An improved mechanistic model for predicting bubble characteristic size in subcooled flow boiling

Abstract

Bubble nucleation and its life cycle in subcooled flow boiling follows a sequence of processes known as bubble ebullition cycle, where the nucleating vapor bubble grows, followed by sliding and departure from the heated surface before the cycle is repeated. In the present work an analytical model has been developed to predict bubble departure and lift-off diameter in subcooled flow boiling. Present model is based on mechanistic force balance approach and it considers few unresolved issues of existing analytical models. Wall contact diameter and relative velocity of sliding bubble with respect to coolant flow have been identified as key parameters which have been either ignored or used as constants in existing analytical models. In the force balance approach dominant forces responsible for bubble departure have been considered while others are ignored. Relative velocity of the vapor bubble is premeditated during bubble lift off predictions and its value is used for optimizing the wall contact diameter while predicting the departure diameter. Present model has been validated with reported experimental data of subcooled flow boiling for a wide range of operating conditions. Compared to available analytical models, present model further reduces the prediction error in estimating bubble characterisctic size.