Computational studies of gas-liquid flow in a multi-branch manifold

•The volume of fluid method with a detached eddy simulation turbulence treatment predict well gas-liquid flows in a nuclear header/feeder system.•The “free surface” rises with increasing liquid and/or gas flow rate.•The flow distribution in the feeders is affected by the mixture pressure and temperature. Three-dimensional, time-dependent numerical simulations of gas-liquid flow in a multi-branch manifold (an idealised model of the header/feeder system of a CANDU nuclear reactor) were carried out using the volume of fluid approach to separate the phases and the detached eddy simulation model to simulate turbulence. Interest was focusse n the distribution of the liquid to different feeders. Numerical results for a header connected to a small number of vertical feeders were in fair agreement with in-house experimental data. The rates of change of liquid discharge following changes of inlet conditions were estimated and found to depend on feeder location. The interface between an upper region of the header that was occupied by mostly air and a lower region that was occupied by an air-water mixture was found to rise with an increase in either air or liquid inlet flow rate. Simulations were performed to quantify the effects of differences in the values of fluid properties of air-water mixtures at approximately standard atmospheric pressure and temperature from those of saturated steam-water mixtures at significantly higher pressures (up to 10 MPa) and temperatures (up to 310 °C). The liquid flow rate through a feeder that was directly below the header inlet was found to decrease markedly with increasing mixture pressure and temperature. Pilot simulations of air-water flows in a header connected to multiple feeders with inlets at different elevations and orientations revealed that, under certain conditions, some of these feeders discharged little liquid.