TRANSIENT CONJUGATED HEAT-TRANSFER ANALYSIS FROM A SPHERE WITH NONLINEAR BOUNDARY-CONDITIONS

The problem of conjugate unsteady convective and radiative heat transf er from a solid spherical particle is numerically investigated for Rey nolds numbers up to 100 using a Chebyshev-Legendre spectral method. Th e treatment of nonlinear boundary condition of the radiation heat tran sfer from the sphere surface is assessed and successfully implemented. This work is an extension of the previous effort of simulating flow a round a sphere using spectral method to include heat transfer. The ass umption of quasi-steady flow field for the unsteady heat transfer calc ulation is compared with the fully transient treatment of both the flo w and the temperature fields. It is found that the quasi-steady assump tion underestimates the overall heat transfer rate at very early time stages (up to 9% underestimation for the mean Nusselt number). However , the discrepancy becomes smaller as time elapses. The underprediction of the quasi-steady assumption becomes larger as the Reynolds number increases for a fixed Prandtl number. The results for different altern ate radiation-conduction number cases are presented. (C) 1994 Academic Press, Inc.