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The term refrigeration refers to cooling an area or substance below the environmental temperature, the process of removing heat. Mechanical refrigeration uses the evaporation of a liquid refrigerant to absorb heat. The refrigerant goes through a cycle so that it can be reused, the main cycles are: vapour-compression, absorption, steam-jet or steam-ejector, and air.

Prior to mechanical refrigeration systems, people found different ways of preserving their food. Some people preferred to use cooling systems of ice or snow found either locally or brought down from mountains and sometimes stored in cellars. The first forms of cellars were simply holes dug in the ground, lined with straw or wood and filled with snow and ice. Others used the methods of salting, pickling, drying, spicing and smoking their food. Using those techniques meant that diets would have consisted of very little fresh food or fruits and vegetables, but mostly of bread, cheese and salted meats. Milk and cheeses were difficult to keep fresh, they were usually stored in a cellar or window box, but despite those methods, they could not prevent rapid spoilage. People at that time did not understand about pasteurization and therefore, bacterial infestation was widespread. During the warm weather months, it was not uncommon in colonial days to die of ‘summer complaint’ due to spoiled food. People were more than ready for a better system of preserving food.

Creative thinkers in India recognized this need. India was the first location where evaporative cooling was used. When a liquid vaporizes quickly, it expands rapidly and the rising vapour molecules quickly increase their kinetic energy. The increase in energy is drawn from the immediate surroundings of the vapour, which causes the surroundings to cool.

Later on, it was discovered that adding chemicals like sodium nitrate or potassium nitrate to water caused the temperature to fall. Cooling wine with this technique was first recorded in 1550, as was the term "to refrigerate”. Cooling drinks became very popular by 1600 in Europe, especially in Spain, Italy and France. Instead of cooling water at night, people used a new technique; rotating long necked bottles in water which held dissolved saltpeter. The solution was used to create very low temperatures and even to make ice. By the end of the 17th century, iced drinks including frozen juices and liquors were very popular in French society.

A demand for ice soon became very strong. In 1799, ice was first shipped commercially out of Canal Street in New York City to Charleston, South Carolina. The attempt was a failure as there was very little ice left when the shipment arrived. Frederick Tudor and Nathaniel Wyeth of New England saw the great potential that existed for the ice business and revolutionized the industry with their efforts in the first half of the 1800s. Tudor, who was known as the “Ice King”, was more focused on shipping ice to tropical climates. To ensure his product would arrive safely, he experimented with different insulating materials and built icehouses that decreased melting losses from 66 percent to less than 8 percent. Wyeth developed a method of cheaply and quickly cutting uniform blocks of ice that transformed the ice industry. He made speed handling techniques in storage, transportation and distribution possible, with less waste. The ice industry grew very quickly as more companies entered the business, prices decreased, and refrigeration using ice became more available. In 1879 there were 35 commercial ice plants in America, over 200 a decade later, and 2,000 by 1909. About 15 million tons of ice was consumed in 1907, which was almost triple the amount consumed in 1880. Ponds everywhere were being scraped for ice production for example; 1,000 tons of ice were extracted each day in Thoreau’s Walden Pond in 1847.

Eventually it became clear that the ice being scraped was not all clean and was causing health problems. It was becoming an increasingly difficult task to find clean sources of natural ice and by the 1890’s, pollution and sewage dumping had made the job seem even more impossible. The first signs were noticed in the brewing industry, and then the meat packing and dairy industries became seriously affected. Some sort of clean, mechanical refrigeration was desperately needed.

Many inventive men were involved in the eventual creation of the refrigerator, through different discoveries that each built on the next. Dr. William Cullen, a Scotsman, was the first to study the evaporation of liquids in a vacuum in 1720. He later demonstrated the first known artificial refrigeration at the University of Glasgow in 1748 by letting ethyl ether boil into a partial vacuum.

Olvier Evans, an American inventor, designed the first refrigeration machine to use vapor instead of liquid in 1805. Although he did not actually build it, an American physician named John Gorrie, produced one very similar to Evans’ in 1842 to cool the patients with yellow fever in a Florida hospital. His basic principle is still the most often used in refrigerators today. He found the best way to cool the air was by compressing a gas, then cooling it by sending it through radiating coils, and then expanding it to lower the temperature even more. He was granted the first U.S. patent for mechanical refrigeration in 1851 after giving up his medical practice to focus on his experimentation with ice making.

In 1820 Michael Faraday, a Londoner, first liquefied ammonia to cause cooling. Ferdinand Carre of France developed the first ammonia/water refrigeration machine in 1859. Carl von Linde was also very influential in the creation of refrigeration. In 1873 he designed the first practical and portable compressor refrigeration machine in Munich and in 1876 he began using an ammonia cycle rather than the methyl ether he used in his earlier models. Linde later developed a new method (Linde technique) for the liquefaction of large quantities of air in1894.

The brewing industry was one of the first to realize the major benefits that refrigeration could offer. In the 1840s, German lager beer came to America with the German immigrants and tasted much better than the American ale. Thanks to refrigeration, the breweries were able to make a uniform product all year round. One of the first types of refrigerators (an absorption machine) was used by S. Liebmann’s Sons Brewing Company in Brooklyn, New York in 1870. Almost every brewery had refrigerating machines by 1891.

The meat packing industry in Chicago was the next to adopt mechanical refrigeration nearly a decade later. By 1914 almost all American packing plants were using the ammonia compression refrigeration system which had a capacity of over 90,000 tons a day. Armour, Swift, Morris, Wilson, and Cudahy (the five large meat packers) were especially fond of the refrigeration technology and used it in cars, branch houses and other cold storage facilities. The industry was greatly improved thanks to refrigeration, curing was possible all year round and since animals could be brought to market at any time, not just winter, the meat quality was much higher.

The refrigeration technology quickly became popular in society, with refrigerators being as common as stoves or sewing machines and creations like the ice wagon in 1884 delivering ice to Americans who posted their ‘Ice Today’ signs in their windows. Although their popularity continued to grow, there were a few glitches in the system.

Refrigerators that were built in the late 1800s to 1929 used the toxic gases; methyl chloride, ammonia and sulphur dioxide as refrigerants. There were numerous fatal accidents that occurred in the 1920s when methyl chloride leaked out of refrigerators. After the terrible incidents, three American companies began researching less dangerous methods of refrigeration. That research lead to the discovery of chlorofluorocarbons (Freon), which quickly became the standard used in compressor refrigerators. Freon was safer for those nearby but was later discovered in 1973 by Prof. James Lovelock, to be harmful to the ozone layer. To prevent further damage, new developments were made, such as Hydroflourocarbons which have no known effect on the ozone layer. Chlorofluorocarbons are no longer used; they are outlawed in several places, making refrigeration far safer today than it has ever been.