Two-Phase Flow of Gas-Liquid Binary Mixtures Through a Rectangular Microchannel

Pressure measurements inside microchannels are scarce in the literature due to challenges pertaining to fabrication of integrated pressure sensors in microfluidic devices. A non-intrusive pressure measurement technique, employed in our studies, allowed us to measure the pressure profile for gas-liquid slug flows in microchannel. We investigated the pressure drop in gas-liquid slug (Taylor) flows where the gas fraction gradually expanded along the channel from ~5% to 85% due to reduction in pressure. Interestingly, the pressure profile was remarkably similar to that in a single-phase incompressible laminar flow; linear.

The local pressure measurements along the microchannel showed that the pressure gradient is nearly constant in a flow where gas bubbles progressively expand due to large pressure drop (1500-1600 kPa), and the fluid viscosity and density changes. This expansion of the gas phase leads to a significant increase in the void fraction (Fig. 1) along the microchannel, causing considerable increase in the mean flow velocity.

Figure  SEQ Figure \* ARABIC 1: Snapshot from experimental video shows the variation of void fraction in the test section for C₁-C₁₂ flow. The flow direction in the microchannel is shown on top. The grey line segments are the liquid slugs in the image.

The pressure drop in the microchannel was studied for two binary soluble gas-liquid mixtures: methane-decane (C₁-C₁₀) and methane-dodecane (C₁-C₁₂). The local pressure was measured along the microchannel by using a series of embedded membranes acting as pressure sensors. Our investigations of the pressure drop showed a linear trend over a wide range of void fractions (Fig. 1) and flow conditions. The lengths and the velocities of the liquid slugs and the gas bubbles along the microchannel were also studied by employing a video imaging technique.

A model describing the gas-liquid slug flow in a long microchannel was also developed. An equation of state model was used to determine the variation of fluid properties with pressure. We observed an excellent agreement between the developed model and our experimental data up to a void fraction of 70%.