On the Development of Correlations for Bubble Liftoff Parameters During Subcooled Nucleate Flow Boiling Using Nonintrusive Dynamic Measurements

Accurate prediction of bubble dynamic parameters is essential to improve boiling heat transfer models. Considering the complexities and challenges associated with performing a large number of boiling experiments, researchers have realized the importance of experimental correlations for predicting bubble dynamic parameters. In this direction, we report an experimental work concerned with the development of correlations for various bubble liftoff parameters during nucleate flow boiling regime. As a definite advancement, the experimental measurements have been performed in a purely nonintrusive manner, thereby minimizing the errors arising due to the interaction of any external probe with the process under study. The measurement approach makes use of a gradient-based imaging technique to simultaneously map the bubbling features and thermal field around a single vapor bubble generated under subcooled flow boiling conditions. Experiments have been performed in a rectangular channel for a wide range of heat fluxes (q" = 20-50 kW/m(2)), subcooling level (Delta T-sub = 2-9 K), and Reynolds numbers (Re = 600-6000) with water as the working fluid. Results show a strong dependence of bubble liftoff parameters on Reynolds number, subcooling level, and applied heat flux. Based on the experimental measurements, empirical correlations have been developed for various bubble liftoff parameters as a function of Jacob number and Reynolds number. Predictions made through the developed correlations are found to be in good agreement with the measured values as well as with the values reported in the available literature. Of all the bubble parameters, maximum deviation between the predicted and measured values (approximate to 23%) was found to be in bubble release frequency.