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On the Evaluation of the Exit Boundary Condition for the Axial Dispersion Bioreactor System
Author(s) -
Lee T. T.,
Wang F. Y.,
Newell R. B.
Publication year - 1998
Publication title -
chemical engineering and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.403
H-Index - 81
eISSN - 1521-4125
pISSN - 0930-7516
DOI - 10.1002/(sici)1521-4125(199811)21:11<901::aid-ceat901>3.0.co;2-q
Subject(s) - boundary value problem , dispersion (optics) , mechanics , flow (mathematics) , steady state (chemistry) , flow conditions , boundary conditions in cfd , boundary (topology) , plug flow , partial differential equation , instability , control theory (sociology) , mathematics , mathematical analysis , physics , computer science , chemistry , mixed boundary condition , robin boundary condition , control (management) , artificial intelligence , optics
Employment of the axial dispersion theory to model chemical or biochemical processes often results in coupled parabolic partial differential equations (PDEs). The classical Danckwerts boundary conditions have been widely used to solve these PDEs despite the fact that artificial suppression of the exit concentration gradient to zero may be physically unrealistic and may cause numerical instability. In this study, a recently developed exit boundary condition is shown to be inapplicable to model processes which demonstrate significant differences in the dynamics of components – typically found in biochemical processes. Using an activated sludge process and a pilot‐scale subsurface flow (SSF) constructed wetland as case studies, we demonstrated in this study that a time‐dependent exit boundary condition is more appropriate for use with the Danckwerts inlet boundary condition and the axial dispersion theory to model a biological system operating at near‐plug flow conditions. Instead of using steady‐state results we found that evaluation of alternative exit boundary condition using dynamic simulation results is more realistic.