Wall Friction Factor and Void Fraction in Vertical Pipes under Flooding Conditions

Abstract

We measured counter-current flow limitation (CCFL), pressure gradient dP/dz, and void fraction α_G 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, f_w and f_i. We compared CCFL, dP/dz, α_G, f_w 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. f_w was expressed by the correlation for single-phase flows in the region of a large liquid Reynolds number Re_L, but was much larger than that from the f_w correlation for single-phase flows in the region of a low Re_L. Therefore, we obtained a f_w correlation for the region of the low Re_L as a function of Re_L or the liquid Kutateladze number K_L*, and we evaluated uncertainty of liquid volume fraction α_L = 1－α_G when α_G was obtained from the f_w correlation and dP/dz data.