Mass transfer in bubbly flows is important in many engineering applications. Simulation of such processes on technical scales is feasible by the Euler-Euler two-fluid model, which relies on suitable closure relations describing interfacial exchange processes. In comparison with the pure fluid dynamics of bubbly flows however, modeling and simulation of bubbly flows including mass transfer is significantly less developed.
In particular, previous simulation studies have focused almost exclusively on absorption in bubble columns without liquid flow. However, recent experiments on single bubbles suggest that the simultaneous desorption of dissolved inert gases in general cannot be neglected. This requires consideration of changing bubble composition in addition to bubble size. In addition imposing a liquid flow allows a steady state to be achieved also when the mass transfer is accompanied by a chemical reaction, which greatly simplifies the analysis of reactive mass transfer problems.
Therefore, the present study first considers a larger variety of conditions including desorption and counter-current (downward) flow for which experimental data for a first comparison are available from the literature. Then a simple sandbox test case is used to illustrate how the bubble composition may be tracked as a secondary property in addition to bubble size within a population balance framework. An analytical solution can be found for this test case, which facilitates verification of the software implementation of the discretized population balance equation.
In this way, further building blocks for a more complete numerical treatment of mass transfer in bubbly flows are now available. A thorough validation for realistic applications however requires yet further experimental work to provide suitable measurement data.