Thermal design of power electronics enclosure

- Sep 22, 2018 -

The casing of an electronic device is an important heat transfer link that receives heat from the inside of the device and dissipates it into the surrounding environment. The design of the enclosure is particularly important in the use of natural cooling and some closed electronics. Tests have shown that the heat dissipation effects of different structural forms and coated casings are quite different. The thermal design of the enclosure should pay attention to the following issues:

(1) Increasing the blackness of the inner and outer surfaces of the casing, and opening the ventilation holes (louvers) to reduce the temperature of the internal components of the electronic device;

(2) The heat dissipation effect of the inner and outer surfaces of the casing is better than the natural convection effect of the two measuring louvers. When the inner and outer surfaces are high black, the internal average temperature is lowered by about 20 °C, and when the louvers are opened on both sides (the inner and outer surfaces are bright), Its temperature is only reduced by about 8 °C;

(3) The effect of high blackness on the inner and outer surfaces of the casing is better than that of single-sided high blackness, especially increasing the blackness of the outer surface is an effective way to reduce the surface temperature of the casing;

(4) On the basis of the blackening of the inner and outer surfaces of the casing, reasonable improvement of the ventilation structure (such as the top plate, the bottom plate, the left and right sides of the plate opening vents, etc.) to enhance the air convection can significantly reduce the internal temperature environment of the equipment;

(5) The position of the vent should pay attention to the short-circuit of the airflow and affect the heat dissipation effect. The inlet and outlet of the ventilating hole should be opened at the two places with the largest temperature difference, the air inlet should be low, and the air outlet should be high. The tuyere should be close to the heating element, and the cold air directly acts as a cooling element;

(6) In the natural heat dissipation, the calculation of the ventilation hole area is very important. Figure 3 shows the relationship between the ventilation hole area and the heat dissipation amount. It can be used as a basis for designing the ventilation port, and can also be dissipated by the ventilation port according to the equipment requirements. The amount of the vent hole is calculated by the following formula.

S0=Q/7.4×10-5·H · △t1. 5 (4)

In the formula:

S0——the total area of the air inlet or outlet (cm2);

Q——The heat of the natural heat dissipation of the ventilating hole (the total power consumption of the device minus the heat dissipated by the natural convection and radiation of the wall) [W];

H——the height difference between the inlet and outlet vents [cm];

Δt == t2 - t1 - the difference between the internal air temperature t2 of the device and the outside air temperature t1 [0C].

(7) There are many structural forms of vents, such as metal mesh, blinds, etc., according to the needs of heat dissipation, it is necessary to make the structure simple, not easy to fall ash, but also to meet the strength, electromagnetic compatibility requirements and elegant appearance.

(8) The heat dissipation of the sealed casing mainly depends on convection and radiation, which is determined by the surface area and blackness of the casing. It can increase the conduction heat resistance of the heating device and the casing, and enhance the internal air convection (such as the fan) to increase the surface area of the casing ( Set the heat sink ribs and the blackness of the case surface to reduce the internal ambient temperature.

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