With the increasing integration, complexity, and intelligence of power equipment, the number of components is constantly increasing, and the power density of components is also significantly improving.
When the heat flux density of the radiator exceeds 0.1W/㎡, ordinary air cooling can no longer meet the heat dissipation requirement, and most solutions use liquid cooling for heat dissipation. Compared with traditional self cooling and air cooling , liquid cooling has the advantages of strong heat carrying capacity, sealing and dust prevention, and flexible use, and is widely used in the heat dissipation of power products.
The working principle of liquid cooling is to remove the heat emitted by high-power electronic components arranged on the surface of the liquid cooled plate by the coolant flowing through the flow channels processed inside the plate, thereby achieving the heat dissipation of the entire equipment. As the core component of the liquid cooling system, the heat dissipation performance of the liquid cooling plate directly determines the overall performance of the cooling system.
This article tested and analyzed three common liquid cooled plate flow channels through experiments, and compared the heat dissipation capabilities of finned liquid cooled plates, cylindrical liquid cooled plates and copper tube embedded liquid cooled plates.
1. Design model and related parameters of liquid cooling plate
This article designs three types of liquid cooling plates, they are finned fins liquid cooling plate, cylindrical fins liquid cooling plate, and embedded copper tube liquid cooling plate. The external dimensions of the liquid cooled cold plate are 300mm × 227mm × 22mm, and the material is 6063 aluminum alloy.
According to engineering experience, the thickness of finned fins is generally 1.5~3mm. Considering that machining is too thin is difficult, and vacuum brazing requires a certain fins thickness to connect with the rear cover plate, so the fins thickness of 2mm is chosen. To avoid excessive flow resistance, the net fins spacing is set to 3mm (generally, a tooth thickness tooth spacing of 1:1 is considered the limit of fins density).
According to engineering experience, the fins height is generally 5~10mm. Considering that the shorter the fins, the smaller the flow cross-section, the higher the flow velocity, and the greater the flow resistance, within a reasonable design range, the fins height is set to 8mm.
The diameter of the cylinder is generally 3~5mm based on engineering experience. Considering that the narrowest part of the channel width is only 20mm, in order to ensure that there are two cylinders in the width direction of the narrow channel, the cylinder diameter is designed to be 3mm. The minimum clear distance between cylinders is set to 3mm, and the column height is also set to 8mm.
The embedded copper tube liquid cooling plate adopts a copper tube with an outer diameter of 10mm and a wall thickness of 1mm embedded into the liquid cooling plate and then flattened and fixed. Epoxy resin adhesive is filled between the copper tube and the liquid cooling plate to reduce contact thermal resistance.
Dimensions of finned and cylindrical liquid cooling plate structures
Dimensions of embedded copper tube liquid cooling plate structures
Internal flow channel of finned liquid cooling plate
Internal flow channel of cylindrical liquid cooling plate
The thickness of the liquid cooled cold plate substrate is uniformly designed to be 10mm, which can fully reduce the diffusion thermal resistance and avoid screws from breaking through the water channel.
The heat source distribution of the liquid cooled plate is shown in below. The liquid cooled cooling plate consists of 5 modules that generate heat and are evenly arranged on the flow channel. There are two IGBT modules above the liquid cooled plate, each with a heat consumption of 600W; There are three diode modules below, each with a heat consumption of 200W and a total heat consumption of 1800W. To improve the contact thermal resistance, thermal grease is filled between the heating module and the liquid cold plate.
measurement system
The main measurement system of this test bench is shown in the following figure, including flow measurement, pressure measurement, and temperature measurement.
The layout of temperature measurement points is shown in the figure. A total of 8 temperature measurement points were arranged for this experiment. Among them, T1 to T6 are arranged on the liquid cooling plate, and the other two points are used to measure the inlet and outlet fluid temperatures, which are respectively arranged on the three-way valves of the inlet and outlet pressure gauges. The reason why the temperature points for measuring the inflow and outflow of water are arranged here, separated from the liquid cooling plate, is mainly to avoid being affected by the heating system on the liquid cooling plate.
testing and data analysis
This tested three types of liquid cooled plates and obtained test data as shown in Tables 1, 2, and 3.
Through analysis of test data, it was found that under the same flow rate and inlet temperature conditions, the temperature at each temperature measurement point of the finned liquid cooling plate is the lowest, followed by the cylindrical liquid cooling plate, and the embedded copper tube liquid cooling plate has the highest temperature.
The average temperature of cylindrical liquid cooling plate is 2.5 ℃ higher than that of finned liquid cooling plate, the average temperature of copper tube embedded liquid cooling plate is 8.5 ℃ higher than that of finned liquid cooling plate, and the average temperature of copper tube embedded liquid cooling plate is 6 ℃ higher than that of cylindrical liquid cooling plate.
Table 1 Test data of finned liquid cooling plate
Table 2 Test data of cylindrical liquid cooling plate
Table 3 Test data of embedded copper tube liquid cooling plate
conclusion
This article tested three common liquid cooled plates, which are finned liquid cooled plates, cylindrical liquid cooled plates, and embedded copper tube liquid cooled plates, through experiments.
After analyzing the test data, it was found that under the same operating conditions, the finned liquid cooled plate had the lowest test temperature and the best heat dissipation effect; The cylindrical liquid cooling plate is second, with an average temperature 2.5 ℃ higher than that of the finned liquid cooling plate; The copper tube type liquid cooling plate has the highest test temperature and the worst heat dissipation effect, with an average temperature 8.5 ℃ higher than that of the fin type liquid cooling plate.
Although the heat dissipation effect of the embedded tube liquid cooling plate is poor, its processing cost is the lowest among these three types of liquid cooling plates. Under the premise of thermal design allowance, using the copper tube embedded liquid cooling plate can reduce costs.
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