Velocity Profiles of Liquid Flow in Backward Facing Step Microchannel

2012 ◽  
Author(s):  
Zaliman Sauli ◽  
Steven Taniselass ◽  
Wei Lim ◽  
Ahmad H. M. Shapri ◽  
Wan M. W. Norhaimi ◽  
...  
Keyword(s):  
Liquid Flow ◽  
Velocity Profiles ◽  
Backward Facing Step

Numerical Prediction of Particulate Flow Over a Backward-Facing Step Followed by a Filter Medium

2012 ◽  
Author(s):  
A. K. Dange ◽  
K. C. Ravi ◽  
F. W. Chambers
Keyword(s):  
Porous Medium ◽  
Recirculation Zone ◽  
Stokes Number ◽  
Velocity Profiles ◽  
Experimental Results ◽  
Phase Model ◽  
Discrete Phase Model ◽  
Backward Facing Step ◽  
Zone Length ◽  
Discrete Phase

Flow in air filter housings often is characterized by separation upstream of the filter. The effect of the separation on the motion of particles and their distribution at the filter is important to filter performance. The current research investigates these effects by applying CFD modeling to turbulent particulate flows over a backward-facing step followed by a porous medium representing a filter. The two-dimensional step flow was selected as it is an archetype for separated flow with many studies in the literature. The flow examined has a step expansion ratio of 1:2, with an entrance length of 30 step heights to the step followed by a length of 60 step heights. Computations were performed at step Reynolds numbers of 6550 and 10,000 for the step without a porous medium and with the medium placed 4.25 and 6.75 step heights downstream of the step. The mesh was developed in ICEM CFD and modeling was done using the Fluent commercial CFD package. The carrier phase turbulence was modeled using the RNG k-epsilon model. The particles were modeled using the discrete phase model with dispersion modeled using stochastic tracking. The boundary conditions are uniform velocity at the inlet, no-slip at the walls, porous jump at the porous medium, and outflow at the outlet. The particle boundary condition is “reflect” at the walls and “trap” at the filter. The numerical results for the no filter case matched experimental results for recirculation zone length and velocity profiles at 3.75 and 6.25 step heights well. The computed velocity profiles at 3.75 step heights do not match experimental profiles for the filter at 4.25 step heights so well, though the results show a profound effect on the recirculation zone length, matching the experiments. Differences are attributed to different velocity profiles at the step. With the medium 6.75 step heights downstream, the effect on the recirculation zone is negligible, again matching experimental results. The discrete phase model tracks injected particles and provides results which are qualitatively similar to the literature. It is observed that particles with lower Stokes number, and thus lower momentum, tend to follow the flow and enter the recirculation zone while particles with higher Stokes number tend to move directly to the porous medium. When the filter is moved downstream to 6.75 step heights, the increased length of the recirculation zone results in more particles entering the recirculation zone. Results for monodispersed and polydispersed particles agree.

Experiments on Backward-Facing Step Flows Preceding a Filter

2007 ◽  
Author(s):  
S. Yao ◽  
C. Krishnamoorthy ◽  
F. W. Chambers
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Velocity Profiles ◽  
Step Height ◽  
Reattachment Point ◽  
Backward Facing Step ◽  
Air Filters ◽  
Air Filter

The resistance of automotive air filters alters upstream pressure gradients and thereby affects flow separation, the velocity distributions over the filter, and the performance of the filter. Air filters provide a resistance sufficient to alter flows, but not enough to make face velocities uniform. The backward-facing step flow is an archetype with a separation that resembles those found in automotive air filter housings. To gain insight to the problem of separation and filters, experiments were conducted measuring velocity fields for air flows in a 10:1 aspect ratio rectangular duct with a backward-facing step with and without the resistance of an air filter mounted downstream. The expansion ratio for the step was 1:2. The filter was mounted 4.25 and 6.75 step heights downstream of the step; locations both upstream and downstream of the nominal 6 step-height no-filter reattachment point. Experiments were performed at four Reynolds numbers between 2000 and 10,000. The Reynolds numbers were based on step height and inlet maximum velocity. The inlet velocity profiles at the step were developed. A Laser Doppler Anemometer (LDA) was used to measure velocity profiles and map separated regions between the step and the filter. The results indicate that the filter tends to decrease the streamwise velocity on the non-separated side of the channel and increase it on the separated, step, side compared to the no-filter flow. Non-separated flow tends to separate due to the deceleration and separated flow reattaches before the filter, whether the filter is placed at 4.25 or 6.75 step heights. The literature shows that without a filter the reattachment location depends on the Reynolds number in the laminar and transitional regimes, but is constant for turbulent flow. However, the area of the reversed flow may vary with Reynolds number for turbulent flow. With the filter at 4.25 step heights, the area of reversing flow is reduced significantly, and the Reynolds number has little effect on the main properties of the flow. With the filter at 6.75 step heights, the reversing flow area decreases as the Reynolds number increases though the reattachment point is fixed just upstream of the filter.

Liquid Flow Measurement by Cross-Correlation of Temperature Fluctuations

1972 ◽  
Vol 5 (11) ◽  
pp. 435-439 ◽  
Author(s):  
S A Abesekera ◽  
M S Beck
Keyword(s):  
Laminar Flow ◽  
Liquid Flow ◽  
Flow Measurement ◽  
Cross Correlation ◽  
Correlation Method ◽  
Velocity Profiles ◽  
Pulsating Flow ◽  
Flow Conditions ◽  
Viscous Liquids ◽  
Better Than

The applicability of the temperature cross-correlation method to the measurement of liquid flow under steady and pulsating flow conditions is investigated and some further results to those published earlier are presented. The method is proved to be an accurate and reliable method of flow measurement in laminar flow of highly viscous liquids and turbulent flow of liquids under steady and pulsating flow conditions. In laminar flow, the measurement is dependent on the velocity profiles and hence sensitive to any disturbances which may distort the velocity profiles. In pulsating flow, the measurement is dependent on a parameter called the ‘Frequency parameter’ (KR). Only if KR <1 can the flow meter, calibrated for steady flow measurement, meter pulsating flow accurately. This condition is easily satisfied by highly viscous liquids. The measurement technique provides a linear output and an accuracy better than 3% can be achieved.

Modelling of the Near-Wall Liquid Velocity Field in Subcooled Boiling Flow

2005 ◽  
Author(s):  
Franz Ramstorfer ◽  
Bernd Breitscha¨del ◽  
Helfried Steiner ◽  
Gu¨nter Brenn
Keyword(s):  
Experimental Data ◽  
Surface Roughness ◽  
Flow Velocity ◽  
Liquid Flow ◽  
Axial Velocity ◽  
Velocity Profiles ◽  
Subcooled Boiling ◽  
Test Channel ◽  
Boiling Flow ◽  
Near Wall

The subject of the present work is the modelling of the liquid streamwise flow velocity in the two-phase boundary layer in subcooled boiling flow under the influence of the vapor bubbles. Subcooled boiling flow experiments were carried out in a horizontal test channel in order to investigate the interaction between the bubbles and the liquid phase. The heater surface was located at the bottom of the test channel. The near-wall liquid flow velocity was measured using a two-component laser-Doppler anemometer. Based on the experimental data a model is proposed to describe the impact of the gaseous phase on the motion of the liquid in the subcooled boiling regime. It was observed that the axial velocity profiles near the wall follow a logarithmic law similar to that used in turbulent single-phase flow over rough surfaces. Based on this finding it is suggested to model the influence of the bubbles on the liquid flow analogously to the effect of a surface roughness. The correlation developed for an equivalent surface roughness associated with the bubbles yields good agreement of the modeled axial velocity profiles with the experimental data.

Numerical Simulations of Laminar Backward-Facing Step Flow With FEMLAB 3.1

2005 ◽  
Author(s):  
Carlo Gualtieri
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Numerical Simulations ◽  
Close Agreement ◽  
Velocity Profiles ◽  
Channel Height ◽  
Backward Facing Step ◽  
Step Flow ◽  
Dimensionless Velocity

The paper presents 2-D numerical simulations of laminar backward-facing step flow using the FemLab 3.1 modeling package. Results demonstrated that primary reattachment lengths predicted by FemLab were in close agreement with experimental data up to step Reynolds number Reh = 300. Also, dimensionless velocity profiles along the channel height calculated by FemLab were successfully compared with the experimental data.

scholarly journals Forced and mixed convection experiments in a confined vertical backward facing step at low-Prandtl number

2021 ◽  
Vol 63 (1) ◽  
Author(s):  
Thomas Schaub ◽  
Frederik Arbeiter ◽  
Wolfgang Hering ◽  
Robert Stieglitz
Keyword(s):  
Boundary Condition ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Mixed Convection ◽  
Permanent Magnet ◽  
Local Nusselt Number ◽  
Velocity Profiles ◽  
Thermal Boundary Condition ◽  
Backward Facing Step ◽  
Heating Plate

Abstract In this paper, we present experimental results for a non-isothermal vertical confined backward facing step conducted with a low-Prandtl number fluid. The eutectic alloy gallium–indium–tin is used as the working fluid. We conducted experiments for different Reynolds and Richardson numbers covering both forced and mixed convection regimes. Time-averaged velocity profiles were measured at six streamwise positions along the test section center-plane with so-called permanent magnet probes. The local Nusselt number was measured in streamwise and spanwise directions along the heating plate mounted right after the step. We further ran RANS simulations of the experiment to study the qualitative influence of assuming a constant specific heat flux thermal boundary condition for the experiment heating plate. The measured velocity profiles show the expected behavior for both studied convection regimes, while the measured streamwise local Nusselt number profiles do not. This is explained by how the heating plate thermal boundary condition is defined. We performed an order of magnitude estimate to estimate the forced- to mixed convection transition onset. The estimate shows good agreement with the experimental data, although further measurements are needed to further validate the estimated transition threshold. The measurement of fluctuating quantities remains an open task to be addressed in future experiments, since the permanent magnet probe measurement equation needs further adjustments. Graphical Abstract

Measurement of Bubbly Flow in a Vertical Pipe Using Ultrasonic Doppler Method

2003 ◽  
Author(s):  
Hideki Murakawa ◽  
Hiroshige Kikura ◽  
Masanori Aritomi ◽  
Michitsugu Mori
Keyword(s):  
Flow Structure ◽  
Void Fraction ◽  
Flow Rate ◽  
Liquid Flow ◽  
Bubble Size ◽  
Bubbly Flow ◽  
Velocity Profiles ◽  
Circular Pipe ◽  
Vertical Pipe ◽  
Doppler Method

In order to clarify the microscopic flow structure, the ultrasonic Doppler method was applied to the measurement of two-phase bubbly flow in vertical pipe (i.d.50mm). Liquid flow structure might strongly be influenced by the characteristic of the injected bubbles, i.e. bubbles’ size and void fraction. In this study, a bubble generator was newly designed with the purpose to control the bubble size and void fraction, independent of liquid main-flow rate. The experiment was performed at z/d = 66 from the bubble generator. Liquid flow rates were of the Reynolds numbers ranging from Rem = 3700 to 6200. The gas flow rate was constant at JG = 0.00348(m/s) at the measurement position. By analyzing the bubbles’ picture, it was confirmed that bubble size distribution and average bubble size were almost constant if the liquid flow rate were changed. The ultrasonic Doppler method has the capability of measuring the instantaneous velocity profiles of both phases at the same time. By processing the data based on pattern recognition, the recorded data can be classified to several groups. Using this method, the authors have tried to measure the bubbly flow in rectangular channel. In the present study, the application of this method to bubbly flow in circular pipe was satisfactory to obtain the liquid velocity distribution in bubbly flow and surrounding bubbles. From these results, it was clarified that velocity profile in bubbly flow in circular pipe has a maximum value near the pipe wall. Furthermore, velocity profiles around the bubble are influenced by leading bubbles.

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