Biblioteca Digital

In the development of a ventricular assist device, computational fluid dynamics (CFD) analysis is an efficient tool to obtain the best design before making the final prototype. In this study, different designs of a centrifugal blood pump were developed to investigate flow characteristics and performance. This study assumed the blood flow as being an incompressible homogeneous Newtonian fluid. A constant velocity was applied at the inlet; no slip boundary conditions were applied at device wall; and pressure boundary conditions were applied at the outlet. The CFD code used in this work was based on the finite volume method. In the future, the results of CFD analysis can be compared with flow visualization and hemolysis tests.

The heat transfer coefficient at the metal-mold interface (h MM) has been determined for the first time during the centrifugal casting of a Fe-C alloy tube using the inverse solution method. To apply this method, a centrifugal casting experiment was carried out to measure cooling curves within the tube wall under a mold rotation speed of 900 rpm, imposing a centrifugal force 106 times as large as the gravity force (106 G). As part of the solution method, a comprehensive heat transfer model of the centrifugal casting was also developed and coupled to an optimization algorithm. Finally, the evolution of h MM with time that gives the minimum squared error between measured and calculated cooling curves was obtained. The determined h MM is approximately 870 W m−2 K−1 immediately after melt pouring, decreasing to about 50 W m−2 K−1 when the average temperature of the tube is ~973 K (700 °C), after the end of solidification. Despite the existence of a centrifugal force that could enhance the metal-mold contact, these values are lower than those generally reported for static molds with or without an insulating coating at the mold inner surface. The implemented model shows that the heat loss by radiation is dominant over that by convection at the tube inner surface...

A análise de tensões em impelidores de ventiladores centrífugos pelo método dos elementos finitos revela que seus componentes são altamente solicitados e sujeitos a campos de tensões complexos. Tradicionalmente, o projeto estrutural de impelidores centrífugos é realizado a partir do cálculo das tensões estáticas provenientes da força centrífuga, e o comportamento dinâmico do impelidor é frequentemente verificado através de estudos de vibrações livres frente ao conhecimento das fontes de excitação. Por tal abordagem não é realizada qualquer avaliação quanto aos níveis de tensões dinâmicas nos componentes do impelidor. Neste trabalho, contudo, a determinação das tensões dinâmicas é apresentada como uma importante ferramenta para avaliar a integridade estrutural de um impelidor centrífugo durante a sua operação. Para tanto, cálculos de resposta são realizados no rotor e, isoladamente, no impelidor de um ventilador centrífugo, conduzindo a uma nova metodologia para a análise estrutural destes equipamentos através do método dos elementos finitos.; Stress analysis of centrifugal fan impellers through the finite element method reveals that its components are highly stressed and subjected to complex stress fields. Traditionally...

Este trabalho tem como objetivo melhorar a eficiência energética de um ventilador centrífugo produzido pela empresa Projelmec ventilação industrial Ltda., através de simulação numérica em Volumes Finitos, utilizando o software comercial CFX 11.0. Uma malha hexaédrica é utilizada no modelo numérico, após estudo de independência de malha. O escoamento turbulento é tratado com o modelo SST k-Ômega. Após isto, são propostas melhorias na geometria do bocal de entrada do ventilador e um novo tamanho de duto de saída é testado. Todos os modelos testados neste trabalho apresentaram melhoria na eficiência energética em relação ao modelo atual.; The objective of this paper is to improve the energy efficiency of a centrifugal fan produced by Projelmec ventilação industrial Ltda. through numerical simulation in finite volumes, using the commercial software CFX 11.0. A hexahedral mesh is used in the numerical model, after a study of mesh independence. The turbulent flow is treated with the SST k-omega model. After this, improvements are proposed in the shape of the inlet nozzle fan and a new length of output pipe is tested. All models tested in this study showed improvement in energy efficiency over the current model.

Apesar de bastante presente em todo o mundo, a tecnologia de aviação aero agrícola não tem geralmente as mesmas inovações tecnológicas que os outros ramos da indústria. O sistema de pulverização do avião consiste em uma turbina eólica acoplada a uma bomba centrífuga. O presente trabalho apresenta um estudo para análise de uma bomba centrífuga previamente fabricada em polioximetileno, com o intuito de verificar a integridade do componente polimérico quando submetido às condições de contorno de operação. Foram estudados alguns modelos constitutivos para a simulação do comportamento do material, alguns destes levando em conta os efeitos de não-linearidade do material através de curvas que foram obtidas experimentalmente. Os resultados das simulações numéricas são apresentados e discutidos, e conclui-se que frente às condições de contorno de operação, a bomba resiste aos esforços em todos modelos utilizados, embora apenas um dos modelo seja capaz de representar adequadamente os dados experimentais disponíveis.; Despite being used all over the world, aerial application doesn’t usually share the same technological innovations like other industries. The spraying system consists of a wind turbine and a centrifugal pump. The present work presents a methodology to analyze a previously made centrifugal pump casing made of polyoxymethylene...

O método de elevação artificial através do bombeio centrífugo submerso (BCS) é amplamente conhecido na produção de petróleo. Uma alternativa a este método é o hydraulic submersible pump (HSP) que consiste de uma bomba submersa acoplada ao mesmo eixo de uma turbina hidráulica, que é acionada através do fluido a elevada pressão fornecido por uma bomba booster na superfície. As vantagens do sistema HSP em comparação ao (BCS) nas aplicações offshore tem sido discutidas, principalmente devido as suas características de ampla faixa operacional, altas velocidades de rotação e maior tempo médio entre falhas. Em vista disto, o presente estudo avalia o desempenho de uma bomba centrífuga operando como turbina, ou seja, operando em modo reverso, para o acionamento de outras bombas em sistemas de elevação de petróleo. O rotor de uma bomba submersa convencional, operando como turbina, foi investigado. Um arranjo experimental específico foi construído para as medidas dos parâmetros de desempenho, torque, velocidade de rotação, vazão e altura manométrica na turbina, coletados de acordo com dois procedimentos propostos. Curvas de desempenho de altura manométrica, potência de eixo e eficiência são apresentadas e uma comparação com o desempenho do mesmo rotor operando como bomba é discutida. Um método disponível na literatura para estimar os parâmetros de desempenho da turbina a partir dos respectivos parâmetros da bomba...

O bombeio centrífugo submerso (BCS) é o segundo método de elevação artificial mais utilizado em poços de petróleo no mundo. Nestes poços, o equipamento está sujeito à influência de fluidos viscosos e à presença de gás livre, os quais impactam significativamente seu desempenho já que este é resultado da dinâmica de fluidos nos impelidores e difusores da bomba. Historicamente, devido ao escoamento de gás e de fluidos viscosos se tratarem de situações distintas, as maiorias dos estudos realizados analisam estes fenômenos separadamente vistos a complexidade e particularidades existentes de cada. O objetivo deste trabalho é a realização de um estudo experimental de avaliação do desempenho de uma bomba centrífuga sob os dois fenômenos, onde foi mensurado o impacto e a interação das principais variáveis que afetam seu desempenho. Para isto, foi construída uma bancada experimental constando de uma bomba centrífuga do tipo voluta, permitindo medir seu desempenho com água e fluido viscoso juntamente com os efeitos de fração de vazio, diâmetro de bolha e pressão de entrada. Foi também avaliada uma proposta existente de mapeamento do comportamento de uma bomba centrífuga operando com escoamento monofásico em função de números adimensionais que traduzem os efeitos combinados da viscosidade e da rotação. Foram sugeridas modificações e correlações baseadas nesta proposta e seus resultados comparados aos dados experimentais obtidos.; The Electrical Submersible Pumping (ESP) is the second most commonly used artificial lift method worldwide...

Absorvedores de Vibração Pendulares Centrífugos (ou CPVAs) são uma tecnologia criada em 1911, que trouxe excelentes resultados na redução de vibração torcional de muitos sistemas. Porém, sua aplicação em trens de potência automotivos para redução de vibração no virabrequim tornou-se inviável ao final da década de 1940 pela existência de dampers viscosos à base de silicone, uma solução mais barata e com performance similar em certas aplicações. Contudo, a vibração torcional transmitida a transmissões manuais ou automatizadas, em certas velocidades críticas, pode gerar ruído em níveis inaceitáveis, e as soluções atuais para a atenuação deste tipo de vibração, em algumas aplicações, são ou pouco efetivas, como o atrito em discos de embreagem, ou muito custosas, como volantes de dupla massa. Por isso, neste trabalho busca-se a aplicação de absorvedores de vibração pendulares em um disco de embreagem de um trem de potência automotivo equipado com uma transmissão automatizada para a redução de vibração torcional na transmissão, reduzindo possivelmente o ruído de rattle. Para este fim, primeiramente testes são realizados no veículo em estudo para o levantamento de dados torcionais do trem de potência...

In the development of a ventricular assist device, computational fluid dynamics (CFD) analysis is an efficient tool to obtain the best design before making the final prototype. In this study, different designs of a centrifugal blood pump were developed to investigate flow characteristics and performance. This study assumed the blood flow as being an incompressible homogeneous Newtonian fluid. A constant velocity was applied at the inlet; no slip boundary conditions were applied at device wall; and pressure boundary conditions were applied at the outlet. The CFD code used in this work was based on the finite volume method. In the future, the results of CFD analysis can be compared with flow visualization and hemolysis tests.

Al-Al3Zr and Al-Al3Ti functionally graded materials (FGMs) were produced by a centrifugal method from Al-5wt% Zr and Al-5wt% Ti alloys, respectively. Applied centrifugal forces were 30, 60 and 120G (units of gravity). Microstructural characterization was performed to evaluate the intermetallic particles’ distribution and orientation. Knoop hardness tests were carried out, with the indenter’s long diameter normal to the centrifugal force direction. Both the Al3Zr and the Al3Ti intermetallic particles are platelet in morphology. These platelets tend to be oriented normal to the centrifugal force direction. Higher applied centrifugal force increases both the intermetallic platelet volume fraction as well as their orientation in the outer regions of the fabricated FGM rings. Also higher orientation and volume fraction distribution are observed in the Al- Al3Ti FGMs. Knoop hardness measurements in general follow the same trend as the intermetallic particle volume fraction for each sample.

The centrifugal solid-particle method has proved to be effective in producing functionally graded materials (FGMs). In this study, Al-Al3Ti FGMs, were produced by this centrifugal method, from an Al-5 wt % Ti master alloy. Applied centrifugal forces were 30, 60 and 120G (units of gravity). Samples from the outer surface of each specimen were cut and aluminum matrix texture analyzed by Schulz reflection method. Analysis of the resulting pole figures indicates a preferred orientation along the (200) plane for the aluminum matrix crystals. Furthermore, increasing the applied centrifugal force enhances the orientation effect. Al3Ti platelet orientation and area fraction at the samples’ outer surface along three observation planes were also measured. The Al3Ti platelets in the outer region are orientated perpendicular to the centrifugal force direction along two of the observed planes, also an increase in centrifugal force leads to an increase in orientation in those two planes. The intermetallic particle volume fraction also increases with higher applied centrifugal force, although not significantly. A correlation appears to exist between particle orientation and the preferred orientation of the matrix.

Tese de doutoramento em Engenharia Mecânica (ramo de conhecimento em Mecânica de Materiais); Many structural components encounter service conditions and, hence, required materials performance, which vary with location within the component. It is well known that abrupt transitions in materials composition and properties within a component often result in sharp local concentrations of stress, whether the stress is internal or applied externally. It is also known that these stress concentrations are greatly reduced if the transition from one material to the other is made gradual. By definition, functionally graded materials are used to produce components featuring engineered gradual transitions in microstructure and/or composition, the presence of which is motivated by functional performance requirements that vary with location within a part. With functionally graded materials, these requirements are met in a manner that optimizes the overall performance of the component. The research on functionally graded materials (FGMs) is encouraged by the need for properties that are unavailable in any single material and the need for graded properties to offset adverse effects of discontinuities for layered materials. Centrifugal casting is a very common method for obtaining functionally graded materials...

This paper employs the volume of fluid (VOF) method to numerically investigate the effect of the width, height, and contact angles on burst frequencies of super hydrophilic and hydrophilic capillary valves in centrifugal microfluidic systems. Existing experimental results in the literature have been used to validate the implementation of the numerical method. The performance of capillary valves in the rectangular and the circular microfluidic structures on super hydrophilic centrifugal microfluidic platforms is studied. The numerical results are also compared with the existing theoretical models and the differences are discussed. Our experimental and computed results show a minimum burst frequency occurring at square capillaries and this result is useful for designing and developing more sophisticated networks of capillary valves. It also predicts that in super hydrophilic microfluidics, the fluid leaks consistently from the capillary valve at low pressures which can disrupt the biomedical procedures in centrifugal microfluidic platforms.

Centrifugal compressors are a key piece of equipment for modern production. Among the components of the centrifugal compressor, the impeller is a pivotal part as it is used to transform kinetic energy into pressure energy. Blade crack condition monitoring and classification has been broadly investigated in the industrial and academic area. In this research, a pressure pulsation (PP) sensor arranged in close vicinity to the crack area and the corresponding casing vibration signals are used to monitor blade crack information. As these signals cannot directly demonstrate the blade crack, the method employed in this research is based on the extraction of weak signal characteristics that are induced by blade cracking. A method for blade crack classification based on the signals monitored by using a squared envelope spectrum (SES) is presented. Experimental investigations on blade crack classification are carried out to verify the effectiveness of this method. The results show that it is an effective tool for blade crack classification in centrifugal compressors.

This is Part I of a two-part paper documenting the development of a novel asymmetric flow control method to improve the stability of a high-pressure-ratio turbocharger centrifugal compressor. Part I focuses on the nonaxisymmetrical flow in a centrifugal compressor induced by the nonaxisymmetrical geometry of the volute while Part II describes the development of an asymmetric flow control method to avoid the stall on the basis of the characteristic of nonaxisymmetrical flow. To understand the asymmetries, experimental measurements and corresponding numerical simulation were carried out. The static pressure was measured by probes at different circumferential and stream-wise positions to gain insights about the asymmetries. The experimental results show that there is an evident nonaxisymmetrical flow pattern throughout the compressor due to the asymmetric geometry of the overhung volute. The static pressure field in the diffuser is distorted at approximately 90 deg in the rotational direction of the volute tongue throughout the diffuser. The magnitude of this distortion slightly varies with the rotational speed. The magnitude of the static pressure distortion in the impeller is a function of the rotational speed. There is a significant phase shift between the static pressure distributions at the leading edge of the splitter blades and the impeller outlet. The numerical steady state simulation neglects the aforementioned unsteady effects found in the experiments and cannot predict the phase shift...

This paper presents the optimization of vibrations of centrifugal pump considering fluid-structure interaction (FSI). A set of centrifugal pumps with various blade shapes were studied using FSI method, in order to investigate the transient vibration performance. The Kriging model, based on the results of the FSI simulations, was established to approximate the relationship between the geometrical parameters of pump impeller and the root mean square (RMS) values of the displacement response at the pump bearing block. Hence, multi-island genetic algorithm (MIGA) has been implemented to minimize the RMS value of the impeller displacement. A prototype of centrifugal pump has been manufactured and an experimental validation of the optimization results has been carried out. The comparison among results of Kriging surrogate model, FSI simulation, and experimental test showed a good consistency of the three approaches. Finally, the transient mechanical behavior of pump impeller has been investigated using FSI method based on the optimized geometry parameters of pump impeller.

Centrifugal microfluidic platforms have emerged as point-of-care diagnostic tools. However, the unidirectional nature of the centrifugal force limits the available space for multi-stepped processes on a single microfluidics disc. To overcome this limitation, a passive pneumatic pumping method actuated at high rotational speeds has been previously proposed to pump liquid against the centrifugal force. In this paper, a novel micro-balloon pumping method that relies on elastic energy stored in a latex membrane is introduced. It operates at low rotational speeds and pumps a larger volume of liquid towards the centre of the disc. Two different micro-balloon pumping designs have been developed to study the pump performance and capacity at a range of rotational frequencies from 0 to 1500 rpm. The behaviour of the micro-balloon pump on the centrifugal microfluidic platforms has been theoretically analysed and compared with the experimental data. The experimental data shows that, the developed pumping method dramatically decreases the required rotational speed to pump liquid compared to the previously developed pneumatic pumping methods. It also shows that within a range of rotational speed, desirable volume of liquid can be stored and pumped by adjusting the size of the micro-balloon.

The enteroparasitosis remains as an important public health problem in children in the Brazil, showing variable prevalence, according to the State and evaluated population. Studies with day-care center children are scarce, however, already knows that the exposure of the children in these places increased the susceptibility to parasitosis. Among the parasitosis the protozoary Giardia lamblia is responsible for severe diarrhea cases in children and the routine diagnosis methods presents many false negative results. The aim of this study was investigate the enteroparasitosis prevalence in children from a day-care public center of Rio Grande county, Rio Grande do Sul State and compare diagnosis techniques in samples of their fecal material to Giardia lamblia , the ELISA immunoassay and the centrifugal-sedimentation methods. 165 fecal samples where evaluated and processed by centrifugal-sedimentation and centrifugal-flotation methods, stained by trichromium and Kinyoun after the concentration by centrifugal-sedimentation. The general prevalence of enteroparasitosis was 64,2% (106/165). The most prevalent nematods species founded was Trichuris trichiura (24,2%) and Ascaris lumbricoides (22,4%) and the the most prevalent protozoary specie was Giardia lamblia (30...

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...

Several faecal examination techniques have shown variable sensitivity in demonstrating Spirocerca lupi (S. lupi) eggs. The objective of this study was to determine which faecal examination technique, including a novel modified centrifugal flotation technique, was most sensitive to diagnose spirocercosis. Ten coproscopic examinations were performed on faeces collected from 33 dogs confirmed endoscopically to have spirocercosis. The tests included a direct faecal examination, a faecal sedimentation/flotation test, 4 direct faecal flotations and 4 modified faecal centrifugal flotations. These latter 2 flotation tests utilised 4 different faecal flotation solutions: NaNO3 (SG 1.22), MgSO4 (SG 1.29), ZnSO4 (SG 1.30) and sugar (SG 1.27). The sensitivity of the tests ranged between 42 % and 67 %, with the NaNO3 solution showing the highest sensitivity in both the direct and modified-centrifugal flotations. The modified NaNO3 centrifugal method ranked 1st with the highest mean egg count (45.24 ± 83), and was superior (i.e. higher egg count) and significantly different (P < 0.05) compared with the routine saturated sugar, ZnSO4 and MgSO4 flotation methods. The routine NaNO3 flotation method was also superior and significantly different (P < 0.05) compared with the routine ZnSO4 and MgSO4 flotation methods. Fifteen per cent (n =5)of dogs had neoplastic oesophageal nodules and a further 18 % (n = 6) had both neoplastic and non-neoplastic nodules. S. lupi eggs were demonstrated in 40 % of dogs with neoplastic nodules only and 72.9 % of the dogs with non-neoplastic nodules. The mean egg count in the non-neoplastic group (61) was statistically greater (P = 0.02) than that of the neoplastic group (1). The results show that faecal examination using a NaNO3 solution is the most sensitive in the diagnosis of spirocercosis. The modified centrifugal flotation faecal method using this solution has the highest egg count. The study also found that dogs with neoplastic nodules shed significantly fewer eggs than dogs with non-neoplastic nodules.