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The Refrigeration Cycle

The Refrigeration Cycle

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 the following 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:

The compressor compresses the ammonia gas. You can think of the expansion valve as a small hole. On one side of the hole is highpressure ammonia liquid. That noise is the sound of highpressure liquid refrigerant flowing through the expansion valve.

Pure ammonia gas is highly toxic to people and would pose a threat if the refrigerator were to leak, so all home refrigerators dont use pure ammonia. You may have heard of refrigerants know as CFCs chlorofluorocarbons, originally developed by Du Pont in the 1930s as a nontoxic replacement for ammonia. CFC12 dichlorodifluoromethane has about the same boiling point as ammonia. However, CFC12 is not toxic to humans, so it is safe to use in your kitchen. Many large industrial refrigerators still use ammonia.

In the 1970s, it was discovered that the CFCs then in use are harmful to the ozone layer, so as of the 1990s, all new refrigerators and air conditioners use refrigerants that are less harmful to the ozone layer.