Numerical Simulation On Flow In Airlift Bioreactor

Airlift-loop reactor (ALR) was deveopled from Bubble column. It has been well known that the conventional ALR is mainly composed of a column, a draft tube and a sparger and that it has predominant fluid mixing performance and high liquid volume mass transfer coefficient without mechanical stirrer. ALR is finding increasing applications in chemical in -dustry, biochemical fermentation and biological wastewater treatment processes .For design of an airlift reactor, it is necessary to have accurate estimates of the phase holdups and velocities in the riser and downcomer. However, the two-phase flow field in airlift-loop reactors is too complex to be characterized with analytical method. As a result, the choose, design and scale-up of ALR are still depended only on experimental validation and expert experience, lacking of support of theories and consuming much money and time. Computational Fluid Dynamics(CFD) can not only save a lot of resource,but also get some important local data that cannot be gathered in experiment. Now CFD technology is playing more and more important in the fields of the reactor design and optimization.This article deals with the physical modeling and numerical simulation of two-phase bubbly flow in an airlift internal loop reactor. The objective is to show the ability of computational fluid dynamics (CFD) to correctly simulate hydrodynamics in such a bubbly reactor. The modeling of two-phase bubbly flow is based on the so-called two-fluid model derived from Reynolds-averaged Navier-Stokes equations in two-phase flow. The turbulence is described using the k-εmodel. Interactions between the bubbles and the liquid play significant role in fluid flow and gas holdup. Interfacial momentum transfer includes added mass, drag and turbulent pressure. The paper investigated the effects of added mass and three kinds of drag models (Schiller and Naumann, Clift and Karamanev and Nikolov)on fluid flow and gas holdup in ALF. The program about the exchange -coefficient models is made out.The fluid flow and gas holdup are calculated in ALR in a range of superficial gas velocities. Sensitivity analysis of fluid flow is then presented to highlight the bubble diameter parameters. Numerical simulations are discussed after comparison with experimental data. The expe-rimental results are compared with different drag model. The Clift model shows excellent agreement with the measured data on gas holdup, liquid velocity in the downcomer and in the riser. The developed CFD model has the potential of being applied as a tool for scaling up.