Experimental investigation of droplet formation in coaxial microchannels with different geometries of inner channel
The droplet generation process of the water-silicone oil system in the coaxial microchannel was studied.Under different continuous capillary number Cac and dispersed phase Weber number Wed,two different flow patterns,dripping flow and jet flow,were observed.Experiments examined the effects of two-phase flow,viscosity,and inner tube structure on droplet size and droplet generation frequency.The results showed that droplet size increased with the increase of dispersed phase flow rate and decrease of flow rate and viscosity of continuous phase.Additionally,with the increase of Wed,jetting occurrence was found to be easier in relatively larger capillary,which in turn generated larger droplets.The generation frequency of droplet increased fast firstly then slow down to a plateau with the increasing of Cac and Wed.When the hydraulic diameters of inner channel were almost same,the deviation in the generation frequency of droplet obtained from different geometries of inner channel was small at fixed Cac.And the generation frequency of droplet increased with the decrease in the hydraulic diameters of inner channel.Based on the obtained results,an empirical correlation was proposed to predict the droplet size with good prediction performance.