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Researchers publish paper about smaller temperature-reducing device

By Stephen Liu

Oct. 3, 2017 1:41 a.m.

This post was updated Oct. 4 at 6:50 p.m.

A team of UCLA engineers hope their miniature cooling device can eventually prevent heated disputes over the thermostat.

Engineers in the department of materials science and engineering developed a cooling device using a material like plastic that changes temperature in an electric field. The device, which is flexible and roughly the size of a few layers of Band-Aids, could potentially allow individuals to customize the temperature in the space around them. The engineers published the results of their research in a paper in the journal Science last month.

In the paper, the engineers showed the device could cool an overheated smartphone battery by 15 degrees Fahrenheit in five seconds. Without the device, the battery only cooled five degrees in 50 seconds at room temperature.

Qibing Pei, a professor of material science and engineering and senior author of the paper, said traditional air conditioners in buildings waste electricity because they cool large and unoccupied spaces. People also have different temperature preferences, he added.

“A lot of times we need to cool down the whole building for the few occupants to feel comfortable,” Pei said. “(Still) some people complain the room is too hot, some say it’s too cold.”

In addition to consuming a lot of electricity, air conditioning units are also bulky and require motors to pump refrigerants, said Yongho Sungtaek Ju, a professor of mechanical and aerospace engineering who also worked on the project. As the refrigerant circulates in the unit, it repeatedly absorbs heat from the cold end of the unit and transfers it to the hot end.

Ju added refrigerants are pollutants that contribute to global warming. Refrigerants leaked into the atmosphere can trap 100 times more heat than a similar mass of carbon dioxide.

In contrast, the cooling device the UCLA engineers built does not use refrigerants or mechanical pumps, Ju said. It uses a thin film that changes temperature in an electric field, a phenomenon called the electrocaloric effect. This technology has the potential to be more efficient than existing heat pumps, he added.

The electrocaloric film is composed of repeating molecules that can be aligned with an electric field, Ju said. When the field is on, the molecules align, and the film becomes hotter and can release heat. When the field is off, the molecules become disordered, and the film becomes colder and can absorb heat.

Rujun Ma, a postdoctoral researcher in materials science and engineering and a co-leading author of the paper, said the engineers inserted the film between two surfaces and applied another electric field to attract the film to either surface. This way, the film can alternate contact between the two surfaces, repeatedly transferring heat from the cold surface to the hot surface.

If the film were left stationary, then it would not be able to act as a cooling device, Ma said. Because the film moves without needing a mechanical pump, the device can be compact, he added.

“A lot of researchers worked on how to improve the material’s properties, but no one fabricated a real device,” Ma said. “Ours is the first practical device.”

Pei said he hopes to help manufacturing companies develop the device for commercial use. He added the research group is working to shrink the electrical components used to power the device.

Other researchers are studying which body parts are most sensitive to temperature, which would help the engineers decide where the device could be placed, Pei added. The device could be unnoticeable, for example, if it were built inside shoe insoles, he said.

Ziyang Zhang, a graduate student in materials science and engineering and co-leading author of the paper, said that because the device can control temperature better than ice packs, he thinks it can be useful in sports or medicine. He added he thinks making the device wearable could make it fashionable.

“It’s just so small, the film is so thin, it’s so light,” Zhang said. “Maybe in the future people can have some jacket (with the cooling device), and even (though) outside (it) is 100 degrees Fahrenheit, you can feel really cool and look cool.”

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Stephen Liu
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