An inhomogeneous-musig CFD validation of the condensation of large steam bubbles directly injected into flowing subcooled water in a vertical pipe

A comparison between simulations of large steam bubbles directly injected into a flowing subcooled water using the monodispersed approach and the inhomogeneous MUSIG approach is conducted. The goal of this study is to verify the influence of adopting the more accurate representation of the existing bubble-size and rising velocity distributions of the simulated cases by the inhomogeneous MUSIG model versus the previously applied monodispersed model. Calculations of the Inhomogeneous MUSIG model were conducted applying same geometry, mesh, boundary conditions, and physical models of the monodispersed model. Additionally, a bubble-size and a rising velocity distributions were extracted from experimental data and applied into the inhomogeneous MUSIG model which allows the calculation of a separate momentum transfer (steam velocity) for each of the adopted bubbles classes. Obtained steam fraction distributions were compared against experimental ones and against calculations of the monodispersed calculations. The comparisons show that the monodispersed approach was able to yield a good agreement with experimental results despite its simplicity against the inhomogeneous MUSIG model. However, the inhomogeneous MUSIG model gives more insight into the simulations results and it results in a better agreement with experimental data if the provided distributions were accurate enough. Simulations show the complex behavior of adopting a multi-disperse approach against a simple monodispersed one, and this was possible through the availability of an experimental 2D steam fraction distribution that was extracted out of experimental data. Current results confirm previous conclusions from the monodispersed simulations of the need for a further investigation of the dynamics of large steam bubbles. It also shows the necessity of adopting a bubble-size adapted condensation rate (Nu-Re) correlation when the bubbles are composed of a wide range of bubbles classes (small and large). Finally current simulations showed the effect of the added mass force upon stability of the conducted simulations.