Establish the thermal budget allowed and external conditions surrounding the heat sink

Classify the airflow as either:
1. Natural
2. Low-flow mixed or
3. High-flow forced convection

Determine the required volume of the heat sink by dividing the volumetric thermal resistance by the required thermal resistance.

Optimum fin spacing is strongly related to two parameters:
1. Flow velocity and 2. Fin length in the direction of the flow