Whether they sit in your kitchen or inside your personal computer, refrigerators and other cooling devices are typically bulky, often noisy and frequently power-hungry. A team at Pennsylvania State University recently found that certain plastics cool off a significant amount—12 degrees Celsius—when an applied electric field is removed. Should the technique become feasible, the resulting solid-state coolers could efficiently and quietly eliminate heat from, say, integrated-circuit boards, enabling smaller, faster computers.

Engineers have long known of so-called electrocaloric substances that drop in temperature when an external electric field is withdrawn, but the amount of chilling either was too small at practical temperatures or occurred at too high a temperature to be useful. Effective chip cooling, for instance, requires reductions of at least 10 degrees C from typical operating temperatures—about 85 degrees C, says G. Dan Hutcheson, chief executive officer at VLSI Research, a microelectronics industry market research firm in Santa Clara, Calif. Computers usually require heat sinks, radiators, fans, heat pipes or even fluid-based heat pumps to extract the surplus degrees.

If successful, the new technology should be compact and at least 10 times more energy-efficient than conventional cooling techniques, according to Penn State electrical engineer Qiming Zhang, who led the team. The group found that a micron-thick film of a polyvinylidene fluo­ride co-polymer—polyvinylidene fluo­ride trifluoroethylene—heats up a dozen degrees C when zapped with 120 volts at ambient temperatures as low as 55 degrees C. Such a rise constitutes an order of magnitude improvement over other electrocaloric materials (mostly ceramics) at that temperature range.

Zhang, who in the past worked on plastic “artificial muscles” that alter shape under electric fields, says that years ago he “started thinking about melting ice into water, which is one of the most effective ways to cool objects.” That effect is based on a phase change in which an ordered system (solid ice) transforms in­to a disordered one (liquid water). In time, the scientists identified several promising polymers in which an applied voltage caused the atoms or molecules to align, thus creating greater order.

The electrocaloric materials, Zhang reports, consist of long molecular chains with a positive electric charge on one end and negative on the other. These dipolar chains, which can move around freely, are normally oriented randomly. But “when you apply an electric field, the dipoles tend to spin around until they align with the field,” he says. Thermodynamically speaking, this molecular ordering lowers the system’s entropy, so the system compensates by heating up as a consequence of energy conservation. When the field is disengaged, the chains randomize and the polymer cools off. The rigid microstructures of electrocaloric ceramics, in contrast, “can move only a little bit,” Zhang notes, which accounts for their weak temperature response. The polymers can also absorb seven times as much heat as the ceramics.

In an ideal solid-state refrigerator, a chilling cycle starts when contact breaks between the polymer and the object that is being cooled, thermally isolating the polymer. An applied electric field causes the temperature of the polymer to rise. It is then placed into momentary thermal contact with a heat sink, which absorbs any heat and entropy that the polymer has. The polymer is next isolated from the heat sink; the electric field is then lowered, which reduces the temperature of the polymer and enables it to cool the target object once again.

A workable system could in particular prove a boon for the computer industry. Silicon chips run hotter than is desirable for optimal performance, comments Benson Inkley, a senior power/thermal engineer at Intel in Hillsboro, Ore. Cooling with electrocaloric plastics offers intriguing possibilities, Inkley states: “Imagine coating an entire circuit board with a layer of polymer, in effect, forming a cooling blanket.”

3 Comments

1. 1. sci-cmjones 01:07 AM 11/1/08

   Magnetic Heat Pipes are none moving and made of co-polymers. It was estimated that a heat pipe could also be made smaller to run a wrist watch but this theory is fundamentally the same principle. The Magnetic Heat Pipe gets hot at one end and cool at the other end. Magnetism initializes the chilling cycle that transfers its heat coefficient to a anti-freeze solution chamber in the appliance with a controller to establish a artificial atmosphere resultant from the flow of the anti-freeze instead of a direct contact of the plastic-magnetic device where a failure of performance is obvious. Consider the answer as a non-moisture result with a factor for evaporation and condensation then apply each for a cycle in tubing from a chamber that is a anti-freeze container capable of carrying the cold antifreeze to the inside evaporator and the hot anti-freeze to the outside condenser. I believe this would work best in a automobile and I would like to see "artificial muscles" in automobiles as well, adding to stronger hydraulics to hold hoods open or the rear hatchbacks open and create electrical power in shock absorbers keeping them cooler during operation. Solving the riddle means using valves to flow the fluid from half the chamber always which is hot into the condenser system pipe and not allowing the other cooling chambe to flow anything, switching between chambers and Magnetci Heat Pipes will always flow a hot fluid (anti-freeze) into the condenser system, while a cooling flow will always flow the cooler fluid into the evaporator system. This requires a dual evaporator and condenser for each side of the chamber to work when the magnetic switch occurs changing the flow efficiency. This ideology is based only on two dual valve moving parts, however a swish plate valve (flat rotated valve to open access from the chamber to the piping having four ports and only two for each cycle opens) could do the trick for both dual valves in one valve, no motors are employed. Another new type valve would be inside a pipe which is activated magnetically instead of the new swish plate vale and does not have any moving parts other than sealing the pipe inside by contraction like a "artificial muscle" in a pipe to close its flow and the flow then flows the other pipe and there are still four flows to control in this mannerism.

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2. 2. sci-cmjones 02:30 AM 11/1/08

   Performing the switching cycle of the anti-freeze flow per chamber side inside a pipe using a new "artificial muscle" valve allows the cold to flow to the evaporator always and the hot flow always to the condenser so each chamber does both requiring two openings for input and output to the chamber which is a dual operation not just a single pipe being opened for that chamber flow which would blog down the flow. Similar to a solar heating unit where a pipe delivers the hot fluid to the house and the cooler fluid return to the solar panel creating no void. Flows are a function of a Closed System Hydraulic Ram Pump.
   
   Design Factors:
   1. Vertical Fall - Height difference between anti-freeze source and hydraulic ram
   2. Lift - Height difference between hydraulic ram and anti-freeze storage
   3. Quality - low available from anti-freeze source
   4. anti-freeze quality received
   5. Drive Pipe - Pipe length from anti-freeze source to hydraulic ram
   6. Delivery Pipe - Pipe length from hydraulic ram to anti-freeze storage
   
   Calculate amount of anti-freeze that can be supplied by a closed system hydraulic ram
   
   The formula is: D=(S x F x E)/L Where:
   
   D = Amount delivered in liters per 24 hours
   S = Quantity of water supplied in liters per minute
   F = The fall or height of the source above the ram in meters
   E = The efficiency of the ram (for commercial models use 0.66, for home built use 0.33 unless otherwise indicated)
   L = The lift height of the point of use above the ram in meters.
   
   This assumes a measurement which would always be recycled to the solution source chamber.
   
   Components for the Closed System Hydraulic Ram Pump
   
   1. Supply Line to direct anti-freeze to the Drive Pipe of either quality (Evaporator or Condenser). The Supply Line is required to be one pipe diameter larger than the Drive pipe.
   2. Drive Pipe must not be flexible material for maximum efficiency. Perhaps a rolled/layered Buckypaper pipe and is affixed to the surface of the refrigerator to prevent movement.
   3. Typical Range for Drive Pipe lengths. Lift starts a siphon effect and is all that is needed to start a flow of anti-freeze. A Drive Pipe length of 5 mm can therefore lift 5 cm diameter of anti-freeze.
   4. The length of the Drive Pipe is four to six times the Vertical Fall.
   5. Hydraulic Rams can be constructed using commercially available Check Valves or by fabricating Check Valves. Hydraulic Rams can be used in tandem to pump anti-freeze if one ram is not large enough to supply the need. Each Hydraulic Ram must have its own drive pipe, but all can pump through a common delivery pipe.
   6. Storage Tank - Located at a level to provide anti-freeze solution to the point of use. The size is based on the maximum demand per day.
   7. Installation requires the Hydraulic Ram to be level, securely attached to an immovable base. The pump can-not operate when submerged. The Hydraulic Ram functions on a 24 hour basis.
   
   Another interesting pump is one which is a ball socket when moved up and down in a solution forced the fluid into a lengthy tube and flows out the other end but this requires a mechanical nature as opposed to the Closed System Hydraulic Ram Pump.
   
   

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3. 3. R.Blakely 11:21 PM 7/16/11

   Pressure can change the temperature of most plastics. For example, using a piezo-material to pressurize a plastic can vary the plastic's temperature. The effect works on fluids like mineral oil also.

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