Project Details
Projekt
Direct numerical simulation of multi-physics reactive mass transfer at single and multiple bubbles
Applicant
Professor Dr. Dieter Bothe
Subject Area
Chemical and Thermal Process Engineering
Mathematics
Mathematics
Term
from 2014 to 2021
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 256739956
Reactive mass transfer from rising gas bubbles is the basis for many chemical processes of industrial importance. The necessary process intensification leads to faster process steps and highly concentrated systems. In such two-phase flows with complex local interaction between mass transfer, transport and chemical reactions, additional multi-physics becomes relevant. This includes: volume effects for dissolving bubbles; partly immobilized bubble surfaces due to contamination or additives; ionic species with strong coupling of diffusive fluxes by the intrinsic electrical field, typically leading to local electro-neutrality of the mixture away from the interface; cross-diffusion effects as well as non-idealities in systems of higher concentrations. These complexities add to the multi-scale nature of reactive mass transfer with extremely thin concentration boundary layers due to convection-dominated transport. Besides experimental investigations, a thorough understanding of the local interplay of elementary sub-processes requires numerical simulations based on rigorous mathematical modeling. Our approach employs continuum physics based on the two-phase balances of mass, momentum and species mass. Based on the Volume of Fluid (VOF)-method, we built on our two-scalar approach for 3D Direct Numerical Simulations of mass transfer at gas bubbles. The approach employs a subgrid-scale model which has been strongly improved in the first funding period to allow for realistic Schmidt numbers. In the second funding period, the method will be extended and applied to groups of several bubbles, rising in a computational box with periodic boundary conditions, thus simulation an infinite bubble swarm. Moreover, the existing approach to account for contamination effects will be improved by including a variable Gibbs elasticity to model a partly immobilized bubble interface. Detailed numerical simulations will yield deep insights into reactive mass transfer processes and bulk mixing around bubbles under swarm-like conditions. Within the network of the priority program, these techniques allow to simulate the mass transfer in bubbly flows with different model chemistry, developed in other projects. In particular, the oxidation of iron complexes in methanol and the nitration of iron complexes in water will be considered. In addition to local Sherwood numbers and enhancement, the influence of system parameters on yield and selectivity will be studied. Besides the investigation of freely rising bubble groups/chains, the project will contribute to the guiding measure of Taylor bubbles/flow with simulations including bubble shrinkage and conjugate mass transfer. Finally, the influence of electro-migration of ionic species due to the inherent electrical field will be analyzed. All simulation results for experimental setups will be discussed with the cooperating colleagues. Improved correlations for a scale-reduced modeling will be developed in cooperation within the SPP.
DFG Programme
Priority Programmes
