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.

Community is an integrative motif and the central message of the Bible. The divine goal of history is God's establishment of community. The Triune God is the origin of community and community is the mode of existence of God. Christian community is derived from God's community. The church is a community restored by the Triune God, and so the essence of the church is Christian community. The Bible is the history of community involving the beginning of community, the destruction of community, the restoration of community, and the completion of community. Christian community is a channel of realization of the kingdom of God. As a restored community, the early church was a loving, sharing, praying, and witnessing community. The early church's common possession and sharing of materials in brotherly love had continuously been practiced throughout the churches as indicated in the books of Acts and the Epistles. The early church is a model of Christian community that believers must always strive for and constantly return to. It is possible to live the life of the early church community even now. This is proven by the history of the Protestant community and contemporary Protestant communities. Christian community is not just a conceptual, but also a practical community. Christian community can be practiced in various forms. Protestant community includes the four modes: intentional Christian community, monastic community, church community, and cell group community. These four modes have an equal value in a sense that they exert the communal spirit in diverse ways. These four modes of Protestant community have appeared throughout the history of Protestant community. Protestant communities influenced the renewal of the established church through their devoted community life of love. They have been the wellsprings of renewal in Protestantism. Protestant communities also become a place of reconciliation between divided Christians and denominations. The communities have a role as mediator of reconciliation among divided churches and denominations. Community movements have also acted as the main mission movement in the history of Protestant mission. The main missions such as the Anabaptists, Moravians, and modern mission societies all exerted a powerful mission in a communal basis. The contribution of the Moravian missionaries of the Herrnhut community, beginning half a century before William Carey, brought about a shift of emphasis in missionary awareness within Protestantism. The Herrnhut community included the centripetal mission and centrifugal mission by living an intentional community and sending Moravian missionaries. Mission should be exerted from a community dimension, not an individual level. The history of Protestant mission and contemporary Protestantism testifies that mission through community is the most effective and powerful method of mission. Up to now mission has usually been confined to centrifugal mission at an individual level, which emphasized preaching the gospel to foreign regions. It is a phenomenon of unbalanced mission. A balanced mission includes both centripetal and centrifugal mission. Mission is not only a matter of the scope of preaching the gospel to the ends of earth, but also a matter of content. The content of mission is a radical discipleship and whole gospel in all–inclusiveness, containing centripetal and centrifugal mission, Christian presence and Christian proclamation, and the New Commandment and the Great Commission. Community is an essence of church and an essence of mission. / Thesis (Ph.D. (Missiology))--North-West University, Potchefstroom Campus, 2011.

Community is an integrative motif and the central message of the Bible. The divine goal of history is God's establishment of community. The Triune God is the origin of community and community is the mode of existence of God. Christian community is derived from God's community. The church is a community restored by the Triune God, and so the essence of the church is Christian community. The Bible is the history of community involving the beginning of community, the destruction of community, the restoration of community, and the completion of community. Christian community is a channel of realization of the kingdom of God. As a restored community, the early church was a loving, sharing, praying, and witnessing community. The early church's common possession and sharing of materials in brotherly love had continuously been practiced throughout the churches as indicated in the books of Acts and the Epistles. The early church is a model of Christian community that believers must always strive for and constantly return to. It is possible to live the life of the early church community even now. This is proven by the history of the Protestant community and contemporary Protestant communities. Christian community is not just a conceptual, but also a practical community. Christian community can be practiced in various forms. Protestant community includes the four modes: intentional Christian community, monastic community, church community, and cell group community. These four modes have an equal value in a sense that they exert the communal spirit in diverse ways. These four modes of Protestant community have appeared throughout the history of Protestant community. Protestant communities influenced the renewal of the established church through their devoted community life of love. They have been the wellsprings of renewal in Protestantism. Protestant communities also become a place of reconciliation between divided Christians and denominations. The communities have a role as mediator of reconciliation among divided churches and denominations. Community movements have also acted as the main mission movement in the history of Protestant mission. The main missions such as the Anabaptists, Moravians, and modern mission societies all exerted a powerful mission in a communal basis. The contribution of the Moravian missionaries of the Herrnhut community, beginning half a century before William Carey, brought about a shift of emphasis in missionary awareness within Protestantism. The Herrnhut community included the centripetal mission and centrifugal mission by living an intentional community and sending Moravian missionaries. Mission should be exerted from a community dimension, not an individual level. The history of Protestant mission and contemporary Protestantism testifies that mission through community is the most effective and powerful method of mission. Up to now mission has usually been confined to centrifugal mission at an individual level, which emphasized preaching the gospel to foreign regions. It is a phenomenon of unbalanced mission. A balanced mission includes both centripetal and centrifugal mission. Mission is not only a matter of the scope of preaching the gospel to the ends of earth, but also a matter of content. The content of mission is a radical discipleship and whole gospel in all–inclusiveness, containing centripetal and centrifugal mission, Christian presence and Christian proclamation, and the New Commandment and the Great Commission. Community is an essence of church and an essence of mission. / Thesis (Ph.D. (Missiology))--North-West University, Potchefstroom Campus, 2011.

Heart disease is the developed world's biggest killer, and the shortage of donor hearts has accelerated the development of mechanical alternatives. Scientists, engineers and clinicians have attempted to replicate the human heart with a mechanical device for over 50 years. Although a number of pulsating devices have been developed, and in some cases worked briefly, they have invariably failed to match the success of heart transplantation. In an attempt to produce a suitable alternative, current research is focused on devices that do not replace the heart; but rather work along side it to assist its function. Many of these devices help the failing left ventricle; however some patients require the additional implantation of a second device to assist a failing right ventricle. This increases implantation time and associated risk, and because of the size of the current devices, reduces the access of smaller patients to this vital technology. The overall thesis objective focuses on the progressive design, development and preliminary evaluation of two novel centrifugal type ventricular assist devices, a bi-left ventricular device (Bi-LVAD) and a single bi-ventricular assist device (Bi-VAD). The devices have the respective capability to assist either the left ventricle, or both ventricles of a failing heart. The current concept for each VAD employs both magnetic and hydrodynamic suspension techniques to float a rotating double impeller, a technique that aims to reduce blood damage and component wear, two of the major problems encountered with current generation devices. Each VAD design was developed by conducting experimentation and drawing conclusions from a variety of engineering research fields, such as flow visualization, rotary pump design and testing, fluid dynamics, hemodynamics and heart failure, and magnetic motor bearing design. In order to evaluate pump prototype designs, it was necessary to design and develop a novel pulsatile systemic and pulmonary mock circulation loop capable of reproducing the hemodynamics of heart failure in the systemic and pulmonary circuits. The investigation then specifically examined the static hydraulic forces on the impeller of a centrifugal blood pump during operation in this mock circulation loop. The recorded magnitude and direction of radial and axial thrust then influenced the selection of magnetic and hydrodynamic bearing configurations to minimise impeller touchdown in the intended hemodynamic environment. This research required the development of correctly designed impeller (semi-open/closed) and volute (single, double, circular) components for each ventricular assist application and a unique test facility to isolate impeller hydraulic forces in addition to the mock circulation loop. The proposed Bi-LVAD incorporates symmetrical blade designs on each side of the double sided impeller. The device assists the function of the left ventricle only with symmetrical axial pressure distribution and elimination of stagnant regions beneath the impeller. These features improve axial touchdown capacity and reduce thrombus formation respectively. The proposed Bi-VAD incorporates different blade designs on each side of the double impeller to augment the function of both the left and right cardiac chambers. The design has the additional potential to act as a total artificial heart (TAH). To date there is no Bi-VAD/TAH system available that incorporates an LVAD and RVAD in one rotary pump. Successful development of each innovative VAD will provide an alternative to heart transplantation, potentially saving lives of many terminal heart patients each year. No longer would heart transplant candidates need to wait for the untimely death of a donor to provide a suitable heart. Instead, this new generation device would be available immediately, and be almost universally compatible with all patients. It has the potential to dramatically increase a patient’s expected lifetime, and to deliver them a higher quality of life.

The high ozone depletion and global warming potentials of fluorocarbon refrigerants have resulted in prohibitions and restrictions in many markets. Hydrocarbon refrigerants have low environmental impacts and are successfully used in domestic refrigerators and car air conditioners but replacing fluorocarbons in centrifugal chillers for air conditioning applications is unknown. Hydrocarbon replacements need a heat transfer correlation for refrigerant in flooded evaporators and predictions for operating conditions, capacity and performance. Safety precautions for large quantities of hydrocarbon refrigerants are needed and control of overpressure in plantrooms requires accurate prediction. Reliable correlations exist for forced convection in a single phase flow, condensation outside tubes and evaporation off sprayed tubes. For flooded evaporators this thesis proposes a new correlation for forced convection boiling of any refrigerant. An enhancement factor is combined with a modified Chen coefficient using recent pool boiling and forced convection correlations outside tubes. This correlates within typically a factor of two to known boiling literature measurements for CFC-113, CFC-11, HCFC-123, HFC-134a and HC-601. The operating conditions, capacity and performance of replacement hydrocarbons in centrifugal chillers were predicted using fluorocarbon performance as a model. With the new heat transfer correlation hydrocarbon predictions for flooded evaporators were made. For any fluorocarbon refrigerant there exists a replacement mixture of hydrocarbons which with a rotor speed increase about 40% gives the same cooling capacity in the same centrifugal chiller under the same operating conditions. For example replacing HCFC-123 in a flooded evaporator with HC-601/602 [90.4/9.6] and increasing the rotor speed by 43% will increase the coefficient of performance by 4.5% at the same cooling capacity. The maximum plantroom overpressure considered was from leakage and ignition of a uniform air/refrigerant mixture with maximum laminar burning velocity. Flow was modelled using a turbulence viscosity due to Launder and Spalding and turbulent deflagration using a reaction progress variable after Zimont. These partial differential equations were solved approximately for two and three dimensional geometries using finite volume methods from the Fluent program suite. Simple overpressure predictions from maximum flame area approximations agreed with Fluent results within 13.7% promising safe plantroom design without months of computer calculation.

The main focus of this study is to improve the profitability, availability and condition monitoring of Liquefied Natural Gas (LNG) Floating Production Storage and Offloading platforms (FPSOs). Propane pre-cooled, mixed refrigerant (C3MR) liquefaction is the key process in the production of LNG on FPSOs. LNG liquefaction system equipment has the highest failure rates among the other FPSO equipment, and thus the highest maintenance cost. Improvements in the profitability, availability and condition monitoring were made in two ways: firstly, by making recommendations for the use of redundancy in order to improve system reliability (and hence availability); and secondly, by developing an effective condition-monitoring algorithm that can be used as part of a condition-based maintenance system. C3MR liquefaction system reliability modelling was undertaken using the time-dependent Markov approach. Four different system options were studied, with varying degrees of redundancy. The results of the reliability analysis indicated that the introduction of a standby liquefaction system could be the best option for liquefaction plants in terms of reliability, availability and profitability; this is because the annual profits of medium-sized FPSOs (3MTPA) were estimated to increase by approximately US$296 million, rising from about US$1,190 million to US$1,485.98 million, if redundancy were implemented. The cost-benefit analysis results were based on the average LNG prices (US$500/ton) in 2013 and 2014. Typically, centrifugal turbines, compressors and blowers are the main items of equipment in LNG liquefaction plants. Because centrifugal equipment tops the FPSO equipment failure list, a Condition Monitoring (CM) system for such equipment was proposed and tested to reduce maintenance and shutdown costs, and also to reduce flaring. The proposed CM system was based on a novel FFT-based segmentation, feature selection and fault identification algorithm. A 20 HP industrial air compressor system with a rotational speed of 15,650 RPM was utilised to experimentally emulate five different typical centrifugal equipment machine conditions in the laboratory; this involved training and testing the proposed algorithm with a total of 105 datasets. The fault diagnosis performance of the algorithm was compared with other methods, namely standard FFT classifiers and Neural Network. A sensitivity analysis was performed in order to determine the effect of the time length and position of the signals on the diagnostic performance of the proposed fault identification algorithm. The algorithm was also checked for its ability to identify machine degradation using datasets for which the algorithm was not trained. Moreover, a characterisation table that prioritises the different fault detection techniques and signal features for the diagnosis of centrifugal equipment faults, was introduced to determine the best fault identification technique and signal feature. The results suggested that the proposed automated feature selection and fault identification algorithm is effective and competitive as it yielded a fault identification performance of 100% in 3.5 seconds only in comparison to 57.2 seconds for NN. The sensitivity analysis showed that the algorithm is robust as its fault identification performance was affected by neither the time length nor the position of signals. The characterisation study demonstrated the effectiveness of the AE spectral feature technique over the fault identification techniques and signal features tested in the course of diagnosing centrifugal equipment faults. Moreover, the algorithm performed well in the identification of machine degradation. In summary, the results of this study indicate that the proposed two-pronged approach has the potential to yield a highly reliable LNG liquefaction system with significantly improved availability and profitability profiles.

Made available in DSpace on 2016-06-02T19:55:39Z (GMT). No. of bitstreams: 1 6040.pdf: 2233550 bytes, checksum: 85c4a2a63a2588091a17f8cbba6ee93c (MD5) Previous issue date: 2014-03-28 / Adhesion between powders and surfaces plays an important role in various technological areas and processes, such as paste drying operations, fluidization of fine particles, microencapsulation, xerography and in food and pharmaceutical processes. Adhesion of small particles to solid surfaces is a phenomenon closely associated with industrial hygiene and air pollution studies. The centrifuge technique to determine adhesion force is based on the detachment of particles from a substrate surface due to centrifugal force. In this technique, a substrate with particles deposited on its surface is rotated at successively increasing speeds, and after each rotation at a given speed, the number of particles remaining on the surface is determined. This technique uses imaging analysis to determine the number of adhered particles on the proof disk surface before and after each centrifugation. After applying a specific press-on, images of the substrates containing particles from the pulverized materials were taken by optical microscope Olympus BX60 (Olympus Co. Tokyo Japan and processed by an image analyzer (Image-Pro Plus 7.0).The results were treated statistically to obtain the mean particle adhesive force. The powder used was a polydisperse sample of microcrystalline cellulose (ρ=1.62 kg m−3). The materials used as substrates were a membrane of cellulose ester 0.2 μm of porosity, brand Shleicher & Shuell - Filtration Life Science, and a compressed particulate (tablets) made of microcrystalline cellulose (Sigma-Aldrich). A microcentrifuge that reached a maximum rotation speed of 14000 rpm which contained specially designed centrifuge tubes was used in the adhesion force measurements. Compression speeds (presson) were applied to each of the experimental runs at 1000, 2000 and 5000 rpm. To detach the particles from the substrate surface, eight cleaning speeds (spin-off) were used. Detachment was done at the centrifugal speeds of: 1000, 3000, 5000, 7000, 9000, 11000, 13000, and 14000 rpm for 1 min. Five particle diameter sizes were studied: 9 15, 15.1 22, 22.1 30, 30.1 42, and 42.1 60 μm. It was observed that the adhesion force increases linearly with the particle diameter, within the range studied and that increased compression speed has an influence on the process of particles detaching. It was possible to obtain a relationship between the adhesion force and diameter of the particles adhered to substrates analyzed The adhesion force experimental results and the adhesion force theoretical values using the models proposed by Derjaguin, Muller and Toporov (DMT) and Johnson, Kendall and Roberts (JKR) were compared. Although the JKR Model was the closest one to the experimental results, the adhesion force theoretical values were far higher than the experimental values. Finally a correction constant (kc) was proposed in order to correlate the theoretical values of adhesion force to the experimental values. / Adesão entre pós e superfície desempenha um papel importante em diversas áreas tecnológicas, tais como as operações de secagem, microencapsulação, xerografia e impressão, e processos farmacêuticos e de alimentos. A adesão de partículas em superfícies sólidas é um fenômeno intimamente associado com estudos de higiene industrial e da poluição do ar. A técnica centrífuga para determinar a força de adesão é baseada no desprendimento de partículas de uma superfície do substrato, devido a força centrífuga. Esta técnica utiliza a análise de imagens para determinar o número de partículas aderidas sobre a superficie do substrato. O substrato com as partículas depositadas na sua superfície é rotacionado sucessivamente a velocidades cada vez mais elevadas e depois de cada rotação a uma determinada velocidade o número de partículas restantes na superfície é determinado e para isso utilizou-se o microscópio óptico (Olympus BX60) e o analisador de imagens Image Pro- Plus 7.0. Os resultados são tratados estatisticamente para obter a força de adesão média entre partícula e substrato. O pó utilizado foi uma amostra polidispersa de celulose microcristalina (ρ=1,62Kg m-3). Os materiais utilizados como substratos foram uma membrana filtrante de éster de celulose de 0,2 μm de porosidade, marca Shleicher & Shuell - Filtration Life Science, e um comprimido de celulose microcristalina (Sigma-Aldrich). Utilizou-se, nos experimentos, uma microcentrífuga (MA 860, Marconi Equipamentos), com velocidade máxima de rotação era de 14000 rpm que continha dois tubos nos quais foram colocados adaptadores, cuja finalidade era de sustentar os substratos contendo o material pulverulento distribuído em sua superfície. Para cada substrato foi aplicada a força de compressão (press-on), de 1000, 2000 e 5000 rpm e para separar as partículas da superfície do substrato foram aplicadas forças de desprendimento (spin-off), de 1000, 3000, 5000, 7000, 9000, 11000, 13000 e 14000 rpm. As faixas de diâmetro das partículas de celulose microcristalina utilizadas nos experimentos foram: 9 15, 15,1 22, 22,1 30, 30,1 42 e 42,1 60 μm. Constatou-se que a força de adesão aumentou com o acréscimo da velocidade de rotação da centrífuga aplicada na compressão e com o aumento do tamanho das partículas do material pulverulento. Foi possível obter uma relação entre a força de adesão e o diâmetro das partículas aderidas para os substratos analisados. Os resultados experimentais da força de adesão e os valores teóricos da força de adesão calculados usando os modelos de Derjaguin, Muller and Toporov (DMT) e Johnson, Kendall and Roberts (JKR) foram comparados e embora o modelo de JKR tenha sido o que mais se aproximou dos resultados experimentais, os valores de força de adesão teórica foram distantes e superiores aos valores obtidos experimentalmente. Finalmente, foi possível obter constantes de correção kc que relacionam a força de adesão teórica com a força de adesão observada experimentalmente.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2011 / Smart (SMA-Shape Memory Alloy) Technology continues to advance rapidly as engineers move closer to and understand better the industrial and commercial needs for SMA. As a matter of fact, all types of products, which exercise some type of control over their function, are rapidly making their way into the marketplace [36] Nonetheless, nowhere has been evidence in the development of a SMA impeller. Unlike traditional impellers with no control over their function and sometimes fixed angle of attack, this paper demonstrates numerical investigations using analytical algorithms (Matrix laboratory programming and excel spread sheet) and advanced computer simulation package, Engineering Fluid dynamics (EFD) into the feasibility of using a smart impeller to study the performance of a pumping system and the best angle of attack for a Shape Memory Impeller. Primarily, Bench mark data and dimensions are obtained from a standard centrifugal pump run on a FM21 demonstration unit. Using the same standard centrifugal pump, and keeping all other dimensions the same but altering the angle of attack, EFD simulations where made. From analytical algorithm and EFD comparison, it was evident that the best angle of attack is 12 degree at the outlet angle with respect to the inlet angle. From EFD results, it is palpable that, by increasing the angle of attack from 35 degree to 45 degree at the outlet there will be huge increase in flow rate by 63.47% There is also a slight decrease in the impeller Torque from 35 degrees to 42 degrees by 0.72%. It is economically feasible to work at an outlet angle of 42 degrees due to increase in efficiency of 62.1% and a drop in torque of 0.72% by varying the outlet angle from 35 degrees to 42 degree. Understanding how critical actuator design is, it should be suggested that any shape memory impeller should never be used in critical components without a prior history of thermal and mechanical loading. Therefore, a NiTi impeller constitutive model can be designed, with impeller blades made from NiTi plates, trained to remember its best angle of attack (Martensitic phase). NiTi shape memory metal alloy (plates-blades) can exist in a two different temperature-dependent crystal structures (phases) called martensite [9](lower temperature-normal pumping condition) and austenite [9] (higher temperature or parent phase-trained best angle of attack.)

Made available in DSpace on 2014-12-17T14:58:07Z (GMT). No. of bitstreams: 1 JulioCS_DISSERT.pdf: 3237837 bytes, checksum: 5158084ee6f945389663f9068eb38d4d (MD5) Previous issue date: 2011-09-17 / The oil industry`s need to produce with maximum efficiency, not to mention the safety and the environment aspects, encourages the optimization of processes. It makes them look for a level of excellence in acquisition of equipment, ensuring the quality without prejudice security of facilities and peoples. Knowing the reliability of equipment and that this stands for a system is fundamental to the production strategy to seeks the maximum return on investment. The reliability analysis techniques have been increasingly applied in the industry as strategy for predicting failures likelihood ensuring the integrity of processes. Some reliability theories underlie the decisions to use stochastic calculations to estimate equipment failure. This dissertation proposes two techniques associating qualitative (through expertise opinion) and quantitative data (European North Sea oil companies fault database, Ored) applied on centrifugal pump to water injection system for secondary oil recovery on two scenarios. The data were processed in reliability commercial software. As a result of hybridization, it was possible to determine the pump life cycle and what impact on production if it fails. The technique guides the best maintenance policy - important tool for strategic decisions on asset management. / A necessidade da ind?stria do petr?leo de produzir com o m?ximo de efici?ncia, sem esquecer os aspectos de seguran?a e meio ambiente, incentiva a otimiza??o dos processos produtivos, faz com que se busque atingir um n?vel de excel?ncia na aquisi??o de equipamentos, garantindo a qualidade sem preju?zo da seguran?a de instala??es e de pessoas. Conhecer a confiabilidade de um equipamento e o que esta representa para um sistema ? de fundamental import?ncia ? estrat?gia de produ??o quando se visa o m?ximo de retorno sobre o capital investido. As t?cnicas de an?lise de confiabilidade v?m sendo cada vez mais aplicadas na ind?stria como uma ferramenta estrat?gica para a predi??o da probabilidade de falhas e a garantia da integridade dos processos. Alguns fundamentos e teorias na ?rea de confiabilidade embasam as decis?es de se utilizar c?lculos estoc?sticos na estimativa de falhas de equipamentos. Esta disserta??o prop?e o uso de duas t?cnicas capazes de associar aspectos qualitativos (atrav?s de informa??es coletadas no campo com a opini?o de especialistas) e quantitativos (provenientes de bancos de dados de registros de falhas elaborados por empresas do segmento petrol?fero do mar do norte Europeu, mais conhecidos como Oreda). Este trabalho trata do uso dessas duas t?cnicas aplicadas em uma bomba centr?fuga, cujo sistema de inje??o de ?gua produzida ocorre em dois cen?rios poss?veis de opera??o : com manuten??o e sem manuten??o. Os dados obtidos nas avalia??es foram processados em software comercial de confiabilidade. Com o resultado desse hibridismo, foi poss?vel determinar o ciclo de vida da Bomba Centr?fuga e sua disponibilidade nesse per?odo e qual ser? o impacto na produ??o caso este venha a falhar. O uso dessa t?cnica permitir? orientar qual a melhor pol?tica de manuten??o ferramenta importante para a tomada de decis?es estrat?gicas na gest?o do ativo.

Orientador: Prof. Dr. Jean-Jacques Bonvent / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Biotecnociência, 2017.