Pure Pedantry

A compressor-free refrigerator

Engineers at Penn State have developed a new method of running a refrigerator that doesn’t require a compressor. Rather, it changes the level of organization in a solid to change the temperature. This change in entropy results in heat-transfer.

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.

Aside from the issue of environmental contamination from some coolants, this technology looks like it would be really helpful in making smaller cooling elements. While the actual temperature where these experiments were performed was around 160 degrees F (70 degrees C) — a little high to use in a refrigerator, the researchers indicate that there are many different types of these polymers. Some may be functional at lower temperatures.

Interesting stuff. The actual paper is here.

Hat-tip: Slashdot


  1. #1 CRM-114
    August 12, 2008

    Smaller cooling elements, such as a mini-fridge in a cubicle? That would be nice. And quiet.

  2. #2 GrayGaffer
    August 12, 2008

    What are the advantages of this over absorption refrigeration systems? We have had those for a long time – our Electrolux in the 50’s ran on a gas pilot light, could use any heat source, and had no moving parts. RV gas-powered refrigerators also use this technology, plus have a heating coil alternative to keep cool while driving and the gas has to be turned off.

    Compressor technology holds (held?) sway for economic reasons, though we now know there are many losses not accounted for in those economics.

  3. #3 phisrow
    August 13, 2008

    I’d be very interested to see if this could be bodged into some of the places that currently use peltiers. Silent, totally solid-state heat pumps are really cool(seriously, pick up a cheap one on ebay some time, just to play with); but peltiers are annoyingly power hungry and a lot of them are rather touchy about moisture and elevated temperatures.

  4. #4 George
    August 15, 2008

    Honestly I believe they are dumbing down my trade. It is difficult for a normal person off the street to understand that the cold – suction line is coming from the house, and the hot – discharge is what’s feeding the house.
    I’m the only 4th generation refrigeration mechanic in Canada at this time. Refrigeration is literally in my blood, and it was my family that brought the trade into Canada and established it.
    The stories that they say about refrigerants poking holes in the ozone is a lot of BS. How can something heavier than air reach the ozone? All of this is because they mixed the CFC’s and HCFC’s and other refrigerants with O3 and found it broke it down doesn’t mean squat.
    Our best bets is actually to be using a more dangerous substance which was already commented on is Ammonia. What was used in RV’s that worked on a pilot light. An Ammonia absorption system, combined with micro-turbine systems are the most efficient set up I have ever seen, and can literally produce power, as well as cool an entire grocery store, and use very little natural gas.
    The other reason why they would go to a polymer is because our trade for years has been encroached upon by unqualified people, such as plumbers and sheet metal mechanics. How much easier would it be for a plumber to work with sticky goo and a few pipes? I think they’re already working on that.
    I’d like to see some more numbers, specifics to this polymer. What’s the COP? What’s the weight of the liquid? GPM? Voltage of crystallization? That’s exactly what it looks like; the polymer must crystallize in the order under a voltage to release heat. What kinds of tubing did they use, copper, stainless steel, plastic?
    This article here and its non-specifics was poorly done. Not only was it a slap in the face to anyone who truly knew the trade, but its lack of true numbers is damning.

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