Natural Convection Heat Sink
The most common reason to require natural convection heat sink is the elimination of fans/blowers from the system. Fans provide an additional failure point, thereby reducing the system’s reliability. Fans also increase the noise of the system, can introduce dust and contaminants, and require additional power. For any one of these reasons, a system designer may wish to exclude fans from the system and use natural convection heatsinks.
Since the air passing over the fins rises upwards as it absorbs heat from fins, the heat sink has to be positioned in a way so as to align the individual fins along the vertical. Also the gap between two fins has to be larger to allow for required air flow. Such constraints have to be taken into account when considering a natural convection (or passive cooled) heat sink for use.
A natural convection heat sink should be positioned so that:
(1). heat can be dissipated upward through the fins,
(2). no significant obstructions to impede air flow.
Any other heat-generating components near by the heat sink would increase the ambient air temperature.
Note:- Heat sink can be either heat pipe based or thermal siphon based.