Pos­si­ble Re­place­ment For Con­ven­tional Cool­ing Meth­ods.

Chemical Industry Digest - - New Developments -

Re­searchers

from Columbia Univer­sity have cre­ated a high-per­for­mance, pas­sive day­time ra­dioac­tive cool­ing (PDRC) poly­mer coat­ing with nano-to-mi­croscale air voids that act as a spon­ta­neous air cooler and can be fab­ri­cated, dyed or painted on rooftops, build­ings, wa­ter tanks and ve­hi­cles to cool them down. The air voids, cools down the sur­face by re­flect­ing sun­light and ra­di­at­ing heat to the colder at­mos­phere.

This new de­sign is an ex­ten­sion of pre­vi­ous re­search, where the group found that sim­ple plas­tics and poly­mers like acrylic, sil­i­cone and PET are good heat ra­di­a­tors that could be used for PDRCs. To over­come the dif­fi­culty of the us­age of sil­ver mir­rors as re­flec­tors in nor­mal trans­par­ent poly­mers, the re­searchers used a so­lu­tion-based phase-in­ver­sion tech­nique to give the poly­mer a por­ous foam-like struc­ture, al­low­ing the air voids to scat­ter and re­flect sun­light be­cause of the dif­fer­ence in the re­frac­tive in­dex be­tween the air voids and the sur­round­ing poly­mer. The poly­mer then turns white to avoid so­lar heat­ing while its in­trin­sic emit­tance causes it to ef­fi­ciently lose heat to the sky.

The re­searchers found that the poly­mer coat­ings had a so­lar re­flectance (R) above 96 per­cent and a ther­mal emit­tance at about 97 per­cent, which kept the sur­face sig­nif­i­cantly cooler than its en­vi­ron­ment un­der dif­fer­ent con­di­tions. The poly­mer was six de­grees Cel­sius cooler in the desert of Ari­zona and three de­grees CCel­sius cooler in the trop­i­cal cli­mate of Bangladesh.

This can also be a re­place­ment for con­ven­tional coolin­ing meth­ods like air con­di­tion­ing which can be ex­penssive, re­quire sub­stan­tial amount of en­ergy and have a strong green house ef­fect. The re­searchers are now re­fin­ing the de­sign so it can be bet­ter ap­plied, while also ex­plor­ing other pos­si­bil­i­ties like the use of com­pletely bio­com­pat­i­ble poly­mers and sol­vents.

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