Application and exploitation of radiative properties

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The fact that real materials are not gray can be used as an advantage. Some materials, such as white paint, naturally have major changes in absorptivity and emissivity with wavelength. It is also possible to tailor materials to enhance the wavelength dependence. This is commonly done by placing thin oxide coatings on a highly polished metallic substrate. At short wavelengths, the oxide layer is highly absorbing, while at longer wavelengths, the radiation penetrates the layer, and the absorptivity takes on the low absorptivity of the metallic substrate. The transition from high to low absorptivity for such surfaces can be quite abrupt; the wavelength at which the transition occurs is called the cutoff wavelength.


Spacecraft thermal design

Because spacecraft operate in the vacuum of space, convection and conduction exchanges with the environment are not possible, and radiative exchange is the only available mechanism for energy transfer. Spacecraft are exposed to solar energy except when in the Earth's shadow, so they generally absorb solar energy through part of their orbit unless they are actively oriented to minimize solar absorption. Controlling the temperature of a satellite requires a careful balance between absorbed and emitted radiation.

See Main Article Spacecraft thermal design

Solar thermal energy collectors

So called flat plate collectors are used to gather thermal energy, such as those employed for swimming pool heating, domestic hot water production, residential and commercial building heating, and possibly for use with thermally-driven cooling cycles. The collector is made up of an absorber plate, which absorbs the solar radiation, and transfers it to a fluid flowing through channels in the plate. These are often of fin-tube design. For low temperatures such as for swimming pool heaters, the absorber surface is often uncovered. For intermediate to higher temperatures, convective losses to the environment become significant, and a transparent cover plate may be placed above the absorber plate to add additional resistance to losses. The back of the collector is insulated.

See Main Article Solar thermal energy collectors

Selective surface for radiation

In certain applications, it is desired to minimize solar absorption while maximizing radiative loss from a surface. This is the case in hot climates, where rooftops may be painted white to minimize solar absorption.

See Main Article Selective surface for radiation


Faghri, A., Zhang, Y., and Howell, J. R., 2010, Advanced Heat and Mass Transfer, Global Digital Press, Columbia, MO.

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