Computational fluid dynamics studies of fixed bed heat transfer

Fluid flow and heat transfer in a fixed bed of tube to particle ratio 2.86 were studied by solving the 3D Navier-Stokes and energy equations using a commercial finite element code, ANSYS/FLOTRAN. The geometry model consisted of an arrangement of eight spheres. Boundary conditions were given at the wall and the inlet, similar to an experimental setup, to determine the velocity and temperature at various locations. The main objective of this study was to use computational fluid dynamics (CFD) to obtain values for the dimensionless wall heat transfer coefficient, Nu(w) and the radial effective thermal conductivity ratio, k(r)/k(f) using air as the fluid. Nu(w) and k(r)/k(f) were evaluated from the calculated temperatures at different locations in the bed by fitting these with the analytical solution of the usual two-dimensional pseudo-homogeneous model, using a non-linear least squares analysis. Results were obtained for Reynolds numbers in the range 9-1450. The Nu(w) and k(r)/k(f) values showed reasonable qualitative agreement with both experimental values and values predicted by a model-matching theory based on experimental measurements. Studies were also carried out to verify the depth, pressure and wall temperature dependence of the effective heal parameters. The effect of the temperature profile measurement position above the bed on the estimated parameters, was investigated. (C) 1998 Elsevier Science S.A.