Effect of mean velocity gradient and mixing time on particle removal in seawater induced flocculation

1994 ◽  
Vol 78 (1-2) ◽  
pp. 179-188 ◽  
Author(s):  
S. -I. Lee ◽  
I. -S. Seo ◽  
B. Koopman
Keyword(s):  
Velocity Gradient ◽  
Mixing Time ◽  
Particle Removal ◽  
Mean Velocity

scholarly journals A Method for Evaluation of Suspension Quality Easy Applicable To Practice: The Effect of Mixing on Floc Properties

2011 ◽  
Vol 59 (3) ◽  
pp. 184-195 ◽  
Author(s):  
Petra Ebubakova ◽  
Martin Pivokonsky ◽  
Lenka Pivokonska
Keyword(s):  
Drinking Water ◽  
Steady State ◽  
Water Treatment ◽  
Velocity Gradient ◽  
Mixing Time ◽  
Drinking Water Treatment ◽  
Inexpensive Method ◽  
Mean Velocity ◽  
Operation Conditions ◽  
Floc Properties

A Method for Evaluation of Suspension Quality Easy Applicable To Practice: The Effect of Mixing on Floc PropertiesThe paper introduces thetest of aggregationas a simple, inexpensive method of evaluating suspension quality during drinking water treatment, suitable for use in both laboratory and operation conditions. The procedure and derivation of theaggregation testis described. The method is used for a demonstration of the influence of mean velocity gradient and mixing time on floc properties formed during the aggregation in a Couette reactor. It was proved that with increasing velocity gradient, the size of the aggregates present in the suspension decreases, and the suspension is substantially more homogeneous than with use of lower gradients. Further, it was confirmed that the size of aggregates reaches the steady state after a specific mixing time, which becomes shorter with increasing value of velocity gradient.

scholarly journals Resolved Gas Kinematics in a Sample of Low-Redshift High Star-Formation Rate Galaxies

2016 ◽  
Vol 33 ◽  
Author(s):  
Mathew Varidel ◽  
Michael Pracy ◽  
Scott Croom ◽  
Matt S. Owers ◽  
Elaine Sadler
Keyword(s):  
Star Formation ◽  
Velocity Gradient ◽  
Velocity Dispersion ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Local Effect ◽  
Line Of Sight ◽  
Mean Velocity ◽  
Gas Kinematics ◽  
Integral Field Spectroscopy

AbstractWe have used integral field spectroscopy of a sample of six nearby (z ~ 0.01–0.04) high star-formation rate ($\text{SFR} \sim 10\hbox{--}40$$\text{M}_\odot \text{ yr$^{-1}$}$) galaxies to investigate the relationship between local velocity dispersion and star-formation rate on sub-galactic scales. The low-redshift mitigates, to some extent, the effect of beam smearing which artificially inflates the measured dispersion as it combines regions with different line-of-sight velocities into a single spatial pixel. We compare the parametric maps of the velocity dispersion with the Hα flux (a proxy for local star-formation rate), and the velocity gradient (a proxy for the local effect of beam smearing). We find, even for these very nearby galaxies, the Hα velocity dispersion correlates more strongly with velocity gradient than with Hα flux—implying that beam smearing is still having a significant effect on the velocity dispersion measurements. We obtain a first-order non parametric correction for the unweighted and flux weighted mean velocity dispersion by fitting a 2D linear regression model to the spaxel-by-spaxel data where the velocity gradient and the Hα flux are the independent variables and the velocity dispersion is the dependent variable; and then extrapolating to zero velocity gradient. The corrected velocity dispersions are a factor of ~ 1.3–4.5 and ~ 1.3–2.7 lower than the uncorrected flux-weighted and unweighted mean line-of-sight velocity dispersion values, respectively. These corrections are larger than has been previously cited using disc models of the velocity and velocity dispersion field to correct for beam smearing. The corrected flux-weighted velocity dispersion values are σm ~ 20–50 km s−1.

Added stresses because of the presence of FENE-P bead–spring chains in a random velocity field

1997 ◽  
Vol 337 ◽  
pp. 67-101 ◽  
Author(s):  
HESHMAT MASSAH ◽  
THOMAS J. HANRATTY
Keyword(s):  
Shear Stress ◽  
Velocity Field ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Velocity Gradient ◽  
Gradient Field ◽  
Shear Stresses ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Random Velocity

FENE-P bead–spring chains unravel in the presence of large enough velocity gradients. In a turbulent flow, this can result in intermittent added stresses and exchanges of energy between the chains and the fluid, whose magnitudes depend on the degree of unravelling and on the orientations of the bead–spring chains. These effects are studied by calculating the average behaviour at different times of an ensemble of chains, contained in a fluid particle that is moving around in a random velocity field obtained from direct numerical simulation of turbulent flow of a Newtonian fluid in a channel. The results are used to evaluate theoretical explanations of drag reduction observed in very dilute solutions of polymers.In regions of the flow in which the energy exchange with the fluid is positive, the possibility arises that turbulence can be produced by mechanisms other than the interaction of Reynolds stresses and the mean velocity gradient field. Of particular interest, from the viewpoint of understanding polymer drag reduction, is the finding that the exchange is negative in velocity fields representative of the wall vortices that are large producers of turbulence. One can, therefore, postulate that polymers cause drag reduction by selectively changing the structures of eddies that produce Reynolds stresses. The intermittent appearance of large added shear stresses is consistent with the experimental finding of a stress deficit, whereby the total local shear stress is greater than the sum of the Reynolds stress and the time-averaged shear stress calculated from the time-averaged velocity gradient and the viscosity of the solvent.

Response behaviour of hot wires in shear flow

1971 ◽  
Vol 47 (3) ◽  
pp. 449-468 ◽  
Author(s):  
F. B. Gessner ◽  
G. L. Moller
Keyword(s):  
Shear Flow ◽  
Velocity Gradient ◽  
Response Curves ◽  
Mean Velocity ◽  
General Applicability ◽  
Response Characteristics ◽  
Response Behaviour ◽  
Intensity Measurements ◽  
Temperature Distributions ◽  
Infrared Microscope

The response characteristics of a hot wire operated at constant temperature and exposed to a mean-velocity gradient along its length are examined both analytically and experimentally. The shear sensitivity of local wire temperature distributions, as measured with an infrared microscope, are compared with predicted temperature distributions in order to select a convective heat transfer correlation which can be applied locally along a wire in shear flow. On the basis of this correlation, the steady-state and dynamic response behaviour of platinum and tungsten wires in shear flow are examined by means of computer-generated data. Response curves of general applicability are presented which can be used to correct local mean-velocity and turbulence intensity measurements whenever a mean-velocity gradient exists along a wire.

Transient Lubricating Films With Inertia—Turbulent Flow

1984 ◽  
Vol 106 (1) ◽  
pp. 134-139 ◽  
Author(s):  
H. G. Elrod ◽  
I. Anwar ◽  
R. Colsher
Keyword(s):  
Steady State ◽  
Turbulent Flow ◽  
Stream Function ◽  
Velocity Gradient ◽  
Eddy Viscosity ◽  
Mean Velocity ◽  
Steady State Operation ◽  
Pressure Development ◽  
Transient And Steady State

This paper presents some new equations for the treatment of turbulent lubricating films when the effects of inertia cannot be neglected. The eddy-viscosity concept is used to represent the turbulent stresses in terms of mean-velocity gradient. Transient and steady-state operation are both considered by means of a generalized stream-function-pressure development.

An Exact Periodic Solution of a Hydromagnetic Flow of an Oldroyd Fluid in a Channel

1999 ◽  
Vol 66 (4) ◽  
pp. 974-977 ◽  
Author(s):  
R. N. Ray ◽  
A. Samad ◽  
T. K. Chaudhury
Keyword(s):  
Periodic Solution ◽  
Unsteady Flow ◽  
Velocity Gradient ◽  
Separation Of Variables ◽  
The Other ◽  
Parallel Plates ◽  
Hydromagnetic Flow ◽  
Mean Velocity ◽  
Oldroyd Fluid ◽  
Viscoelastic Parameters

The unsteady flow of a conducting Oldroyd fluid between two parallel plates, one of which is at rest and the other oscillating in its own plane with a constant mean velocity, has been investigated. Using separation of variables an exact periodic solution for the problem is obtained. Effects of viscoelastic parameters on velocity gradient, skin friction amplitude, and phase angle of the flow are discussed with graphs.

The Mach wave field radiated by supersonic turbulent shear flows

1965 ◽  
Vol 21 (4) ◽  
pp. 641-657 ◽  
Author(s):  
J. E. Ffowcs Williams ◽  
G. Maidanik
Keyword(s):  
Experimental Evidence ◽  
Boundary Layers ◽  
Velocity Gradient ◽  
Shear Flows ◽  
Approximate Equation ◽  
Mean Velocity ◽  
Mach Wave ◽  
Wave Condition ◽  
Low Speed ◽  
Rocket Exhaust

Theoretical studies of aerodynamic noise suggest that the sound field of supersonic flows will be dominated by eddy Mach waves. Recent experimental evidence supports this view. In supersonic turbulent boundary layers, and rocket exhaust flows, turbulence occurs in regions of high mean velocity gradient. At low speed, such gradients are known to amplify the sound emitted by turbulence. This paper deals with the corresponding Mach wave problem. The exact equations of sound radiation by turbulence are rearranged in a form where the equivalent sources, derivatives of the turbulence stress tensor, are shown to be dominated by one term. That term is formed from the product of the mean velocity gradient and the rate of change of density. It seems that its resemblance to the dominant source of sound in low speed shear flows is largely fortuitous. In the Mach wave case, the theory is designed to include effects of both temperature gradients and density perturbations, and the approximations of the estimate are of a type that would not be expected to be valid away from the Mach wave condition. The basic theory is used to make an estimate of the sound radiated from supersonic boundary layers, and an approximate equation relating the radiated pressure to the surface pressure is derived. Experimental evidence is then examined to show that the equation is in excellent agreement with observation. The theory is then applied to annular shear flows of the rocket exhaust type. Again an approximate equation relating near and far field pressures is established, and the paper concludes with suggestions for experiments that could check the result.

Effects of Impeller Rotational Speed and Immersion Depth on Flow Pattern, Mixing and Interface Characteristics for Kanbara Reactors using VOF-SMM Simulations

Metals ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 1596
Author(s):  
Qiang Li ◽  
Suwei Ma ◽  
Xiaoyang Shen ◽  
Mingming Li ◽  
Zongshu Zou
Keyword(s):  
Free Surface ◽  
Flow Pattern ◽  
Vortex Core ◽  
Mixing Time ◽  
Immersion Depth ◽  
Operating Parameters ◽  
Mean Velocity ◽  
Discharge Flow ◽  
Mixing Behavior ◽  
Core Depth

The Kanbara Reactor (KR) is a primary desulfurization technology in the hot metal pretreatment refining process that is widely employed in the modern steelmaking industry. The operating parameters of KR impeller immersion depth (IID) and rotation speed (IRS) have a crucial impact on the process performance and the desulfurization effect. Still, their influences have not been fully understood. This study systematically investigated the effects of IID and IRS on the flow pattern, mixing behavior, vortex core depth, and free surface characteristics for KR processes based on a 3D Volume of Fluid (VOF) model coupled with the sliding mesh method (SMM). The model was validated via scale-down water model experiments and then applied to the KR process, and simulations found that IID and IRS have different impacts on the flow pattern. Specifically, the discharge flow location moves downward with IID increasing, but the discharge strength and mean velocity hardly changes. Comparatively, the rise of IRS significantly increases the mean velocity, but few changes occur to the discharge flow position. Increasing IRS improves bath hydrodynamics, strengthens recirculation, and efficiently shortens mixing time, but IID has a neglectable effect on these features. The minimum mixing time is 55 s at a maximum IRS of 260 rpm. Moreover, the vortex core depth and free surface velocity visibly increase with the increase of IRS. Comparatively, IID has a limited effect on the flow and mixing behavior but directly impacts the distribution of recirculation regions at the axial direction and the velocity gradient on the free surface at the radial direction. Furthermore, the correlation equations of these critical parameters as a function of the operating parameters were obtained. The results from this study may provide references for operating optimizations and industrial practices of KRs.

Aerodynamic and Aeroelastic Characteristics of Oscillating Loaded Cascades at Low Mach Number—Part I: Pressure Distribution, Forces, and Moments

1980 ◽  
Vol 102 (2) ◽  
pp. 344-351 ◽  
Author(s):  
H. Atassi ◽  
T. J. Akai
Keyword(s):  
Mach Number ◽  
Pressure Distribution ◽  
Velocity Gradient ◽  
Degrees Of Freedom ◽  
Incompressible Flows ◽  
Complete Theory ◽  
Mean Velocity ◽  
Two Degrees Of Freedom ◽  
Low Mach Number ◽  
Unsteady Pressure

A complete theory is developed in Part I of these two papers for the analysis of oscillating airfoils in cascade in uniform incompressible flows. The theory fully accounts for the geometry of the airfoils and cascade parameters. It is shown that the strong mean velocity gradient near the leading edges of the airfoils significantly affects the unsteady pressure, forces and moments acting upon the airfoils. In Part II the aeroelastic characteristics of a loaded cascade are investigated for one and two degrees of freedom oscillations.

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