On magnetohydrodynamic flow in rectangular ducts: an extension of the Hunt—Stewartson approach

1970 ◽  
Vol 42 (2) ◽  
pp. 245-248 ◽  
Author(s):  
T. Z. Fahidy
Keyword(s):  
Boundary Layer ◽  
Magnetic Flux ◽  
Fluid Velocity ◽  
Magnetohydrodynamic Flow

The Hunt–Stewartson technique of estimating fluid velocity and magnetic flux profiles in rectangular ducts is generalized for the entire secondary boundary layer.

scholarly journals Numerical Analysis of Heat Transfer of Eyring Powell Fluid Using Double Stratification of Magneto-Hydrodynamic Boundary Layer Flow

2020 ◽  
pp. 91-108
Author(s):  
Wekesa Waswa Simon ◽  
Winifred Nduku Mutuku
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Thermal Stratification ◽  
Fluid Velocity ◽  
Double Stratification ◽  
Hydrodynamic Boundary Layer ◽  
Layer Flow ◽  
The Magnetic Field

Heat transfer fluids play a vital role in many engineering and industrial sectors such as power generation, chemical production, air-conditioning, transportation and microelectronics. Aim: To numerically investigate the effect of double stratification on magneto-hydrodynamic boundary layer flow and heat transfer of an Eyring-Powell fluid. Study Design: Eyring-Powell fluid is one of the non-Newtonian fluid that possess different characteristics thus different mathematical models have been formulated to describe such fluids by appropriate substitution into Navier-Stoke’s equations. The challenging complexity and the nature of the resultant equations are of great interest hence attract many investigations. Place and Duration of Study: Department of Mathematics and Actuarial Science, Kenyatta University, Nairobi, Kenya between December 2019 and October 2020. Methodology: The resultant nonlinear equations are transformed to linear differential equations by introducing appropriate similarity transformations. The resulting equations are solved numerically by simulating the predictor-corrector (P-C) method in matlab ode113. The results are graphically depicted and analysed to illustrate the effects of magnetic field, thermophoresis, thermal stratification, solutal stratification, material fluid parameters and Grashoff number on the fluid velocity, temperature, concentration, local Sherwood number and local Nusselt number. Results: The results show that increasing the magnetic field strength, thermophoresis, thermal stratification and solutal stratification lead to a decrease in the fluid velocity, temperature, Sherwood number, Nusselt number and skin friction while an increase in the magnetic field strength, thermal stratification, solutal stratification, and thermophoresis increases the fluid concentration. Conclusion: The parameters in this study can be varied to enhance heat ejection of Eyring-Powell fluid and applied in industries as a coolant or heat transfer fluid.

scholarly journals Numerical method approach for magnetohydrodynamic radiative ferrofluid flows over a solid sphere surface

2021 ◽  
Vol 25 (Spec. issue 2) ◽  
pp. 379-385
Author(s):  
Yasin Mat ◽  
Muhammad Mohamed ◽  
Zulkhibri Ismail ◽  
Basuki Widodo ◽  
Mohd Salleh
Keyword(s):  
Boundary Layer ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Solid Sphere ◽  
Skin Friction Coefficient ◽  
Fluid Temperature ◽  
Sphere Surface ◽  
Boundary Layer Equations ◽  
Keller Box Method ◽  
Layer Flow

In this paper, the theoretical study on the laminar boundary-layer flow of ferrofluid with influences of magnetic field and thermal radiation is investigated. The viscosity of ferrofluid flow over a solid sphere surface is examined theoretically for magnetite volume fraction by using boundary-layer equations. The governing equations are derived by applied the non-similarity transformation then solved numerically by utilizing the Keller-box method. It is found that the increments in ferro-particles (Fe3O4) volume fraction declines the fluid velocity but elevates the fluid temperature at a sphere surface. Consequently, the results showed viscosity is enhanced with the increase of the ferroparticles volume fraction and acts as a pivotal role in the distribution of velocity, temperature, reduced skin friction coefficient, and reduced Nusselt number of ferrofluid.

Influence of fluid velocities on the degradation of volatile aromatic compounds in membrane bound biofilms

1994 ◽  
Vol 29 (10-11) ◽  
pp. 253-262 ◽  
Author(s):  
O. Debus ◽  
H. Baumgärtl ◽  
I. Sekoulov
Keyword(s):  
Boundary Layer ◽  
Gas Phase ◽  
Process Analysis ◽  
Fluid Velocity ◽  
Experimental Investigations ◽  
Good Correspondence ◽  
Bulk Fluid ◽  
Fluid Velocities ◽  
Total Process ◽  
Laboratory Reactor

In a cylindrical laboratory reactor, in which a biofilm was grown on a gas-permeable silicone membrane tubing through which oxygen was supplied, the removal of xylene from the bulk fluid was investigated. Two days after starting the experiment 98 % of xylene was degraded and was no longer transferred into the gas phase. Using polarographic microelectrodes the thickness of the biofilm and the boundary layer as well as the oxygen profiles in both layers have been measured. The fluid velocity had three major influences: it affected the boundary layer thickness, the biofilm density and the sloughing of the biofilm. At higher fluid velocities (Reynolds numbers) high oxygen consumption within the biofilm could be quantified. At these higher fluid velocities the biofilm was grown with a higher density and adhered better to the membrane. By application of higher oxygen partial pressures in the gas phase and higher fluid velocities in the liquid phase, the mean degradation efficiency was increased from 38 to 96 %. A computer simulation showed good correspondence with the experimental investigations and allowed a total process analysis. Membrane-biofilm reactors are preferred for technical applications as, e.g., treatment of landfill leachates with high contents of volatile organics.

Experimental study of negatively buoyant finite-size particles in a turbulent boundary layer up to dense regimes

2019 ◽  
Vol 866 ◽  
pp. 598-629 ◽  
Author(s):  
Lucia J. Baker ◽  
Filippo Coletti
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Large Scale ◽  
Fluid Velocity ◽  
Outer Region ◽  
Finite Size ◽  
Working Fluid ◽  
Channel Height ◽  
Reynolds Stresses ◽  
Volume Fractions

We experimentally investigate the two-phase interplay in an open-channel turbulent boundary layer laden with finite-size particles at global volume fractions between 4 and 25 %. The working fluid (water) and the dispersed phase (hydrogel spheres) have closely matched refractive indices, allowing us to measure the properties of both phases using particle image velocimetry and particle tracking velocimetry, respectively. The particles have a diameter of approximately 9 % of the channel depth and are slightly denser than the fluid. The negative buoyancy causes a strong vertical concentration gradient, characterized by discrete and closely spaced particle layers parallel to the wall. Even at the lowest considered volume fractions, the near-wall fluid velocity and velocity gradients are strongly reduced, with large mean shear throughout most of the channel height. This indicates that the local effective viscosity of the suspension is greatly increased due to the friction between particle layers sliding over one another. The particles consistently lag the fluid and leave their footprint on its mean and fluctuating velocity profiles. The turbulent activity is damped near the wall, where the nearly packed particles disrupt and suppress large-scale turbulent fluctuations and redistribute some of the kinetic energy to smaller scales. On the other hand, in the outer region of the flow where the local particle concentration is low, the mean shear produces strong Reynolds stresses, with enhanced sweeps and ejections and frequent swirling events.

Unsteady MHD Natural Convective Flow of a Rotating Walters’-B Fluid Over an Oscillating Plate with Fluctuating Wall Temperature and Concentration

2017 ◽  
Vol 34 (4) ◽  
pp. 519-532 ◽  
Author(s):  
J. K. Singh ◽  
N. Joshi ◽  
P. Rohidas
Keyword(s):  
Boundary Layer ◽  
Natural Frequency ◽  
Wall Temperature ◽  
Flow Direction ◽  
Fluid Velocity ◽  
Porous Plate ◽  
Regular Perturbation ◽  
Primary Flow ◽  
Viscoelastic Parameter ◽  
Walters B Fluid

AbstractIn the present study, unsteady MHD boundary layer flow of a rotating Walters’-B fluid (viscoelastic fluid) over an infinite vertical porous plate embedded in a uniform porous medium with fluctuating wall temperature and concentration taking Hall and ion-slip effects into consideration is discussed. The MHD flow in the rotating fluid system is induced due to the non-torsional oscillations of the plate in its own plane and the buoyancy forces arises from temperature and concentration differences in field of gravity. The partial differential equations governing the fluid motion are solved analytically by using regular perturbation and variable separable methods by assuming very small viscoelastic parameter. Solution for velocity field in the case when natural frequency due to rotation and Hall current is equals to the frequency of oscillations i.e. in the case of resonance is also obtained. In order to note the influences of various system parameters and to discuss the important flow characteristics, the numerical results for fluid velocity in the non-resonance case, temperature and species concentration are computed and depicted graphically versus boundary layer parameter whereas skin friction, Nusselt number and Sherwood number at the plate are computed and presented in tabular form. An interesting observation recorded that there arises flow reversal in the primary flow direction due to high rotation. When natural frequency is greater than the frequency of oscillations the fluid velocity in the primary flow direction is maximum at the plate whereas incase when natural frequency is smaller than the frequency of oscillations, it is maximum in the neighborhood of the plate.

scholarly journals Multiscale Momentum Flux and Diffusion due to Whitecapping in Wave–Current Interactions

2011 ◽  
Vol 41 (5) ◽  
pp. 837-856 ◽  
Author(s):  
Juan M. Restrepo ◽  
Jorge M. Ramírez ◽  
James C. McWilliams ◽  
Michael Banner
Keyword(s):  
Boundary Layer ◽  
Wave Breaking ◽  
Fluid Velocity ◽  
Gaussian Model ◽  
Ocean Surface ◽  
Stokes Drift ◽  
Surface Boundary ◽  
Relative Role ◽  
Wave Groups ◽  
Energy Convergence

Abstract Whitecapping affects the Reynolds stresses near the ocean surface. A model for the conservative dynamics of waves and currents is modified to include the averaged effect of multiple, short-lived, and random wave-breaking events on large spatiotemporal scales. In this study’s treatment, whitecapping is parameterized stochastically as an additive uncertainty in the fluid velocity. It is coupled to the Stokes drift as well as to the current velocity in the form of nonlinear momentum terms in the vortex force and the Bernoulli head. The effects of whitecapping on tracer dynamics, mass balances, and boundary conditions are also derived here. Whitecapping also modifies the dynamics and the size of the sea surface boundary layer. This study does not resolve the boundary layer, however, the authors appeal to traditional viscosity parameterizations to include these diffusive effects, modified for the context of wave–current interactions. The parameterized breaking velocity field is endowed with empirical rules that link their generation in space and time to properties and dynamics of wave groups. The energy convergence rate of wave groups is used as an indicator for the onset of wave breaking. A methodology is proposed for evaluating this criterion over an evolving random Gaussian model for the ocean surface. The expected spatiotemporal statistics of the breaking events are not imposed, but rather computed, and are found to agree with the general expectation of its Poisson character. The authors also compute, rather than impose, the shear stress associated with the breaking events and find it to agree with theoretical expectations. When the relative role played by waves and breaking events on currents is compared, this study finds that waves, via the vortex force, purely advect the vorticity of currents that are essentially only dependent on transverse coordinates. The authors show that currents will tend to get rougher in the direction of steady wind, when whitecapping is present. Breaking events can alter and even suppress the rate of advection in the vortex force. When comparing the rates of transport, the waves will tend to dominate the short term and the whitecapping of the long-term rate.

Non-isothermal flow of Maxwell fluids above fixed flat plates under the influence of a transverse magnetic field

2011 ◽  
Vol 225 (4) ◽  
pp. 909-916 ◽  
Author(s):  
M M Heyhat ◽  
N Khabazi
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Boundary Layer ◽  
Fluid Velocity ◽  
Maxwell Fluid ◽  
Transverse Magnetic ◽  
Deborah Number ◽  
Flat Plates ◽  
Two Dimensional Flow ◽  
Energy Equations

In this article, the magnetohydrodynamic flow and heat transfer of an upper-convected Maxwell fluid is studied theoretically above a flat rigid surface with constant temperature. It is assumed that the Reynolds number of the flow is high enough for boundary layer approximation to be valid. Assuming a laminar, two-dimensional flow above the plate, the concept of stream function coupled with the concept of similarity solution is utilized to reduce the governing equations, which are continuity, momentum, and energy equations, into two ordinary differential equations. The spectral method is used for solving the equations numerically. The effects of magnetic field, and Deborah, Prandtl, and Eckert numbers on the fluid velocity field and heat transfer behaviour are shown in several plots. Obtained results show that fluid velocity can be decreased by increasing the magnetic number while it increases by increasing the Deborah number. Moreover, the thickness of the thermal boundary layer is decreased by increasing the Deborah and Prandtl numbers. It is increased by an increase in the Eckert number.

scholarly journals Velocity difference changes between fluid and sand particles in boundary-layer and very near wake area

2021 ◽  
Vol 25 (6 Part A) ◽  
pp. 4217-4224
Author(s):  
Sha Sha ◽  
Xiantang Zhang ◽  
Zhiang Wang ◽  
Han Liu ◽  
Huiyao Zhang
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Cylindrical Surface ◽  
Dynamic Pressure ◽  
Fluid Velocity ◽  
Near Wake ◽  
Two Phase ◽  
Velocity Change ◽  
Sand Flow ◽  
Sand Particles

Fluent simulates the water-sand flow around a cylinder. Monitoring lines are set up at different positions in the cylindrical surface and the very near wake area behind the cylinder, in order to explore the speed difference of fluid and sand in the water-sand two-phase flow in the boundary-layer and the very near wake area. The results show that the sand particles stay for the longest time on the back of the cylindrical surface and in the very near wake area, and a small part of the sand particles are sticky on the back of the cylindrical pier. When the height of the cylinder is z/D ? (1.57, 3.14), the turbulent flow on the cylindrical surface is fully developed. The dynamic pressure of the flow field in the very near wake area be-hind the cylinder fluctuates greatly, and the water-sand flow is extremely unstable. At the monitoring position of the cylinder, there is a sudden decrease in the velocity of the fluid, while the velocity of the sand particles changes little and remains finally at about -0.02 m/s. The water-sand flow field near the wall changes drastically, but the velocity change of sand particles has obvious hysteresis compared with fluid. When leaving the near-wall position but still in the cylindrical wake area (x/D ? 3), the changes in the water-sand flow field are more intense and the velocity of the sand particles is still slightly larger than the fluid velocity.

Turbulent Flow Boundary Layer and Heat Transfer Characteristics for the Intermediate Heat-Exchanger Simulation of a VHTR

2014 ◽  
Author(s):  
Yannan Wu ◽  
Yujie Dong ◽  
Kun Yuan
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
High Temperature ◽  
Heat Exchanger ◽  
Turbulent Flow ◽  
Fluid Velocity ◽  
Wall Friction ◽  
Suitable Model ◽  
Flow Boundary ◽  
Intermediate Heat Exchanger

In order to improve the thermal efficiency of the intermediate heat exchanger (IHX) in high temperature gas-cooled reactor, the article takes a theoretical calculation and simulation analysis of different turbulence models on the turbulent flow boundary layer of the IHX. And a suitable model for the high temperature and high pressure unit of the IHX is built. According to the boundary layer distribution of different models and the fluid velocity and temperature changes of central region, we find the related characteristics and cut-off point of the boundary layer area and the Poiseuille flow area. At the same time, the paper verifies the three kinds of turbulence model and the formula with solution theory, including the relationship of Nu (Nusselt) number and Re (Reynolds) number and the partial wall friction resistance. These results provides theoretical support for the next step of the heat transfer enhancement research using the artificial roughness elements.

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