Natural Convection Heat Seat

Natural convection heat sink used for low-power applications, its thermal resistance, Q , 2.0 oC /watt for dimensions of 5 "x3 "x l"
A natural convection heat sink should be positioned so that:

Heat can be dissipate upward through the fins.

No significant obstructions to impede air flow.

Any other heat-generating components near by the heat sink would increase the ambient air temperature.
A black anodized finish on aluminum heat sink can lower the Q by 4 %.

The Q is proportional to inverse of total surface area. It is desirable to use a heat sink as large as practical without blocking the air flow. However, too reduce the Q by one-half, the extruded heat sink volume has to be increased by a factor of four.  The structure member of an enclosure or mounting frame is often used to remove heat from a device. This technique is effective for small amount of heat.