Notes on the Phenomenological Model of Subcooled Liquid Boiling

Abstract

It is shown that the Snyder–Bergles model seems to be the best phenomenological one while describing the process of forced boiling of the liquid considerably subcooled relative to the saturation temperature. This model most likely (without contradictions) accounts for the main physical subprocesses that accompany subcooled liquid boiling (liquid microlayer evaporation below the bubble, vapor condensation at the bubble dome, liquid inflow to the microlayer), meets modern concepts on the boiling mechanism, and agrees with the experimental data. Based on experiments at the Joint Institute for High Temperatures, Russian Academy of Sciences (JIHT RAS) using high-speed video recording (at a rate of up to 100 thousand frames per second) and other studies, some subprocceses incorporated into the model are refined. They are as follows: deactivation of the nucleation sites, heat removal from the bubble dome via unsteady heat conduction, and the bubble size evolution in time as the balance of masses of the evaporated and condensed vapor. It is shown that the main mechanism through which heat from the bubble dome is transferred to the surrounding liquid is unsteady heat conduction, the intensity of which is inversely proportional to the square root of the bubble existence time. The evolution of bubble sizes is caused by the balance of masses of the evaporating liquid microlayer and steam condensing on the bubble dome. With high heat flux densities supplied to the heating surface and low liquid subcooling values, the imbalance shifts toward the evaporation side, as a result of which conditions may emerge for a growth of large bubbles and their subsequent merging and occurrence of large vapor agglomerates in the coolant flow.