Soldiers, firefighters and others who risk exposure to hazardous materials must wear hot, heavy protective clothing for prolonged periods. Research at the Department of Energy's Pacific Northwest National Laboratory (PNL) in Richland, Wash., is leading to a small, lightweight heat pump that could be worn inside such garments to provide hours of cooling relief.

Heat pumps use the condensation-evaporation cycle of a working fluid to move heat from one place to another. The PNL device mechanically constrains the fluid to microchannels in a film only about 100 micrometers thick-10 times thinner than in conventional heat pumps. The thin film maximizes the surface-to-volume ratio and hence the efficiency of heat transfer between the fluid and the environment, says PNL researcher Michele Friedrich. Based on tests of the individual components, Friedrich believes it will be possible to build a prototype of a portable heat pump weighing only about 5 kilograms.