This paper presents a study of flushing non-condensable (NC) gases out of a chamber by a saturated steam flow. During the flushing and mixing process, significant heat transfer occurs among the NC gases, steam and the chamber wall, with a coupled steam condensation. The flushing effectiveness hence is strongly dependent upon the mixing, condensation characteristics, the steam feeding rate as well as the thermal capacity of wall. The objective of this study is to explore modeling approaches on such a process which would be applied to assist the optimization of the process design and operation. An experimental system has been developed to provide a set of data for model validations. A simple mechanistic model based has also been developed to show the " equilibriumbased"flushing characteristics. However, to account for finite rate of heat and mass transfer and non-uniform mixing, a more complicated full-field computational fluid dynamics modeling and simulation must be involved. The typical boundary conditions in most commercial CFD codes (such as FLUENT) cannot be directly applied to the flushing processes due to the coupled surface condensation. Hence, in this paper, we have also proposed the condensation-based boundary conditions for the CFD simulations. Full-field CFD simulations with those boundary conditions are being investigated.