Heat transfer in fluidized beds with immersed surface: Effect of geometric parameters of surface

In this work CFD simulations of a fluidized bed with an inserted heated surface were carried out in order to study heat transfer, focusing on the effect of the surface geometry in this phenomenon. The Eulerian-Eulerian model along with the kinetic theory of granular flows were used to describe the gas-solid behavior. The experimental set-up consisted of a bed with 1.8 m height and 0.1 m diameter with glass bead particles. Gas was introduced at a constant velocity. To define the best setup for this case, different drag models, specularity coefficients, and a turbulence model were tested. It was verified that the best results were obtained with the Gidaspow drag model, a specularity coefficient equal to 0.1, and the kappa-epsilon RNG dispersed turbulence model. Inside the bed, ten different immersed heated surface geometries were described, including cylinders, spheres and cones. The spheres resulted in the highest heat transfer coefficient, and the cylinders, the lowest. An increase in the diameter of the immersed cylinder led to drastic changes in the bed hydrodynamics and a consequent decrease in the heat transfer coefficient. (C) 2016 Elsevier B.V. All rights reserved.