Gas–liquid two-phase flow patterns in microchannels with reentrant cavities in sidewall

• Two-phase flow pattern in microchannel with uniform reentrant cavities.
• Evolution characteristic for two-phase flow pattern along flow direction.
• Correlation for describing two-phase flow pattern transition.

Two-phase flow patterns in two horizontal microchannels with uniform reentrant cavities in sidewall were experimentally studied, using deionized water and air as working fluids. The hydraulic diameter of microchannels in the constant rectangular cross-section is 133.3 μm. Two structures (fan-shaped and triangular) of reentrant cavity are arranged to be mounted in sidewall with 0.25 mm spacing to develop two new microchannels with variable cross-sections. The liquid and gas superficial velocities in the microchannels cover the 0.1–0.5 m/s and 0.1–10 m/s ranges, respectively. High-performance CCD digital imaging camera with a Nikon microscope is used to determine the flow patterns in the two new proposed microchannels. Two distinct flow patterns were observed: intermittent flow and separated flow. Evolution characteristic for different flow patterns along the flow direction are presented. Flow pattern maps using gas and liquid superficial velocities as coordinates and the correlations to describe flow pattern transition for the newly proposed microchannel test sections are obtained, respectively.