Study On The Dynamics Behavior Of Bubble In Power-law Fluids In Microchannels

With the rapid development of microfluidic technology,microreactors have been widely used in many frontier fields such as chemistry,biology and information due to advantages of large specific surface area,high safety and easy amplification.The multiphase flow behavior in the microchannel has a significant effect on the performance of the microreactor.Therefore,in this paper,considering the complex physical properties of fluids commonly encountered in practical applications,the dynamics behavior of bubble in power-law fluids in microchannels was systematically studied by visual experimental methods,which mainly includes characteristics of bubble formation and breakup.The experimental results provide theoretical guidance for the design of microreactors.Firstly,the bubble formation characteristics in a flow-focusing microchannel were studied by visual experiments.Two kinds of flow patterns were observed,including the slug flow and the bubble flow.The formation process of the Taylor bubble could be divided into four stages: waiting,expansion,squeezing and pinch-off.The velocity of the bubble head tip increased linearly with time in the stage of squeezing and pinchoff,while the width of bubble neck has a linear relationship with the remaining time in the pinch-off stage.The bubble formation length and slug length were power function and linear function relations with the power-law fluid flow rates respectively.Then,the flow pattern of bubble in the symmetrical T-junction microchannel in power-law fluids and the bubble dynamics behavior during the process of symmetrical breakup were studied.Four kinds of flow patterns were observed in the experiment,including bubble breakup with complete obstruction,breakup with the tunnel,asymmetrical breakup and no breakup.When the bubble breakup symmetrical,the breakup process could be divided into squeezing stage and rupture stage.The length of the bubble increased linearly with time in the whole process.While the neck width of the bubble increased exponentially with the remaining time in the pinch-off stage,and the power index increased with the development of rupture.Finally,the flow pattern and the bubble volume distribution ratio in the asymmetrical T-junction microchannel in power-law fluids were studied.It was observed that the bubble breakup with complete obstruction,breakup with the tunnel and no breakup.The volume distribution ratio of the bubble in the asymmetrical Tjunction microchannel decreased with the increase of power-law fluids concentrations.While with the increase of power-law fluids flow rates,the volume distribution ratio of bubbles in the unequal length T-junction microchannel increased first and then tended to be stable,while the volume distribution ratio of bubbles in unequal width T-junction microchannel increased first and then decreased.This paper contains 36 figures,8 tables and 98 references.