What process takes place in the refrigerator

Internal energy - heat capacity

In the pipe system of a refrigerator there is a coolant that has a boiling point of approx. -30 ° C at normal pressure.

This coolant enters the refrigerator in liquid form at approx. 1 bar. Since it is warmer than -30 ° C in the refrigerator, the coolant evaporates in the so-called Evaporator. The evaporation energy required for this is withdrawn from the food in the cupboard. The now gaseous coolant is through the compressor sucked off.

If the pressure of approx. 1 bar of the gaseous coolant were to be maintained, the temperature would have to be outside the refrigerator Condenser be lower than -30 ° C if the gaseous coolant should become liquid again (condensation). Since this is usually not the case (the condenser is located on the back of the refrigerator, usually at room temperature), a "trick" is used:

One takes advantage of the fact that the condensation temperature of a gas increases when the gas is under increased pressure (see, for example, the increase in the boiling point in the steam pot). The compressor increases the pressure of the gaseous coolant to approx. 8 bar, which increases the boiling or condensation temperature of the coolant to room temperature.

The gaseous coolant, which is under high pressure, releases energy into the surrounding air in the condenser pipe system, and the coolant becomes liquid. The heat of condensation released in the process is also given off to the environment. Through a reducing valve (throttle) the pressure of the liquid coolant is now reduced (to approx. 1 bar) so that the boiling temperature is -30 ° C again. This relaxed coolant is now fed back into the refrigerator and the whole process is repeated.