X-Message-Number: 3157 Date: 18 Sep 94 12:59:17 EDT From: "Andrew J. Clifford" <> Subject: CRYONICS SUPERCOLD REFRIGERATORS The 10th September issue of "New Scientist" carries an article (by Daniel Pendrick of Wisconsin) which details the imminent development of refrigerators capable of cooling their internal temperature to that of liquid HYDROGEN, (yes, they mean much colder than liquid nitrogen!). And further that these supercold fridges will be available for domestic use in a hydrogen powered society. These fridges are less than 10 years away from production. There is no mention of cryonics but the implications are obvious. "The principle behind the new refrigeration techniques is that some metals become hot when magnetised and cool down when demagnetised. The magnetocaloric effect. So if the metals are moved during this cycle, they can transfer heat from one place to another. The phenomenon was first discovered in 1918 and has been used by scientists since the 1920s to cool matter to temperatures close to absolute zero. But what makes magnetic refrigeration a hot topic today is the discovery earlier this year of a magnetocaloric material, an alloy made of aluminium, erbium and dysprosium, that could make these machines cheap and efficient enough to compete with conventional refrigeration techniques at liquefying hydrogen." "Conventional fridges rely on a process known as the gas-compression cycle. During this cycle, an easily liquefied gas is pumped round the fridge, absorbing heat from the inside and transferring it to outside. [..] the best gas-compression fridges are only 40 per cent efficient. But fridges using magnetic cooling do not use gases and can reach efficiencies of up to 60 per cent of the theoretical limit." The magnetic fridges also are environmentally safe as they do not use CFCs or similar substitutes. "Such systems could be available for certain niche markets within ten years says Lewis Lawton, director of the Astronautics laboratory. At present, magnetic refrigerators that work near room temperature use alloys of gadolinium, a rare-earth metal, but this costs about $500 per kilogram." "Karl Gschneidner, a materials scientist at the US Department of Energy Ames Laboratory at Iowa State university, announced that an alloy made of aluminium, erbium and dysprosium can transfer heat 30 per cent faster." [and is 75% cheaper.] Instead of improving the materials the fridges can be made to remove heat more efficiently, in stages. "The Astronautics fridge is a joint project with the US Department of Energy's Oak Ridge National Laboratory in Tennessee and together $2 million on the programme. The researchers believe that magnetic refrigeration could coot the next generation of superconducting devices to temperatures below -269 C.." The main problem with the fridges at present is heat leaking into the system until the efficiency of the cooling falls to 0% . This means the temperature reduction can only be done for a limited range, whether 20 C to -60 C or -200 C to -270 C. "The cost of building superconducting magnets is one of the main reasons why magnetic fridges are so expensive. In 1989, a study sponsored by the Department of Energy estimated that a magnetic chiller for storing milk and processed foods in supermarkets would cost about $55 000 compared with about $10 000 for a conventional chiller.". "But John Barclay, a researcher who helped build the test devices at Astronautics and now at the University of Victoria in Canada, does not believe that customers will be willing to pay so much more for a relatively small increase in efficiency. Magnetic cooling's best hope, he says, lies in liquefying gases at low temperatures. Natural gas, for example, becomes liquid at -163 C and hydrogen at -253 C. "The major advantages come when these machines span large temperature ranges," says Barclay. Further progress should see the fridges capable of cooling from room temperature to liquid hydrogen. This has significant implications for cryonics. Cooling would be simpler, cracking and damaged minimized, and the ultimate storage temperature set at an arbitrary level for optimum results. The irony is that all those jokes about patients thawing when the electricity is cut off become plausible. However, a diesel generator or solar panel backup is far easier to arrange than ones own source of liquid nitrogen in an emergency. Regards, AJC Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=3157