Dissertations / Theses on the topic 'Centrifugal pumps – Performance'

In centrifugal pumps the leakage and dynamic characteristics of annular seals are important factors for pump performance. Both seal leakage and dynamics are greatly affected by the relationship between fluid flow and wall friction. In this thesis explicit friction factors were developed which relate the turbulent fluid flow in the seal to wall friction for seals with rectangular grooves. Computational Fluid Dynamics (CFD) was used to study a range of groove width to depth ratios between 1 and 16 and groove depth to clearance ratios between 0.2 and 25.8. In this range an optimal groove geometry for leakage reduction was found which may increase the volumetric effciency of pumps considerably. Based on a similarity assumption for grooves and hole patterns a friction factor was proposed for hole pattern seals.

Based on the developed friction factors extensions were made to a theory for predicting dynamic characteristics of plain seals to deal with grooved and hole-patterned seals or a combination of both. The method does not require calibration to experiments in order to give useful results. A parameter study indicated that for certain stator hole patterns the cross-coupled stiffness could be greatly reduced compared to that of a smooth seal. This means that self excited vibrations from the seal may be prevented and the range of stable operation of the pump may be increased. Another extension of the theory accounts for angular stiffness, damping, and added mass moment of inertia for tapered seals. A previously published isotropic friction factor based on pipe flow in the transition between laminar and fully turbulent flow was also invluded in the theory for predicting dynamic coefficients. Results compared well to previously published theoretical results, however, comparisons to experimental results indicate that this friction factor is of limited use for seals.

Inlet and exit conditions of seals affect both seal leakage and rotordynamic coefficients to some extent. An experimental study of inlet and exit losses for seals with sharp, chamfer, and protruding edge inlet and exit geometrics was carried out for a range of axial and tangential flow veloocities. The inlet loss was sensitive to geometry changes, while the exit loss was not. The commonly used assumptions of no rotational speed dependency for entrance and exit losses holds well when the average tangential flow is less than or equal to the axial flow. However, as the tangential flow became much alrger than the axial flow this assumption did not hold well. In the same study leakage for seals with shallow grooves was studied. Experimental leakage results for shallow grooves on the rotor corresponded well with theoretical predictions based on the friction factor developed in this thesis.

Thesis (MTech(Civil Engineering))--Cape Peninsula University of Technology, 2006.
The performance of a centrifugal pump is altered for slurry or viscous materials (Stepanoff, 1969) and this needs to be accounted for. Usually, the suitable selection and evaluation of centrifugal pumps is based only on water pump performance curves supplied by the pump manufacturer (Wilson, Addie, Sellgren & Clift, 1997). In 1984 Walker and Goulas conducted a number of pump performance tests with kaolin clay slurries and coal slurries on a Warman 4/3 AH horizontal slurry pump and a Hazleton 3-inch B CTL horizontal pump (Walker and Goulas, 1984). Walker and Goulas have analysed the test data and correlated the performance derating both at the best efficiency flow rate (BEP) and at 10% of the best efficiency flow rate (0.1 BEP) to the modified pump Reynolds number (NRep). They have noticed that the head and the efficiency reduction ratio decreased for the pump Reynolds number less then 10⁶. Furthermore, Walker and Goulas obtained a reasonably good agreement (± 5%) between pump test data for non-Newtonian materials and pump performance prediction using the Hydraulics Institute chart. Sery and Slatter (2002) have investigated pump deration for non-Newtonian yield pseudoplastic materials. The NRep was calculated using the Bingham plastic viscosity (µp). Results have shown good agreement with regard to head and efficiency reduction ratios in comparison with previous work. However, Sery and Slatter's pump performance correlation using the HI chart did not reach the same conclusion. Error margin of ± 20% and ± 10% were found for head and efficiency respectively. This study is an attempt to reconcile the differences between Walker and Goulas (1984) and Sery and Slatter (2002) and extend the evaluation of these derating methods to pseudoplastic materials. The test work was conducted in the Flow Process Research Centre laboratory of the Cape Peninsula University of Technology using two centrifugal pumps; a Warman 6/4 and a GrW 4/3. The materials used were water, CMC solution bentonite and kaolin suspension at different concentrations (7% and 9% by weight for bentonite; 5%, 6% and 7% by weight for CMC; 17%, 19% and 21% by volume for kaolin).

This thesis study is focused on experimentally investigating pump noise at design and off-design operations and its relations with pressure fluctuations. Small size pumps are placed in a semi-anechoic chamber and operated at various system conditions and various rotational pump speeds. Pump operational data, noise data and time dependent pressure data are recorded. Fast Fourier Transform spectra of noise and pressure data are compared. Coherence spectrum between sound pressure level and hydraulic pressures are obtained. Data processing, Fast Fourier Transform and cross correlation are conducted with specific software Soundbook SAMURAI. The experiments have indicated that system characteristics or pump size do not have any influence on the noise of pump. On the other hand, pump characteristics are found to be distinguishable by means of peak frequencies on the sound spectra which are proportional to blade passing frequency. Results of cross correlations also show that, pump outlet pressure is a more significant source of noise than pump inlet pressure.

[Truncated abstract] Centrifugal pumps are the most prevalent, electrically powered rotating machines used today. Each pump is designed to deliver fluid of a given flow rate at a certain pressure. The point at which electrical energy is converted most efficiently into increased pressure is known as the Best Efficiency Point. For a variety of reasons, pumps often operate away from this point (intentionally or otherwise), which not only reduces efficiency, but also increases the likelihood of premature component failure. Acoustic emissions (AE) are high frequency elastic waves, in the range of 20-2000kHz, released when a material undergoes localised plastic deformation. Acoustic emission testing is the process of measuring and analysing these stress waves in an attempt to diagnose the nature and severity of the underlying fault. AE sensors mounted on the surface of a machine or structure also detect any stress waves generated within the fluid being transmitted through to the structure. Unfortunately, attempts to detect incipient component faults in centrifugal pumps using acoustic emission analysis have been complicated by the sensitivity of AE to a pump?s operating state. Therefore, the aim of this thesis was to determine how acoustic emission monitoring could be used to identify the hydraulic conditions within a pump. Data was collected during performance tests from a variety of small end-suction pumps and from one much larger double-suction pump. A system was developed to collect, process and analyse any number of AE features (be they related to discrete AE events, or due to the continuous background AE level) from continuously operating equipment. ... Unfortunately, results from smaller pumps were less conclusive, particularly at low flows, probably due to the relatively small changes in hydraulic energy across the range of flows, and consequent sensitivity to the testing process. However, even in these pumps consistent patterns in hit energies were observed resulting in the conclusion that low to medium flows in centrifugal pumps are typified by a very large number of very low energy (VLE) events. These decrease in number and increase in energy as flow approaches BEP and/or is reduced to very low flows. High flows above BEP are marked by an absence of these VLE events, with bursts having significantly higher energies and spread over a much greater range. Unfortunately, these VLE events are too small to affect averaged trends, indicating that further work on a suitable filter is required. vi

Due to the increasing demand, nonclog type sewage pumps are designed and manufactured in large amounts all over the world. However, a methodology on the design of these special duty pumps is not encountered in the literature. Therefore, the manufacturers tend to develop their own empirical methodologies. In this thesis, a nonclog pump is designed and constructed on the basis of suitable approaches of known centrifugal pump design methods. In this frame, a nonclog type submersible pump that is capable of handling solids, up to a diameter of 80 mm is aimed to be designed. The designed pump delivers 100 l/s flow rate against a head of 24 m. The rotational speed of the pump is 1000 rpm. Design procedure and the important points that differ nonclog pump design from standard centrifugal pump designs are given. In addition, hydraulic characteristics of two nonclog pumps, one of which is the pump designed in this study, are investigated by means of computational fluid dynamics (CFD) code. The designed pump is manufactured and tested in Layne Bowler Pump Company Inc. The test result indicates that design point is reached with a deviation in the limits of the related standard. Wire to water total best efficiency obtained by the test is 60%. Close agreement between results of actual test and numerical experimentation performed by CFD code shows that CFD analysis is a quite useful tool in predicting the hydraulic characteristics of nonclog pumps. Moreover, the pump is tested at 750 rpm and the test results are found to be in good agreement with the similitude anaysis results.

CAPES
A bomba centrífuga submersa (BCS) é utilizada na indústria do petróleo como uma técnica de elevação artificial. Entretanto, o bombeamento de petróleo está associado a escoamentos de óleo de diferentes viscosidades. Esta condição leva a degradação do desempenho em relação à operação com água, na qual a bomba é originalmente projetada. Neste cenário no presente trabalho é desenvolvido um estudo numérico do escoamento em três estágios de duas BCSs semi-axiais. As equações transientes da conservação da massa e do balanço da quantidade de movimento, que modelam o escoamento nas BCSs, são resolvidas numericamente utilizando o programa computacional comercial Ansys-CFX. A turbulência do escoamento foi modelada utilizando o modelo SST. Os resultados numéricos obtidos foram comparados contra dados experimentais e de catálogo mostrando uma boa concordância, para uma grande faixa de viscosidades e rotações. Grupos adimensionais (n, n, n e Re) foram usados para avaliar a degradação do desempenho das BCSs. Além disso, os fenômenos envolvidos no escoamento no interior do rotor das bombas centrífugas foram analisados através dos campos de velocidade obtidos numericamente. A partir dos resultados numéricos foi verificado que a degradação do desempenho é diretamente relacionada com o número de Reynolds de rotação, Re. Também, observou-se que a degradação do desempenho ocorre para uma rotação específica normalizada constante n, no qual bombas de diferentes geometrias apresentaram degradação do desempenho similar. Além disso, dados experimentais e os resultados numéricos obtidos foram consistentes quando comparados com a relação entre os fatores de correção para a vazão e altura de elevação propostas por Stepanoff (1967). Uma definição de número de Reynolds modificado foi proposta e relaciona o fator de correção para altura de elevação com a viscosidade. Além disso, uma correlação entre o fator de correção para altura de elevação e o número de Reynolds modificado foi proposta, apresentando boa concordância. A partir das correlações obtidas, foi proposto um método para prever o desempenho de bombas centrífugas operando com fluidos de alta viscosidade, sendo comparado com outras metodologias encontradas na literatura. Certamente, as informações extraídas são relevantes para o entendimento do escoamento de fluidos de alta viscosidade em bombas, especialmente em BCSs semi-axiais de múltiplos estágios.
Electrical Submersible Pump (ESP) is used as an artificial lift technique. However, pumping viscous oil is generally associated with low Reynolds number flows. This condition leads to a performance degradation respect to the performance expected from the regular operation with water that most of the centrifugal pumps are originally designed for. These issues are considered in this investigation through a numerical study of the flow in two different multistage, semi-axial type ESPs. This investigation is carried out numerically using a Computational Fluid Dynamics (CFD) package, where the transient RANS equations are solved numerically. The turbulence is modeled using the SST model. Head curves for several operating conditions are compared with manufacturer’s curves and experimental data for a three-stage ESP, showing good agreement for a wide range of fluid viscosities and rotational speeds. Dimensionless numbers (n, n, n e Re) are used to investigate performance degradation of the ESPs. In addition, flow phenomena through the impellers of the ESPs are investigated using flow field from numerical results. Results show that performance degradation is directly related to rotational Reynolds number, Re. In addition, it was verified that performance degradation occurs for constant normalized specific speedn, which shows that performance degradation occurs similarly for different centrifugal pumps. Moreover, experimental data and numerical results agreed with a correlation from literature between head and flow correction factors proposed by Stepanoff (1967). A definition of modified Reynolds number was proposed and relates the head correction factor to viscosity. A correlation between head correction factor and the modified Reynolds number was proposed, which agreed well with numerical and experimental data. Then, a method to predict performance degradation based on the previous correlations was proposed. This method was compared with others from literature. In general, results and conclusions from this work can also be useful to bring more information about the flow of highly viscous fluids in pumps, especially in semi-axial, multistage ESPs.

A review was carried out which revealed that no simple mathematical model was available which could be used to predict the performance of a centrifugal pump when it is operating under two phase flow conditions. Experimental analyses were carried out to aid the development of such a model. A rotating channel test rig was designed to study the structure of airwater flow through an impeller passageway. The observations generated a large amount of qualitative data. A full scale centrifugal pump was also tested which provided data that allowed the results of the rotating channel experiments to be considered in more quantitative terms. These two sets of experimental work allowed a conceptual model of the two phase flow through a centrifugal pump to be constructed. The model assumes that forces act on the bubbles as they pass through the impeller passageway because of the rotation and the curvature of the impeller passageway. These forces cause the bubbles to decelerate and coalesce creating a stationary air void which leads to a partial blockage of the channel. This causes the velocity of the fluid passing through the pump to be modified. The model uses a onedimensional velocity vector approach adjusted for hydraulic losses to calculate the head raised by the pump under such conditions. The model presented provides the basis upon which a predictive tool could be developed and used in the development engineering environment. Currently operational problems that arise because of two phase flow are often quantified using scaled hydraulic models, which are expensive, or within the actual application where costly engineering solutions may be required to give acceptable performance. A mathematical model is a much more cost effective tool and its application allows the engineer to decide whether system performance would be compromised by the two phase conditions encountered and propose possible solutions. In recommending the development of such a model it is necessary to consider where and how in the project cycle it should be used. A number of companies were canvassed and it was concluded that in many cases such models are used too late in the project cycle to provide maximum return. In the case of projects which include participants from a number of companies it is suggested that an inter-company team should be constructed if development models are to be widely used. This team should be used to plan and implement the use of development models efficiently and ensure that the data produced is communicated effectively and is of the maximum value to the participants.

Heart failure (HF) is a common cause of hospitalisation and mortality across industrialised countries. The number of hospitalisations and deaths attributed to heart failure is increasing, and this trend is predicted to continue. Numerical and in-vitro simulations of the human cardiovascular system constitute the basic tools for enhancing diagnostic and therapeutic technologies for HF and this would in turn, have significant effects on morbidity,mortality, and healthcare expenditure. Mechanical Circulatory Support (MCS) as a destination therapy for HF is rising significantly as it provides a cost-effective alternative to long-term treatment and cardiac transplantation. However, long-term versatility is far from ideal and incidence of transient and permanent neurological events is still high. To this end, evolution of MCS devices calls for more sophisticated design and evaluation methods. The purpose of this work is to develop a numerical model and to implemented a novel in-vitro model of the cardiovascular system with the intention of evaluating the performance characteristics of a purposely selected centrifugal pump impeller for the treatment of both Class III and IV HF conditions when placed in series with the heart at two different anatomic locations: Ascending Aorta and Descending Aorta. An existing lumped-parameter model of the CV system, that included models for the heart, the pulmonary and the systemic circulatory loops by adapting a modified version of the fourth-element Windkessel model was enhanced by dividing the systemic circulation into six parallel vascular beds, and by including an autoregulatory system to control both pressures and volumes throughout the system. As part of the novelty of the present work, a volume reflex loop was included with the purpose of simulating volume overload conditions, as commonly found in HF conditions, and obtaining a more realistic analysis of volume displacement, while using a MCS device. The in-vitro model implemented in this work adopted most of the features included in the mathematical counterpart with the purpose of validating the numerical results. As a result of the combination of models and proper optimisation of the system parameters, predictions of pathophysiological trends and MCS usage are satisfactorily obtained. The models implemented in this work offer a valuable tool for the selection and performance evaluation of MCS devices for the treatment of HF conditions.

PETROBRAS
Ao longo dos últimos anos a utilização de bombas centrífugas submersas (BCS) se tornou o segundo método de elevação artificial mais usado na indústria petrolífera. Como a produção típica dos poços petrolíferos submarinos consiste em misturas contendo óleo e gás, as bombas centrífugas estão sujeitas a operar com escoamento bifásico. A presença de gás livre no escoamento provoca instabilidades e degradação da curva de ganho de pressão da bomba. Essa degradação se torna muito grande quando ocorre o fenômeno de surging. Este fenômeno é caracterizado por um grande acúmulo de gás nos canais do rotor, sendo seu início identificado como um ponto na curva de ganho de pressão a partir do qual o desempenho cai de forma abrupta com a diminuição da vazão do líquido. Dependendo da fração de gás na entrada da bomba, pode ocorrer o bloqueio dos canais do rotor, fenômeno conhecido como gas locking, fazendo com que a vazão de líquido e o incremento de pressão sejam praticamente nulos. Portanto, é fundamental o conhecimento das condições operacionais e padrões de escoamento ligados à ocorrência de surging para uma operação adequada da bomba. Nesse cenário, o presente trabalho tem por objetivo avaliar o desempenho de uma bomba centrífuga operando com escoamento bifásico ar-água. Para esse fim, foram levantadas as curvas de ganho de pressão de uma bomba centrifuga convencional de dois estágios com rotores de tipo radial. Os testes foram feitos utilizando água e ar como fluidos de trabalho, com frações volumétricas de gás entre 0 e 10%, velocidades de rotação entre 300 e 600 rpm, com vazões de água entre 0,2 e 1,5 vezes o ponto de máxima eficiência e uma pressão de sucção de 160 kPa. Ao mesmo tempo, foram identificados os diferentes padrões de escoamento dentro do rotor em diferentes condições operacionais. Para construção da bancada, a carcaça da bomba e o rotor original de seu primeiro estágio foram substituídos por outros de material transparente, o que permitiu fotografar a distribuição de gás na bomba com a ajuda de uma câmera de alta velocidade. Além de se utilizar o modelo homogêneo (não deslizamento) como referência para calcular a fração de vazio de entrada em cada teste, um sensor de malha de eletrodos (wire mesh) foi instalado na sucção da bomba com o objetivo de medir frações de vazio reais, que posteriormente foram comparadas com os resultados do modelo homogêneo e o de deslizamento (drift flux). As imagens obtidas foram associadas às instabilidades observadas nas curvas de desempenho da bomba, como forma de se compreender os fenômenos relacionados à queda de desempenho em operação com escoamento bifásico, em especial nas condições de surging. Esse procedimento, associado à medida da fração de vazio real na entrada da bomba, não apenas contribui com o entendimento do escoamento bifásico líquido-gás em bombas, como também oferece uma fonte interessante de dados de entrada e de validação de modelos teóricos e numéricos para outros trabalhos.
Over the last years the use of electric submersible centrifugal pumps (ESPs) has become the second most widely used artificial elevation method in the oil industry. As the typical production of submarine oil wells consists of mixtures containing oil and gas, the centrifugal pumps are subjected to operate with two-phase flow. The presence of free gas in the flow causes instabilities and degradation of the pump pressure-rise curve. This degradation becomes severe when the surging phenomenon occurs, which is characterized by large gas accumulations inside the impeller, with its initiation identified as the point in the pressure-rise curve from which the performance falls abruptly with the decrease of the liquid flow rate. Depending on the intake gas fraction, the rotor channels can be completely blocked (gas locking), causing the liquid flow rate and the pressure-rise to be almost null. Therefore, knowledge of operating conditions and flow patterns linked to the occurrence of surging for proper pump operation is critical. In this scenario, the present work aims to evaluate the performance of a centrifugal pump operating with two-phase air-water flow. To this end, the pressure-rise curves of a conventional two-stage centrifugal pump with radial rotors were measured. The tests were done using water and air as working fluids, with volumetric gas fractions between 0 and 10%, rotational speeds between 300 and 600 rpm, water flow rates between 0.2 and 1.5 times the best efficiency point and a suction pressure of 160 kPa. At the same time, different flow patterns were identified inside the rotor under different operating conditions. For this purpose, the pump casing and the original rotor of its first stage were replaced by equivalent transparent pieces, which allowed photographing the gas distribution inside the pump with the help of a high-speed camera. In addition to using the homogeneous (non-slip) model as a reference to calculate the inlet gas volume fraction in each test, a wire mesh sensor was installed in the intake pipe in order to measure the actual void fractions, which were later compared with the results from the homogeneous and the drift flux models. The images obtained were associated with the instabilities observed in the performance curves of the pump, as a way to understand the phenomena related to the performance degradation in two-phase flow operation, especially under surging conditions. This procedure, together with the measurement of the actual gas volume fractions in the pump intake, not just contributes to the understanding of gas-liquid flows in pumps, but also provides an interesting source of data for input and validation of theoretical and numerical models for other investigations.

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.

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 aim of the diploma thesis is to design the pump impeller. The classical design of the impeller is made for one operating point, in which pump is assumed to operate most of the time. The aim of this diploma thesis is to design a pump, whose pump cover and pump drive discs are designed for each other operating point and then compare the results of both design methods.

碩士
國立屏東科技大學
機械工程系所
96
This research analyzes the influence on output effects of blade number of a centrifugal pump. According to the size of the pump’s impeller, the number of blades used can be decided by engineering empirical method. The 3D physical model can be constructed and following meshed （discretized） by Gambit, and the flowfield can be solved by FLUENT. Once the flowfield is solved, the pump efficiency, required power, pressure distribution…etc, can be determined. The results of CFD simulation shows that when the pump speed is set at 1450rpm, the flow rate of the 7-blade pump reach the highest（maximum） efficiency 74.43%.

碩士
南台科技大學
機械工程系
95
The impeller type left ventricular assist device (LVAD) uses rotating impeller pumping blood. It mainly falls two categories. They are the one with centrifugal type impeller and that with axial-flow impeller. The study concentrates on centrifugal type impeller design of the LVAD.We initially design three casing model with different outlet width and eccentric geometries in rotating impeller condition. the research chooses the best model in efficiency among them.then we design two clearance type of parallel gap between impeller and casing.Flow analysis around the impeller is performed by using the finite volume method to solve the fully incompressible three-dimensional Navier-Stokes equations. We adopt the software of CFX 4.3 and ANSYS-CFX-10 to simulate the flow pattern and shear stress under different flow conditions. Results provide a comprehension of flow velocity, pressure and shear stress distribution of the flow domain for the designs.Performances of the two designs are evaluated by the comparison of the corresponding flow rate - rotation speed - pressure curves. On the other hand, shear stress is evaluated and a detailed comparison of the shear stress field of the two designs is demonstrated as well.

碩士
國立成功大學
機械工程學系碩博士班
95
The parallel type machine tool has the ability to process complicated curved surface, also has the advantages of high speed and high-accuracy. The present approach considers the difficulty to manufacture when the centrifugal pump impellers are composed of the three-dimension to turn back the curved surfaces. This design suggest using the efficiency of the impeller to improve the impeller manufacturing. For this purpose, this research proposes a specific method of parallel type machine tool and centrifugal pump impellers that raise its manufacturing feasibility. Since the contour of centrifugal pump impellers consist of five-axis manufacturing process that combines numerical curve of rational B-spline as well as its applications in calculating flow centrifugal pump’s performance by TASCflow of CFD. With this object, it conducts centrifugal pump impellers of execellent performance for workpiece of parallel type machine tool which is made up of centrifugal pump impellers. The research uses of geometric constraints and non-geometric constraints to determine feasibility of manufacturing work. The result of calculation shows the situation that joint angle of moving platform is too big to work. The proposing methods of situation are (1) install the joint are at an angle (2) manufacture in dividing sections. The results of this research shows the geometric constraints and non-geometric constraints are all in limit range. Meanwhile, the speed of manufacture is fairly better than five-axis manufacturing process, under the situation of matching the fourth axle and workpiece to rotate. In this research, the results indicate when install the joint are at an angle and manufacture of divide section, those which are manufactured in the centrifugal pump impellers for superior speed and feasibility.

碩士
國立臺灣科技大學
機械工程系
93
Abstract Pump is widely used to the fluid transportation in the industry. Recently, the small centrifugal pump has drawn increasing attention on its application in the design of artificial heart. There is a substantial need to realize the flow patterns and shear-stress distribution generated by the pump for a safe application on human body. Therefore, this work aims at the application of the numerical code to simulate the associated flow field inside a small BI centrifugal pump. The numerical outcomes are utilized for the flow visualization to identify the possibility of performance enhancement. The designs of impeller and spiral housing adopted the design scheme that was recommended in the previous literatures. Consequently, a water pump comprised a 72.6-mm-diameter scroll housing and an impeller with 50-mm-diameter and seven airfoil blades is designed to meet the 5 l/min volume-flow-rate requirement for the artificial heart. Then, the efficiencies of pump with different blade outlet angles are analyzed numerically. The analysis shows that the max flowrate will be 4.08 l/min when the blade outlet angle is set at 30 . For the case of 22.5 blade outlet angle, the pressure around the rotor distributes uniformly and thus generates the tiniest vibrations on the pump. However, the results from the above analyses did not approach our previous design goal. Hence, this research intends to remove the rotor hub in order to enlarge the inlet area for producing extra mass flowrate. Numerical simulation indicates that the max flow rate increases about 69.5% while the pump’s output pressure enhances dramatically. In conclusion, this numerical result is not only matching the original design target but also proving that the inlet area affects the pump efficiency and performance substantially.

碩士
國立成功大學
機械工程學系碩博士班
94
A centrifugal pump impeller design covers many fields, including fluid dynamics, structural mechanics, vibration and manufacturing etc. In order to obtain blade shapes that could lead to good hydrodynamic performance and machined practicably, an impeller design approach combining five-axis manufacturing process and numerical curve is proposed in this research. The blade shapes are generated from the tool paths constructed ruled surface by the concept of generative machining method, and the cubic spline and the rational B-spline are used to compose the blade curve. For the numerical simulation, the commercial CFD software (CFX-TASCflow) is used to solve the three-dimensional Reynolds-averaged Navier-Stokes equations in a rotating cylindrical coordinate system. 　　In order to evaluate structure reliability and check if vibrations take place, the CAE modules of CATIA are introduced to blade structure analysis and modal analysis in this research. In the aspect of five-axis machining, the NC code for professional-type machine and general-type machine are derived by the transformation of coordinates. Besides, differential geometry is used to check if the interference and undercutting taken place during machining. Finally, kinematic performance of five-axis machining is compared between different blade curves and different five-axis machine. 　　The kinematic analysis results of five-axis machining show impellers whose blade curves composed by the rational B-spline is the prefer choice in the machining concerns. Besides, after the difference between incident angle and blade angle at blade tip is decreased by cutting blade leading edge, both flow field simulation and blade structure analysis results also show impellers whose blade curves composed by the rational B-spline are quite workable.

The Electrical Submersible Pump (ESP) manufactured by Baker Hughes, model no. WJE-1000 is designed for wells that are expected to have a high content of abrasive solids. It is a mixed flow, tandem compression type pump. Although the erosion of the pump diffuser and impeller stages are significant, the ESP study shows that the most sever failure is due to components that affect the pump’s rotor dynamics such as radial bearings and impeller seals when eroded with 100 mesh sand. Erosion of these seals will result in an internal leakage that can significantly affect stage pressure rise, efficiency, power consumption, vibration, pump life and running cost. The erosion study utilizing 100 mesh fracture sand at 0.2% concentration, with the pump operating at 3600 RPM, 40 PSI intake pressure, 1150 GPM for over 117 hours comparisons are made to the pump’s baseline performance. Measurements of the rotor bearings, impeller seals and their corresponding stators showed that the wear patterns generally increase with time and differ by location. Stage 1 bearings and seals suffered the least amount of erosion and stage 3 rotor components suffered the most erosion. The maximum change in stage 3 bearing clearances was 223% and the maximum change in stage 3 impeller seal clearances was 300%. Performance wise the total pump efficiency dropped by 6.77%, the total pressure rise dropped by 6.3%, the pump’s best efficiency point decreased by 0.78%, and the power consumption increased by 0.49%. Pump vibration patterns also changed with time and by location. The maximum shaft orbit diameter was at stage 3 and it grew 643% in diameter after 117 hours of erosion. The waterfall plots of the pump’s ramp up changed significantly with time. After 117 hours at 3600 RPM, sub-synchronous oscillations at 67% of the synchronous speed dominated the amplitude peaks showing that the rotor vibration locked with the rotor’s first natural frequency at around 2500 RPM. After 117 hours, another sub-synchronous started showing a peak at the rotor’s second natural frequency at 1500 RPM.