Atmospheric Bubbling Fluidized Bed Risers: Effect of Cone Angle on Fluid Dynamics and Heat Transfer

In this paper, a comparative study of fluid dynamics and thermal characteristics of sand particles has been carried out numerically and experimentally in bubbling fluidized bed risers for five-cone angles of the riser wall having 0°, 5°, 10°, 15° and 20°. An Eulerian model with a k-e turbulence model is used to explore the numerical analysis, and the findings are compared to those of the experiments. For the study, the inlet air velocity is fixed at 1.5 m/s with sand particles filled up to 30 cm to maintain bubbling conditions in the risers. The results indicate that when the cone angle increases while maintaining the amount of bed materials constant, there is a corresponding reduction in pressure drop. The expansion of particles along the riser is observed to decrease with an increase in cone angle. The radial solid volume fraction profile transforms to a U shape from the W-type profile as the cone angle increases. Correspondingly, the solid velocity is found to have an inverted U-type and W-shaped profile for the risers. The granular temperature is also found to increase with a decrease in the solid percentage at any location. The average bed temperature, interphase, and bed-to-wall heat transfer coefficient at a location of 10 cm axial height also increase with the cone angle. As a result, the conical riser, when designed with a greater cone angle, exhibits more efficiency in terms of heat transfer characteristics.