The effects of wall surface roughness on the rate of heat transfer and temperature profiles in turbulent gas-solid flows in pipes at different inclination angles were studied. The earlier developed computational model for 3D flows including the four-way interactions was extended and used in this study for evaluating the mean flow, turbulence intensity and thermal fields. Interaction of particles with the rough wall was included by introducing the available stochastic wall roughness models (shadow effect model) for the dispersed phase in the computational program. It was found that changes in the particle dispersion and particle concentration altered the Nusselt number and heat transfer rate in different regions of the pipe. The Nusselt number decreased in the lower part of the duct for horizontal and inclined pipes due to the reduction in the settling velocity. The surface roughness also altered the heat transfer coefficient in the periphery of the vertical riser. The simulation results showed that the fluid temperature was reduced in the pipe core and increased near the wall region for inclined pipes. On the other hand, particle temperature increased and flattened in the entire pipe cross section.

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