Abstract: The forced convection heat transfer in high porosity metal-foam filled tube heat exchangers are studied in this paper. The Brinkman Darcy momentum model and two energy equations for both solid and fluid phases in porous media are employed .The study shows that using metal-foams can significantly improve the heat transfer in heat exchangers.
Abstract: A numerical study on the influence of forward-facing
cavity length upon forward-facing cavity and opposing jet combined
thermal protection system (TPS) cooling efficiency under hypersonic
flow is conducted, by means of which the flow field parameters, heat
flux distribution along the outer body surface are obtained. The
numerical simulation results are validated by experiments and the
cooling effect of the combined TPS with different cavity length is
analyzed. The numerical results show that the combined configuration
dose well in cooling the nose of the hypersonic vehicle. The deeper the
cavity is, the weaker the heat flux is. The recirculation region plays a
key role for the reduction of the aerodynamic heating.
Abstract: In this research, a 2-D computational analysis of
steady state free convection in a rectangular enclosure filled with an
electrically conducting fluid under Effect of Magnetic Field has been
performed. The governing equations (mass, momentum, and energy)
are formulated and solved by a finite volume method (FVM)
subjected to different boundary conditions. A parametric study has
been conducted to consider the influence of Grashof number (Gr),
Prantdl number (Pr) and the orientation of magnetic field on the flow
and heat transfer characteristics. It is observed that Nusselt number
(Nu) and heat flux will increase with increasing Grashof and Prandtl
numbers and decreasing the slope of the orientation of magnetic field.
Abstract: Natural convection heat transfer from a heated
horizontal semi-circular cylinder (flat surface upward) has been
investigated for the following ranges of conditions; Grashof number,
and Prandtl number. The governing partial differential equations
(continuity, Navier-Stokes and energy equations) have been solved
numerically using a finite volume formulation. In addition, the role of
the type of the thermal boundary condition imposed at cylinder
surface, namely, constant wall temperature (CWT) and constant heat
flux (CHF) are explored. Natural convection heat transfer from a
heated horizontal semi-circular cylinder (flat surface upward) has
been investigated for the following ranges of conditions; Grashof
number, and Prandtl number, . The governing partial differential
equations (continuity, Navier-Stokes and energy equations) have
been solved numerically using a finite volume formulation. In
addition, the role of the type of the thermal boundary condition
imposed at cylinder surface, namely, constant wall temperature
(CWT) and constant heat flux (CHF) are explored. The resulting flow
and temperature fields are visualized in terms of the streamline and
isotherm patterns in the proximity of the cylinder. The flow remains
attached to the cylinder surface over the range of conditions spanned
here except that for and ; at these conditions, a separated flow
region is observed when the condition of the constant wall
temperature is prescribed on the surface of the cylinder. The heat
transfer characteristics are analyzed in terms of the local and average
Nusselt numbers. The maximum value of the local Nusselt number
always occurs at the corner points whereas it is found to be minimum
at the rear stagnation point on the flat surface. Overall, the average
Nusselt number increases with Grashof number and/ or Prandtl
number in accordance with the scaling considerations. The numerical
results are used to develop simple correlations as functions of
Grashof and Prandtl number thereby enabling the interpolation of the
present numerical results for the intermediate values of the Prandtl or
Grashof numbers for both thermal boundary conditions.
Abstract: In this paper, we show that the association of the PI
regulators for the speed and stator currents with a control strategy
using the linearization by state feedback for an induction machine
without speed sensor, and with an adaptation of the rotor resistance.
The rotor speed is estimated by using the model reference adaptive
system approach (MRAS). This method consists of using two
models: The first is the reference model and the second is an
adjustable one in which two components of the stator flux, obtained
from the measurement of the currents and stator voltages are
estimated. The estimated rotor speed is then obtained by canceling
the difference between stator-flux of the reference model and those
of the adjustable one. Satisfactory results of simulation are obtained
and discussed in this paper to highlight the proposed approach.
Abstract: In this paper, fully developed flow and heat transfer of
viscoelastic materials in curved ducts with square cross section under
constant heat flux have been investigated. Here, staggered mesh is
used as computational grids and flow and heat transfer parameters
have been allocated in this mesh with marker and cell method.
Numerical solution of governing equations has being performed with
FTCS finite difference method. Furthermore, Criminale-Eriksen-
Filbey (CEF) constitutive equation has being used as viscoelastic
model. CEF constitutive equation is a suitable model for studying
steady shear flow of viscoelastic materials which is able to model
both effects of the first and second normal stress differences. Here, it
is shown that the first and second normal stresses differences have
noticeable and inverse effect on secondary flows intensity and mean
Nusselt number which is the main novelty of current research.
Abstract: Numerical study of two dimensional supersonic
hydrogen-air mixing layer is performed to investigate the effect of
turbulence and chemical additive on ignition distance. Chemical
reaction is treated using detail kinetics. Advection upstream splitting
method is used to calculate the fluxes and one equation turbulence
model is chosen here to simulate the considered problem. Hydrogen
peroxide is used as an additive and the results show that inflow
turbulence and chemical additive may drastically decrease the
ignition delay in supersonic combustion.
Abstract: A numerical investigation of surface heat transfer
characteristics of turbulent air flows in different parallel plate
grooved channels is performed using CFD code. The results are
obtained for Reynolds number ranging from 10,000 to 30,000 and for
arc-shaped and rectangular grooved channels. The influence of
different geometric parameters of dimples as well as the number of
them and the geometric and thermophysical properties of channel
walls are studied. It is found that there exists an optimum value for
depth of dimples in which the largest wall heat flux can be achieved.
Also, the results show a critical value for the ratio of wall thermal
conductivity to the one of fluid in which the dependence of wall heat
flux to this ratio almost vanishes. In most cases examined, heat
transfer enhancement is larger for arc-shaped grooved channels than
rectangular ones.
Abstract: Electromagnetic flow meter by measuring the varying of magnetic flux, which is related to the velocity of conductive flow, can measure the rate of fluids very carefully and precisely. Electromagnetic flow meter operation is based on famous Faraday's second Law. In these equipments, the constant magnetostatic field is produced by electromagnet (winding around the tube) outside of pipe and inducting voltage that is due to conductive liquid flow is measured by electrodes located on two end side of the pipe wall. In this research, we consider to 2-dimensional mathematical model that can be solved by numerical finite difference (FD) solution approach to calculate induction potential between electrodes. The fundamental concept to design the electromagnetic flow meter, exciting winding and simulations are come out by using MATLAB and PDE-Tool software. In the last stage, simulations results will be shown for improvement and accuracy of technical provision.
Abstract: Calcium [Ca2+] is an important second messenger
which plays an important role in signal transduction. There are
several parameters that affect its concentration profile like buffer
source etc. The effect of stationary immobile buffer on Ca2+
concentration has been incorporated which is a very important
parameter needed to be taken into account in order to make the
model more realistic. Interdependence of all the important parameters
like diffusion coefficient and influx over [Ca2+] profile has been
studied. Model is developed in the form of advection diffusion
equation together with buffer concentration. A program has been
developed using finite volume method for the entire problem and
simulated on an AMD-Turion 32-bit machine to compute the
numerical results.
Abstract: The performance of Advection Upstream Splitting
Method AUSM schemes are evaluated against experimental flow
fields at different Mach numbers and results are compared with
experimental data of subsonic, supersonic and hypersonic flow fields.
The turbulent model used here is SST model by Menter. The
numerical predictions include lift coefficient, drag coefficient and
pitching moment coefficient at different mach numbers and angle of
attacks. This work describes a computational study undertaken to
compute the Aerodynamic characteristics of different air vehicles
configurations using a structured Navier-Stokes computational
technique. The CFD code bases on the idea of upwind scheme for the
convective (convective-moving) fluxes. CFD results for GLC305
airfoil and cone cylinder tail fined missile calculated on above
mentioned turbulence model are compared with the available data.
Wide ranges of Mach number from subsonic to hypersonic speeds are
simulated and results are compared. When the computation is done
by using viscous turbulence model the above mentioned coefficients
have a very good agreement with the experimental values. AUSM
scheme is very efficient in the regions of very high pressure gradients
like shock waves and discontinuities. The AUSM versions simulate
the all types of flows from lower subsonic to hypersonic flow without
oscillations.
Abstract: This paper presents a synthetic jet air blower actuated
by PZT for air blowing for air-breathing micro PEM fuel cell. The
several factors to affect the performance of air-breathing PEM fuel cell
such as air flow rate, opening ratio and cathode open type in the
cathode side were studied. Especially, an air flow rate is critical
condition to improve its performance. In this paper, we developed a
synthetic jet air blower to supply a high stoichiometric air flow. The
synthetic jet mechanism is a zero mass flux device that converts
electrical energy into the momentum. The synthetic jet actuation is
usually generated by a traditional PZT actuator, which consists of a
small cylindrical cavity, in/outlet channel and PZT diaphragms. The
flow rate of the fabricated synthetic jet air blower was 400cc/min at
550Hz and its power consumption was very low under 0.3W. The
proposed air-breathing PEM fuel cell which installed synthetic jet air
blower was higher performance and stability during continuous
operation than the air-breathing fuel cell without auxiliary device to
supply the air. The results showed that the maximum power density
was 188mW/cm2 at 400mA/cm2. This maximum power density and
durability were improved more than 40% and 20%, respectively.
Abstract: The tubes in an Ammonia primary reformer furnace
operate close to the limits of materials technology in terms of the
stress induced as a result of very high temperatures, combined with
large differential pressures across the tube wall. Operation at tube
wall temperatures significantly above design can result in a rapid
increase in the number of tube failures, since tube life is very
sensitive to the absolute operating temperature of the tube. Clearly it
is important to measure tube wall temperatures accurately in order to
prevent premature tube failure by overheating.. In the present study,
the catalyst tubes in an Ammonia primary reformer has been modeled
taking into consideration heat, mass and momentum transfer as well
as reformer characteristics.. The investigations concern the effects of
tube characteristics and superficial tube wall temperatures on of the
percentage of heat flux, unconverted methane and production of
Hydrogen for various values of steam to carbon ratios. The results
show the impact of catalyst tubes length and diameters on the
performance of operating parameters in ammonia primary reformers.
Abstract: Doubly fed induction machines DFIM are used
mainly for wind energy conversion in MW power plants. This paper
presents a new strategy of field oriented control ,it is based on the
principle of a double flux orientation of stator and rotor at the same
time. Therefore, the orthogonality created between the two oriented
fluxes, which must be strictly observed, leads to generate a linear and
decoupled control with an optimal torque. The obtained simulation
results show the feasibility and the effectiveness of the suggested
method.
Abstract: In this paper presents a technique for developing the
computational efficiency in simulating double output induction
generators (DOIG) with two rotor circuits where stator transients are
to be included. Iterative decomposition is used to separate the flux–
Linkage equations into decoupled fast and slow subsystems, after
which the model order of the fast subsystems is reduced by
neglecting the heavily damped fast transients caused by the second
rotor circuit using integral manifolds theory. The two decoupled
subsystems along with the equation for the very slowly changing slip
constitute a three time-scale model for the machine which resulted in
increasing computational speed. Finally, the proposed method of
reduced order in this paper is compared with the other conventional
methods in linear and nonlinear modes and it is shown that this
method is better than the other methods regarding simulation
accuracy and speed.
Abstract: To calculate the temperature distribution of the slab in
a hot rolled reheating furnace a mathematical model has been
developed by considering the thermal radiation in the furnace and
transient conduction in the slab. The furnace is modeled as radiating
medium with spatially varying temperature. Radiative heat flux within
the furnace including the effect of furnace walls, combustion gases,
skid beams and buttons is calculated using the FVM and is applied as
the boundary condition of the transient conduction equation of the
slab. After determining the slab emissivity by comparison between
simulation and experimental work, variation of heating characteristics
in the slab is investigated in the case of changing furnace temperature
with various time and the slab residence time is optimized with this
evaluation.
Abstract: Bead-on-plate welds were carried out on AISI 316L
(N) austenitic stainless steel (ASS) using flux cored arc welding
(FCAW) process. The bead on plates weld was conducted as per L25
orthogonal array. In this paper, the weld bead geometry such as depth
of penetration (DOP), bead width (BW) and weld reinforcement (R)
of AISI 316L (N) ASS are investigated. Taguchi approach is used as
statistical design of experiment (DOE) technique for optimizing the
selected welding input parameters. Grey relational analysis and
desirability approach are applied to optimize the input parameters
considering multiple output variables simultaneously. Confirmation
experiment has also been conducted to validate the optimized
parameters.
Abstract: We report here, the results of molecular dynamics
simulation of p-doped (Ga-face)GaN over n-doped (Siface)(
0001)4H-SiC hetero-epitaxial material system with one-layer
each of Ga-flux and (Al-face)AlN, as the interface materials, in the
form of, the total Density of States (DOS). It is found that the total
DOS at the Fermi-level for the heavily p-doped (Ga-face)GaN and ndoped
(Si-face)4H-SiC hetero-epitaxial system, with one layer of
(Al-face)AlN as the interface material, is comparatively higher than
that of the various cases studied, indicating that there could be good
vertical conduction across the (Ga-face)GaN over (Si-face)(0001)4HSiC
hetero-epitaxial material system.
Abstract: The production and consumption of natural gas is on
the rise throughout the world as a result of its wide availability, ease
of transportation, use and clean-burning characteristics. The chief use
of ethane is in the chemical industry in the production of Ethene
(ethylene) by steam cracking. In this simulation, obtained ethane
recovery percent based on Gas sub-cooled process (GSP) is 99.9 by
mole that is included 32.1% by using de-methanizer column and
67.8% by de-ethanizer tower. The outstanding feature of this process
is the novel split-vapor concept that employs to generate reflux for
de-methanizer column. Remain amount of ethane in export gas cause
rise in gross heating value up to 36.66 MJ/Nm3 in order to use in
industrial and household consumptions.
Abstract: Bubble generation was observed using a high-speed
camera in subcooled flow boiling at low void fraction. Constant heat
flux was applied on one side of an upward rectangular channel to
make heated test channel. Water as a working fluid from high
subcooling to near saturation temperature was injected step by step to
investigate bubble behavior during void development. Experiments
were performed in two different pressures condition close to 2bar and
4bar. It was observed that in high subcooling when boiling was
commenced, bubble after nucleation departed its origin and slid
beside heated surface. In an observation window mean release
frequency of bubble fb,mean, nucleation site Ns and mean bubble
volume Vb,mean in each step of experiments were measured to
investigate wall vaporization rate. It was found that in proximity of
PNVG vaporization rate was increased significantly in compare with
condensation rate which remained in low value.