Albert EINSTEIN / Leo SZILARD
20 September 2008
Einstein fridge design can help global
Scientists relaunch a 1930 invention that uses no
electricity and would reduce greenhouse gases
An early invention by Albert Einstein has been rebuilt by
scientists at Oxford University who are trying to develop an
environmentally friendly refrigerator that runs without
Modern fridges are notoriously damaging to the environment. They
work by compressing and expanding man-made greenhouse gases called
freons - far more damaging that carbon dioxide - and are being
manufactured in increasing numbers. Sales of fridges around the
world are rising as demand increases in developing countries.
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
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 1950s. That meant a
switch to using freons.
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,' said
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
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.
'No moving parts is a real benefit because it can carry on going
without maintenance. This could have real applications in rural
areas,' he said.
McCulloch's is not the only technology to improve the
environmental credentials of fridges. Engineers working at a
Cambridge-based start-up company, Camfridge, are using magnetic
fields to cool things. 'Our fridge works, from a conceptual point
of view, in a similar way [to gas compressor fridges] but instead
of using a gas we use a magnetic field and a special metal alloy,'
said managing director Neil Wilson.
'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.' He added: '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.'
Doug Parr, chief scientist at Greenpeace UK, said creating greener
fridges was hugely important. 'If you look at developing
countries, if they're aspiring to the lifestyles that we lead,
they're going to require more cooling - whether that's air
conditioning, food cooling or freezing. Putting in place the
technologies that are both low greenhouse-gas refrigerants and low
energy use is critical.'
McCulloch's fridge is still in its early stages. 'It's very much a
prototype; this is nowhere near commercialised,' he said. 'Give us
another month and we'll have it working.
[ PDF ]
Machine frigorifique à condenseur
Machine réfrigérante avec pompage du liquide par élévation
intermittente de la pression de vapeurs
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