Effect of tube shape on the hydrodynamics and tube-to-bed heat transfer in fluidized beds

In the present work, the multiphase flow dynamics in fluidized beds is modelled using the Two-Fluid Model (TFM) where the characteristics of a granular solid phase are described by the Kinetic Theory of Granular Flow (KTGF). A drag function and heat transfer coefficients are used to describe the interaction and heat exchange between different phases, respectively. The effective thermal conductivity is defined as a function of phase volume fraction and thermal properties and is used to calculate the heat transfer coefficient from immersed tube to fluidized beds. The effects of different tube shapes on the flow characteristics and local heat transfer coefficients are investigated and the time-averaged heat-transfer coefficient is compared with the experimental data in the literature. The simulated results show that the heat transfer processes are significantly influenced by the reintroduction of solid particles around the immersed surfaces and the heat transfer coefficients vary sensitively with the distribution of the solid phase. The simulated heat transfer coefficients are in the same order as the experimental data which indicates that it can be quantitatively employed to aid the configuration of heating tubes during industrial design of the fluidized bed reactors. (C) 2012 Elsevier Ltd. All rights reserved.