Numerical modeling of large-scale bubble plumes accounting for mass transfer effects

A mathematical model for dilute bubble plumes is derived from the two-fluid model equations. This is coupled to a mass transfer model to get a closed CFD formulation. The mass transfer equations used are the same as those implemented in the 1D model proposed, so as to get a CFD formulation and a 1D integral formulation that are fully consistent. In fact, the 1D model can be rigorously derived from the CFD one. The mathematical derivation is detailed pointing out the approximations involved. Results of both models for typical conditions of isolated aeration plumes in deep wastewater reservoirs are presented. Good agreement is reported between them, emphasizing on the most relevant variables such as gas dissolution rates, gas holdup, liquid's velocity and bubbles' radius. Furthermore, entrainment rates evaluated from the CFD results are shown to lie within the experimental range. Finally, CFD-based assessment of the approximations involved in the 1D model proves them to hold within a few percents of relative accuracy. A solid basis for applying CFD models to aeration plumes, as natural extensions of the popular integral models, emerges from the investigation.