In this work, various aerosol particle transport and deposition mechanisms were studied through the computational fluid dynamics (CFD) modeling, including inertial impaction, gravitational effect, lift force, interception, and turbophoresis, within different practical applications including aerosol sampling inlet, filtration system and turbulent pipe flows. The objective of the research is to obtain a better understanding of the mechanisms that affect aerosol particle transport and deposition, and to determine the feasibility and accuracy of using commercial CFD tools in predicting performance of aerosol sampling devices. Flow field simulation was carried out first, and then followed by Lagrangian particle tracking to obtain the aerosol transport and deposition information. The CFD-based results were validated with experimental data and empirical correlations. In the simulation of the aerosol inlet, CFD-based penetration was in excellent agreement with experimental results, and the most significant regional particle deposition occurred due to inertial separation. At higher free wind speeds gravity had less effect on particle deposition. An empirical equation for efficiency prediction was developed considering inertial and gravitational effects, which will be useful for directing design of similar aerosol inlets. In the simulation of aerosol deposition on a screen, a "virtual surface" approach, which eliminates the need for the often-ambiguous user defined functions, was developed to account for particle deposition due to interception. The CFD-based results had a good agreement compared with experimental results, and also with published empirical correlations for interception. In the simulation of turbulent deposition in pipe flows, the relation between particle deposition velocity and wall-normal turbulent velocity fluctuation was quantitative determined for the first time, which could be used to quantify turbulent deposition, without having to carry out Lagrangian particle tracking. It suggested that the Reynolds stress model and large eddy simulation would lead to the most accurate simulated aerosol deposition velocity. The prerequisites were that the wall-adjacent y+ value was sufficiently low, and that sufficient number of prism layers was applied in the near-wall region. The "velocity fluctuation convergence" would be useful criterion for judging the adequacy of a CFD simulation for turbulent deposition.

RELAP5-3D has been coupled with both DAKOTA and STAR-CCM+ in order to expand the capability of the thermal-hydraulic code and facilitate complex studies of desired systems. In the first study, RELAP5-3D was coupled with DAKOTA to perform a sensitivity study of the South Texas Project (STP) power plant during steady-state and transient scenarios. The coupled software was validated by analyzing the simulation results with respect of the physical expectations and behavior of the power plant, and thermal-hydraulic parameters which caused greatest sensitivity where identified: inlet core temperature and reactor thermal power. These variables, along with break size and discharge coefficients, were used for further investigation of the sensitivity of the RELAP5-3D LOCA transient simulation under three difference cases: two inch break, six inch break, and guillotine break. Reactor thermal power, core inlet temperature, and break size were identified as producing the greatest sensitivity; therefore, future research would include uncertainty quantification for these parameters. In the second study, a small scale experimental facility, designed to study the thermal hydraulic phenomena of the Reactor Cavity Cooling System (RCCS) for a Very High Temperature Reactor (VHTR), was used as a model to test the capabilities of coupling Star-CCM+ and RELAP5-3D. This chapter discusses the capabilities and limitations of the STAR-CCM+/RELAP5-3D coupling, and a simulation, on the RCCS facility, was performed using STAR-CCM+ to study the flow patterns where expected complex flow phenomena occur and RELAP5-3D for the complete system. The code showed inability to perform flow coupling simulations and it is unable, at this time, to handle closed loop systems. The thermal coupling simulation was successful and showed congruent qualitative results to physical expectations. The locations of large fluid vortices were located specifically in the pipes closest to the inlet of the bottom manifold. In conclusion, simulations using coupled codes were presented which greatly improved the capabilities of RELAP5-3D stand-alone and computational time required to perform complex thermal-hydraulic studies. These improvements show greatly benefit for industrial applications in order to perform large scale thermal-hydraulic systems studies with greater accuracy while minimizing simulation time.

This thesis investigates the accuracy and scalability of RANS and LES approaches applied to external automotive aerodynamics. Due to the availability of considerable experimental and computational data available on the Ahmed body, this reference model was chosen for this study. The relative simple geometry of the Ahmed body model is able reproduce the common flow features of a hatch back style vehicle. The 25° slant angle configuration was used as it is a major challenge in terms of flow prediction. The RANS model used included the Standard K-ε, RNG K-ε, Realizable k-ε and K-ω SST. The LES simulations were run with the Smagorinsky-Lilly SGS model. Three grids with different level of refinement were generated. A viscous hybrid mesh approach was used for all the simulations. This type of mesh is commonly used by automotive manufactures and motorsport organizations. The commercial package Fluent 12 was used as a solver. The K-ω SST and LES models showed good agreement with the experimental data. LES in particular was the only model to predict flow re-attachment over the slant angle as seen on the experimental and computational data available in literature. The richness of the unsteady data available from the LES simulations and correct interpretation of flow topology balance in part the major computational requirements compared to the RANS models. Taking into account the hardware resources available to automotive manufactures, the LES is suitable to be part of the design process.

Den här rapporten undersöker hur strömningsmotståndet och tätheten i en vridspjällsventil påverkas av form på spindel och spjäll. I rapporten undersök också storleken på det hydrodynamiska moment som fluiden utövar på ventilens spindel. Rapporten utgår från en referensventil som ingår i SOMAS (SOMAS Instrument AB) produktsortiment och är av typen MTV med dimensionen DN 150. Modifieringar görs på referensventilens spindel och spjäll. Som mått på strömningsmotstånd används ventilens egenkarakteristik och som mått på täthet används storleken på den elastiska deformationen på spindel och spjäll då ventilen är stängd. Kraven som ställs då spindel och spjäll modifieras är att spindeln ska vara delad, spindel och spjäll ska gå att montera in i referensventilens ventilhus och referensventilen skall vara tät då ett modifierat spjäll med delad spindel monterats in i referensventilen. För att skatta egenkarakteristik, hydrodynamiskt moment och täthet har CFD- och strukturmodeller byggts upp i COMSOL Multiphysics version 4.0a. Det har också gjorts en experimentell flödesanalys för att ta fram strömningsmotståndet på referensventilen. I examensarbetet har två modifierade spjäll med delad spindel tagits fram. De modifierade spjällen med delad spindel går att montera in i referensventilens ventilhus. CFD-analysen visar att det går att minska strömningsmotståndet i referensventilen då spjällen med delad spindel monteras in i ventilhuset. Analysen visar också att det hydrodynamiska momentet är lågt. Strukturanalysen visar att referensventilen är tät då de modifierade spjällen med delad spindel monteras in i ventilhuset. / This report investigates how design on disc and shaft affects the inherent flow characteristic and the shutoff rating on a butterfly valve. This report also investigates the size of the hydrodynamic torque acting on the shaft. Design modifications are made on a reference valve which is a butterfly valve of model MTV with dimension DN 150 and is a part of SOMAS (SOMAS Instrument AB) products. A measurement of shutoff rating is the size of the elastic deformation of the disc and the shaft. The demands of the design on disc and shaft are: the shaft will be a split type shaft, the disc and the shaft shall fit the valve body of the reference valve, the reference valve will have a shutoff rating that prevents leakage when the disc and the shaft are mounted in the body of the reference valve. To estimate the inherent flow characteristic, the hydrodynamic torque and the shutoff rating CFD-models and structural-models has been built in COMSOL Multiphysics version 4.0a. An experimental analysis has also been made to determine the inherent flow characteristic of the reference valve. This report presents two different discs with a split shaft that fits the body of the reference valve. When a newly designed disc and shaft are mounted in the body of the reference valve the CFD-analysis shows a greater inherent flow characteristic of the reference valve compared to the original design. The analysis shows that the hydrodynamic torque acting on the shaft is low. The structural analysis shows that the reference valve has a shutoff rating which prevents leakage when a newly designed disc and shaft are mounted in the body.

Hollow fiber ultrafiltration is a viable low cost alternative technology for the concentration or separation of protein solutions. However, membrane fouling and solute build up in the vicinity of the membrane surface decrease the performance of the process by lowering the permeate flux. Major efforts have been devoted to study membrane fouling and design more efficient ultrafiltration membrane systems. The complexity of membrane fouling, however, has limited the progress to better understand and predict the occurrence of fouling. This work was motivated by the desire to develop a microscopic Computational Fluid Dynamics (CFD) model to capture the complexity of the membrane fouling during hollow fiber ultrafiltration of protein solutions. A CFD model was developed to investigate the transient permeate flux and protein concentration and the spatial fouling behavior during the concentration of electroacidified (pH 6) and non- electroacidified (pH 9) soy protein extracts by membrane ultrafiltration. Electroacidification of the soy protein to pH 6 was found to decrease the permeate flux during UF which resulted in longer filtration time. Lower electrostatic repulsion forces between the proteins at pH 6 (near the protein isoelectric point) resulted in a tighter protein accumulation on the membrane surface suggested to be responsible for the lower permeate flux observed in the UF of the electroacidified soy protein extract. A new transient two-component fouling resistance model based on the local pressure difference, permeate velocity and protein concentration was implemented in the resistance-in-series flux model to describe the dynamics of the reversible and irreversible fouling during the filtration and the effect of pH on the membrane fouling. Good agreement between the experimental data and the model predictions was observed. Mathematical modeling was performed to estimate the osmotic pressure and diffusion coefficient of the proteins bovine serum albumin (BSA) and soy glycinin, one of the major storage proteins in soy, as a function of protein concentration, pH, and ionic strength. Osmotic pressure and diffusion coefficient of proteins play vital roles in membrane filtration processes because they control the distribution of particles in the vicinity of the membrane surface, often influencing the permeation rate. Therefore, understanding the behavior of these properties is of great importance in addressing questions about membrane fouling. An artificial neural network was developed to analyze the estimated data in order to find a simple relation for osmotic pressure as a function of protein concentration, pH, and ionic strength. For both proteins, the osmotic pressure increased as pH diverged from the protein isoelectric point. Increasing the ionic strength, however, reversed the effect by shielding charges and thereby decreasing the osmotic pressure. Osmotic pressure of glycinin was found lower than that of BSA. Depending on how much pH was far from the isoelectric point of the protein, osmotic pressure of BSA could be up to three times more than the glycinin’s. Two different trends for diffusion coefficient at specified pH and ionic strength were observed for both proteins; diffusion coefficient values that decreased with protein concentration and diffusion coefficient values that passed through a maximum. A rigorous CFD model based on a description of protein interactions was developed to predict membrane fouling during ultrafiltration of BSA. BSA UF was performed in a total recycle operation mode in order to maintain a constant feed concentration. To establish a more comprehensive model and thereby alleviate the shortcomings of previous filtration models in literature, this model considered three major phenomena causing the permeate flux decline during BSA ultrafiltration: osmotic pressure, concentration polarization, and protein adsorption on the membrane surface. A novel mathematical approach was introduced to predict the concentration polarization resistance on the membrane. The resistance was estimated based on the concentration and thickness profile of the polarization layer on the membrane obtained from the solution of the equation of motion and continuity equation at a previous time step. Permeate flux was updated at each time step according to the osmotic pressure, concentration polarization resistance, and protein adsorption resistance. This model had the ability to show how microscopic phenomena such as protein interactions can affect the macroscopic behaviors such as permeate flux and provided detailed information about the local characteristics on the membrane. The model estimation was finally validated against experimental permeate flux data and good agreement was observed.

Pulsating flows in a Helmholtz pulse combustor tailpipe were numerically simulated by a commercial CFD software package, FLUENT. The effects of ambient temperature on the characteristics of the pulsating tailpipe flows were studied. Two study cases, with high and low levels of ambient temperature, were simulated with compressible flow equations. An additional case, with high ambient temperature, was simulated with incompressible (temperature-dependent density) flow equations. Results showed that the effect of ambient temperature on the mean temperature profile in the tailpipe was limited to the distance where the ambient fluid traveled into the tailpipe during the period of flow reversal. In this region, the amplitude of mass flow rate oscillation significantly increased, due to higher density associated with low ambient temperature. The overall effects of cooler ambient temperature included an increase in mean pressure at the entrance of the tailpipe and a decrease in the magnitude of velocity amplitude profile along the tailpipe. Interestingly, the mean velocities along the tailpipe, even at the tailpipe exit, were not affected by the cooler ambient air. The mean velocity at the exit corresponded to the higher temperature of fresh fluid from upstream, which was not affected by the ambient temperature, driven out of the tailpipe in each oscillation cycle. The linear acoustic theory with appropriate assumptions could be used to calculate the magnitude of the profiles of velocity amplitude along the tailpipe as a fair approximation, at least for the study cases in this thesis.

A computational study was conducted on the flow, both compressible and incompressible, in a labyrinth seal at various geometries and rotation rates. The computations were performed using the commercial software Fluent® which solves the k-ε model to predict the flow field in the seal. Various clearance-pitch ratios were used to study the effect of clearance on the flow. The aspect ratio, which is defined as the pitch-height ratio was varied to study the influence of the depth of the cavity on the flow as a whole. These studies span a range of Taylor's number that is defined accordingly, while fixing the Reynolds number at 1000. The effects of clearance, aspect ratio and rotational rates are studied using carry-over coefficient and discharge coefficient. It is observed that a secondary recirculation zone (SRZ) occurs inside a seal cavity at above certain Taylor's number. This significantly changes the flow field in the seal and the cavity which results an increases in pressure drop across the seal for a given flow boundary condition. This formation of SRZ's is more evident in incompressible flow and occur at prohibitively high rotational speeds in case of air (compressible flow). It is also observed that flow with teeth on rotor are characterized by SRZ's while it's not case with teeth on stator. A flow map which shows the onset and presence of SRZ's is shown. The ratio of tangential velocity of the shaft to the average of the swirl velocity in a cavity at various geometries of the cavities are presented. They seem to be decreasing with decreasing depth and follow a linear pattern with the aspect ratios of the cavity.

Abstract A method using CFD-based computer simulations as a virtual reactor was proposed for cost-effective CVD reactor design. The virtual reactor was developed by combining the chemical reactor mechanism and rate constants obtained from kinetic studies using a small-scale, with the momentum, mass and heat transport processes simulated using a CFD code. The effect of the flow structure on the film thickness uniformity is demonstrated for the growth of GaAs from a Ga(CH3)3 -AsH3- H2 mixture. We present a modeling study of the growth of gallium arsenide layers deposited onto a high-temperature susceptor in a cylindrical metalorganic chemical vapor deposition reactor. We analyzed the deposition process with a two-dimensional model that is axisymmetric about the vertical axis. We attempted to control the extent of the consecutive reaction by modifying the flow pattern. For the output of side walls, because the gas velocity increase near the wafer edge, the residence time was lower in the central part of the wafer than near the edge. Therefore, it can be controlled by locating the outlet such that residence time above the entire wafer is uniform. And the study finds that decreasing the hole size lowered the film uniformity. This occurred because relative to the velocity at the center of the wafer, the velocity near the wafer edge increased with decreasing hole size. This result confirms that the control of the boundary layer thickness is very important for the film thickness uniformity. We also find that decreasing the shower-to-wafer distance increased velocity near the wafer and therefore increased the growth rate. The present study indicates that we can design a MOCVD reactor and optimize the operating conditions efficiently using a computer simulation with other¡¦s experiments.

Research was performed to optimize high-efficiency jet ejector geometry (Holtzapple, 2001) by varying nozzle diameter ratios from 0.03 to 0.21, and motive velocities from Mach 0.39 to 1.97. The high-efficiency jet ejector was simulated by Fluent Computational Fluid Dynamics (CFD) software. A conventional finite-volume scheme was utilized to solve two-dimensional transport equations with the standard k-?? turbulence model (Kim et. al., 1999). In this study of a constant-area jet ejector, all parameters were expressed in dimensionless terms. The objective of this study was to investigate the optimum length, throat diameter, nozzle position, and inlet curvature of the convergence section. Also, the optimum compression ratio and efficiency were determined. By comparing simulation results to an experiment, CFD modeling has shown high-quality results. The overall deviation was 8.19%, thus confirming the model accuracy. Dimensionless analysis was performed to make the research results applicable to any fluid, operating pressure, and geometric scale. A multi-stage jet ejector system with a total 1.2 compression ratio was analyzed to present how the research results may be used to solve an actual design problem. The results from the optimization study indicate that the jet ejector efficiency improves significantly compared to a conventional jet-ejector design. In cases with a subsonic motive velocity, the efficiency of the jet ejector is greater than 90%. A high compression ratio can be achieved with a large nozzle diameter ratio. Dimensionless group analysis reveals that the research results are valid for any fluid, operating pressure, and geometric scale for a given motive-stream Mach number and Reynolds ratio between the motive and propelled streams. For a given Reynolds ratio and motivestream Mach number, the dimensionless outlet pressure and throat pressure are expressed as Cp and Cpm, respectively. A multi-stage jet ejector system with a total 1.2 compression ratio was analyzed based on the optimization results. The result indicates that the system requires a lot of high-pressure motive steam, which is uneconomic. A high-efficiency jet ejector with mixing vanes is proposed to reduce the motive-steam consumption and is recommended for further study.

Non-contacting annular seals are internal sealing devices used in rotating machinery, such as multistage centrifugal pumps and compressors. Their design affects both efficiency and rotor stability. Traditional plain and labyrinth seals are being replaced with stators containing different roughness patterns to reduce leakage and enhance rotor response. Several roughened seal experiments with liquid and air have produced leakage data indicating that the friction factor increases as the seal clearance is increased. Simplified models based on bulk flow theory and Moody’s approach to characterize wall friction in pipes cannot explain this outcome. This research is an extension of a 2-D numerical analysis of flat plate experiments with water which found that friction factor of these surfaces is governed by the roughness’ ability to develop high static pressures. An exhaustive 3-D numerical analysis of several experiments with liquid annular seals has been performed using a CFD code. Direct numerical simulations (DNS) of turbulent channel flow and smooth seals were replicated within 1% using Reynolds-averaged Navier-Stokes (RANS) equations and turbulence modeling. Similarly, measured groove seal leakage rates were reproduced within 2%. On the other hand, no turbulence model combination predicts the leakage in most 3-D pattern roughened seals with the same accuracy. Present results reproduce the friction factor ‘plateau’ behavior predicted with the 2-D analysis and observed in the flat plate experiments. They also reproduce the friction-factor-to-clearance indifference behavior, the maximum friction factor observed in a specific roughness pattern size is independent of the actual clearance in a certain Reynolds number range, but clarify the role of the roughness length-to-clearance ratio and the actual roughness size in defining the friction-factor-toclearance proportionality. All simulations indicate that roughened surface area and roughness aspect ratios are the parameters defining the friction factor at a given seal clearance. The roughness pattern size, relevant in determining the friction-factor-to-clearance proportionality, plays a moderate role once the above cited ratios are defined. In any shape and size, shallow patterns are predicted and observed to provide larger friction factors than deep patterns. Predictions also confirm limited experimental data showing that friction factor is affected by the mean flow orientation relative to the roughness pattern. Solving RANS equations is sufficient to model simple seal geometries but might not be enough to replicate turbulent flow in liquid annular seals with roughened surfaces.