9

Radiation Heat Transfer

The transfer of heat energy by radiation based on electromagnetic waves has several unique characteristics. A medium is not required for radiant heat transfer. The amount of radiation and the quality of the radiation depend on temperature. It is propagated at the speed of light (3 × 108 m/s) in vacuum. The wavelength range of thermal radiation is 0.1−100 μm. The Sun emits radiation in wave lengths between 0.1 μm and 3 μm. This portion of the spectrum is known as solar radiation.

Let Qr, Qa, and Qt are the fractions of incident radiation energy Qi on a surface which are reflected, absorbed, and transmitted, respectively, as shown in Fig. 9.1.

 

 

Figure 9.1 Incident Radiation

 

 

where ρ, a, and τare reflectivity, ...

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