Similarities and differences in the flow patterns and void fraction in vertical upward and downward two phase flow

Most of the research in vertical two phase flow is dedicated to the vertical upward flow whereas the vertical downward two phase flow has received considerably little attention. In this study we have presented the experimental results of the flow patterns and the void fraction measurements for vertical upward and downward two phase flow. As a consequence of the interaction of the liquid inertia and the buoyancy force a definite difference in the appearance of the upward and downward two phase flow was observed. The analysis of the 1208 and 909 experimental data points for up and down flow showed a definite tendency of the variation of the void fraction with varying phase flow rates. The investigation is principally concerned with the differences in the flow patterns and void fraction for both orientations. Another important aspect of this investigation was the performance analysis of the available void fraction correlations. The results of the top five performing correlations among the pool of 52 correlations for vertical upward and 26 correlations for vertical downward orientation are presented.

► Experimental investigation of flow patterns and void fraction.
► Interaction of buoyancy, gravity and liquid inertia forces on void fraction.
► Variation of void fraction with respect to the flow patterns.
► Performance analysis of the available void fraction correlations.
► Recommendations for an ideal void fraction correlation.