MODELING OF VERTICAL BUBBLE-DRIVEN FLOWS

Bubbly flows comprise a large number of different flow situations, e.g ., dispersed pipe flows, flows in multiphase agitated tanks, flows in multiphase fixed-and fluidized-bed reactors, and typical bubble-column and loop-reactor flows. This paper focuses on bubble-driven flows. Th ese are flow situations were the bubble movement itself is the main so urce of momentum to the now field and are often characterized by low s uperficial liquid velocities, relatively high superficial gas velociti es, and no mechanical support of the now (e.g., agitation). Only verti cal now situations are considered. An overview of the verified forces acting on bubbles is given, and examples of both classical and more re cent modeling approaches are shown. This include gravity, buoyancy, ce ntrifugal forces, conventional Magnus and Saffman forces, form and fri ction drag, and added mass as well as turbulent migration and other in stability mechanisms. Special emphasis is placed on mechanisms creatin g bubble movement in the radial direction. Important literature on the subject with regard to the use of computational fluid dynamics to mod el gas-driven bubbly flows is reviewed, and the various approaches are evaluated, i.e., dynamic vs steady-state descriptions and Euler/Lagra nge vs Euler/Euler formulations. Results from steady-state Euler/Euler simulations are given and discussed, and the demand for amplified mod eling including more accurate and stable numerical solution schemes an d algorithms is stressed.