Abstract
We measured counter-current flow limitation (CCFL), pressure gradient dP/dz, and void fraction αG in a 40 mm diameter vertical pipe with the rounded top and bottom ends and working fluids of air and water under flooding conditions, and we obtained the wall and interface friction factors, fw and fi. We compared CCFL, dP/dz, αG, fw and fi with those obtained from our previous experiments in the vertical pipes with the rounded top and sharp-edged bottom ends, and the sharp-edged top and rounded bottom ends. As a result, the shape of the upper end affected flow characteristics in vertical pipes under flooding conditions stronger than the shape of the lower end did. fw was expressed by the correlation for single-phase flows in the region of a large liquid Reynolds number ReL, but was much larger than that from the fw correlation for single-phase flows in the region of a low ReL. Therefore, we obtained a fw correlation for the region of the low ReL as a function of ReL or the liquid Kutateladze number KL*, and we evaluated uncertainty of liquid volume fraction αL = 1－αG when αG was obtained from the fw correlation and dP/dz data.
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