Prediction of the onset of flow instability in transient subcooled flow boiling

A new model to predict the onset of flow instability (OFI) in transient subcooled flow boiling has been developed. The model is based upon the influence on vapor bubble departure of the single-phase temperature profile. The steady-state result of the present model was compared to the experimental data of Whittle and Forgan and Dougherty et al., showing an excellent agreement. The model was then employed in a transient analysis of OFI for vertical downwards turbulent flow to predict whether OFI takes place. The condition for OFI to occur in transient flow situations was also predicted by this model. Two modes for pressure gradient change inside the channel are considered in the present study: Step change and ramp change. The calculations were made for various combinations of the flow operating condition and the mode of pressure drop change. (orig.)