Numerical investigation of SO2 absorption into a droplet: deformation and internal flow facilitating mass transfer

Abstract

The SO2 absorption into a droplet falling freely is investigated numerically based on a detailed three-dimensional mode in this work. Gas-liquid multiphase flow simulations coupled with interphase mass transfer are performed using the coupled Level-set and Volume of Fluid method (CLSVOF) to trace the gas-droplet interface. The results of simulation reveal that droplet would deform and deviate from the standard sphere during falling, with an approximately 5.6 % increase in surface area under the discussed working conditions. The evolution mechanism of the internal circulation in the droplet is clarified: the increase in the relative velocity of gas-droplet facilitates the formation and intensification of the internal circulation in the droplet. As the internal circulation develops into the stable stage, the convective mass transport would dominate the mass transfer process and promote the mass transfer. The distribution laws of the local mass transfer rate and coefficient over the droplet surface are found analogous to the typical case of heat transfer around a sphere. Finally, considering the effects of both droplet deformation and internal circulation on mass transfer concurrently, the variation of Sh as a function of Reynolds number is obtained, which appears the same trend but yields slightly higher values compared to the results of empirical correlations.