Most of the food that is consumed is not eaten immediately after it is obtained. This creates a necessity to preserve the food and keep it from spoiling before it can be eaten. Different methods are used to ensure that food does not spoil..
Refrigerators are an essential part of every kitchen. While just about every home makes use of a refrigerator, most consumers know nothing about the history of refrigeration and the invention of the refrigerator.
Before mechanical refrigeration systems were introduced, people cooled their food with ice and snow, either found locally or brought down from the mountains. The first cellars were holes dug into the ground and lined with wood or straw and packed with snow and ice: this was the only means of refrigeration for most of history.
The first efforts that eventually led to the modern refrigeration process that continues to form the basis for the fridges that grace kitchens all over the world today. William Cullen of the University of Glasgow first developed a process to create an artificial cooling medium in 1748. At the time, there did not appear to be much interest in applying the medium to use in commercial or home applications, so the process created little in the way of interest beyond the scientific community. It would take the better part of a century before someone would apply the basic principles discovered by Cullen and create a design for a refrigerating machine.
Today, refrigerators are more of a necessity than a luxury. With needs for preservation, manufacturing, construction and comfort, refrigeration can be applied mainly to three different applications - domestic, commercial, and industrial refrigeration. Domestic refrigerators are used at home or offices to preserve food and keep drinks cool. Commercial refrigerators tend to be used at hotels, restaurants, stores, and large businesses. These facilities store, display, process, and dispense their products in refrigerators. Industrial refrigeration usually deals with manufacturing processes such as heat treatment, processing of food and textiles, photographic material and construction engineering. Applications such as ice plants, large food plants, oil refineries, and chemical plants are typically preserved or manufactured in industrial refrigerators. Often mistaken, many people believe that refrigerators lower original temperatures to cool the items in the fridge. Refrigerators actually contain an evaporating gas called a 'refrigerant'; this gas draws the heat away making the items, leaving them much cooler. A refrigerator typically includes two storage compartments, a frozen compartment and another compartment that requires refrigeration. Surrounded by heat-exchanging pipes and powered by a compressor, pure ammonia runs through the entire system. While the ammonia evaporates, the gas absorbs more heat, making the temperature rise. The cool ammonia then draws heat from the warmer items in the fridge but not as much from the freezer. After the gas is drawn back into the compressor, the entire cycle is run again. With numerous refrigerator manufactures such as Whirlpool, LG, Samsung and many more, several types of refrigerators are available in various sizes, colors, and designs. Portable refrigerators are also popular and are used in home bars, RVs, etc to store items in smaller quantities.
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