A Unified System Mean Void Fraction Model for Predicting Transient Phenomena Associated with Complete or Incomplete Evaporating and Condensing Flows

Abstract

The system mean void fraction model has been developed for two-phase transient evaporating and condensing flow systems. It allows for separated flows, and for an axial distribution of local void fraction. Thus it is a distributed model. The principal governing equations are written in integral form, encompassing a finite region upstream of a particular representative propagating void. Incorporating the concept of a system mean void fraction, the governing equations can be formulated such that they are identical for complete or incomplete evaporating and condensing flows. These equations often result in relatively simple closed-form solutions. The purpose of this paper is to present this unified model, and to demonstrate the versatility of its predictive capability for a wide variety of transient phenomena.