Measuring maldistribution of two-phase flows in multi-parallel microchannels

Liquid flow distributions were measured in nine parallel microchannels with inner diameters of 0.8 mm connected to a common header, fed by air-water flows through a single tube. Flow maldistribution in the microchannels was analyzed considering the combined effects of the two-phase flow characteristics (flow pattern, gas quality, mass fluxes and superficial velocities), microchannel-header arrangements (horizontal or vertical), and microchannel flow and header feeding orientations (horizontal, vertical upward or vertical downward). The header was loaded with two-phase mass fluxes of 72, 144 and 216 kg/m2 s and the gas quality ranged from 0 to 0.75. An increase in the flow rate homogeneity was noted for the arrangement horizontal header and horizontal microchannels, when the header was loaded parallel to the microchannels or perpendicularly from the header bottom. Highly heterogenous flow distributions occurred for the arrangement vertical header and horizontal microchannels. Preferential liquid feeding occurred in the microchannels far from the inlet feeding tube for inlet flows with high gas quality (over 10%) and high gas superficial velocity (over 20 m/s) and with the inlet tube parallel to the microchannels. Preferential liquid feeding occurred in the microchannels close to the inlet feeding tube for inlet flows with a horizontal header and upward flows through the microchannels. The results and conclusions of this study represent an important contribution to this field, which could enhance the design of evaporators and condensers in compact heat exchangers.