Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Micro gas turbines used in the aerospace industry require high performance with a compact frontal area. These micro gas turbines are often considered unattractive and at times impractical due to their poor fuel consumption and low cycle efficiency. This led to a joint effort to investigate and analyze the components of a particular micro gas turbine to determine potential geometry and performance improvements. The focus of this investigation is the radial vaned diffuser which forms part of a centrifugal compressor. The size of the diffuser is highly constrained by the compact gas turbine diameter. The micro gas turbine under consideration is the BMT 120 KS. The radial vaned diffuser is analyzed by means of 1-D and 3-D (CFD) analyses using CompAero and FINETM/Turbo respectively. The aim is to design a diffuser that maximizes the total-to-static pressure recovery and mass flow rate through the compressor with minimal flow losses. An experimental test facility was constructed and the numerical computations were validated against the experimental data. Three new diffusers were designed, each with a different vane geometry. The static-to-static pressure ratio over the radial diffuser was improved from 1.39 to 1.44 at a rotational speed of 120 krpm. The static pressure recovery coefficient was improved from 0.48 to 0.73 with a reduction in absolute Mach number from 0.47 to 0.22 at the radial diffuser discharge. / AFRIKAANSE OPSOMMING: Mikro-gasturbines wat in die lugvaart industrie gebruik word, vereis ‘n hoë werkverrigting met ‘n kompakte frontale area. Hierdie gasturbines word menigmaal onaantreklik geag weens swak brandstofverbruik en n lae siklus effektiewiteit. Dit het gelei tot ‘n gesamentlike projek om elke komponent van ‘n spesifieke mikro-gasturbine te analiseer en te verbeter. Die fokus van dié ondersoek is die radiale lem diffusor wat deel vorm van ‘n sentrifugaalkompressor. Die deursnee van die diffusor word deur die kompakte gasturbine diameter beperk. Die mikro gasturbine wat ondersoek word is die BMT 120 KS. Die radiale lem diffusor word geanaliseer deur middel van 1-D en 3-D (BVD) berekeninge met behulp van CompAero en FINETM/Turbo onderskeidelik. Die doelwit is om ‘n diffusor te ontwerp met ‘n verhoogde massavloei en drukverhouding oor die kompressor. ‘n Eksperimentele toetsfasiliteit is ingerig om toetse uit te voer en word gebruik om numeriese berekeninge te bevestig. Die staties-tot-stasiese drukstyging oor die radiale diffusor is verbeter van 1.39 tot 1.44 by ‘n omwentelingspoed van 120 kopm. Die statiese drukherwinningskoeffisiënt is verbeter van 0.48 tot 0.73 met ‘n vermindering in die absolute Machgetal vanaf 0.47 tot 0.22 by die radiale diffusor uitlaat.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The use of gas turbines in central receiver solar power plant cycles has become an increasingly popular research topic. This has led to the need to investigate and analyse the effect of the solar receiver on the gas turbine cycle. The aim of this thesis is to construct an experimental gas turbine setup to accommodate further research on utilizing solar energy to power gas turbines. The gas turbine under consideration is the Rover Gas Turbines 1S/60. The focus of this investigation is the centrifugal compressor of the gas turbine. An increase in static pressure is required for the gas turbine to cope with anticipated pressure drops in the central receiver that will be part of the gas turbine cycle. The standard compressor design is analysed by means of 3-D (CFD) analysis using CFX® and experimental data. The new centrifugal compressor is designed by means of 1-D and 3-D (CFD) analysis using CompAero and CFX®. The aim is to design a compressor that maximizes the total-to-static pressure ratio. The size of the compressor is highly constrained by the geometry parameters of the gas turbine. Since the turbine rotor will remain unchanged, the power input, mass flow rate and rotational speed must stay the same. The experimental setup was build and the numerical results of the standard compressor were validated against the experimental results. A new centrifugal compressor was designed. The total-to-static pressure ratio was increased from 2.50 to 3.30 at an operating speed of 46 krpm. The efficiency of the compressor was improved from 63.8% to 85.6%. The input power of the new compressor design deviated 1.6% from the set benchmark, and 1.3% from the numerical data of the standard compressor. / AFRIKAANSE OPSOMMING: Die gebruik van gasturbines in sonkragstasiesiklusse met ’n sentrale ontvanger het gegroei tot ’n gewilde navorsingsonderwerp. Dit het gelei tot die behoefte om die effek van die sonontvanger op die gasturbinesiklus te ondersoek en te analiseer. Die doel van hierdie tesis is om ’n eksperimentele gasturbine opstelling te bou vir verdere navorsing oor die benutting van sonenergie om ’n gasturbine aan te dryf. Die gasturbine in oorweging is die Rover Gas Turbines 1S/60. Die fokus van hierdie ondersoek is die sentrifugale kompressor van die gasturbine. ’n Toename in statiese druk word benodig vir die gasturbine om die verwagte drukverlies in die sentrale ontvanger, wat deel uit maak van die gasturbinesiklus, te hanteer. Die standaard kompressor ontwerp is geanaliseer deur middel van 3-D Berekenings Vloeimeganika (BVM) analises met behulp van CFX® en eksperimentele data. Die nuwe sentrifugale kompressor is ontwerp deur middel van 1-D en 3-D BVM analises met behulp van CompAero en CFX®. Die doel is om ’n kompressor te ontwerp wat die totale-tot-statiese drukverhouding maksimeer. Die grootte van die kompressor is beperk deur die geometrie van die gasturbine omhulsel. Aangesien die turbinerotor onveranderd sal bly, moet die insetdrywing, massa-vloeitempo en rotasiespoed dieselfde bly. Die eksperimentele opstelling is gebou en die numeriese resultate van die standaard kompressor is teenoor die eksperimentele resultate gevalideer. ’n Nuwe sentrifugale kompressor is ontwerp. Die totale-tot-statiese drukverhouding is verhoog van 2.50 tot 3.30 teen ’n rotasiespoed van 46 000 omwentelings per minuut. Die doeltreffendheid van die kompressor is verbeter van 63.8% tot 85.6%. Die insetdrywing van die nuwe kompressor ontwerp het met 1.6% afgewyk van die vasgestelde maatstaf, en met 1.3% van die numeriese data van die standaard kompressor.

Thesis (PhD (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / The main research objective of this dissertation was to determine the performance parameters of particle dampers (PDs) under centrifugal loads. A test bench was developed consisting of a rotating cantilever beam with a PD at the tip. Equal mass containers with di erent depths, filled with a range of uniform sized steel ball bearings, were used as PDs. For all the tests, the total PD mass was identical. During operation the tip of the beam was displaced, and after release, the beam could vibrate freely. The decay in the vibratory motion of the tip of the beam was measured over a range of centrifugal loads. The experiments were duplicated numerically with a discrete element method (DEM) model, calibrated against the experimental data. This model could then be used for a more in-depth investigation of phenomena occurring when PDs are under centrifugal loads. From the data analysis, it can be concluded that there are two zones of damping, one with a high and one with a low damping factor. These damping zones depend on the ratio between the peak vibration acceleration and the centrifugal loading. Each zone has a limit in terms of the centrifugal loading beyond which the PD cannot function if the vibration amplitude is fixed. In the high damping zone, it was found that the excitation state of the particles was high enough for the system vibration frequency to change. In the low damping zone, there is only limited motion between the particles. The main parameters that influence the performance of the PDs are the friction between the particles themselves and with the container, the PD length/diameter aspect ratio, and the particle size. An important finding is that a PD with less layers (increase in particle size) will still function at a higher centrifugal load compared to one with a smaller number number of layers.

The recovery and recycling of the spent chemicals from the kraft pulping process are economically and environmentally essential in an integrated kraft pulp and paper mill. The recovery process can be optimised by firing high-solids black liquor in the recovery boiler. Unfortunately, due to a corresponding increase in the liquor viscosity, in many mills, black liquor is fired at reduced solids concentration to avoid possible rheological problems. Online measurement, monitoring and control of the liquor viscosity are deemed essential for the recovery boiler optimization. However, in most mills, including those in New Zealand, black liquor viscosity is not routinely measured. Four batches of black liquors having solids concentrations ranging between 47 % and 70 % and different residual alkali (RA) contents were obtained from Carter Holt Harvey Pulp and Paper (CHHP&P), Kinleith mill, New Zealand. Weak black liquor samples were obtained by diluting the concentrated samples with deionised water. The viscosities of the samples at solids concentrations ranging from 0 to 70 % were measured using open-cup rotational viscometers at temperatures ranging from 0 to 115 oC and shear rates between 10 and 2000 s-1. The effect of post-pulping process, liquor heat treatment (LHT) on the liquors’ viscosities was investigated in an autoclave at a temperature >=180 oC for at least 15 mins. The samples exhibit both Newtonian and non-Newtonian behaviours depending on temperature and solids concentration; the onsets of these behaviours are liquor-dependent. In conformity with the literature data, at high solids concentrations (> 50 %) and low temperatures, they exhibit shear-thinning behaviour with or without thixotropy but the shear-thinning/thixotropic characteristics disappear at high temperatures (>= 80 oC). Generally, when the apparent viscosities of the liquors are <= ~1000 cP, the liquors show a Newtonian or a near-Newtonian behaviour. These findings demonstrate that New Zealand black liquors can be safely treated as Newtonian fluids under industrial conditions. Further observations show that at low solids concentrations (< 50 %), viscosity is fairly independent of the RA content; however at solids concentrations > 50 %, viscosity decreases with increasing RA content of the liquor. This shows that the RA content of black liquor can be manipulated to control the viscosity of high-solids black liquors. The LHT process had negligible effect on the low-solids liquor viscosity but led to a significant and permanent reduction of the high-solids liquor viscosity by a factor of at least 6. Therefore, the incorporation of a LHT process into an existing kraft recovery process can help to obtain the benefits of high-solids liquor firing without a concern for the attending rheological problems. A variety of the existing and proposed viscosity models using the traditional regression modelling tools and an artificial neural network (ANN) paradigm were obtained under different constraints. Hitherto, the existing models rely on the traditional regression tools and they were mostly applicable to limited ranges of process conditions. On the one hand, composition-dependent models were obtained as a direct function of solids concentration and temperature, or solids concentration, temperature and shear rate; the relationships between these variables and the liquor viscosity are straight forward. The ANN-based models developed in this work were found to be superior to the traditional models in terms of accuracy, generalization capability and their applicability to a wide range of process conditions. If the parameters of the resulting ANN models can be successfully correlated with the liquor composition, the models would be suitable for online application. Unfortunately, black liquor viscosity depends on its composition in a complex manner; the direct correlation of its model parameters with the liquor composition is not yet a straight forward issue. On the other hand, for the first time in the Australasia, the limitations of the composition-dependent models were addressed using centrifugal pump performance parameters, which are easy to measure online. A variety of centrifugal pump-based models were developed based on the estimated data obtained via the Hydraulic Institute viscosity correction method. This is opposed to the traditional approaches, which depend largely on actual experimental data that could be difficult and expensive to obtain. The resulting age-independent centrifugal pump-based model was implemented online as a black liquor viscosity soft sensor at the number 5 recovery boiler at the CHHP&P, Kinleith mill, New Zealand where its performance was evaluated. The results confirm its ability to effectively account for variations in the liquor composition. Furthermore, it was able to give robust viscosity estimates in the presence of the changing pump’s operating point. Therefore, it is concluded that this study opens a new and an effective way for kraft black liquor viscosity sensor development.

Most current designs for Left Ventricular Assist Devices (LVAD) are based on rotary pumps due to their small size and lack of valves. However, the majority of FDA approved LVADs are larger, positive displacement pumps. One reason for this may be because positive displacement pumps produce pulsatile flow, similar to that of the natural heart, while rotary pumps produce continuous flow. Continuous flow has been shown to support the circulation for short periods of time during open-heart surgery, but it has seen limited success with long-term support. It is thought that pulsatile flow provides many metabolic advantages to patients with high total peripheral resistance (TPR) and lower flowrates. This study focused on modifying a continuous flow multiple disk centrifugal pump (MDCP) into a pulsatile pump, to allow for the combined benefits of the pulsatility from positive displacement pumps and the small size and valveless design of rotary pumps. An efficiency study was carried out by evaluating the hydraulic work output and the power requirements of the pump. The pump was evaluated in both pulsatile and continuous flow modes. In continuous mode, the pump was able to maintain a flow of 5.5 L/min against a pressure head of 60mmHg at 1155rpm. Other LVADs have reported rotational speeds around 2400rpm for centrifugal and 10,000rpm for axial pumps to produce flows around 5 L/min. This indicates that the MDCP is capable of producing flowrates at lower rotational speeds than other LVADs, lessening the mechanical wear of the parts, thus potentially increasing the device's lifespan. In pulsatile mode, cardiac outputs of 5 L/min were achieved against a 55/27mmHg outlet pressure. Higher pressures were unattainable with our current testing apparatus, but the results from the pulsatile tests prove that the MDCP can be operated in a pulsatile fashion and produce normal flowrates at low pressures. The pump efficiency was lower than expected, around 0.7-9% in continuous mode and 3-18% in pulsatile mode, consuming 3.5-28W and 0.5-2.3W, respectively. Utilizing a smaller motor may produce higher efficiencies, since the power requirements will be less without decreasing the flowrates, but a further study should be conducted in order to verify this.

The TurboPiston Pump was invented to make use of merits such as, high flow rates often seen in centrifugal pumps and high pressures associated with positive displacement pumps. The objective of this study is to manufacture a plastic model 12” TurboPiston Pump to demonstrate the working principle and a metal prototype for performance testing. In addition, this research includes the study of the discharge valve to estimate the valve closing time and fluid mass being recycled back into the cylinder through hand calculations. Furthermore, a transient simulation was performed in CFD using Fluent to provide a better estimate of what will happen in the actual pump while running. Additionally, an experimental rig was designed to investigate the performance of the first generation valve on the TurboPiston Pump known as the flapper valve. Means to improve the hydrodynamic performance of both valves have been identified for future study.

Diante do expressivo aumento do número de refinarias de petróleo, bem como, com a crescente modernização das tecnologias de processo, englobando também o ramo petroquímico e de fertilizantes, notou-se que o consumo de energia de compressores centrífugos e suas eficiências tornaram-se de suma importância. Uma consequência desta nova realidade, está na necessidade de melhoria dos métodos estimativos para pré-dimensionamento e performance destas máquinas, o que necessariamente implica em uma previsão precisa de sua eficiência politrópica. Além disso, tais métodos devem também estimar as dimensões básicas de cada seção de compressão. A maior parte da literatura atual, versando sobre compressores centrífugos, tipo multiestágio, não está atualizada no que diz respeito à estimativa de eficiências politrópicas, quando comparadas com as eficiências alcançadas por compressores de fornecimento recente. Sendo assim, o principal objetivo da presente dissertação foi estimar um compressor centrífugo multiestágio, utilizando métodos adequados de cálculo. Isto implicou em comparar três métodos de estimativas, refletindo três procedimentos clássicos de cálculo, normalmente utilizados. Após pesquisa foram identificados três métodos, dois otimizados recentemente e um terceiro de abordagem mais antiga, proveniente de alguns fornecedores de compressores. Os métodos em análise são: Método das relações de Semelhança Otimizado por Sandberg (2016), Método de Lüdtke (2004), com correções propostas por Busaid e Pilidis (2016) e finalmente o Método dos Expoentes Politrópicos (N-Method), apresentado por Gresh (2001) e editado novamente em Gresh (2018). Os dois métodos mais recentes, embora baseados em diferentes critérios, apresentam estimativas de desempenho, dentro de uma precisão razoável, quando comparada aos dados reais de teste, enquanto que o método mais antigo, apresenta desvios significativos. Nesta dissertação, serão estimados seis casos reais de compressores, cujos resultados serão comparados aos estimados pelos três métodos de cálculo. Analisando os métodos, à luz dos desvios indicados nas tabelas para os seis casos, pode-se afirmar que o Método Simplificado e Corrigido de Lüdtke foi o que apresentou melhores resultados. O desvio relativo máximo apresentado foi na potência de eixo, cujo valor foi de 5,1%. Considerando o Método de Sandberg, verifica-se a partir dos desvios listados nas tabelas, que não cumpriu com o limite de aceitabilidade no tocante à potência no eixo para dois dos casos estudados. Entretanto, com exceção a estes dois casos, o método mostrou-se bastante satisfatório. Finalmente, analisando o Método dos Expoentes Politrópicos, citado por Gresh (2018), pode-se dizer que este método só foi aceitável para dois casos. Para os demais, segundo os desvios indicados nas tabelas, o método mostrou-se inadequado devido a desvios significativos na sua eficiência politrópica. / With the crescent number of modern fertilizer plants and hydrocracking process units in oil refineries, the consumption of energy and consequently the efficiency of centrifugal compressors were made of paramount importance in present day. A consequence of this new reality is the necessity of improvement of the methods that estimate the polytropic efficiency of these compressors. Furthermore, new methods also need to predict the basic geometric parameters of each machine. On the other side, most of the literature, which deals with polytropic efficiencies, is not up to date with the values performed by modern compressors. The main scope of present work is to provide background information and present a comparison between two up to date methods and a third classical old method, based on different approach, but capable to predict the performance and sizing of multistage centrifugal compressors. The methods under analysis are: Sandberg (2016) Optimized Similarity Method, Lüdtke\'s Method (2004), with corrections proposed by Busaid and Pilidis (2016) and finally the Politropic Exponent Method (N-Method), presented by Gresh (2001) and edited again in Gresh (2018). Both the newer methods present good agreement with the values performed by several compressors, as demonstrated when these methods are adopted, whilst the old method presents some deviations, mainly in the gas power. In this paper, six real cases will be estimated by the three methods and compared against supplier data; the results will be justified. Analyzing the methods, in respect of the deviations indicated in the tables for the six cases, it can be stated that the Simplified and Corrected Method of Lüdtke was the one that presented the best results. The maximum relative deviation presented was in the brake horsepower, whose value was of 5.1%. Considering the Sandberg Method, it can be verified from the deviations listed in the tables, that it did not meet the limit of acceptability regarding power on the axis for two of the cases studied. However, with the exception of these two cases, the method was quite satisfactory. Finally, analyzing the Politropic Exponents Method, quoted by Gresh (2018), it can be said that this method was only acceptable for two cases. For the others, according to the deviations indicated in the tables, the method proved to be inadequate, due to significant deviations in its polytropic efficiency.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 182-188. / by Juan J. Manzano-Ruiz. / Ph.D.

Os objetivos principais deste trabalho foram planejar, executar e analisar os resultados de uma campanha de ensaios de concentração de minerais em um jigue centrífugo. O programa de ensaios permitiu a análise da influência de variáveis operacionais do equipamento no desempenho metalúrgico do processo de concentração. As investigações tiveram por meta estabelecer o desempenho metalúrgico por faixas granulométricas discretas tanto em termos de recuperações como de enriquecimentos. Para tanto foi selecionado o rejeito de uma operação de concentração de minerais sulfetados polimetálicos. O método de trabalho consistiu na caracterização tecnológica do rejeito e execução dos ensaios de concentração no jigue centrífugo Kelsey variando três parâmetros principais: velocidade de rotação, freqüência e amplitude de pulsação. Os resultados dos ensaios foram analisados em termos de recuperações e enriquecimentos dos elementos de interesse, como níquel, cobre e enxofre, além de óxido de magnésio, principal contaminante dos concentrados. O desempenho da campanha de ensaios indicou valores significativos de recuperação e enriquecimento dos elementos de interesse, bem como redução importante de óxido de magnésio nos concentrados obtidos. / The present work describes an experimental program designed to assess the metallurgical performance of a centrifugal jig. The variations in the main operating conditions were analysed in terms of both metallurgical recovery and grades by size fraction in concentrates. The tailings of a sulphide mineral concentration plant were sampled, prepared and submited to technical characterization as a preparation for the testing campaign. A Kelsey centrifugal jig was used in the testing program which included variation in rotating speed, frequency and stroke of pulse. The results were analysed in terms of recovery and concentration of nickel, copper and sulphur, as well as magnesium oxide which was the main contaminant. The general performance of the tests indicated high values in recovery of the selected elements, as well as significant reductions of contaminant in the concentrates.

Le compresseur d'air alimentant en oxygène la pile est un élément important dans les systèmes pile à combustible. Le compresseur peut consommer jusqu'à 20% de l'électricité produite dans les cas les plus défavorables. Le choix et le dimensionnement du compresseur, ainsi que son système de contrôle associé, sont directement liés à la performance du système global. La taille et le poids du système de compression d'air doivent être réduits pour le rendre plus adapté aux applications automobiles. En outre, le contrôle du système de compression d'air est également une problématique importante car il affecte l'efficacité et la sécurité de fonctionnement de la pile à combustible. Pour éviter une sous-alimentation en oxygène de la pile, le débit massique d’air fourni doit être géré de façon appropriée en fonction de la demande de la charge électrique. Pendant ce temps, la pression ne doit pas montrer de trop grandes variations ou ondulations qui peuvent endommager la membrane de la pile.Un contrôle à découplage proposé récemment dans la littérature, nommé contrôle à découplage de perturbation (DDC), est utilisé pour le système de compression centrifuge. Le DDC traite les interactions internes comme une perturbation, puis les éliminent dans le contrôle. Les performances du DDC sont comparées à un dispositif de commande en mode glissant décentralisé. Grâce à la comparaison de ces deux contrôleurs, les résultats montrent que le DDC proposé est performant tant pour des cas stables que dynamiques. Le compresseur centrifuge est donc utilisable pour les systèmes pile à combustible automobiles. Sur un banc d'essai hardware-in-the-loop (HIL), le contrôleur proposé est validé avec un modèle de pile à combustible de 10 kW avec des demandes de charge variables. En outre, une méthode d'évitement d’instabilité, à savoir un limiteur de référence, est proposé pour empêcher le dépassement de la ligne de pompage du compresseur. Les résultats expérimentaux montrent que, dans tous les cas, la zone d’utilisation du compresseur est bien cantonnée à droite de la ligne de pompage. / Air compressor supplying the oxygen to the stack is an important component in the fuel cell systems. The compressor can consumes up to 20 % of the generated power in the most severe cases. The selecting of the compressor and corresponding control are directly related to the performance of the fuel cell. The size and weight of the air compressor has to be reduced to make them more feasible for automotive applications. Moreover, the control of the air compression system is also an important issue, which affects the efficiency and the safety of the fuel cell. To avoid oxygen starvation of the stack, the mass flow of the supplied air has to be controlled appropriately according to the load demand. Meanwhile, the pressure should not have large deviations or ripples which may damage the stack membrane.A recently proposed disturbance decoupling control (DDC) is used for the centrifugal compression system. DDC treats the internal interactions as a disturbance and then eliminates them in the control. The performance of the DDC is compared with a decentralized sliding mode controller. Through the comparison of those two controllers, the results show that the proposed DDC performs better in both the steady state and dynamic conditions, making the centrifugal compressor is capable of applying to the fuel cell in automotive applications. On a hardware-in-the-loop (HIL) testbench, the proposed controller is validated with a 10 kW fuel cell model under varied load demands. Moreover, a surge avoidance method, namely reference limiter, is proposed to prevent the compressor from surging. The experimental results show that the operation is restricted to the right of the surge line.