Use of models for lift, wall and turbulent dispersion forces acting on bubbles for poly-disperse flows

Closure laws are needed for the qualification of CFD codes for two-phase flows. In case of bubbly and slug flow, forces acting on the bubbles usually model the momentum transfer between the phases. These forces depend on the liquid flow field as well as on the size and the shape of the bubbles. The validation of these forces base on a detailed experimental database for vertical pipe flows, which contains data on the radial distribution of bubbles of different size and local bubble size distributions. A one-dimensional model resolving the variables in radial direction and considering a large number of bubble size classes, is used for an analysis of several bubble force models. Results of this model were compared to results of 3D simulations done by the commercial code CFX-5.7 for simplified cases with only one bubble class. The effects of the number of bubbles classes as well as the effect of the lateral extension of the bubbles were analysed. For the validation of bubble force models measured bubble size distributions were taken as an input for the model. On basis of the assumption of equilibrium of the lateral bubble forces, radial volume fraction profiles were calculated separately for each bubble class. In the result of the validation of different models for the bubble forces, a set of Tomiyama lift and wall force, deformation force and Favre averaged turbulent dispersion force was found to reflect the experimental data with best agreement. Some discrepancies remain at high liquid superficial velocities.