158*

Resolving Flow Conditions In CatalyticReactor Beds Using CFD

D i p l . - I n g . G . O l b e r t

D r . - I n g . M . M e g a h e d

BASF AG, Logica pdv GmbH

Reactor beds have been investigated using simplified methods, thereason being restrictions in resolving the reactor bed geometry.Such methods require empirical data which essentially restrictthe generality and reliability of the predictions.

It is proposed to resolve the reactor bed geometry usinga digitalisation method, importing the 3-D geometric informationinto the CFD code, generating a computational grid automaticallyand conducting detailed analysis of the fluid flow regime, heattransfer and chemical reactions tacking place.

Preliminary simulations of a reactor bed ± void fraction72% ± predict an overall heat transfer coefficient within 15% of theexperimental value.

159*

Application of Coupled SolverTechnology to CFD Modelling ofMultiphase Flows with CFX

A l a n B u r n s 1

H e n n i n g E i c k e n b u s c h 2

P a u l G u i l b e r t 1

D e w e i Y i n 1

1)AEA Technology CFX International, 8.19 Harwell, OxfordshireOX11 0RA, U.K.

2)AEA Technology GmbH, Staudenfeldweg 12, D-83624 Otterfing,Germany

Multiphase flows are involved in almost all of the processes in che-mical engineering; for example: gas bubbles in liquid columns, solidparticles in mixing vessels, liquid droplets in spray dryers. Multi-phase flow problems are inherently very complex, many of the phy-sical processes (heat, mass and momentum) are linked and coupledbetween the phases. Despite the difficulties, many successful CFDcalculations have been made and reported in the literature. In mostof the current CFD algorithm for multiphase flows a segregatedsolution method is used. The momentum, continuity and otherequations are solved in separated steps. The whole calculation se-quent must be repeated or iterated many times (typically thousandsof iterations) for the solution to address all the coupling terms prop-erly and converge to the final solution. For single-phase flows con-vergence speed can be improved by using what is known as acoupled solver technology. Within this technique the governingtransport equations are solved all at a time. This strategy hasbeen implemented in CFX-5 to model and simulate two-phaseflows. This paper describes the coupled solver technology imple-mented in the CFX-5 software and examines the advances ofthis technology in terms of CFD performance by way of engineer-ing examples. Validation tests modeling bubbly flow in an airliftreactor demonstrate good convergence characteristics and linearscalability of the solver with respect to both problem size and par-allel computation. Numerical results of the simulation are in verygood agreement with a previously published study.

160*

CFD Modeling of Large-Scale Pool Fires

C . K u h r

A . S c h oÈ n b u c h e r

Gerhard-Mercator-UniversitaÈ t Duisburg, FB 6 Technische Chemie,Lotharstr. 1, 47057 Duisburg, Germany, Tel.: +49 (0)203 3792714

Kerosene pool fires with pool diameters 8 m � d � 25 m have beenmodeled using the CFX-4.3 code by AEATechnology. The employedsoftware includes a low Reynolds number k-e turbulence modeland, as far as the combustion process is concerned, a version ofthe eddy break up model. Calculations of transient flow velocitiesand temperature fields were made and axisymmetry was assumed.The results show a periodically rise of vortices from the flame base

Figure.Digitalised segment of catalytic reactor bed.

638 C o m p u t a t i o n a l E n g i n e e r i n gChemie Ingenieur Technik (73) 6 I 2001