History of Chiller (1)
Unlike the current freezing method using a freezer/chiller, the primitive method of refrigeration using natural ice has been used for a long time. The most widely used method was to collect natural ice in the winter, store it in an insulated warehouse, and use it in the summer, a method that was widely used around the world until the 19th century. In the past, in Korea, the method of using underground warehouses such as stone ice storage was widely used by the government starting from the Silla Dynasty until the end of the Joseon Dynasty. In general, in rural areas, natural ice was stored deep in rice husk piles and used in the summer.
Another method used in Egypt, a dry region, was to put water or wine in an earthenware vessel and use the heat of evaporation from the natural evaporation of water seeping from the surface of the earthenware vessel to cool or even freeze the fluid inside the vessel.
Unlike these primitive methods, a very artificial method was used that used the heat of melting of saltpeter. When a liquid or solid dissolves in water, it absorbs or radiates a certain amount of heat. Substances such as potassium nitrate and sodium nitrate are representative substances that undergo an endothermic reaction by absorbing surrounding heat when dissolved in water. For example, potassium nitrate (KNO3) absorbs 82.42 kcal of heat per kg when dissolved in water. In the 17th century, French society used this method of freezing, and the general public put saltpeter and water in a bottle with a narrow mouth and shook it to create an endothermic reaction, and this was used to make cold drinks and ice.
Unlike these one-time methods, the method of freezing or cooling using machines began in Europe in the 18th century, when science and technology began to develop due to the Industrial Revolution. In 1755, Dr. William Cullen of the University of Glasgow, England, first proposed a refrigeration method using the heat of evaporation by evaporating ethyl ether using a vacuum generator using an air pump. However, he did not put this method into practical use.
The design concept of the refrigeration machine by Dr. William Cullen
Additionally, around 1824, British physicist Michael Faraday also proposed a very practical theoretical cycle for the current compression refrigeration system and absorption refrigeration cycle that uses the heat of evaporation of liquefied ammonia. The method he discovered was to use ammonia as a refrigerant and silver chloride as an absorbent on both sides of an inverted U-shaped tube, with one side acting as an evaporator and condenser, and the other side acting as an absorber and generator.
Refrigeration machines at Smithonian Museum
The ammonia liquid evaporates and is absorbed into the silver chloride, which can be cooled on one side. When the silver chloride powder that has absorbed the ammonia is heated, it is released again and the ammonia is regenerated. This absorption refrigeration method, which allows intermittent but cycle freezing, uses only water as the absorbent. It has been widely used until recently. Two refrigeration machines on display at the Smithsonian Museum demonstrate this type of refrigeration device.
