Dynamics of disturbance waves in an adiabatic coaxial gas-liquid annular flow

Numerical modeling of two-phase annular flow in adiabatic situations is carried out inside a tube of 11 mm diameter using computational multifluid dynamics as a part of research conducted for numerical model developments for the Advanced Heavy Water Reactor (AHWR) under the 3rd Generation Indian Nuclear Power Generation Program. Simulating disturbance waves and their impact on entrainment and deposition is important from a safety point of view in nuclear reactors, as it plays vital role in dryout of the heated surfaces. Volume of fluid (VOF) is incorporated for capturing the interface, and surface tension is modeled with continuum surface force (CSF). The proposed numerical methodology is validated with available experimental data in literature. Three different cases of varying gas-liquid relative flow rates are considered for the simulation of the present study. The mechanism behind evolution of the disturbance wave generation is explained with 2D and 3D contours of gas-liquid flow. Bulging of liquid at the disturbance wave is illustrated which in turn results in droplet entrainment and deposition. Local reversal of velocity at the liquid film above the disturbance wave is observed, and wall shear stress is calculated to substantiate the same. The liquid film thickness over various sections of the tube is plotted over time to predict wave frequency and average film thickness. The liquid film thickness has shown to be a decreasing trend over the axial distance. Wave velocity is found to decrease with an increase in liquid inlet flow rate. © 2021 by Begell House, Inc. www.begellhouse.com