Effects of channel inclination on two-phase flow characteristics for small diameter channels

An experimental investigation was carried out to elucidate the effect of the channel inclination on two-phase flow characteristics. Air/water flow was investigated inside a rectangular channel, 6.0 mm deep and 6.5 mm wide. The channel inclination varied from -90o to +90° relative to the horizontal plane. Flow patterns were identified and pressure drop was measured for mass velocities between 90 and 760 kg/m2s, corresponding to gas and liquid superficial velocities ranging from 0.09 to 19.4 m/s, and from 0.1 to 0.76 m/s, respectively. Flow patterns maps were developed according to the following approaches: (i) subjective approach based on flow images captured through a high-speed video camera; (ii) objective approach based a data-grouping algorithm, using metrics based on signals from the two-phase flow. Three flow patterns were identified: bubble, intermittent and annular. Stratified flows were not observed. Major differences in flow patterns transitions are observed comparing upward and downward flow. In general, the total pressure drop increased with increasing channel inclination, due to the contribution of the gravitational pressure drop parcel. In this study, the frictional pressure drop was estimated from the total pressure drop using different void fraction methods to estimate the gravitational parcel during inclined flow.