In 1930, Albert Einstein and another physicist patented a refrigerator with no moving parts; why did their invention never reach your kitchen?

A refrigerator usually works quietly in the background, keeping food cold while electricity powers the machinery hidden behind it. But nearly a century ago, Albert Einstein and physicist Leo Szilard imagined a very different way to make cold. Their refrigerator had no electric motor, no pump and no compressor. Instead, it relied on a carefully arranged cycle involving ammonia, butane, water and heat, as per a report by Wired.

The idea was strikingly simple in principle. Heat went into one part of the system, while another part became cold. Yet despite the involvement of one of the most famous physicists in history, the refrigerator never became a commercial product.

So what happened to Einstein and Szilard's unusual refrigerator?

How did Albert Einstein's refrigerator work?

The basic principle described in the patent was based on an absorption refrigeration cycle. Liquid butane was placed inside an evaporator, the part of the system located in the chamber that needed to be cooled. Ammonia gas was introduced into the evaporator alongside the butane.

The presence of ammonia reduced the partial pressure of the butane. That allowed the butane to evaporate. As it changed from liquid to gas, it absorbed heat from its surroundings, producing the cooling effect. The resulting mixture of butane vapor and ammonia then moved into a condenser.

There, the gases came into contact with water. Ammonia is highly soluble in water, while butane is comparatively insoluble. The ammonia therefore dissolved into the water, separating it from the butane.

The butane could then condense back into liquid form. Because liquid butane was lighter than the ammonia-water solution, the two liquids separated, with the butane floating above the solution.

The liquid butane then returned to the evaporator, ready to begin the cycle again.

Why did it need no compressor?

The unusual feature of the design was the way it moved the different substances through the system. Instead of relying on a mechanical pump or compressor, the apparatus used gravity, heat and differences in pressure to keep the cycle going.

The ammonia-water solution flowed from the condenser toward the generator. Heat applied to the generator drove ammonia out of the solution and turned it back into gas. That ammonia travelled through a conduit toward the evaporator, where it once again lowered the partial pressure of the butane and allowed the refrigerant to evaporate.

Meanwhile, weak ammonia-water solution was moved back toward the condenser. Additional heating created vapor that helped lift liquid through the system.



The patent also described heat exchange between the hot weak solution and the cooler strong solution. The weak solution was further cooled by water before reaching the condenser, preparing it to absorb ammonia again.

In this way, the system could continue circulating its working substances without the conventional moving machinery found in an ordinary refrigerator.

Leo Szilard later explained the attraction of the design in simple terms.

"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."

Why didn't Einstein's refrigerator become common?

The biggest problem was efficiency. Although Einstein and Szilard's design could produce refrigeration without electricity or mechanical moving parts, it did not cool as efficiently as a modern refrigerator for the amount of energy supplied. That limitation helped keep the invention from becoming a commercial refrigerator. The idea did not disappear completely, however. Swedish company Electrolux licensed the scientific duo's most promising patents, even though the refrigerator itself never became a commercial product.

Decades later, researchers and engineers became interested in the design again.

An Oxford team led by Malcolm McCulloch constructed a prototype refrigerator in 2008. A German group also recreated the refrigerator, while Georgia Tech Ph.D. student Andy Delano had built another version in 1998.

The renewed interest was not simply about reproducing something connected to Einstein. The design had another potential advantage: it did not require freon or electricity.

That raised the possibility of using the basic refrigeration concept as a simpler alternative in poorer countries, where access to electricity can be limited.

The Oxford team also believed the system could be improved substantially. According to the supplied account, the researchers thought modifications could quadruple the cooling output.

What did Einstein and Szilard actually patent?

The patent described a refrigeration apparatus built around a generator, condenser, evaporator and container connected by conduits. The generator contained ammonia dissolved in water. Heat expelled the ammonia from the solution, sending it toward the evaporator. Inside the evaporator, the ammonia interacted with liquid butane. The resulting evaporation of butane absorbed heat, creating refrigeration.

The butane and ammonia mixture then travelled to the condenser. Water absorbed the ammonia, allowing the butane to condense and return to the evaporator.

The patent also specified arrangements designed to maintain the movement of the fluids through gravity, liquid columns and heat.

The result was a refrigeration system that could operate without the familiar mechanical components associated with conventional refrigerators.

The invention was patented in the United States on November 11, 1930, giving Einstein one of his relatively few ventures into practical engineering.

His other United States patent concerned a light-intensity self-adjusting camera designed to produce correctly exposed photographs under different lighting conditions.

Szilard had more patents, although many of his later patent activities were connected with nuclear reactors and were assigned to the Atomic Energy Commission.

Einstein's refrigerator therefore stands out as an unusual chapter in his career. A scientist famous for highly theoretical physics had turned his attention to something far more ordinary: keeping things cold.

The refrigerator ultimately did not become the appliance found in homes. Its efficiency remained a significant disadvantage compared with modern refrigeration.

Yet the concept continued to attract attention because of what it demonstrated. By combining chemical absorption, gravity, pressure and heat, Einstein and Szilard created a refrigeration system capable of producing cold without electricity-driven moving machinery.

Nearly a century later, researchers were still rebuilding and examining the design.

The refrigerator may never have reached the kitchen, but the underlying idea survived as an intriguing example of Einstein stepping outside his better-known world of theoretical physics and into the practical problem of refrigeration.

Source: REFRIGERATION Filed Dec. 16 1927 Patented Nov. 11, 1930 UNITED STATES PATENT OFFICE ALBERT EINSTEIN, OF BERLIN, AND LEO SZILARD, OF BERI IN-WILMERSDORF, GER- MANY, ASSIGNORS TO ELECT-ROLUX SERVEL CORPORATION, OF NEW YORK, N. Y., .A.

FAQs

Why did Einstein’s refrigerator never become common?
It was less efficient than modern refrigerators, producing less cooling for the energy used.

How did Einstein’s refrigerator work without moving parts?
It used ammonia, butane, water, gravity and heat to keep the refrigeration cycle moving.