Study of Flow Patterns and Void Fraction in Vertical Downward Two Phase Flow

Abstract

An experimental investigation on the flow patterns and void fraction in vertical downward two phase flow was carried out accompanied by exhaustive literature review. The flow patterns and the variation of the void fraction with the flow patterns were compared against the experimental data in the present study. Detailed flow visualization was helpful for insightful discussion on the appearance of the flow patterns. Drift flux model was examined and it was shown that the void fraction correlations developed for vertical upward flow can be applied to predict the void fraction in vertical downward flow. Finally this thesis concluded by a rigorous analysis of the void fraction correlations followed by the recommendation of the best flow pattern independent correlation. Flow visualization confirmed the existence of the five major flow patterns in the downward two phase flow. The characteristics of the bubbly and slug flow were elucidated on the basis of photographic evidences. The experimental measurement of the void fraction contributed in assembly of a comprehensive void fraction data set. Owing to the flexibility of the drift flux model it was found to be the most successful model to predict the void fraction in downward two phase flow. The performance analysis of the void fraction correlations was useful in identifying the top performing flow pattern independent void fraction correlations. This analysis gave a better understanding of the physical structure of the drift flux models and concluded with the recommendation of the requirements of an ideal downward two phase void fraction model.