Scientists at Lawrence Berkeley National Laboratory have developed a novel potential means of alternative refrigeration: ionocaloric cooling. The method involves electrically charged atoms or molecules (ions) changing the melting point of a solid material, much like adding salt to roads before a winter storm changes how ice will form. Their proof-of-principle experiment used salt made with iodine and sodium along with an organic solvent to achieve energy-efficient cooling, according to a recent paper published in the journal Science.
“The landscape of refrigerants is an unsolved problem: No one has successfully developed an alternative solution that makes stuff cold, works efficiently, is safe, and doesn’t hurt the environment,” said co-author Drew Lilley. “We think the ionocaloric cycle has the potential to meet all those goals if realized appropriately.”
There’s a long history of scientists looking for better alternatives for refrigeration, including a refrigerator designed by physicists Albert Einstein and Leo Szilard. The impetus for the two men’s collaboration occurred in 1926, when newspapers reported the tragic death of an entire family in Berlin due to toxic gas fumes that leaked throughout the house while they slept—the result of a broken refrigerator seal. Such leaks were occurring with alarming frequency as more people replaced traditional ice boxes with modern mechanical refrigerators which relied on poisonous gases like methyl chloride, ammonia, and sulfur dioxide as refrigerants. Einstein was deeply affected by the tragedy and told Szilard that there must be a better design.
Einstein and Szilard focused their attention on absorption refrigerators, in which a heat source—in that time, a natural gas flame—is used to drive the absorption process and release coolant from a chemical solution, instead of a mechanical compressor. An earlier version of this technology had been introduced in 1922 by Swiss inventors, and Szilard found a way to improve on their design, drawing on his expertise in thermodynamics. His heat source drove a combination of gases and liquids through three interconnected circuits: pressurized ammonia, butane, and water, with no need for electricity to operate the appliance (depending on your choice of heat source) and no moving parts.
One side contained a flask filled with butane (the evaporator), which was injected by a new vapor (the ammonia) just above the butane, creating that all-important differential. This would decrease the boiling temperature, and as the liquid water boiled off, it sapped energy from its surroundings, chilling the compartment in the process. Einstein and Szilard’s refrigerator concept never became a commercial product. The introduction of the non-toxic refrigerant, Freon, in 1930 proved more economical.