Research on frictional pressure drop of air-water Co-current upward flow in vertical rectangular channels with different sizes

An experiment of air-water two-phase co-current upward flow has been conducted in adiabatic vertical channels under atmospheric conditions to investigate the frictional pressure drop affected by cross-sectional sizes of rectangular channels. Four channels with a cross-section of 4 × 66 mm, 6 × 66 mm, 8 × 66 mm, 10 × 100 mm were selected, and the superficial velocities of water and air were 0.25–3 and 0–20 m/s, respectively. The void fraction was measured by flat electrodes. Based on the Lockhart-Martinelli and Chisholm correlations, the result shows that with the increase of the hydraulic diameter of the channel, the parameter C rises to 28. In this study, the mechanism of frictional pressure drop was analyzed, and a new model was proposed based on the Chisholm model. In addition, the other frictional multiplier model was proposed based on the effects of void fraction, Reynolds number, and hydraulic diameter. Both of the models proposed in this study can predict the frictional pressure drop in rectangular channels well with a high accuracy, and the errors are below 15% in most conditions.