Before studying the operation of the mechanical refrigerator, it is important to understand the physical and thermal properties of mechanisms and substanes used to exsrat heat. Removing heat from insede a refigerator is somewhat like removing water from a leaking canoe. A sponge may be used to soak up the water. The spoge is held over the side, squeezed, and the water is released overboard. The operation may be repeated as often as necessary to transfer the water from the canoe into the lake. In a refregerator, heat instead of water is transferred. Inside the refregerator, heat is absorbed, “soaked up” by the liquid refregerant in the evaporator (cooling unit). This happens as the refrigerant changes from a liquid to avapor (gas). After the refrigerant has absorbed het and has turned into vapor, it is pump into the condensing unit located outside the refrigerant space. Here it is compressed. The head is “squeezed” out by high pressure and high temperture. Then it is cooled in the condenser. This cycle repeats until the desired temperture is obtained. Heat gets into a refrigerator in many ways. It leaks in though the insulation and enters with the warmer air when the door is opened. Still more is introduced when warm substances are placed in the refrigerator. Heat is not destroyed to make the refrigerator cold; it is simply removed from the refrigerted space and released outside. See fig. An elementary mechanical refrigerator. In operation, liquid refrigerant under high pressure flows from liquid receiver to pressure reducing valve (refrigerant control) and into evaporator. Here pressure is greatly reduced, liquid refrigerant boils and absorbs heat from evaporator. Refigerant is now a vapor, flows back to compressor and is compressed to a high pressure, its temperature is greatly increased and in the condeser the heat is transferred to surrouding air, the refrigerant is cooled and becomes a liquid again.it flows back into the liquid receiver from which its cooling cycle is repeated.
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