Electrocaloric refrigerator offers alternative way to cool everything from food to computers

June 26, 2017 by Lisa Zyga, Phys.org feature

(Left) Photograph of one of the twelve electrocaloric elements that form a ring. (Right) Illustration of the electrocaloric device with rotating rings. Credit: Zhang et al. ©2017 American Institute of Physics
(Phys.org)—Researchers have built an electrocaloric refrigerator the size of a beverage coaster that can generate a temperature difference of about 2 K between the hot and cold ends of the device. The cooling mechanism, which is based on the electrocaloric effect, involves alternately applying and removing an electric field to a material to increase and decrease the material's temperature, respectively. The new cooling method can potentially achieve a higher efficiency than current methods, indicating that electrocaloric cooling devices may one day replace today's refrigerators and other cooling devices.

"Compared with traditional cooling methods, the new cooling method described here has higher cooling efficiency and cooling power with a more compact size," coauthor Qiming Zhang, Distinguished Professor of Electrical Engineering and Materials Science at Pennsylvania State University, told Phys.org.

"With the continued development of electrocaloric materials, electrocaloric cooling devices have the potential to replace traditional vapor-compression-cycle-based cooling, which is widely used in air conditioners and refrigerators. Specifically, it can be used in wine chillers, computer cooling, localized climate control (distributed air conditioners), medical applications, and electric vehicles."

Zhang and his coauthors have published a paper on the electrocaloric refrigerator in a recent issue of Applied Physics Letters.

Although there have been other electrocaloric cooling devices, these devices typically use active regenerators as the heat transfer materials, and active regenerators experience heat loss due to the cyclic temperature changes they must endure. The electrocaloric device demonstrated here does not use active regenerators, which offers the potential of achieving a higher cooling efficiency and cooling power.

The new device contains multiple ceramic rings, each consisting of about a dozen coin-sized elements. Adjacent rings rotate in opposite directions at a rate of several revolutions per minute. When the elements of a ring rotate toward the hot end, an electric field is applied to the elements, causing them to eject heat. Conversely, when the elements rotate toward the cold end, the is reduced to zero, causing the elements to absorb heat. Heat is exchanged between adjacent rings rotating in opposite directions, which further cools the cold end and heats the hot end of the device.

In previous work, some of the researchers of the current study showed in simulations how the device works, and the new study marks the first time that they have experimentally demonstrated the concept. Their prototype exhibits a of 2 K between the hot and cold ends, corresponding to a regeneration factor that is on par with that of the best similar cooling devices. Since the prototype uses commercial ceramic materials and only two electrocaloric rings, the researchers expect that the device's performance can be significantly improved with better materials and additional rings. Developing ceramic materials with large electrocaloric effects is an area of active of research, and the researchers anticipate that some of these materials may be ideally suited for this type of .

"In the future, we will focus on developing electrocaloric materials (including polymer and ceramic) which can generate the electrocaloric effect at very low voltage," Zhang said. "We will also work on scaling up the current state-of-the-art electrocaloric to the commercial scale, which can be used reliably with an applied voltage of less than 200 volts."

Explore further: Cooling chips with the flip of a switch

More information: Tian Zhang et al. "An electrocaloric refrigerator with direct solid to solid regeneration." Applied Physics Letters. DOI: 10.1063/1.4986508

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5 / 5 (1) Jun 26, 2017
Escaping the physical carnot cycle efficiency limitations could certainly enable higher efficiency. I suspect however that the actual efficiency in this simple prototype isn't very good, simply because of the low temp difference achieved.

I do wish that hard numbers however would have been presented. I also wonder what the inherent efficiency limits of this type of device are, or even if they have been worked out. Note that spinning the rotors effectively consumes power not available for cooling for example. Also the efficiency of all current magnetocaloric effect materials isn't great. It would be interesting to see a study on what the theoretical efficiency limitations inherent in this type of material really are.
5 / 5 (1) Jun 27, 2017
I remember when thermo-electric coolers (pelltiers) were going to replace compressors. Didn't happen. Too power consumptive. Lets hope this isn't another dead-end. Says a lot that 100 year old tech is still the best.
5 / 5 (3) Jun 27, 2017
Escaping the physical carnot cycle efficiency limitations could certainly enable higher efficiency.

You cannot, since the Carnot cycle is not "physical" but the ideal thermodynamic cycle that is limited by conservation of energy. All the other heat pump/engine cycles approach the Carnot efficiency limits, but never reach it, because overcoming the Carnot limits would create energy out of nothing.

It would be like putting a water wheel in a stream and trying to harness all the kinetic energy of the flow without stopping it - which is patently impossible; the river must flow for the wheel to turn and therefore you can only have so much.

People who claim to surpass it are cranks and charlatans.
not rated yet Jun 28, 2017
I remember when thermo-electric coolers (pelltiers) were going to replace compressors. Didn't happen. Too power consumptive. Lets hope this isn't another dead-end. Says a lot that 100 year old tech is still the best.

They did replace compressors in all sorts of small applications like wine coolers and cold boxes, which were previously too cumbersome and expensive for having a compressor.

Peltiers are fine when you design them right. The problem is that most of the applications aren't designed in so much as they're just assembled, and the cheap styrox box with a peltier cooler in the lid only barely works.

A properly designed peltier cooler can achieve a coefficient of power above 1, meaning that it shifts as much heat as its input power, but poorly designed and built units typically get something like 0.1 for CoP, which is what people observe - the cold box won't cool anything - it only barely keeps already cold things cold.
not rated yet Jun 28, 2017
Usually those devices try to cut cost by having only one small 50 W TEC sandwiched between two undersized heatsinks, straight from the car's cigarette lighter plug. Using two or three elements in parallel at reduced voltage would improve the efficiency dramatically, but it would add maybe $25 to the parts cost, and because it would improve heat transfer you'd have to use a proper heatsink inside the box to prevent it frosting over from condensation - the small aluminium block in the lid gets too cold and the moisture inside the box freezes on it.

Jun 28, 2017
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