Eulerian computation of heat transfer in fluidized beds

Basically two different methods exist for the numerical simulation of parti cle laden multiphase flows. Whereas the Lagrangian approach for dilute flow s handles each particle separately, the Eulerian formulation of the governi ng equations treats the particulate phase as a continuous phase. The Euleri an formulation can be realized using the kinetic theory of granular flows, which describes the physical properties of the particle phase. In the past, promising results of the fluid dynamics in a bubbling fluidized bed (Boeme r, A. (1996) Euler/Euler-Simulation der Fluiddynamik blasenbildender Wirbel schichten, Dissertation, at RWTH Aachen, Germany) were achieved by estimati ng the solids pressure and the solid viscosity based on the kinetic theory. One parameter of this theory is the so-called granular temperature, which is a quantity of the macroscopic particle fluctuating energy. In addition t o the fluid dynamics the numerical simulation of the heat transfer between a fluidized bed and immersed heat transfer surfaces is of particular intere st. This work shows different physical models which are needed to give an E ulerian formulation of the particulate enthalpy equation. Besides the heat transfer between the phases, the effective thermal conductivity of the part icle phase has to be specified. The combination of these models has been te sted in a simple two-dimensional test case consisting of a heated horizonta l tube immersed in a fluidized bed. To examine the influence of rising bubb les on the heat transfer, which usually leads to enhanced heat transfer coe fficients as a consequence of the turbulent mixing of the particles, bubble s are generated periodically with the help of a pulsed jet. (C) 1999 Elsevi er Science Ltd. All rights reserved.