In two-phase flow models, the void fraction is the key parameter for predicting flow pattern transitions, heat transfer, and pressure drops and, moreover, for determining the two-phase density and viscosity and the relative average velocity of the two phases. Thus, a comprehensive review of analytical and empirical void fraction models is presented. Various methods have been proposed for predicting void fractions and two-phase pressure drops for shell-side flows. However, these have been developed from very limited databases and have not been compared to independent data. It is shown here that the liquid static head is much larger than the combined influence of frictional and acceleration pressure drops at normal operating conditions, and, hence, void fraction becomes the most important parameter in predicting two-phase pressure drops for flooded evaporators. Also, completing the review, two-phase flow patterns and flow pattern maps for flows over tube bundles are surveyed.

Units: Dual