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The prediction of shut-off head within a centrifugal pump or fan has historically relied on the use of a combination of empirical formulae, together with experience. This reliance has been forced on designers due to both a lack of information regarding the flow at shut-off and the available tools with which to gain more accurate insights. To improve understanding the following investigation examines the capability of the commercial CFD package, FLUENT, to model the flow in a centrifugal pump at shut-off conditions. The computational model was validated using experimental measurements from a purpose built two-dimensional centrifugal pump rig. The rig used air as the working fluid and was similar in design to that used by Miner. Measurements were made of both the fluctuating velocities, using LDA, and the fluctuating pressures, using microphones, within the volute of the pump. The CFD model uses a sliding mesh which enables the full time-dependent rotor/stator interaction of the pump to be modelled. The results show the volute flow contains two patterns, a recirculating eddy in the outlet duct and a volute flow circulating around the rotor. This volute flow separates partway around the volute, with re-attachment on the discharge side of the tongue. The major effect of the volute at shut-off is to act as a diffuser with a strong circumferential pressure gradient over approximately the first 1200 after the tongue. A comparison of the experimental and computational results showed that good qualitative agreement was obtained at most positions at shut-off and considerable insight was gained into the flow mechanisms. However, the results showed that the CFD model over predicted the measured shut-off head by 25%. This was attributed to an over prediction of the effective viscosity due to the use of the k-s turbulence model.

This investigation is concerned with the assessment of the performance of a novel spinning disc reactor (SDR) for the polymerisation of chemically initiated freeradical polymerisation of styrene. The application of high acceleration fields such as those created on the surface of the grooved rotating disc to the polymerising system is aimed at intensifying the polymerisation rate and producing a better quality polymer product. As part of the experimental programme, four separate sets of experimental runs were conducted on a 360 mm diameter grooved rotating disc at a fixed temperature of 88-90°C to explore the effects of disc rotational speed and prepolymer feed conversion/viscosity on the extent of monomer conversion and molecular weight properties (M., MW and MWD) of the product from the SDR. The performance data of the SDR was compared with conventional batch polymerisation data. Both the disc rotational speed and prepolymer feed conversion/viscosity variables were found to have a profound influence on the performance of the SDR. A steady increase in conversion, rate of polymerisation and hence time saving in one pass in the SDR were observed with a rise in the prepolymer feed conversion and rotational speed until, for the latter, an optimal speed of rotation which gave the highest rate of polymerisation was reached. The results have been explained in relation to the effect of disc speed and prepolymer feed viscosity on mean film thickness, mean residence time and film surface instabilities. Furthermore, the SDR product is seen to have generally improved characteristics in terms of narrower molecular weight distribution when compared to polymer prepared in the batch at the same conversion. The large enhancement of the rate of styrene polymerisation in the SDR was discussed in terms of a possible improvement in the BPO initiator efficiency f and non-stationary state polymerisation conditions likely to be prevalent on the rotating disc. The general improvement in SDR product quality was ascribed to the combined effects of a reduced diffusion path length and an intense mixing mechanism within the thin film. A separate experimental study exploring the effects of micromixing efficiency on the conversion and molecular weight properties of styrene polymerisation in the batch was also undertaken. The opposing effects of enhanced micromixing in batch and continuous polymerisation systems were contrasted in a theoretical manner. A theoretical case study highlighting the energy efficiency of the SDR was also carried out. Savings in energy of more than 70% was calculated for a semi-batch process using an industrially adapted spinning disc reactor in comparison to a purely batch process. Finally, a two-stage continuous industrial process for free-radical polymerisation has been proposed consisting of an enhanced tubular reactor in the first stage followed by a parallel arrangement of several rotating disc surfaces. Improvements in intrinsic safety and minimised risks of polymer degradation and thermal runaways are the expected potential benefits. Keywords: Process Intensification, Thin Film, Spinning Disc Reactor, Free Radical Polymerisation, Polystyrene

Thesis (M. Phil.)--University of Hong Kong, 1995. / Includes bibliographical references (leaves 188-196).

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 116-124). Also available on the World Wide Web.

Orientador: José Geraldo Trani Brandão / Banca: Fernando de Azevedo Silva / Banca: Paulo Cesar Ribeiro Quintairos / Resumo: Este estudo mostra as variáveis dinâmicas do processo de fundição centrífuga de cilindros de laminação, que são utilizados para realização de conformação em gaiolas de laminação. O objetivo desse estudo é analisar as principais variáveis dinâmicas do processo de fundição centrifugada de cilindros de laminação e estudar as relações entre estas variáveis. Os processos de fundição centrífuga podem ser classificados em fundição centrífuga vertical e horizontal. Para a fundição centrífuga vertical, são elaborados os envelope de carga de dois modelos de máquinas centrífugas verticais existentes na literatura, onde se consegue determinar o tipo de rolamento de apoio utilizado na máquina. Para a fundição centrífuga horizontal, são estudadas variáveis como rotação, razão G, "aspect ratio", espessura e vibração de uma amostra de aproximadamente 1.000 cilindros de ferro fundido, aço rápido e aço alto cromo. Desta amostra, verifica-se que a causa de sucateamento de parte dos cilindros não está ligada a adoção de variáveis dinâmicas incorretas no processo. Também é visto que diferentemente do alumínio, os cilindros de ferro fundido, aço rápido e aço alto cromo exigem maior rotação quanto maior a espessura da casca fundida. / Abstract: This paper shows the dynamic variable of centrifugal casting process of rolling mill rolls which are used to compress the metal in rolling mill process. The main goal is to analyze the main dynamic variable and to study its relation in the process. There are two type of centrifugal casting: horizontal and vertical. For the horizontal centrifugal casting, two load envelopes are done, being possible to determine the bearing model used on the vertical centrifugal casting machine. For the horizontal centrifugal casting, variable such as rotating, ratio G, aspect ratio, thickness and vibration are studied to a sample of 1,000 casting rolls made of casting iron, high speed steel and high chromium steel. From this sample, it is seen that the cause of scrapping is not related to incorrect adoption of dynamic variables in the process. It is also verified that differently from the aluminum, cast iron, high speed steel and high chrome steel rolls demand greater speed with the increasing the shell casting thickness. / Mestre

Made available in DSpace on 2014-10-09T12:25:28Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:02:56Z (GMT). No. of bitstreams: 0 / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Detailed flow measurements made in a 1 metre diameter, shrouded, centrifugal (Ghost) impeller running at 500 rpm are presented. Relative velocities and rotary stagnation pressures $(p*=p-\frac{1}{2}\ρω^{2}r^{2}+\frac{1}{2}\ρW^{2})$ were measured on five cross-sectional planes between the impeller inlet and the outlet, using probes which were traversed within the rotating impeller passage. The reduced static pressures $(p_{r} = p-\frac{1}{2}\ρω^{2}r^{2})$, calculated from the flow measurements, are also presented. Measurements were made in a 'design' flow (approximately zero incidence at the blade leading edge), a 'below design' flow and an 'above design' flow. A wake flow was observed in all three flows and there were two major sources of the wake fluid. Firstly, from the separation of the shroud boundary layer and secondly, from the accumulation of low p* fluid from the other boundary layers by secondary flows. The results showed that the wake's position at the outlet moved from the suction side in the 'below design' flow, to the suction-side/shroud corner region in the 'design' flow and to the shroud in the 'above design' flow, because of the change in the relative strengths of the secondary flows generated by rotation and curvature. The modifications to turbulent mixing, by curvature and rotation, probably influenced the wake size. In order to predict the wake's location at the impeller discharge, a simple secondary flow model, which represented the impeller as a pipe bend, was devised. This model was successfully tested on two analytically soluble flows, in a stationary bend and in a rotating straight pipe. The model was then used for the more complex flows in a rotating axial-to-radial bend and in the Ghost and Eckardt's centrifugal impellers. The theoretical results for these impellers showed several of the features observed in the flow measurements.

Orientador: Antonio Carlos Bannwart / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências / Made available in DSpace on 2018-08-27T23:44:09Z (GMT). No. of bitstreams: 1 Fleischfresser_NataliaArgeneLovatePereira_M.pdf: 3225949 bytes, checksum: 3fa7cfd39e0757130d24fa627a6c856c (MD5) Previous issue date: 2015 / Resumo: A performance hidráulica de bombas centrífugas depende de várias entre suas dimensões hidráulicas, mas a maioria delas não é facilmente acessível. Por este motivo, a performance hidráulica da bomba deve sempre ser disponibilizada pelo seu fabricante. No entanto, para proteger sua propriedade intelectual, fabricantes raramente compartilham com o público informações mais detalhadas sobre a hidráulica da bomba. Como consequência, os usuários dos equipamentos e pesquisadores não têm acesso a todas as informações de que podem necessitar. Na literatura há diversos modelos propostos para predizer a performance hidráulica de bombas centrífugas. No entanto, até as melhores simulações por CFD não conseguem predizer a performance das bombas com precisão. Neste trabalho, uma abordagem simples (modelo) disponível na literatura, baseada nos princípios de fluido dinâmica, que prediz a performance hidráulica de bombas com poucas e acessíveis dimensões hidráulicas, é validada com uma grande variedade de dados experimentais. Os dados de oitenta testes de diferentes tipos de bomba, cobrindo uma ampla extensão de velocidades específicas, foram considerados. A partir desta análise, correlações entre os coeficientes da equação do modelo e os principais dados hidráulicos das bombas foram propostas. Em seguida, diversos métodos de predição da altura no shut-off disponíveis na literatura foram analisados para que fosse possível definir o que melhor predissesse a altura no shut-off considerando os dados de teste. Finalmente, para cada tipo de bomba, a melhor combinação entre correlações e método de predição de altura no shut-off foi selecionada para reduzir o erro na predição das curvas de altura completas. Dadas todas as premissas e simplificações, o objetivo deste trabalho é apresentar um método aplicável para diversos tipos de bomba que facilmente prediz a curva de altura com erro razoável / Abstract: The hydraulic performance of centrifugal pumps depends on several hydraulic dimensions of the pump, but most of them are not easily accessible. Therefore, the pump¿s hydraulic performance always has to be informed by the pump manufacturer. Furthermore, in order to protect their intellectual property, manufacturers rarely share more detailed information about the pump hydraulics with the public. As a consequence, pump users and researchers don¿t have access to all the data they possibly need. In literature, there are several proposed models to predict the hydraulic performance of centrifugal pumps. However, even the best CFD simulations can¿t predict the pump performance accurately. In this work, a simple approach (model) available in literature, based on fluid dynamics principles, that predicts a pump¿s hydraulic performance with only a few accessible hydraulic dimensions, is validated with several experimental data. Eighty tests of different types of pumps, with a large range of specific speeds were considered. From this analysis, correlations among the coefficients of the model equation and the main hydraulic data of the pumps were proposed. Afterwards, several shut-off head prediction methods available in literature were analyzed in order to define the one that best predicts the shut-off head of the given tested data. Finally, for each pump type, the best combination of correlations and shut-off head prediction method was selected to reduce the error on the whole head curve prediction. Given all the assumptions and simplifications, the objective of this work is to present a method applicable to several pump types that easily provides a prediction of the whole head curve with reasonable error / Mestrado / Explotação / Mestra em Ciências e Engenharia de Petróleo