Study On The Breakup Mechanisms Of Cylindrical Power Law Liquid Jets

Although liquid jets have been studied widely for their intricate mechanism and various applications,most works have been focused on Newtonian liquids whose basic principles have been identified and necessary theories have been developed.To those power law fluid jets,breakup processes are much more complicated.So far,it still lacks adequate understanding to relevant fundamental principles.The research work presented in this thesis is aiming at examining characteristics of power law fluid jets in terms of their formation,developing and breakup processes and meanwhile trying to build required models for describing natures.By developing a mathematics model for 3D cylindrical jets of power law fluid,a dispersion equation for describing the jet's linear instability has been derived and instability curves in temporal domain for various conditions have been produced to demonstrate effects of practical and dimensionless jet parameters on surface wave's instability.Theoretical analysis results suggest that both power law fluid jet's instability and influences of relevant jet parameters to the instability are very different for different order mode.Instable surface waves of various modes are induced by combined actions by gas-liquid interaction surface tension,viscos force and power law character.In general,the gas-liquid interaction is contributing to enhancing the breakup.Other factors including surface tension,viscos force and power law exponent are resistances for the breakup process.But different degrees of effects to power law fluid jet's instability by every factor exsit in each order mode.If other conditions are kept constant,the increase in jet velocity will result in and enhance instable surface waves of high mode orders.With regard to experimental works,a test rig has been built.High speed imaging with shadow image method and PDA can be applied on the test rig for examining breakup processed of power law fluid jet,including the jet breakup droplet size and velocity distributions under high ambient pressure.High speed image results have shows various multi-mode instable surface waves and frozen breakup status of power law fluid jets,under high ambient pressure and temperature.By processing jet breakup length,cone angle,droplet size and velocity distributions which are normally used as measures for characteristics of jet breakup,results for effects of relevant jet and ambient parameters on the jet breakup and development trend have been achieved.Experimental results show that high order modes of instable surface waves will be induced and enhanced with the increase of power law fluid jet velocity.High injection pressure,high jet velocity at the nozzle exit,high ambient pressure,high surrounding gas density and temperature will be helpful for promoting the instability of power law fluid jet,then speeding up the breakup,reducing the breakup length,increasing the jet cone angle and creating smaller droplets.On the other hand,consistency index and power law exponent mainly play roles of obstacles for the breakup,in particular the consistency index.In terms of droplet size distributions,SMD(Sauter Mean Diameter)keeps decreasing with the distance from the nozzle exit along the jet axis.SMD variation along radial direction is not very obvious,although it keeps increase with the distance from the axis.Generally effects of various parameters on axial and radial distributions of droplet size are limited.In summary,results of both theoraticcal analysis and experimental investigation to power law fluid jet instable surface wave,breakup process,droplets size and velocity distributions are in very good agreement with each other.Both them all made significant contributions for understanding characteristics of power law fluid jet's breakup.