DIRECT NUMERICAL SIMULATION OF MASS TRANSFER FROM A SINGLE BUBBLE VIA AN IMPROVED SUBGRID SCALE MODEL

Abstract

Hydrogenation, oxidation and alkylation are just some of the processes which are performed in bubble columns. One of the reasons to use a bubble column for these processes is the high interfacial mass transfer coefficients. Trying to simulate the mass transfer around the bubbles is however challenging due to the typically high Schmidt numbers of liquids, meaning that the mass boundary layer is very thin compared to the momentum boundary layer. To resolve this thin mass boundary layer, a subgrid scale model can be used. This work focuses on improving the subgrid scale model that we have embedded in our in-house front tracking framework of Claassen et al., AIChe J 2019. In the current implementation the unphysical numerical back diffusion at the grid into the bubble has been prevented with a staircase immersed boundary implementation. A verification has been performed by comparing the simulated, local and global Sherwood number with the analytical solution in creeping and potential flow regimes. Furthermore, the model was validated for 20 free rising bubbles of different shapes at industrial relevant Schmidt numbers (103-105). The model was able to correctly predict the Sherwood numbers.