The Einstein refrigerator is a single-pressure absorption refrigerator, which has no moving parts and requires only a heat source to operate. Unlike the most familiar single pressure cycle using ammonia as the refrigerant, the Einstein refrigeration cycle uses butane. Its most marketable quality is that it does not require electricity to operate, being able to be powered by a small gas burner or solar energy. This makes it highly attractive in remote areas with no access to the electricity grid.

It was this attribute of the Einstein refrigerator that revived interest in it. In late 2008, Malcolm McCulloch of Oxford University’s Department of Engineering Science started a three-year project to develop more robust appliances that could be used in places without access to electricity, with his team having completed a prototype Einstein refrigerator. The team aspires to quadruple the refrigerator’s efficiency by improving the design and changing the types of gasses used. This opens new doors to a possible application in the future, as the original patents on the design by Einstein were bought by manufacturers developing competing refrigeration technologies.

The Einstein refrigeration cycle

The Einstein refrigerator is a single-pressure absorption refrigerator using three working fluids at a single pressure. Single-pressure cycle machines achieve cooling by lowering the partial pressure of the refrigerant thus allowing it to evaporate.

The most well-known single pressure cycle is the ammonia-water-hydrogen cycle, patented by Platen and Munters in 1928, which utilises ammonia as the refrigerant and water as the absorbent. The water separates the ammonia from the inert gas, hydrogen. Unlike the Platen and Munters cycle, the Einstein cycle uses the hydrocarbon butane as the refrigerant, ammonia as the pressure-equalising fluid and water as the absorbing fluid. Ammonia now acts as an inert gas to lower the partial pressure over the refrigerant, butane, while water later provides separation by absorbing the ammonia.

Previous work on the Einstein refrigeration cycle & alternative refrigerants

It is not the first time the Einstein refrigeration cycle attracts attention. In 1998, it had been the subject of research for Andrew Delano, a Georgia Institute of Technology graduate student.
 
Delano developed general criteria for working fluids of the cycle, which originally used butane, ammonia, and water, as the refrigerant fluid, the inert fluid, and the absorbing fluid respectively. The study found that while water was possibly the best absorbing fluid, viable alternatives existed for the refrigerant and absorbing fluids. The hydrocarbons iso-butane, n-pentane, iso-pentane, and neo-pentane were studied as alternatives to the n-butane refrigerant fluid. Calculations made for a base case found that the iso-butane, ammonia, water cycle produces the highest coefficient of performance.

Finally, Delano used his analytical model as a guide to build and successfully operate a conceptual demonstration prototype which was charged with ammonia, water, and butane.

Background

Assuming that a device without moving parts would eliminate the potential for seal failure, Einstein and Leo Szilard collaborated on exploring practical applications for different refrigeration cycles. Their work, carried out between 1926 and 1933, eventually accrued 45 patents for three different models. The most promising patents were quickly bought by the Swedish company AB Electrolux to protect its refrigeration technology from competition.