Fridges that run without electricity!

September 21st, 2008 - 4:34 pm ICT by IANS  

London, Sep 21 (IANS) An Oxford electrical engineer has come up with a refrigerator that runs without electricity. Not his own idea. He has based it on a model invented by Albert Einstein in 1930. Einstein and his colleague, Hungarian physicist Leo Szilard, patented a fridge that had no moving parts and used only pressurised gases to keep things cold.

The idea is to eventually stop using modern refrigerators, which use gas that harm the environment. They work by compressing and expanding man-made greenhouse gases called freons - far more damaging that carbon dioxide.

Almost every household in the developed world owns a fridge and its sales are rising as demand increases in developing countries.

Malcolm McCulloch, an electrical engineer at Oxford who works on green technologies, is leading a three-year project to develop fridges that can be used in places without electricity.

The Einstein-Szilard model design was partly used in the first domestic refrigerators but the technology was abandoned when more efficient compressors became popular in the 1950s.

Einstein and Szilard’s idea avoids the need for freons. It uses ammonia, butane and water and takes advantage of the fact that liquids boil at lower temperatures when the air pressure around them is lower.

“If you go to the top of Mount Everest, water boils at a much lower temperature than it does when you’re at sea level, and that’s because the pressure is much lower up there,” says McCulloch.

At one side is the evaporator, a flask that contains butane. “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,” says McCulloch. “That’s what makes it cold.”

He is not the only one interested in environment-friendly fridges. Engineers working at a Cambridge-based start-up company, Camfridge, are currently using magnetic fields, instead of gas, to cool things.

Managing director Neil Wilson says: “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.”

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