Consequent Cooling

Consequent Cooling

The refrigerator works on the state changes of refrigerant
There are three states in matters, namely, the solid, liquid and gaseous states. In everyday life, we know the three states of water as solid ice, liquid water and gaseous steam respectively. The refrigerator works on the state changes of refrigerant, e.g. between liquid and gaseous states, as heat transfer takes place in such process.

  • Evaporation – changing state from a liquid to a gas – requires heat to take place, which is absorbed from the contents of the refrigerator.
  • The reverse change – condensation – gives out heat, which is released from the refrigerant to the outside of the refrigerator.

The latter is carried out by a compressor [1] which compresses the refrigerant and pumps it into the condenser (it is in the form of narrow pipe, highlighted in green in the figure), to form liquid. Heat is given out in the condenser, which contacts closely with thin metal vanes [3] on the back of the refrigerator. The vane transfers heat to the outside quicker and easier. Liquid refrigerant then flows to the evaporator (a wide pipe, highlighted in purple in the figure) after leaving the expansion valve [4], expands and evaporates due to the low pressure there, thus drawing in heat from the interior of the refrigerator. That is to say, we obtain a lower temperature (-20oC) inside the refrigerator cabinet. Warmer vapor flows back to the compressor and the whole cycle begins over again. Generally, the evaporator is installed around the icebox [2].

Convection currents carry cold air from the refrigerator, which is cooled to around 2.7oC. Internal temperature is controlled by a thermostat: this consists of a sealed, air-filled tube terminating in the refrigerator [5]. As air within the tube warms up, it expands, pushing out a set of bellows [6]. The expanding bellows close an electrical switch [7], which switches on the compressor. The refrigerator cabinet is made of polyurethane foam [8]: this functions as an insulator as well as giving mechanical strength.

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