A Solid-State Fridge in Your Pocket


UCLA and SRI’s solid-state chiller cools a smartphone battery by 8° C in 5 seconds. Photo: UCLA Engineering

Can you imagine an electric cooler compact enough to fit in your pocket and flexible enough to wear? If not, think again because engineers at the University of California at Los Angeles and SRI International have one working: A 5-millimeter-thick device that is the world’s first solid-state cooler combining practicality, energy efficiency, and high performance.

Solid-state cooling has become a highly-competitive field in recent years as researchers race to develop alternatives to conventional compressor-based refrigerators and air conditioners, which gobble considerable energy and rely on refrigerants that are potent greenhouse gases. In 2014 General Electric heralded a “breakthrough” using materials that heat and cool when moved near and away from magnets, enthusing that its “magnetocaloric” system could be “inside your fridge by the end of the decade.”

Other teams are exploring a myriad of alternate approaches, including “elastocaloric” materials that heat and cool in response to pressure. But the comparatively simple working device from UCLA and SRI, reported in today’s issue of the journal Sciencemay give these competitors the chills.

UCLA materials science and engineering professor Qibing Pei, who led the work, says he was motivated by the prospect of delivering personalized comfort with little energy. “It may be placed in a shoe insole or in a hat to keep a runner comfortable in the hot Southern California sun. In a way, it’s like a personal air conditioner,” says Pei.

The UCLA-SRI device relies on the electrocaloric effect, which occurs in materials whose molecules have positively and negatively charged ends. An electric field aligns the molecules, increasing the order in the material and thus increasing its temperature.

Fundamentally, it is the same thermodynamic behavior that causes a steam burn, where water condensing on your skin jumps in temperature as it morphs from a disordered gas to a comparatively orderly liquid. And the electrocaloric effect is just as reversible: Relax the electric field on the material and its temperature drops. Continue reading


Physicists Talk Tough on Efficiency and The War

I recall well a meeting of journalists at the Kennedy School of Government in 2003 where I was regarded as a wingnut + conspiracy theorist for seeing a linkage between U.S. intransigence on greenhouse gas controls and the War in Iraq. Never have I felt as alienated as an American intellectual. These days I reflect instead on how far the national conversation has come in the years since. I happened upon the latest sign of hope quite unexpectedly in a report on energy efficiency issued earlier this month by the American Physical Society: “Energy = Future. Think efficiency.” 

I’d been feeling guilty about letting the APS report pass by without a mention. Energy efficiency is a tough story for journalists — making do with less energy simply lacks the sex appeal of faster cars or new power generating technologies such as high-tech techniques for pollution-free coal power or the latest in photovoltaics. And yet, as the APS rightly points out, the U.S. is in a better position than most countries to meet its need for clean, domestic energy by squeezing a bigger bang out of every joule of energy consumed.

What will be useful about the APS report is its explicit connection between the technologies available to boost efficiency in the key sectors of transportation and buildings, and the shortcomings in science & technology policy that thwart their ready adoption or rapid adoption.

But what I really appreciated was the no-nonsense manner in which the analysis unfolds. The relatively frank prose of the executive summary (considering the genre) sets the stage for what follows:

“Nowhere is the standard of living more rooted in energy than in the United States, and, with its defense forces deployed in the most distant regions around the world, nowhere is the security of a nation more dependent on energy…Yet only in times of extreme turbulence — the OPEC (the Organization of Petroleum Exporting Countries) oil embargo in 1973, the overthrow of the shah of Iran in 1979 and the Persian Gulf War in 1991 — when public frustration became politically intolerable did American officials devote serious attention to energy policy. Although some of the policy initiatives yielded significant benefits, others were left on the drafting board as the nation reverted to a business-as-usual energy routine once the turbulence passed and public dissatisfaction dissipated.”

How refreshing. Now, let’s get to work.

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This post was created for Tech Talk – Insights into tomorrow’s technology from the editors of IEEE Spectrum.