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Experimental characterization of unsteady gravity currents developing over smooth and rough beds

Nogueira, Helena Isabel dos Santos
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
66.51%
Gravity currents are flows driven by density diff erences between two contacting fluids resulting from temperature gradients, dissolved substances or solid particles in suspension. The release of pollutants into rivers, oil spillage on the sea environment and desalination plant outflows are a few of man-made gravity currents that occur in water masses and frequently cause negative environmental impacts. Examples of gravity currents occurring spontaneously in nature are the sea-breeze and oceanic fronts, underwater debris flows and turbidity currents. Despite the comprehensive knowledge to date on such flows, their dynamics and impact are still topics for research. The aim of the present work is to experimentally investigate the influence of the initial density gradient and of the bed roughness on the kinematics and dynamics of unsteady gravity currents. The lock-exchange technique is herein used, in which two fixed volumes of fluids with diff erent densities, initially at rest in a tank, are put in contact when the gate separating them is rapidly removed, originating a dense current flowing near the tank bed while, simultaneously, a current formed by lighter fluid flows above the dense current, in the opposite direction. Focus is here given to the denser current and to its time-varying complex flow pattern. Two sets of lock-exchange experiments were performed using both image analysis and Particle Image Velocimetry (PIV) techniques. An image analysis technique was herein developed to assess the two-dimensional width-averaged instantaneous density field. This technique...

Estudos de Reaeração com Velocimetria por Imagens de Partículas - Sistema S-PIV-3D; Rearation Studies with Particle Image Velocimetry - S-PIV-3D System

SZELIGA, Marcos Rogério; ROMA, Woodrow Nelson Lopes
Fonte: ABES Publicador: ABES
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
96.48%
Particle Image Velocimetry (PIV) é uma técnica recente de medição não-intrusiva de campos de velocidades em escoamentos. Neste trabalho, foi desenvolvido um equipamento de medição com características similares aos convencionais, porém com algumas características exclusivas, como o método óptico de aquisição de imagens e a calibração de coordenadas, que resultaram na utilização de uma única câmera convencional para obtenção de imagens e dados tridimensionais em escoamentos de baixa turbulência, proporcionando significativa economia na implantação. Foi desenvolvido um software específico e os resultados consistem em campos de velocidades tridimensionais. A aplicação destinou-se à medição de velocidades na superfície do escoamento em um tanque de grades oscilantes de forma a correlacionar a turbulência superficial com a capacidade de reaeração dos corpos da água.; Particle Image Velocimetry (PIV) is a recent technique of flow measurement labeled as a non-intrusive methodology. The system developed in this paper used principles similar to conventional systems including some exclusive characteristics as the optical method of image acquisition and the calibration process of the coordinate system. The measurement system...

Análise da dispersão turbulenta em aeração de corpos hídricos usando a técnica PIV (velocimetria por imagem de partículas); Turbulent dispersion analysis in water bodies aeration using PIV (particle image velocimetry)

Oliveira, Andreza Bortoloti Franco de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 14/11/2008 PT
Relevância na Pesquisa
76.27%
Questões de aeração forçada ou natural estão intimamente ligadas à capacidade de autodepuração dos corpos hídricos, ou seja, oxidar substâncias agressivas para resultar em baixo teor de toxicidade. Uma das etapas do processamento de efluentes consiste na dissolução de oxigênio em água e, para realizar essa dissolução, utilizam-se aeradores que são unidades (tanques) onde o ar é borbulhado no meio líquido, o qual se desloca em um regime contínuo de escoamento. Esta pesquisa refere-se à obtenção experimental de valores de viscosidade turbulenta para inserção em modelagem fenomenológica da transferência de oxigênio das bolhas de ar para o meio líquido. Tais modelos, se bem realísticos, podem contribuir aos estudos de gestão de recursos hídricos ou em operações nos tratamentos de efluentes líquidos. O método experimental empregado foi a velocimetria por imagem de partículas, no qual foi possível obter velocidades instantâneas do fluido (água). Estas consideram o movimento turbulento, que é o principal responsável pelo transporte de oxigênio da superfície para o seio do corpo hídrico, sendo que essa superfície pode ser livre para o ambiente, ou a superfície de uma bolha. Praticamente, o método consiste em correlacionar posições de partículas traçadoras em suspensão no fluido...

High Dynamic Velocity Range Particle Image Velocimetry Using Multiple Pulse Separation Imaging

Persoons, Tim; O’Donovan, Tadhg S.
Fonte: Molecular Diversity Preservation International (MDPI) Publicador: Molecular Diversity Preservation International (MDPI)
Tipo: Artigo de Revista Científica
Publicado em 23/12/2010 EN
Relevância na Pesquisa
66.32%
The dynamic velocity range of particle image velocimetry (PIV) is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets) still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS) technique (i) records series of double-frame exposures with different pulse separations, (ii) processes the fields using conventional multi-grid algorithms, and (iii) yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods.

Echo Particle Image Velocimetry

DeMarchi, Nicholas; White, Christopher
Fonte: MyJove Corporation Publicador: MyJove Corporation
Tipo: Artigo de Revista Científica
Publicado em 27/12/2012 EN
Relevância na Pesquisa
66.36%
The transport of mass, momentum, and energy in fluid flows is ultimately determined by spatiotemporal distributions of the fluid velocity field.1 Consequently, a prerequisite for understanding, predicting, and controlling fluid flows is the capability to measure the velocity field with adequate spatial and temporal resolution.2 For velocity measurements in optically opaque fluids or through optically opaque geometries, echo particle image velocimetry (EPIV) is an attractive diagnostic technique to generate "instantaneous" two-dimensional fields of velocity.3,4,5,6 In this paper, the operating protocol for an EPIV system built by integrating a commercial medical ultrasound machine7 with a PC running commercial particle image velocimetry (PIV) software8 is described, and validation measurements in Hagen-Poiseuille (i.e., laminar pipe) flow are reported.

Aplicabilidad de la energía cinética como parámetro indicador del inicio de la inestabilidad en materiales granulares en un tambor rotador empleando la técnica PIV (Particle Image Velocimetry)

Correa Uribe, Camilo José; Maldonado Rodríguez, Mateo
Fonte: Pontifícia Universidade Javeriana Publicador: Pontifícia Universidade Javeriana
Tipo: bachelorThesis; Trabajo de Grado Pregrado Formato: Pdf
Relevância na Pesquisa
66.43%
Se presenta un estudio del comportamiento de materiales granulares sometidos a procesos de inestabilidad. Determinadas granulometrías se ensayan en diferentes montajes, para la captura de imágenes consecutivas del proceso de flujo de los materiales presentes en el tambor rotador. El procesamiento de las imágenes es realizado mediante la técnica de Particle Image Velocimetry (PIV) para así poder determinar los vectores de desplazamiento y el campo de velocidad de las partículas, utilizando el toolbox de Matlab llamado Pivlab. Posteriormente se calcula la energía cinética y se determina su aplicabilidad mediante el análisis de la variación de este parámetro en los procesos de inestabilidad y su relación con las granulometrías de los materiales y las velocidades de rotación del tambor.; A study of the behavior of materials under granular instability processes is presented. Determinates particle sizes tested in different assemblies, to capture consecutive images of the process flow of the materials present in the rotator drum. The image processing is performed by the technique of Particle Image Velocimetry (PIV) in order to determine the displacement vectors and particle velocity field, using the Matlab toolbox called Pivlab. Subsequently kinetic energy is calculated and its applicability is determined by analyzing oscillation of this parameter on instability processes and its relationship with the grain sizes of materials and speeds of rotation of the drum.

Two dimensional fluidized bed dynamics

Sánchez Delgado, Sergio
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
ENG
Relevância na Pesquisa
66.3%
There are different equipments where solid-gas reactions can take place. One of the most used equipments for these processes, are the uidized beds due to their high reaction rate per unit reactor volume. This complex gas-solid flow is often difficult to model because of the very different length scales that are present, so that additional fundamental investigations are needed before reliable models can be developed for the performance of fluidized beds. Among the different aspects in need of additional research, this PhD thesis focuses on the experimental investigation of the uid dynamics of the fluidized bed by use of pressure probes as well as nonintrusive measurements, based on Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA) techniques, to characterize the flow in a two-dimensional experimental facility. In particular, the DIA technique is employed for the interpretation of images taken with a high-speed camera for different operating conditions. A clear difference between the dense phase and the bubble phase is established, thereby enabling different bubble parameters such as equivalent diameter, bubble mass center and bubble velocity to be quantified. In addition, the selected DIA technique allows us to detect and characterize dynamical bubble phenomena including bubble formation...

Initial particle velocity spatial distribution from 2-D erupting bubbles in fluidized beds

Santana Santana, Domingo José; Nauri, S.; Acosta-Iborra, Antonio; García-Hernando, Néstor; Macías-Machín, A.
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf
Publicado em 31/01/2005 ENG
Relevância na Pesquisa
76.31%
Some results on particle image velocimetry (PIV) in 2-D freely bubbling fluidized beds are presented. The PIV applications were used in order to determine the initial particle velocity of bubble eruptions. A two-dimensional non-reacting fluidized bed was constructed to measure the origin of the ejected particles and the initial particle velocity distribution, using coarse sand particles. The bubble ejection mechanism was observed taking into account the origin of particles ejected, the initial particle velocity distributions as well as the effect of other neighbor exploding bubbles. Our results show that the assumption of linear dependence of initial velocity with the angle predicts the velocity faithfully only for purely vertical-ascent bubbles. Measurements of ejection velocities show that initial velocities in the combined layer are higher than those of the particles in the nose of the leading bubble. Avoiding coalescence of bubbles at the bed surface can lead to less particle entrainment out of the bed and consequently to shorter fluidized beds; The financial support from Ministerio de Ciencia y Tecnología of the Spanish Government is appreciated (project number DPI2002-02453)

Maps of deformations in a cantilever beam using particle image velocimetry (PIV) and speckle patterns

Braga Jr.,Roberto Alves; Magalhaes,Ricardo Rodrigues; Melo,Rafael Pego; Gomes,Joao Vitor
Fonte: Escola de Minas Publicador: Escola de Minas
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2015 EN
Relevância na Pesquisa
96.41%
PIV (particle image velocimetry) has been spreading in studies that use the movement of particles to monitor the displacement of an object or the flow of a fluid by means of velocity vectors using optical techniques and second order statistics. PIV is also known as laser speckle velocimetry when associated with speckle patterns. This technique has been used in works involving fluids, in general, building a map of velocity vectors representing the flow under analysis. This paper presents an approach by using PIV associated to speckle patterns for deformation measurements in a cantilever beam (ASTM A36 steel), one of the most common examples used in civil engineering, without the introduction of external particles. Results showed that the difference between PIV associated to speckle patterns and the analytic displacement values is increased along the beam length for a load of 1.96 N as an evidence of sensitivity of the proposed measurement method. This indicates that PIV is also capable for detecting displacement fields associated with laser speckle patterns in solid mechanics generating a map of deformation as an additional option for non-destructive tests.

Pulsatile flow characterization in a vessel phantom with elastic wall using ultrasonic particle image velocimetry technique: the impact of vessel stiffness on flow dynamics

Qian, M.; Niu, L.; Wong, K.K.L.; Abbott, D.; Zhou, Q.; Zheng, H.
Fonte: Institute of Electrical and Electronics Engineers (IEEE) Publicador: Institute of Electrical and Electronics Engineers (IEEE)
Tipo: Artigo de Revista Científica
Publicado em //2014 EN
Relevância na Pesquisa
96.36%
This study aims to experimentally investigate the impact of vessel stiffness on the flow dynamics of pulsatile vascular flow. Vessel phantoms with elastic walls were fabricated using polyvinyl alcohol cryogel to result in stiffness ranging from 60.9 to 310.3 kPa and tested with pulsatile flows using a flow circulation set-up. Two-dimensional instantaneous and time-dependent flow velocity and shear rate vector fields were measured using ultrasonic particle image velocimetry (EchoPIV). The waveforms of peak velocities measured by EchoPIV were compared with the ultrasonic pulse Doppler spectrum, and the measuring accuracy was validated. The cyclic vessel wall motion and flow pressure were obtained as well. The results showed that vessel stiffening influenced the waveforms resulting from vessel wall distension and flow pressure, and the fields of flow velocity and shear rate. The stiffer vessel had smaller inner diameter variation, larger pulse pressure and median pressure. The velocity and shear rate maximized at peak systole for all vessels. The results showed a decrease in wall shear stress for a stiffer vessel, which can initiate the atherosclerotic process. Our study elucidates the impact of vessel stiffness on several flow dynamic parameters...

Particle Image Velocimetry Study on the Stripe Formation in Vertically Vibrated Granules

Deng, Rensheng; Wang, Chi-Hwa
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 254286 bytes; application/pdf
EN_US
Relevância na Pesquisa
96.39%
Recently, granules under vertical vibrations receive many attentions due to their importance in theoretical research and engineering application. In this paper, a two-dimensional Particle Image Velocimetry (PIV) system was used to examine the f/2 stripe pattern forming in a vertically vibrated granular layer. Since the PIV sampling frequency does not match with the vibrating frequency, a special identification-coupling method was adopted to combine the images taken in different cycles to offer the information in one complete cycle. The measured velocity vectors showed exactly the particle motions at various stages of a motion cycle, illustrating the alternating peaks and valleys on the layer top. Furthermore, quantitative results on the temporal evolution of velocity profiles were obtained and some other interesting phenomena were observed, such as the appearance of local structures (e.g. dual-phase layer structure) and the moving feature of the 'standing point'. The mechanism accounting for the occurrence of stripes on the surface is also discussed. This work will be of interest to a better understanding on pattern formation in the vibrating granular bed.; Singapore-MIT Alliance (SMA)

Particle image velocimetry (PIV) and modelling of horizontal coherent liquid jets impinging on and draining down a vertical wall

Aouad, W.; Landel, J. R.; Dalziel, S. B.; Davidson, J. F.; Wilson, D. I.
Fonte: Elsevier Publicador: Elsevier
Tipo: Article; accepted version
EN
Relevância na Pesquisa
86.28%
This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Elsevier.; The flow patterns created by a coherent horizontal liquid jet impinging on a vertical wall at moderate flow rates (jet flowrates 0.5-4.0 L min-1, jet velocities 2.6-21 m s-1) are studied with water on glass, polypropylene and polymethylmethacrylate (acrylic, Perspex?) using a novel particle image velicometry (PIV) technique employing nearly opaque liquid doped with artificial pearlescence to track surface velocity. Flow patterns similar to those reported in previous studies are observed on each substrate: their dimensions differed owing to the influence of wall material on contact angle. The dimensions are compared with models for (i) the radial flow zone, reported by Wang et al. (2013b), and (ii) the part of the draining film below the jet impingement point where it narrows to a node. For (ii), the model presented by Mertens et al. (2005) is revised to include a simpler assumed draining film shape and an alternative boundary condition accounting for surface tension effects acting at the film edge. This revised model gives equally good or better fits to the experimental data as compared with the Mertens et al. model. The effective contact angle which gives good agreement with the data is found to lie between the measured quasi-static advancing and receding contact angles...

On errors of digital particle image velocimetry

Huang, H.; Dabiri, D.; Gharib, M.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /12/1997
Relevância na Pesquisa
66.35%
The goal of the present study is to quantify and reduce, when possible, errors in two-dimensional digital particle image velocimetry (DPIV). Two major errors, namely the mean bias and root-mean-square (RMS) errors, have been studied. One fundamental source of these errors arises from the implementation of cross correlation (CC). Other major sources of these errors arise from the peak-finding scheme, which locates the correlation peak with a sub-pixel accuracy, and noise within the particle images. Two processing techniques are used to extract the particle displacements. First, a CC method utilizing the FFT algorithm for fast processing is implemented. Second, a particle image pattern matching (PIPM) technique, usually requiring a direct computation and therefore more time consuming, is used. Using DPIV on simulated images, both the mean-bias and RMS errors have been found to be of the order of 0.1 pixels for CC. The errors of PIPM are about an order of magnitude less than those of CC. In the present paper the authors introduce a peak-normalization method which reduces the error level of CC to that of PIPM without adding much computational effort. A peak-compensation technique is also introduced to make the mean-bias error negligible in comparison with the RMS error. Noise in an image suppresses the mean-bias error but...

Simulating particle deposition in a human replica lung model

Rai, Pravir
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
76.31%
Tobacco consumption causes a variety of respiratory diseases including lung cancer and chronic obstructive pulmonary disease. These diseases occur when pathogens present in cigarette smoke enter into the respiratory system and deposit in the airways or gas exchanging membranes. Computational Fluid Dynamics (CFD) package FLUENT has been applied to study the deposition patterns of cigarette smoke particles from sidestream and mainstream smoke, as well as carcinogen size specific particles for NNK and BaP. A three dimensional cast of an ideal three generation Weibel lung model and a three dimensional morphologically accurate human replica lung model were used in the analysis. The human replica model was made from MRI scans of a hollow cast taken from autopsy, and represents the left half of an adult tracheobronchial region. Velocity profiles, secondary flows and wall shear rate were investigated at each airway bifurcation. Particle deposition, both local and total was determined for a range of respirable particles and breathing conditions. The general trend of the deposition data for the ideal cast agreed well with our understanding of particle physics, indicating the commercial CFD software accounted for the effects of gravity, particle inertia and molecular diffusion. The deposition results were compared to experimental data (U. California...

Stereoscopic particle image velocimetry analysis of healthy and emphysemic acinus models

Berg, Emily Jean
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
96.42%
Inhaled particles reaching the alveolar walls have the potential to cross the blood gas barrier and enter the blood stream. Pulmonary dosimetry, however, is not well understood. Numerical and experimental studies shed some light on the mechanisms of particle transport, but realistic geometries have not been investigated. In order to accurately predict particle deposition, the characteristics that affect deposition need to be understood. This includes, but is not limited to, fluid flow, lung morphology, breathing conditions, and particle concentration. Various geometries have been used for research, but very few are close representations to in vivo geometry. Most studies have used simplified or idealized geometries based on published dimensions, but none replicate actual in vivo geometry; even fewer examine the differences that exist between healthy and diseased lung geometries. The following work analyzes and compares the flow fields that exist in replica healthy and emphysemic lungs by using realistic geometries and breathing conditions. Actual human lung casts for in vivo healthy and emphysemic geometries were obtained, scanned, and used to reconstruct three dimensional replica models. From these geometries, hollow compliant models were created and used to simulate breathing under healthy and diseased conditions. It was shown that major geometric differences exist between the healthy and emphysemic models. Specifically...

Optimization of particle image velocimetry measurements using the in-cylinder velocity flow fields in an optical engine

Chmiel, David
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
96.47%
Research work was performed in cooperation with Delphi Automotive Systems to optimize Particle Image Velocimetry (PIV) measurements using the in-cylinder velocity flow fields in Delphi's optical engine. It entailed comprehending PIV theory, making a purchased PIV system work on Delphi's optical engine, investigation of PIV seeding techniques, applying PIV to steady-state liquid and air flow fields, calibrating/validating the PIV system operation, understanding the operation of Delphi's optical engine, performing optical engine velocity flow field measurements, comparing measurement results with Delphi's computational fluid dynamic (CFD) model, and optimizing the measurement technique for varying 2-D velocity flow fields. All the mentioned targets of the thesis were met by comprehending PIV theory and applying this knowledge to make the purchased PIV system work on a liquid flow field. Then seeding techniques for air flow fields were investigated and honed so that PIV could be performed on Delphi's optical engine. The optical engine was used extensively and the operation fully understood before any PIV data was taken on the engine. PIV data was acquired on the engine and the results were compared with CFD models. From this experimentation on the engine...

Flow field analysis in an expanding healthy and emphysematous alveolar model using particle image velocimetry

Oakes, Jessica
Fonte: Rochester Instituto de Tecnologia Publicador: Rochester Instituto de Tecnologia
Tipo: Tese de Doutorado
EN_US
Relevância na Pesquisa
96.46%
Particle deposition in the acinus region of the lung is a significant area of interest, because particles can potentially travel into the bloodstream through the capillaries in the lung. Drugs, in the form of aerosols, small particulates in a volume of air, may be delivered through the respiratory system. Also, toxic, airborne, particles could enter the body through the pulmonary capillaries in the acinus region of the lung. In order to accurately predict particle deposition, the aspects that influence deposition needs to be understood. Many physiological features may influence flow and particle deposition in the lung; the geometry of the acinus, expansion and contraction of the alveolar walls due to breathing mechanics, heterogeneities in the lung, breathing flow rate, and the number of breaths. In literature, streamlines and pathlines have been examined, both experimentally and computationally, in models representing the alveolar region of the lung. Some of these studies suggest the presence of irreversible flow, which would significantly influence particle deposition. However, none of these models incorporated all significant features: non-symmetric, three dimensional, expanding geometry. Therefore, flow mechanics, behind particle deposition...

Particle image velocimetry measurements of blood velocity in a continuous flow ventricular assist device

Day, Steven; McDaniel, James; Wood, Houston; Allaire, Paul; Landrot, Nicolas; Curtas, Anthony
Fonte: ASAIO Journal Publicador: ASAIO Journal
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
96.5%
The third prototype of a continuous flow ventricular assist device (CFVAD3) is being developed and tested for implantation in humans. The blood in the pump flows through a fully shrouded four-bladed impeller (supported by magnetic bearings) and through small clearance regions on either side of the impeller. Measurements of velocities using particle image velocimetry of a fluid with the same viscosity as blood have been made in one of these clearance regions. Particle image velocimetry is a technique that measures the instantaneous' velocity field within an illuminated plane of the fluid field by scattering light from particles added to the fluid. These measurements have been used to improve understanding of the fluid dynamics within these critical regions, which are possible locations of both high shear and stagnation, both of which are to be avoided in a blood pump. Computational models of the pump exist and these models are currently being used to aid in the design of future prototypes. Among other things, these models are used to predict the potential for hemolysis and thrombosis. Measurements of steady flow at two operating speeds and flow rates are presented. The measurements are compared with the computed solutions to validate and refine...

A Prototype HeartQuest ventricular assist device for particle image velocimetry measurements

Day, Steven; McDaniel, James; Wood, Houston; Allaire, Paul; Song, Xinwei; Lemire, Phillip; Miles, Scott
Fonte: Artificial organs Publicador: Artificial organs
Tipo: Abstract
EN_US
Relevância na Pesquisa
96.39%
The objective of this study is to fully characterize the flow within the HeartQuest ventricular assist device (VAD), a magnetically levitated centrifugal VAD, using particle image velocimetry (PIV) to identify regions of potential high shear or stagnation and validate and refine computational models of the flow. An acrylic model of the pump was designed and constructed to allow optical access into all interior regions of the pump. The geometry of the exterior housing and the use of a novel working fluid make quantitative measurements of velocity within the exit volute, blade passage, cut-water, blade tip clearance, and pump inlet possible. Highly accurate velocity measurements using particle PIV have been made in one region (the inlet elbow), and measurements in the other critical regions of the pump will be made. These measurements are used for investigation of regions with potential for hemolysis resulting from high shear stress or with potential for thrombosis caused by recirculation or stagnation. Quantitative velocity data are also needed for comparison with computational fluid dynamics (CFD) models of the VAD. In this study, experiments have again proven to be an essential complement to CFD for thorough investigations of the flow inside the pump.; Journal of Artificial organs article. Please see http://www3.interscience.wiley.com/journal/118914196/abstract for more information.

Analysis of the capillary extrusion of low-density polyethylene by using velocimetry

Rodríguez-González,F.; Pérez-González,J.; Marín-Santibáñez,B.M.
Fonte: UAM, Unidad Iztapalapa, División de Ciencias Básicas e Ingeniería Publicador: UAM, Unidad Iztapalapa, División de Ciencias Básicas e Ingeniería
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2011 EN
Relevância na Pesquisa
76.27%
The knowledge of the flow kinematics of polymer melts is relevant for their processing; as well as for the de sig n of molds and dies. However, the analysis of the flow behavior of polymer melts during extrusion has been typically performed by using rheometric measurements and numerical simulation. In this work, a description of the kinematics of a low-density polyethylene flowing under continuous extrusion through a transparent capillary die was performed by using the particle image velocimetry (PIV) technique coupled with rheometric measurements. The velocity maps for the polymer melt exhibited fully developed flow, meanwhile the flow rate data obtained from the velocity profiles agreed very well with the rheometric ones. The maximum difference in the volumetric flow rates by using the two methods was 6.5%, which shows the reliability of the PIV technique to describe the flow behavior of the polymer melt. The true flow and viscosity curves for the polymer melt were obtained from the measured wall shear stress and velocity profiles, in a wider shear rate range ihan the accessible by the capillary measurements, including the transition between the Newtonian and power-law regions. This allowed the viscosity data to be very well fitted by a Carreau constitutive equation.