Radiation

  • Radiation heat transfer involves the transfer of heat by electromagnetic radiation that arises due to the temperature of the body. Radiation does not need  matter.

  • Emissive power per unit surface area: \[q = \sigma \epsilon T^4 \tag*{(Stefan's Boltzmann law)}\] where

    \(\sigma\) = Stefan-Boltzmann constant
    = \(5.67 \times 10^{-8}\) W/m\(^2\).K\(^4\)
    \(\epsilon\) = emissivity, which is a surface property
    (\(\epsilon=1\) is black body)
    \(T\) = absolute temperature of the surface (K)


    The above equation describes a gross heat emission rather than heat transfer.