Refrigerators and freezers take heat from inside the appliance and transfer it to the outside. To do this, they repeatedly evaporate and condense a substance called a refrigerant.
The heat needed to make the refrigerant evaporate (or change from liquid to gas) is taken from inside the compartments. Then, when the refrigerant is condensed (or changed from gas to liquid), it gives out heat, which is released outside the appliance.
A Journey Through Your Fridge:
An electric motor drives the compressor, which pressurises the refrigerant gas and pumps it around the system. Compressing the gas causes energy to be released in the form of heat.
The gas then passes through small radiators on the back of the appliance called the condenser coils, which give off heat into the room. Cooling the pressurised gas condenses it into a liquid.
The cooled liquid refrigerant then passes through a dryer to remove particles of dirt. Immediately after, it enters a very narrow capillary tube under pressure. The liquid flows to the evaporator coils where it passes through an expansion chamber, causing the pressure, and therefore the boiling point, to immediately drop. The liquid expands rapidly and boils, turning into a cold gas.
Walls and compartments
The cold gas passes through the evaporator coils, or plate, which pass through the walls of the freezer and fridge. Heat is conducted through the interior walls from the compartments into the cold gas, warming it.
The gaseous refrigerant then flows at low pressure from the evaporator coils down to the compressor to begin the cycle again.
A thermostat connected to the control knob case maintains the fridge or freezer's temperature by switching the compressor on and off according to the selected temperature setting.
The Cooling Process:
A fridge, like a pressure cooker, alters the pressure within a sealed unit to change the boiling point of a liquid.
Fridges lower the pressure to lower the boiling point of the liquid refrigerant, whereas pressure cookers raise the pressure so that water boils at a higher temperature.
- Refrigerant gas is compressed by a pump.
- The compression forces it to lose some of its energy, because the molecules cannot move so freely and thus collide in the reduced space. This energy, in the form of heat, is dissipated by a radiator called the condensor.
- Here the gas condenses into a warm liquid, which then passes into a narrow tube.
- When it exits this tube, its pressure drops, causing it to boil.
- The liquid boils as it draws heat energy from its surroundings - the evaporator and inside of the fridge.