Design of finned heat sinks for household appliances

The use of passive heat sinks is still the means of cooling preferred in the industrial practice, owing to its lack of moving parts and noiseless operation, and it is employed whenever possible in the case of household appliances, which are required to have long operative lives without maintenance. The power densities of IGBTs usually employed in control boards of e.g. washing machines (around 5 Wcm-2) falls normally in the range which free-convection heat sinks can handle under normal design conditions. This, however, is seldom the case, as the heat sink is often encased in a plastic hull to comply with safety regulations, which prevents cool air from washing over the fins. In the present study, an extant heat sink for washing machines PCBs is experimentally analysed in terms of thermal resistance both when placed unconstrained in the air and encased in its service hull, and a new heat sink is designed. A prototype of the new heat sink is tested and it is proven that, although the thermal resistance of the new model is higher when considering direct convection to ambient air, its performance is consistently superior in real operating conditions (i.e. when encased).