Heat Sink Basics
A heat sink is a device that spreads heat from a small heat source to extended surfaces and thus improves the heat dissipation (convection) to the surroundings (air, water, etc.). The performance of a heat sink can be improved by increasing the thermal conductivity of the material, the surface area, or the heat transfer coefficient.
The most common heat sink is the plate fin heat sink, which has rectangular fins and is the best choice if there is external airflow in the direction of the fins. Round pin heat sinks have omni-directional properties and are the best choice when the airflow is very low or its direction is unknown (or can change). Elliptical pin heat sinks have small pressure drop than plate fin heat sinks and allow the air to approach from a direction that is not perfectly parallel. Although not fully omni-directional, it performs better than the round pin heat sinks when the airflow speed is high.
For a given space (width, length and height) and environmental parameters (ambient temperature, airflow speed, orientation, etc.), an optimized heat sink can be found that provides the lowest thermal resistance (and the best heat dissipation). Due to the availability of materials, limitation of manufacturing means, and economic considerations, the actual “optimized” heat sink may deviate slightly from the mathematically optimized heat sink. But knowing (and calculating) the mathematically optimized heat sink provides the great way to guide the heat sink design.