Keeping it Cool

Our refrigerator broke the other day. My roommate and I had not realized how great we had it until the refrigerator was gone. With this in mind and our current lessons about heat transfer, I decided to do my last Physics news post on refrigerators!

Refrigerators are particularly interesting because they seem to move heat in the reverse direction. In general, heat cannot move from cold body to a hot body. Yet refrigerators are 'pumping' heat out of a system. This does not defy the second law of thermodynamics, because refrigerators and other cooling systems like air conditioners use an external power source to make this possible.

Refrigerators use a refrigerant (like Freon 12 or ammonia) contained in an evaporator, a chamber into which heat from the refrigerated compartment flows. The gas in the evaporator liquifies easily at a low pressure in the presence of heat. This gas travels along a pipe to the compressor, which pumps it at a high pressure into a condenser. The long squiggly pipes on the back of most refrigerators is the condenser. In this chamber, pressure turns the gas into liquid.

While traveling through the condenser, the gas heats up. This heat is released from the back of the refrigerator, which explains why the back of the refrigerator is always the warm to the touch.