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Experimental studies on the flow pattern and the pressure gradient of gas-liquid co-current two-phase flow in a mini-channel were conducted. The test section was a transparent circular channel of 1.6 mm inner diameter. The working fluids were air and water. The superficial velocities of gas and liquid were in the range of 0.025-66.300 m/s and 0.033-4.935 m/s, respectively. In the present works, the flow pattern and the pressure gradient data were obtained by analyzing the flow images captured bya high-speed camera, and by using the pressure transducer, respectively. As a result, it was found that (1) the obtained flow patterns were bubbly, plug, slug-annular, annular, and churn flows, (2) new experimental correlations on the bubble and plug lengths were proposed, whereas the lengths are the function of the homogeneous void fraction, (3) both gas and liquid superficial velocities affect proportionally to the pressure gradient, whereas it increases with the increase both of JG and JL. In addition, the obtained flow patterns are in a good agreement with that of the available flow pattern maps in the open literatures, such as, Triplett et al. (1999) and Chung and Kawaji (2004).

Void fraction is an important parameter in two-phase flow. In the present work, the adiabatic two-phase air-water flow void fraction in a horizontal minichannel has been studied experimentally. A transparent circular channel with 1.6 mm inner diameter was employed as the test section. Superficial gas and liquid velocities were varied in the range of 1.25 - 66.3 m/s and 0.033 - 4.935 m/s, respectively. Void fraction data were obtained by analyzing the flow images being captured by using a high-speed camera. Here, the homogeneous (β) and the measured void fractions (e), respectively, were compared to the existing correlations. It was found that: (1) for the bubbly and slug flows, the void fractions increases with the increase of JG, (2) for churn, slug-annular, and annular flow patterns, there is no specific correlation between JG and void fraction was observed due to effect of the slip between gas and liquid, and (3) whilst for bubbly and slug flows the void fractions are close to homogeneous line, for chu...