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Photovoltaic (PV) cells have long been an attractive alternative for the consumption of fossil fuels but current manufacturing practices suffer from poor energy efficiency, large carbon footprints, low material utilization, high processing temperatures and high solvent usage. A critical step in PV production is the deposition of CdS as a thin film to serve as a "buffer layer" between the optically absorbent layer and the transparent conducting oxide (TCO) layer to complete an effective p-n junction. The development of an inexpensive, low temperature, constant flow deposition process for producing CdS films is investigated. Micro-assisted solution concepts are implemented to promote the selectivity of heterogeneous surface reactions over homogeneous bulk precipitation. Analytical models based off Hagen-Poiseuille equation for fluid flow are coupled with computational fluid dynamic simulations to produce uniform flow fields within the deposition step permitting uniform film coverage on large substrates. / Graduation date: 2011 / Access restricted to the OSU Community at author's request from Jan. 11, 2011-Jan. 11, 2012.

La transition vers la turbulence pour un fluide rhéofluidifiant avec seuil en écoulement dans une conduite cylindrique est étudiée. Une analyse linéaire de stabilité est effectuée moyennant des approches modale et non modale. Les résultats numériques montrent que l'écoulement de Hagen-Poiseuille d'un fluide à seuil est linéairement stable. L'effet du comportement rhéologique du fluide sur les caractéristiques de la perturbation optimale est clairement mis en évidence. Pour de faibles valeurs du nombre d'Herschel-Bulkley (Hb << 1), la perturbation optimale se présente pratiquement sous forme de rouleaux longitudinaux et l'amplification de l'énergie est assurée par le mécanisme lift-up. Par contre pour des valeurs suffisamment élevées de Hb, la perturbation optimale est axisymétrique et l'amplification de l'énergie est assurée par le mécanisme Orr. D'un point de vue expérimental, l'écoulement d'une solution de Carbopol à 0.2 % en masse dans une conduite cylindrique est étudié à partir de la mesure des profils des vitesse axiale et analyse statistique des fluctuations de celle-ci. Il a été constaté qu'en régimes laminaire et turbulent, les profils moyens (au sens temporel) sont axisymétriques et présentent une asymétrie croissante avec le nombre de Reynolds lors de la transition. Une description tridimensionnelle de cette asymétrie a été obtenue à partir des profils de vitesse axiale mesurés à différentes positions angulaires. Les résultats obtenus suggèrent l'existence d'une structure cohérente robuste constituée de deux rouleaux longitudinaux contra-rotatifs de longueur comparable à celle du dispositif expérimental. L'analyse statistique des fluctuations de la vitesse axiale fait apparaître deux phases lors de la transition vers la turbulence. Dans la première phase, le système passe du régime laminaire à un état non linéaire asymétrique où les spectres de puissance sont très similaires à ceux observés dans le cas d'une turbulence bidimensionnelle. La deuxième phase correspond au passage de cet état asymétrique à un régime turbulent avec apparition de spots classiques de la turbulence hydrodynamique. / The transition to turbulence for shear-thinning fluid with a yield-stress in a cylindrical pipe flow is studied. A linear stability analysis is performed using modal and non-modal approches. The numerical results show that the Hagen-Poiseuille flow of yield stress fluid is linearly stable. The effect of rheological behavior of the fluid on the characteristics of the optimal perturbation is clearly highlighted. At very low Herschel-Bulkley number (Hb << 1), the optimal perturbation consists of almost streamwise vortices, and the amplification of the kinetic energy is provided by the lift-up mechanism. In contrast for sufficiently large values of $Hb$, the optimal perturbation is axisymmetric and the growth of the kinetic energy is provided by the Orr-mechanism. From experimental point of view, the flow of 0.2 wt % aqueous solution of Carbopol 940 in a pipe is investigated from the measurement of the mean, i.e., time-averaged, axial velocity profiles as well as the statistical analysis of the fluctuations. It is observed that the velocity profiles are axisymmetric in the laminar and turbulent regimes, and present an increasing asymmetry with increasing Reynolds number in the transitional regime. A three-dimensional description of this asymmetry is provided from velocity profiles measurements at different azimuthal positions. The observed transitional flow suggest the existence of a robust non-linear coherent structure characterized by two weakly modulated counter-rotating longitudinal vortices, which length is comparable to that of the test section. The statistical analysis of the axial velocity fluctuations indicate that the transition occurs essentially in two stages. The first stage corresponds to the transition from the laminar regime to a stable non linear asymmetric state, where the spectra of axial velocity fluctuations are similar to those obtained in the case of two-dimensional turbulence. The second stage corresponds to the transition from this non linear asymmetric state to the hydrodynamic turbulence with the apparition of the classical spots of turbulence.

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Indiana University-Purdue University Indianapolis (IUPUI) / With the recent advancement of computation and imaging technology, Image-based computational fluid dynamics (ICFD) has emerged as a great non-invasive capability to study biomedical flows. These modern technologies increase the potential of computation-aided diagnostics and therapeutics in a patient-specific environment. I studied three components of this image-based computational fluid dynamics process in this work. To ensure accurate medical assessment, realistic computational analysis is needed, for which patient-specific image segmentation of the diseased vessel is of paramount importance. In this work, image segmentation of several human arteries, veins, capillaries, and organs was conducted to use them for further hemodynamic simulations. To accomplish these, several open-source and commercial software packages were implemented. This study incorporates a new computational platform, called InVascular, to quantify the 4D velocity field in image-based pulsatile flows using the Volumetric Lattice Boltzmann Method (VLBM). We also conducted several parametric studies on an idealized case of a 3-D pipe with the dimensions of a human renal artery. We investigated the relationship between stenosis severity and Resistive index (RI). We also explored how pulsatile parameters like heart rate or pulsatile pressure gradient affect RI. As the process of ICFD analysis is based on imaging and other hemodynamic data, it is often time-consuming due to the extensive data processing time. For clinicians to make fast medical decisions regarding their patients, we need rapid and accurate ICFD results. To achieve that, we also developed surrogate models to show the potential of supervised machine learning methods in constructing efficient and precise surrogate models for Hagen-Poiseuille and Womersley flows.

The diploma thesis is divided into four main parts. The first part deals with the issue of waste management and its energy utilization in waste incineration. Processed harmful substances produced by incineration as well as emission limits. It deals with the types of catalytic carriers, their description, production and more detailed processing of ceramic foam VUKOPOR. The second part is devoted to technologies utilizing catalytic processes and a more detailed specification of the process. In the third part there is processed the calculation methods for pressure losses for individual types of carriers. Fourth, the most extensive part describes the INTEQII experimental device, its technology and construction, as well as the principle of the practical part, measuring of the pressure losses of carriers. It includes the evaluation of pressure losses in separate categories of carriers, such as the bed, HoneyComb and VUKOPOR ceramic foam. Subsequently, a comparison of the pressure losses of all carriers is made relative to the reference size of 1 m. The impact of bonding of VUKOPOR foam samples on the size of pressure losses is discussed. At the end of this section, the suitability of calculation methods for individual carriers is evaluated, depending on the experimental pressure loss data.

<p>  </p> <p>With the recent advancement of computation and imaging technology, Image-based computational fluid dynamics (ICFD) has emerged as a great non-invasive capability to study biomedical flows. These modern technologies increase the potential of computation-aided diagnostics and therapeutics in a patient-specific environment. I studied three components of this image-based computational fluid dynamics process in this work.</p> <p>To ensure accurate medical assessment, realistic computational analysis is needed, for which patient-specific image segmentation of the diseased vessel is of paramount importance. In this work, image segmentation of several human arteries, veins, capillaries, and organs was conducted to use them for further hemodynamic simulations. To accomplish these, several open-source and commercial software packages were implemented. </p> <p>This study incorporates a new computational platform, called <em>InVascular</em>, to quantify the 4D velocity field in image-based pulsatile flows using the Volumetric Lattice Boltzmann Method (VLBM). We also conducted several parametric studies on an idealized case of a 3-D pipe with the dimensions of a human renal artery. We investigated the relationship between stenosis severity and Resistive index (RI). We also explored how pulsatile parameters like heart rate or pulsatile pressure gradient affect RI.</p> <p>As the process of ICFD analysis is based on imaging and other hemodynamic data, it is often time-consuming due to the extensive data processing time. For clinicians to make fast medical decisions regarding their patients, we need rapid and accurate ICFD results. To achieve that, we also developed surrogate models to show the potential of supervised machine learning methods in constructing efficient and precise surrogate models for Hagen-Poiseuille and Womersley flows.</p>