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Keywords:

  • radiation;
  • heat transfer;
  • energy equation;
  • optical thickness;
  • blackbody

Abstract

The transient changes in the temperature of a solid material heated by radiation were obtained by numerical calculations using an unsteady one-dimensional (1-D) energy equation. The radiative loss of heat from the surface of a heated solid increases with an increase in the radiation flux. Therefore, the net blackbody radiation into a semi-infinite solid keeps a higher proportion of the initial flux at a lower dimensionless initial flux I0(0)/αk(Tb − T0). In the case of bidirectional radiation to a finite solid, the relatively homogeneous heating can be accomplished at the optical thickness αL ≅ 100. The heating rate is very low at αL ≲ 10−1 resulting from the absorption of a small part of the radiation energy. On the other hand, the heating rate is high at αL ≳ 101, but the heating is limited to a region near the wall, which results in an inhomogeneous temperature profile. At αL ≳ 102, the temperature profiles become identical with that obtained for αL [RIGHTWARDS ARROW] ∞. © 2005 American Institute of Chemical Engineers AIChE J, 2006