Sci­en­tists cre­ate a pocket air con­di­tioner

Elec­tri­cal field shunts heat through a poly­mer, al­low­ing greater en­ergy ef­fi­ciency

Baltimore Sun Sunday - - NEWS - By Amina Khan

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 re­cently in a re­port 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 in­ter­ested in de­vel­op­ing the technology for con­sumers.

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