EXPERIMENT STUDY ON THE LIQUID FILM BEHAVIORS OF ANNULAR FLOW IN THE RECTANGULAR CHANNEL

Critical heat flux (CHF) is the most important parameter related to the safety performance of heat exchanging equipment, whose triggering mechanisms are very complex and complicated. The prediction of dry-out critical heat flux in a narrow rectangular flow channel was usually based on the accurate prediction on the instantaneous liquid film spatial distribution and its characteristics in annular flow, such as liquid film thickness and disturbance wave destruction rate, and other key parameters. Therefore, it is essential to conduct detailed research on the liquid film behaviors for the annular flow in the narrow rectangular channel. In order to obtain the liquid film thickness, the plate-type liquid film sensor was developed by utilizing the huge differences of electrical conductivity between gas and liquid. The corresponding relationship between the measured voltage and the real void fraction was established with calibration of empirical model, and then the void fraction was converted into liquid film thickness theoretically. Based on the plate-type liquid film sensor, the liquid film was measured in the narrow rectangular channel with a cross-section of 4 mm x 66 mm at different flow conditions. The effects of liquid flow velocity and gas flow velocity on the averaged liquid film thickness and dynamic fluctuation characteristics were analyzed. This study provided data support and theoretical guidance for the accurate prediction of the dry-out type critical heat flux, and was helpful for the design of the fuel assemblies consisting of narrow rectangular channel and the safety assessment of nuclear reactor systems.