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The system mean void fraction model has been successful in the prediction of a variety of transient evaporating and condensing flow phenomena; however, applications of the model have been restricted to physical situations involving complete vaporization or condensation. The major contribution of this paper is the development of a generalization of the existing system mean void fraction model, applicable to the broader class of transient two-phase flow problems involving incomplete vaporization. Present applications of the generalized system mean void fraction model to transient evaporating flows indicate good agreement with experimental void fraction and mass flux response data available in the literature. These data represent a variety of different flow geometries, types of fluids, and a wide range of operating conditions.

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This paper presents the results of an experimental and theoretical investigation of an unstable flow phenomenon that leads to sustained limit-cycle type of oscillations of large amplitude, and which under certain conditions, can involve flow reversals. This unstable behavior normally exists for conditions of low outlet throttling. Upstream compressible volume and downstream inertia appear to be the dominant energy storage mechanisms for the self-sustained oscillations. A linearized analysis based on the system mean void fraction model successfully predicts the experimentally observed stability boundary.