The study of the influence of slug density on the mixing performance in the reactor vessel, using PLIF experiment and FLUENT simulation

Highlights: • PLIF was used to study the influence of density on the mixing performance in the vessel down-comer. • The mixing behavior is observed intuitively in the vessel down-comer for different slug densities. • FLUENT code results agree with the experimental data. • Better mixing is achieved when the density of the slug is closest to that of the ambient water. The study of the influence of different densities on the mixing behavior is very important in industries such as nuclear reactors. In this study a PLIF experiments and CFD simulation were performed to study the effect of slug densities on the mixing process in the vessel down-comer. Three different tests of different injected slug densities 1028, 1060 and 1090 kg/m³ were performed in HEU facility. Mixing of injected slug of 0.014 mg/L concentration of Rhodmine-B and ambient water in the vessel investigated by the Laser induced fluorescence technique. To provide a qualitative analysis of the results, the average values of the mass fraction at specified locations (y = 0 cm and y = 5 cm below the inlet part) were calculated for each experiment test and contour plots were created. These contours represent snapshots of the concentration field captured for the three tests. It is observed from the results, the mixing behavior in the vessel down-comer was strongly depend on the slug density. The mixing was slower when the density difference between the slug and ambient water was high and conversely the mixing behavior was higher when the density difference was low. A selected experimental result was used to validate CFD. The CFD simulations were carried out with FLUENT code and the turbulent model that used in this simulation was Reynolds stress model (RSM). A good agreement was achieved between experimental data and CFD-Fluent simulation.