28 SCIENCE REPORTER, JANUARY 2015 SHORT FEATURE S S H HORT E EA A T TUR RE E F W E know Albert Einstein as a theoretical physicist, whose name is synonymous with the Theory of relativity, E=mc 2, Photoelectric emission, Brownian motion, and so on. There is a story about Einstein that once he was asked by a reporter why he has not been associated with a famous research lab. In reply Einstein pulled out his notebook and said, “With this, my pencil and my brain, I have all the laboratory I need.” The reply shows his keen interest in theoretical physics, but how many of us know that he also worked on many more everyday tasks, like developing an energy-efficient refrigerator. Let’s go down the bylanes of history and take a look at this story. History behind Einstein’s Refrigerator In 1921, Einstein was awarded the Nobel Prize in Physics for his explanation of the photoelectric effect. From 1926 to 1933 Einstein and Leo Szilard, considered by many to be the father of the nuclear age, dedicated themselves to improving home refrigeration technology. So, why did a man with a Nobel Prize, worldwide fame, and genius intellect waste his valuable time working on such a mundane project like refrigerators. For Einstein this was a very important project. According to most accounts, while Einstein was in Germany one day in the early 1920s he came across a newspaper article that described the death of an entire family – mother, father, and their children. Apparently, they had been killed in their sleep by a poisonous coolant that had leaked out of their refrigerator. All of the coolants available in those days of refrigeration (ammonia, sulfur dioxide, and methyl chloride) were very toxic and would kill if they leaked out into the home. People were afraid to use a refrigerator. Einstein knew that there had to be a better way. So he took that challenge. Szilard was just starting his career at that time. These two great scientific minds came together and concluded that the problem with refrigeration was not just limited to the poisonous coolant. The mechanical parts of the refrigerators were the real culprit. Anyone with even the slightest mechanical experience knows that moving parts cause wear and tear on any system. Eliminate the moving parts and the system will probably never leak. As great physicists, these two men realized that they could use their knowledge of thermodynamics to produce a cooling system that did not involve any type of mechanical motion. And finally, they came up with a refrigerator without any moving parts, which was a unique piece of work. Now let’s see how a refrigerator works. The main principle behind a refrigerator is based on the second law of thermodynamics according to which without any external work heat cannot flow from a lower temperature to a higher temperature. Here refrigeration DHRUBAJYOTI CHATTOPADHYAY temperatures (sink) and for this external work is required. On the basis of this external work, refrigerator system is of two types – Vapor Compression Type and Vapor Absorption Type. In compression type the input energy is electricity and the energy consuming element is the compressor. On the other hand, in the absorption type refrigerator the input energy is low-grade energy like heat. Here compressor is absent, a pump acts as the energy-consuming element. In both cases two types of working pressure are being created. In the evaporator the pressure becomes very low, as a result liquid transforms to gas by absorbing latent heat which creates the refrigeration effect. When it moves to the compressor the pressure increases and the gas loses heat to its surroundings and becomes liquid. This liquid comes again to the expansion device through the throttle valve. In this way it works in a cyclic order. This is the working principle of a refrigerator. cycle is the reverse of the Carnot cycle. Carnot cycle is the heat engine which takes heat from higher temperature (source), converts some portion of this heat to work and releases the rest to the sink. Refrigeration cycle is also a heat engine which takes the heat from a lower temperature (source) to higher Einstein and Szilard Higher Temperature Work Lower Temperature Refrigerator Cycle Carnot Cycle The idea that had been gathering dust for 70 years was resurrected recently when Andy Delano started research into Albert Einstein’s work and produced some chilling results.