Condensation of Steam Bubbles Injected into Sub-Cooled Water

Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modeling of the condensation process. The effect of bubble sizes was clearly shown in experimental investigations done at the TOPFLOW facility of FZD. Steam bubbles were injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices were used to vary the initial bubble size distribution. Measurements were done using a wire-mesh sensor. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. In a previous work a simplified test solver, developed especially to test models for vertical pipe flow was used to simulate these effects. Now the results will be transferred to the CFD code CFX from ANSYS. Recently the Inhomogeneous MUSIG model was implemented into the code enabling the simulation of poly-dispersed flows including the effects of separation of small and large bubbles due to bubble size dependent lift force inversion. It allows to divide the dispersed phase into size classes regarding the mass as well as regarding the momentum balance. Up to now transfers between the classes in the mass balance can be considered only by bubble coalescence and breakup (population balance). Now an extension of the model is proposed to include the effects due to phase transfer. The paper discusses the necessary extensions of the Inhomogeneous MUSIG model and presents the new experimental setup for the investigation on steam bubble condensation.