Power devices in the use of the most important thing is how to produce effective dissemination of the heat out in order to obtain high reliability.
Most common method of heat dissipation device is installed in the radiator, the heat radiation plate to heat the air to go around, and through natural convection to distribute heat.
Generally speaking, from the air around the radiator to the heat flux (P) can be said that under the cases.
P = hA η △ T
Where
h overall heat transfer for the radiator conductivity (W/cm2 ℃), A the surface area for heat sink (cm2), η the efficiency for the radiator, △ T the maximum temperature for the radiator and the ambient temperature difference (℃).
Where the h is to determine the radiation and convection, η is the formation of the radiator to decide.
In short, the greater the surface area of the radiator, and the greater the difference between the ambient temperature, the heat radiation plate heat more effectively.
(1) Thermal radiation
Expressed in the following approximation of radiation heat
hr = 2.3 × 10-11 × ε (△ T / 2 +237) 3 (W/cm2 ℃)
Where ε is the surface emissivity, with the radiator surface conditions. Smooth grinding surface of the product ε = 0.05 ~ 0.1 means that the rate of poor radiation. However, the radiator surface to paint, by the oxidation can ε = 1.
(2) heat convection
Power devices installed on the device when the framework, the use of convection heat more effectively than radiation cooling. In an atmospheric pressure of air, the use of convection heat sink similar to the conductivity type from that under the.
hc = 4.3 × 10-4 × (△ T / H) 1 / 4 (W/cm2 ℃)
Where, H is the vertical radiator is more effective than the horizontal direction.
(3) radiator efficiency η
If the radiator with a thin material, the farther away from the heat source, the lower surface temperature, the worse the thermal effect. The above formula is assumed that the temperature distribution are in fact the edge of the cooling plate the lower parts of the surface temperature.
This temperature by the radiator itself, the radiator is determined by the efficiency coefficient, which indicates that the actual cooling plate and heat transfer equipment is installed as part of the maximum temperature when the uniform distribution of the ratio of heat.
η used mainly by the heat sink size and thickness of the material to the decision. Generally speaking, high thermal conductivity material such as aluminum (2.12W/cm2 ℃) and copper (3.85W/cm2 ℃) and steel (0.46W/cm2 ℃) is quite good at all.
In addition, the thickness of the radiator to thick for some good, and with the length of the radiator is proportional to the square of the best. According to the above, apply to the radiator power devices should meet the following requirements:
(Ⅰ) has more surface area, as far as possible
(Ⅱ) anodizing the surface of the radiator, black handle
(Ⅲ) radiator configuration should be easy flow of air to take a long vertical edge is better
(Ⅳ) use a good thermal conductivity of aluminum and copper as a heat sink material
(Ⅴ) more for a good radiator thickness, thickness and length proportional to the square