Распределение жидкости между ядром и жидкой пленкой в газокапельных потоках при высоких приведенных давлениях

Abstract

The aim of the study is to develop an approximate but well-grounded model of droplet entrainment and deposition processes in annular two-phase flows at high reduced pressures. Very scarce experimental data are available for these conditions except for the indicators obtained by Nakazatomi and Sekoguchi (1996), who studied the distribution of liquid between the core and liquid film in a two-phase flow of air--water mixture at high pressures up to 20 MPa. These data feature an abnormally high fraction of entrained liquid in the flow core at pressures above 10 MPa and manifest very strong deviation from any known empirical correlations, including the Cioncolini and Thome's procedure published in 2012. The proposed droplets entrainment model takes into consideration 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 the mutual spacing of which is determined by the Weber number for steam flow. This spacing and the liquid film thickness are the parameters governing the detached droplet diameter. An equation for calculating the entrainment intensity at high reduced pressures was constructed proceeding from these assumptions. However, it is rather difficult to verify this equation directly against experimental data because only the integral effect (i.e., the liquid flow rate in the film at dynamic equilibrium between entrainment and deposition) is usually measured in the experiments. The balance between the droplet entrainment and deposition flows due to turbulent diffusion corresponds to the dynamic equilibrium. The equation obtained proceeding from this balance contains one unknown numerical multiplier and allows one to calculate the liquid flow rate in the film. A comparison between the calculation results and the experimental data for a water–air flow at high reduced pressures has shown their good agreement at the universal value of a numerical constant in case of using an additional dimensionless parameter reflecting the ratio of phase densities.