Study On Droplet Characteristics Of Annular Flow In Vertical Narrow Rectangular Channel

The coolant channel of the miniaturized nuclear power plant using the plate-shaped fuel assembly is a narrow rectangular channel.The entrainment of droplets in the annular flow affects the heat transfer between the gas-liquid two-phase interface and the pressure drop in the system.Therefore,the research on the characteristics of the annular flow droplets in the narrow rectangular channel is important for improving the energy utilization efficiency and safe operation of nuclear power plants.has important practical significance.The flow characteristics of the annular flow in the vertical narrow rectangular channel are similar to those in the circular tube,but the thickness of the liquid film on the narrow side is larger than that on the broad side.By observing the droplet entrainment in the annular flow image and the laser measurement area,within the scope of this experiment,the annular flow all entrained droplets.Combined with the experimental conditions,the current droplet entrainment initiation model is analyzed,and the current droplet entrainment initiation model has poor applicability in narrow rectangular channels.The annular flow droplet generation methods in the vertical narrow rectangular channel include: wave crest shear entrainment,disturbance wave entrainment,liquid block entrainment,giant wave entrainment,bubble breakage entrainment and droplet impact entrainment.Compared with the liquid droplet entrainment mode in the vertical tube,it is found that the annular flow droplet entrainment has different entrainment modes in different channel structures.Within the parameters of the experimental conditions,the droplet size distribution of the annular flow in the vertical narrow rectangular channel has two distributions: unimodal and bimodal;the gas conversion velocity has a great influence on the droplet size,while the liquid conversion velocity has a significant The droplet size has little effect.The existing formula for calculating the average diameter of droplet Sauter is not suitable for narrow rectangular channels.Based on the experimental data and combined with the influence factors of droplet particle size,the correlation of the average diameter of the annular flow droplet in the narrow rectangular channel is proposed.The relationship between the calculation formula and the prediction result of the average particle size of the droplet Sauter is within 10%.In this paper,the relevant laws of the characteristics of the annular flow droplets in the vertical narrow rectangular channel are obtained through experiments,the starting boundary of the annular flow droplet entrainment is discussed,and the entrainment method of the annular flow droplet in the vertical narrow rectangular channel is analyzed.The particle size characteristics and distribution rules of the droplets were obtained from the measurement results of the annular flow droplets,which provided a reference for the follow-up research on the annular flow droplets in the narrow rectangular channel under heating conditions.