Experimental Study And Numerical Simulation Of The Bubble Dynamics In Micron Level Orifice

Visualization experiments and numerical simulations were carried out to investigate the bubble dynamic behaviours at the submerged micron orifice.The diameters of orifices under the water were from 0.136 mm to 0.238 mm.Bubble formation process was recorded by a high speed video camera and detailed bubble characteristics were obtained through image processing and analysis by Matlab.The numerical simulation studies emphasized on the distribution of pressure and velocity during the bubble growth process under low gas flow rate conditions.The results show that under low gas flow rate,the bubble grows and detaches in form of a single individual.And the bubble's formation progress can be divided into three stages.The difference between micron level orifice and millimetre level orifice mainly focuses on the initial stage of bubble's formation.When in micron level,the bubble is strongly affected by capillary pressure.It causes a long waiting time which is much better in millimetre level.It's found that in the experiments the bubble shape depends on the instantaneous bubble volume only but has nothing to do with the gas flow rate,and the bubble volume at the detachment does not change with the flow rate.Under higher gas flow rate,we observed the coalescence bubbling regimes,different from multi-period formation mechanism in millimetre level.The final bubble volume demonstrates an index increasing relationship with gas flow rate.At the last of experimental part,the bond number and Weber number are used to drawn the bubbling regimes map,realizing the unity of the whole experiment results.This map can be used to predict in what gas flow rate range some other dimension nozzles will appear corresponding bubble dynamic behaviours.Additionally,volume-of-fluid method(VOF)was used to numerical simulate the formation process.The study shows that numerical simulations can well predict the dynamic characteristics of bubbles in contrast with the experiments under low gas flow rate conditions(0.95~4.83 ml/min).And we found that when the neck shrinkage fractured a small gas jet injected into the bubble from the bottom,which had important significance in the bubble surface oscillation after detached.The simulation work is helpful to the understanding of bubble dynamic behaviours.