The Einstein–Szilard or Einstein refrigerator is an absorption refrigerator which has no moving parts, operates at constant pressure, and requires only a heat source to operate. It was jointly invented in 1926 by Albert Einstein and his former student Leó Szilárd, who patented it in the U.S. on November 11, 1930. The three working fluids in this design are water, ammonia, and butane. The Einstein refrigerator is a development of the original three-fluid patent by the Swedish inventors Baltzar von Platen and Carl Munters.
Annotated patent drawing
An absorption refrigerator is a refrigerator that uses a heat source to provide the energy needed to drive the cooling process. Solar energy, burning a fossil fuel, waste heat from factories, and district heating systems are examples of convenient heat sources that can be used. An absorption refrigerator uses two coolants: the first coolant performs evaporative cooling and then is absorbed into the second coolant; heat is needed to reset the two coolants to their initial states. Absorption refrigerators are commonly used in recreational vehicles (RVs), campers, and caravans because the heat required to power them can be provided by a propane fuel burner, by a low-voltage DC electric heater or by a mains-powered electric heater. Absorption refrigerators can also be used to air-condition buildings using the waste heat from a gas turbine or water heater in the building. Using waste heat from a gas turbine makes the turbine very efficient because it first produces electricity, then hot water, and finally, air-conditioning—trigeneration.
Domestic absorption refrigerator. 1. Hydrogen enters the pipe with liquid ammonia 2. Ammonia and hydrogen enter the inner compartment. Volume increase causes a decrease in the partial pressure of the liquid ammonia. The ammonia evaporates, taking heat from the liquid ammonia (ΔHVap) lowering its temperature. Heat flows from the hotter interior of the refrigerator to the colder liquid, promoting further evaporation. 3. Ammonia and hydrogen return from the inner compartment, ammonia returns to absorber and dissolves in water. Hydrogen is free to rise.
Thermal image of a Domestic absorption refrigerator of a comparable type to the one in the labelled image above. Colour indicates relative temperature: blue=cold, red is hottest. The heat source (7) is contained entirely within the insulation section (6).
