Effect of bubble interactions on mass transfer in bubbly flow

The effect of bubble interactions on mass transfer in a multi-bubble system is examined by numerical simulations. Since mass transfer in the liquid phase of gas–liquid multiphase flows usually takes place at a considerably slower rate than the transfer of momentum, the mass flux boundary layers are much thinner than the momentum boundary layers. In direct numerical simulations the resolution requirements for flows with mass transfer are therefore considerably higher than for flows without mass transfer. Here, we use a multiscale approach for the computations of the mass transfer near the bubble surface, in order to reduce the cost, and examine the effect of void fraction and bubble Reynolds number on the mass transfer from bubbles in periodic domains. Specifically, we compare results for a single bubble in a periodic domain with results for several bubbles in a larger domain with the same void fraction. It is shown that even though the average Reynolds number of freely moving bubbles drops after a while, in most cases the mass transfer from the bubbles increases slightly. When the bubbles start to wobble, in most cases the increase in bubble–bubble interactions compensate for the reduction in Reynolds number.