image credit wikivisual
TreeHugger has published a lot of posts about absorption refrigerators; they are common in off-grid situations and because they run on heat, they are possibly key to the holy grail of solar powered air conditioning. Jennifer Ouellette explains on io9 that Albert Einstein and Leo Szilard developed and patented an absorption fridge from 1928 to 1933, eventually getting 45 separate patents for three different models. (Szilard also was Einstein's partner in writing a famous letter, shown above, to Frankin D Roosevelt in 1939)
It didn't take over the world at the time:
Despite filing more than 45 patent applications in six different countries, none of Einstein and Szilard's alternative designs for refrigerators ever became a consumer product, although several were licensed, thereby providing a tidy bit of extra income for the scientists over the years. The prototypes were not energy efficient, and the Great Depression hit many potential manufacturers hard. But it was the introduction of a new non-toxic refrigerant, freon, in 1930 that spelled doom for the Einstein/Szilard refrigerator. The economics supported the freon-based mechanical compressor technology, and that's what most folks still use today.
The original patent drawing shown above shows a fairly conventional absorption unit, but there was evidently another technical advance:
One of the components the two physicists designed for their refrigerator was the Einstein-Szilard electromagnetic pump, which had no moving parts, relying instead on generating an electromagnetic field by running alternating current through coils. The field moved a liquid metal, and the metal, in turn, served as a piston and compressed a refrigerant. The rest of the process worked much like today's conventional refrigerators.
But it was very noisy and used a highly reactive potassium-sodium alloy mixture. More at io9. See also a Design Analysis of the Einstein Refrigeration Cycle and US Patent 1781541
More on absorption cooling:
Solar Powered Air Conditioning Just Makes Sense
Challenge: Build the Solar Powered Air Conditioner
Small-Scale Solar Powered Air Conditioning Is Here (in Spain, Anyways)
Still Seeking the Solar Powered Air Conditioner
Is This "The World's First Solar Powered Air-Conditioning Unit"?
The Rebirth of the Cool: 7 Innovations in Air Conditioning
Wayback Machine: Solar Powered Refrigerator (in 1935!)