The onset of significant void in up-flow boiling of water at low pressure and velocities

Abstract

Results of experiments to determine the point of onset of significant void (OSV) for up-flow boiling of water at low pressure ( $ ̃ 150 kPa) and low velocities (<0.5m s −1) show that the sub-cooling at OSV increases as liquid inlet velocity increases. According to the Saha and Zuber OSV correlation there should be no effect of velocity under the experimental conditions since the Peclet number is less than 70 000. At higher Peclet numbers, empirical evidence and existing correlations and models show that the subcooling at OSV decreases as liquid velocity increases. A model, based on the findings of Winterton on bubble departure, has been developed which predicts the observed trend of sub-cooling at OSV with velocity in these experiments as well as the opposite trend observed by others at higher velocities.