Efficiency of interphase coupling algorithms in fluidized bed conditions

When the coupling of phases in multi-phase flows is very tight, a special t reatment of interphase coupling terms is required in order to avoid diverge nce of iterative sequential solvers. In this article the efficiency of thes e special treatments is studied in typical fluidized bed conditions, where the coupling of momentum equations is moderate. The interphase coupling alg orithms studied are the partially implicit treatment, the Partial Eliminati on Algorithm (PEA) and the Simultaneous solution of Non-linearly Coupled Eq uations (SINCE). In addition to these special treatments of linearized coup ling terms in momentum equations, the fundamental ideas of the SINCE are ap plied also to the Semi-Implicit Method for Pressure-Linked Equations (SIMPL E (C)) type pressure correction equation in the framework of the interphase slip algorithm (IPSA). The resulting solution algorithm referred to as the Interphase Slip Algorithm-Coupled (IPSA-C) then incorporates interface cou plings also into the mass balancing shared pressure correction step of the solution. It is shown that these advanced methods to treat interphase coupl ing terms result in a faster convergence of momentum equations despite the increased number of computational operations required by the algorithms. Fo r solving of the entire equation set, this better solution efficiency is th en almost lost partly because of the sequential structure of the IPSA and, more importantly, because of the assumption of constant volume fractions du ring the pressure correction step. All the computations are done in the con text of a collocated multi-block control volume solver CFDS-FLOW3D. (C) 199 9 Elsevier Science Ltd. All rights reserved.