Refrigeration
Refrigeration is the process of removing heat from a substance to produce a low temperature. Heat always flows from a warmer to a cooler body or substance. Refrigeration works by placing something to be cooled near a refrigerant, something cooler that will absorb heat. Since ancient times, people have used refrigeration to help preserve food. Storage at or near 32° F (0 ° C) inhibits the growth of food-spoiling organisms and also decreases enzymes that change the texture, color, and flavor of food.
As early as 1000 b.c., the Chinese cut and stored ice. The Greeks and Romans filled cellars with mountain snow. Natural-ice refrigeration became a large-scale industry in nineteenth-century America. Entrepreneurs like Frederic Tudor harvested and shipped tons of northern pond ice to southern states and the tropics.
As cities and towns grew in both Europe and the United States during the 1800s, however, the need for mechanized refrigeration became critical. Ever-expanding amounts of food had to be transported over long distances without spoiling. Natural-ice refrigeration could not meet the need. It was also discovered that ice harvested from lakes and ponds contained microbes that caused disease. It had been previously thought that freezing killed microorganisms in the same manner as boiling.
Inventors worldwide rose to the task—scores of ice-making and cooling machines were patented throughout the nineteenth century. These operated on the principle that liquids absorb heat when they change into a gas. Both compression and absorption systems were used to change a liquid refrigerant into a gas and then back into a liquid again in a continuing, self-contained cycle.
The first known artificial refrigeration devices were developed in Scotland. In 1758, William Cullen evaporated ethyl ether in a partial vacuum, obtaining a small amount of ice. In 1777, Gerald Nairne accelerated Cullen's process by using sulfuric acid to absorb the water. In 1805, the American inventor Oliver Evans (1755-1819) designed a compressed-ether refrigeration machine with a closed cycle; however, the Evans machine never advanced beyond the prototype stage. Two early refrigeration machines were patented in 1834. Jacob Perkins (1766-1849), a Massachusetts inventor living in London, England, designed a compression machine with a closed cycle that used ether as the refrigerant. L. W. Wright patented an ice-making machine that used an air-compression process.
In 1844, Florida doctor John Gorrie (1803-1855), in the mistaken belief that malaria was caused by hot, humid air, designed a compressed-air refrigerating machine--an air conditioner and ice-maker--to cure his patients. Gorrie patented his ice-making machine in 1851, but the idea was ridiculed by New York newspapers. James Harrison, an immigrant from Glasgow, Scotland, improved the Perkins ether-compression system and installed the world's first commercial refrigerating machinery in an Australian brewery in 1851. Harrison and fellow British immigrant Thomas Mort later attempted to ship frozen beef to England from Australia.
Ferdinand Carré of France patented the first absorption refrigeration system in 1859, with ammonia as the refrigerant and water as the absorbent. Refrigerators using Carré's design came into wide use industrially. Ferdinand's younger brother, Edmond, put Cullen and Nairne's ideas into practical use with his 1866 water vapor refrigerating machine. Swiss physicist Raoul-Pierre Pictet (1846-1929) developed a compression refrigeration system in 1874 that used sulfur dioxide as the refrigerant. Pictet's machine made possible the world's first artificial skating rink, installed in London in 1876. The first successful compression system using ammonia was designed by Karl Paul Gottfried von Linde in 1876 for a German brewery, although an earlier patent for such a system was obtained in 1872 by David Boyle, a Scottish-American inventor. After some years of research, Linde converted his industrial design into a unit suitable for home use.
Today's domestic refrigerators use essentially the same cooling system that Linde had devised in the 1870s. A serious problem with the use of ammonia as a refrigerant is that ammonia is highly toxic; therefore, leaks are very hazardous. In the early twentieth century, refrigeration engineers searched for a viable ammonia substitute. The most well known of these was freon (dichlorodifluoromethane), a synthetic substance developed by Thomas Midgley and Albert Henne of General Motors. Artificial refrigerants are now used in systems worldwide.
As artificial ice and mechanical refrigeration became widely available, cold storage and transportation of perishable foods expanded greatly. As early as 1870, chilled beef was being shipped successfully from the United States to England, using an ice-salt coolant. The refrigerator boxcar and, later, the refrigerated truck distributed fresh foods throughout the United States.
Home storage of perishables became much more feasible. The use of ice and iceboxes expanded greatly after 1880. Linde marketed some of the first domestic mechanical refrigerators in the 1880s. The Kelvinator, designed by Nathaniel Wales, appeared in the United States in 1918, followed by the Frigidaire in 1919. Mass production began in 1931 with the Electrolux in Sweden and the Servel in America.
Such technical developments as smaller and more efficient equipment, safe artificial refrigerants, and the electric motor contributed to an expansion of the refrigeration industry from the 1930s to the present. Mechanical refrigeration is important today for many uses beyond food preservation-for example, air conditioning, storage of medical supplies and drugs, medical and surgical techniques, and manufacturing and industrial processes of all kinds, including liquid-air applications.
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