Let us first consider what refrigeration is. "Cold" is merely the absence of heat, and any means of absorbing heat which will lower the temperature to between 40 and 500 will give us the refrigeration we require in the home.
A piece of ice placed in the ice box absorbs heat by melting - changing from a solid to a liquid at a low temperature. Certain substances known as refrigerants, such as sulphur dioxide and ammonia, absorb heat by vaporizing - changing from a liquid to a gas - at a low temperature. If, then, we can permit this refrigerant to vaporize inside the chamber we wish to cool, and then change it back to a liquid outside of that chamber, we will have continuous refrigeration.
The electric machines accomplish this job by means of a compressor driven by an electric motor. The refrigerant is put under a high pressure in the compressor and it will then turn to a liquid at ordinary room temperatures. This liquid is then carried by a pipe to the freezing unit inside of the refrigerator, where the pressure is reduced by a valve. As the liquid refrigerant passes the valve it vaporizes, takes up heat in so doing, and cools the box. The refrigerant, which is now in the form of a gas, is returned to the compressor through another pipe and the circulating operation repeated.
The gas refrigerator makes use of a small boiler to raise the pressure of the refrigerant, so that it can be changed back to a liquid at ordinary temperatures. The major steps in the cycle of the gas-fired refrigerator are as follows:
Ammonia dissolved in water is placed in the boiler and heat, from a gas flame, applied. The ammonia is driven out of the water as a gas under pressure, and is then condensed to a liquid. The liquid flows to the freezing unit and is vaporized, taking up heat and cooling the box.
1 Adapted from "How the Gas Refrigerator Works," Domestic Engineering, December, 1928.
The ammonia, now in the form of a gas, is absorbed again in cold water and flows back to the boiler.
At the present time the operating cost of the gas refrigerator is slightly higher than the electric, although less than the cost of ice. The gas refrigerator, however, has no moving parts, which means that few repairs will be necessary.
The "generator-absorber" contains "aqua-ammonia" (that is, water and ammonia). It is the same kind of solution known all over the world as "household ammonia" and familiar to every housekeeper. For our purpose the percentage of ammonia is greater.
A gas burner is located under the "generator-absorber." The heat from this burner causes the ammonia in the liquid to become vapor.
This vapor passes along to the "condenser," where it is cooled by circulating water. Under this treatment the vapor becomes liquid and flows down into the "receiver."
This process continues until a sufficient quantity of the ammonia has been "vaporized" out of the aqua-ammonia in the "generator-absorber."
The circulating water is then automatically discontinued in the condenser, and diverted to the cooling coil of the "generator-absorber," and the gas is automatically turned out.
When the "generator-absorber" has cooled down to a predetermined point of temperature, the liquid ammonia refrigerant commences to pass from the "receiver" through the expansion valve into the expansion coil.
This coil is located in the ice chamber of the refrigerator itself.
The evaporation of ammonia gas, from this liquid, draws the heat from the refrigerator and its contents.
Cold is merely the absence of heat. This process of drawing out the heat creates a perfectly dry cold atmosphere in the refrigerator.
The spent ammonia gas then passes back to the "generator-absorber"- (which first generated the gas, and again, when its work has been accomplished, re-absorbs it). Thus the whole process of refrigeration has been completed; matters stand where they were in the beginning. The "generator-absorber" is again in readiness to repeat the operation which is automatically done as often as is necessary to provide the refrigeration required.