The asymmetric breakups of a droplet in an axisymmetric cross-like microfluidic device are investigated by using a three-dimensional volume of fluid (VOF) multiphase numerical model. Two kinds of asymmetries (droplet location deviation from the symmetric geometry center and different flow rates at two symmetric outlets) generate asymmetric flow fields near the droplet

which results in the asymmetric breakup of the latter. Four typical breakup regimes (no breakup

one-side breakup

retraction breakup and direct breakup) have been observed. Two regime maps are plotted to describe the transition from one regime to another for the two types of different asymmetries

respectively. A power lawmodel

which is based on the three critical factors (the capillary number

the asymmetry of flow fields and the initial volume ratio)

is employed to predict the volume ratio of the two unequal daughter droplets generated in the direct breakup. The influences of capillary numbers and the asymmetries have been studied systematically in this paper. The larger the asymmetry is

the bigger the oneside breakup zone is. The larger the capillary number is

the more possible the breakup is in the direct breakup zone. When the radius of the initial droplet is 20 μm

the critical capill

ary numbers are 0.122

0.128

0.145

0.165

0.192 and 0.226 for flow asymmetry factor A

S

= 0.05

0.1

0.2

0.3

0.4 and 0.5

respectively

in the flow systemwhose asymmetry is generated by location deviations. In the flowsystemwhose asymmetry is generated by two different flow rates at two outlets

the critical capillary numbers are 0.121

0.133

0.145

0.156 and 0.167 for A

S

= 1/21

3/23

1/5

7/27 and 9/29

respectively.