Drift-flux correlation development for two-phase flow in rod bundles

A rod bundle drift-flux correlation is developed with intended application across a wide range of two-phase flow conditions. Special consideration is made for fluid flow mechanisms at low liquid velocity and low pressure conditions. In these instances, gravitational forces from the density difference of the associated fluid phases are more significant. Secondary flow patterns may develop as a result and a drift-flux correlation would need to make appropriate adjustments. Earlier correlations may have increased error at these conditions if they have been formulated with respect to relatively higher pressures or flow rates. In the present work, area-average void fraction data at low liquid velocity and low pressure conditions is considered. This data was collected from an adiabatic 8 x 8 rod bundle test facility using air and water as working fluids. Superficial liquid velocity ranged from 0 to 1.0 m/s and superficial gas velocity ranged from 0.030 to 10.0 m/s. A distribution parameter correlation is developed with respect to this data, an existing drift velocity correlation, and the kinematic constitutive relation of the drift-flux model. Using this approach, a significant increase in distribution parameter at low liquid velocity and relatively low void fraction is observed. This is attributed to secondary flow patterns and the newly developed correlation accounts for this behavior. A performance analysis demonstrates the new correlation as more appropriate for calculating gas velocity and void fraction than earlier correlations. A scaling analysis is provided to demonstrate that the new correlation is also applicable to prototypic plant pressures. Finally, the independent dependence of drift velocity and distribution parameter on void fraction is presented to establish further confidence in the new correlation