thermal conductivity coefficient according to formula (1);

[0015] The temperature change of the liquid working medium and the temperature change simulation curve of the composite material when the liquid working medium flows through the micro-channel are established according to the first thermal conductivity coefficient K1 and the flow rate of the liquid working medium, and the temperature difference ΔT1 of the liquid working medium and the composite material at the initial liquid outlet is obtained, and then the temperature difference ΔT0 when the thermal conductivity coefficient of the composite material at the liquid outlet changes from the first thermal conductivity coefficient to the second thermal conductivity coefficient is calculated according to ΔT1, the first thermal conductivity coefficient K1 and the second thermal conductivity coefficient K2 according to formula (2);

[0016] The temperature difference ΔT0 is divided into N parts, and along the direction from the liquid inlet to the liquid outlet, points with a temperature drop of ΔT0 / N are found on the composite material in turn, and the micro-channel is divided into N segments, the logarithmic mean temperature difference drop of each segment of the micro-channel is calculated, the composite heat transfer coefficient of each segment of the micro-channel is calculated according to formula (2), and then the thermal conductivity coefficient of the composite material of each segment of the micro-channel is calculated according to formula (1), and based on the thermal conductivity coefficient of the composite material of each segment of the micro-channel, the volume fraction of the reinforcing body in each segment of the composite material is calculated, wherein N is a natural number greater than or equal to 2.

[0017] Formula (1) is

[0018] in,

[0019] U — Composite heat transfer coefficient / W / (m 2 ·K)

[0020] h——convective heat transfer coefficient / W / (m 2 ·K)

[0021] K — Thermal conductivity of the composite material / W / (m·K)

[0022] d o —Outer diameter of microchannels / m

[0023] d i —Inner diameter of the microchannel / m;

[0024] Formula (2) is Q = UAΔT

[0025] in,

[0026] Q - Heat flow / W

[0027] U — Composite heat transfer coefficient / W / (m 2 ·K)

[0028] A – Cross-sectional area of ​​the microchannel / m 2

[0029] ΔT — Temperature difference between the liquid working fluid and the composite material / °C.

[0030] Optionally, after setting the thermal conductivity of the composite material at the initial liquid outlet as the first thermal conductivity K1, before calculating the composite heat transfer coefficient at the initial liquid outlet according to formula (1) based on the first thermal conductivity, the following steps are also included:

[0031] According to formulas (3) and (4), the Nusselt number Nu and the convective heat transfer coefficient h of the liquid working medium at the initial outlet are calculated respectively.

[0032] The formula (3) is

[0033] The formula (4) is

[0034] in,

[0035] D h —Equivalent diameter of microchannel cross-section / m

[0036] L – Length of the microchannel / m

[0037] k — Thermal conductivity of water / W / (m·K)

[0038] Re – Reynolds number of water

[0039] Pr – Prandtl number of water.

[0040] Optionally, after setting the thermal conductivity of the composite material at the initial outlet as the first thermal conductivity K1, before calculating the Nusselt number and convective heat transfer coefficient of the liquid working medium according to formulas (3) and (4), the calculation of the Reynolds number and Prandtl number of the liquid working medium is also included.

[0041] Optionally, the Reynolds number and Prandtl number of the liquid working fluid are calculated as follows:

[0042] The flow rate of the liquid working medium is obtained, and the temperature, dynamic viscosity, density, thermal conductivity, specific heat capacity at constant pressure, and equivalent diameter of the microchannel cross section of the liquid working medium at the initial outlet are obtained. The Reynolds number Re and Prandtl number Pr of the liquid working medium are calculated according to formulas (5) and (6), respectively.

[0043] The formula (5) is

[0044] in,

[0045] D h —Equivalent diameter of microchannel cross-section / m

[0046] ρ — density of water / kg / m³ 3

[0047] μ — Dynamic viscosity of water / kg / (m·s)

[0048] v — water velocity / m / s

[0049] The formula (6) is

[0050] in,

[0051] C p Specific heat capacity of water at constant pressure / J / (kg·℃)

[0052] k — Thermal conductivity of water / W / (m·K)

[0053] μ——Dynamic viscosity of water / kg / (m·s).

[0054] Optionally, obtaining the equivalent diameter of the microchannel cross-section includes measuring the width and height of the microchannel and calculating the equivalent diameter of the microchannel cross-section according to formula (7);

[0055] The formula (7) is

[0056] in:

[0057] b — width of the microchannel / m

[0058] h — height of the microchannel / m.

[0059] Optionally, the reinforcement may be pretreated by: tungsten plating on the surface of the reinforcement, and then annealing the tungsten-plated reinforcement.

[0060] The temperature uniformity microchannel device provided in this application is formed by multiple microchannels in a composite material. By making the volume fraction of the reinforcement in the composite material vary gradually along the extension direction of the microchannel, the thermal conductivity of the microchannel increases gradually along the flow direction of the liquid working fluid. This can compensate for the disadvantage of poor temperature uniformity in traditional microchannel heat dissipation devices. This is because in traditional microchannel heat dissipation devices, the liquid working fluid will continuously heat up as it flows through the microchannel, causing the temperature difference between the liquid working fluid and the material to continuously decrease, resulting in a continuous decrease in heat dissipation efficiency during the heat dissipation process. This application adopts a segmented design, which allows the thermal conductivity of the microchannel to continuously increase, making the heat transfer efficiency more uniform throughout the heat dissipation process, improving temperature uniformity and thermal conductivity. Attached Figure Description

[0061] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0062] Figure 1 This is a front view of a schematic diagram of a temperature equalization microchannel device in one embodiment;

[0063] Figure 2 This is a left view of a schematic diagram of the structure of a temperature equalization microchannel device in one embodiment;

[0064] Figure 3 This is a top view of a schematic diagram of a temperature equalization microchannel device in one embodiment;

[0065] Figure 4 The figures show the temperature change curves of water flowing at a velocity of 0.6 m / s through a diamond / copper composite material with a thermal conductivity of 400 W / m·K, as well as the temperature change curve of the composite material itself, in one embodiment.

[0066] Figure 5 The graph shows the variation of thermal conductivity of the composite material under different diamond volume fractions.

[0067] 1. Main body; 2. Microchannel; 21. Liquid inlet; 22. Liquid outlet.

[0068] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0069] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0070] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0071] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the term "and / or" throughout the text includes three solutions; taking A and / or B as an example, it includes technical solution A, technical solution B, and a technical solution that simultaneously satisfies A and B. Furthermore, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of a person skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0072] refer to Figures 1 to 5 This application provides a temperature equalization microchannel device, which includes a main body 1 made of composite material. Multiple microchannels 2 are formed inside the main body 1 and are evenly spaced. The microchannels 2 are used for the flow of liquid working fluid. The composite material is composed of a metal matrix and a reinforcement. The reinforcement is evenly distributed in the metal matrix. The volume fraction of the reinforcement in the composite material varies gradually along the extension direction of the microchannels 2 so that the thermal conductivity of the microchannels 2 increases gradually along the flow direction of the liquid working fluid.

[0073] The temperature uniformity microchannel device provided in this application is formed by multiple microchannels 2 formed from a composite material. By making the volume fraction of the reinforcement in the composite material vary gradually along the extension direction of the microchannel 2, the thermal conductivity of the microchannel 2 increases gradually along the flow direction of the liquid working fluid. This can compensate for the disadvantage of poor temperature uniformity in traditional microchannel heat dissipation devices. This is because in traditional microchannel heat dissipation devices, the liquid working fluid will continuously heat up as it flows through the microchannel 2, causing the temperature difference between the liquid working fluid and the material to continuously decrease, resulting in a continuous decrease in heat dissipation efficiency during the heat dissipation process. This application adopts a segmented design, which allows the thermal conductivity of the microchannel 2 to continuously increase, making the heat transfer efficiency more uniform throughout the heat dissipation process, improving temperature uniformity and heat conduction effect.

[0074] Specifically, the liquid working medium is water.

[0075] Specifically, the metal matrix is ​​high-purity spherical copper powder with a purity greater than 99.99%, and the reinforcement is diamond. Copper is a metal with relatively high thermal conductivity, widely used and technologically mature in heat dissipation, but it suffers from a high coefficient of linear expansion, making it difficult to match with semiconductor materials. Diamond / copper composite materials can significantly improve thermal conductivity, while the coefficient of linear expansion is controllable, showing broad application prospects in the heat dissipation of high-power devices. Therefore, this application designs a heat dissipation device with good thermal conductivity and strong temperature uniformity based on diamond / copper composite materials. The composite material is segmented, and the volume fraction of diamond at different segments is changed, thereby altering the thermal conductivity of different segments and enhancing the temperature uniformity of the heat dissipation device.

[0076] Diamond possesses extremely high thermal conductivity, making it one of the best heat conductors on Earth, with a thermal conductivity five times that of copper or even higher. Combining diamond particles or surface-treated diamond powder with a copper matrix effectively enhances the thermal conductivity of the composite material. Copper is an excellent thermal and electrical conductor with exceptional thermal conductivity. When diamond and copper are combined, the copper matrix acts as a thermal bridge, rapidly transferring heat and reducing thermal resistance. The copper matrix's good thermal stability and conductivity effectively distribute the thermal load from the diamond particles, resulting in a more uniform heat conduction profile in the entire composite material.

[0077] This invention provides a heat dissipation device made of segmented composite materials, which solves the problem of difficult-to-machine diamond by processing the composite material. The combination of diamond and copper combines the characteristics of both; the hardness, wear resistance, and high thermal conductivity of diamond are combined with the good plasticity of copper, resulting in significantly enhanced material properties. Compared to pure diamond materials, diamond / copper composites are generally more economical because copper is a relatively inexpensive metal, reducing manufacturing costs. Copper is a very easy-to-machine and shape metal; combining it with diamond retains its machinability, making diamond / copper composites easier to process into various shapes and structures. By adjusting the ratio of diamond to copper in the diamond / copper composite material, the coefficient of thermal expansion of the composite material can be adjusted, making it better suited to the needs of various engineering applications.

[0078] Specifically, the microchannel 2 has an inlet 21 and an outlet 22. The liquid working fluid enters the microchannel 2 through the inlet 21 and then flows out from the outlet 22. The volume fraction of the reinforcement in the composite material increases in a gradient from the inlet 21 to the outlet 22.

[0079] This application also provides a method for preparing a uniformly heated microchannel device, comprising the following steps:

[0080] S1. Preparation of composite material: The types of metal matrix and reinforcement are predetermined. The metal matrix is ​​selected as high-purity spherical copper powder with a purity greater than >99.99%, and the reinforcement is diamond. The reinforcement is pretreated, which includes tungsten plating on the surface of the reinforcement, followed by annealing. The reinforcement and metal matrix are mixed evenly in different proportions to obtain mixtures with different ratios. The mixtures with different ratios are assembled in molds to produce a segmented effect. Finally, hot pressing and sintering are performed to obtain the composite material. The volume fraction of the reinforcement varies according to a predetermined rule.

[0081] S2. Fabrication of Microchannels 2: Multiple microchannels 2 are fabricated within the composite material using femtosecond laser processing technology. Femtosecond pulsed lasers can generate extremely high power densities (up to several gigawatts) at relatively low average power (100mW). Such high power densities can cause the C-C covalent bonds in the diamond lattice to dissociate. The diamond-graphitization transformation under laser irradiation increases the interatomic spacing of carbon atoms, reduces the density of states, and alters the physicochemical properties of the solid. Within the extremely short pulse duration, the possibility of heat-affected zone formation is minimized, allowing for precise fabrication of the diamond surface structure with minimal thermal damage.

[0082] In order to obtain the composite material, the present invention also designed a method for calculating the thermal conductivity and diamond volume fraction of different sections, so that the volume fraction of the reinforcement can change according to a preset rule.

[0083] In this embodiment, the temperature-equalizing microchannel device used has dimensions of 34mm × 17.5mm; microchannel 2 is 0.5mm wide, 1mm deep, and 34mm long; the spacing between microchannels 2 is 0.5mm, with a total of 16 microchannels 2. The total width of the microchannels 2 and the spacing is 15.5mm, with 1mm on each side of the outermost edge, for a total width of 17.5mm. (Reference) Figures 1 to 3 .

[0084] refer to Figure 4 This method uses Figure 4 The temperature change of the diamond / copper composite microchannel 2 with a flow velocity of 0.6 m / s and a thermal conductivity of K1 = 400 W / m·K is simulated.

[0085] Specifically, Figure 4 The left end is the liquid outlet 22, and the right end is the liquid inlet 21.

[0086] Specifically, the first thermal conductivity K1 is set to 400 because the thermal conductivity of copper is close to 400. If the value is lower than 400, the advantage of the material's high thermal conductivity cannot be reflected.

[0087] Further, refer to Figure 4 The temperature of the water at the outlet 22 of microchannel 2 was found to be approximately T = 65℃ = 65 + 273.15 = 338.2 K. According to available data, the dynamic viscosity of water at this temperature is μ = 3.24 × 10⁻⁶. -4 The density of water is ρ = 958.4 kg / (m·s), the thermal conductivity of water is k = 0.6 W / (m·K), and the specific heat capacity of water at constant pressure is 4187 J / (kg·℃).

[0088] Furthermore, according to Reynolds' formula:

[0089]

[0090] In the formula:

[0091] D h —Equivalent diameter of microchannel 2 cross section / m

[0092] ρ — density of water / kg / m³ 3

[0093] μ — Dynamic viscosity of water / kg / (m·s)

[0094] υ—Water flow velocity / m / s

[0095] and the equivalent diameter formula

[0096]

[0097] In the formula:

[0098] b — Width of microchannel 2 / m

[0099] h — Height of microchannel 2 / m

[0100] get

[0101] Further, calculate the Prandtl number. According to the formula:

[0102]

[0103] In the formula:

[0104] C p Specific heat capacity of water at constant pressure / J / (kg·℃)

[0105] k — Thermal conductivity of water / W / (m·K)

[0106] μ — Dynamic viscosity of water / kg / (m·s)

[0107] Solving

[0108] Furthermore, the Nusselt number Nu and the convective heat transfer coefficient h were calculated using the Gnielinski relation:

[0109]

[0110] In the formula:

[0111] D h —Equivalent diameter of microchannel 2 cross section / m

[0112] L – Length of microchannel 2 (m)

[0113] k — Thermal conductivity of water / W / (m·K)

[0114] Re – Reynolds number of water

[0115] Pr—Prantz number of water

[0116] Solving for Nu, we get Nu ≈ 26.6, h = 23820.9 W / (m²). 2 ·K)

[0117] Furthermore, the composite heat transfer coefficient is calculated using the composite heat transfer formula.

[0118]

[0119] In the formula:

[0120] U — Composite heat transfer coefficient / W / (m 2 ·K)

[0121] h——convective heat transfer coefficient / W / (m 2 ·K)

[0122] k — Thermal conductivity of the material / W / (m·K)

[0123] d o ——Outer diameter / m

[0124] d i ——Inner diameter / m

[0125] Reference Figures 1 to 3 The first thermal conductivity of the composite material is K1 = 400 W / (m·K); d i =0.5mm, the spacing between each microchannel 2 in the model is 0.5mm, therefore d o It can be approximated as 1 mm. The calculated value is U1 = 563.4 W / (m²). 2 ·K)

[0126] Furthermore, if the thermal conductivity of the composite material at the outlet is changed to the second thermal conductivity K2 = 900 W / (m·K), then: U2 = 1231.3 W / (m·K) 2 ·K).

[0127] Specifically, the second thermal conductivity K2 is set to 900 W / (m·K), because 900 is the upper limit of the thermal conductivity of diamond / copper composite materials; the highest thermal conductivity that diamond / copper composite materials can achieve is 900 W / (m·K). Furthermore, considering the steady state at the outlet, and assuming the water temperature and heat flow are constant, when the thermal conductivity of the composite material changes from the first thermal conductivity K1 = 400 W / (m·K) to the second thermal conductivity K2 = 900 W / (m·K), according to the formula:

[0128] Q=UAΔT (2)

[0129] In the formula:

[0130] Q - Heat flow / W

[0131] U — Composite heat transfer coefficient / W / (m 2 ·K)

[0132] A – Cross-sectional area of ​​the microchannel (m²) 2

[0133] ΔT — Temperature difference between fluid and material / °C

[0134] Furthermore, when the thermal conductivity of the composite material is 400 W / (m·K), i.e. U1 = 563.4 W / (m·K), 2 When K), by Figure 4It can be seen that ΔT1≈145℃. Substituting U1, U2, and ΔT1 into formula (2), we get:

[0135] ΔT2≈67℃

[0136] Furthermore, calculations show that when the thermal conductivity of the composite material at the liquid outlet changes from 400 W / (m·K) to 900 W / (m·K), the temperature drop ΔT0 = ΔT1 - ΔT2, where ΔT0 is approximately 78℃.

[0137] Furthermore, in the figure, we assume that the heat exchange of the system is constant, therefore the trend line of water temperature change is constant, and the temperature of the composite material at the inlet and the temperature of the liquid working fluid are also constant. At the end of the composite material, the thermal conductivity changes from 400 W / (m·K) to 900 W / (m·K), and the temperature drops by 78℃. Since the thermal conductivity of the composite material at the initial inlet is set as the first thermal conductivity K1, the temperature difference is divided equally, and the points where the temperature drops to 62.4℃, 46.8℃, 31.2℃, and 15.6℃ are found respectively. Based on this, the microchannel 2 of the composite material is divided into 5 segments, and the logarithmic average temperature difference of each segment is calculated. Then, the composite heat transfer coefficient of each segment of the composite material is calculated according to formula (2), and finally, the thermal conductivity of each segment of the composite material is calculated according to formula (1), and the thermal conductivity of each segment of the material is given.

[0138] Specifically, the temperature of the composite material at the outlet can be calculated using the above formula when the thermal conductivity of the composite material changes from 400 W / (m·K) to 900 W / (m·K). Then, the temperature trend lines at the outlet and inlet when the thermal conductivity is 900 W / (m·K) can be plotted and compared with the temperature change simulation curve of the composite material when the thermal conductivity is 400 W / (m·K) to obtain the temperature points at each point.

[0139] Specifically, the average thermal temperature difference ΔTm = (ΔT 复合材料 -△T 水 ) / ln(△T 复合材料 / △T 水 ), △T 复合材料 Let ΔT be the temperature difference between the composite material at its current temperature and the inlet temperature. 水 This represents the temperature difference between the water at its current temperature and the temperature at the inlet.

[0140] Since the temperature curve does not change uniformly, it is preferable to segment it in places where the temperature changes drastically, that is, to select points where the temperature drops by ΔT0 / N in sequence.

[0141] The microchannel in this application is divided into N segments. In this embodiment, N=5. This is because more segments will result in more uniform temperature. However, too many segments will make the preparation of composite materials very difficult. Selecting 5 segments is a more preferred option based on the actual situation.

[0142] Furthermore, according to Figure 5 The first curve in the thermal conductivity distribution diagram of each composite material segment and the thermal conductivity distribution diagram of the composite material under different diamond volume fractions is the Hasselman-Johnson model curve, which gives the diamond volume fraction of each composite material segment.

[0143] In this embodiment, along the direction from the inlet to the outlet of the microchannel, the thermal conductivity of the composite material for each segment of the microchannel is 448.5, 505.0, 570.1, 677.6, and 900, respectively. Figure 5 As can be seen from the data, the volume fraction of diamond in each composite material segment is 10%, 16%, 22%, 32%, and 48%, respectively.

[0144] This application uses the Gnielinski relation to calculate the Nusselt number (Nu), which is applicable to convective heat transfer problems of various fluids under various flow conditions, including heat transfer within circular pipes and heat transfer through pipe walls, demonstrating strong applicability. The Gnielinski relation is an empirical formula based on extensive experimental data, providing relatively accurate Nusselt number calculation results, which helps predict heat transfer conditions and optimize engineering design. Using the Gnielinski relation simplifies the calculation process of convective heat transfer, eliminating the need for complex mathematical derivations or experimental data processing, and allowing for rapid estimation of the Nusselt number. This invention uses a composite heat transfer formula for calculation, which can simultaneously consider and integrate multiple heat transfer modes, such as convective heat transfer, radiative heat transfer, and conductive heat transfer, making it suitable for the analysis and calculation of various complex heat transfer problems. Considering the combined effect of multiple heat transfer modes, the composite heat transfer formula can more accurately describe the actual heat transfer process, improving the accuracy and reliability of the calculation.

[0145] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural transformations made using the contents of the specification and drawings of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A method for preparing a uniformly heated microchannel device, characterized in that: Includes the following steps: Preparation of composite materials: The types of metal matrix and reinforcement are predetermined. After pretreatment of the reinforcement, the reinforcement and metal matrix are mixed uniformly in different proportions to obtain mixtures with different ratios. The mixtures with different ratios are assembled in molds to make the volume fraction of the reinforcement in the composite material change in a gradient, thereby producing a segmented effect. Finally, hot pressing and sintering are performed to obtain the composite material, wherein the volume fraction of the reinforcement changes according to a predetermined law. Fabricating microchannels: Multiple microchannels are fabricated within composite materials using femtosecond laser processing technology; The volume fraction of the reinforcement varies according to a preset rule, including: The thermal conductivity of the composite material at the initial inlet and outlet is set as the first thermal conductivity K1. The composite heat transfer coefficient at the initial outlet is calculated according to formula (1) based on the first thermal conductivity. Set a second thermal conductivity K2, and convert the thermal conductivity of the composite material at the liquid outlet to the second thermal conductivity K2. The second thermal conductivity is greater than the first thermal conductivity. Calculate the composite heat transfer coefficient corresponding to the second thermal conductivity K2 according to formula (1). Based on the first thermal conductivity K1 and the flow rate of the liquid working medium, establish simulation curves of the temperature change of the liquid working medium and the temperature change of the composite material when the liquid working medium flows through the microchannel. The temperature difference ΔT1 between the liquid working medium and the composite material at the initial outlet is obtained. Then, based on ΔT1, the first thermal conductivity K1 and the second thermal conductivity K2, calculate the temperature difference ΔT0 when the composite material at the outlet changes from the first thermal conductivity to the second thermal conductivity according to formula (2). Divide the temperature difference ΔT0 into N equal parts. Along the direction from the inlet to the outlet, find the points on the composite material where the temperature drops by ΔT0 / N. Divide the microchannel into N segments and calculate the logarithmic mean temperature difference drop of each segment. Calculate the composite heat transfer coefficient of each segment of the microchannel according to formula (2). Then, calculate the thermal conductivity of the composite material of each segment of the microchannel according to formula (1). Based on the thermal conductivity of the composite material of each segment of the microchannel, calculate the volume fraction of the reinforcement in each segment of the composite material. Where N is a natural number greater than or equal to 2. Formula (1) is in, U — Composite heat transfer coefficient / W / (m 2 ·K) h——convective heat transfer coefficient / W / (m 2 ·K) K — Thermal conductivity of the composite material / W / (m·K) d o —Outer diameter of microchannels / m d i —Inner diameter of the microchannel / m; Formula (2) is Q = UAΔT in, Q - Heat flow / W U — Composite heat transfer coefficient / W / (m 2 ·K) A – Cross-sectional area of ​​the microchannel / m 2 ΔT — Temperature difference between the liquid working fluid and the composite material / °C.

2. The method for preparing the uniformly heated microchannel device according to claim 1, characterized in that, The metal matrix is ​​copper powder with a purity greater than 99.99%, and the reinforcing agent is diamond.

3. The method for preparing the uniformly heated microchannel device according to claim 2, characterized in that, After setting the thermal conductivity of the composite material at the initial liquid outlet as the first thermal conductivity K1, before calculating the composite heat transfer coefficient at the initial liquid outlet according to formula (1) based on the first thermal conductivity, the following steps are also included: According to formulas (3) and (4), the Nusselt number Nu and the convective heat transfer coefficient h of the liquid working medium at the initial outlet are calculated respectively. The formula (3) is The formula (4) is in, D h —Equivalent diameter of microchannel cross-section / m L – Length of the microchannel / m k — Thermal conductivity of water / W / (m·K) Re – Reynolds number of water Pr – Prandtl number of water.

4. The method for preparing the uniformly heated microchannel device according to claim 3, characterized in that, After setting the thermal conductivity of the composite material at the initial liquid outlet as the first thermal conductivity K1, before calculating the Nusselt number and convective heat transfer coefficient of the liquid working medium according to formulas (3) and (4), the calculation of the Reynolds number and Prandtl number of the liquid working medium is also included.

5. The method for preparing the uniformly heated microchannel device according to claim 4, characterized in that, The Reynolds number and Prandtl number of the liquid working fluid were calculated as follows: The flow rate of the liquid working medium is obtained, and the temperature, dynamic viscosity, density, thermal conductivity, specific heat capacity at constant pressure, and equivalent diameter of the microchannel cross section of the liquid working medium at the initial outlet are obtained. The Reynolds number Re and Prandtl number Pr of the liquid working medium are calculated according to formulas (5) and (6), respectively. The formula (5) is in, D h —Equivalent diameter of microchannel cross-section / m σ — density of water / kg / m³ 3 μ — Dynamic viscosity of water / kg / (m·s) v — water velocity / m / s The formula (6) is in, Σ p Specific heat capacity of water at constant pressure / J / (kg·℃) k — Thermal conductivity of water / W / (m·K) μ——Dynamic viscosity of water / kg / (m·s).

6. The method for preparing the uniformly heated microchannel device according to claim 5, characterized in that, The process of obtaining the equivalent diameter of the microchannel cross-section includes measuring the width and height of the microchannel and calculating the equivalent diameter of the microchannel cross-section according to formula (7); The formula (7) is in: b — width of the microchannel / m h — height of the microchannel / m.

7. The method for preparing the uniformly heated microchannel device according to claim 1, characterized in that, The pretreatment of the reinforcement includes: tungsten plating on the surface of the reinforcement, and then annealing the tungsten-plated reinforcement.

8. A temperature-equalizing microchannel device prepared by the method of preparing a temperature-equalizing microchannel device according to any one of claims 1-7, characterized in that, include: The main body is made of composite material and has multiple microchannels inside for the flow of liquid working fluid. The composite material is composed of a metal matrix and a reinforcement, with the reinforcement disposed within the metal matrix. The volume fraction of the reinforcement in the composite material varies gradient along the extension direction of the microchannels to increase the thermal conductivity of the microchannels gradient along the flow direction of the liquid working fluid.

9. The temperature-equalizing microchannel device according to claim 8, characterized in that, The microchannel has an inlet and an outlet. The liquid working fluid enters the microchannel through the inlet and then flows out through the outlet. The volume fraction of the reinforcement in the composite material increases gradually from the inlet to the outlet. The thermal conductivity of the microchannel also increases gradually from the inlet to the outlet.

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