Euler-Euler-modelling of poly-disperse bubbly flows

Bubbly flows occur in various industrial processes. For medium and large industrial scales the Euler-Euler approach is frequently applied in CFD-simulations. To derive the corresponding balance equations for mass, momentum and energy averaging procedures are applied and in the result information on the gas-liquid interface gets lost. Models reflecting the physics at the non-resolved scale are required to close the problem. This concerns the momentum transfer between bubbles and liquid (bubble force models), modulation of turbulence by the bubbles (BIT – bubble induced turbulence), bubble-bubble interactions (coalescence and breakup) and mass and heat transfer between the phases (boiling, condensation, heterogeneous chemical reactions). Most of these closure models sensitively depend on the bubble size and even may change their sign in dependency on the bubble size (lateral lift force). Correspondingly an appropriate modelling requires the consideration of the bubble size distribution and in general also the sub-division of the gas phase in phases representing bubbles of a specific range of sizes.
Still there is no consensus on the closure models in literature. Often closures and open parameters are tuned to obtain agreement with experimental data. To achieve a consolidation of the modelling and more reliable predictions the so-called baseline model concept was proposed by HZDR. In the baseline model all closure models including constants are well defined and the fixed model is used for the simulation of different flow situations involving bubbles in the mm-range and larger without any modification.
The lecture presents the baseline model concept, introduces the baseline model for poly-disperse bubbly flows (including the definition of closures for bubble forces, BIT, coalescence and breakup), the inhomogeneous MUSIG model for the consideration of the bubble size distribution and the modelling of phase transfer and chemical reaction. The baseline model for poly-disperse bubbly flows was validated for more than 150 single experiments. Examples for the validation are given and perspectives of the future modelling are discussed.