Switching of heating and cooling modes using thermal radiation films

Abstract

We study emissivity (epsilon)-dependent radiative heat transfer phenomena in remote and contact configurations. To demonstrate the emissivity-dependent radiative heating mode in a remote configuration, we fabricated miniature greenhouses covered with low (0.34)and high-epsilon (0.86) polyethylene films and monitored temperatures on the floors, insides, and covers of the greenhouses during 24 h. The high-epsilon greenhouse yielded a 9 degrees C increase in floor temperature relative to the low-epsilon greenhouse at a one-sun solar irradiance because the high-epsilon film effectively trapped floor radiation. In contrast, the cover temperature remained lower in the high-epsilon greenhouse due to intensified radiation released from the high-epsilon film. This self-cooling effect was more evident when an emissive film was in physical contact with an object. While bare copper heated up to 55 degrees C, a high-epsilon film coated copper substrate was kept cooler by 4 and 2 degrees C compared with the bare and low-epsilon film coated copper samples, respectively.