CPFD simulation of bed-to-wall heat transfer in a gas-solids bubbling fluidized bed with an immersed vertical tube

Based on previous experimental study, CPFD method was used to simulate the bed-to-wall heat transfer between an immersed vertical heat tube and bed material in a gas-solids fluidized bed of fine particles. Radial and axial profiles of heat transfer coefficients at different superficial gas velocities, as well as their circumferential profiles around heat tube surface were obtained. By comparing with experimental results, it is found that trends of the predicted radial and axial profiles of heat transfer coefficients at different superficial gas velocities agree well with experimental results. However, all the simulated values of heat transfer coefficients are smaller than experimental values due to the default heat transfer coefficient correlation for dense particle phase in the built-in heat transfer module of Barracuda. There exists strong heterogeneity on the distribution of heat transfer coefficient around the circumference of the heat tube, especially near the column wall. The circumferential uniformity of heat transfer coefficient becomes worse as heat tube moves to the column wall and at increasing superficial gas velocities. Both averaged and instantaneous results show a good linear correlation between heat transfer coefficient and solids renewal flux, demonstrating the dominant role of solids renewal on the efficiency of fluidized heat exchangers. (C) 2017 Elsevier B.V. All rights reserved.