A prediction method for entrained liquid fraction in adiabatic gas-liquid flow at high reduced pressure

A goal of the study is development of an approximate but well-grounded model of entrainment/deposition processes in annular two-phase flow at high reduced pressures (p/p_cr>0.45). Nakazatomi and Sekoguchi (1996) have presented the unique experimental data on liquid distribution between the core and the film in air/water two-phase flow at high pressures, up to 20 MPa; at pressures higher 10 MPa the data feature with abnormally high fraction of entrained liquid and manifest very strong deviation from any known empirical correlations, including the recent one by Cioncolini and Thome (2012). In deducing the approximate model of droplets entrainment, we used the experimental observations, according to which a liquid film becomes thin and smooth at high reduced pressures. A plenty of tiny droplets detach from the liquid film surface at the points, which spacing is determined as a length scale in Weber number for gas flow. This spacing and the liquid film thickness are assumed being the parameters controlling a droplet departure diameter. These assumptions allow developing an equation for calculating entrainment intensity at high reduced pressures. A balance between the flows of droplets entrainment and deposition due to turbulent diffusion corresponds to the dynamic equilibrium. The equation based on this balance contains one unknown numerical factor and allows one to calculate liquid distribution in a channel cross section. Comparing the calculation results with the experimental data for the water–air flows at high reduced pressures (more than 0.45) has shown their good agreement at the universal value of the numerical constant. (paper)