Computational fluid dynamics simulations of fluid flow and heat transfer at the wall–particle contact points in a fixed-bed reactor

Abstract

An accurate description of the fluid flow and heat transfer within a fixed-bed reactor is desirable. The prevailing models of fluid flow invoke either a constant velocity (plug-flow) profile, or make use of a single axial velocity component with radial variation across the tube diameter. However, difficulties in predicting reactor performance and the wide disagreement between effective heat transfer coefficients suggest that these are oversimplified pictures of the real-flow situation. Computational fluid dynamics is a means that could improve our understanding of fixed-bed fluid flow and heat transfer, by solving the 3D Navier–Stokes equations. Simulations are presented for an improved geometry, compared to previous studies, of 10 solid spheres in a tube with a tube-to-particle ratio of 2.43, that includes both particle to particle and also wall to particle contacts. Simulations are also reported with heat generation from the spheres. The simulation results show strong flow components towards the wall and away from the wall, thereby transporting heat. The flow around the contact points themselves shows stagnant regions, due to the high shear of the solid surfaces. A high velocity gradient in the radial direction is observed between two layers of spheres, which clearly shows how the heat transfer is increased within the bed. Regions of back-flow are also observed, in qualitative agreement with literature experimental studies.