A New Heat Balance for Flow Boiling

Abstract Recently, one of the authors suggested calculating void fraction, an essential element in thermalhydraulics, working with the ‘thermodynamic’ quality instead of the usual ‘flow’ quality. However, the standard heat balance is currently stated as a function of the ‘flow’ quality. Therefore, we should search a new energy balance between the mixture enthalpy, based on ‘thermodynamic’ quality, and the absorbed heat. This work presents the results of such analysis based on accurate measurements of the axial profile of the cross-sectional average void fraction in the region of boiling with subcooling for water at medium and high pressures taken by Moscow Power Institute (MPI) and Argonne National Laboratory (ANL). As main results, we find that, under uniform heat flux, the mixture enthalpy suffers an abrupt reduction of its slope in passing saturation, and a new slip ratio could balance heat with such mixture enthalpy.