An experimental study of single-phase and two-phase flows in microchannels

Recent literature on pressure drop and flow rate measurements in microchannels indicate that both the liquid and gas flow may deviate significantly from convention. Thus, an evaluation was made of the friction factor constant for laminar flow and critical Reynolds number for the laminar-to-turbulent flow transition. Experiments were performed to study the single-phase flow behaviour of water or nitrogen gas through a 100 μm circular microchannel. The liquid flow data were well predicted by the conventional friction factor equations for larger channels, and the critical Reynolds number was close to tradition. For single-phase gas flow, the measured friction factor agreed with theory if the effect of compressibility was considered. Rarefaction did not contribute to the experimental results.; The effect of scaling on two-phase flow was investigated to identify micro-scale phenomena. Experiments were conducted with a mixture of nitrogen gas and water in circular channels of 530–50 μm diameter. The two-phase flow was characterized by the flow patterns, void fraction, and frictional pressure drop. In the 530 and 250 μm channels, the flow characteristics were typical of those obtained in minichannels. In the 100 and 50 μm channels, the flow behaviour was unconventional—the occurrence of slug flow dominated, the void fraction-volumetric quality relationship departed from tradition, and mass flux no longer influenced the two-phase frictional multiplier. Unique to these channels, the slug flow exhibited a ring-shaped liquid film or serpentine-like gas core. The sizing effect indicates that the critical diameter for a microchannel lies between 250 and 100 μm. A new model is proposed to expose physical insight into the observed flow patterns.; To investigate the effect of channel geometry on two-phase microchannel flow, the same experiment was conducted in a 96 μm square microchannel and the data were compared with those obtained in the 100 μm circular microchannel. The channel shape did not affect the two-phase frictional pressure drop or the void fraction-to-volumetric quality relationship. A region of ring-slug flow that appears in the circular microchannel collapsed in the square microchannel, possibly due to the suppression of the liquid-ring film in the corners of the square channel.