Liquid blockage and flow maldistribution of two-phase flow in two parallel thin micro-channels

•Two-phase flow in two parallel thin micro-channels is experimentally investigated.•Ratio of the gas flow rates Q2Q1 is defined to measure flow maldistribution.•The derived two-phase multiplierϕ is the inverse function of the ratio Q2Q1.•Three trends of Q2Q1are observed with the lowest ~0.2 (severe maldistribution).•ϕ obtained in single-ch testing may not be used to measure multi-ch maldistribution. In this study, flow maldistribution in a system of two parallel thin micro-channels with shared inlet and outlet manifolds is experimentally investigated with one channel subject to single-phase flow and the other to two-phase one. The flow pattern, pressure drop, gas flow rate in the single-phase flow channel Q1 and two-phase flow channel Q2 are studied. Film flow patterns are observed for all the cases of the study, consistent with literature work. The Q2Q1 ratio is defined as a direct measure to flow maldistribution. Theoretical derivation shows that Q2Q1 is inverse of the two-phase multiplier ϕ or Q2Q1=1ϕ. Three levels of liquid flow rate are examined and presented to show three representative trends: (1) For the highest water flow rate, i.e. 10−2 m/s, Q2Q1 is found to monotonically increase with the air flow rate, with its value Q2Q1 as low as about 0.2 at 0.86 m/s gas velocity and approaching 0.65 at 3.44 m/s. (2) For the lowest water velocity, i.e. 10-4 m/s, Q2Q1 shows decrease at first, followed by an increase, as the superficial gas velocity increases from 0.86 m/s to 3.44 m/s. It reaches about 0.76 at 0.86 m/s gas velocity and drops to about 0.55 at 1.72 m/s. (3) For the intermediate water velocity, i.e. 10-3 m/s, two “steady” states are identified at 0.86 m/s gas velocity with one having Q2Q1 as high as about 0.69 and the other about 0.52. The rest follows a similar trend as 10-4 m/s liquid velocity. The observed two “steady” states and changing trend at the two low liquid velocities may be due to the altered liquid blockage near the channel exit. It is also indicated that the two-phase multiplier ϕ obtained in single channel testing may not be used to measure flow maldistribution in multiple-channel systems. The work is important to study of two-phase flow, multi-channel design, flow maldistribution, and flow control in micro-channels for PEM fuel cells, electrolyzers, and thermal devices.