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 (U.S. Patent 1,781,541). 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.
From 1926 until 1934 Einstein and Szilárd collaborated on ways to improve home refrigeration technology. The two were motivated by contemporary newspaper reports of a Berlin family who had been killed when a seal in their refrigerator failed and leaked toxic fumes into their home. Einstein and Szilárd proposed that a device without moving parts would eliminate the potential for seal failure, and explored practical applications for different refrigeration cycles. Einstein had worked in the Swiss Patent Office, and used his experience to apply for valid patents for their inventions in several countries. The two were eventually granted 45 patents in six countries for three different models.
It has been suggested that most of the actual inventing was done by Szilárd, with Einstein merely acting as a consultant and helping with the patent-related paperwork, but others assert that Einstein contributed design work to the project.
The refrigerator was less efficient than existing appliances, although having no moving parts made it more reliable; the introduction of non-toxic Freon — later found to be responsible for serious depletion of the Earth's ozone layer — to replace toxic refrigerant gases made it even less attractive commercially. The Great Depression of 1929 dried up funding for development, and the widespread political violence in Nazi Germany, where the inventors lived, particularly towards Jews such as Einstein and Szilard, contributed to the device's lack of commercial success. (The inventors fled Germany in the early 1930s.) It was not immediately put into commercial production, although the most promising of the patents were quickly bought up by the Swedish company Electrolux. Einstein and Szilárd earned $750 (the equivalent of $10,000 in 2017). A few demonstration units were constructed from other patents.
In 2007, a prototype of a commercial refrigeration device intended for use as a vaccine cooler was shown by Adam Grosser at a TED Talk; the prototype operates at constant pressure, and is powered by heating in a fire. Once heated, the prototype would serve as a refrigerator for 24 hours. As of 2020 Grosser's prototype had not been put into commercial production.
In 2008, electrical engineers at Oxford University's Energy and Power Group, part of the university's Department of Engineering Science, revived the Einstein refrigerator as an attempt to produce a refrigerator suitable for use in rural areas without electricity. The group, led by Malcolm McCulloch noted that the design was still "nowhere near commercialised", but might allow the efficiency of the original Einstein-Szilárd design to be quadrupled.
- Rudolf Goldschmidt (for the Einstein–Goldschmidt hearing aid)
- Timeline of low-temperature technology
- "Einstein's Refrigerator Using No Electricity/No Freon Revived at Oxford". The Green Optimistic. 6 February 2015.
- Dannen, Geene (1997). "The Einstein–Szilard Refrigerators". Scientific American. 276 (1): 90–95. Bibcode:1997SciAm.276a..90D. doi:10.1038/scientificamerican0197-90. Archived from the original on 2013-02-01.
- Kean, Sam (2017). Caesar's Last Breath. New York: Hachette. ISBN 9780316381635. Retrieved 24 July 2017.
- Bisno, Adam (8 December 2020). "The Einstein-Szilard Refrigerator". Lemelson Center for the Study of Invention and Innovation, Smithsonian Museum.
- Grosser, Adam (2007). "A mobile fridge for vaccines". TED.
- "Malcolm McCulloch - Profile". Affordable Energy for Humanity (AE4H). University of Waterloo. Retrieved 12 November 2019.
- Alok, Jha (21 September 2008). "Einstein fridge design can help global cooling". The Guardian. Retrieved 12 November 2019.
- Einstein, A., L. Szilárd, "Refrigeration" (Appl: 16 December 1927; Priority: Germany, 16 December 1926) U.S. Patent 1,781,541, 11 November 1930.
- Einstein, A., L. Szilárd, "Accompanying notes and remarks for Pat. No. 1,781,541". Mandeville Special Collections Library USC. Box 35, Folder 3, 1927; 52 pages.
- Einstein, A., L. Szilárd, "Improvements Relating to Refrigerating Apparatus." (Appl: 16 December. 1927; Priority: Germany, 16 December 1926). Patent Number 282,428 (United Kingdom). Complete accept.: 5 November 1928.
- Flanigan, Allen, " (German site) Wolfgang Engels from the University of Oldenburg rebuilt the original concept— the housing is manufactured out of concrete, i.e. the total mass of the completed apparatus is around 400 kg with 20 kg of alcohol in the refrigeration cycle. The project was completed in 2005.
- Patent document US1781541 (European Patent Office)
- Patent document GB282428 (European Patent Office)
- How kerosene refrigerators work. Archived version of page.