Experimental Investigation On The Spray Characteristics Of Power-law Fluid In Swirl Injectors

The swirl injector is widely used in the field of liquid spray for its simple structure,good atomization performance and low cost.The breakup of power law fluid exists widely in engineering application such as ink jet and nanometer material spraying.There are still lots of problems remained to be understood better about the breakup of power law fluid for its complexity.Studying the spray characteristics of power law fluid in swirl injectors not only has important guiding significance in engineering field,but also helps to deepen and enrich the understanding of power law fluid breakup mechanism.In this experiment,Carbopol gel is prepared as power law fluid and swirl injector with cyclone core tube and sleeve structure is used.The high-speed photography is used to obtain the spray images and analyze the spray patterns.And by using three-dimensional phase Doppler system,the velocity and droplet size distribution of particles are measured.The effects of jet parameters,physical parameters and geometry parameters on the atomization characteristics are studied.The experimental results show that the spray patterns of power law fluid swirl jet can be classified in three types with injection pressure increasing and they are rotating cylinder jet,ligament-droplet coexistence and fully developed hollow cone.With the increase of fluid viscosity,the jet needs greater injection pressure to reach the same spray pattern.The rotating cylinder jet pattern cannot appear for water swirl jet.The breakup length drops sharply at first and then keeps constant with the increment of injection pressure.However,the spray angle increases first and then stabilize.At the same injection pressure,the fluid with high viscosity has larger breakup length and smaller spray angle.In swirl jet of power law fluid the axial velocity w and radial velocity u are small in center area and big on both sides at different X positions,the distribution of w has a better symmetry,and the tangential velocity v is very close to zero and do not change much;The 3-D velocities at different Z positions decrease with the increment of Z value.The 3-D velocities distribution has a big difference in the upstream area for various fluid because of the updraft in swirl jet.The viscosity inhibits the increasing of jet speed.SMD decreases with nozzle diameter decreasing,while nozzle length-to diameter ratio,swirl chamber diameter and tangential inlet diameter have little effect on SMD.The nozzle diameter also plays an important role in SMD distribution.For larger nozzle diameter,SMD decreases from edge area to center area along X direction.For smaller one,SMD does not change much along X and Z direction.SMD gets smaller by increasing injection pressure.And the viscosity prevents jet from breaking up.The injection pressure and liquid viscosity have more obvious influence on droplets' secondary breakup.In general,the relative size range ?s is small when SMD is large at measuring points for one injector.The liquid viscosity,injection pressure and nozzle diameter influence?s while swirl chamber diameter,tangential inlet diameter and nozzle length-to diameter ratio have little effect on relative size range?A correlation to predict SMD for power law fluid swirl jet breakup is proposed with experimental data.The correlation considers the effect of physical parameters(especially the rheological properties),jet parameters and geometry parameters on SMD.The predicted results agree well with the experimental values.