thermos

There is a clear space in the vacuum flask is the best insulator to keep the soup hot. In recent years, the team found that the theory of the photonic crystal structure is known to heat flow route can be even better than the vacuum. October Physical Review B total current theory explaining the phenomenon, and it turns out that the structure of the independent ability of the insulating surprisingly structured data. Their work suggests that photonic crystals,which have promising applications in communications and computing, might one day be used for their thermal properties, perhaps in devices that turn the sun's heat into usable energy.

Hot soup in a thermos is surrounded by a vacuum between the inner and outer walls, which prevents heat from conducting directly through the sides, as it would if the walls were a one-piece solid. But the soup still loses heat by "glowing" in infrared light because the light radiated through the walls takes energy away with itShanhui Fan of Stanford University in California and his colleagues wondered if photonic crystals--periodic structures famous for blocking narrow frequency ranges of light--could block the broad range of infrared frequencies radiated by a warm body. Last year they studied a stack of alternating silicon and vacuum layers theoretically,

calculating the thermal conductance--the ease with which infrared photons could pass through. The team evaluated different layer-thicknesses, numbers of layers, and temperatures and showed that for a 100-micron-thick stack containing 10 one-micron-thick silicon layers, at room temperature and above, the thermal conductance plunged to about half that of a vacuumSo soup in a photonic crystal thermos would stay hot longer than in a normal thermos.In their new paper, the team undertakes a complete theoretical analysis of the problem, rather than solving specific cases. Photonic crystal theorists usually calculate the narrow ranges of frequency blocked by the structure, the so-called band gaps.