Cool tool: This preliminary version of an energy-efficient magnetic fridge shows a ring-shaped 1.2-tesla magnet. The magnet can encompass a movable cylinder containing materials that heat up in the presence of a magnetic field and cool down when the field is removed. As it cools, the material absorbs heat from its surroundings.
Christian Bahl
A new magnetic-cooling system could lead to more-energy-efficient refrigerators.
Modern coolers and fridges may not cause holes in the ozone layer like their pre-1994 counterparts, but they still use greenhouse gases that are warming the planet. Their compressors also consume a lot of energy: air conditioners and refrigerators used about 340 billion kilowatt hours in 2005--nearly 30 percent of the total energy used in U.S. homes.
Researchers at the Risoe National Laboratory, in Roskilde, Denmark, are now one step closer to building a magnetic-cooling system that promises energy-efficient, environmentally friendly, and completely silent fridges. Temperatures in conventional fridges swing between −20 and 20 ºC. Achieving this 40 ºC temperature span is one of the most significant challenges with magnetic refrigeration. The Danish researchers have built a refrigerator that can vary temperature by almost 9 ºC.
This is an important step toward practical temperature spans of 40 ºC, says Nini Pryds, a senior scientist at Risoe who is leading the work. The research team is now working with Danfoss, one of the largest compressor manufacturers in the world, to build a commercial prototype; the company says that it should be ready by 2010.
Magnetic-cooling technology exploits materials that heat up when exposed to a magnetic field and cool down when the magnetic field is removed. As the material cools down, it pulls heat out of its surroundings. The larger the difference between the hottest and coldest temperatures achieved under the influence of a magnetic field, the better the material is at cooling.
Magnetic coolers have been used for years in laboratories for cryogenic temperatures tens of degrees below zero. In 1995, Ames Laboratory, in Iowa, demonstrated the first magnetic refrigerator that cooled contents in a room-temperature environment. The company used the metal gadolinium.
Since then, researchers have found many other materials that work at room temperature. The problem is that the temperature swings in all these substances is only a few degrees. "Achieving a large change of temperature is easy if you use a superconducting magnet," Pryds says. But superconducting magnets are large and require cooling themselves, making them impractical for everyday appliances such as household fridges and air conditioners. For these applications, he says, "the only way to go is a permanent magnet." Ideally, it should be a small, cheap magnet with a field of less than one tesla.
Getting large temperature spans with a permanent magnet calls for some clever engineering. Typically, it means using cooling liquids such as water. The material, with water circulating around it, is alternately placed in and out of a magnetic field. When it's in the field, it heats up. The circulating water draws heat from the material and transfers it to a heat sink. Then the magnetic field is removed, and the material, which was already being cooled by the water, cools down even more. As it cools, it absorbs heat from the water, making it cold enough to be used as the refrigerator. This hot-cold cycle is repeated over and over.
A new catalyst breaks down greenhouse gases and pollutants at room temperature.
Magnetic refrigeration promises smaller, more efficient cooling if researchers can overcome some material problems.
Energy $ vs efficiency vs Capital $
How much does it cost (Capital $) and how much (Energy $) does it save?
It would proably be best to first have the conventional condenser coils simply outdoors. Having such refrigerant plumbing running to ordinary residential refrigerators is impractical, because of the likelihood of leakage / contamination of the sealed system and/or the cost of installing / servicing?
For Temperate and Continental climates (having winter / summer seasons), why not have dual / hybrid systems?
In the colder / winter seasons, use an outdoor radiator that doesn't require as great a termperature differential? Operating more so, during the colder night, versus conventional refrigerants with indoor condenser coils for day time / hot / summer conditions?
Alternatively, use this magnetic non-hydrofluorocarbon refrigerant system to act as a "booster" ("pre-cooler"?) for the conventional system? Providing an additional degree of cooling, via non-hydrofluorocarbon refrigerant, to the conventional sealed condenser coil? Thus only needing the (less energy efficient) conventional system to operate less often and/or at a greater efficiency / reduced temperature differential?
Could cascading these new magnetic refrigerant systems, to achieve greater total temperature differential, still end up being more energy efficient than the current conventional system?
Re: Energy $ vs efficiency vs Capital $
Yes, every time I look at my refrigerator, with it's hot coils warming up my kitchen on a hot summer evening when it's cooler outside and I'm trying to cool off the house inside, I think it's idiotic. And then in the winter, when it's close to freezing outside, the fridge is still sitting in my nice natural-gas-warmed kitchen trying to keep itself cold. Or how about an air conditioner sitting up on the roof in the middle of the day in the blazing hot sun trying to cool. If I were really hot the last thing I would do is go up and sit on my roof.
There is at least one company trying to introduce smarter A/C systems, that use good old standard refrigeration technology. It's called Ice Energy. They basically make ice all night when its cooler, the greater temp. differential making the process more efficient. Then the refr. is shut down during the day, using just the ice and fans to produce the cool air. This saves about 30% of the energy and switches the energy consumed from peak to cheaper nighttime rates. Smart.
For a refrigerator, I've often thought that pulling the heat radiator off the unit and putting it outdoors would make a whole lot of sense, or alternatively, have some switchable ducting that could intake and exhaust the air from/to wherever it made the most sense given the interior/exterior air temperatures. In winter, the duct is configured to pull in cool air from outside and exhaust heated air into the house, whereas in summer it might switch from a daytime mode to a nighttime mode.
At any rate, I think there's a lot that could be done not with new technology, but rather just by smarter use of existing technology.
Environmental Cost of Materials
Going back to a story recently about the environmental cost to manufacture the battaries in hybrid engine configuations for automobiles, would there be environmental off sets in obtaining and manufacturing the components for the magnetic refrigeration system's components?
Current top HVAC compressors are very close to 60% of Carnots efficiency and operate between -40°C and +60°C flawlessly. Technology is improving year after year.
Most compressors are not optimized for efficiency or weight or size because this would require big changes in manufacturing plants, etc... but the power/volume ratio of compressors for a condensing temperature of +50°C and evaporating temperature of +10°C is around 1W/cm3 and will go up if needed, there is plenty of room for improvement.
Check a nice compressor at
http://www.aspensystems.com/minicompressor.html
Remember, a system is composed of many parts, if 1 part is 100% efficient and 10 other (were each depends on the other, only 80%), in the end effect you have a 10% efficient system (this is what magnetic refrigeration is all about).
At magnetic refrigeration, btw, you have no phase change (solid to liquid or liquid to gas) ;) Do you get the message ?
Manufacturing in the United States is in trouble. That's bad news not just for the country's economy but for the future of innovation.
This document is part of the “How-To Guide for Most Common Measurements” centralized resource portal. This tutorial provides a detailed guide for measurement and device considerations to take temperature measurements using thermocouples. Get an introduction to thermocouples, which are inexpensive sensing devices widely used with PC-based data acquisition systems. Also review some specific thermocouple examples and learn how thermocouples work and ways to integrate them into a data acquisition measurement system.
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SVE
51 Comments
magnetic coolers
I always thought the advantages of magnetic cooling were that you needed only solids - not liquids - to achieve cooling. You only needed to rotate a special solid into and out of a magnetic field with some motor on bearings to transport heat from one location to another. This kind of arrangement would be ideal for machines that have to run in vacuum at very low ambient temperatures where fluids would freeze or be impossible to seal - such as space. Fluids/gases were just a pain. And the efficiency would be improved because there were no viscosity losses like with liquid plumbing.
However, in this application, they don't need the advantages of a solid state system, fluids are not so bad at room temperatures and pressures. And they suffer the disadvantages of the magnetic cooling technology of a thermodynamic material - gadolinium? - that is not as active as the equivalent freon. Plus they still have all the other problems they mentioned like having to still use liquids to carry heat to an external radiator, just like today's refrigerators.
I dunno, it sure sounds like potentially one small advance, and lots of worse engineering problems. I wonder if it nets out positive over today's technology.
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ArtInvent
67 Comments
Re: magnetic coolers
I guess you missed the part about 60% better efficiency. Seeing as how refrigeration and AC units are easily the most power hungry electrical equipment in most homes and many industries and offices, consuming huge amounts of power and thus producing vast amounts of greenhouse gas, and being largely responsible for grid overloads during heat waves, just a single digit increase in efficiency would be worth pursuing, even if the equipment cost were increased.
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SVE
51 Comments
Re: magnetic coolers
I didn't miss that 60% part. I just don't believe it. And I don't think they were even talking about AC which would be ridiculous (kilowatts not just 100's watts cooling), just refrigerators. As far as getting a few percent more refrigerator efficiency, climb in the back and blow the dust off the coils. And if you really care, buy a unit with better insulation. Or you could wait for miracle ceramic material bathed in circulating water while moving in and out of an array of permanent magnets all with plumbing to an external heat exchanger and with pumps and motors that don't leak. Kenmore here we come.
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grosser
5 Comments
Re: magnetic coolers
You got it! No phase change, no cooling. If you magnetize or demagnetize Gd you can pump around 300J/kg. Thats it :) If you evaporate 1 kg of Isobuthane (R600) for example, you can extract around 200.000 J/kg of heat from the environment you are expanding the fluid. This is not the fairest comparison, but gives you a good idea about the problem we are talking about.
I wish the money invested in this technology could be spent in other cooling solutions with greater potential (adsorption, absorption, thermoelectric, etc...)
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