

On the Use of RotatingDisk Geometry for Evaluating the DragReducing Efficiency of Polymeric and Surfactant Additives


Pages :
15


Authors :
S. Jafargolinejad,
A. Pishevar,
K. Sadeghy,
In this study we will examine the applicability of the flow induced by a rotating disk in evaluating the performance of
polymeric and surfactant additives in reducing skin friction drag and effect of viscosity on drag reduction capability
of polymeric and surfactant solutions. It is shown that these additives can dramatically reduce friction drag provided
that the flow is occurring under turbulent conditions while they have no effect on Taylor instabilities. Based on the
experimental data, a drag reduction in the range of 10% can be achieved with the effect becoming more pronounced
the higher the Reynolds number.





Mass Transfer and Heat Generation Effects on MHD Free Convection Flow past an Inclined Vertical Surface in a Porous Medium


Pages :
711


Authors :
M. G. Reddy,
N. B. Reddy,
A steady twodimensional MHD free convection and mass transfer flow past an inclined semiinfinite vertical surface
in the presence of heat generation and a porous medium has been studied numerically. The governing partial
differential equations are reduced to a system of ordinary differential equations by introducing similarity
transformations. The nonlinear similarity equations are solved numerically by applying the RungeKutta method of
fourth order with shooting technique. The numerical results are presented graphically for different values of the
parameters. Finally, the numerical values of the local skinfriction coefficient, local Nusselt number and Sherwood
number are shown in Table 1.





Network Simulation of Laminar Convective Heat and Mass Transfer over a Vertical Slender Cylinder with Uniform Surface Heat and Mass Flux


Pages :
1323


Authors :
J. Zueco,
O. A. Bég,
H. S. Takhar,
G. Nath,
The steady, laminar axisymmetric convective heat and mass transfer in boundary layer flow over a vertical thin
cylindrical configuration in the presence of significant surface heat and mass flux is studied theoretically and
numerically. The governing boundarylayer equations for momentum, energy and species conservation are
transformed from a set of partial differential equations in a (x,r) coordinate system to a () system using a group of
similarity transformations. The resulting equations are solved using the Network Simulation Method (NSM) for the
buoyancyassisted pure free convection and also the pure forced convection cases, wherein the effects of Schmidt
number, Prandtl number and surface mass parameter on velocity, temperature and concentration distributions in the
regime are presented graphically and discussed. For the buoyancyassisted pure free convection case, nondimensional
velocity (f/) is found to increase with a rise in surface mass transfer (S) but decrease with increasing
Prandtl number (Pr), particularly in the vicinity of the cylinder surface (small radial coordinate, ). Dimensionless
temperature () decreases however with increasing S values from the cylinder surface into the free stream; with
increasing Prandtl number, temperature is strongly reduced, with the most significant decrease at the cylinder surface.
Dimensionless concentration () is decreased continuously throughout the boundary layer regime with an increase in
S; conversely is enhanced for all radial coordinate values with an increase in Prandtl number. For the pure forced
convection case, velocity increases both with dimensionless axial coordinate () and dimensionless radial coordinate
() but decays smoothly with increasing Prandtl number and increasing Schmidt number, from the cylinder surface to
the edge of the boundary layer domain. The model finds applications in industrial metallurgical processes, thermal
energy systems, polymer processing, etc.





Wall Shear Rates in Taylor Vortex Flow


Pages :
2531


Authors :
V. Sobolik,
T. Jirout,
J. Havlica,
M. Kristiawan,
Wall shear rate and its axial and azimuthal components were evaluated in stable Taylor vortices. The measurements
were carried out in a broad interval of Taylor numbers (52725) and several gap width (R1/R2 = 0.5 – 0.8) by two
threesegment electrodiffusion probes and three single probes flush mounted in the wall of the outer fixed cylinder.
The axial distribution of wall shear rate components was obtained by sweeping the vortices along the probes using a
slow axial flow. The experimental results were verified by CFD simulations. The knowledge of local wall shear rates
and its fluctuations is of primordial interest for industrial applications like tangential filtration, membrane reactors
and bioreactors containing shear sensitive cells.





Experimental Study of a Beta Stirling Thermal Machine Type Functioning in Receiver and Engine Modes


Pages :
3342


Authors :
R. Gheith,
F. Aloui,
S. Ben Nasrallah,
In this paper we studied a beta type Stirling machine. At first, we present the adopted theoretical quasistationary
model. Then, we pass to the physical and geometrical presentation of this machine. The Latter was experimented
according to two configurations: motor configuration and receiver configuration. For the first configuration, in order
to improve the performances of the machine, we proceeded to the insulation of the machine hot room to reduce losses
by radiation. For the second configuration, the machine is experimented as a heat pump and refrigerator.
Comparisons between the theoretical and experimental results are also presented. We finally validated the results
obtained by the model with experiments.





An Investigation of Heat Transfer in a Mechanically Agitated Vessel


Pages :
4350


Authors :
A. Debab,
N. Chergui,
K. Bekrentchir,
J. Bertrand,
The objective of this study is to optimize experimental conditions of agitating a nonNewtonian liquid using
experimental design methodology. The measurements of the temperatures have been carried out in a jacketed vessel
equipped with Turbine impellers. The rheological properties of aqueous solutions of carboxymethylcellulose sodium
salt had been studied using shear stress/shear rate data. The results of the experimental studies, concerning the effect
of the diameter of the impeller, the impeller speed and baffled or unbaffled vessel on the overall heat transfer
coefficient have been approximated in the form of equations. Based on the optimization criterion, an agitated vessel
equipped with Flat Blade Disc Turbine (FBDT) of diameter ratio d/D = 0.6 and baffles is proposed as the most
advantageous for heat transfer processes.





Reorganization of Coherent Structures Downstream a Circular Cylinder Located between Two Parallel Walls


Pages :
5156


Authors :
F. Rehimi,
F. Aloui,
S. B. Nasrallah,
Experiments were performed at low Reynolds numbers in the range 75 Re 275 in the wake of a circular cylinder
of dc diameter placed symmetrically between two parallel walls of H height. 2D2C particle image velocimetry
(PIV) was used to investigate the flow downstream the cylinder. In the unsteady flow regime downstream the
cylinder, the detached primary vortices (Pi) interact with walls generating secondary ones (Pi’) and modify the
cylinder wake dynamic. The kinematical properties (advection velocity, circulation, rotation kinetic energy, etc.) of
the generated secondary vortices are studied and compared with the primary ones in order to show how the walls
influence the von Kármán vortex street. The authors propose here a relation between the circulations and kinetic
energies of primary and secondary vortices.





On the Enhanced Heat Transfer in the Oscillatory Flow of Liquid Metals


Pages :
5762


Authors :
K. Shailendhra,
S. P. AnjaliDevi,
The enhanced heat transfer in the oscillatory flow of liquid metals between two thermally insulated infinite parallel
plates, when a constant axial temperature gradient superimposed, is investigated. The fluid is set to oscillation by
oscillating both the plates axially along with an axial oscillatory body force, having the same frequency as that of the
plates. The effective average thermal diffusivity is calculated and the effect of oscillation of the plates and the
oscillatory body force on the enhancement of heat transfer are discussed and compared.





Control of Local Mass Transfer in the Separated and Reattaching Flow by a Periodic Forcing


Pages :
6367


Authors :
M. Bouterra,
Z. Mehrez,
A. E. Cafsi,
A. Belghith,
P. L. Quéré,
A numerical study based on the Large Eddy Simulation (LES) methodology was made of mass transfer in locally
forced turbulent separated and reattaching flow over a backward facing step. The local forcing was given to the flow
by a sinusoidally blowing /suction of the fluid into a separated shear layer. The Reynolds number was fixed at 33000
and Schmidt number at 1. The forcing frequency was varied in the range 0 St 2, where St is the Strouhal number
of forcing. The obtained results revealed the existence of an optimum forcing frequency value, St = 0.25, in terms of
the reduced reattachment length. At this frequency the mass transfer is significantly enhanced in the recirculation
zone. The influence of the frequency and the amplitude of forcing, in the maximum mass transfer positions and the
maximum Sherwood number, are analyzed.





Temperature Spectra from a Turbulent Free Thermal Plume and in Interaction with its Material Environment


Pages :
6976


Authors :
J. Zinoubi,
T. Naffouti,
R. B. Maad,
In this work we study the interaction of an axysymmetric thermal plume with a thermosiphon flow that surrounds it.
The thermal plume is created by a circular disk heated by joule effect at constant temperature. The disk is placed at an
open ended vertical cylinder on a quiet constant temperature. The internal wall of the cylinder heats up under the
effect of thermal radiation emitted by the hot source. The confinement of the fluid causes, in the bottom part of the
cylinder, an aspiration of the fresh air. It is a thermosiphon flow that comes to interact with the plume. By studying
the average and fluctuating thermal fields it was found that the flow of the plume is strongly influenced by the
presence of nearby walls. It was noted that the vertical transport becomes more intense and the structure of the flow
becomes more turbulent. On the other hand, we attend a fast homogenization of the flow in the upper cylinder. To
obtain more detailed information of this flow, we develops, during this study, a spectral analysis of the fluctuating
thermal fields for the case of a plume evolving in unlimited and in an enclosed environment. The energy spectra
study shows an important shift of the energy peaks toward the high frequencies under the effect of the thermosiphon.
As destroying structures them on a big scale generated by the plume, the thermosiphon provokes a fast mixture of the
fluid thus while leading to vortex of weaker size.





Flow Improvement in Rectangular Air Intake by Submerged Vortex Generators


Pages :
7786


Authors :
A. R. Paul,
K. Kuppa,
M. S. Yadav,
U. Dutta,
Rectangular Sduct diffusers are widely used in airintake system of several military aircrafts. A welldesigned
diffusing duct should efficiently decelerate the incoming flow, over a wide range of incoming conditions, without the
occurrence of streamwise separation. A short duct is desired because of space constraint and aircraft weight
consideration, however this results in the formation of a secondary flow to the fluid within the boundary layer. The
axial development of these secondary flows, in the form of counter rotating vortices at the duct exit is responsible for
flow nonuniformity and flow separation at the engine face. Investigation on Sshaped diffusers reveals that the flow
at the exit plane of diffusers is not uniform and hence offers an uneven impact loading to the downstream components
of diffuser. Experiments are conducted with an Sshaped diffuser of rectangular crosssection at Re = 1.34 105 to find
out the effects of the corners (i.e. sharp 90º, 45º chamfered etc.) on its exit flow pattern. A ‘fishtail’ shaped
submerged vortex generators (VG) are designed and introduced at different locations inside the diffusers in multiple
numbers to control the secondary flow, thereby improving the exit flow pattern. It is found that the locations of the
VG have a better influence on the flow pattern rather than the number of the VG used. The best combination
examined in this study is a 45 chamfered duct with 3 3 VG fixed at the top and bottom of the duct inflexion plane.
The results exhibit a marked improvement in the performance of Sduct diffusers. Coefficient of static pressure
recovery (CSP) and coefficient of total pressure loss (CTL) for the best configuration are reported as 48.57% and
3.54% respectively. With the best configuration of VG, the distortion coefficient (DC60) is also reduced from 0.168
(in case of bare duct) to 0.141.





Similarity Solution for Unsteady MHD Flow Near a Stagnation Point of a ThreeDimensional Porous Body with Heat and Mass Transfer, Heat Generation/Absorption and Chemical Reaction


Pages :
8794


Authors :
A. J. Chamkha,
S. E. Ahmed,
The problem of unsteady mixed convection heat and mass transfer near the stagnation point of a threedimensional
porous body in the presence of magnetic field, chemical reaction and heat source or sink is analyzed. An efficient,
iterative, tridiagonal implicit finite difference method is used to solve the transformed similarity equations in the
boundary layer. Three cases were considered, namely, accelerating flow, decelerating flow and the steadystate case.
The obtained results are presented in graphical and tabulated forms to illustrate the influence of the different physical
parameters such as the magnetic field parameter, transpiration parameter, unsteadiness parameter, ratio of velocity
gradients at the edge of the boundary layer parameter, heat generation/absorption parameter and the chemical reaction
parameter on the velocity components in the xand y directions, temperature and concentration distributions, as well
as the skinfriction coefficients and Nusselt and Sherwood numbers.





Effects of Rotation and Magnetic Field on Unsteady Couette Flow in a Porous Channel


Pages :
95103


Authors :
G. S. Seth,
Md. S. Ansari,
R. Nandkeolyar,
Unsteady hydromagnetic Couette flow of a viscous incompressible electrically conducting fluid in a rotating system
in the presence of a uniform transverse magnetic field is studied. The plates of the channel are considered porous and
fluid flow within the channel is induced due to the impulsive movement of the upper plate of the channel. General
solution of the governing equations is obtained which is valid for every value of time t. For small values of time t, the
solution of the governing equations is obtained by Laplace transform technique. The expression for the shear stress at
the stationary plate due to the primary and secondary flows is obtained in both the cases. It is found that the solution
obtained by Laplace transform technique converges more rapidly than the general solution when time t is very small.
Magnetic field retards the fluid flow in both the primary and secondary flow directions. Rotation retards primary flow
whereas it accelerates secondary flow. There exists incipient flow reversal near the stationary plate on increasing
rotation parameter K2. Suction accelerates primary flow whereas it retards secondary flow. Injection retards both the
primary and secondary flows.





Blade Exit Angle Effects on Performance of a Standard Industrial Centrifugal Oil Pump


Pages :
105119


Authors :
W. G. Li,
The effects of blade discharge angle on the performance of a standard industrial centrifugal oil pump of type 65Y60
were investigated experimentally as the pump handled both water and viscous oil. A onedimensional hydraulic loss
model was established to identify such effects mathematically. The effects have been estimated analytically by using
the model at various viscosities. The results showed that the blade discharge angle has significant but equal influence
on the head, shaft power and efficiency of the centrifugal oil pump at various viscosity conditions. For any viscosity,
the total hydraulic loss in the impeller and volute rises with increasing blade exit angle. The diffusion loss in and
behind the impellers as well as the friction loss in the volute are noticed in the pump, especially for highly viscous
liquids. The hydraulic loss in the impellers is about 0.80.6 times the loss in the volute. In order to improve the pump
performance, the hydraulic loss in the volute must be kept as small as possible.





New Trends in Multiscale and Multiphysics Simulation of Transport Phenomena in Novel Engineering Systems


Pages :
121127


Authors :
D. Lakehal,
The paper reports on the progress made in predicting large and smallscale single and twophase flows with heat
transfer using the CMFD code TransAT. In the multiphase context, the code uses the Level Set approach as the
“Interface Tracking Method” of reference. The solver incorporates phasechange capabilities, surface tension and
tripleline dynamics models, Marangoni effects, electric and magnetic fields, and a wall microfilm subgrid scale
model for lubrication. Complex 3D examples shown here were treated using a fully automatized version of the code,
using the Immersed Surfaces Technique (IST) to map complex components into a simple rectangular Cartesian grid.
It is shown that real coupled twophase heat transfer (conjugate) problems are within reach of modern CMFD code
using interface tracking, with relatively fast response times: 3D coupled twophase flow heat transfer can run on a
simple Linux PC cluster within 24 H time.





UnderVentilated Wall Fire Behaviour during the Post Flashover Period


Pages :
129135


Authors :
J. M. Most,
J. B. Saulnier,
This work is aimed the evolution of the behaviour of a strongly contained wall fire in an enclosure during the postflashover
period. It has characterised the fire intensity decay up to extinction of a wall fire by lack of oxygen and the
effects of a sudden door opening on the formation of an air gravity wave capable to bring the backdraft phenomenon.
To better understand these two sequential fire scenarios, the study was divided into two complementary parts
performed in the same laboratory scale experimental setup. The first part consists to stabilise a steady wall fire at the
rear of the compartment and to follow its evolution when a door closes the aperture leaving only a thin slot opened to
limit the air entering. It has been observed the formation of a ghosting flame moving through the compartment before
dying at the aperture. By supposing the continuation of the fuel solid pyrolysis after flame extinction due to the
radiation of the hot environment, fuel vapours continue to fill the compartment. The second part will study the effects
of a reopening of the door. It has been observed and characterised the formation and the propagation of a gravity
wave through the enclosure. This is representative of the development of the first stage of the backdraft. Tests are
performed to measure the aerodynamic properties of the flow behaviour.





Convective Heat Transfer in Impinging Gas Jet Arrangements


Pages :
137149


Authors :
J. M. Buchlin,
The paper deals with heat transfer by convection between impinging gas jets and solid surfaces. It considers both
single and multiple jet systems. It emphasizes the flow and geometrical parameters as well as the environment
conditions at which the jet emerges. In particular, it points out the effect of the jet tilting, thermal entrainment and jet
confinement. ASN and ARN schemes are illustrated through industrial and aeronautical applications. Design
correlations are proposed. Experimental data obtained from infrared thermography are compared to CFD simulations.





