In 1873, German chemist and engineer Karl. Von. Linde invented the refrigerator using ammonia as a refrigerant. Linde used a small steam engine to drive a compression system that repeatedly compressed and evaporated ammonia to produce refrigeration. Linde first used his invention at the Sedumal brewery in Wiesbaden, where he designed and built an industrial refrigerator. Later, he improved the industrial refrigerator. Making it smaller, he built the world's first artificially cooled domestic refrigerator in 1879. This steam-powered refrigerator soon went into production, and by 1891, 12,000 units had been sold in Germany and the United States.
The first refrigerator to work with a compressor driven by an electric motor was invented by Swedish engineers Brighton and Mendes in 1923. An American company later bought their patent and produced the first domestic refrigerators in 1925. The first refrigerators had separate electric compressors and freezers, with the latter usually placed in the home's floor kiln or storage room and connected to the electric compressor by piping, before being combined into one.
Before the 1930s, most of the refrigerants used in refrigerators were unsafe, such as ether, ammonia, sulfuric acid, etc., or flammable, or corrosive, or irritating and so on. Then the search for a safer refrigerant began, and resulted in the discovery of Freon. Freon is non-toxic, non-corrosive, non-flammable fluorine compounds, it soon became a variety of refrigeration equipment refrigerant, has been used for more than 50 years. However, it was discovered that Freon had a destructive effect on the ozone layer of the earth's atmosphere. So people began to look for new and better refrigerants.
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Many people treat the refrigerator as a "food sterilizer" and think that the food stored in the refrigerator is hygienic. In fact, the refrigerator for long-term storage of food and not often cleaned, will breed a lot of bacteria.
Dr. Michael Conan Doyle, director of the Center for Food Safety at the University of Georgia, suggests that the food in the refrigerator may look fresh on the outside, but in fact it is already spoiled. For cooked meat foods should not be stored in the refrigerator for more than four days.
The common refrigerator temperature for keeping food in the fridge is 4 to 8 degrees Celsius, where the growth of the vast majority of bacteria slows down. However, some bacteria are cold-loving, such as Yersinia pestis, Listeria monocytogenes, etc. in this temperature, but can rapidly grow and multiply, if you eat the food infected with such bacteria, will cause intestinal diseases.
And the refrigerator freezer, the temperature is generally at -18 ℃ or so, at this temperature, the general bacteria will be inhibited or killed, so this is stored in the food has a better preservation effect. However, freezing is not equal to the ability to completely sterilize, there are still some bacteria with strong resistance to freezing will survive. Therefore, although freezing can be a longer-term preservation of food, but the food microorganisms did not die, once the temperature rises, they will still continue to grow and reproduce. Therefore, the refrigerator preserved food, before eating, must be re-boiled, otherwise it will also cause intestinal infectious diseases, and even food poisoning.
Baidu Encyclopedia - Refrigerator (a refrigeration device that maintains a constant low temperature)