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Heat Transfer: Theory and Problems by K. Mayilsamy, R. Rudramoorthy

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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 upon 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 wavelengths between 0.1 µm and 3 µm. This portion of the spectrum is known as solar radiation.

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

 

 

Figure 9.1 Incident radiation.

 

 

 

where ρ,α and τ are the reflectivity, ...

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