Fluid Velocity Measurements Research Articles

Impact of Crack Length into Pipe Conveying Fluid Utilizing Fast Fourier transform Computer Algorithm

<p>One of the most prominent problems experienced by the oil facilities is leakage of oil from the pipes. This problem caused 55% of oil refineries to be shut off. Oil leakage is a common problem that often results in oil waste, damage, and hazard to public health. Therefore, it is necessary to use Modern technologies to reduce this phenomenon and avoid them in advance. Pipes that convey fluids have many uses in various industries and living facilities. Risk increases when the fluid inside the pipe is flammable. In this work, main case that cause damage to the pipe, longitudinal crack is investigate.This work presents a new experimental model based on computer applications with a Fast Fourier transform (FFT) algorithm for testing the effect of longitudinal crack length by frequency and ultrasonic measurements to measure fluid velocity. The method is used for plastic pipe with 2 cm internal diameter, 3 cm external diameter, and 1 m length. The modulus of elasticity of the material is 800 N/mm2 according to the ISO 178 test method. The pipe conveys oil with simply supported ends. The results show that FFT model shows better features compared with other ways that depends on visual inspection or localized measurements which gave an external perception of pipeline damage. FFT model offers a reliable and cheap style for ensuring pipeline integrity and warning the risks before its occurrence. From the observations made the fundamental natural frequency (FNF) decreases by increasing of crack length in the pipe that conveys fluid</p>

Multiple velocity estimation by maximum likelihood from MRI complex signals

The measurement of fluid velocity by encoding it in the phase of an MRI signal could allow the discrimination of the stationary spins signals from those of moving spins. This results in a wide variety of applications i.e. in medicine, in order to obtain more than angiograms, blood velocity images of veins, arteries and other vessels without having static tissue perturbing the signal of fluid in motion. This paper presents a novel theoretical and experimental method for the estimation of multiple velocities from MRI complex signals in the presence of stationary spins.

Fluid flow measurement in rotor ventilation ducts

Engineers are constantly developing different ways to cool electrical machines more efficiently. Ventilation ducts/channels are common in the stators of large electrical machines. Lately ventilation ducts on rotors of electrical machines are also being introduced. While measurement of fluid velocities inside stationary ventilation ducts, such as those present in and around the stator core of electrical machines, are relatively easy, measurement of fluid velocities inside rotating ventilation ducts, such as those present on the rotors of electrical machines, is quite challenging. This study describes a method which enables the measurement of fluid velocities inside rotating ducts on the rotor of electrical machines.

Influence of respiration-induced B0 variations in real-time phase-contrast echo planar imaging of the cervical cerebrospinal fluid.

Respiration induces temporal variations of the main magnetic field B0 along the spinal cord. These variations are typically not compensated for in velocity quantifications using phase-contrast MRI. The goal of this study was to analyze errors caused by respiration-induced B0 variations in real-time phase-contrast echo planar imaging (PCEPI) of cervical cerebrospinal fluid (CSF) velocity measurements and to evaluate this effect for various sequence parameters using numerical simulations. Real-time B0 measurements with double gradient echo sequence and PCEPI measurements were acquired in the cervical CSF of 10 healthy subjects. Dynamic phase offsets attributed to respiration-induced B0 variations were analyzed by quantifying amplitudes and comparing the temporal behavior with respiratory signals. In experiments and simulations, the influence of the echo time (TE) and the delay between PCEPI images (Δt) with respect to respiration on the dynamic phase offsets were investigated. A good agreement was found between phase offsets extracted from both acquisition types. Furthermore, respiratory signals qualitatively matched the temporal behavior of the measured phase offsets showing a dependency on subject-dependent local B0 distribution and respiration physiology. Simulations revealed residual background phases in PCEPI velocity quantification varying with TE and Δt. Respiration-induced B0 variations result in dynamic background phases in real-time PCEPI velocity quantifications of the CSF in the cervical spine. The current work underlines that these background phases need to be corrected to avoid confounding effects.

Observation of sediment suspension by breaking-wave-generated vortices using volumetric three-component velocimetry

The distribution of suspended sediment in plunging regular waves was measured simultaneously with the three-dimensional (3D) turbulent velocity field on a 1 in 40 plane slope using a volumetric three-component velocimetry (V3V) system. White solid glass spheres (diameter 0.25 mm, specific gravity 2.5) were used as sediment particles. The V3V system was positioned to capture the impingement of the first or second splash-up vortices on the bottom. The measurement volume encompassed the lower 25% of the water column and a bottom area of length and width equal to approximately ½ the local water depth. Phase separation of glass spheres and fluid tracers in the V3V images was performed by varying the settings of four particle processing parameters in the commercial software INSIGHT™ V3V 4G. The measured fluid velocity fields were decomposed into a wave-induced component and a turbulence component by ensemble averaging 28 experiment runs conducted under the same incident wave condition. The two-phase flow measurements were used to delineate the process of sediment entrainment, to determine the turbulent flow properties around the suspended sediment, and to investigate the relationships between sediment pickup rate and the different flow parameters. The two dominant mechanisms of sediment suspension observed were the deflected flow created when breaking wave vortices impinged on the bottom and the up-wash induced by the transverse vortices. The suspension process was associated with large apparent shear stresses and positive vertical velocities greater than or equal to the sediment fall velocity. It was observed that sediment trapping by transverse vortices with horizontal axis and columnar vortices with vertical axis was an important mechanism for keeping sediment in suspension for transport by the organized wave-induced flow (mean flow). It was found that measured sediment pickup rates generally correlated better with total apparent shear stress than bed shear stress or turbulent kinetic energy. The experimental results suggest that sediment suspension by breaking-wave-generated vortices cannot be modeled by bed shear stress alone but will also require information on the vertical velocities induced by these vortices over the bed.

A Sensor Based on a Spherical Parallel Mechanism for the Measurement of Fluid Velocity: Experimental Development

In this paper, an experimental demonstration was developed, to measure the velocity of a fluid by using a sensor based on the spherical parallel mechanism with three degrees-of-freedom. This sensor transforms the kinetic energy of the fluid into potential energy by deforming the parallel mechanism. This deformation is due to the impact of the fluid on a sphere attached to the platform of the parallel mechanism. Through the acquisition of data from an inertial measurement unit in the sphere, an algorithm calculates the velocity and direction of the fluid. The mathematic model and algorithm of the velocity measurement was developed in a previous article. This paper built and tested the sensor with the objective of demonstrating the theoretical basis for the sensor. The experiment is based on the underwater movement of the sensor in a linear way along a rail. The velocity that is measured by the linear encoder is equal to the fluid’s relative velocity that is measured by the sensor. The measurements taken by the encoder and the sensor were compared in three experiments. The results show that the two measurements were similar, demonstrating that the sensor can accurately measure the velocity of the fluid.

PIV adaptive interrogation and sampling with image projection applied to water sloshing

The measurement of fluid velocity in the vicinity of wavy interfaces by means of Particle Image Velocimetry (PIV) still constitutes a challenge. Besides the experimental complexities such as appropriate seeding, reflections due to gradients in refractive indices, aberrations, etc., also the image processing phase constitutes a critical component. Ignoring bias errors introduced by laser reflections near the interface, strong velocity gradients are typically encountered near the curved liquid/gas interface and are detrimental to the common cross-correlation analysis. These effects are exacerbated by the use of traditional rectangular static cross-correlation windows. Moreover, dynamic boundaries suffer from a certain loss in reliability due to the difference in number of particles located in a specific physical region between the two frames. In this paper we present an improved algorithm enhancing the accuracy of the velocity vector detection in dynamic wavy flows. This algorithm divides the fluid domain in subregions (i.e. bulk, intermediate, vicinity and interface) and applies to each region different features (such as image patching, window relocation and forward difference finite schemes) and ad hoc predictors. Its assessment is performed on the basis of synthetic images, which reproduce a wavy motion similar to the one encountered when fluid in a cylindrical reservoir undergoes sloshing. When juxtaposed with a standard PIV code, numerical errors are shown to strongly diminish while improving the spatial resolution approaching the interface. The algorithm is finally applied to experimental PIV images of water sloshing in a cylindrical reservoir to provide more reliable results at the interface, contrary to standard PIV codes.

A method for reducing mean flow in oscillating-grid turbulence

Oscillating-grid turbulence (OGT) is an experimental tool that has been widely used to study the role of turbulent fluctuations under conditions of small mean flow. We report experiments to investigate the structure of the turbulent flow produced by an oscillating grid, using velocity measurements obtained through the application of two-dimensional particle image velocimetry in the vertical plane through the centre of the grid. Ensemble averages of the fluid velocity measurements at specific stages of the grid’s oscillation indicate that mean flow is induced in OGT by the merging of grid-induced jets close to the tank sidewalls. The installation of an open-ended ‘inner box’ (with its top edge positioned just below the bottom of the grid’s oscillation) is shown to inhibit the merging of the jets, thereby resulting in a reduction in the magnitude of the mean flow within the interior of the inner box region. Measurements of the time-averaged root-mean-square turbulent velocity components and the time-averaged turbulent kinetic energy flux indicate that the installation of the inner box results in turbulence that is in good agreement with the well-established models of OGT across the central 50% of the inner box’s width, but that distinct anisotropic regions exist adjacent to the vertical sidewalls. We anticipate that this simple amendment to reduce the mean flow present in OGT can be readily used in future work that utilises OGT to isolate the effects of turbulent fluctuations from those of the mean flow.Graphical abstract

Experimental investigation of turbulent suspensions of spherical particles in a square duct

We report experimental observations of turbulent flow with spherical particles in a square duct. Three particle sizes, namely$2H/d_{p}=40$, 16 and 9 ($2H$being the duct full height and$d_{p}$being the particle diameter), are investigated. The particles are nearly neutrally buoyant with a density ratio of 1.0035 and 1.01 with respect to the suspending fluid. Refractive index matched–particle image velocimetry (RIM–PIV) is used for fluid velocity measurement even at the highest particle volume fraction (20 %) and particle tracking velocimetry (PTV) for the particle velocity statistics for the flows seeded with particles of the two largest sizes, whereas only pressure measurements are reported for the smallest particles. Settling effects are seen at the lowest bulk Reynolds number$Re_{2H}\approx$10 000, whereas, at the highest$Re_{2H}\approx 27\,000$, particles are in almost full suspension. The friction factor of the suspensions is found to be significantly larger than that of single-phase duct flow at the lower$Re_{2H}$investigated; however, the difference decreases when increasing the flow rate and the total drag approaches the values of the single-phase flow at the higher Reynolds number considered,$Re_{2H}=27\,000$. The pressure drop is found to decrease with the particle diameter for volume fractions lower than$\unicode[STIX]{x1D719}=10\,\%$for nearly all$Re_{2H}$investigated. However, at the highest volume fraction$\unicode[STIX]{x1D719}=20\,\%$, we report a peculiar non-monotonic behaviour: the pressure drop first decreases and then increases with increasing particle size. The decrease of the turbulent drag with particle size at the lowest volume fractions is related to an attenuation of the turbulence. The drag increase for the two largest particle sizes at$\unicode[STIX]{x1D719}=20\,\%$, however, occurs despite this large reduction of the turbulent stresses, and it is therefore due to significant particle-induced stresses. At the lowest Reynolds number, the particles reside mostly in the bottom half of the duct, where the mean velocity significantly decreases; the flow is similar to that in a moving porous bed near the bottom wall and to turbulent duct flow with low particle concentration near the top wall.

Industrial radiotracer application in flow rate measurement and flowmeter calibration using 99mTc and 198Au nanoparticles radioisotope

The flow rate or fluid velocity measurement is important to maintain fluid flow quality performance in the systems. This study focuses on determination of volumetric flow rate measurement and to calibrate the conventional flowmeter using industrial radiotracer approach in quadrilateral gas-liquid bubble column reactor. In this work, two different radioisotopes which emit γ-ray have been chosen as radioactive tracer which is 99mTc produced from 99Mo/99mTc radioisotope generator and 198Au nanoparticle form neutron activation at research nuclear reactor TRIGA Mark II. Both radioisotopes representing liquid and solid tracer purposely designed for tracing liquid flow. The peak to peak radiotracer method known as pulse velocity method was applied to determine the volumetric flow rate. The radiation signals were monitored using 4 unit NaI scintillation detectors located at 4 different points nearby the inlet and outlet of the quadrilateral bubble column reactor process stream. The water volume inside the bubble column reactor was fixed at 0.04 m3 and liquid flow rates in this reactor were specified on installed flowmeter at different reference value which is 4 lpm, 8 lpm, and 12 lpm, respectively. The experimental result shows very good linearity and repeatability by following the theoretical equations with less uncertainty in volumetric flow rate measurement. The obtained results also validated the effectiveness of the proposed method for the installed flowmeter calibration efficiency.

Investigation of Sand Ripple Dynamics with Combined Particle Image and Tracking Velocimetry

AbstractAccurately assessing the response of sediments to oscillatory flows requires high-resolution fluid velocity and sediment transport measurements at the fluid–sediment interface. Fluid and sediment grain velocities were measured simultaneously with combined particle image and tracking velocimetry under oscillatory flows over movable sand ripples. Three high-speed cameras equipped with varying optical filters were used to distinguish between fluorescent fluid tracers and the grains, from which the fluid and grain velocities were determined, respectively. Individual grains were tracked during transport to determine velocities and trajectories. Sediment grains were first mobilized by a vortex impacting the bed during flow reversal and suspended into the water column just prior to vortex ejection from the ripple crest, similar to previous observations. During phases of maximum flow velocity, additional grains were mobilized by the shear stress and were subsequently suspended. The flow reversed and similar observations were made in the opposite direction. Consequently, four peaks in suspended sediment concentration were observed throughout the flow cycle, consistent with previous observations. However, some previous researchers attributed peaks in suspended sediment concentration occurring during phases of maximum flow velocity to sediment-laden vortices that were shed from adjacent ripples. The measured sediment grain velocities were of similar magnitude and phase to the near-bed fluid velocities when the grains were being advected with the flow. Measurements of suspended sediment concentration agreed well with semiempirical formulations having an average root-mean-square deviation of approximately 4 × 10−5m3m−3. Predictions of settling velocity also compared well with the laboratory estimates, agreeing to within 90%.

Convectively Dominated Heparin Leakage From Multiple Catheter Designs: An In Vitro Experimental Study.

Central venous catheters (CVCs) are routinely filled with a heparin lock while not in use to avoid thrombus formation near the tip. However, heparin leakage is known to occur, and the lock effectiveness remains in question. It was recently shown that convective fluxes from the blood flow in the host vein transport the majority of locking solution away from the tip of hemodialysis catheters immediately after instillation. Combined with the low diffusivity of heparin, this results in concentrations of heparin at the catheter tip that are orders of magnitude lower than at instillation for the majority of the interdialytic phase, diminishing the antithrombotic effectiveness of the lock. In this study, heparin losses from three different CVCs with different tip designs are measured in a pulsatile flow loop. Planar laser-induced fluorescence and particle image velocimetry measurements of heparin concentration and fluid velocity are recorded downstream of the catheters and combined to evaluate heparin losses from each of the different catheter designs. Additionally, locking solution losses are measured from one catheter (Hickman) subjected to three different flow conditions. Heparin losses are shown to depend weakly on flow condition but be highly dependent on catheter design. Convective losses from the Hickman catheter, with no side holes, are minimal (1-2%), although losses from the other two catheter types, both with a number of side holes, are significantly higher (7%). These results indicate the potential to maintain a high concentration of locking solution during the interdialytic phase with proper catheter design, particularly focusing on side hole distribution and shape.

A Sensor Based on a Spherical Parallel Mechanism for the Measurement of Fluid Velocity: Physical Modelling and Computational Analysis.

In this article, a new method was developed to measure the velocity of a fluid using a sensor, based on the use of a spherical parallel mechanism with three degrees-of-freedom (DOF). This sensor transforms the kinetic energy of the fluid into potential energy by deforming the parallel mechanism. This deformation is due to the impact of the fluid on a sphere attached to the platform of the parallel mechanism. Through the acquisition of data from a sensor using an inertial measurement unit (IMU) in the sphere, an algorithm calculates the velocity and direction of the fluid. In this article, a mathematical model of the mechanism and an algorithm for correctly measuring the velocity and direction of the fluid is developed; this algorithm is tested through a simulation in the Adams software, and the MATLAB software is used to execute the algorithm. The results show that the algorithm calculates the velocity and the direction of the fluid correctly, demonstrating the technical feasibility of the sensor.

Bubbles and microbubbles for hydrodynamic test facilities

Bubbles are known to have important effects in hydrodynamic facilities such as cavitation tunnels, hydraulic flow loops, pumps, valves and turbines test facilities, towing tanks etc. They are also used to simulate real two-phase flows with various void fractions or bubble size distributions under different pressure and velocity conditions. In order to manage safely these problems or to simulate at best the prototype conditions, an arsenal of theoretical and experimental techniques is necessary, including: – The control of dissolved air, which is under the form of independent molecules moving in the water. – The control of nuclei which are generally microbubbles of some tens of micrometers. – The injection of emulsions. Emulsions are a mixture of water and bubbles of millimetric size. – The separation of free air. Free air concerns bubbles of any size. – The resorption and the control of bubbles growing or shrinking by diffusion of air in water. The production and control of bubbles also implies the use of dedicated measuring techniques. Among these are devices to measure the void fraction and size of bubbles in emulsions as well as dissolved gas: – Local optical and electrical probes [14], – Optical techniques, – Venturi measurements (susceptibility meters). Susceptibility is the pressure at which a nucleus must be submitted to explode and create a vapor bubble. – Optical and polarographic gages for dissolved O2 analysis. Finally, microbubbles can be utilized as non-polluting tracers for optical velocity measurements in water and transparent fluids, such as LDV or PIV. Many of these techniques have been developed by YLEC Consultants. Some of these can be utilized in fluids other than water, such as liquid metals.

Density and velocity determination for single-phase flow based on radiotracer technique and neural networks

Measuring the density and velocity of fluids is one of the important tasks in oil and petroleum industries. The article demonstrates the measurements of these parameters precisely for different fluids and various diameters of pipes by using radiotracer injection and Artificial Neural Network (ANN). The required data for training and testing the ANN model were obtained by the MCNPX code simulations. Before using the simulation results for training the ANN, simulation geometry was validated with an experimental setup. The experimental setup consists of two 2-inch NaI(Tl) detectors that are positioned in distance of 120 mm from each other and one 133Ba radioactive source as a tracer. It is shown that the estimated Mean Relative Error (MRE) of the density determination in presented system was less than 0.9%. The relative combined standard uncertainty of the fluid velocity measurement did not exceed 0.5%.

A validation of commonly used CFD methods applied to rotor stator mixers using PIV measurements of fluid velocity and turbulence

Computational fluid dynamics (CFD) has been applied extensively for studying rotor-stator mixers (RSM) in the past, both as a design-tool and in modelling mixing and emulsification. Modelling is always a balance between accuracy and computational cost. The theoretically soundest methods (i.e. fully resolved transient simulations) have often been deemed unfeasible, and the majority of previously published studies use severe simplifications (i.e. k-ε models for turbulence and multiple reference frame for rotation). High quality experimental validation is in great need, but are rare, due to the lack of local fluid velocity measurement.Experimental validations of CFD on RSMs have previously been provided using laser Doppler anemometry. This study provides the first validation using particle image velocimetry, allowing for substantially higher spatial resolution than with the previously used techniques. The objective of this study is to map the possibilities and limitations of these commonly used CFD modelling approaches for RSMs. Special emphasis is put on validating the dissipation rate of turbulent kinetic energy (TKE). Despite being the parameter used for linking CFD to mixing or dispersion models, this has not been the subject of experimental validation in previous studies.Based on the validations, a list of best practice recommendations are given (in terms of turbulence model, mesh resolution and rotation formulation). When adhering to these, the CFD model accurately captures power draw, flow number, and the detailed velocity field inside the region where mixing and dispersion takes place. The dissipation rate of TKE is captured qualitatively but underestimate experimental values. Implications in terms of limitations are discussed in detail, including estimations of accuracy implications for emulsification and mixing modelling.

Impact pressure and void fraction due to plunging breaking wave impact on a 2D TLP structure

Violent impacts due to the plunging breaking wave impingement on a 2D tension-leg platform (TLP) structure were experimentally investigated in a laboratory. Simultaneous pressure, void fraction, fluid velocity, and structure motion measurements were performed on the multiphase, turbulent flow. The maximum mean impact pressure is 2.3ρC 2 with C being the wave phase speed. The pressure maximum and its rise time are negatively correlated, and the rise time for impulsive-type impacts is less than 15 ms or 0.18H/C with H being the wave height. Different approaches show that impact coefficients vary from 0.6 to 9.7, including relating the impact pressure maxima to the wave phase speed, local velocity, and void fraction. By modeling the plunging breaking wave impact as a filling flow, a pressure–aeration relationship was investigated and compared with the approximate solution derived by Peregrine and Thais (J Fluid Mech 325:377–397, 1996). The measured data show that a high aeration level tends to reduce the impact pressure maximum so the cushioning effect is significant for breaking wave impacts on a moving vertical wall.

Fluid flow investigations within a 37 element CANDU fuel bundle supported by magnetic resonance velocimetry and computational fluid dynamics

The current work presents experimental and computational investigations of fluid flow through a 37 element CANDU nuclear fuel bundle. Experiments based on Magnetic Resonance Velocimetry (MRV) permit three-dimensional, three-component fluid velocity measurements to be made within the bundle with sub-millimeter resolution that are non-intrusive, do not require tracer particles or optical access of the flow field. Computational fluid dynamic (CFD) simulations of the foregoing experiments were performed with the hydra-th code using implicit large eddy simulation, which were in good agreement with experimental measurements of the fluid velocity. Greater understanding has been gained in the evolution of geometry-induced inter-subchannel mixing, the local effects of obstructed debris on the local flow field, and various turbulent effects, such as recirculation, swirl and separation. These capabilities are not available with conventional experimental techniques or thermal-hydraulic codes. The overall goal of this work is to continue developing experimental and computational capabilities for further investigations that reliably support nuclear reactor performance and safety.

Multiple velocity encoding in the phase of an MRI signal

The measurement of fluid velocity by encoding it in the phase of a magnetic resonance imaging (MRI) signal could allow the discrimination of the stationary spins signals from those of moving spins. This results in a wide variety of applications i.e. in medicine, in order to obtain more than angiograms, blood velocity images of veins, arteries and other vessels without having static tissue perturbing the signal of fluid in motion. The work presented in this paper is a theoretical analysis of some novel methods for multiple fluid velocity encoding in the phase of an MRI signal. These methods are based on a tripolar gradient (TPG) and can be an alternative to the conventional methods based on a bipolar gradient (BPG) and could be more suitable for multiple velocity encoding in the phase of an MRI signal.

Effect of the 6PBT stirrer eccentricity and off-bottom clearance on mixing of pseudoplastic fluid in a stirred tank

The aim of this work is to investigate the effect of the shaft eccentricity on the flow field and mixing characteristics in a stirred tank with the novel stirrer composed of perturbed six-bent-bladed turbine (6PBT). The difference between coaxial and eccentric agitations is studied using computational fluid dynamics (CFD) simulations combined with standard k−ε turbulent equations, that offer a complete image of the three-dimensional flow field. In order to determine the capability of CFD to forecast the mixing process, particle image velocimetry (PIV), which provide an accurate representation of the time-averaged velocity, was used to measure fluid velocity. The test liquid used was 1.25%(wt) xanthan gum solution, a pseudoplastic fluid with a yield stress. The comparison of the experimental and simulated mean flow fields has demonstrated that calculations based on Reynolds-averaged Navier-Stokes equations are suitable for obtaining accurate results. The effects of the shaft eccentricity and the stirrer off-bottom distance on the flow model, mixing time and mixing efficiency were extensively analyzed. It is observed that the microstructure of the flow field has a significant effect on the tracer mixing process. The eccentric agitation can lead to the flow model change and the non-symmetric flow structure, which would possess an obvious superiority of mixing behavior. Moreover, the mixing rate and mixing efficiency are dependent on the shaft eccentricity and the stirrer off-bottom distance, showing the corresponding increase of the eccentricity with the off-bottom distance. The efficient mixing process of pseudoplastic fluid stirred by 6PBT impeller is obtained with the considerably low mixing energy per unit volume when the stirrer off-bottom distance, C, is T/3 and the eccentricity, e, is 0.2. The research results provide valuable references for the improvement of pseudoplastic fluid agitation technology.