The influence of expanded portion’s geometry configurations on droplets coalescence process

Numerical simulations and Taguchi method were used to investigate the influence of expended portion’s geometry configurations on droplets coalescence process. Flow-focusing geometry including a 3-dimensional channel layout was designed to generate droplets. For the adaptive design, the L 9 (3 4 ) orthogonal array on expanded portion length( L e ), expanded cavity width( W e ) and expanded portion shape( S e ) was used for analysis of sensitivity of each parameter in droplets coalescence process. In order to obtain the suitably size droplets for good performance of droplet fusion, the flow velocities of continuous phase and dispersed phase were set to vary in 0.01~0.025m/s and 0.001~0.015m/s separately. 10cp silicone oil and deionized water were used as the continuous phase and the dispersed phase respectively. It is found that oil/water interfacial tension could lead to the droplets spontaneous coalescence by observing the distribution and change in inner flow fields of droplets coalescence process. Additionally, the value of adjacent droplets’ contact time versus liquid film’s drainage time is the key parameter to estimate the efficiency of droplets fusion. The degree of sensitivity using the Taguchi method can be ranked as: W e > L e > S e . The combination of W e of outlet’s half width, L e of three time’s droplet pitch and rectangular S e is optimum design with high fusion efficiency when two-phase flow rate is fixed. Results are benefit to improve the efficiency of micro-droplets coalescence and determine the final position of droplets coalescence.