The refrigerator in your kitchen uses a cycle that is similar to the one described in the previous section. But in your refrigerator, the cycle is continuous. In thefollowing example, we will assume that the refrigerant being used is pure ammonia, which boils at -27 degrees F. This is what happens to keep the refrigerator cool:
1. The compressor compresses the ammonia gas. The compressed gas heats up as it is pressurized (orange).
2. The coils on the back of therefrigerator let the hot ammonia gas dissipate its heat. The ammonia gas condenses into ammonia liquid (dark blue) at high pressure.
3. The high-pressure ammonia liquid flows through the expansionvalve.
You can think of the expansion valve as a small hole. On one side of the hole is high-pressure ammonia liquid. On the other side of the hole is a low-pressure area (because thecompressor is sucking gas out of that side).
4. The liquid ammonia immediately boils and vaporizes (light blue), its temperature dropping to -27 F. This makes the inside of the refrigerator cold.
5.The cold ammonia gas is sucked up by the compressor, and the cycle repeats.
By the way, if you have ever turned your car off on a hot summer day when you have had the air conditioner running, you mayhave heard a hissing noise under the hood. That noise is the sound of high-pressure liquid refrigerant flowing through the expansion valve.
Pure ammonia gas is highly toxic to people and would pose athreat if the refrigerator were to leak, so all home refrigerators don't use pure ammonia. You may have heard of refrigerants know as CFCs (chlorofluorocarbons), originally developed by Du Pont inthe 1930s as a non-toxic replacement for ammonia. CFC-12 (dichlorodifluoromethane) has about the same boiling point as ammonia. However, CFC-12 is not toxic to humans, so it is safe to use in your...