In this work

the computational fluid dynamics method is used to study the liquid hydrodynamics behavior in the microchannel without central insert (MC1) and the central insert microchannel (MC2)

respectively. The maximum deviation between simulation and experiment is 24%. The formations of flow patterns are explained based on contours and force analysis where the flow pattern maps are established by two-phase flow rate. The effects of aqueous phase viscosity and two-phase flow rate on the characteristic sizes of each flow pattern are also explored. Specifically

four unconventional flow patterns are found in MC2

namely the unique droplet flow

the unique slug flow

the unique coarse annular flow and the unique film annular flow. Though the insert occupies part of the channel

the pressure difference in the channel is significantly reduced compared with MC1. Moreover

the insert significantly changes the formation velocity range of each flow pattern

greatly broadens the formation range of annular flow and also has an important influence on the characteristic size of the flow pattern. The organic-phase dimensionless axial size (

L

o

/

W

) and the dimensionless radial size (

D

o

/

W

) of the droplet

(slug) are negatively related to the aqueous-phase viscosity (

μ

a

) and flow rate (

u

a

). The

D

o

/

W

of the annular is negatively correlated with

μ

a

and positively correlated with organic-phase flow rate (

u

o

). This study provides direct numerical evidence that the insert is key to the formation of bicontinuous phase flow pattern

as well as further strengthens our understanding of the flow characteristics and optimization design of insert microchannels.