Abstract: The aim of the performed work is to establish the 2D
and 3D model of direct unsteady task of sample heat treatment by
moving source employing computer model on the basis of finite
element method. Complex boundary condition on heat loaded sample
surface is the essential feature of the task. Computer model describes
heat treatment of the sample during heat source movement over the
sample surface. It is started from 2D task of sample cross section as a
basic model. Possibilities of extension from 2D to 3D task are
discussed. The effect of the addition of third model dimension on
temperature distribution in the sample is showed. Comparison of
various model parameters on the sample temperatures is observed.
Influence of heat source motion on the depth of material heat
treatment is shown for several velocities of the movement. Presented
computer model is prepared for the utilization in laser treatment of
machine parts.
Abstract: This work deals with the problem of MHD mixed
convection in a completely porous and differentially heated vertical
channel. The model of Darcy-Brinkman-Forchheimer with the
Boussinesq approximation is adopted and the governing equations are
solved by the finite volume method. The effects of magnetic field and
buoyancy force intensities are given by the Hartmann and Richardson
numbers respectively, as well as the Joule heating represented by
Eckert number on the velocity and temperature fields, are examined.
The main results show an augmentation of heat transfer rate with the
decrease of Darcy number and the increase of Ri and Ha when Joule
heating is neglected.
Abstract: This paper presents the result of an experimental
investigation regarding the use of Fe2O3 nanoparticles added to
kerosene as a working fluid, under magnetic field for Copper
Oscillating Heat pipe with inclination angle of 0°(horizontal), 15°,
30°,45°, 60°,75° and 90° (vertical). The following were examined;
measure the temperature distribution and heat transfer rate on
Oscillating Heat Pipe (OHP), with magnetic field under different
angles. Results showed that the addition of Fe2O3 nanoparticles under
magnetic field improved thermal performance of OHP especially in
75°.
Abstract: Radiative heat transfer in participating medium was
carried out using the finite volume method. The radiative transfer
equations are formulated for absorbing and anisotropically scattering
and emitting medium. The solution strategy is discussed and the
conditions for computational stability are conferred. The equations
have been solved for transient radiative medium and transient
radiation incorporated with transient conduction. Results have been
obtained for irradiation and corresponding heat fluxes for both the
cases. The solutions can be used to conclude incident energy and
surface heat flux. Transient solutions were obtained for a slab of heat
conducting in slab and by thermal radiation. The effect of heat
conduction during the transient phase is to partially equalize the
internal temperature distribution. The solution procedure provides
accurate temperature distributions in these regions. A finite volume
procedure with variable space and time increments is used to solve
the transient radiation equation. The medium in the enclosure
absorbs, emits, and anisotropically scatters radiative energy. The
incident radiations and the radiative heat fluxes are presented in
graphical forms. The phase function anisotropy plays a significant
role in the radiation heat transfer when the boundary condition is
non-symmetric.
Abstract: Thermal enhancement of a single mini channel in
Proton Exchange Membrane Fuel Cell (PEMFC) cooling plate is
numerically investigated. In this study, low concentration of Al2O3 in
Water - Ethylene Glycol mixtures is used as coolant in single channel
of carbon graphite plate to mimic the mini channels in PEMFC
cooling plate. A steady and incompressible flow with constant heat
flux is assumed in the channel of 1mm x 5mm x 100mm. Nano
particle of Al2O3 used ranges from 0.1, 0.3 and 0.5 vol %
concentration and then dispersed in 60:40 (water: Ethylene Glycol)
mixture. The effect of different flow rates to fluid flow and heat
transfer enhancement in Re number range of 20 to 140 was observed.
The result showed that heat transfer coefficient was improved by
18.11%, 9.86% and 5.37% for 0.5, 0.3 and 0.1 vol. % Al2O3 in 60:40
(water: EG) as compared to base fluid of 60:40 (water: EG). It is also
showed that the higher vol. % concentration of Al2O3 performed
better in term of thermal enhancement but at the expense of higher
pumping power required due to increase in pressure drop
experienced. Maximum additional pumping power of 0.0012W was
required for 0.5 vol % Al2O3 in 60:40 (water: EG) at Re number 140.
Abstract: In this numerical work, mixed convection and entropy
generation of Cu–water nanofluid in a lid-driven square cavity have
been investigated numerically using the Lattice Boltzmann Method.
Horizontal walls of the cavity are adiabatic and vertical walls have
constant temperature but different values. The top wall has been
considered as moving from left to right at a constant speed, U0. The
effects of different parameters such as nanoparticle volume
concentration (0–0.05), Rayleigh number (104–106) and Reynolds
numbers (1, 10 and 100) on the entropy generation, flow and
temperature fields are studied. The results have shown that addition
of nanoparticles to the base fluid affects the entropy generation, flow
pattern and thermal behavior especially at higher Rayleigh and low
Reynolds numbers. For pure fluid as well as nanofluid, the increase
of Reynolds number increases the average Nusselt number and the
total entropy generation, linearly. The maximum entropy generation
occurs in nanofluid at low Rayleigh number and at high Reynolds
number. The minimum entropy generation occurs in pure fluid at low
Rayleigh and Reynolds numbers. Also at higher Reynolds number,
the effect of Cu nanoparticles on enhancement of heat transfer was
decreased because the effect of lid-driven cavity was increased. The
present results are validated by favorable comparisons with
previously published results. The results of the problem are presented
in graphical and tabular forms and discussed.
Abstract: Operation enhancement in an air cooler depends on
rate of heat transfer, and pressure drop. In this paper for a given heat
duty, study of the effects of FPI (Fin Per Inch) and fin type (circular
and hexagonal fins) on heat transfer, and pressure drop in an air
cooler in Iran, Arvand petrochemical. A program in EES
(Engineering Equations Solver) software moreover, Aspen B-JAC
and HTFS+ softwares are used for this purpose to solve governing
equations. At first the simulated results obtained from this program is
compared to the experimental data for two cases of FPI. The effects
of FPI from 3 to 15 over heat transfer (Q) to pressure drop ratio
(Q/Δp ratio). This ratio is one of the main parameters in design, and
simulation heat exchangers. The results show that heat transfer (Q)
and pressure drop increase with increasing FPI steadily, and the Q/Δp
ratio increases to FPI=12 and then decreased gradually to FPI=15,
and Q/Δp ratio is maximum at FPI=12. The FPI value selection
between 8 and 12 obtained as a result to optimum heat transfer to
pressure drop ratio. Also by contrast, between circular and hexagonal
fins results, the Q/Δp ratio of hexagonal fins more than Q/Δp ratio of
circular fins for FPI between 8 and 12 (optimum FPI)
Abstract: During welding or flame cutting of metals, the
prediction of heat affected zone (HAZ) is critical. There is need to
develop a simple mathematical model to calculate the temperature
variation in HAZ and derivative analysis can be used for this purpose.
This study presents analytical solution for heat transfer through
conduction in mild steel plate. The homogeneous and nonhomogeneous
boundary conditions are single variables. The full field
analytical solutions of temperature measurement, subjected to local
heating source, are derived first by method of separation of variables
followed with the experimental visualization using infrared imaging.
Based on the present work, it is suggested that appropriate heat input
characteristics controls the temperature distribution in and around
HAZ.
Abstract: MHD chemically reacting viscous fluid flow towards
a vertical surface with slip and convective boundary conditions has
been conducted. The temperature and the chemical species
concentration of the surface and the velocity of the external flow are
assumed to vary linearly with the distance from the vertical surface.
The governing differential equations are modeled and transformed
into systems of ordinary differential equations, which are then solved
numerically by a shooting method. The effects of various parameters
on the heat and mass transfer characteristics are discussed. Graphical
results are presented for the velocity, temperature, and concentration
profiles whilst the skin-friction coefficient and the rate of heat and
mass transfers near the surface are presented in tables and discussed.
The results revealed that increasing the strength of the magnetic field
increases the skin-friction coefficient and the rate of heat and mass
transfers toward the surface. The velocity profiles are increased
towards the surface due to the presence of the Lorenz force, which
attracts the fluid particles near the surface. The rate of chemical
reaction is seen to decrease the concentration boundary layer near the
surface due to the destructive chemical reaction occurring near the
surface.
Abstract: This paper aims to study the heat transfer and fluid
flow characteristics of nanofluids used in spray cooling systems. The
effect of spray height, type of nanofluids and concentration of
nanofluids are numerically investigated. Five different nanofluids
such as AgH2O, Al2O3, CuO, SiO2 and TiO2 with volume fraction
range of 0.5% to 2.5% are used. The results revealed that the heat
transfer performance decreases as spray height increases. It is found
that TiO2 has the highest transfer coefficient among other nanofluids.
In dilute spray conditions, low concentration of nanofluids is
observed to be more effective in heat removal in a spray cooling
system.
Abstract: This paper presents a study on the effect of
second-order slip and jump on forced convection through a long
isothermally heated or cooled planar microchannel. The fully
developed solutions of thermal flow fields are analytically obtained on
the basis of the second-order Maxwell-Burnett slip and Smoluchowski
jump boundary conditions. Results reveal that the second-order term in
the Karniadakis slip boundary condition is found to contribute a
negative velocity slip and then to lead to a higher pressure drop as well
as a higher fluid temperature for the heated-wall case or to a lower
fluid temperature for the cooled-wall case. These findings are contrary
to predictions made by the Deissler model. In addition, the role of
second-order slip becomes more significant when the Knudsen
number increases.
Abstract: The present study applies the inverse method and
three-dimensional CFD commercial software in conjunction with the
experimental temperature data to investigate the heat transfer and fluid
flow characteristics of the plate-fin heat sink in a rectangular closed
enclosure. The inverse method with the finite difference method and
the experimental temperature data is applied to determine the
approximate heat transfer coefficient. Later, based on the obtained
results, the zero-equation turbulence model is used to obtain the heat
transfer and fluid flow characteristics between two fins. T0 validate
the accuracy of the results obtained, the comparison of the heat transfer
coefficient is made. The obtained temperature at selected
measurement locations of the fin is also compared with experimental
data. The effect of the height of the rectangular enclosure on the
obtained results is discussed.
Abstract: The development of transport systems has negative
impacts on the environment although it has beneficial effects on
society. The car policy caused many problems such as: - the
spectacular growth of fuel consumption hence the very vast increase
in urban pollution, traffic congestion in certain places and at certain
times, the increase in the number of accidents. The exhaust emissions
from cars and weather conditions are the main factors that determine
the level of pollution in urban atmosphere. These conditions lead to
the phenomenon of heat transfer and radiation occurring between the
air and the soil surface of any town. These exchanges give rise, in
urban areas, to the effects of heat islands that correspond to the
appearance of excess air temperature between the city and its
surrounding space. In this object, we perform a numerical simulation
of the plume generated by the cars exhaust gases and show that these
gases form a screening effect above the urban city which cause the
heat island in the presence of wind flow. This study allows us: 1. To
understand the different mechanisms of interactions between these
phenomena.2. To consider appropriate technical solutions to mitigate
the effects of the heat island.
Abstract: This work consists of a numerical simulation of
convective heat transfer in a vertical plane channel filled with a heat
generating porous medium, in the absence of local thermal
equilibrium. The walls are maintained to a constant temperature and
the inlet velocity is uniform. The dynamic range is described by the
Darcy-Brinkman model and the thermal field by two energy
equations model. A dimensionless formulation is developed for
performing a parametric study based on certain dimensionless groups
such as, the Biot interstitial number, the thermal conductivity ratio
and the volumetric heat generation, q '''. The governing equations are
solved using the finite volume method, gave rise to a multitude of
results concerning in particular the thermal field in the porous
channel and the existence or not of the local thermal equilibrium.
Abstract: This paper presents a computational study of steady
state three dimensional very high turbulent flow and heat transfer
characteristics in a constant temperature-surfaced circular duct fitted
with 900 hemispherical inline baffles. The computations are based on
realizable k-ɛ model with standard wall function considering the
finite volume method, and the SIMPLE algorithm has been
implemented. Computational Study are carried out for Reynolds
number, Re ranging from 80000 to 120000, Prandtl Number, Pr of
0.73, Pitch Ratios, PR of 1,2,3,4,5 based on the hydraulic diameter of
the channel, hydrodynamic entry length, thermal entry length and the
test section. Ansys Fluent 15.0 software has been used to solve the
flow field. Study reveals that circular pipe having baffles has a higher
Nusselt number and friction factor compared to the smooth circular
pipe without baffles. Maximum Nusselt number and friction factor
are obtained for the PR=5 and PR=1 respectively. Nusselt number
increases while pitch ratio increases in the range of study; however,
friction factor also decreases up to PR 3 and after which it becomes
almost constant up to PR 5. Thermal enhancement factor increases
with increasing pitch ratio but with slightly decreasing Reynolds
number in the range of study and becomes almost constant at higher
Reynolds number. The computational results reveal that optimum
thermal enhancement factor of 900 inline hemispherical baffle is
about 1.23 for pitch ratio 5 at Reynolds number 120000.It also shows
that the optimum pitch ratio for which the baffles can be installed in
such very high turbulent flows should be 5. Results show that pitch
ratio and Reynolds number play an important role on both fluid flow
and heat transfer characteristics.
Abstract: In this study, the experiments were carried out to
determine the best coolant for the quenching process among waterbased
silica, alumina, titania and copper oxide nanofluids (0.1 vol%).
A sphere made up off brass material was used in the experiments.
When the spherical test specimen was heated at high temperatures, it
was suddenly immersed into the nanofluids. All experiments were
carried out at saturated conditions and under atmospheric pressure.
After the experiments, the cooling curves were obtained by using the
temperature-time data of the specimen. The experimental results
showed that the cooling performance of test specimen depended on
the type of nanofluids. The silica nanoparticles enhanced the
performance of boiling heat transfer and it is the best coolant for the
quenching among other nanoparticles.
Abstract: The comprehensive CFD models have been used to
represent and study the heterogeneous combustion of biomass. In the
present work, the operation of a global flue gas circuit in the sugarcane
bagasse combustion, from wind boxes below primary air grate
supply, passing by bagasse insertion in swirl burners and boiler
furnace, to boiler bank outlet is simulated. It uses five different
meshes representing each part of this system located in sequence:
wind boxes and grate, boiler furnace, swirl burners, superheaters and
boiler bank. The model considers turbulence using standard k-ε,
combustion using EDM, radiation heat transfer using DTM with 16
ray directions and bagasse particle tracking represented by Schiller-
Naumann model. The results showed good agreement with expected
behavior found in literature and equipment design. The more detailed
results view in separated parts of flue gas system allows observing
some flow behaviors that cannot be represented by usual
simplifications like bagasse supply under homogeneous axial and
rotational vectors and others that can be represented using new
considerations like the representation of 26 thousand grate orifices by
144 rectangular inlets.
Abstract: Heat transfer due to forced convection of copper water
based nanofluid has been predicted by Artificial Neural network
(ANN). The present nanofluid is formed by mixing copper
nanoparticles in water and the volume fractions are considered here
are 0% to 15% and the Reynolds number are kept constant at 100.
The back propagation algorithm is used to train the network. The
present ANN is trained by the input and output data which has been
obtained from the numerical simulation, performed in finite volume
based Computational Fluid Dynamics (CFD) commercial software
Ansys Fluent. The numerical simulation based results are compared
with the back propagation based ANN results. It is found that the
forced convection heat transfer of water based nanofluid can be
predicted correctly by ANN. It is also observed that the back
propagation ANN can predict the heat transfer characteristics of
nanofluid very quickly compared to standard CFD method.
Abstract: This paper analyses the heat transfer performance and
fluid flow using different nanofluids in a square enclosure. The
energy equation and Navier-Stokes equation are solved numerically
using finite volume scheme. The effect of volume fraction
concentration on the enhancement of heat transfer has been studied
icorporating the Brownian motion; the influence of effective thermal
conductivity on the enhancement was also investigated for a range of
volume fraction concentration. The velocity profile for different
Rayleigh number. Water-Cu, water AL2O3 and water-TiO2 were
tested.
Abstract: A comprehensive CFD model is developed to
represent heterogeneous combustion and two burner designs of
supply sugar-cane bagasse into a furnace. The objective of this work
is to compare the insertion and burning of a Brazilian south-eastern
sugar-cane bagasse using a new swirl burner design against an actual
geometry under operation. The new design allows control the
particles penetration and scattering inside furnace by adjustment of
axial/tangential contributions of air feed without change their mass
flow. The model considers turbulence using RNG k-, combustion
using EDM, radiation heat transfer using DTM with 16 ray directions
and bagasse particle tracking represented by Schiller-Naumann
model. The obtained results are favorable to use of new design swirl
burner because its axial/tangential control promotes more penetration
or more scattering than actual design and allows reproduce the actual
design operation without change the overall mass flow supply.