Understanding Forced-Air Cooling

December 11, 2009

Forced air cooling can make a significant difference to thermal management, improving the heatsink-to-air thermal resistance by as much as an order of magnitude with the right combination of hardware. Making the right choices, however, means interpreting and matching the convection data for both the heatsink and the fan.

The first step is to calculate the maximum heatsink-to-air thermal resistance for the system: next, the operating airflow through the heatsink is determined. Airflow from the fan, expressed in cubic feet per minute (CFM), is plotted against the curve for pressure drop, shown in inches of water. The intersection between the airflow curve for the heatsink and the pressure drop curve for the fan determines the operating airflow through the heatsink (see figure 1)

Only the airflow through the cross-sectional area between the fins of the heatsink should be used to calculate the operating airflow. However, if the estimated thermal resistance is close to minimum value, then a larger fan should be specified.

Additional tips and techniques for using forced-air cooling with Vicor converters can be found in the below links:

Thermal and Module Mounting Considerations
Thermal Performance Information
Thermal Considerations: Assuring Performance OF Vicor’s Maxi, Mini, Micro Series High-Density DC-DC Converter Modules
Thermal Calculations

Figure 1 Airflow vs. resistance

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