Please cite this article in press as: Liao, Y., et al., Application of new closure models for bubble coalescence and breakup to steam–water vertical pipe flow. Nucl. Eng. Des. (2014), http://dx.doi.org/10.1016/j.nucengdes.2014.02.015 ARTICLE IN PRESS G Model NED-7753; No. of Pages 11 Nuclear Engineering and Design xxx (2014) xxx–xxx Contents lists available at ScienceDirect Nuclear Engineering and Design jou rn al hom ep age: www.elsevier.com/locate/nucengdes Application of new closure models for bubble coalescence and breakup to steam–water vertical pipe flow Yixiang Liao ∗ , Dirk Lucas, Eckhard Krepper Helmholtz-Zentrum Dresden-Rossendorf e.V., Institute of Fluid Dynamics, PO Box 510 119, 01314 Dresden, Germany h i g h l i g h t s • New development in closure models for bubble coalescence and breakup. • Application of new coalescence and breakup model for condensing steam bubbles. • Considerable improvement brought by the new model. • General applicability of the new model for air–water and steam–water flows. • Uncertainty in inlet liquid sub-cooling affects the results significantly. a r t i c l e i n f o Article history: Received 20 February 2014 Accepted 25 February 2014 Keywords: Coalescence and breakup Steam condensation Bubbly flow Vertical pipe a b s t r a c t New closure models for bubble coalescence and breakup proposed in Liao et al. (2011), Nucl. Eng. Des. 241, 1024, are assessed for the case of condensing steam–water pipe flows. Steady-state CFD calculations are performed employing the commercial CFD solver ANSYS CFX. Predicted evolution of cross-section averaged bubble size and gas volume fraction distribution along the pipe is compared with the measure- ments provided by the TOPFLOW facility (Lucas et al., 2010. CFD4NRS-3, Int. Workshop on Experimental Validation and Application of CFD and CMFD Codes to Nuclear Reactor Safety Issues, Paper 13.1, 14.16.09, Washington D.C., USA.). It is shown that for cases with small initial bubble size and low gas volume frac- tion, bubble coalescence and breakup can be taken to be nearly negligible and the change of bubble size is primarily due to condensation. Nevertheless, with the increase of initial bubble size or gas volume frac- tion, bubble coalescence and breakup become more prevalent. Performance of new and standard closure models of bubble coalescence and breakup is investigated It is shown that both models overestimated the breakup rate; in particular, the standard model. The numerical results are also found to be dependent on the inlet liquid temperatures and inter-phase heat transfer models have a significant impact on the results. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The phenomena of gas–liquid flows are omnipresent in our daily life as well as having being significant in industrial applica- tions and scientific investigations. With increasing computational power, computer-aided simulation of computational fluid dynam- ics (CFD) is increasingly becoming an important analysis tool of fluid flow phenomena. Furthermore, in recent CFD simulations of gas–liquid flows, instead of assuming mono-dispersity it is crucial that the change of local bubble size is adequately predicted. In order to aptly predict the bubble size distribution, additional closure ∗ Corresponding author. Tel.: +49 3512602389. E-mail address: y.liao@hzdr.de (Y. Liao). models are needed in the Eulerian framework for the description of the interfacial processes that change the bubble size or interfacial area density such as coalescence and breakup. Although there has been considerable development of theories and models, the prediction of bubble coalescence and breakup rates remains one of the weakest links in the modern CFD simulation of poly-dispersed bubbly flows (Krepper et al., 2008). Concrete limi- tations of existing models can be summarized by one issue, that is, the transferability is limited (Liao and Lucas, 2009a, 2010). Starting from this point, new models have been presented in our previous work, which attempts to accommodate all important mechanisms leading to the coalescence and breakup of bubbles in a turbulent flow (Liao and Lucas, 2009b; Liao et al., 2011). The new models of coalescence and breakup have been vali- dated for air–water vertical pipe flows over a wide range of gas and http://dx.doi.org/10.1016/j.nucengdes.2014.02.015 0029-5493/© 2014 Elsevier B.V. All rights reserved.