While countless different manufacturers and models of refrigerators are available today, this was not always the case. In the early days of refrigerator technology, advances were slow and designs were still being perfected. The first widely available and affordable refrigerator was built by General Electric and was called the "Monitor Top" model. It was released in 1927.
Old refrigerators such as the Monitor Top operated with the same principles as modern appliances, but used different technology to create the cooling effect. Early refrigerators featured large cooling pumps and coils on top of the unit. The two substances used as refrigerants on these early models were sulfur dioxide and methyl formate. Both of these compounds are harmful and have since been banned and replaced.
The core of old refrigerators is the pump, powered by household electricity. Connected to the pump is tubing which contains either sulfer dioxide or methyl formate liquid. When the pump activates, this liquid circulates through a series of coils, or bends in the tubing. As the liquid moves further up, it lowers in pressure and becomes a vapor.
When the coolant begins to evaporate into a vapor, it takes heat with it. This is the same effect that creates cooling on the skin when sweat evaporates. As heat is pulled away from the coils, the coolant lowers in temperature.
After moving through the coils, the now-vapor coolant continues to circulates through the rest of the refrigerator. The cool vapor absorbs heat throughout the unit, resulting in a cooling effect in every area of the refrigerator.
By the time the coolant has circulated completely through the refrigerator, it has started to rise in temperature due to the absorbed heat. The pump moves it back through the coils, where it is recompressed and turned back into a liquid. This cooling cycle continues as long as the pump stays activated.
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