Method and device for calculating thermal resistance of air-cooled profile radiator based on equivalent circuit

Abstract

The invention discloses a method and a device for calculating the thermal resistance of an air-cooled profile radiator based on an equivalent circuit. The method comprises the steps that an air-cooled profile radiator thermal resistance equivalent circuit is established, parameters such as radiator structure parameters and external cooling conditions of power electronic equipment can be described conveniently, and the structure parameters involved in the thermal resistance calculation method can describe all the appearance of the radiator; the total heat resistance of the air-cooled profile radiator comprises heat conduction heat resistance and heat convection heat resistance, and the characteristic size, the material, the external cooling condition and the like of the radiator can influence the total heat resistance of the radiator. In conclusion, the thermal resistance calculation method disclosed by the invention is a thermal resistance calculation method for the air-cooled profile radiator, which can completely reflect the structural parameters, the external cooling conditions and the appearance structural parameters of the radiator.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal design of power electronic devices, and in particular relates to a method and a device for calculating the thermal resistance of an air-cooled profile heat sink based on an equivalent circuit. Background Art

[0002] Thanks to the advantages of high reliability, low cost, simple structure and easy maintenance, air-cooled profile radiators are widely used in the heat dissipation of high-power power electronic devices. The combined heat dissipation method of fans and radiators can cover the heat dissipation needs of power electronic devices ranging from hundreds of watts to hundreds of kilowatt-hours.

[0003] Thermal resistance from heat sink to environment in general power electronic device cooling system (s-a) The largest proportion of the total thermal resistance of the system is reduced (s-a) It is the main way to optimize the heat dissipation system of power electronic devices, and calculating the total thermal resistance of the heat sink is the key. However, the existing empirical formula for calculating the thermal resistance of air-cooled profile heat sinks can only reflect the influence of some structural parameters of the heat sink on the heat dissipation effect, especially in the thermal design of high-power electronic equipment, the error is large, and it cannot describe parameters such as heat sink structural parameters and external cooling conditions, and does not take all heat sink shape structural parameters into consideration.

[0004] Therefore, there is an urgent need for a thermal resistance calculation method for air-cooled profile radiators that can fully reflect the radiator structural parameters, external cooling conditions and appearance structural parameters. Summary of the invention

[0005] Purpose of the invention: The present invention provides a method and device for calculating the thermal resistance of an air-cooled profile heat sink based on an equivalent circuit. The method can fully describe the external structural parameters of the heat sink, solving the problem that the existing empirical formula for calculating the thermal resistance of an air-cooled profile heat sink can only reflect the influence of some structural parameters of the heat sink on the heat dissipation effect, but cannot describe the entire external shape of the heat sink, especially the problem of large errors in the thermal design of high-power electronic equipment.

[0006] Technical solution: A method for calculating the thermal resistance of an air-cooled profile radiator, comprising the following steps:

[0007] Step 1, establishing a thermal resistance equivalent circuit of an air-cooled profile heat sink, wherein the air-cooled profile heat sink comprises a substrate and a plurality of fins fixed on the substrate; wherein the substrate corresponds to the substrate conduction thermal resistance in the equivalent circuit, each of the fins corresponds to a branch in the equivalent circuit, and each branch comprises a fin conduction thermal resistance and a fin convection thermal resistance connected in series;

[0008] Step 2: Classify the conductive thermal resistance of the substrate and the conductive thermal resistance of the fin as conductive thermal resistance, and classify the convection thermal resistance of the fin as convection thermal resistance. Calculate the conductive thermal resistance and convection thermal resistance respectively, and finally obtain the total thermal resistance of the air-cooled profile radiator.

[0009] Furthermore, each of the fins is independent of each other, has the same thickness, and is arranged on the substrate at equal intervals.

[0010] Furthermore, in step 1, branches in the equivalent circuit corresponding to each fin are connected in parallel according to the heat transfer path to form a fin part; and then the substrate conduction thermal resistance is connected in series with the fin part to form a thermal resistance equivalent circuit of a complete air-cooled profile heat sink.

[0011] Furthermore, the thermal resistance in the thermal resistance equivalent circuit described in step 2 is calculated, and the conduction thermal resistance θ1 and the convection thermal resistance θ2 are calculated respectively, and finally the total thermal resistance θ of the air-cooled profile heat sink is obtained. 总 , the formula is:

[0012] θ 总 =θ1+θ2

[0014] Furthermore, the fin conduction thermal resistance and the substrate conduction thermal resistance are used as the conduction thermal resistance θ1, and the calculation formula is:

[0015]

[0016] Among them, λ is the thermal conductivity of the heat sink material, x1 is the width of the heat sink, x2 is the length of the heat sink, x3 is the total height of the heat sink, x6 is the thickness of the heat sink substrate, δ is the thickness of the heat sink fins, and G is the number of heat sink air ducts.

[0017] Furthermore, the fin convection thermal resistance is taken as the convection thermal resistance θ2, and the calculation formula is:

[0018]

[0019] Where μ is the convection heat transfer coefficient in the convection thermal resistance, S t is the Standen number, k 空气 is the thermal conductivity of cooling air, P r is the Prandtl number, υ is the dynamic viscosity of the cooling air, ξ is the average velocity on the windward side, ρ is the fluid density, N u is the Nusselt number.

[0020] Furthermore, the calculated total thermal resistance of the air-cooled profile heat sink is substituted into the power electronic device heat dissipation system to perform device junction temperature verification. The heat dissipation process of the power electronic device heat dissipation system is:

[0021] (1) Heat flows from the die of the device to the housing and then dissipates into the environment through convection and radiation;

[0022] (2) After the heat is transferred to the tube shell, the heat is conducted to the contacting heat sink substrate through the thermal conductive interface material and dissipated into the environment through convection and radiation.

[0023] Furthermore, the total thermal resistance of the power electronic device heat dissipation system can be expressed as:

[0024]

[0025] θ (c-a) is the device case-ambient thermal resistance, θ (c-s) is the device case-heat sink thermal resistance, θ (s-a) is the heat sink-ambient thermal resistance, θ (j-c) is the device junction-to-case thermal resistance, θ (s-a) That is, the total thermal resistance of the aforementioned air-cooled profile radiator θ 总 .

[0026] Furthermore, according to the total thermal resistance of the air-cooled profile heat sink and the thermal resistance equivalent circuit of the power electronic device heat dissipation system, the junction temperature T of the verification device is calculated. j , the formula is:

[0027] T j =T a +Q×θ (j-a)

[0028] Where, T a is the temperature of the environment, Q is the power consumption of the device, θ (j-a) is the total thermal resistance of the device.

[0029] A device for calculating the thermal resistance of an air-cooled profile heat sink based on an equivalent circuit, comprising:

[0030] The equivalent circuit part is used to establish a thermal resistance equivalent circuit of an air-cooled profile heat sink, wherein the air-cooled profile heat sink comprises a substrate and a plurality of fins fixed on the substrate; wherein the substrate corresponds to the substrate conduction thermal resistance in the equivalent circuit, and each of the fins corresponds to a branch in the equivalent circuit, and each branch comprises a fin conduction thermal resistance and a fin convection thermal resistance connected in series;

[0031] The thermal resistance calculation part is used to classify the substrate conduction thermal resistance and the fin conduction thermal resistance as conduction thermal resistance, and classify the fin convection thermal resistance as convection thermal resistance, and calculate the conduction thermal resistance and convection thermal resistance respectively, and finally obtain the total thermal resistance of the air-cooled profile radiator.

[0032] The present invention provides a method and device for calculating the thermal resistance of an air-cooled profile radiator based on an equivalent circuit. Compared with the empirical formula for calculating the thermal resistance of a general air-cooled profile radiator, the thermal resistance calculation method involved in the present invention can fully describe the structural parameters of the radiator; at the same time, factors such as the radiator material and external cooling conditions are added to quickly establish an equivalent thermal resistance of the full description of the air-cooled profile radiator, and complete the rationality verification of the radiator design. The method is a method for calculating the thermal resistance of an air-cooled profile radiator that can fully reflect the structural parameters, external cooling conditions and appearance structural parameters of the radiator. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a flow chart of thermal resistance calculation and verification of an air-cooled profile heat sink based on an equivalent circuit.

[0034] Figure 2 It is a schematic diagram of the thermal resistance equivalent circuit of the air-cooled profile heat sink of the present invention.

[0035] Figure 3 It is a schematic diagram of the structure of the air-cooled profile radiator of the present invention.

[0036] Figure 4 It is a schematic diagram of the thermal resistance equivalent circuit of the power electronic device heat dissipation system of the present invention.

[0037] Figure 5 The figure is a schematic diagram of the heat dissipation path of the heat dissipation system for power electronic devices of the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention, so that those skilled in the art can implement and use the present invention and combine it with specific application backgrounds. The described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0039] A method for calculating the thermal resistance of an air-cooled profile heat sink based on an equivalent circuit, the steps comprising:

[0040] Step 1: Create a thermal resistance equivalent circuit diagram of the air-cooled profile heat sink.

[0041] The air-cooled profile heat sink consists of a base plate and fins. Each fin is independent of each other and is arranged on the base plate at equal intervals. Each fin contains heat conduction and heat convection parts. The diffusion thermal resistance of the base plate is the main consideration of its heat conduction part. From the heat transfer path, the thermal resistance network of the air-cooled profile heat sink can be made into a circuit equivalent. Figure 2 As shown, the substrate thermal conduction resistance θ in the equivalent circuit of the substrate 1-2, one fin corresponds to a branch in the equivalent circuit, which contains the fin conduction thermal resistance θ' 1-1 and the fin convection thermal resistance θ'2, the branch corresponding to the other fin contains θ" 1-1 And θ"2, and so on. All the branches corresponding to the fins are connected in parallel to form the fin part of the equivalent circuit. Then the thermal resistance of the substrate is calculated. 1-2 Connected in series, they form a thermal resistance equivalent circuit of the air-cooled profile radiator.

[0042] Step 2: Calculate the thermal resistance of each part of the radiator separately, including the conduction thermal resistance and the convection thermal resistance, and obtain the total thermal resistance of the air-cooled profile radiator.

[0043] Figure 3 The following is a schematic diagram of the structure of an air-cooled profile radiator, where x1 is the width of the radiator, x2 is the length of the radiator, x3 is the total height of the radiator, x4 is the fin spacing of the radiator, x5 is the fin thickness of the radiator, and x6 is the thickness of the radiator substrate. In each cooling channel of the air-cooled profile radiator, there is heat conduction and heat convection. The characteristic dimensions of the radiator, such as radiator length, fin height, fin thickness, fin spacing, number of fins, as well as materials, external cooling conditions, etc., will affect the thermal resistance of the radiator. The total thermal resistance of the radiator can be divided into the substrate conduction thermal resistance, the fin conduction thermal resistance, and the fin convection thermal resistance, which are expressed as:

[0044] Thermal conduction resistance, including baseplate thermal conduction resistance and fin thermal conduction resistance:

[0045]

[0046] Convection thermal resistance, including fin convection thermal resistance:

[0047]

[0048] Total thermal resistance of heat sink:

[0049] θ 总 =θ1+θ2.

[0050] In the formula, θ 总 is the total thermal resistance of the heat sink, θ1 is the conduction thermal resistance, θ2 is the fin convection thermal resistance, all in K / W; λ is the thermal conductivity of the heat sink material; x1 is the width of the heat sink, x2 is the length of the heat sink, x3 is the total height of the heat sink, x6 is the thickness of the heat sink substrate, δ is the thickness of the heat sink fin, all in m, G is the number of heat sink air ducts, S t is the Standen number, and μ is the convection heat transfer coefficient in the fin convection thermal resistance.

[0051] The convection heat transfer coefficient μ in the fin convection thermal resistance can be obtained by the following formula:

[0052]

[0053] In the formula, k 空气 is the thermal conductivity of cooling air, which is 0.0234 W / MK at one atmospheric pressure and an ambient temperature of 40°C; P r is the Prandtl number, which is 0.7; υ is the dynamic viscosity of the cooling air, which is 1.91×10 -5 m 2 / s; ξ is the average flow velocity on the windward side.

[0054] After derivation, the fin convection thermal resistance in the radiator cooling channel is:

[0055]

[0056] Where x4 is the distance between the radiator fins and G is the number of radiator air ducts.

[0057] In summary, the total thermal resistance calculation formula of the air-cooled profile radiator in this embodiment can be expressed as:

[0058]

[0059] Using the thermal resistance of the air-cooled profile heat sink obtained by this method, the following is established: Figure 4 The thermal resistance equivalent circuit of the heat dissipation system of the power electronic device is shown to verify the junction temperature of the device and the rationality of the heat sink design.

[0060] The main heat dissipation paths of the device are as follows: Figure 5 As shown, it mainly includes:

[0061] (1) Heat flows from the die of the device to the housing and then dissipates into the environment through convection and radiation;

[0062] (2) After the heat is transferred to the tube shell, the heat is conducted to the contacting heat sink substrate through the thermal conductive interface material and dissipated into the environment through convection and radiation.

[0063] In the heat dissipation system of power electronic devices, the device case-ambient thermal resistance θ (c-a) Relative to the device case-heat sink thermal resistance θ (c-s) and heat sink-ambient thermal resistance θ (s-a) The value is very large, which is consistent with the device case-heat sink thermal resistance θ (c-s) and heat sink-ambient thermal resistance θ (s-a) When connected in parallel, it can be ignored. The device junction-case thermal resistance θ (j-c) Mainly determined by the device process and packaging materials, etc., provided by the chip specification; device case-heat sink thermal resistance θ (c-s) It is mainly determined by the roughness of the contact surface between the device housing and the heat sink, as well as the interface material, and is calculated from the thermal conductivity, thickness, and contact area of ​​the thermal conductive material. Figure 5 As shown, the total thermal resistance of the device can be expressed as:

[0064]

[0065] In the formula, θ (c-a) is the device case-ambient thermal resistance, θ (c-s) is the device case-heat sink thermal resistance, i.e. the thermal interface thermal resistance, θ (s-a) is the heat sink-ambient thermal resistance, θ (j-c) is the junction-to-case thermal resistance of the device, and the unit is K / W.

[0066] According to the total thermal resistance of the air-cooled profile heat sink and the thermal resistance equivalent circuit of the power electronic device heat dissipation system, the junction temperature of the verification device is calculated. The junction temperature of the device can be expressed as:

[0067] T j =T a +Q×θ (j-a)

[0068] Where, T j is the device junction temperature, T a is the temperature of the environment, in °C; Q is the power consumption of the device, in W; θ (j-a) is the total thermal resistance of the device.

[0069] In order to facilitate the understanding of the thermal resistance calculation method and device based on the thermal resistance equivalent circuit proposed by the present invention, a certain air-cooled profile radiator is used as an example to calculate the total thermal resistance of the radiator and verify the junction temperature of the device. The parameter values ​​of this air-cooled aluminum profile radiator are: λ = 180W / MK, x3 = 0.065m, x6 = 0.012m, G = 42, x1 = 0.455m, x2 = 0.35m, δ = 0.007m, x4 = 0.007m, ξ = 2m / s.

[0070] The thermal resistance values ​​of each part of the air-cooled profile radiator are obtained by the method described in the present invention: the conduction thermal resistance θ1=0.002K / W, the fin convection thermal resistance θ2=0.043K / W, thereby obtaining the total thermal resistance θ of the air-cooled profile radiator. 总 =0.045K / W.

[0071] Assuming that a high-power electronic device consumes 500W, refer to Figure 4 The heat dissipation system thermal resistance equivalent circuit shown in the figure, combined with the thermal resistance parameters provided in the device data sheet and the performance parameters of the thermal conductive interface material, can be used to calculate the junction temperature T of the device through the device junction temperature calculation formula. j =90°C, which is lower than the long-term stable operating temperature requirement. The heat sink is reasonably designed to complete the device junction temperature verification. The present invention solves the problem of being able to quickly and accurately evaluate the device junction temperature in the early stage of electronic heat dissipation design.

[0072] In addition, this embodiment is verified by means of CFD numerical simulation software. By structurally modeling the electronic device, thermal interface material, and heat sink in this embodiment, setting the same material properties, and inputting the same boundary conditions, the device simulation temperature of 88°C can be finally obtained, and the error of 90°C obtained by theoretical calculation is 2.3%. Therefore, the thermal resistance calculation method based on air-cooled profile heat sink proposed in the present invention is accurate and feasible.

[0073] Utilizing the technical solution of the present invention, or those skilled in the art designing a similar technical solution inspired by the technical solution of the present invention to achieve the above-mentioned technical effects, all of which should fall within the scope of protection required by the present invention.

Claims

1. A method for calculating the thermal resistance of an air-cooled profile radiator, characterized in that: The following steps are involved: Step 1, establishing a thermal resistance equivalent circuit of an air-cooled profile heat sink, wherein the air-cooled profile heat sink comprises a substrate and a plurality of fins fixed on the substrate; The substrate corresponds to the substrate conduction thermal resistance in the equivalent circuit, each of the fins corresponds to a branch in the equivalent circuit, and each branch includes a fin conduction thermal resistance and a fin convection thermal resistance connected in series; Step 2: Classify the conductive thermal resistance of the substrate and the conductive thermal resistance of the fin as conductive thermal resistance, and classify the convection thermal resistance of the fin as convection thermal resistance. Calculate the conductive thermal resistance and convection thermal resistance respectively, and finally obtain the total thermal resistance of the air-cooled profile radiator.

2. The thermal resistance calculation method according to claim 1, characterized in that: Each of the fins is independent of each other, has the same thickness, and is arranged on the base plate at equal intervals.

3. The thermal resistance calculation method according to claim 2, characterized in that: Step 1: According to the heat transfer path, the branches in the equivalent circuit corresponding to each fin are connected in parallel to form a fin part; then the substrate conduction thermal resistance is connected in series with the fin part to form a thermal resistance equivalent circuit of a complete air-cooled profile heat sink.

4. The thermal resistance calculation method according to claim 3, characterized in that: The thermal resistance in the thermal resistance equivalent circuit described in step 2 is calculated. First, the conduction thermal resistance θ1 and the convection thermal resistance θ2 are calculated respectively, and finally the total thermal resistance θ of the air-cooled profile heat sink is obtained. 总 , the formula is: i 总 =θ1+θ2.

5. The thermal resistance calculation method according to claim 4, characterized in that: The fin conduction thermal resistance and the substrate conduction thermal resistance are taken as the conduction thermal resistance θ1, and the calculation formula is: Among them, λ is the thermal conductivity of the heat sink material, x1 is the width of the heat sink, x2 is the length of the heat sink, x3 is the total height of the heat sink, x6 is the thickness of the heat sink substrate, δ is the thickness of the heat sink fins, and G is the number of heat sink air ducts.

6. The thermal resistance calculation method according to claim 5, characterized in that: The fin convection thermal resistance is taken as the convection thermal resistance θ2, and the calculation formula is: Where μ is the convection heat transfer coefficient in the convection thermal resistance, S t is the Standen number, k 空气 is the thermal conductivity of cooling air, P r is the Prandtl number, υ is the dynamic viscosity of the cooling air, ξ is the average velocity on the windward side, ρ is the fluid density, N u is the Nusselt number.

7. The thermal resistance calculation method according to claim 1, characterized in that: The calculated total thermal resistance of the air-cooled profile heat sink is substituted into the power electronic device cooling system to verify the device junction temperature; The heat dissipation process of the power electronic device heat dissipation system is as follows: (1) Heat flows from the die of the device to the housing and then dissipates into the environment through convection and radiation; (2) After the heat is transferred to the tube shell, the heat is conducted to the contacting heat sink substrate through the thermal conductive interface material and dissipated into the environment through convection and radiation.

8. The device junction temperature verification according to claim 7, characterized in that: An equivalent circuit of thermal resistance of the heat dissipation system of power electronic devices is established. The total thermal resistance of the heat dissipation system of power electronic devices can be expressed as: θ (c-a) is the device case-ambient thermal resistance, θ (c-s) is the device case-heat sink thermal resistance, θ (s-a) is the heat sink-ambient thermal resistance, θ (j-c) is the device junction-to-case thermal resistance, θ (s-a) That is, the total thermal resistance of the aforementioned air-cooled profile radiator θ 总 .

9. The device junction temperature verification according to claim 8, characterized in that: The junction temperature T of the verification device is calculated based on the total thermal resistance of the air-cooled profile heat sink and the thermal resistance equivalent circuit of the power electronic device heat dissipation system. j , the formula is: T j =T a +Q×θ (j-a) Where, T a is the temperature of the environment, Q is the power consumption of the device, θ (j-a) is the total thermal resistance of the device.

10. A device for calculating the thermal resistance of an air-cooled profile heat sink based on an equivalent circuit, characterized in that: include: An equivalent circuit part is used to establish a thermal resistance equivalent circuit of an air-cooled profile heat sink, wherein the air-cooled profile heat sink includes a base plate and a plurality of fins fixed on the base plate; The substrate corresponds to the substrate conduction thermal resistance in the equivalent circuit, each of the fins corresponds to a branch in the equivalent circuit, and each branch includes a fin conduction thermal resistance and a fin convection thermal resistance connected in series; The thermal resistance calculation part is used to classify the substrate conduction thermal resistance and the fin conduction thermal resistance as conduction thermal resistance, and classify the fin convection thermal resistance as convection thermal resistance, and calculate the conduction thermal resistance and convection thermal resistance respectively, and finally obtain the total thermal resistance of the air-cooled profile radiator.

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