Experimental investigation of liquid entrainment in vertical upward annular flow based on fluorescence imaging

摘要

The liquid entrainment in annular flow is essential for the prediction of the critical heat flux (CHF), which is one of the important thermal hydraulics parameters in the nuclear boiling water reactor (BWR). However, few investigations have focused on the liquid entrainment in the annular flow inside pipe. In this paper, the liquid entrainment in the vertical upward gas-liquid annular flow was investigated by the Planar Laser-induced Fluorescence. Five types of entrainment have been observed and studied on the basis of the fluorescence imaging and the quantitative measurements. The frequency of occurrence for each entrainment is investigated, and the influencing factors are further discussed. The results show that for entrainment types 2 and 3, the frequency of occurrence decreases with the increasing of wave frequency, while for the entrainment types 4 and 5 that increases as the fluctuation amplitude of the liquid film increases. Finally, the frequency of occurrence for the five types of entrainment is statistically analyzed, and the influences of flow conditions on the fraction distribution of the entrainment are investigated. With the increase of the gas-liquid superficial velocity, the fraction distribution moves to the left and the right respectively. The transformation of fraction distribution corresponds to the variations in the contributions of entrainment types 1-5 to the total entrainment frequency, which could reveal the essence that the gas-liquid superficial velocity affects the size distributions of liquid entrainments. These results can provide a key solution to investigate the characteristics of liquid entrainment and contribute to better understanding of the liquid entrainment in the gas liquid annular flow.