ANALYSIS AND EXPERIMENT OF NON-DARCIAN CONVECTION IN HORIZONTAL SQUARE PACKED-SPHERE CHANNELS .2. MIXED CONVECTION

This paper presents an analysis and experiment of fully developed non-Darcian mixed convection in horizontal packed-sphere channels. The non-Darcian effects of no-slip boundary, flow inertia, channeling and thermal dispersion are considered. The theoretical results are found to be in agreement with the experimental results for the channel of D(e)/d = 10, but the predictions of Nusselt number are higher than the experimental data, partly due to theoretical overestimation of the thermal dispersion effect and partly due to the entrance effect existing in the experiments for D(e)/d = 19. The analysis shows that the buoyancy effect significantly affects the secondary flow structure and heat transfer rate when the Peclet number is low, but even under a fixed Rayleigh number, the effect of buoyancy will be suppressed when the Peclet number increases. The values of Nusselt number in the fully developed region depend on Rayleigh number, Peclet number and the diameter ratio of channel to sphere (D(e)/d).