Numerous pressure drop correlations for microchannels have been proposed; most of them can be classified
as either a homogeneous flow model (HFM) or a separated flow model (SFM). However, the predictions
of these correlations have not been compared directly because they were developed in experiments
conducted under a range of conditions, including channel shape, the number of channels, channel material
and the working fluid. In this study, single rectangular microchannels with different aspect ratios and
hydraulic diameters were fabricated in a photosensitive glass. Adiabatic water-liquid and Nitrogen-gas
two-phase flow experiments were conducted using liquid superficial velocities of 0.06–1.0 m/s, gas
superficial velocities of 0.06–72 m/s and hydraulic diameters of 141, 143, 304, 322 and 490 lm. A pressure
drop in microchannels was directly measured through embedded ports. The flow pattern was visualized
using a high-speed camera and a long-distance microscope. A two-phase pressure drop in the
microchannel was highly related to the flow pattern. Data were used to assess seven different HFM viscosity
models and ten SFM correlations, and new correlations based on flow patterns were proposed for
both HFMs and SFMs.