leave the liquid. The molecules left behind have less energy and so the liquid becomes colder. Thus, the air inside therefrigerator is chilled.Scientists and inventors from around the world developed artificial refrigeration during the eighteenth and nineteenthcenturies. William Cullen demonstrated artificial refrigeration in Scotland in 1748, when he let ethyl ether boil into a partialvacuum. In 1805, American inventor Oliver Evans designed the first refrigeration machine that used vapor instead of liquid. In1842, physician John Gorrie used Evans's design to create an air-cooling apparatus to treat yellow-fever patients in a Floridahospital. Gorrie later left his medical practice and experimented with ice making, and in 1851 he was granted the first U.S.patent for mechanical refrigeration. In the same year, an Australian printer, James Harrison, built an ether refrigerator afternoticing that when he cleaned his type with ether itbecame very cold as the ether evaporated. Five years later, Harrisonintroduced vapor-compression refrigeration to the brewing and meatpacking industries.Brewing was the first industry in the United States to use mechanical refrigeration extensively, and in the 1870s,commercial refrigeration was primarily directed at breweries. German-born Adolphus Busch was the first to use artificialrefrigeration at his brewery in St. Louis. Before refrigeration, brewers stored their beer in caves, and production wasconstrained by the amount of available cave space. Brewing was strictly a local business since beer was highly perishable andshipping it any distance would result in spoilage. Busch solved the storage problem with the commercial vapor- compressionrefrigerator. He solved the shipping problem with the newly invented refrigerated railcar, which was insulated with ice bunkersin each end. Air came in on the top, passed through the bunkers, and circulated through the car by gravity. In solving Busch'sspoilage and storage problems, refrigeration also revolutionized an entire industry. By 1891, nearly every brewery was
MÃ ĐỀ2082/ 4VnDoc - Tải tài liệu, văn bản pháp luật, biểu mẫu miễn phíequipped with mechanical refrigerating machines.The refrigerators of today rely on the same basic principle of cooling caused by the rapid evaporation and expansionof gases. Until 1929, refrigerators used toxic gases - ammonia, methyl chloride, and sulfur dioxide - as refrigerants. After thosegases accidentally killed several people, chlorofluorocarbons (CFCs) became the standard refrigerant. However, they werefound to be harmful to the earth's ozone layer, so refrigerators now use a refrigerant called HFC 134a, which is less harmful tothe ozone.Question 6. What is the main reason that people developed methods of refrigeration?