Flexible Cooling Strip Breakthrough for Heat Removal

Promo image. UCLA Engineering

Imagine using your personal cooling pad to remain fresh and composed at work, while the company saves energy and money be setting the air conditioning to what would otherwise be somewhat uncomfortable temperatures. Cooling clothing would be welcome for a jog on a hot day. And a cooling strip in the brim of a Panama hat might be key to surviving as we experience more days that push temperatures into the danger zone, where a human cannot maintain a safe body temperature with its own cooling tricks.

Unfortunately, current refrigeration solutions have many drawbacks, not least of which is that they serve poorly in the types of applications envisioned above. So news that engineers and scientists from UCLA and SRI International, a nonprofit research and development organization, have announced a breakthrough in the use of solid materials for cooling comes like a refreshing breeze.

The phenomenon of using solid materials that display temperature changes when an electric field is turned on or off, known as the electrocaloric effect, has been studied for decades. But lack of efficiency has killed any potential for practical cooling applications.

Most cooling relies on gases that can be compressed into liquids, because the rapid expansion of a gas creates a powerful cooling effect.This effect arises based on the relative order (or disorder) of the system -- you may remember the word "entropy" bandied about in high school chemistry as the official technical word to describe the extent of order or disorder.

In the case of a gas cooled to a liquid, the liquid represents a higher degree of order - the molecules have less freedom to move about within the liquid state. When the molecules that inherently crave to fly free are released by removing the pressure from the liquid, they quickly suck heat out of the surrounding environment in order to fuel their flight to greater freedom.

The theory is similar in the electrocaloric effect. The application of an electric field (i.e. turning it "on") causes the arrangement of molecules in a polymer film to change between lower and higher entropy levels. The problem has been getting enough of a change in entropy and harvesting the temperature differential efficiently enough to achieve a useful amount of cooling.

The UCLA/SRI team reports that their "EC [electrocaloric] device produced a specific cooling power of 2.8 watts per gram and a COP [coefficient of performance] of 13. The team considers this efficient enough to apply for a patent and start dreaming of cool new cooling solutions.

In addition to revolutionizing personal cooling, this technology could enable breakthroughs in electronics by offering a solution to the constant challenge of removing heat as systems get smaller and faster.

The study is published in Science magazine: Highly efficient electrocaloric cooling with electrostatic actuation
DOI: 10.1126/science.aan5980