Contact

Dr. Eckhard Krepper
Computational Fluid Dynamics
e.krepperAthzdr.de
Phone: +49 351 260 - 2067
Fax: +49 351 260 - 12067

Dr. Dirk Lucas
Head Computational Fluid Dynamics
d.lucasAthzdr.de
Phone: +49 351 260 - 2047
Fax: +49 351 260 - 12047

Polydispersed flow in vertical tubes

The general aim of the work in the field of thermal fluid-dynamics of multiphase systems is the qualification of Computational Fluid Dynamics (CFD) codes for the simulation of complex two-phase flows with relevance for industrial applications. To achieve this goal closure models are needed for the interaction between the phases, i.e. mass, momentum and heat transfer. For the special case of dispersed bubbly flow all these transfers strongly depend on the local bubble size. For this reason in case of poly-dispersed the gas phase has to be split into a number of size groups. Transfers between these groups are amongst others determined by bubble coalescence and fragmentation. The theoretical work is based on experiments at the TOPFLOW test facility using advanced two-phase measuring instrumentation, which is developed in this framework. Detailed studies on model concepts, required number of bubble size classes and the suitability of different closure models were done using a Multi Bubble Size Test Solver, which was especially developed for this purpose. In the result of these investigations the concept of the so-called Inhomogeneous MUSIG (MUlti Bubble SIze Group) model was developed and finally implemented into the CFD code CFX together with the code-developer ANSYS®.

This Inhomogeneous MUSIG model approach uses a number of subsize bubble size fractions for the simulation of bubble coalescence and fragmentation. These subsize fractions are assigned to a limited number of gas velocity field groups (see Fig. 1).

Grundprinzip des inhomogenen MUSIG-Modells

Fig. 1: General principle of the inhomogeneous MUSIG approach: Several bubble size fractions are assigned to few gas velocity groups

The experimental data basis for upwards flow in vertical pipes obtained at the TOPFLOW facility was used for the test and validation of the model. The simulations were done for air-water flows as well as for steam water flows under adiabatic conditions, i.e. with negligible phase transfer. For all the cases considered two velocity groups for the gas phase were sufficient for a qualitative agreement with the experimental findings. The separation of small and large bubbles is well reflected by the simulations, what confirms the potential of the model. Problems arise from the models for bubble coalescence and breakup. After tuning the coefficients of the implemented models in fact good agreement was achieved, but no parameter set could be found, which is applicable for a range of different flow parameters. Further investigations for the improvement of such models are required. Simulations for the validation of the Inhomogeneous MUSIG models were also done using experimental data obtained at the TOPFLOW facility for bubbly flows in complex geometries.

MUSIG Bild2

Fig. 2: Bubble size distribution (left) and the radial gas fraction profiles (right) of the simulation of the air/water test case TOPFLOW 118 at the distance levels from the gas injection of 0.335 m (C) and 7.802 m (R) (JL=1.017 m/s; JG=0.2194 m/s)

Main publications

  • Krepper, E.; Frank, T.; Lucas, D.; Prasser, H.-M.; Zwart, P., 2008. A population balance approach for polydispersed bubbly flows considering size dependent bubble forces, 6th International Conference on COMPUTATIONAL FLUID DYNAMICS in the Oil & Gas, Metallurgical and Process Industries, 10.-12.06.2008, Trondheim, Norway
  • Krepper, E. ,Lucas, D.,  Frank, Th. Prasser, H.-M.,  Zwart, Ph. J., 2008. The inhomogeneous MUSIG model for the simulation of polydispersed flows, Nuclear Engineering and Design 238,  1690–1702
  • Frank, T., Zwart, PJ.,  Krepper, E.,  Prasser, H.-M.,  Lucas, D., 2008. Validation of CFD models for mono- and polydisperse air–water two-phase flows in pipes, Nuclear Engineering and Design 238, 647-659
  • Krepper, E.; Frank, T.; Lucas, D.; Prasser, H.-M.; Zwart, Philip J., 2007. Inhomogeneous MUSIG model – a population balance approach for polydispersed bubbly flows, The 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-12), 30.09.-04.10.2007, Pittsburgh, USA
  • Krepper, E.; Frank, T.; Lucas, D.; Prasser, H.-M.; Zwart, Philip J. 2007. Inhomogeneous MUSIG model – a population balance approach for polydispersed bubbly flows, 6th International Conference on Multiphase Flow, ICMF06, 09.-13.07.2007, Leipzig, Germany, Paper No S_6_Thu_B_51
  • Krepper, E.; Beyer, M.; Frank, T.; Lucas, D.; Prasser, H.-M., 2007. Application of a population balance approach for polydispersed bubbly flow, 6th International Conference on Multiphase Flow,  ICMF06, 09.-13.07.2007, Leipzig, Germany, Poster No PS6_6
  • Frank, T.; Zwart, P.; Krepper, E.; Prasser, H.-M.; Lucas, D. 2006. Validation of CFD models for mono- and polydisperse air-water two-phase flows in pipes, OECD/NEA International Workshop on The Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS, 05.-09.09.2006, Garching, Germany, Proceedings paper B6-32
  • Frank, T.; Zwart, P.; Shi, J.-M.; Krepper, E.; Lucas, D.; Rohde, U. 2005. Inhomogeneous MUSIG model – a population balance approach for polydispersed bubbly flows, International Conference Nuclear Energy for New Europe, 05.-08.09.2005, Bled, Slovenia
  • Krepper, E., Lucas, D., Prasser, H.-M., 2005. On the Modelling of bubbly flow in vertical pipes, Nuclear Engineering and Design  235, 597-611
  • Shi, J.-M., Zwart, P.-J., Frank, T., Rohde U. and Prasser, H.-M., 2004. Development of a multiple velocity multiple size group model for poly-dispersed multiphase flows. Annual Report of Institute of Safety Research. Forschungszentrum Dresden-Rossendorf, Germany, 2004, pp. 21 – 26
  • Burns, A. D.; Frank, T.; Hamill, I.; Shi, J.-M., 2004. The Favre Averaged Drag Model for Turbulent Dispersion in Eulerian Multi-Phase Flows, 5th International Conference on Multiphase Flow, ICMF 04, JSME, ASME, 30.05.-04.06.04, Yokohama, Japan, paper No. 392

Acknowledgements

The work is carried out as a part of current research projects funded by the German Federal Ministry of Economics and Technology, project numbers 150 1215, 150 1265 and 150 1329 .

Cooperations

  • ANSYS Germany, Otterfing

Contact

Dr. Eckhard Krepper
Computational Fluid Dynamics
e.krepperAthzdr.de
Phone: +49 351 260 - 2067
Fax: +49 351 260 - 12067

Dr. Dirk Lucas
Head Computational Fluid Dynamics
d.lucasAthzdr.de
Phone: +49 351 260 - 2047
Fax: +49 351 260 - 12047