1930: Albert Einstein and fellow nuclear scientist Leo Szilard receive an American patent for a new kind of refrigerator that requires no electricity.
The most famous physicist of the 20th century wasn’t a Thomas Edison: The fridge would prove to be one of Einstein’s few forays into the world of commonplace engineering.
The refrigerator uses chemical reactions of ammonia, butane and water to turn a heat input into a cold output.
Ammonia gas is released into a chamber with liquid butane in it. This reduces the boiling point of the butane, causing it to evaporate, and draw in energy from the environment, cooling the area outside the evaporator. The mix of gases pass through to a condenser filled with water. The ammonia dissolves into the water, and the butane condenses into liquid, which sits atop the water-ammonia mixture. The butane runs back into the evaporator, a heat source is used to drive the ammonia back into gas, and the ammonia heads to the evaporator to begin the cycle again.
Though the fridge never became a commercial product, Swedish company Electrolux did license the scientific duo’s most promising patents. And in recent years, some academics have built coolers based on the cycle Einstein and Szilard described.
An Oxford team led by Malcolm McCulloch built a prototype fridge in 2008. A German group (pictured at right) also re-created the fridge, as did Georgia Tech Ph.D. student Andy Delano in 1998.
Beyond the desire to retrace Einstein’s footsteps, the refrigerator is intriguing because it doesn’t use freon or electricity, which could make it a cleaner, simpler alternative in poor countries.
“It’s basically an absorption-type refrigerator that uses ammonia, water and butane to create a chemical phenomenon that allows you to run the whole thing at a constant pressure, so you don’t need moving parts like a pump or a compressor,” Delano explained. “It provides cooling with only heat as an input. Literally, you heat one end, and the other end gets cold.”
The only problem is that compared to a modern refrigerator, Einstein’s design isn’t very efficient at cooling per unit of energy input. The Oxford team, however, thinks it can quadruple the cooling output with some tweaks to the system.
Einstein’s only other United States patent was for a “light-intensity self-adjusting camera” (.pdf) that would have correctly exposed your photos, no matter what the lighting conditions were.
Szilard was a bit more productive in the patent realm, but most of his related to nuclear reactors and assigned to the Atomic Energy Commission.
Images: 1. Nuclear physicists Albert Einstein and Leo Szilard submitted this drawing with their patent for an electricity-free refrigerator. (U.S. Patent Office)
2. Wolfgang Engels (left) and Falk Riess built a reproduction of the Einstein-Szilard refrigerator. (Courtesy Carl Von Ossietzky University of Oldenburg, Germany)
Correction: As originally posted, this article gave the wrong year for the patent and the wrong home nation for Electrolux.
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Alexis Madrigal is now a senior editor at The Atlantic. He’s the author of Powering the Dream: The History and Promise of Green Technology.