Short Eaturre

SHORTHORT FEATUREEATURE DHRUBAJYOTI CHATTOPADHYAY

E know Albert Einstein as a The idea that had been Wtheoretical physicist, whose name gathering dust for 70 years is synonymous with the Theory of relativity, E=mc2, Photoelectric emission, was resurrected recently Brownian motion, and so on. There is when Andy Delano started a story about Einstein that once he was research into Albert Einstein’s asked by a reporter why he has not been work and produced some associated with a famous research lab. In reply Einstein pulled out his notebook chilling results. Einstein and Szilard and said, “With this, my pencil and my Szilard was just starting his career temperatures (sink) and for this external brain, I have all the laboratory I need.” at that time. These two great scientific work is required. The reply shows his keen interest minds came together and concluded that On the basis of this external work, in theoretical physics, but how many of the problem with refrigeration was not refrigerator system is of two types – us know that he also worked on many just limited to the poisonous coolant. The Vapor Compression Type and Vapor more everyday tasks, like developing mechanical parts of the refrigerators were Absorption Type. the real culprit. Anyone with even the an energy-efficient refrigerator. Let’s go In compression type the input energy slightest mechanical experience knows down the bylanes of history and take a is electricity and the energy consuming that moving parts cause wear and tear on look at this story. element is the compressor. On the other any system. Eliminate the moving parts hand, in the absorption type refrigerator and the system will probably never leak. History behind Einstein’s the input energy is low-grade energy like Refrigerator As great physicists, these two heat. Here compressor is absent, a pump men realized that they could use their In 1921, Einstein was awarded the Nobel acts as the energy-consuming element. knowledge of thermodynamics to produce Prize in Physics for his explanation of the In both cases two types of working a cooling system that did not involve any photoelectric effect. From 1926 to 1933 pressure are being created. In the type of mechanical motion. And finally, Einstein and Leo Szilard, considered by evaporator the pressure becomes very they came up with a refrigerator without many to be the father of the nuclear age, low, as a result liquid transforms to gas any moving parts, which was a unique dedicated themselves to improving home by absorbing latent heat which creates piece of work. refrigeration technology. So, why did a the refrigeration effect. When it moves man with a Nobel Prize, worldwide fame, Now let’s see how a refrigerator to the compressor the pressure increases and genius intellect waste his valuable works. The main principle behind a and the gas loses heat to its surroundings time working on such a mundane project refrigerator is based on the second law and becomes liquid. This liquid comes like refrigerators. of thermodynamics according to which again to the expansion device through the without any external work heat cannot throttle valve. In this way it works in a For Einstein this was a very flow from a lower temperature to a cyclic order. This is the working principle important project. According to most higher temperature. Here refrigeration of a refrigerator. accounts, while Einstein was in Germany cycle is the reverse one day in the early 1920s he came across of the Carnot cycle. a newspaper article that described the Carnot cycle is the Higher death of an entire family – mother, father, heat engine which Temperature and their children. Apparently, they had takes heat from been killed in their sleep by a poisonous higher temperature coolant that had leaked out of their (source), converts Carnot refrigerator. some portion of this Cycle Work All of the coolants available in those heat to work and days of refrigeration (ammonia, sulfur releases the rest to the Refrigerator Cycle dioxide, and methyl chloride) were very sink. Refrigeration Lower toxic and would kill if they leaked out cycle is also a heat Temperature into the home. People were afraid to use engine which takes a refrigerator. Einstein knew that there the heat from a had to be a better way. So he took that lower temperature challenge. (source) to higher SCIENCE REPORTER, JANUARY 2015 28 SHORT FEATURE ammonia generator chamber and will Diagram of Einstein’s be heated by the external heat (the input of this system). This ammonia will mix Refrigerator again to form a butane ammonia mixture. In this way the cycle will go on.

What happened to the Einstein-Szilard Refrigerator? Einstein and Szilard had to overcome many challenges. Some of the designs were too noisy, some not as efficient as they would have liked. Still, they received 45 patents in six countries for refrigeration technology. Yet none of their inventions ever reached the customers. The project was dropped for a number of reasons. The worldwide depression certainly didn’t help things. But the 1930 invention of Freon was the real killer of the Einstein- Szilard refrigerator. Freon was a non- toxic refrigerant, so the danger of leaking was eliminated. There was no longer a need to redesign the refrigerator. Though the commercial production of this refrigerator stopped, the pump was later incorporated into the cooling systems of nuclear breeder reactors. Is the Einstein-Szilard refrigerator relevant today only from the historical point of view? Times have changed. A refrigerator that lasts 100 years and uses Science Behind Einstein’s less energy looks highly attractive today Refrigerator In conventional refrigerators, two as we are trying to discover ways to It is a single pressure absorption type operating pressures work. A refrigerant evaporates at a temperature-dependent live with more efficient, less disposable refrigerator. Here butane is used as things. Besides, the coolant Freon is now refrigerant, ammonia as pressure pressure. Evaporation absorbs heat from whatever is being cooled, and the vapor recognized as a serious environmental controlling agent and water as absorbing hazard. So, are there any chances that fluid. In any absorbing refrigerator, two flows to a compressor. In Einstein’s refrigerator, in the evaporator they used Einstein’s refrigerator may come back in fluids are required, one for refrigerant some modified way? and another as absorbent. For example, in a mixture of ammonia and butane. Let the the ammonia-water cycle, ammonia is the pressure of the system is Ps, and partial It just might be. Actually, The idea refrigerant and water is the absorbent. pressure of ammonia be Pa and butane that had been gathering dust for 70 years In Einstein’s refrigerator, Einstein be Pb. Then P=Pa+Pb. Here butane was resurrected recently when Andy and Leo Szilard used two flow loops changes its phase (from liquid to gas) Delano, a Georgia Tech graduate, started (ammonia flow loop and water flow due to its own partial pressure Pb and research into Albert Einstein’s work and loop) and three fluids (ammonia, water creates the cooling effect and ammonia produced some chilling results. In 2008, and butane) and successfully avoided act ass pressure equalizer. The expansion “Time” honored scientists at Oxford the moving parts by applying their of butane (liquid state to a gaseous state) University – led by engineer Dr. Malcolm knowledge of physics. With the standard acts as a pump and helps to flow the moist McCulloch – with a “best invention” working fluids, a water-flow loop serves ammonia to another loop. award for new research based on the as an ammonia pump, and the ammonia- In the condenser the ammonia gets Einstein-Szilárd designs. flow loop serves as a butane pump. dissolved in water, as a result the partial Although it’s more than 80 years Ammonia and water are suitable choices pressure of butane increases, which helps old, the Einstein refrigerator could be one because ammonia is highly soluble in to change its phase (gaseous to liquid). As example of an idea that is relevant today. water and its solubility declines steeply it is insoluble in water, it floats over it and Mr Dhrubajyoti Chattopadhyay is Education Offi cer, ammonia will act as a pump to move it to with increasing temperature. Butane is a North Bengal Science Centre (Under National the other loop. suitable choice for the refrigerant because Council of Science Museums), P.O. Matigara, it has a suitably low boiling point and is On the other hand, the mixture Siliguri, Dist. Darjeeling, West Bengal-734010; virtually insoluble in water. of ammonia water will move into the Email: [email protected] 29 SCIENCE REPORTER, JANUARY 2015