A study of void fraction correlations used slip-ratio models

Abstract

Void fraction, the fraction of the channel cross-sectional area occupied by the gas phase, is an important parameter in thermal-hydraulic two-phase flow study. Based on that, the component pressures, flow rate, heat transfer, and flow pattern transitions are determined. However, this parameter cannot be computed directly from the flow rate of each phase as the gas phase is generally considered to move faster than the liquid phase in a two-phase flow. The purpose of this study is to evaluate the void fraction model by using different slip ratio models. The void fraction is affected by mixture quality, temperature, pressure, flow direction, circulation mode, wall friction, and system geometry. Theoretically, the void fraction is defined as a function of slip, quality, density, and viscosity ratios. At a given pressure, the variables are mainly determined using the steam table. To evaluate void fraction models, we employ experimental data measured at different pressures on both horizontal and vertical tests. The comparison results show that while the original Smith void fraction correlation with k = 0.4 is applicable to horizontal tests, the modified one with k = 0.2 applies to vertical tests