Heat spreader

A heat spreader is most often simply a copper plate, having high thermal conductivity. Functionally, it is a primary heat exchanger that moves heat between a heat source and a secondary heat exchanger. The secondary heat exchanger is always larger in cross sectional area, surface area and volume. By definition, the heat is "spread out", such that the secondary heat exchanger has a larger cross sectional area contacting the heat spreader than the heat source. The heat flow is the same in both heat exchangers, but the heat flux density is less in the secondary, so it can be made of a less expensive material such as aluminum, and is a better match to an air heat exchanger, since the low heat transfer coefficient for air convection implies a low heat flux. A heat spreader is generally used if an only if the heat source has a rather high heat-flux density, (high heat flow per unit area), and for whatever reason, can not be conducted away effectively by the secondary heat exchanger. For instance this may be because it is an air-cooled type, instead of liquid-cooled, since the liquid type has as a higher heat transfer coefficient, and this is often sufficient to avoid the need for a heat spreader.

The use of a heat spreader is an important part of an economically optimal design for transferring high from high heat flux to low heat flux.Examples:

* A copper-clad bottom on a stove-top cooking container made of steel or stainless steel
* Air-cooling a CPU computer microprocessor
* Air-cooling a photovoltaic cell in a concentrated photovoltaics system