Bubbly flows are commonly used in many industries as found, for example, in boiling water nuclear reactors and steam generators, refrigeration and air conditioning equipment, and bubble column reactors. Large eddy simulation coupled with a Lagrangian bubble tracking routine are used in this work to study the dynamics of microbubbles in vertical channel upflows and downflows of water at shear Reynolds numbers of 150 and 590. A dynamically calibrated Smagorinsky subgrid-scale model was used with the large eddy simulation, and a stochastic Markov model was employed to account for the effect of the subgrid-scale velocity fluctuations on bubble dispersion. The microbubbles, of diameters 110 and 220 μm, were uniformly dispersed within the flows, momentum coupled with the fluid, and subjected to drag, lift, pressure gradient, gravity/buoyancy and added mass forces. Predictions were validated against direct numerical simulations for a limited number of cases, showing good agreement. Predictions are used to understand the effect of the microbubbles’ presence on the fluid flow and the turbulence in the continuous field. Microbubbles concentration profiles are analysed, with microbubbles segregating at the wall in upflow and moving towards the channel centre in downflow. The different forces acting on the bubbles and the effect of the turbulence on the bubble concentration are also considered.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)