Euler-Euler-modeling of reactive flow in bubble columns
In contrast to mere fluid dynamics, mass transport has been considered in the context of Euler-Euler simulations of bubbly flows only in relatively few works, in particular with simultaneous occurrence of a chemical reaction. An overview of the processes that need to be modeled and their relation is shown in the following figure 1.
These processes were investigated in the frame of a project in the first phase within the the recently finished DFG priority program 1740 “Influence of Local Transport Processes on Chemical Reactions in Bubble Flows” . Presently these studies are continued in a DFG-project in cooperation with the Otto-von-Guerike Universität Magdeburg.
An important parameter is the time scale of the reaction: fast reactions are essentially completed within the boundary layer around the bubbles, slow reactions in contrast take place predominantly in the bulk of the liquid phase. Slow reactions can be described as a succession of non-reactive mass transfer and reaction in the liquid. To this end, models are needed for the (physical) mass transfer coefficient [1-3] as well as the turbulent mass transport and the micromixing taking into account the bubble-induced turbulence . In the case of fast reactions a model is required for the enhancement-factor [5-7], which multiplies the mass transfer coefficient. The turbulent mass transport then is relevant only for the removal of reaction products (reverse direction of reactant B in the figure). For reactions of intermediate rate all of these processes play a non-negligible role. In addition the enhancement-factor becomes a function of the concentration of the transferred species (reactant A) in the bulk liquid.