

Experimental and Numerical Approach to Enlargement of Performance of Primary Settling Tanks


Pages :
112


Authors :
A. Razmi,
B. Firoozabadi,
G. Ahmadi,
Circulation regions always exist in settling tanks. These regions would result in shortcircuiting enlargement of the dead
zone and high flow mixing problems and avoid optimal particle sedimentation. Therefore, the main objective of the tank
design process is to avoid formation of the circulation zone, which is known as dead zone. Experiments show that the tank
performance can be improved by altering the geometry of the tank which leads to a different velocity distributions and flow
patterns. In this paper, the presence of a baffle and its effect on the hydrodynamics of the flow field has been investigated in
a primary settling tank. Hydrodynamics of the flow field in these basins is sophisticated. Therefore a numerical simulation
has been provided to discover such flow field. Then, the flow structure was simulated by an unsteady twophase finite
volume method, with VOF (Volume of Fluid) model. Besides, the RNG turbulence model was used in the numerical
calculations. Successively, in order to validate the mentioned method and for a better understanding of the phenomenon,
experimental tests have been carried out using ADV (Acoustic Doppler Velocimeter) and a 0.2 m breadth rectangular model
tank. Results depict the ability of this model in predicting the velocity profiles and circulation districts. Eventually, the
optimum position of the baffle for enhancing the performance of the primary settling tank was determined by applying the
above mentioned numerical scheme.





Effects of Variable Thermal Conductivity and Heat Source / Sink on MHD Flow Near a Stagnation Point on a Linearly Stretching Sheet


Pages :
1321


Authors :
P. R. Sharma,
G. Singh,
Aim of the paper is to investigate effects of variable thermal conductivity and heat source/sink on flow of a viscous
incompressible electrically conducting fluid in the presence of uniform transverse magnetic field and variable free stream
near a stagnation point on a nonconducting stretching sheet. The equations of continuity, momentum and energy are
transformed into ordinary differential equations and solved numerically using shooting method. The velocity and
temperature distributions are discussed numerically and presented through graphs. Skinfriction coefficient and the Nusselt
number at the sheet are derived, discussed numerically and their numerical values for various values of physical parameter
are presented through Tables.





Effects of Varying Viscosity and Thermal Conductivity on Steady Free Convective Flow and Heat Transfer Along an Isothermal Vertical Plate in the Presence of Heat Sink


Pages :
2328


Authors :
N. C. Mahanti,
P. Gaur,
Aim of the paper is to investigate the effects of linearly varying viscosity and thermal conductivity on steady
free convective flow of a viscous incompressible fluid along an isothermal vertical plate in the presence of heat
sink. The governing equations of continuity, momentum and energy are transformed into coupled and nonlinear
ordinary differential equations using similarity transformation and then solved using RungeKutta fourth
order method with shooting technique. The velocity and temperature distributions are discussed numerically and
presented through graphs. Skinfriction coefficient and Nusselt number at the plate are derived, discussed
numerically and their numerical values for various values of physical parameters are presented through Tables.





Experimental Study of a Thermal Plume Evolving in a Confined Environment: Application to Fires Problems


Pages :
2938


Authors :
T. Naffouti,
M. Hammami,
M. Rebay,
R. B. Maad,
We propose to study the natural convection flow resulting from the interaction of a fire with walls that surround it. Indeed,
when a fire occurs in a tunnel or in a tower block, it creates a thermal plume causing a heating of the neighbouring walls.
This heating by thermal radiation of the walls creates a phenomenon of thermosiphon which interacts with the plume. To
study this flow we simulated the problem at the laboratory where we placed a rectangular source heated by Joule effect at
the entrance of an openended vertical canal. The flow visualization by laser plan and the exploration of the thermal and
dynamic fields inside the canal enabled us to describe the flow structure. In order to better characterize this flow, we carried
out a fine analysis by studying the spectra of temperature fluctuations. This spectral analysis allowed us to clarify the
energetic evolution of the vortexes during their ascension and verify some known spectral laws.





Experimental Studies of Flow Patterns of Different Fluids in a Partially Filled Rotating Cylinder


Pages :
3943


Authors :
P. R. Mukunda,
R. A. Shailesh,
A. S. Kiran,
S. R. Shrikantha,
An attempt has been made to investigate the various parameters affecting the fluid behaviour, partially filled in a rotating
cylinder. When the cylinder is rotating at ‘high’ speed, a liquid forms a hollow cylinder. Different patterns are observed in
the fluids for the rotatioal speeds below a critical speed. This study should give us some insight into molten metal behaviour
during centrifugal casting. An extensive experimental investigation is required to obtain an appropriate functional
relationship by knowing and understanding some dimensionless parameters. Here the effect of dimensionless parameters ε
(which is 2 g/ω2d, where g, ω and d denotes gravitational acceleration, container rotation rate and inner diameter of liquid
cylinder) and G (number of times the gravity) was studied as variation of rotation speed, viscosity and aspect ratio of the
mould.





Simulation of Water Movement through Unsaturated Infiltration Redistribution System


Pages :
4553


Authors :
T. Bunsri,
M. Sivakumar,
D. Hagare,
This paper deals with the movement of water in a natural unsaturated zone, focusing on infiltrationredistribution system.
Infiltration refers to the downward movement of water due to the gravitational force and redistribution defines the upward
movement of water due to the capillary rise. Under natural conditions, the movement of water through an infiltrationredistribution
depended upon the relations among water content, hydraulic conductivity and tension of soil pore. Various
combinations of water balance concepts, Richards’ equation, soilphysics theory and capillary height concepts were applied
to mathematically model the movement of water through infiltrationredistribution system. The accuracy and computational
efficiency of the developed model were evaluated for the case study. Besides the laboratory scale sand/soil columns with the
inner diameter of 10.4 cm were investigated in order to provide the supporting data for model calibration. Sand/soil layers
were packed with a bulk density of 1.80 and 1.25 g/cm3, respectively. The infiltration was sprayed uniformly at the soil
surface with the constant rate of 66.1 and 7.18 cm3/h for sand and soil columns, respectively. The redistribution process was
developed by which water arriving at the column base enter to the sand/soil column due to capillary rise. The laboratory
observations were simulated using the developed model. The results indicate that the developed model could well estimate
the movement of water in the infiltrationredistribution system that observed in the case study and the experiments.





Transient Thermal Behavior of a Vertical Solar Storage Tank with a Mantle Heat Exchanger During NoFlow Operation


Pages :
5569


Authors :
A. Barzegar,
A. A. Dehghan,
Transient thermal behavior of a vertical storage tank of a domestic solar heating system with a mantle heat exchanger has
been investigated numerically in the charging mode. It is assumed that the tank is initially filled with uniform cold water. At
an instant of time, the hot fluid from collector outlet is uniformly injected in the upper section of the mantle heat exchanger
and after heat transfer with the fluid inside the tank, withdrawn from the bottom part of the heat exchanger. The
conservation equations in the cylindrical coordinate and in axissymmetric condition have been used according to the
geometry under investigation. Governing equations have been discretized by employing the finite volume method and the
SIMPLER algorithm has been used for coupling between momentum and pressure equations. The Low Reynolds Number
(LRN) k −ω model is utilized for treating turbulence in the fluid. First, the transient thermal behavior of heat storage tank
and the process of formation of thermal stratification in the heat storage tank were investigated. Then, the influence of
Rayleigh number in the heat storage tank, Reynolds number in the mantle heat exchanger and vertical positioning of mantle
on the flow and thermal fields and the formation of the thermal stratification was investigated. It is found that for higher
values of Rayleigh number, a more suitable thermal stratification is established inside the tank. Also it is noticed that
increasing the incoming fluid velocity through the mantle heat exchanger causes a faster formation of the thermal
stratification. A superior thermal performance was achieved when the mantle heat exchanger is positioned at the middle
height of the storage tank.





A Generalized Lattice Boltzmann Method for ThreeDimensional Incompressible Fluid Flow Simulation


Pages :
7196


Authors :
A. R. Rahmati,
M. Ashrafizaadeh,
In this work, a 19bit Incompressible Generalized Lattice Boltzmann (IGLB) method has been proposed for threedimensional
incompressible fluid flow simulation, for the first time. Equilibrium moments in moment space are derived
from an incompressible BGKLB method. The incompressible Navier–Stokes equations can be recovered through the
ChapmanEnskog multiscale expansion without artificial compressible effects. To compare the performance of proposed
model, several benchmark problems (such as a cubic liddriven cavity flow, flow over a backwardfacing step, and a double
shear flow) are solved and the results are compared with those of both 19bit Incompressible BGK Lattice Boltzmann
(IBGKLB) method and existing CFD simulations. It is shown that the stability and accuracy of the 19bit IGLB method is
better than those of the 19bit IBGKLB method; in fact with the IGLB model we can increase the Reynolds number by
factor of 2.5 and still get stable results. The proposed 3D IGLB method is successfully expanded and applied to simulation
of the 3D incompressible buoyancy driven flows. The results of the 3D steadystate natural convection in an airfilled
differentially heated cubic cavity obtained by the extended model comply well with the existing data in literature. In
addition, natural convection from a discrete heat source which is mounted flush with the bottom wall of a horizontal
enclosure is simulated. The obtained results indicate that the proposed method is very convenient for simulation of thermally
driven flow problems.





