Sensitivity Study on Modeling an Internal Airlift Loop Reactor Using a Steady 2D Two‐Fluid Model

Abstract

The sensitivity study of bubbly flow in an internal airlift loop reactor is presented using a steady Reynolds averaging two-fluid model. Comparative evaluation of different drag formulations, drag coefficient correlations, turbulence effect on the drag coefficient, outlet slip velocity, and bubble size is performed and the respective influence to the simulation results is highlighted. It is found that a complicated drag formulation may not result in reliable predictions. All the drag coefficient correlations underpredict the gas holdup if the influence of turbulence on the drag coefficient is not well incorporated. Fortunately, the global hydrodynamics is not sensitive to the outflow slip velocity for a wide range, so a steady two-fluid model can be used to simulate the bubbly flow when the flow field is fully developed. The correct estimation of bubble size with properly selected correlations play an important role in successful simulation of gas-liquid bubbly flow in airlift loop reactors.

Modeling transport phenomena and reactions in a pilot slurry airlift loop reactor for direct coal liquefaction

“…The outflow boundary of the reactor is simplified and assumed to be a Neumann type, and special treatments are required to accelerate the rate of convergence for the steady simulations (Huang et al, 2008). As far as we know, there is no open publication on a steady model with the continuous mode of operation, and it is very complicated to approximate it because of the coupling between the velocity and the fraction for each phase in bubbly flows.…”

“…As far as we know, there is no open publication on a steady model with the continuous mode of operation, and it is very complicated to approximate it because of the coupling between the velocity and the fraction for each phase in bubbly flows. A developed boundary condition, which is extended from the work of Huang et al (2008) for the semicontinuous operation at ambient condition, is taken here, and the outflow boundary is thought to be flat and the vertical gas velocity component relative to the liquid is simply defined as the terminal slip velocity of bubbles in quiescent slurry. The revised boundary condition is proposed regarding to both fluids operated with a continuous mode as follows:…”

“…For simulation of the bubbly flow, a validated Reynolds averaging two-fluid model is used here (Huang et al, 2007(Huang et al, , 2008. In this approach, mass and momentum balance equations are solved for each phase, and the coupling between gas and liquid is achieved through interphase momentum exchange terms.…”

“…Although there have been significant research efforts concerning the fundamental characteristics of IALRs under ambient conditions (Heijnen et al, 1997;Huang et al, 2007Huang et al, , 2008Lin et al, 1997aLin et al, , 1997bMudde and Van den Akker, 2001;Talvy et al, 2007aTalvy et al, , 2007b, the scale effect on the flow structure is still not fully understood. Sound understanding of the hydrodynamic behavior in IALRs (e.g., flow regime, phase holdup, bubble characteristics, interfacial phenomenon, backmixing, and interphase transport) is therefore essential in designing and scaling up these slurry reactors, especially under the condition of elevated pressure and high temperature with relevance to industrial reactive processes.…”

Bubbly flow in an airlift column: a CFD study

“…Airlift columns in contrast have received comparatively less attention in simulation studies. Recent simulations of bubbly flow in the internal loop type are given in the literature . In most of these studies, comparison with experiment has been made only for integral data like the total gas holdups in riser and downcomer or the average liquid circulation velocity.…”