27 January 2009

The Einstein Refrigerator Revisited

Wikipedia tells us

The Einstein refrigerator is an absorption refrigerator which has no moving parts and requires only a heat source to operate. It was jointly invented in 1926 by Albert Einstein and his former student Leó Szilárd and patented in the US on November 11, 1930 (U.S. Patent 1,781,541 ). This is an alternative design from the original invention of 1922 by the Swedish inventors Baltzar von Platen and Carl Munters.
This Guardian article  tells us that the Einstein refrigerator still has some uses:
Now Malcolm McCulloch, an electrical engineer at Oxford who works on green technologies, is leading a three-year project to develop more robust appliances that can be used in places without electricity.
Pressurised gas fridges based around Einstein's design were replaced by freon-compressor fridges partly because Einstein and Szilard's design was not very efficient. But McCulloch thinks that by tweaking the design and replacing the types of gases used it will be possible to quadruple the efficiency. He also wants to take the idea further. The only energy input needed into the fridge is to heat a pump, and McCulloch has been working on powering this with solar energy.

 This Green Optimistic post  gives a little more detail on McCulloch's invention.
McCulloch describes the device rebuilt by him. At one side is the evaporator, a flask that contains butane gas. “If you introduce a new vapour above the butane, the liquid boiling temperature decreases and, as it boils off, it takes energy from the surroundings to do so. That’s what makes it cold”, he says.

But the fridge developed by Einstein and Szilard was inefficient with that time’s technology, so the producers passed on to using freon gas and compressors. McCulloch, on the other hand, believes that by modifying the design and replacing the gas types he uses, he will be able to obtain 4 times Einstein’s efficiency. Going a little bit further, he wants to insert a solar powered heat pump (to be green). ‘No moving parts is a real benefit because it can carry on going without maintenance. This could have real applications in rural areas,’ he says.His team has completed a prototype of a type of fridge patented in 1930 by Einstein and his colleague, the Hungarian physicist Leo Szilard. It had no moving parts and used only pressurised gases to keep things cold. The design was partly used in the first domestic refrigerators, but the technology was abandoned when more efficient compressors became popular in the 19
50s. That meant a switch to using freons.
The article goes on to discuss using  magnetic fields for cooling:
Other researchers, working at Cambridge, got the idea of cooling without adding extra energy by using magnetic fields. “Our fridge works, from a conceptual point of view, in a similar way (to freon fridges) but instead of using a gas we use a magnetic field and a special metal alloy. When the magnetic field is next to the alloy, it’s like compressing the gas, and when the magnetic field leaves, it’s like expanding the gas. This effect can be seen in rubber bands - when you stretch the band it gets hot, and when you let the band contract it gets cold.” said managing director Neil Wilson.
Another Green Optimistic post  discusses a Danish group doing work on the same topic
A group of researchers at the Technical University of Denmark’s project laboratory in Risø have discovered a cooling method that uses magnetic materials instead of electricity, reported daily free newspaper Nyhedsavisen.
The invention will allow for refrigerators to replace existing electric refrigerators in homes and businesses with a fully environmentally friendly power source. Although the first prototype will not be ready until 2010, the project’s researchers say the appliance’s cooling cycle efficiency will be 60 percent greater than that of conventional refrigerators.
The new method uses opposing magnetic fields to increase the temperature of the materials employed. The heat energy is transported through a non-volatile fluid, such as water, and then thermodynamically reversed to a cold temperature. The scientists have already been able to cool a 20° C room to 11°C using the new technology.

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