Nathaniel Doane
Amst. 205
Project 5


Electric Refrigerators for the Greenbelt Museum Refrigerator Exhibit



For years keeping something cold was accomplished by putting ice in or around it. People would have to go out and collect ice to store food in or if they lived in the cities and towns ice was delivered in wagons.(1) With the advent of mechanical refrigeration this was no longer a necessary burden. Originally there were two competing methods of refrigeration, electric and gas. To learn more about gas refrigeration click here . The rest of this document will deal with electric refrigeration.
In 1938 the most popular and most widely used systems of refrigeration (was) the compression system.(2) The compression system is another name for the electric system. As can be guessed from the name the electric system utilizes the compression and expansion of vapor and liquid to cool the refrigerator. There are many different models of the compression system that different manufacturers had developed by the thirties.(2)
Both of these two systems work on the principle that when a liquid changes to a gas, it cools the items around it. This is because the evaporation absorbs the thermal energy to convert the liquid to a vapor. Like wise if a gas is decompressed it will cool down.(3) The main difference in the compression systems and the gas absorption systems is in how the vapor is removed from the cooling system. In the case of the compression system the vapor is removed from the cooling system by suction from a pump. The vapor is then liquefied.(2) There are four main components to the compression system: an expansion device; vaporizing process; compression of vapor in a compressor; and condensation of vapor.(2) By lowering the pressure on the gas, there is a lowering of the boiling point (the point at which the liquid becomes a gas.) By having the right combination of chemicals, such that the boiling point is easily obtained, the expander will vaporize the liquid. This cooled gas then absorbs heat from the container. The hot vapor is then pumped out of the container and compressed by the compressor. The condenser then turns the compressed vapor into a liquid, and lets cool, external air flow around it to take away the heat of vaporization.(4) Once the chemicals are liquid again, they are put through the expander and begin the proccess again.
The specifics of each manufactures designs vary a great deal. Some manufacturers were Westinghouse and General Electric. Even though the components varied, there were some basic models that were followed during that era. One was the coolants. The coolants used in the absorption system were ones that: had boiling points around atmospheric pressure, so they could easily be vaporized; condensing temperature must be low so that the vapor will liquefy at room temperature; the amount of cooling when vaporized must be great, so that amount of cooling produced is a maximum; none corrosive to the metal of the refrigerator; had to be no-flammable or explosive, for safety reasons; and they should not be hazardous to peoples health.(5) Some of the common refrigerants that meet these criteria are sulphur dioxide, ammonia, F-114, methyl chloride, methyl formate, F-12, isobutane and carrene.(2) Depending on which coolant a system used it would make a difference in the precise design of the compressor. The two main types of compressors that were in operation, were the reciprocating and rotary types.(6) The reciprocating compressor uses a piston to compress and expand the refrigerant. When the piston is lowered a low pressure cavity is formed. This sucks in the warm vapor. Then as the piston reaches its down swing the valve to the low-density vapor is closed. The vapor is then compressed until a release valve is opened and allowed the high density vapor to go to the condenser. Then the process is started over again.(6) The rotary compressor has a roller that is forced through a cylinder by springs or driving blades. As it is rolled around the cylinder intake and release valves are covered and uncovered. This traps the air in the chamber and as the roller continues on its path compresses the air. Once the air is compressed it then released.(7) In most of the refrigerators of the 30s the condensers were simply air cooled. Since by the time the vapor gets to the condenser it is already at a high pressure and thus a high boiling point, all that needs to be done is to cool the vapor to room temperature. The most rapid way to get the vapor cooled is to get as much exposure to the room temperature air as possible. This is done in two ways, having a fan blow air over the condenser and to make the vapor in the condenser have as much surface area exposed to the air as possible.(7) This is why there are so coils of tubing on the back of most refrigerators of the time. There are a vast number of expanders and contact cooling in the refrigerator chamber. There is not a good general model for how that was done.
The absorption refrigerator was in competition with the gas absorption refrigerator when they originally were invented. As item progressed the gas model went into more and more disuse. Even in 1938 it was felt that the compression model was going to win the battle.(2) The compression system continues to improve and change, but it was the refrigerator that most people by the 1940s had in their homes.



Notes

(1) Lynes, p. 123
(2) Wostrel & Praetz, p. 7
(3) Wostrel & Praetz, p. 5
(4) Wostrel & Praetz, p. 8
(5) Wostrel & Praetz, p. 10
(6) Wostrel & Praetz, p. 21
(7) Wostrel & Praetz, p. 25


References


1. Lynes, Russel . The Domesticated Americans. Harper & Row, Publishers. New York. 123.

2. Wostrel, John F. and Praetz, John G. 1938. Household Electric Refrigeration. Mcgraw-Hill Book Company, Inc. New York. 6-30


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