Michiel Nijemeisland

Comparison of CFD simulations to experiment for convective heat transfer in a gas-solid fixed bed

Abstract Computational fluid dynamics (CFD) studies can improve understanding of fixed bed fluid flow and heat transfer. Our long-term objective is to use the CFD results in the development of tractable reactor models that are based on a good understanding of the fluid flow phenomena. The CFD simulations of fluid flow and heat transfer require verification to increase confidence in their use for model development. Results of a quantitative comparison between CFD results and heat transfer experimental data are given here. Simulations are presented for a model geometry of 44 solid spheres in a tube with tube-to-particle diameter ratio equal to 2. Velocity vector profiles and temperature contours have been obtained with emphasis on the wall–particle region. Comparisons are made with measured temperature profiles in a typical experimental setup with the same geometry. Several correction factors were required to compensate for non-ideal experimental measurements, and for phenomena that were not included in the CFD model. After correction, excellent agreement could be obtained between simulation and experiment.

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.

Packed Tubular Reactor Modeling and Catalyst Design using Computational Fluid Dynamics

Abstract Computational fluid dynamics (CFD) is rapidly becoming a standard tool for the analysis of chemically reacting flows. For single-phase reactors, such as stirred tanks and “empty” tubes, it is already well-established. For multiphase reactors such as fixed beds, bubble columns, trickle beds and fluidized beds, its use is relatively new, and methods are still under development. The aim of this chapter is to present the application of CFD to the simulation of three-dimensional interstitial flow in packed tubes, with and without catalytic reaction. Although the use of CFD to simulate such geometrically complex flows is too expensive and impractical currently for routine design and control of fixed-bed reactors, the real contribution of CFD in this area is to provide a more fundamental understanding of the transport and reaction phenomena in such reactors. CFD can supply the detailed three-dimensional velocity, species and temperature fields that are needed to improve engineering approaches. In particular, this chapter considers the development of CFD methods for packed tube simulation by finite element or finite volume solution of the governing partial differential equations. It discusses specific implementation problems of special relevance to packed tubes, presents the validation by experiment of CFD results, and reviews recent advances in the field in transport and reaction. Extended discussion is given of two topics: heat transfer in packed tubes and the design of catalyst particles for steam reforming.

Systematic mesh development for 3D CFD simulation of fixed beds: Single sphere study

Abstract To develop and validate meshes for computational fluid dynamics (CFD) simulations of transport in fixed beds, a single particle is often used as a test case. We present results for drag coefficient (CD) and heat transfer Nusselt number (Nu) for flow past a sphere, focusing on high flow rates typical of industrial steam reformers (400