The influence of the temperature profile on the fluid flow and heat transfer in a fixed bed of tube to particle ratio of 2.86 was studied by solving the 3D Navier-Stokes and energy equations by means of a commercial finite element code, ANSYS/FLOTRAN. The geometry model, representing a fixed bed, consisted of an arrangement of eight spheres in a tube. The difference in heat-transfer parameters between a wall-cooled and wall-heated reactor was studied, using air as a fluid. The dimensionless wall heat-transfer coefficient, Nu,, and the radial effective conductivity ratio, k(r)/k(f), were evaluated from the calculated temperatures at different locations in the bed by comparing these with the analytical solution of a two-dimensional pseudohomogeneous model, using a nonlinear least-squares analysis. Results were obtained for Reynolds numbers in the range 9-1450. Though for high Re there was no real difference between a wall-cooled or a wall-heated tube, for low Re a significant difference was found. The effect of the viscosity, conductivity, and density variations, as a consequence of temperature variations, was studied using a hydrocarbon mixture as the fluid. Results indicated that the temperature profile had an influence on the fluid and heat flow and thus on the effective parameters, although at high Re numbers the influence became less.