Abstract: This paper introduces and proves new concept of salt
dissolving in water as very tiny solid sodium chloride particles of
nanovolumes, from this point of view salt water can be desalinated by
collision with special surface characterized by smoothness upon nano
level, high rigidity, high hardness under appropriate conditions of
water launching in the form of thin laminar flow under suitable speed
and angle of incidence to get desalinated water.
Abstract: The indoor airflow with a mixed natural/forced convection
was numerically calculated using the laminar and turbulent
approach. The Boussinesq approximation was considered for a simplification
of the mathematical model and calculations. The results
obtained, such as mean velocity fields, were successfully compared
with experimental PIV flow visualizations. The effect of the distance
between the cooled wall and the heat exchanger on the temperature
and velocity distributions was calculated. In a room with a simple
shape, the computational code OpenFOAM demonstrated an ability to
numerically predict flow patterns. Furthermore, numerical techniques,
boundary type conditions and the computational grid quality were
examined. Calculations using the turbulence model k-omega had a
significant effect on the results influencing temperature and velocity
distributions.
Abstract: The Lattice Boltzmann Method (LBM) with double populations is applied to solve the steady-state laminar natural convective heat transfer in a triangular cavity filled with water. The bottom wall is heated, the vertical wall is cooled, and the inclined wall is kept adiabatic. The buoyancy effect was modeled by applying the Boussinesq approximation to the momentum equation. The fluid velocity is determined by D2Q9 LBM and the energy equation is discritized by D2Q4 LBM to compute the temperature field. Comparisons with previously published work are performed and found to be in excellent agreement. Numerical results are obtained for a wide range of parameters: the Rayleigh number from to and the inclination angle from 0° to 360°. Flow and thermal fields were exhibited by means of streamlines and isotherms. It is observed that inclination angle can be used as a relevant parameter to control heat transfer in right-angled triangular enclosures.
Abstract: The present study deals with the modeling and simulation of flow through an annular reactor at different hydrodynamic conditions using computational fluid dynamics (CFD) to investigate the flow behavior. CFD modeling was utilized to predict velocity distribution and average velocity in the annular geometry. The results of CFD simulations were compared with the mathematically derived equations and already developed correlations for validation purposes. CFD modeling was found suitable for predicting the flow characteristics in annular geometry under laminar flow conditions. It was observed that CFD also provides local values of the parameters of interest in addition to the average values for the simulated geometry.
Abstract: Laminar natural-convective heat transfer from a
horizontal cylinder is studied by solving the Navier-Stokes and
energy equations using higher order compact scheme in cylindrical
polar coordinates. Results are obtained for Rayleigh numbers of 1,
10, 100 and 1000 for a Prandtl number of 0.7. The local Nusselt
number and mean Nusselt number are calculated and compared with
available experimental and theoretical results. Streamlines, vorticity -
lines and isotherms are plotted.
Abstract: The present study has been conducted to characterize
the prophenoloxidase (PPO) system of the desert locust, Schistocerca
gregaria following injection of Bacillus thuringiensis kurstaki (Bt).
The bulk of PPO system was associated with haemocytes and a little
amount was found in plasma. This system was activated by different
activators such as laminarin, lipopolysaccharide (LPS) and trypsin
suggesting that the stimulatory mechanism may involve an enzyme
cascade of one or more associated molecules. These activators did
not activate all the molecules of the cascade. Presence of
phenoloxidase activity (PO) coincides with the appearance of protein
band with molecular weight (MW) 70.154 KD (Kilo Dalton).
Abstract: The present project was conducted with the
circumferential-fuel-jets inverse diffusion flame (CIDF) burner
burning liquefied petroleum gas (LPG) enriched with 50% of
hydrogen fuel (H2). The range of stable operation of the CIDF burner
in terms of Reynolds number (from laminar to turbulent flow regions),
equivalence ratio and fuel jet velocity of LPG of the 50% H2-LPG
mixed fuel was identified. Experiments were also carried out to
investigate the flame structures of the LPG flame and LPG enriched H2
flame. Experimental results obtained from these two flames were
compared to fully explore the influence of hydrogen addition on flame
stability. Flame heights obtained by burning these two kinds of fuels at
various equivalence ratios were compared and correlated with the
Global Momentum Ratio (GMR).
Abstract: Thermal conductivity is an important characteristic of
a nanofluid in laminar flow heat transfer. This paper presents an
improved model for the prediction of the effective thermal
conductivity of nanofluids based on dimensionless groups. The
model expresses the thermal conductivity of a nanofluid as a function
of the thermal conductivity of the solid and liquid, their volume
fractions and particle size. The proposed model includes a parameter
which accounts for the interfacial shell, brownian motion, and
aggregation of particle. The validation of the model is verified by
applying the results obtained by the experiments of Tio2-water and
Al2o3-water nanofluids.
Abstract: A numerical study is made of laminar, unsteady flow
behind a rotationally oscillating circular cylinder using a recently
developed higher order compact (HOC) scheme. The stream function
vorticity formulation of Navier-Stokes (N-S) equations in cylindrical
polar coordinates are considered as the governing equations. The
temporal behaviour of vortex formation and relevant streamline
patterns of the flow are scrutinized over broad ranges of two
externally specified parameters namely dimensionless forced
oscillating frequency Sf and dimensionless peak rotation rate αm for
the Reynolds-s number Re = 200. Excellent agreements are found
both qualitatively and quantitatively with the existing experimental
and standard numerical results.
Abstract: The development of biomimetic micro-aerial-vehicles
(MAVs) with flapping wings is the future trend in military/domestic
field. The successful flight of MAVs is strongly related to the
understanding of unsteady aerodynamic performance of low Reynolds
number airfoils under dynamic flapping motion. This study explored
the effects of flapping frequency, stroke amplitude, and the inclined
angle of stroke plane on lift force and thrust force of a bio-inspiration
corrugated airfoil with 33 full factorial design of experiment and
ANOVA analysis. Unsteady vorticity flows over a corrugated thin
airfoil executing flapping motion are computed with time-dependent
two-dimensional laminar incompressible Reynolds-averaged
Navier-Stokes equations with the conformal hybrid mesh. The tested
freestream Reynolds number based on the chord length of airfoil as
characteristic length is fixed of 103. The dynamic mesh technique is
applied to model the flapping motion of a corrugated airfoil. Instant
vorticity contours over a complete flapping cycle clearly reveals the
flow mechanisms for lift force generation are dynamic stall, rotational
circulation, and wake capture. The thrust force is produced as the
leading edge vortex shedding from the trailing edge of airfoil to form a
reverse von Karman vortex. Results also indicated that the inclined
angle is the most significant factor on both the lift force and thrust
force. There are strong interactions between tested factors which mean
an optimization study on parameters should be conducted in further
runs.
Abstract: Fluid flow in cylinders of elliptic cross-section was investigated. Fluid used is Liquefied petroleum gas (LPG). LPG found in Nigeria contains majorly butane with percentages of propane. Commercial available code FLUENT which uses finite volume method was used to solve fluid flow governing equations. There has been little attention paid to fluid flow in cylindrical elliptic pipes. The present work aims to predict the LPG gas flow in cylindrical pipes of elliptic cross-section. Results of flow parameters of velocity and pressure distributions are presented. Results show that the pressure drop in elliptic pipes is higher than circular pipe of the same cross-sectional area. This is an important result as the pressure drop is related to the pump power needed to drive the flow. Results show that the velocity increases towards centre of the pipe as the flow moves downstream, and also increases towards the outlet of the pipe.
Abstract: This paper presents a study of laminar to turbulent transition on a profile specifically designed for wind turbine blades, the DU91-W2-250, which belongs to a class of wind turbine dedicated airfoils, developed by Delft University of Technology. A comparison between the experimental behavior of the airfoil studied at Delft wind tunnel and the numerical predictions of the commercial CFD solver ANSYS FLUENT® has been performed. The prediction capabilities of the Spalart-Allmaras turbulence model and of the γ-θ Transitional model have been tested. A sensitivity analysis of the numerical results to the spatial domain discretization has also been performed using four different computational grids, which have been created using the mesher GAMBIT®. The comparison between experimental measurements and CFD results have allowed to determine the importance of the numerical prediction of the laminar to turbulent transition, in order not to overestimate airfoil friction drag due to a fully turbulent-regime flow computation.
Abstract: Composite laminates are relatively weak in out of
plane loading, inter-laminar stress, stress concentration near the edge
and stress singularities. This paper develops a new analytical
formulation for laminated composite rotating disc fabricated from
symmetric sequential quasi isotropic layers to predict three
dimensional stress and deformation. This analysis is necessary to
evaluate mechanical integrity of fiber reinforced multi-layer
laminates used for high speed rotating applications such as high
speed impellers. Three dimensional governing equations are written
for rotating composite disc. Explicit solution is obtained with
"Frobenius" expansion series. Based on analytical results, there are
two separate zones of three dimensional stress fields in centre and
edge of rotating disc. For thin discs, out of plane deformations and
stresses are small in comparison with plane ones. For relatively thick
discs deformation and stress fields are three dimensional.
Abstract: The RANS method with Saffman-s turbulence model
was employed to solve the time-dependent turbulent Navier-Stokes
and energy equations for oscillating pipe flows. The method of
partial sums of the Fourier series is used to analyze the harmonic
velocity and temperature results. The complete structures of the
oscillating pipe flows and the averaged Nusselt numbers on the tube
wall are provided by numerical simulation over wide ranges of ReA
and ReR. Present numerical code is validated by comparing the
laminar flow results to analytic solutions and turbulence flow results
to published experimental data at lower and higher Reynolds
numbers respectively. The effects of ReA and ReR on the velocity,
temperature and Nusselt number distributions have been di scussed.
The enhancement of the heat transfer due to oscillating flows has
also been presented. By the way of analyzing the overall Nusselt
number over wide ranges of the Reynolds number Re and Keulegan-
Carpenter number KC, the optimal ratio of the tube diameter over
the oscillation amplitude is obtained based on the existence of a
nearly constant optimal KC number. The potential application of the
present results in sea water cooling has also been discussed.
Abstract: Lattice Monte Carlo methods are an excellent
choice for the simulation of non-linear thermal diffusion
problems. In this paper, and for the first time, Lattice Monte
Carlo analysis is performed on thermal diffusion combined
with convective heat transfer. Laminar flow of water modeled
as an incompressible fluid inside a copper pipe with a constant
surface temperature is considered. For the simulation of
thermal conduction, the temperature dependence of the
thermal conductivity of the water is accounted for. Using the
novel Lattice Monte Carlo approach, temperature distributions
and energy fluxes are obtained.
Abstract: The frequency dependence of the phase field
model(PFM) is studied. A simple PFM is proposed, and is tested in a
laminar boundary layer. The Blasius-s laminar boundary layer
solution on a flat plate is used for the flow pattern, and several
frequencies are imposed on the PFM, and the decay times of the
interfaces are obtained. The computations were conducted for three
cases: 1) no-flow, and 2) a half ball on the laminar boundary layer, 3) a
line of mass sources in the laminar boundary layer. The computations
show the decay time becomes shorter as the frequency goes larger, and
also show that it is sensitive to both background disturbances and
surface tension parameters. It is concluded that the proposed simple
PFM can describe the properties of decay process, and could give the
fundamentals for the decay of the interface in turbulent flows.
Abstract: In this study the mixed convection heat transfer in a
coil-in-shell heat exchanger for various Reynolds numbers and
various dimensionless coil pitch was experimentally investigated.
The experiments were conducted for both laminar and turbulent flow
inside coil and the effects of coil pitch on shell-side heat transfer
coefficient of the heat exchanger were studied. The particular
difference in this study in comparison with the other similar studies
was the boundary conditions for the helical coils. The results indicate
that with the increase of coil pitch, shell-side heat transfer coefficient
is increased.
Abstract: Direct numerical simulation (DNS) is used to study the evolution of a boundary layer that was laminar initially followed by separation and then reattachment owing to generation of turbulence. This creates a closed region of recirculation, known as the laminar-separation bubble. The present simulation emulates the flow environment encountered in a modern LP turbine blade, where a laminar separation bubble may occur on the suction surface. The unsteady, incompressible three-dimensional (3-D) Navier-Stokes (NS) equations have been solved over a flat plate in the Cartesian coordinates. The adverse pressure gradient, which causes the flow to separate, is created by a boundary condition. The separated shear layer undergoes transition through appearance of ╬ø vortices, stretching of these create longitudinal streaks. Breakdown of the streaks into small and irregular structures makes the flow turbulent downstream.
Abstract: The purpose of this article is to study the effects of
plants cover on overland flow and, therefore, its influences on the
amount of eroded and transported soil. In this investigation, all the
experiments were conducted in the LEGHYD laboratory using a
rainfall simulator and a soil tray. The experiments were conducted
using an experimental plot (soil tray) which is 2m long, 0.5 m wide
and 0.15 m deep. The soil used is an agricultural sandy soil (62,08%
coarse sand, 19,14% fine sand, 11,57% silt and 7,21% clay). Plastic
rods (4 mm in diameter) were used to simulate the plants at different
densities: 0 stem/m2 (bared soil), 126 stems/m², 203 stems/m², 461
stems/m² and 2500 stems/m²). The used rainfall intensity is 73mm/h
and the soil tray slope is fixed to 3°. The results have shown that the
overland flow velocities decreased with increasing stems density, and
the density cover has a great effect on sediment concentration.
Darcy–Weisbach and Manning friction coefficients of overland flow
increased when the stems density increased. Froude and Reynolds
numbers decreased with increasing stems density and, consequently,
the flow regime of all treatments was laminar and subcritical. From
these findings, we conclude that increasing the plants cover can
efficiently reduce soil loss and avoid denuding the roots plants.
Abstract: This paper presents and discusses the numerical simulations of transient laminar natural convection cooling of high Prandtl number fluids in cubical cavities, in which the six walls of the cavity are subjected to a step change in temperature. The effect of the fluid Prandtl number on the heat transfer coefficient is studied for three different fluids (Golden Syrup, Glycerin and Glycerin-water solution 50%). The simulations are performed at two different Rayleigh numbers (5·106 and 5·107) and six different Prandtl numbers (3 · 105 ≥Pr≥ 50). Heat conduction through the cavity glass walls is also considered. The propsed correlations of the averaged heat transfer coefficient (N u) showed that it is dependant on the initial Ra and almost independent on P r. The instantaneous flow patterns, temperature contours and time evolution of volume averaged temperature and heat transfer coefficient are presented and analyzed.