Modern refrigeration has many applications. The first, and probably still the most importan, is the preservation of food.
Most foods kept at room temperature spoil rapidly. This is due to the rapid growth of bacteria. At usual refrigeration temperatures of about 4.4 o C (40 F), bacteria grow quite slowly. Food at this temperature will keep much longer. Refregeration preserves food by keeping it cold.
Other important uses of refrigeration include air conditioning, beverage cooling and humidity control. Many manufacturing processes also use refrigeration.
The refrigeration industry became important commercially during the 18th century. Early refrugeration was obtained by the use of ice. Ice from lakes and ponds was cut and stored in the winter in insulated storeerooms for summer use.
The use of natural ice required the building of insulated containers or iceboxes for stores, restaurants, and homes.
Ice was first made artificially about 1820 as an experiment. Not until 1834 did artificial ice manufacturing become practical. Jacob Perkins, an American engineer, invented the appartus which was the forerunner of our modern compression system. In 1885 a Germanengineer produced the first absorption type of refrigerating mechanism, although Michael Farady had discovered the principles for it in 1824.
2. How Mechanical Refrigerator Operates
Removing heat from inside a refrigerator is somewhat like removing water from leaking canoe. A sponge may be used to soak up water. The sponge 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 canoe into the lake.
In a refrigerator heat instead of water is transferred. Inside the refrigerating mechanism, heat is absorbed, "soaked up", by evaporating , the liquid refrigerant changes from a liquid to a vapor (gas), Fig 1-1
Fig 1-1 Elementery mechanical refrigerator
In operation, liquid regrigerant under high pressure (solid red), flow from liquid receiver to pressure reducing valve (refrigerant control) and into evaporator. Here pressure is greatlyincreased and, in condenser, heat is transferred to surrounding air. Refrigerant cools, becoming liquid again. It flows bacreduced. Liquid
refrigerant boils and absorbs heat from evaporator. Now vapor, refrigerant (spoted red line) flows back to compressor and is compressed to high pressure (red dot). Its temperature is greatlyk into liquid receiver and cooling cycle is repead.
After the refrigerant has absorbed heat and has turned into a vapor, it is pumped into the condensing unit located outside the refrigerated space. The condenser works the opposite of the evaporator. In the evaporator, liquid refrigerant enters one end and absorbs heat as it passes through the evaporator.By time it reaches the end of the evaporator, it is all vapor. As this vapor flows through the condenser under high pressure and high temperature, it gives up its heat to the surrounding air. As it reaches the end of the condenser, the refrigerant, now cooled, has become a liquid again. We say that, in the condenser, the heat is "squeezed out". The cycle repeats until the desired temperatureis reached.
Heat enters a refrigegerator in many ways. It leaks through the insulated walls or enters when the door is opened. Still more heat 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 refrigerated space and released outside.
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source:
" Modern Refrigeration and air conditioning " by Andrew D. Carl. H, Alfred F.
