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

Experiments on air-water two-phase swirling annular flows in a vertical pipe of 40mm 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.