scholarly journals Examination of the Bi-Directional Velocity Probe Used in Flames

2009 ◽  
Author(s):  
Brian C. Hogan ◽  
Humberto Bocanegra ◽  
Ramiro Chavez Alarcon ◽  
Nadir Yilmaz ◽  
A. Burl Donaldson ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Particle Image ◽  
Amplification Factor ◽  
Probe Design ◽  
Pressure Measurements ◽  
Bernoulli’S Equation ◽  
Image Velocimetry ◽  
Visualization Techniques ◽  
The Impact ◽  
Measured Pressure

The bidirectional probe has been used in combustion environments to measure localized flame velocities. The device measures the pressure difference between a closed forward-facing cavity, and a closed rearward-facing cavity. Each device must be experimentally calibrated to determine the “amplification factor,” which is unity if the measured differential pressures match Bernoulli’s equation. It is hypothesized that the probe design disrupts the flow, creating turbulence and irreversibilities, resulting in measured pressure differences. This study uses computational fluid dynamics, particle image velocimetry, and flow visualization techniques to examine the flow field around the probe, as well as an experimental study exploring the impact of minor changes in probe design on differential pressure measurements for velocity calculations.

Computational Fluid Dynamics and Particle Image Velocimetry Supported Examination of Bidirectional Velocity Probes for Measurements in Flames

2013 ◽  
Vol 6 (1) ◽  
Author(s):  
Nadir Yilmaz ◽  
Brian C. Hogan ◽  
Humberto Bocanegra ◽  
A. Burl Donaldson ◽  
Walt Gill
Keyword(s):  
Fluid Dynamics ◽  
Experimental Study ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Pressure Difference ◽  
Particle Image ◽  
Amplification Factor ◽  
Local Velocity ◽  
Bernoulli’S Equation ◽  
Image Velocimetry

The bidirectional velocity probe has been used in various flames to measure local velocity. The device is based on the pressure difference between a closed forward facing cavity and a closed rearward facing cavity. The probes have been noted to indicate a pressure difference greater than that which would be predicted based on Bernoulli's equation. Each device must be experimentally calibrated in a wind tunnel at similar Reynolds number to determine its “amplification factor.” This study uses PIV, flow visualization and CFD to examine the flow field around the probe, as well as an experimental study which compares various probe configurations for measurement of velocity by pressure differential. The conclusion is that the amplification factor is indeed greater than unity but use of the wind tunnel for calibration is questionable.

Flow Characteristics in the Improved Impinging Stream Reactor by Means of Particle Image Velocimetry (PIV)

2017 ◽  
Author(s):  
Liu Xueqing ◽  
Lu Luyi
Keyword(s):  
Fluid Dynamics ◽  
Mass Transfer ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Impact Zone ◽  
Inlet Velocity ◽  
Piv Technique ◽  
Image Velocimetry ◽  
The Impact

The impinging Stream is a novel technique in enhancing heat and mass transfer. In the conventional impinging stream reactor (ISR), as the particles in that reactor are affected by the fluid resistance, the energy of the particles is rapidly decreased after the infiltration of the reverse flow, which leads to the effective mixing of the particles. In this paper, we design an improved impinging stream reactor (IISR) that has different fluid inlet velocity but same mean fluid inlet velocity in a period, which still belongs to definition of impinging stream. In the present study, the flow characteristics in the IISR are investigated using particle image velocimetry (PIV) and computational fluid dynamics. The effects of the fluid inlet velocity in the axisymmetric opposed jets are discussed for equal mean volumetric flow rates of the two jets. The impingement plane and the flow filed of the IISR are measured from captured images using the PIV technique. The two fluid inlet velocity with different sinusoidal variations are applied in the improved impinging stream. Besides, the experimental results show that the impingement plane is moving instantaneously with the two inlet velocity changing dynamically, which expands efficient active areas compared with the conventional impinging stream. Besides, computational fluid dynamics are used in combination with the discrete phase model (CFD-DPM) to predict the flow characteristics within the improved Impinging Stream. The simulation results show that impinging stream flow field can be divided into the inlet, the impact zone, the exit zone and the vortex area. At the same time, the impact zone and the impingement plane is also found to be moving The CFD-DPM results give predictions that are in better agreement with the flow filed pictured by the PIV technique. Because of the complexity of the liquid immersion impinging stream, it is difficult to study the trajectory of the particles in the flow field, so we use the numerical simulation to study the motion of the particles in the immersion IISR. Analysis shows the effective mixing region of the particles can be greatly increased, particles’ motion trajectory can be longer and the heat and mass transfer between the particles and the interphase can be further enhanced. Compared with the conventional ISR, the IISR has obvious advantages. The results point out this improved impinging Stream has a good application prospect in future engineering works.

Experimental and Numerical Flow Visualization in Patient Specific Pre Operative Human Airway Geometry

2011 ◽  
Author(s):  
Mathias Vermeulen ◽  
Cedric Van Holsbeke ◽  
Tom Claessens ◽  
Jan De Backer ◽  
Peter Van Ransbeeck ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Particle Image ◽  
Patient Specific ◽  
Lung Volume Reduction ◽  
Cfd Simulations ◽  
Piv Measurements ◽  
Image Velocimetry ◽  
Specific Geometry ◽  
Computational Fluid Dynamics Cfd ◽  
Human Airways

An experimental and numerical platform was developed to investigate the fluidodynamics in human airways. A pre operative patient specific geometry was used to create an identical experimental and numerical model. The experimental results obtained from Particle Image Velocimetry (PIV) measurements were compared to Computational Fluid Dynamics (CFD) simulations under stationary and pulsatile flow regimes. Together these results constitute the first step in predicting the clinical outcome of patients after lung surgeries such as Lung Volume Reduction.

Particle Image Velocimetry Experiment and Computational Fluid Dynamics Simulation of Flow Around Rigid Cylinder

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Guangyao Wang ◽  
Ye Tian ◽  
Spyros A. Kinnas
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Particle Image Velocimetry ◽  
Vector Fields ◽  
Particle Image ◽  
Cfd Simulation ◽  
Dynamics Simulation ◽  
Reynolds Stresses ◽  
Rigid Cylinder ◽  
Image Velocimetry

This work focuses on the study of the flow around a rigid cylinder with both particle image velocimetry (PIV) experiment and computational fluid dynamics (CFD) simulation. PIV measurements of the flow field downstream of the cylinder are first presented. The boundary conditions for CFD simulations are measured in the PIV experiment. Then the PIV flow is compared with both Reynolds-averaged Navier–Stokes (RANS) two-dimensional (2D) and large eddy simulation (LES) three-dimensional (3D) simulations performed with ANSYS fluent. The velocity vector fields and time histories of velocity are analyzed. In addition, the time-averaged velocity profiles and Reynolds stresses are analyzed. It is found that, in general, LES (3D) gives a better prediction of flow characteristics than RANS (2D).

The importance of hydrodynamics in UV advanced oxidation reactors

2007 ◽  
Vol 55 (12) ◽  
pp. 53-58 ◽  
Author(s):  
A. Sozzi ◽  
F. Taghipour
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Distribution ◽  
Fluence Rate ◽  
Reactor Performance ◽  
Image Velocimetry ◽  
Reactor Axis ◽  
Computational Fluid Dynamics Cfd

The flow field of UV reactors was characterised experimentally using particle image velocimetry (PIV) and modelled with computational fluid dynamics (CFD). The reactor flow was integrated with the radiation fluence rate and photolysis kinetics to calculate the overall conversion of photo-reactant components in annular UV reactors with an inlet parallel and perpendicular to the reactor axis. The results indicated that the fluid flow distribution within the reactor volume affects photo-reactor performance.

Particle Image Velocimetry and Computational Fluid Dynamics Analysis of Fuel Cell Manifold

2010 ◽  
Vol 7 (3) ◽  
Author(s):  
Jesper Lebæk ◽  
Marcin Blazniak Andreasen ◽  
Henrik Assenholm Andresen ◽  
Mads Bang ◽  
Søren Knudsen Kær
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Particle Image Velocimetry ◽  
Fuel Cell ◽  
Particle Image ◽  
High Current Density ◽  
Plug Flow ◽  
Flow Distribution ◽  
Image Velocimetry ◽  
Computational Fluid Dynamics Analysis

The inlet effect on the manifold flow in a fuel cell stack was investigated by means of numerical methods (computational fluid dynamics) and experimental methods (particle image velocimetry). At a simulated high current density situation the flow field was mapped on a 70 cell simulated cathode manifold. Three different inlet configurations were tested: plug flow, circular inlet, and a diffuser inlet. A very distinct jet was formed in the manifold, when using the circular inlet configuration, which was confirmed both experimentally and numerically. This jet was found to be an asymmetric confined jet, known as the symmetry-breaking bifurcation phenomenon, and it is believed to cause a significant maldistribution of the stack flow distribution. The investigated diffuser design proved to generate a much smoother transition from the pipe flow to the manifold flow with a subsequent better flow distribution. A method was found in the literature to probe if there is a risk of jet asymmetry; it is however recommended by the author to implement a diffuser design, as this will generate better stack flow distribution and less head loss. Generally, the numerical and experimental results were found in to be good agreement, however, a detailed investigation revealed some difference in the results.

Multilaboratory Particle Image Velocimetry Analysis of the FDA Benchmark Nozzle Model to Support Validation of Computational Fluid Dynamics Simulations

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Prasanna Hariharan ◽  
Matthew Giarra ◽  
Varun Reddy ◽  
Steven W. Day ◽  
Keefe B. Manning ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Particle Image Velocimetry ◽  
Turbulent Flow ◽  
Medical Device ◽  
Particle Image ◽  
Transitional Flow ◽  
Flow Conditions ◽  
Image Velocimetry ◽  
Flow Case

This study is part of a FDA-sponsored project to evaluate the use and limitations of computational fluid dynamics (CFD) in assessing blood flow parameters related to medical device safety. In an interlaboratory study, fluid velocities and pressures were measured in a nozzle model to provide experimental validation for a companion round-robin CFD study. The simple benchmark nozzle model, which mimicked the flow fields in several medical devices, consisted of a gradual flow constriction, a narrow throat region, and a sudden expansion region where a fluid jet exited the center of the nozzle with recirculation zones near the model walls. Measurements of mean velocity and turbulent flow quantities were made in the benchmark device at three independent laboratories using particle image velocimetry (PIV). Flow measurements were performed over a range of nozzle throat Reynolds numbers (Rethroat) from 500 to 6500, covering the laminar, transitional, and turbulent flow regimes. A standard operating procedure was developed for performing experiments under controlled temperature and flow conditions and for minimizing systematic errors during PIV image acquisition and processing. For laminar (Rethroat=500) and turbulent flow conditions (Rethroat≥3500), the velocities measured by the three laboratories were similar with an interlaboratory uncertainty of ∼10% at most of the locations. However, for the transitional flow case (Rethroat=2000), the uncertainty in the size and the velocity of the jet at the nozzle exit increased to ∼60% and was very sensitive to the flow conditions. An error analysis showed that by minimizing the variability in the experimental parameters such as flow rate and fluid viscosity to less than 5% and by matching the inlet turbulence level between the laboratories, the uncertainties in the velocities of the transitional flow case could be reduced to ∼15%. The experimental procedure and flow results from this interlaboratory study (available at http://fdacfd.nci.nih.gov) will be useful in validating CFD simulations of the benchmark nozzle model and in performing PIV studies on other medical device models.

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