Generalization of droplet entrainment rate correlation for annular flow considering disturbance wave properties

A full knowledge of the interfacial disturbance wave effects on droplet entrainment is crucial for accurately predicting entrainment rate in annular flow. However, most entrainment models in literatures do not account for interfacial properties but only consider global flow parameters than precise wave characteristics. In view of this, based on the shearing-off mechanism of disturbance wave crest, a comprehensive model of droplet entrainment rate for annular flow has been established considering the characteristics of disturbance wave. Effects of hydraulic parameters on the instability of disturbance wave and their relationship with the droplet entrainment rate are presented. Results reveal that the gas and liquid flow rate, hydraulic diameter, surface tension and pressure have a great influence on the wave properties, i.e., critical wavelength, wave amplitude and wave velocity, and hence the droplet entrainment rate. Taking these influencing factors into account, a more accurate and reasonable formula for entrainment rate in annular flow is proposed. Comparison of the present correlation with the existing empirical correlations reveals that the new developed correlation can be correlated reasonably well with the experimental data within ±25% deviation for both air-water and steam-water annular flow.