Home Freezing

Santosh Kushwaha        Print Edition: November 2012

A refrigerator consists a thermally insulated compartment and a heat pump that transfers heat from the inside of the fridge to its external environment so that the inside of the fridge is cooled to a temperature below the ambient temperature of the room. A refrigerator maintains a temperature a few degrees above the freezing point of water. Optimum temperature range for storage of perishable foods is 3 to 5 degree centigrade (37 to 41 degree F). A similar device that maintains a temperature below the freezing point of water is called a freezer.


Today, most refrigerators are frost-free. They have automatic defrosting systems so that you don't have to take everything out of your refrigerator and allow it to warm up so you can melt built-up ice in the freezer. An automatic defrost system includes a timer, a limit switch, and a heater, which melts away frost.
1) The liquid coolant enters the condenser coils. As it passes through, the sudden drop in pressure makes it expand, cool, and turn into a gas (just like a liquid aerosol turns into a cool gas when you spray it out of a can).

2) As the coolant flows around condenser coils, it absorbs and removes heat from the food inside.

3) The compressor squeezes the coolant, raising its temperature and pressure. It's now a hot, high-pressure gas.

4)The coolant flows through the thicker, rounded, horizontal evaporator coils on the back of the fridge, giving out its heat and cooling back into a liquid as it does so. The evaporator is made of copper and aluminum tubing. The many thin wires that run between the pipes are simple radiator fins that help to carry the heat away from the pipes and dissipate it into the air.

5) The coolant flows back into the condenser coils and the cycle repeats itself. So heat is constantly picked up from inside the refrigerator and put down again outside it. Usually you find one or more fans that ensure a good air flow through the condenser. When you put your hand there you will feel a warm air flow. This air was used to cool the compressed coolant.

THE CHRONICLE
1748: The first known artificial refrigeration was demonstrated by William Cullen at the University of Glasgow.

1805: The American inventor Oliver Evans, acclaimed as the "father of refrigeration," invented the vapour-compression refrigeration machine.

1834: Jacob Perkins modified Evans' original design, building the world's first refrigerator. He filed the first legal patent for refrigeration using vapour-compression.

1856: Australian James Harrison, an immigrant from Scotland, developed an ice making machine using ammonia and an ether compressor.

1918: Kelvinator Company introduced the first refrigerator with any type of automatic control.

1827: The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator.


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