Interfacial and wall friction factors of swirling annular flow in a vertical pipe

Highlights: • Experiments on two-phase swirling flows in a vertical pipe are carried out. • Interfacial and wall friction factors in swirling annular flows are investigated. • Swirling motion increases the friction factors. - Abstract: Experiments on air–water two-phase swirling annular flows in a vertical pipe of 40 mm diameter were carried out at atmospheric pressure and room temperature to investigate interfacial and wall friction factors, f_i and f_w. The friction factors were evaluated using measured pressure drops and void fractions. Measurements of liquid film thickness and flow observation were also conducted. The ranges of the gas and liquid volume fluxes, J_G and J_L, were 12.5 ≤ J_G ≤ 20.0 m/s and 0.03 ≤ J_L ≤ 0.11 m/s, respectively. The main conclusions obtained are as follows: (1) f_i and f_w in swirling annular flows are several times larger than those in non-swirling flows, (2) f_i is well correlated in terms of the liquid volume fraction and the gas Reynolds number, Re_G, (3) Re_G and the liquid Reynolds number, Re_L, are required for correlating f_w, and (4) the liquid film thicknesses in two-phase swirling flows in a one-fifth model of a BWR separator are well predicted using the two-fluid model and the correlations of f_i and f_w developed based on the experimental data.