Experimental study on two-phase flow and pressure drop in millimeter-size channels

The present paper provides considerable insight into the structure of two-phase flow as well as its characteristics inside mini- and micro-channels. A new test facility was designed and constructed to investigate the two-phase flow regimes and pressure drop in mini- and micro-channels. The two-phase frictional pressure drop measurements and flow regimes experiments were performed with three different test sections, which are 3 mm, 1 mm, and 800 μm in diameter. The experimental pressure drop data was compared with the homogenous model, the Friedel [L. Friedel, Improved friction pressure drop correlations for horizontal and vertical two-phase pipe flow, Paper E2, European Two-Phase Group Meeting, Ispra, Italy, 1979] model, and the Chisholm [D. Chisholm, A theoretical basis for the Lockhart Martinelli Correlation for two-phase flow, Int. J. Heat Mass Transfer, 10, 1967, pp. 1767-1778] model, in order to determine their validity range in mini- and micro-channel flows. The homogenous model and the Chisholm [D. Chisholm, A theoretical basis for the Lockhart Martinelli Correlation for two-phase flow, Int. J. Heat Mass Transfer, 10, 1967, pp. 1767-1778] model showed the most similarities with the data acquired for the 1 mm and 0.8 mm test sections, while the Friedel [L. Friedel, Improved friction pressure drop correlations for horizontal and vertical two-phase pipe flow, Paper E2, European Two-Phase Group Meeting, Ispra, Italy, 1979] model over-predicted the pressure drop for every test section. The two-phase flow patterns were observed for high gas superficial velocities (U_GS {greater than or slanted equal to} 10 m/s) using a 3CCD analog camera, and comparisons were made with the existing flow regime maps. The present data, as well as the available data in literature, were used to develop a simplified flow regime map for horizontal micro-channels. The flow regimes in this map were separated into surface-tension-dominated regimes and inertia-dominated regimes. The regimes were named bubbly, intermittent, churn and annular. The intermittent flow regime regroups all slug and plug flows, as well as all the transition flows occurring in the vicinity of the intermittent region. It was found that the simplified transition lines provide a good approximation of the regime transitions for all existing studies within the allowable range of the map.