The droplet entrainment phenomenon from a liquid film is of significant importance for the safety design of boiling water reactor (BWR) because the amount of droplet entrainment is closely involved in the occurrence of the dryout. In general, when the dryout occurs, heat transfer from the heating wall is deteriorated and the wall temperature rapidly increases. As a result, it might cause the significant accident of nuclear reactor, so the accurate prediction of droplet entrainment phenomenon is required.This entrainment phenomenon can be divided into several types of phenomena. These phenomena are by a shearing off of roll-wave crest, wave undercutting, impingement of the liquid drop, and bursting of nucleation gas bubbles in the liquid film. Then, little is known about the mechanism of the droplet entrainment caused by nucleate boiling, and few studies have focused on the measurement of its rate in forced convection flows. In this present study, we observed the phenomenon to identify the droplet entrainment mechanism caused by nucleate boiling in the condition of air-water two-phase flow.As for the experimental conditions, a liquid film is formed in a rectangular flow channel using air and water at atmospheric pressure, and was heated using a cupper block heater. The heating surface is 11 mm in width and 50 mm length. In this experiment, a heat flux ranged from 0.3 to 1.2 MW/m2&nbsp;and superficial velocity of the gas and the liquid are respectively from 0.4 to 0.8 m/s and from 2 to 9 m/s.&nbsp;We found that the droplet entrainment by nucleate boiling is caused by breakup of filament which is formed when the vapor bubble reaches and collapses at the interface between water and air phase. Besides, we found that the amount of droplet entrainment increases as the heat flux increases, and the droplet entrainment did not occur under the condition of low heat flux which was almost zero nucleate boiling heat transfer and the evaporation from liquid film would be dominant. From these experimental results, it appears that the amount of droplet entrainment by nucleate boiling may be associated with the intensity of nucleate boiling heat transfer. In the future works, we will relate this result to a mechanistic heat transfer model like the heat transfer correlation by Chen and we try to improve the conventional model using by this correlation.

Experimental Observation of Nucleate Boiling Entrainment in a Liquid Film

Paper Proceedings: https://asmedigitalcollection.asme.org/ICONE/ICONE28/volume/85246

2021 28th International Conference on Nuclear Engineering (ICONE28)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.