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At first glance, the modern refrigerator seems like a logical paradox. Electricity, which is normally associated with heat, is used to make warm spaces cold. How is this possible?
To begin to understand how a fridge works, think back to the last time you got relief from warm weather by getting wet, or felt too cold after getting out of the shower. This is because the water is converting to gaseous form and expanding, and all gases cool upon expansion. -
Though the cooling power of water can be enough to chill your skin, it's not powerful enough for a fridge or freezer. Instead, refrigerators use a chemical called tetrafluoroethane. This gas has a much lower boiling and evaporating temperature than water, low enough that it will boil at room temperature. When it does so, it creates very cold temperatures.
However, in order for a fridge to work, the tetrafluoroethane has to be repeatedly converted back into a liquid, then evaporated again for continued cooling. In order to accomplish this, the chemical is circulate through sealed tubes and electronic pumps. The pumps pressurize the gas, forcing the molecules back together an into a liquid state. This liquid is then released into a lower-pressure area, and the process begins again.
The pipes are positioned in the fridge and freezer so that the tetrafluoroethane is inside the freezer/fridge while it is being converted to gas (and thus, pulling heat away from the surrounding air), but outside the freezer/fridge while it is being converted back to liquid (and thus, making its surroundings warmer). There is also a higher density of piping in the freezer area relative to the freezer's size, making this space colder overall. -
The other important part of a refrigerator's functioning is temperature regulation. This is maintained through insulation, thermocoupling and air sealing. The fridge's insulation is simply a matter of making the fridge walls and door out of materials that are poor at conducting heat, keeping the cold temperatures of the fridge from equalizing with the room temperature outside it. The door of the fridge is then sealed with magnets inside rubber for the best air-tight seal, keeping cold air from escaping this way.
The thermocouple on a fridge works in the same way that the thermostat in a home does. A thermometer reads the temperature and starts and stops the gas pumping process as needed to keep the fridge and freezer at consistent temperatures.
