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Modeling the Evolution of Bubbly Flow Along a Large Vertical Pipe

Dirk Lucas, Eckhard Krepper, H.-M. Prasser

Nuclear Technology / Volume 158 / Number 2 / May 2007 / Pages 291-303

Technical Paper / Nuclear Reactor Thermal Hydraulics

A detailed experimental database, obtained for a 195-mm inner diameter, 9-m-long pipe was used for the validation of models applied in computational fluid dynamics codes for the simulation of bubbly flow. Since the bubbles were injected via holes at the pipe wall, very useful information on the bubble migration from the pipe wall toward the pipe's center was obtained by measurements at different distances between gas injection and measuring plane. The bubble migration is determined by the forces acting on the bubbles. The multibubble-size group test solver, introduced earlier but with some new extensions, was used to analyze the data. A comparison of results from a simulation and the experimental findings indicate that the turbulent dispersion force according to the Favre averaged drag model is too strong compared with the drag in the radial direction. No appropriate models for bubble coalescence and breakup, which can be applied for a wide range of gas and liquid volume flow rates, are available as yet. Nevertheless, for selected combinations of volume flow rates, the calculated bubble size distributions and radial gas volume fraction profiles show an acceptable agreement with the experimental data.

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