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See Article on Refrigeration Machines
animation of basic absorption cycle using heat
Absorption cycle refrigeration without need for a pump was invented by two Swedish students, Carl Munters and Balizar von Platen at the Royal Institute of Technology in Stockholm. The machine they invented utilizes the fact that ammonia (NIL) is very soluble in cold water but much less soluble in hot water, while hydrogen is hardly soluble in either and balances the pressure throughout the system.