Numerical Simulation Of Bubble Formation And Movement

The course of two-phase flow widely exists in many industries, such as energyindustry, petrochemical industry, pharmaceutical industry, and food processing industry.The course of bubble formation and movement is the basic problem of describing theprocess of gas-liquid two phase flow. The law of bubble formation and movement hascloserelationshipwiththeworkingconditionofgas-liquidtwophaseflow.Itisimportantforanalyzingthemechanismof gas-liquidtwophaseflow,understandingtheconditionofthe production process and improving the production efficiency to find and accuratelydescribethefactorsofaffectingthebubbleformationandmovement.Based on the visualized vertical bubble column, the technology of numericalsimulationisusedtoresearchtheprocessofbubbleformationandmovement andanalyzethe factors of influencing the process. The specific work that has been finished in thisworkisasfollows:(1) The simulation model is set up by gridding, defining the boundary conditions,selecting proper turbulence model and the algorithm, set fluid physical properties andotherparameters.(2)Accordingtothephasedistributionofthebubblegrowing,theshapechangingofthe bubble forming is observed and the processes of the bubble forming are divided intothree stages: slow growing stage, quick growing stage and detachment stage. Under thepressure distribution of the bubble forming, the pressure inside the bubble is decreasinggradually and the there is no pressure difference inside and outside the bubble. Kinds ofconditions that affect the detachment time and the bubble volume are analyzed: thedetachment time and the bubble volume after detaching increase with the static contactangle's increasing; the detachment time decreases with the orifice flow rate's increasing,but the bubble volume is on the contrary; under the same flow rate, the detachment timeget smaller and the bubble volume get larger because of the bigger orifice diameter; thebubble detachment time and the bubble volume get larger when the liquid density get larger; while the bubble detachment time and the bubble volume are insensitive with theliquid viscosity's changing; the detachment time and the bubble volume increase linearlywiththesurfacetension'sincreasing.(3) According to the velocity distribution of bubble rising, it is explained why thepath of bubble rise is "S" shape. It is analyze of kinds of conditions that influence thebubble motion: With the orifice flow rate's increase, the stable rate of the bubble risingincreases graduallyandtheoscillationfrequencywhenbubblerisedecreasebuttheswingamplitude increases, Liquid viscosity's increasing make the bubble shape's obviouschanging. When the viscosity gets large enough, the bubble rises along an approximatestraight line. The surface tension has an important role on maintaining the bubble shape.The bubble can easily maintain the initial shape when surface tension is large enough.When a bubble enters the wake region of another bubble, the following bubble willaccelerateandtwobubblescoalescenceintoalargebubble.