Compressor-free refrigerator may loom in the future
August 7, 2008Refrigerators and other cooling devices may one day lose their compressors and coils of piping and become solid state, according to Penn State researchers who are investigating electrically induced heat effects of some ferroelectric polymers.
"This is the first step in the development of an electric field refrigeration unit," says Qiming Zhang, distinguished professor of electrical engineering. "For the future, we can envision a flat panel refrigerator. No more coils, no more compressors, just solid polymer with appropriate heat exchangers."
Other researchers have explored magnetic field refrigeration, but electricity is more convenient.
Zhang, working with Bret Neese, graduate student, materials science and engineering; postdoctoral fellows Baojin Chu and Sheng-Guo Lu; Yong Wang, graduate student, and Eugene Furman, research associate, looked at ferroelectric polymers that exhibit temperature changes at room temperature under an electrical field. These polarpolymers include poly(vinylidene fluoride-trifluoroethylene) and poly(vinylidene fluoride-trifluoroethylene)-chlorofluoroethylene, however there are other polarpolymers that exhibit the same effect.
Conventional cooling systems, -- refrigerators or air conditioners -- rely on the properties of gases to cool and most systems use the change in density of gases at changing pressures to cool. The coolants commonly used are either harmful to people or the environment. Freon, one of the fluorochlorocarbons banned because of the damage it did to the ozone layer, was the most commonly used refrigerant. Now, a variety of coolants is available. Nevertheless, all have problems and require energy-eating compressors and lots of heating coils.
Zhang's approach uses the change form disorganized to organized that occurs in some polarpolymers when placed in an electric field. The natural state of these materials is disorganized with the various molecules randomly positioned. When electricity is applied, the molecules become highly ordered and the material gives off heat and becomes colder. When the electricity is turned off, the material reverts to its disordered state and absorbs heat.
The researchers report a change in temperature for the material of about 22.6 degrees Fahrenheit, in today's (Aug. 8) issue of Science. Repeated randomizing and ordering of the material combined with an appropriate heat exchanger could provide a wide range of heating and cooling temperatures.
"These polymers are flexible and can be used for heating and cooling, so there may be many different possible applications," said Zhang, also a faculty member of Penn State's Materials Research Institute.
Besides air conditioning and refrigeration units, applications could include heating or cooling of a variety of clothing including cooling of protective gear for fire fighters, heating of mittens and socks or shoes for athletes, sportsmen and law enforcement officer and even cooling of mascot and cartoon character costumes. Another application would be in electronics, where small amounts of the polymers could effectively cool over heating circuit boards and allow closer packing, and therefore smaller devices.
Source: Penn State
Nov 03, 2009 |
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Good to see the mascot suite over heating problem finally solved,... I mean why even mention anything other than processor and circuit cooling.
You know I keep mentioning this, but what is the material's efficiency? What about of cooling do you get for the number of watts you put in. I think Peiltier coolers are 15% efficient, compressors have gotten up to 40-60% efficient (ala Wikipedia).
In my field of photonics, we use Peltier's about the size of a small postage stamp to keep a photonic circuit at an exact temp, like 34 degrees C exactly within 1/100th of a degree, that is how we tune the frequency of the laser output (the infrared 'color'). There is a circuit that turns the direction of current flow 'backwards' to cool and 'frontwards' to heat, so with tiny temperature sensors called Thermistors and tiny amplifiers, the act together to acheive some exact temperature. The same could be done with these plastics. The key to a viable and improved device is the energy efficiency, that is to say, how many watts does it take to move X amount of calories or BTU's, however you like to call heat, is it going to actually be more efficient than mechanical refrigerators.
All we do with the freon is crowd it into a small space, decreasing orbit, and it speeds up!
Perhaps a belt of the polymer could be made, inside the fridge it leaves the field, absorbs heat, and outside in the radiator part it enters the field and liberates heat. Or alternatively perhaps beads of polymer could be pumped around in a fluid, or just keep the polymer in place and pump the heated or cooled fluid to appropriate places.
I would assume not very much but... I don't want gramps with his pacemaker dying because he went to the frig to get a sandwich.
what is the lens area?
and at what heatsink temperature does your system stabilize? is it even stable at all?
Lens Area = 750 cm2
Heatsink stablization temp time = Approx 8 minutes
Heatsink Temp = 58 degrees Celsius
I use a solar powered fountain pump to move water from the bath into a 8" diameter copper cooling coil, which moves the water down thru the 'cooling tower' and back onto the heatsink . . so there is constant flow of cooled water going on the heatsink.
Hope this helps . . .
The dirty secret of photovoltaics is that they have a half life of 12 years or so. This as to be factored into the total cost. Perhaps they can be recycled and a discount given for the new version.
http://www.youtub...CiSyI9oE
Heat is the transfer of thermal energy from one object to another; the word you're looking for is internal energy.
Nonsense.
There are many forms of internal energy. Absent chemical reactions or phase changes the most important are the rotation and translation of molecules, electrostatic potential energy and vibrational states of molecules. Bound electrons have access to only a few energy levels that are far inbetween; excited electron states do not make a significant contribution to internal energy at room temperature. Conduction band electrons in conductors can be thought of as almost free-moving in the crystal; they make a signficant contribution to the internal energy and heat conduction of those materials.
Electrons are spin-half particles. If you measure their spin the only result you can get is spin half up and spin half down. Absent a strong magnetic field those states are at the same energy level. They are not a significant way to store internal energy.
Nonsense. Compressing a gas heats it up because you are doing work on the gas. Moving a piston will on average give freon molecules an extra push when they bounce of the piston, making them bounce around faster, rotate or vibrate faster.
It's really quite easy, simply layer the material with an electrical insulator but a thermal conductor and set the layers going such that thermal energy released by an interior layer is absorbed by its adjacent layer which closer to the outside of the box. Supposing that the outer layer is cooler than the inside of the fridge then the overall heat flow should be going outside. While changing the frequency would allow you to control the heat flow and hence the temperature inside the fridge.
EDIT: I also want to add that 22.6 degrees Fahrenheit converts to -5.22 degrees Celsius, wow!
Of course we do that now with bar radiators and heat pumps but I gather we are expecting the electricity consumed by these field generators to an order of magnitude less.
Perhaps I am being overly optimistic and that the consumption of electricity will not be any less than already existing heaters and coolers. Lets hope that is not the case. If the consumption of power is no less than currently used but also is not much greater, then these things still will find plenty of applications. As the heat exchange mechanisms that may be used in conjunction with electric fields may include innocuous substances.
I do enjoy explanations that can be understood by lay peoples in all fields but I think a cost factor in terms of power consumed would not be out of order.