Effect Of Rolling Motion On Bubble Behavior In Narrow Channel Under Natural Circulation

Nowadays,subcooled flow boiling has been extensively used in the ship power,nuclear safety and industry production,and the thermal-hydraulic characteristics are different under the special condition,such as natural circulation,narrow channel,ocean condition.Therefore,it's necessary to conduct the bubble dynamic research to further explore the flow boiling mechanics under the complicated condition.In this paper,the experimental research of bubble behavior had been conducted in narrow channel under natural circulation and rolling motion.A natural circulation loop which contains visualization test section,preheater,condenser,had been built.The working fluid was deionized water.A high speed camera was used to record the bubble images.A program was developed to process the vast bubble images automatically.The experimental pressure was kept as 0.2 MPa,and the heat flux and inlet fluid temperature had a range of 100~300 kW/m2 and 20~60 ?.The single bubble behavior and the bubble population behavior were investigated under vertical static condition.It's noticed that there are two typical types of bubbles on the heating surface,rapid growth and condensate bubble and sliding bubble.The bubble growth,contact diameter and motion characteristics of each type bubble were analyzed.The familiar bubble growth model were verified with experimental data.The bubble diameter and velocity probability density distributions of bubble population were obtained under different working conditions.The bubble diameter distributions fit lognormal distribution well,but bubble velocity distributions are agreed with normal distribution.The variations of mean bubble diameter and bubble density were obtained to indicate the effects of heat flux and inlet subcooling.A bubble diameter correlation was proposed based on the main effect factors.The effects of bubble diameter and mass flow rate on bubble velocity also were discussed.Compared with bubble population behaviors under forced circulation,the effect of natural circulation was explored.The investigation of bubble behavior under rolling motion was based on the result of vertical static condition.The variations of bubble diameter,bubble velocity and bubble density were obtained with different rolling conditions.The bubble forces were analyzed to get the main effect factors under rolling motion.The effect factors of bubble diameter under rolling motion are the same as ones under vertical static condition,and the bubble diametercorrelation proposed under vertical static condition applies to calculate diameter under rolling motion.The bubble velocity is equal to the bubble center flow velocity.Compared with bubble parameters under forced circulation and rolling motion,the fluctuation ranges of bubble parameters under natural circulation are larger.