Steam bubble condensation in polydispersed flow experiments and CFD simulations

Steam bubble condensation in polydispersed flow experiments and CFD simulations

Krepper, E.; Schmidtke, M.; Lucas, D.; Beyer, M.

Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
Experiments on steam bubble condensation in vertical co-current steam/water flows have been carried out in a 8m long vertical DN200 pipe. Steam is injected into the pipe and the development of the bubbly flow is measured at different distances to the injection using a wire mesh sensor. By varying the steam nozzle diameter the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore condensate slower. Steam pressures between 1-2 MPa and sub-cooling temperatures from 2 to 6 K were applied. Due to the drop of hydrostatic pressure along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section. The experimental configurations are simulated with the CFD code CFX using an extended MUSIG approach, which includes the bubble shrinking or growth due to condensation or re-evaporation. The development of the vapour phase along the pipe with respect to vapur void fractions and bubble sizes is qualitatively well reproduced in the simulations. For a better quantitative reproduction, reliable models for the heat transfer at high Reynolds number as well as for bubble breakup and coalescence are needed.

Keywords: two phase flow; experiments; CFD simulation; population balance models; mass transfer

  • Contribution to proceedings
    Int. Conf. "Nuclear Energy for New Europe", 06.09.-09.10.2010, Portoz, Slovenien
  • Lecture (Conference)
    Int. Conf. "Nuclear Energy for New Europe", 06.-09.09.2010, Portoz, Slovenien

Publ.-Id: 14464