subject: The Science And Logistics Behind Refrigerators [print this page] There are two things you need know to understand how refrigerators work:
1)A gas cools on expansion.
2)The second law of thermodynamics. If you have to things that are different temperatures that touch or are near one another, the hotter surface cools down and the colder surface warms up.
Older fridges contain a long thin tube that loops back and forth. This tube is connected to a pump that is powered by an electric motor. Within the tube there is a gas called Freon, chemically known as Chlorofluorocarbon or CFC. As we all know, CFC was found to be harmful to the ozone layer; therefore in new fridges a different gas is used in a slightly different process.
The CFC starts out as a liquid. The pump pushes it through a series of coils in the freezer area. It is here that the chemical turns to vapour. When this happens it absorbs some of the heat that is in the freezer compartment. As it does so the coil gets colder and the freezer begins to cool. There are fewer coils in the regular part of your freezer, which is a larger space; therefore less heat is absorbed by the CFC vapour.
The pump then sucks in the CFC as vapour and forces it through the thinner pipes on the outside of the refrigerator. Because the pump is compressing the CFC gas and turning it back into a liquid, heat radiates into the surrounding air. This is why it is always warm behind your fridge. Once the CFC has passed through the outer coils it is ready to start the whole process again.
Modern fridges dont use CFC; this is because of its harmful effect on the ozone, so HFC is used as an alternative. The motor and compressor in the fridge squeeze the HFC, and once compressed, the heated gas passes through the coils on the back of the refrigerator and the warm gas loses its heat to the surrounding air. As it cools the gas turns to liquid, because it is under high pressure. The liquid flows through what is known as an expansion valve this is a small hole that the liquid has to squeeze through. Between the valve and the compressor there is a low-pressure area because the compressor is pulling the ammonia gas out of that side.
When the HFC hits the low-pressure area it boils and thus changes into a gas. The coils then go through the freezer where the colder liquid pulls the heat out of the compartments. This makes the inside of the freezer cold. The compressor then sucks up the cold gas to start the whole process again.
