Imagine being able to put an air conditioner in your pocket or never worrying about your smartphone overheating again. Those dreams could one day be reality, thanks to a pocket-sized cooler developed by researchers at UCLA.
The tiny device, described in the journal Science, could potentially be used to build quieter, more energy-efficient and environmentally friendly cooling systems.
Current air conditioners are loud, heavy and not exactly green; they put a lot of carbon dioxide into the air and typically involve pumping refrigerant fluids that are not good for the environment if a unit is broken or improperly disposed of. Newer devices called thermoelectric coolers need costly ceramic materials, and they don't appear to cool things as efficiently as those traditional vapor-compression devices.
But the new device takes advantage of electrocaloric effects, harnessing an electric field to shunt unwanted heat through specially designed materials, said senior author Qibing Pei, a UCLA materials scientist.
Pei and his colleagues used a polymer with special properties and layered it in an open space between a heat source (the part you want to be cool) and a heat sink (the part that takes in all the unwanted heat). When that polymer is touching the sink, the scientists apply an electric field, causing the polymer's molecules to line up in an orderly fashion — reducing its entropy, or disorder. This forces heat out of the polymer layer and into the heat sink. Then the scientists move the polymer to the heat source side and take away the electric field, allowing the ordered molecules to relax and the temperature to drop. The cooled polymer can now absorb more heat from the source, cooling it down, and then move back to the sink and repeat the process all over again.
This technology is very energy efficient, but there's another reason it could potentially be less costly and better for the environment. Current air conditioners also work by cooling a large space, Pei pointed out. But that's wasteful, because people don't need a whole building cooled, he pointed out.
"When you turn on the air conditioner in your house, you only need to cool down yourself … it's a huge energy waste," Pei said.
By taking a different strategy — like placing a small cooling device on a person's seat, and cooling individuals rather than spaces — companies could potentially cut down the costs of their office A/C bills.
The researchers were able to build the cooling device out of a flexible material and attach it to a Samsung Galaxy S4 battery, cooling it by a whopping 8 degrees Celsius (or 14.4 degrees Fahrenheit) in just five seconds. Compare that to air-cooling the battery, which dipped only by 3 degrees Celsius in 50 seconds.
"Overheating of smartphone batteries under high workloads creates a fire hazard, and prolonged use under thermal overload causes reduced battery lifetime and fatigue of other materials and components in the smartphone," the study authors wrote. "Our flexible cooling approach could help mitigate this problem."
This device could be used in a number of different ways, said Qiming Zhang, a materials and device engineer who was not involved in the research. It could be used as comfort cooling devices in wearable electronics, or used for therapeutic cooling devices for physical inflammation and injury. It could be deployed in homes and office buildings, and used in laboratories. And of course, it can be used to cool electronics like phones and laptops safely and quietly.
"It's pretty exciting," said Zhang, who co-wrote a commentary on the paper. "This is a good first step."
The next step, Pei said, may involve finding companies who are interested in further developing this kind of technology for consumers.
MORE IN SCIENCE