Types of Heat Sinks
There are numerous choices from zipper pack fins to extruded fin stacks, each with their own cost and performance characteristics. While the heat sink choice can markedly affect heat dissipation performance, the biggest performance boost for any type of heat exchanger comes with forced convection.
Estimating Required Heat Sink Volume
By using the simple equation below, we can estimate the overall volume of the heat sink required to cool a heat source.
V= (Q*Rv)/Delta T
Volume is the outer dimensions of the heat sink in cubic centimeters. Q is total power in watts and Rv is the volumetric thermal resistance (cm3-C/W). The table below provides some well established guidelines under different air flow rates. The first thing to notice is the enormous positive affect forced air has on thermal performance. Even with a gentle air flow, volumetric thermal resistance of the heat sink is reduced by two-thirds.
For example, Let’s assume an application with four-200W heat sources (total 800 watts) that need to be cooled with a single condenser. Each heat source has a maximum cast temperature (Tcase) of 80 degrees Celsius while the ambient operating temperature is 40 degrees Celsius. This means that the DeltaT is 40 degrees C (80 – 40). Further, a moderate airflow of 2.5 meters/second is allocated.
Substituting these figures into the equation above, it can be estimated that the total volume of the sink must be 2,300 cubic centimeters. Potential drawbacks of this method are that it does not account for variables to base thickness or material nor the specific LxWxH dimensions of the heat sink – only overall volume. However, when we compare this figure to actual dimensions of the final part, which turned out to be 1,966 cubic centimeters, we see only a 15% difference of estimated to actual dimensions.