(452d) CFD Simulation of a Pulse Jet Mixed Vessel
A Computational Fluid Dynamics (CFD) model was developed for a 1 m diameter pilot scale PJM vessel containing 4 pulse tubes. The vessel fluids were water and a more viscous 30 cP Newtonian liquid of the same density, chosen to bound slurry viscosity. To account for fluid-air interactions, fully transient, 3-D Volume of Fluid (VOF) simulations of the RANS equations were carried out with ANSYS Fluent using the realizable k-e turbulence model with enhanced wall treatment. For normal operation, the pressure profile in the air line feeding the pulse tubes was set to mimic typical cyclic operations. During overblow, pulse tube operation ceased once gas was discharged into the vessel but the evolution of the velocity field was tracked until all bubbles had escaped into the vessel head space. A mesh independence study was conducted and the effect of air compressibility was studied.
The results for normal operation show extremely complex flow patterns throughout the vessel. During drive, mixing layer vortices form between the central up wash plume and the pulse tube bodies and travel upward to the surface. There is weak downward flow close to the vessel walls. During suction, fluid is pulled downward from all vessel locations. There are numerous regions of flow reversal. Increased viscosity impacts the upper regions of the central up wash plume. The mean velocity, deformation and dissipation fields will be discussed in detail. Several overblow scenarios will be presented and contrasted. The effect of air compressibility and bubble expansion on fluid agitation will be shown. Application of the results to Hanford waste treatment plant process operations will be discussed.