Chemical and Biomolecular Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2751
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Item CFD INVESTIGATION OF A PULSE JET MIXED VESSEL WITH RANS, LES, AND LBM SIMULATION MODELS(2023) Kim, Jung; Calabrese, Richard V.; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pulse Jet Mixed (PJM) vessels are used to process nuclear waste due to their maintenance free operation. In this study we model the turbulent velocity field in water during normal PJM operation to gain insight into vessel operations and to evolve a modeling strategy for process design and operator training. Three transient simulation models, developed using Large Eddy Simulation (LES), unsteady Reynolds-Averaged Navier-Stokes (RANS), and Lattice Boltzmann Method (LBM) techniques, are compared to velocity measurements acquired for 3 test scenarios at 3 locations in a pilot scale vessel at the US DOE National Energy Technology Laboratory (NETL). The LES and RANS simulations are performed in ANSYS Fluent, and the LBM simulations in M-STAR.The LES model well predicts the experimental data provided that the operational pressure profile within the individual pulse tubes is considered. While the RANS model failed to predict the data and exhibited significant differences from LES with respect to turbulence quantities, it is a useful comparison tool that can quickly predict averaged flow parameters. The LBM model’s rigid grid system is deemed unsuitable, as currently configured, for the NETL PJM vessel’s wide range of length scales and curved boundaries, resulting in the longest simulation time and least accurate velocity predictions. Predicted velocity and turbulence metrics are explored to better understand the strengths and failures of the three models. Because the LES model produced the most accurate predictions, it is exploited to generate animations and still images on various 2D planes that depict extremely complex flow patterns throughout the vessel with numerous local jets and mixing layer vortices The study concludes with recommendations for future research to improve the model development and validation strategy.Item COMPARISON BETWEEN PARTICLE IMAGE VELOCIMETRY DATA AND COMPUTATIONAL FLUID DYNAMICS SIMULATIONS FOR AN IN-LINE SLOT AND TOOTH ROTOR-STATOR MIXER(2015) Kim, Jung W.; Calabrese, Richard V; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rotor-stator mixers have a broad spectrum of applications in chemical, petrochemical and pharmaceutical processes since they produce the high shear fields for emulsification and dispersion processes. To assess device performance and quantify mixing and dispersion capabilities, analyzing the velocity field data due to the rotor-stator interactions is crucial. Experimental 2-D velocity data have previously been acquired using Particle Image Velocity (PIV) for an in-line IKA prototype mixer which contains single rows of 12 rotor teeth and 14 stator teeth. The working fluid was water in turbulent flow. In this thesis, the development and validation of a Computational Fluid Dynamics (CFD) model is reported along with the comparison between the CFD and PIV data. The CFD model geometry and mesh were developed within ANSYS Workbench with a fully transient sliding mesh 3-D RANS simulations performed with Fluent using the realizable k-ϵ turbulence model. To begin, the effect of mesh density and wall treatment were systematically tested to optimize the CFD simulation settings. With respect to post processing, the numerical data were sampled in a stator slot at 9 rotor tooth positions on a grid that closely mimicked that for PIV data acquisition. The comparisons were made for three different rotor speeds (10, 20, and 26 revolutions per second) but at the same volumetric throughput (1.3 liters per second). The study of near-wall modelling options considered Non-Equilibrium Wall Functions (NEWF) and Enhanced Wall Treatment (EWT). Both produced similar results but EWT showed advantage in computational efficiency. In the mesh independence study, 3 mesh levels were created with approximately 2, 6, and 16 million cells. The study revealed that the mesh level with 6 million cells was sufficient to insure grid independence at reasonable accuracy. The CFD and PIV data compared favorably in many aspects. On average, CFD predicted the location of mixing layer and rotor tip vortices within 6.0% of the stator slot width compared to the PIV data. CFD also successfully identified 23 out of 27 (85.1%) mixing layer and rotor tip vortices captured by PIV. Differences were observed as well. The CFD simulations consistently yielded higherItem COMPUTATIONAL STUDIES ON DROPLET DYNAMICS AT INTERSECTING FLOWS IN MICROFLUIDIC JUNCTIONS(2010) Mamidi, Sai Kishore Reddy; Dimitrakopoulos, Panagiotis; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The current thesis involves a computational study of drop dynamics in microfluidic junctions, at the moderate capillary number of Ca = 0.1. We utilize a three-dimensional Spectral Boundary Element algorithm to determine the drop motion in the presence of intersecting lateral flows in microfluidic, T-junctions and cross-junctions, and analyze the effect on drop deformation and motion with varying shear rates in the channels leading to the junctions, and for viscosity ratios of 0.2 and 20.0 between the drop and the surrounding fluid. We find that the presence of intersecting flows, drastically affects the transient behavior at the junctions, and the drop reaches steady state further away, both up- stream and downstream of these junctions. The time taken to reach steady state in the T-junctions was found to be significantly greater than that in the cross-junction, under identical conditions. Drop velocities were found to be a linear function of the effective shear rate in the channel, and length scale fluctuations as high as 30 percent were observed in the junction region for the cases studied in the thesis. We observed that the excess presure drop with respect to the flow of a single phase fluid was strongly related to the length of the droplet at a given spatial coordinate. The peak surface area of the drop in the junction was found to be a slighly non-linear function of the flow rates in the lateral channels, and almost all the surface area increase was occurring at the head of the drop, in the direction of the flow. Velocity was found to be a weak, inverse function of the viscosity ratio, the increase in drop surface area was found to be greater in drops with lower viscosity. It was found that the junction bend radius/smoothness had a more significant effect on the dynamics of the drop in a T-junction, compared to that in a cross-junction.