CFD-DEM studies of continuous particle drying in a bubbling fluidized bed with large hole perforated plates

Continuous particle drying in a countercurrent bubbling fluidized bed is experimentally and numerically studied by heat and mass transfer coupled CFD-DEM simulations. The aim of this study is to investigate the drying behaviour, flow dynamics, and heat/mass transfer mechanisms in this novel fluidized bed design with large-hole perforated plates to allow continuous particle discharge. Particle temperatures are monitored by considering the air–particle heat transfer heating and water evaporation cooling simultaneously. The swirling particle flow patterns are observed above the plate. The deviations between the predicted dried particle water content and that of experimental results are within 10.5%. The errors are further reduced with a longer simulation time. At higher drying air velocities, the solids hold-up increases and the particle mean residence time increases. The spouting flow patterns cause the time-averaged particle through-hole discharging flux to linearly increase in the radial direction. The effective drying region is found at about 12 particle diameters above the plate, where the solids volume fraction is the highest. The highest water evaporation rate of 6.5 × 10⁻⁶ g/s is observed around the boundary of the bubbles and within the bubbles at the bed centre. The particle Nusselt and Sherwood numbers analyses show that the convective heat and mass transfer are the major drying mechanisms.