The Refrigeration Cycle

Refrigerators stay cool through a continual process of heat transference known as the refrigeration cycle. This process requires a refrigerant fluid that can change from a gas to a liquid and back again. Substances such as ammonia, chlorofluorocarbons (CFCs), and freon have been used as refrigerants in the past, but modern refrigerators use compounds that are environmentally safer. These refrigerants have names like R-134a and R-22.

How refrigeration works

Refrigeration is a cycle, so the same steps are repeated over and over again, but we'll begin with compression. The compressor is a refrigerator part that compresses the refrigerant. This pressure causes the refrigerant to become a hot vapor.

The refrigerant then leaves the compressor and enters the condenser. A refrigerator's condenser allows the refrigerant to transform from a gas to a liquid as pressure eases. Heat exchanging pipes known as condenser coils pick up the heat given off during this transformation and dissipate it into the outside air, which is why the condenser coils are located outside the back of the refrigerator.

The next stage of the refrigeration cycle involves the expansion valve. Even though the refrigerant has condensed and given off heat, it's still under increased pressure from its time in the compressor. The expansion valve is essentially a small hole. As the refrigerant passes through the expansion valve, it enters a low-pressure area. This sudden decrease in pressure causes the refrigerant to vaporize, i.e. evaporate. The process is similar to the pressurized contents of an aerosol can escaping through the spray hole to dissipate into the air.

With pressure reduced, the refrigerant suddenly becomes very cold. At this stage in the refrigeration cycle, the refrigerant has entered the heat-exchanging evaporator, sometimes referred to as the indoor coil or evaporator coil. It's there that the refrigerant absorbs heat from the refrigerator's food compartments.

To understand why this heat transference occurs, it's important to know the second law of thermodynamics, which states that heat travels from warmer areas to cooler areas. As the refrigerant moves through the coils, the compartments cool and the refrigerant gets warmer. To assist with this process and provide even cooling, refrigerators use a blower or fan to move the inside air around the coils.

We're now back to our first stage of the refrigeration cycle. After the refrigerant has passed through the coils, it enters the compressor, and the process starts all over again.