Implementation of Breakup and Coalescence Models in CFD CHEMICAL REACTION ENGINEERING LABORATORY Implementation of Breakup and Coalescence Models in CFD Peng Chen, Chemical Reaction Engineering Laboratory Washington University St. Louis, MO 63130 CREL Group Meeting December 14, 2000

CHEMICAL REACTION ENGINEERING LABORATORY Overview Introduction Bubble number density approach Result Future work

CHEMICAL REACTION ENGINEERING LABORATORY Introduction The drag force term in one of the key issue of two-fluid model and the predictive capabilities of this model depend crucially on the closure. Most numerical simulation resorts to single particle drag correlation with a “mean” bubble size. This is mostly because modeling different sizes of bubbles as individual phase lead to unrealistic computational cost and has numerical convergence problem. However, in reality, bubble-bubble interaction results in local variation in bubble sizes that are substantially different from the “mean” bubble size assumption. In order to get reasonably good simulation result, the “mean” bubble size need to be adjusted so that it could be far away reality.

CHEMICAL REACTION ENGINEERING LABORATORY Motivation Bubble size distribution should be resolved locally by implement bubble coalescence and breakup into CFD framework. There is rare implementation of such bubble breakup/coalescence model in CFD simulation of bubble column reactors. Bubble breakup (Martínez-Bazán, 1999) and coalescence (Luo, 1993) model was implemented using bubble number density approach into FLUENT 5.48 in the context of Algebraic Slip Mixture Model (ASMM).

Bubble Number Density Approach CHEMICAL REACTION ENGINEERING LABORATORY Bubble Number Density Approach The population balance equation for the ith bubble class The source term may be written as

CHEMICAL REACTION ENGINEERING LABORATORY Closures - Breakup Martínez-Bazán et al. (1999)

CHEMICAL REACTION ENGINEERING LABORATORY Closure - Coalescence Luo (1993) , ij = di/dj,

CHEMICAL REACTION ENGINEERING LABORATORY Geometric Grid was used, xi+1 = 2vi. x0 = 1mm. Source term for particles of size xi is

CHEMICAL REACTION ENGINEERING LABORATORY

CHEMICAL REACTION ENGINEERING LABORATORY Result

CHEMICAL REACTION ENGINEERING LABORATORY Overall: 17.5%; Experiment, 19%.

CHEMICAL REACTION ENGINEERING LABORATORY Class 4: d = 2.5 mm; Class 6: d = 4.0 mm

CHEMICAL REACTION ENGINEERING LABORATORY Class 12: d = 16.0 mm; Class 14: d = 25.4 mm

CHEMICAL REACTION ENGINEERING LABORATORY Future Work Tune up the parameters, try to got a universal one or some sort of correlation. Test the sensitivity of boundary condition Test other breakup/coalescence closure Implement area transport equation approach Run 3D simulation Expand to Euler-Euler two fluid model With optical probe data, verify the closures and propose own closures