托福考试历年真题分享

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今天小编给各位分享一下历年的真题,这样各位考生在备考的过程中也可以做个参考。

托福考试历年真题分享-托福考题助手

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Development of refrigeration

1. Cold storage, or refrigeration, is keeping food at temperatures between 32 and 45 degrees F in order to delay the growth of microorganisms—bacteria, molds, and yeast— that cause food to spoil. Refrigeration produces few changes in food, so meats, fish, eggs, milk, fruits, and vegetables keep their original flavor, color, and nutrition. Before artificial refrigeration was invented, people stored perishable food with ice or snow to lengthen its storage time. Preserving food by keeping it in an ice-filled pit is a 4,000-year-old art.

Cold storage areas were built in basements, cellars, or caves, lined with wood or straw, and packed with ice. The ice was transported from mountains, or harvested from local lakes or rivers, and delivered in large blocks to homes and businesses.

2. Artificial refrigeration is the process of removing heat from a substance, container, or, enclosed area, to lower its temperature. The heat is moved from the inside of the container to the outside. A refrigerator uses the evaporation of a volatile liquid, or refrigerant, to absorb heat. In most types of refrigerators, the refrigerant is compressed, pumped through a pipe, and allowed to vaporize. As the liquid turns to vapor, it loses heat and gets colder because the molecules of vapor use energy to leave the liquid. The molecules left behind have less energy and so the liquid becomes colder. Thus, the air inside the refrigerator is chilled.

[3] Scientists and inventors from around the world developed artificial refrigeration during the eighteenth and nineteenth centuries. William Cullen demonstrated artificial refrigeration in Scotland in 1748, when he let ethyl ether boil into a partial vacuum. In 1805, American inventor Oliver Evans designed the first refrigeration machine that used vapor instead of liquid. In 1842, physician John Gorrie used Evans’s design to create an air-cooling apparatus to treat yellow-fever patients in a Florida hospital. 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 after noticing that when he cleaned his type with ether it became very cold as the ether evaporated. Five years later, Harrison introduced vapor-compression refrigeration to the brewing and meatpacking industries. [4] 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 artificial refrigeration at his brewery in St. Louis. Before refrigeration, brewers stored their beer in caves, and production was constrained by the amount of available cave space. Brewing was strictly a local business, since beer was highly perishable and shipping it any distance would result in spoilage. Busch solved the storage problem with the commercial vapor-compression refrigerator.

上面就是历年的真题,希望各位考生可以做个参考。

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