abstract
Aiming at the heat dissipation requirements of power electronic power devices, the heat exchange technology of air-cooled radiators for cooling them has been studied in depth. According to the structural characteristics and technical requirements of the air-cooled radiator for power device cooling, the thermal performance tests of the air-cooled radiator with different structures are carried out, and the simulation calculation software is used for auxiliary verification. Finally, under the same temperature rise test results, the characteristics of air-cooled radiators with different structures in terms of pressure loss, heat dissipation per unit volume, and temperature uniformity of power device mounting surfaces were compared. The research results provide a reference for the design of similar structural air-cooled radiators.
Keywords: radiator; air cooling; thermal performance; heat flux density
0 Preface
With the scientific development of power electronics science and technology, the application of power electronics power devices is more extensive. What determines the service life and performance of electronic devices is the performance of the device itself, and the operating temperature of the electronic device, that is, the heat transfer capacity of the radiator used to dissipate heat from the electronic device. At present, in power electronic equipment with a heat flux density less than 4 W/cm2, most of the air-cooled cooling systems are used. heat sink.
Zhang Liangjuan et al. used FloTHERM to conduct thermal simulation of air-cooled modules, and verified the reliability of the simulation results with experimental test results, and tested the heat dissipation performance of various cold plates at the same time.
Yang Jingshan selected three typical air-cooled radiators (that is, straight fin radiators, rectangular channel radiators filled with metal foam, and radial fin radiators) as research objects, and used CFD software to enhance the heat transfer capacity of the radiators. And optimize the comprehensive performance of flow and heat transfer.
Wang Changchang and others used the heat dissipation simulation software FLoTHERM to simulate and calculate the heat dissipation performance of the air-cooled radiator, combined with the experimental data for comparative analysis, and studied the influence of parameters such as cooling wind speed, tooth density and height on the heat dissipation performance of the air-cooled radiator.
Shao Qiang et al. briefly analyzed the reference air volume required for forced air cooling by taking a rectangular finned radiator as an example; based on the structural form of the radiator and the principles of fluid mechanics, the wind resistance estimation formula of the cooling air duct was derived; combined with a brief analysis of the P-Q characteristic curve of the fan, the actual working point and ventilation air volume of the fan can be quickly obtained.
Pan Shujie chose the air-cooled radiator for research, and briefly explained the steps of heat dissipation calculation, radiator selection, air-cooled heat dissipation calculation and fan selection in heat dissipation design, and completed the simple air-cooled radiator design. Using ICEPAK thermal simulation software, Liu Wei et al. conducted a comparative analysis of two weight reduction design methods for radiators (increasing fin spacing and reducing fin height). This paper introduces the structure and heat dissipation performance of profile, spade tooth and plate-fin air-cooled radiators respectively.
1 Air-cooled radiator structure
1.1 Commonly used air-cooled radiators
The common air-cooled radiator is formed by metal processing, and the cooling air flows through the radiator to dissipate the heat of the electronic device to the atmospheric environment. Among common metal materials, silver has the highest thermal conductivity of 420 W/m*K, but it is expensive;
The thermal conductivity of copper is 383 W/m· K, which is relatively close to the level of silver, but the processing technology is complicated, the cost is high and the weight is relatively heavy;
The thermal conductivity of 6063 aluminum alloy is 201 W/m· K. It is cheap, has good processing characteristics, easy surface treatment, and high cost performance.
Therefore, the material of the current mainstream air-cooled radiators generally uses this aluminum alloy. Figure 1 shows two common air-cooled heat sinks. Commonly used air-cooled radiator processing methods mainly include the following:
(1) Aluminum alloy drawing and forming, the heat transfer area per unit volume can reach about 300 m2/m3, and the cooling methods are natural cooling and forced ventilation cooling;
(2) The heat sink and the substrate are inlaid together, and the heat sink and the substrate can be connected by riveting, epoxy resin bonding, brazing welding, soldering and other processes. In addition, the material of the substrate can also be copper alloy. The heat transfer area per unit volume can reach about 500 m2/m3, and the cooling methods are natural cooling and forced ventilation cooling;
(3) Shovel tooth forming, this kind of radiator can eliminate the thermal resistance between the heat sink and the substrate, the distance between the heat sink can be less than 1.0 mm, and the heat transfer area per unit volume can reach about 2 500 m2/m3. The processing method is shown in Figure 2, and the cooling method is forced air cooling.
Fig. 1. Commonly used air-cooled heat sink
Fig. 2. Processing method of shovel tooth air-cooled radiator
1.2 Plate-fin air-cooled radiator
The plate-fin air-cooled radiator is a kind of air-cooled radiator processed by brazing of multiple parts. It is mainly composed of three parts such as heat sink, rib plate and base plate. Its structure is shown in Figure 3. The cooling fins can adopt flat fins, corrugated fins, staggered fins and other structures. Considering the welding process of the ribs, 3 series aluminum materials are selected for the ribs, heat sinks and bases to ensure the weldability of the plate-fin air-cooled radiator. The heat transfer area per unit volume of the plate-fin air-cooled radiator can reach about 650 m2/m3, and the cooling methods are natural cooling and forced ventilation cooling.
Fig. 3. Plate-fin air-cooled radiator
2 Thermal performance of various air-cooled radiatorsv
2.1 Commonly used profile air-cooled radiators
2.1.1 Natural heat dissipation
Commonly used air-cooled radiators mainly cool electronic devices by natural cooling, and their heat dissipation performance mainly depends on the thickness of the heat dissipation fins, the pitch of the fins, the height of the fins, and the length of the heat dissipation fins along the direction of cooling air flow. For natural heat dissipation, the larger the effective heat dissipation area, the better. The most direct way is to reduce the fin spacing and increase the number of fins, but the gap between the fins is small enough to affect the boundary layer of natural convection. Once the boundary layers of the adjacent fin walls converge, the air velocity between the fins will drop sharply, and the heat dissipation effect will also drop sharply. Through the simulation calculation and test detection of the thermal performance of the air-cooled radiator, when the heat dissipation fin length is 100 mm and the heat flux density is 0.1 W/cm2, the heat dissipation effect of different fin spacing is shown in Figure 4. The best film distance is about 8.0 mm. If the length of the cooling fins increases, the optimal fin spacing will become larger.
Fig.4. Relationship between substrate temperature and fin spacing
2.1.2 Forced convection cooling
The structural parameters of the corrugated air-cooled radiator are fin height 98 mm, fin length 400 mm, fin thickness 4 mm, fin spacing 4 mm, and cooling air head-on velocity 8 m/s. A corrugated air-cooled radiator with a heat flux density of 2.38 W/cm2 was subjected to a temperature rise test. The test results show that the temperature rise of the radiator is 45 K, the pressure loss of the cooling air is 110 Pa, and the heat dissipation per unit volume is 245 kW/m3. In addition, the uniformity of the power component mounting surface is poor, and its temperature difference reaches about 10 °C. At present, to solve this problem, copper heat pipes are usually buried on the installation surface of the air-cooled radiator, so that the temperature uniformity of the power component installation surface can be significantly improved in the direction of the heat pipe laying, and the effect is not obvious in the vertical direction. If vapor chamber technology is used in the substrate, the overall temperature uniformity of the power component mounting surface can be controlled within 3 °C, and the temperature rise of the heat sink can also be reduced to a certain extent. This test piece can be reduced by about 3 °C.
Using thermal simulation calculation software, under the same external conditions, the simulation calculation of straight tooth and corrugated cooling fins is carried out, and the results are shown in Figure 5. The temperature of the mounting surface of the power device with straight-tooth cooling fins is 153.5 °C, and that of corrugated cooling fins is 133.5 °C. Therefore, the cooling capacity of the corrugated air-cooled radiator is better than that of the straight-toothed air-cooled radiator, but the temperature uniformity of the fin bodies of the two is relatively poor, which has a greater impact on the cooling performance of the radiator.
Fig.5. Temperature field of straight and corrugated fins
2.2 Plate-fin air-cooled radiator
The structural parameters of the plate-fin air-cooled radiator are as follows: the height of the ventilation part is 100 mm, the length of the fins is 240 mm, the spacing between the fins is 4 mm, the head-on flow velocity of the cooling air is 8 m/s, and the heat flux density is 4.81 W/cm2. The temperature rise is 45°C, the cooling air pressure loss is 460 Pa, and the heat dissipation per unit volume is 374 kW/m3. Compared with the corrugated air-cooled radiator, the heat dissipation capacity per unit volume is increased by 52.7%, but the air pressure loss is also larger.
2.3 Shovel tooth air-cooled radiator
In order to understand the thermal performance of the aluminum shovel-tooth radiator, the fin height is 15 mm, the fin length is 150 mm, the fin thickness is 1 mm, the fin spacing is 1 mm, and the cooling air head-on velocity is 5.4 m/s. A shovel-tooth air-cooled radiator with a heat flux density of 2.7 W/cm2 was subjected to a temperature rise test. The test results show that the temperature of the radiator power element mounting surface is 74.2°C, the temperature rise of the radiator is 44.8K, the cooling air pressure loss is 460 Pa, and the heat dissipation per unit volume reaches 4570 kW/m3.
3 Conclusion
Through the above test results, the following conclusions can be drawn.
(1) The cooling capacity of the air-cooled radiator is sorted by high and low: shovel-tooth air-cooled radiator, plate-fin air-cooled radiator, corrugated air-cooled radiator, and straight-toothed air-cooled radiator.
(2) The temperature difference between the fins in the corrugated air-cooled radiator and the straight-toothed air-cooled radiator is relatively large, which has a great impact on the cooling capacity of the radiator.
(3) The natural air-cooled radiator has the best fin spacing, which can be obtained by experiment or theoretical calculation.
(4) Due to the strong cooling capacity of the shovel-tooth air-cooled radiator, it can be used in electronic equipment with high local heat flux density.
Source: Mechanical and Electrical Engineering Technology Volume 50 Issue 06
Authors: Sun Yuanbang, Li Feng, Wei Zhiyu, Kong Lijun, Wang Bo, CRRC Dalian Locomotive Research Institute Co., Ltd.
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Post time: Mar-27-2023