THERMAL-INSTABILITY OF A FLUID LAYER INDUCED BY RADIATION

The thermal instability of a fluid layer above a solid boundary induced by incident radiative heat to the upper free surface is studied numerically. Eddington approximation is adopted for the equation of transfer, and the pseudospectral method is used to solve the linearized perturbed equations. The effects of Planck number, optical thickness, Biol number, emis-sivity of the lower plate, and transmissivity of the upper surface on the transition are analyzed for gray and nonscatiering fluids. In general, decreasing the temperature difference between the lower plate and the upper surface by increasing the Planck number and the optical thickness, and by decreasing the emissivity and the transmissivity at fixed Biot number, delays the onset of instability. Biot number plays a unique role for nonra-dialing fluids, and dual roles for radiating fluids on the occurrence of instability. © 1990 by Hemisphere Publishing Corporation.