

Experimental Analysis on the CounterCurrent Dumitrescu Taylor Bubble Flow in a Smooth Vertical Conduct of Small Diameter


Pages :
114


Authors :
S. Benattalah,
F. Aloui,
M. Souhar,
In this paper, an experimental investigation on the DumitrescuTaylor bubble in countercurrent laminar downward
flow in vertical pipe of a small internal diameter pipe is presented. The experimental design is realized to work for
low and stable liquid flow rates. The DumitrescuTaylor bubble may be stationary or can be in motion with an
ascending or descending velocity, and this displacement depends on the downward liquid flow rates. Consequently,
the advantage of this device is to carry out the measurements of the velocities inside the gas DumitrescuTaylor
bubble by Laser Doppler Velocimetry (LDV). Starting from the visual observations and image acquisitions with a
fast camera, a qualitative description was brought on the hydrodynamic behavior of the liquid film and the ripples
created at the bottom of the DumitrescuTaylor bubble. The experimental results show a presence of a long toroïdal
vortex inside the gas bubble. It should be noted that previous work using a hot wire does not show the existence of
this vortex. Additionally, other hydrodynamic magnitudes were measured as the liquid film thickness, the
DumitrescuTaylor bubble rising velocity as well as the erosion bubble. Detailed descriptions are brought concerned
this erosion. Strange phenomena have been observed primarily ahead of the nose of bubble and on the side of its end.





Natural Convection Heat and Mass Transfer in the Boundary Layer along a Vertical Cylinder with Opposing Buoyancies


Pages :
1521


Authors :
M. Si Abdallah,
B. Zeghmati,
The effects of opposing buoyancies on natural convection heat and mass transfer in the boundary layer over a vertical
cylinder immersed in a quiescent Newtonian fluid are presented in this paper. The surface of the cylinder is
maintained at a constant temperature and concentration. The homotopic transformation is proposed to transform the
physical domain into a flat plate. The boundary layer equations and the boundary conditions are solved numerically
using an implicit finite difference scheme and the GaussSeidel algorithm. The buoyancy ratio N, Prandtl number Pr
and Schmidt number Sc are important parameters for this problem. The numerical results for Pr=Sc and Pr≠ Sc,
including the velocity, temperature, concentration fields and the Nusselt number as well as the Sherwood number
along the surface of the cylinder are discussed for aiding and opposing buoyancies. Results show that the Nusselt
(Sherwood) number increases with positive or negative buoyancies ration N (N=Grc/Grt). Moreover, for opposing
flows with Sc<Pr , the flow is completely downward, the thickness of the concentration layer is larger than that of the
thermal layer . For Pr<Sc , the velocity are weak and the thermal layer thickness is much larger.





Estimation of the Effective Thermal Properties in a Metallic Medium by an Inverse Technique using Temperatures Measureme


Pages :
2329


Authors :
A. Sakly,
A. Jemni,
P. Lagonotte,
D. Petit,
In order to master the use of electric machines and to minimize its thermal losses, the knowledge of thermophysical properties of metallic materials that constitute them, is important. This study deals with the estimation of several thermal properties in a metallic medium. The system under investigation is a rectangular metallic plate, which is submitted to an homogenous heat power on the volume sample. The direct problem simulates numerically the system and the experimental conditions. An iterative procedure, based on minimizing a sum of squares norm with the LevenbergMarquardt method, is used to solve the inverse problem. In order to characterize the thermal behavior of metallic materials, an experimental setup was built. The measured temperature data using infrared camera are used to estimate the effective thermal conductivity, the effective volumetric heat capacity as well as the global heat transfer coefficient with the environment.





Influence of Primary Stenosis on Secondary One and Vice Versa in case of Double Stenoses


Pages :
3142


Authors :
D.K Mandal,
N.K Manna,
S. Chakrabarti,
Numerical solutions of the steady viscous flow in the neighborhood of different double stenoses are obtained under laminar flow conditions with the motivation for modeling blood flow through stenosed artery formed due to arterial disease. The flowing blood is considered to be incompressible and Newtonian. A finite volume method has been employed to solve the governing equations. The dynamics of flow features have been studied by wall pressure, streamline contour, and wall shear stress distributions for all models. The results have demonstrated that when the shapes of stenosis change at primary stenosis keeping no change in the shape of secondary stenosis, the impact of changes in primary stenosis on secondary one is noted to be more, whereas, no impact of primary stenosis on secondary stenosis and vice versa is observed in case of changes in the shapes of secondary stenosis keeping no change in the shape of primary stenosis. When Reynolds number changes, the impact of changes in primary stenosis on secondary one is also noted to be higher.





Effect of Rotation on DoubleDiffusive Convection in a Magnetized Ferrofluid with Internal Angular Momentum


Pages :
4352


Authors :
Sunil Kumar,
P. Chand,
A. Mahajan,
P. Sharma,
This paper deals with the theoretical investigation of the effect of rotation in a magnetized ferrofluid with internal
angular momentum, heated and soluted from below subjected to a transverse uniform magnetic field. For a flat fluid
layer contained between two free boundaries, an exact solution is obtained. A linear stability analysis theory and
normal mode analysis method have been carried out to study the onset of convection. The influence of various
parameters like rotation, solute gradient, magnetization and internal angular momentum parameters (i.e. coupling
parameter, spin diffusion parameter and heat conduction parameter) has been analyzed on the onset of stationary
convection. The critical magnetic thermal Rayleigh number for the onset of instability is also determined numerically
for sufficiently large values of buoyancy magnetization parameter M1 and results are depicted graphically. The
principle of exchange of stabilities is found to hold true for the ferrofluid with internal angular momentum heated
from below in the absence of rotation, coupling between vorticity and spin, microinertia and solute gradient. The
oscillatory modes are introduced due to the presence of the rotation, coupling between vorticity and spin, microinertia
and solute gradient, which were nonexistent in their absence. In this paper, an attempt is also made to obtain the
sufficient conditions for the nonexistence of overstability.





Chemically Reactive Solute Distribution in a Steady MHD Boundary Layer Flow over a Stretching Surface


Pages :
5358


Authors :
M.S Uddin,
Krishnendu Bhattacharyya,
G.C Layek,
W.A Pk,
The paper is concerned to find the distribution of the chemically reactant solute in the MHD flow of an electrically conducting viscous incompressible fluid over a stretching surface. The first order chemical reaction and the variable solute distribution along the surface are taken into consideration. The governing partial differential equations along with appropriate boundary conditions for flow field and reactive solute are transformed into a set of nonlinear selfsimilar ordinary differential equations by using scaling group of transformations. An exact analytic solution is obtained for the velocity field. Using this velocity field, we obtain numerical solution for the reactant concentration field. It reveals from the study that the values of concentration profile enhances with the increase of the magnetic field and decreases with increase of Schmidt number as well as the reaction rate parameter. Most importantly, when the solute distribution along the surface increases then the concentration profile decreases.





Effects of Variable Thermal Conductivity and Chemical Reaction on Steady Mixed Convection Boundary Layer Flow with Heat and Mass Transfer Inside a Cone due to a Point Sink


Pages :
5963


Authors :
V. Bisht,
M. Kumar,
Z. Uddin,
The steady incompressible mixed convection boundary layer flow with variable fluid properties and mass transfer
inside a cone due to a point sink at the vertex of the cone have been investigated. The fluid viscosity and thermal
conductivity have been assumed to be temperature dependent. The governing fluid flow equations with boundary
conditions have been transformed into set of coupled ordinary differential equations with the help of similarity
transformations and solved RungeKutta method with shooting technique. The effects of Schmidt number, variable
thermal conductivity parameter, mixed convection parameter, buoyancy parameter and chemical reaction parameter
on velocity distribution, temperature distribution, concentration distribution, heat transfer rate and coefficient of skinfriction
have been investigated. It is observed that concentration decreases with increasing Schmidt number and
temperature increases with increasing values of thermal conductivity parameter. Also with increasing values of mixed
convection parameter, velocity, temperature and concentration decreases. The present study is relevant in conical
nozzle and diffuser flow problems exist in petroleum and chemical industries.





A Flow Model for the Settling Velocities of non Spherical Particles in Creeping Motion


Pages :
6575


Authors :
Yuri Mendez,
This paper undertakes a critical examination of Stokes’ law in its final form. The examination and insights of the viscosity principle substantiate grounds to suspect that the controlling dynamics are viscous shear rates across a geometry set by solid boundaries only. The examination sets grounds to conduct an analysis of the dynamics based on the viscosity principle alone and a flow model is derived. Based on the relationship between the pressure gradient and the shear forces as mandated by the viscosity principle the analysis suggests that the pressure gradient surrounding settling particles can be computed, is a single value and expands as required to mobilize a force equal to the driving force. In this context, the pressure gradient arises as a consequence of the contest between body forces in the fluid and the shear forces promoted by shear rates. The flow model suggests that Stokes’ law may be missing important information. An analysis is conducted for the settling velocity of non spherical particles based on the same dynamics and a mathematical solution is reached. The solution is in good agreement with published measured values and defines the influence of particle shape in settling phenomena.





Solutions in Variably Inclined MHD Flows


Pages :
7783


Authors :
C.S Bagewadi,
S. Bhagya,
We study the plane MHD flows when the velocity and magnetic fields are variably inclined and investigate the steady viscous incompressible flow problems of a fluid having infinite electrical conductivity in the presence of a magnetic field. Accounting for infinite electrical conductivity makes the flow problem realistic and attractive because the magnetic Reynolds number is very small for most liquid metals. Particular problems are discussed when magnetic lines are variably inclined but nowhere aligned with streamlines, when the fluid is viscous and nonviscous. Streamlines are parabolic as shown in the graphs.





On the Flow of a Paramagnetic Fluid in a Differentially Heated Channel


Pages :
8589


Authors :
H. Sadat,
C. Prax,
In the present study, we investigate the flow of a paramagnetic fluid in a two dimensional heated channel when an external magnetic gradient is imposed. In the fully developed regime, an analytical solution shows that a flow reversal may occur; the condition of this is given n terms of the Reynolds number. Numerical simulations are then carried out for more general situations. It is shown that the analytical model gives good qualitative predictions.





Mass Transfer Effects on Unsteady Hydromagnetic Convective Flow past a Vertical Porous Plate in a Porous Medium with Heat Source


Pages :
91100


Authors :
S.S Das,
S.R. Biswal,
U.K. Tripathy,
P. Das,
The objective of this paper is to analyze the effect of mass transfer on unsteady hydromagnetic free convective flow of a viscous incompressible electrically conducting fluid past an infinite vertical porous plate in presence of constant suction and heat source. The governing equations of the flow field are solved using multi parameter perturbation technique and approximate solutions are obtained for velocity field, temperature field, concentration distribution, skin friction and the rate of heat transfer. The effects of the flow parameters such as Hartmann number M, Grashof number for heat and mass transfer Gr, Gc; permeability parameter Kp, Schmidt number Sc, heat source parameter S, Prandtl number Pr etc. on the flow field are analyzed with the help of figures and tables. It is observed that a growing Hartmann number or Schmidt number retards the mean velocity as well as the transient velocity of the flow field at all points. The effect of increasing Grashof number for heat and mass transfer or heat source parameter is to accelerate both mean and transient velocity of the flow field at all points. The mean velocity of the flow field increases with an increase in permeability parameter while the transient velocity increases for smaller values of Kp (≤1) and for higher values the effect reverses. A growing Hartmann number decreases the transient temperature of the flow field at all points while a growing permeability parameter or heat source parameter reverses the effect. The Prandtl number increases the transient temperature for small values of Pr (≤1) and for higher values the effect reverses. The effect of increasing Schmidt number is to reduce the concentration boundary layer thickness of the flow field at all points. The problem has some relevance in the geophysical and astrophysical studies.





Fluctuating Heat and Mass Transfer on Unsteady MHD Free Convection Flow of Radiating and Reacting Fluid past a Vertical Porous Plate in Slip Flow Regime


Pages :
101106


Authors :
K.D Singh,
R. Kumar,
In this paper, an analytical study on unsteady MHD free convective viscous incompressible flow of electricallyconducting fluid with periodic heat and mass transfer past an infinite vertical porous flat plate in slip flow regime is presented. A uniform magnetic field perpendicular to the plate is applied. The effects of thermal radiation and chemical reaction are included. The effects of flow parameters and thermo physical properties on the flow, temperature and concentration fields across the boundary layer are investigated. The forms of the wall shear stress, Nusselt number and Sherwood number are derived. The results are shown in figures and tables followed by a quantitative discussion.





