Halle, Wittenberg, University, Habil.-Schr., 2003.

Thesis (Ph. D.)--University of Washington, 1987. / Vita. Bibliography: leaves [101]-104.

Thesis (M.Phil.)--University of Waikato, 2006. / Includes bibliographical references (leaf 89)

Biot's theory - which explains how sediments respond to stresses - has been applied to different sea-bed sediments. To successfully use Biot's theory as a predictive tool, sensitivity studies showed the following experimental measurements are required: the frame bulk modulus. the shear modulus, the tortuosity, the permeability and the porosity. These properties were determined for turbidite sediments from the North Atlantic Ocean (Site 1). and carbonates from the Western Indian Ocean -. (Site 2). The following experimental observations " were made: the permeability varies over 7 orders of magnitude for turbidites from Site 1 due to technique dependent and intrinsic reasons; in-situ shear moduli are 4 times greater than values determined from samples in the laboratory; shear modulus results from resonant column and bender element transducer techniques agree well: experiments designed for obtaining the frame bulk modulus are problematic, and it is difficult to determine pore size / geometry parameters apart from the tortuosity. Biot's theory was used to predict the response of sea-bed sediments to hydrodynamic and ultrasonic stresses. A new low frequency hydrodynamic boundary-value solution was developed from Biot's theory, allowing predictions of tidally-induced pore-pressures. Comparisons between predictions and in-situ measurements at Site 1 were favourable, verifying Biot's theory at low frequencies. At ultrasonic frequencies, Biot predictions of the velocity and attenuation of fast and slow compressional waves were compared to experimental measurements. The slow wave was argued to be induced at free-flow boundaries. and was found to be very difficult to detect in soft water-saturated sediments. A qualitative agreement was shown between Biot fast wave attenuation predictions and new experimental attenuation measurements on a bar of sandstone. For Sites 1 and 2, Biot predictions for the increases in the fast wave velocity for high porosity - permeability sediments agreed with experimental measurements. Elsewhere in the literature, this behaviour has been linked to an increase of the frame bulk modulus with increases in porosity. Alternatively, it was argued such increases in fast wave velocity can be attributed to Biot's dispersion mechanism. and hence are a verification of his theory at high frequencies.

Orientador: José Roberto Nunhez / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-21T00:15:32Z (GMT). No. of bitstreams: 1 MorenoCardenas_Sebastian_M.pdf: 3545307 bytes, checksum: 797cf7a13df284eafac584f66c5d0826 (MD5) Previous issue date: 2012 / Resumo: Processos comerciais de hidrotratamento (HDT) normalmente operam em regime de leito gotejante "Trickle bed" em concorrente com fluxos descendentes de gás e de líquido, sobre um leito de partículas de catalisador onde ocorrem as reações. É bem conhecido que a remoção de enxofre é fortemente inibida pelo efeito de adsorção competitiva de H2S nos sítios ativos do catalisador. Como consequência disso, é importante manter a concentração de H2S tão baixa quanto possível nestes processos durante a reação para obter um produto com baixo teor de enxofre na saída do reator. De acordo com Ancheyta et al.(2007), um perfil mais conveniente de concentração seria obtido com um reator operando em contracorrente,. Por exemplo, poderia se introduzir a carga na parte superior e o H2 na parte inferior do reator. Assim, na parte inferior do reator, a concentração de H2S é menor e a concentração do H2 é maior, promovendo taxas mais elevadas de reação. Os principais problemas da operação em contracorrente são uma menor eficiência de contato líquido-gás e dificuldade de prevenção de inundação do reator. Com o objetivo de estudar estes processos com mais detalhes, um estudo fluidodinâmico tridimensional do reator em regime de gotejamento "trickle bed" em contracorrente foi realizado com o uso de técnicas de CFD (Fluidodinâmica Computacional), com ênfase na determinação da perda de carga e da distribuição do hold-up de líquido no leito. Um modelo com o uso de CFD tridimensional baseado na abordagem Euleriana - Euleriana foi utilizado para modelar a hidrodinâmica do leito do reator de leito gotejante operando em contracorrente. Os termos de fechamento interfases foram estimados pelo modelo de balanço de forças apresentado por Attou, A et al. (1999), o qual foi usado e validado por Gunjal e Ranade (2007). O perfil de distribuição radial da porosidade foi estimado com o uso da distribuição de Klerk (2003). O modelo foi resolvido com o uso do software comercial ANSYS-CFX 13. Neste documento pode-se encontrar uma revisão bibliográfica do CFD aplicado a reatores de leito gotejante. Posteriormente são mostrados o desenvolvimento matemático e método numérico empregado, e finalmente os resultados dos casos de estudo, os quais forneceram informação de distribuição do líquido, perfis de velocidades, queda de pressão e hold-up do líquido para reatores isotérmicos de leito fixo em escala laboratório (0,0254 m de diâmetro e 0,3 m de comprimento) escoando concorrente e contracorrente / Abstract: Commercial HDT processes usually operate in a trickle-bed regime, with co-current downward flow of gas and liquid over a randomly fixed bed of catalyst particles while reactions take place. It is well known that sulfur removal is strongly inhibited by the competitive adsorption effect of H2S at the sulfided active sites of the catalyst. As a consequence, it is important in these process to maintain the concentration of H2S as low as possible during the reaction to achieve a low sulfur content product at the outlet of reactor. According to Ancheyta et al. (2007), a more convenient profile of H2S concentration can be provided by operating the reactor in countercurrent mode, for instance, introducing the feed at the top and H2 at the bottom of the reactor. Thus, in the lower reactor, the H2S concentration is lower and H2 is greater, promoting higher reaction rates. The main problems of the operation counter are a lower efficiency of gas-liquid contact and difficulty in preventing flooding conditions. In order to investigate the above processes in more detail, a three-dimensional fluid-dynamic study of a countercurrent trickle bed reactor was carried out using CFD (Computational Fluid Dynamics) techniques with emphasis on determining the pressure drop and the distribution of liquid hold-up in the bed. A computational fluid dynamics (CFD) tridimensional model based on an Eulerian - Eulerian multiphase approach was used to model the hydrodynamics of the pseudo two-phase flow in a trickle bed reactor (TBR) in counter-current operation. The closure terms for phase interactions have been addressed by adopting the fluid-fluid interfacial force balance concept (Attou et al. 1999), which was used and validated to simulate co-current HDT reactors by Gunjal e Ranade (2007). Radial variation of porosity was estimated using the Klerk (2003) distribution. Above set of model equations were implemented in commercial software ANSYS-CFX Release 13. In this document it could be found a literature review of CFD models applied to trickle bed reactors, later a mathematical modeling and numerical method to solve the transport equations and finally the results of study cases, which provided information about phase distribution, velocity profiles, pressure drop liquid hold up for a isothermal trickle bed reactor at laboratory scale (0.0254 m diameter and 0.3 length) in co-current and counter-current operation / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

No description available.

Experiments were conducted in a 0.91 m diameter half-cylindrical spouted bed/spout-fiuid bed column equipped with a 60° conical base and semi-circular inlet orifice diameters of 76 to 140 mm. Three particulate solid materials were studied: 3.25 mm polystyrene, 4.72 mm brown beans and 6.71 mm green peas. Beds with static depths of 0.55 to 2.60 m were contacted with air, both in the standard spouted bed and the spout-fluid bed mode. The dependent hydrodynamic parameters studied included minimum spouting velocity, maximum spoutable bed height, spout shape and diameter, fountain height, dead zone dimensions, overall bed pressure drop, fluid distribution in the annulus, longitudinal and radial pressure profiles in the annulus, and regime maps for the spout-fluid bed. Correlations for minimum spouting velocity developed on smaller vessels generally gave poor predictions for the large diameter vessel employed in this work and failed to predict the observed dependence of U[formula omitted]₈ on the static bed height. The empirical correlation due to McNab (1972) was found to predict the average spout diameter very well for standard spouted beds, while the correlation due to Hadzisdmajlovic et al. (1983) gave a reasonable prediction for spout-fluid beds. Substantial dead zone regions where particles were stagnant were observed in the lower portion of the vessel. The Littman et al. (1977) equation overestimated the maximum spoutable bed height, while the McNab and Bridgwater (1977) equation gave a value which appeared to be far too high. The observed fountains were extremely dilute, and their heights always exceeded the corresponding static bed heights for the conditions studied. The Epstein and Levine (1978) equation gave good estimates of overall bed pressure drop. The longitudinal fluid velocity in the annulus was well predicted by the modified Lefroy-Davidson (1969) equation due to Epstein et al. (1978) and was reasonably predicted by the Mamuro-Hattori (1968) model in the cylindrical portion. However, both equations gave poor predictions in the conical base portion. In the conical base section, the Rovero et al. (1983) equation predicted the correct trend, but consistently overestimated U[formula omitted] by a considerable margin. Both the Epstein and Levine (1978) equation and the Lefroy and Davidson (1969) equation were found to be in good agreement with the experimental longitudinal pressure profiles. The radial distribution of pressure in the annulus for any bed level was observed to be nearly constant when there was auxiliary flow. A computer model based on the Ergun equation gave useful qualitative predictions of the fluid flow distribution in the annulus. Four fairly distinct flow regimes were delineated in this work for cases where there were auxiliary air flow: (1) spouting-with-aeration; (2) spout-fluidization; (3) submerged jets, slugs and bubbles in fluidized bed, and (4) packed bed. The minimum total fluid flowrate for spouting-with-aeration always exceeded the minimum spouting flowrate, but was smaller than the minimum fluidization flowrate. The minimum total fluid flowrate for spout-fluidization was found to be equal to the minimum fluidization flowrate. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

No description available.

This study was conducted to determine what regulations are, and should be, involved in opening and operating a bed and breakfast in the State of Texas. Specifically, this study examined bed and breakfast regulations in Texas to identify the existence of, or need for, standards related to various legislation (including, but not limited to, zoning ordinances, building and fire codes, and insurance requirements). Bed and breakfast owners/operators in Texas made up the random sample that produced 106 usable survey responses. Regulations are in place at the state, county, and city levels of government. Bed and breakfast owners/operators were most concerned about insurance related matters, and various aspects of effective promotion and advertising.

Master of Public Health - MPH / Background: The largest focus areas for the department of health is ensuring access to quality healthcare. The district health system (DHS) model remains the vehicle used by the district managers to deliver on the health department’s goals, objectives and priority focus areas. Strengthening the district health system platform is therefore important to the department to improve access and quality of care to the clients serviced in the province. The district hospitals play a fundamental role since they support primary health care (PHC) and serve as the entry point to more specialised care. The efficient management of beds in the district hospitals is the key in ensuring access to care and preventing bed blocking. Bed Utilisation Rate (BUR) and Average Length of Stay (ALOS) are indicators used to measure the efficiency of hospital beds. This study provides a description of the trends in bed utilisation within the inpatient wards of eight district hospitals in the Cape Town metro district in the 2016-2017 financial period. Methodology: To analyse and compare wards a quantitative approach was used. Inpatient ward activity reports for eight district hospitals were accessed from the department of health’s routine data collection repository. A total of fifty-five wards were compared across small and large hospitals for BUR and ALOS during the financial year period 1 April 2016 to 31 March 2017. Data entry was done in MS EXCEL and analyses were done using STATA 11.0.