Study On The Bubble Lifetime In Free Surface And The Characteristics Of Entrainment In Burst

Bubbles exist in the industry and the environment in the process widely.bubbles will burst after reaching to the free surface for a period.The droplets,as a key to the liquid-gas conversion process,have a profound impact on our daily lives in the field of nuclear.In case of severe accidents such as the steam generator tube rupture and even the core meltdown,radioactive aerosols will be produced,natural sedimentation in aerosols and containment spray system under the action of engineering safety facilities,radioactive aerosol will be detained in the liquid pool.The liquid pool will boil to produce bubbles when containment pressure is relieved.In FCVS,the bubble can also generate by injecting the gas into the liquid pool.Film drops produced by bursting of the bubble can entrain radioactive aerosols from the liquid phase to the air.This long-lasting source term may generate considerable aerosol.We need to measure many physical quantities related to the bubble bursting to evaluate this source term.In this paper,the phenomenon of bubble bursting at the liquid surface is studied experimentally.Visual methods combined with a variety of image processing softwares and image processing methods are used to obtain the required physical quantities.This article mainly studies the bursting characteristics of bubbles,the entrainment and releasing characteristics of droplets under different conditions.Among them,the bursting characteristics mainly explore the puncture position of bubble,the lifetime of bubble,film roll-up speed and the cap film thickness,the entrainment characteristics of the liquid droplet mainly investigate the number,velocity,and size of the droplets generated by bubble bursting,The mass of entrained aerosol is calculated on this basis.The main conclusions obtained are as follows:(1)Different fitting formulas of bubble lifetime distribution are given.In a certain range,as the radius of the bubble increases,the lifetime of bubble appears to decrease,the addition of aerosols will increase the lifetime of bubble,and the law of changment with the temperature of the liquid phase is close to that of deionized water.The cap film thickness at busting and the lifetime show an exponential law,and as the liquid temperature increases,the cap film thickness increases,when the gas phase temperature increases,the cap film thickness decreases.(2)As the thickness of the cap film increase(the lifetime of the bubble decreases),the number of droplets generated from bursting bubbles decreases,the size increase,the speed decrease,the number of droplets and the thickness of the cap film show an exponential change.Different fitting formulas of droplet size distribution are given.For deionized water and aerosol suspensions,under the same lifetime,as the liquid temperature increases,the number of droplets increases,the size increase,and the speed decrease.The velocity of the droplets obeys a multimodal distribution.(3)As the superficial velocity increases,the mass of the entrained aerosol increases,and the increase will become smaller and smaller,and eventually stabilize at a specific value.The mass of aerosol entrained by a single bubble burst increases with the increase of liquid phase temperature.