CFD modeling of flow, macro-mixing and axial dispersion in a bubble column

The flow pattern in a bubble column depends upon the column diameter, heigh t, sparger design, superficial gas velocity and the nature of gas-liquid sy stem. In this paper, the effect of some of these parameters have been simul ated using Computational Fluid Dynamics (CFD). The relationship of these pa rameters with the interphase force terms has been discussed. A complete ene rgy balance has been established. Using this methodology, the flow patterns reported by Hills (1974), Menzel et al. (1990), Yao et al. (1991) and Yu a nd Kim (1991) have been simulated. Excellent agreement has been shown betwe en the CFD predictions and the experimental observations. The above model h as been extended to homogenization of an inert tracer. In order to confirm this model, mixing experiments were carried out in a 200 mm i.d. bubble col umn. A radioactive tracer technique was used for the measurement of mixing time. Tc-99m ((99m) Tc), in the form of sodium pertechnate salt, was used a s the liquid phase tracer. Good agreement has been shown between the predic ted and the experimental values of mixing time. The model was further exten ded for the estimation of axial dispersion coefficient (D-L). Excellent agr eement between the simulated and the experimental values of the axial dispe rsion coefficient confirms the predictive capability of the CFD simulations for the mixing process.