CFD simulation of bubble column- an analysis of interphase forces and turbulence models

Abstract

3D transient CFD simulations of bubble column have been performed for a wide range of superficial gas velocity on an industrially relevant cylindrical column and the CFD predictions have been compared with the experiments of Menzel et al. [T. Menzel, T. Weide, O. Staudacher, U. Onken, Reynolds stress model for bubble column reactor, Ind. Eng. Chem. Res. 29 (1990) 988-994]. Simulations have also been performed to understand the sensitivity of different interphase forces (drag, lift, turbulent dispersion and added mass). This work highlights the importance of choosing the C_L value and the drag law in accordance with the bubble size. Further, a laboratory scale bubble column with three different spargers (perforated plate, sintered plate and single hole) has been simulated using three different turbulence closure (k-ε , RSM and LES) models, with the purpose of critically comparing their predictions with experimental data [M.R. Bhole, S. Roy, J.B. Joshi, Laser doppler anemometer measurements in bubble column: effect of sparger, Ind. Eng. Chem. Res. 45 (26) (2006) 9201-9207; A.A. Kulkarni, K. Ekambara, J.B. Joshi, On the development of flow pattern in a bubble column reactor: experiments and CFD, Chem. Eng. Sci. 62 (2007) 1049-1061]. It has been found that the RSM shows better agreement than the k-ε model in predicting the turbulent kinetic energy profiles. Comparatively, the LES has been successful in capturing the averaged behavior of the flow, while at some locations; it slightly over predicts the kinetic energy profiles. Further, it has been able to simulate the instantaneous vortical-spiral flow regime in case of sieve plate column, as well as, the bubble plume dynamics in case of single hole sparger. Thus, LES can be effectively used for study of flow structures and instantaneous flow profiles.