Methods of refrigeration
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In the past, mankind used natural methods of cooling that included the use of ice from polar caps. Natural ice was shipped from the New England states throughout the western world from 1806 until the early 1900s. Sometimes, ice was even harvested in the winter from natural frozen lakes, and stored in ice houses to be used in the summer. Although ice machines were patented in the early 1800s, they could not compete with the natural ice industry. Artificial ice was first commercially manufactured in the southern United States in the 1880s.

Domestic refrigerators were not commercially available until about 1920. During the 1920s, the air-conditioning industry also got its start with a few commercial and home installations. The refrigeration industry has now expanded to touch most of our lives. There is refrigeration in our homes, and air conditioning in our place of work, and even in our automobiles. Refrigeration is used in many industries, from the manufacture of instant coffee to the latest hospital surgical techniques.

Evaporative cooling

Whenever water evaporates into the surrounding air, it produces a cooling effect, because evaporation is an endothermic process. This is the principle behind the cooling of water stored in earth and vessels. And this is also the principle behind the cooling of human bodies on a hot day.

However, there are some limitations to evaporative cooling. It is very effective when the surrounding air is dry, and this is the reason evaporative cooling works very well in dry area such as desert but it does not work well in coastal regions, where it is very humid.

Salt Solutions

Another natural method is cooling by salt solutions. When we dissolve certain salts and certain materials in water the water temperature drops. This is because mixing of these salts with water is an endothermic process. It takes heat from the surrounding water and the resulting solution becomes cold. By changing the salt, you can get different temperatures. However this method again has its own practical limitations because cooling that is produced is generally limited and also the recovery of salt is a difficult process.

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