The rate of heat transfer from a surface at a temperature $T_s$ to the surrounding medium at $T_∞$ is given by Newton’s law of cooling as:

where $A_s$ is the heat transfer surface area and $h$ is the convection heat transfer coefficient.

When the temperatures $T_s$ and $T_∞$ are fixed by design considerations, as is often the case, there are two ways to increase the rate of heat transfer:

• To increase the convection heat transfer coefficient $h$
• To increase the surface area $A_s$

Increasing $h$ may require the installation of a pump or fan, or replacing the existing one with a larger one, but this approach may or may not be practical. Besides, it may not be adequate. The alternative is to increase the surface area by attaching to the surface extended surfaces called fins made of highly conductive materials such as aluminum.