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Issue
1, Volume 5, January 2010
Title of the Paper:
Stabilization Operation Region and Operational Variables Effect on a
Reciprocal Flow Burner
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Authors:
Valeri Bubnovich, Luis Henriquez, Catalina Diaz, Emilio Avila
Abstract: A reciprocal gas flow burner is computationally simulated for
obtaining its stable operation region in terms of equivalence ratio and
filtration velocity, for two energy losses configurations schemes. Equivalence
ratio and filtration velocity were considered over the range [0.1, 1.0] and
[0.25, 1.0] (m/s). The one-dimensional mathematical model consider that porous
media is made by alumina bolls of 5.6 mm diameter , which fill up a quartz
hollow cylinder of 5 cm diameter and 50 cm high. The mathematical model
includes total mass preservation laws, momentum and enthalpy for the solid as
for the gas. Combustion is modeled through global chemical reaction in one
step. Chemical kinetic of methane combustion is treated on the base of
Arrhenius approximation. It is considered besides that system heat transport
occurs at conditions without local thermal equilibrium and includes
convections mechanisms, conduction and thermal radiation. Lateral heat losses
from the system to environment through cylinder lateral surface were studied
at two scenarios: reactor coupled with and without heat exchangers.
Mathematical model are discretized by finite differences method through
implicit scheme and its solution reached by TDMA algorithm. Uniform grid with
801 nodes and time step Δt = 0.01 (s) gave solution independence. Results
demonstrated increased stabilization in temperature profile, thus increased
stabilization region for the reactor coupled with heat exchangers.
Keywords:
Reciprocal Flow Burner (RFB); porous media; filtration combustion; numerical
simulation
Title of the Paper: Heat
and Mass Transfer of a Non-Newtonian Fluid Flow over a Permeable Wedge in
Porous Media with Variable Wall Temperature and Concentration and Heat Source
or Sink
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Authors:
Ali J. Chamkha
Abstract: The problem of steady, laminar, coupled heat and mass transfer by
mixed convective flow of a non-Newtonian power-law fluid over a permeable
wedge embedded in a porous medium with variable surface temperature and
concentration and heat generation or absorption and wall transpiration effects
is considered. A mixed convection parameter for the entire range of
free-forced-mixed convection is employed and a set of non-similar equations
are obtained. These equations are solved numerically by an efficient implicit,
iterative, finite-difference method. The obtained results are checked against
previously published work for special cases of the problem and are found to be
in good agreement. A parametric study illustrating the influence of the
various physical parameters on temperature and concentration profiles as well
as the local Nusselt and Sherwood numbers is conducted. The obtained results
are illustrated graphically and the physical aspects of the problem are
discussed.
Keywords:
Mixed convection, porous media, heat and mass transfer, heat
generation/absorption, non-Newtonian fluid, wall transpiration
Title of the Paper:
Effects of Thermal Radiation and Free Convection Currents on the Unsteady
Couette Flow Between Two Vertical Parallel Plates with Constant Heat Flux at
one Boundary
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Authors:
M. Narahari
Abstract: An exact analysis of the natural convection in unsteady Couette flow
of a viscous incompressible fluid confined between two vertical parallel
plates in the presence of thermal radiation is performed. The flow is induced
by means of Couette motion and free convection currents occurring as a result
of application of constant heat flux on the wall with a uniform vertical
motion in its own plane while constant temperature on the stationary wall. The
fluid considered here is a gray, absorbing-emitting but non-scattering medium,
and the Rosseland approximation is used to describe the radiative heat flux in
the analysis. The dimensionless governing partial differential equations are
solved using Laplace transform technique. Numerical results for the velocity,
the temperature, the skin-friction, the Nusselt number, the volume flow rate
and the vertical heat flux are shown graphically. The effect of different
parameters like thermal radiation parameter, Grashof number, Prandtl number
and time are discussed. It is observed that the momentum and thermal boundary
layer thickness decreases owing to an increase in the value of the radiation
parameter. An increase in the Grashof number is found to increase the velocity
of air and water and to decrease the skin-friction at the moving plate.
Keywords:
Vertical channel, Natural convection, Couette flow, Constant heat flux,
Radiation
Issue
2, Volume 5, April 2010
Title of the Paper: Heat
Pumps – Efficient Heating and Cooling Solution for Buildings
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Authors:
Ioan Sarbu, Calin Sebarchievici
Abstract: In the actual economic and energetic juncture, the reduction of
thermal energy consumption in buildings became a major, necessary and
opportune problem, general significance. The heat pumps are alternative
heating installations more energy-efficient and unless pollutant if we make a
comparison with classic plants (liquid or gas fuel thermal boiler). This paper
presents the necessity to use heat pumps in buildings’ heating-cooling
systems, energy and economic indices of performance, a new underground water
heat pump system using a heat exchanger with special construction, tested in
laboratory and the possibility to obtain the better energy efficiency with
combined heating and cooling by heat pumps. Also, a case study presents the
solution for heating a living building with a water-to-water heat pump, energy
and economic advantages of this system.
Keywords:
Building heating/cooling, Renewable energy sources, Heat pumps, Heat pump
performances, “Geoterm” system, Energy and economic analysis
Title of the Paper:
Energetical Optimization of Central Heating Systems
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Authors:
Ioan Sarbu
Abstract: The main goal of the central heating design process is to obtain
appropriate thermal comfort minimising the investment and operational costs.
This scope could be theoretical realised with the available modern control
techniques. However practice has shown that, if the preconditions are not
fulfilled, the correct operation of the heating system could not be assured
even by the most sophisticated control equipment. Therefore, the control
elements could not fulfil their function if the warm water flow differs from
the designed value and the thermal comfort is not realised unless with higher
energy consumption. We can obtain heating systems with a higher stability and
energy efficiency decreasing in the same time the forward temperature and the
temperature drop. In this paper is studied the operation of unbalanced central
heating systems, and are analysed the thermal comfort and the energy
consumption. Also, are analysed the energy savings in heating systems with
reduced forward temperature, for different types of radiators taking into
account the thermal insulation of the distribution pipes. In this purpose are
developed some calculation models and the effects of thermal agent temperature
variation on the energy saving are illustrated by a numerical example.
Keywords:
Central heating systems, Hydraulic unbalanced operation, Thermal comfort,
Indoor temperature, Energy consumption, Low forward temperature, Energetical
analysis, Energy saving, Computational models
Issue
3, Volume 5, July 2010
Title of the Paper:
Numerical Simulation of Thermal Profile By Gas Tungsten Arc Welding Process in
Copper
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Authors:
A. Moarrefzadeh, M. A. Sadeghi
Abstract: In this paper the Gas Tungsten Arc Welding is studied and copper
temperature field is gained in this process. The thermal effect of arc that
specially depends on the shielding gases type and temperature field of it in
workpiece, is the main key of analysis and optimization of this process, from
which the main goal of this paper has been defined. Energy source properties
of GTA strongly depend on physical property of a shielding gas. In this paper,
carbon dioxide (CO2) was used as an alternative gas for its low cost. The
basic energy source properties of CO2 GTA were numerically predicted ignoring
the oxidation of the electrodes. It was predicted that CO2 GTA would have
excellent energy source properties comparable to that of He, Ar GTA.
Keywords:
Numerical simulation, Tungsten, Copper, Shielding gas, Argon, Helium, CO2,
GTAW
Title of the Paper:
Hyperbolic Heat Equation as Mathematical Model for Steel Quenching of L-shape
and T-shape Samples, Direct and Inverse Problems
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Authors:
Tabita Bobinska, Margarita Buike, Andris Buikis
Abstract: In this paper we develop mathematical model for 2D and 3D hyperbolic
heat equation and construct an analytical solution of inverse problem for thin
L-shape and T-shape samples. Solutions for both direct and inverse problems
are obtained in closed analytical form as 2nd kind iterative integral
equation, which is Fredholm integral equation with respect to space coordinate
and Volterra integral equation with respect to time.
Keywords:
Steel quenching, Hyperbolic heat equation, L-shape sample, T-shape sample,
Direct problem, Inverse problem, Exact solution, Integral equation
Title of the Paper: The
Effects of Suction and Injection on a Moving Flat Plate in a Parallel Stream
with Prescribed Surface Heat Flux
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Authors:
Norfifah Bachok, Anuar Ishak
Abstract: The effect of surface mass flux on a moving flat plate in a moving
fluid with prescribed surface heat flux is studied. The governing partial
differential boundary layer equations are first transformed into ordinary
differential equations before being solved numerically by a finite difference
method. The features of the flow and heat transfer characteristics for
different values of the governing parameters are analyzed and discussed. It is
found that dual solutions exist when the plate and the free stream move in the
opposite directions. The results indicate that the range of known dual
solutions increases with suction and decreases with injection and the rate of
heat transfer increases with increasing heat flux exponent parameter.
Keywords:
Heat transfer, Moving plate, Moving fluid, Boundary layer, Heat flux,
Suction/injection, Dual solutions
Title of the Paper:
Effecienty Solutions to Refresh the Air in Rooms with the Heat Releases
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Authors:
Marius-Constantin Popescu, Nikos E. Mastorakis, Jean-Octavian Popescu
Abstract: The paper focuses on modeling the phenomenon of air recirculation in
rooms with heat releases. Modeling highlights the connections existing between
climatic values (pressure-temperature) and allows the determining of an airing
constant used in describing the efficiency of a passively climatized room. In
the second part of this paper the authors propose efficient solutions to
remove heat from the room, using conventional air conditioning equipment.
Keywords:
Modeling and simulation, Heating systems, Location modes
Title of the Paper: The
Stability of Fire Extinguishing Rocket Motor
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Authors:
Teodor-Viorel Chelaru, Cristina Mihailescu, Ion Neagu, Marius Radulescu
Abstract: The aim of this paper consists in developing a model for realistic
calculation, but at the same time not a very complicated one, in order to
determine the operating parameters of a rocket motor with solid propellant
(RMSP). The model results will be compared with experimental data and the
quality of the model will be evaluated. The study of stability RMSP will be
made accordingly to Liapunov theory, considering the system of parametric
equations perturbed around the balance parameters. The methodology dealing
with the stability problem consists in obtaining the linear equations and the
verification of the eigenvalues of the stability matrix. The results are
analyzed for a functional rocket motor at low pressure, which has the
combustion chamber made of cardboard, motor used for fire extinguishing
rocket. The novelty of the work lies in the technique to tackle the stability
problem for the operation of rocket motors at low pressure, representing
specific applications for civil destination.
Keywords:
Rocket, Motor, Solid propellant, Stability, Liapunov theory, Low pressure,
Fire-extinguishing
Title of the Paper:
Experimental and Numerical Approach of the Thermal Conductivity of Building
Facade Materials
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Authors:
Monica Chereches, Catalin Popovici, Nelu-Cristian Chereches
Abstract: An experimental research has been conducted to assess the
thermo-physical properties of five building materials in both dry and moist
state: beech wood, autoclaved aerated concrete and brick, and in dry state for
expanded and extruded polystyrene. The objectives of the paper envisage the
measurement of the thermal conductivity of these materials through an unsteady
state method. The experimental method used in determining the thermal
conductivity is based on the principle of temperatures at the interface of two
homogeneous semi-infinite bodies of previously altogether different
temperatures. The advantage that this method provides lies mainly in the short
measuring time and the small temperature rise across the samples. The
experimental tests have been accomplished by numerical modeling by means of a
computational program based on the finite element method (FEM). The latter
have been conducted bidimensionally, under transient state conditions for
different lengths of the five materials in dry state. The numerical and
experimental results have shown a good agreement for the temperature of the
contact area.
Keywords:
Thermal conductivity, Contact temperature, Building materials, Finite element,
Determining method, Numerical modeling
Title of the Paper:
Upgrading of a Heating Plant in Central Heating System
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Authors:
Ioan Sarbu, Emilian Valea
Abstract: In the 7-th decade of the previous century it was designed the new
power station for Timisoara Romania. It was predicted to work with lignite. As
load fuel and sustain of flame fuel it was approved natural gas. The initial
profile of the Power Heating Station was: 2?120/150 MW turboalternator groups;
for industrial consumers 3?100 t/h steam boilers with 250 ?C and 15 bar;
thermal central for start steam boiler comprizing 4?10 t/h steam boiler with
300 °C and 16 bar. The main thermal agent, hot water for district heating of
the town had to be prepared in 2?100 Gcal/h (2?116 MW) hot water boiler.
During the power station construction, the consumers for 250 ?C and 15 bar
steam were no more, or they have changed their production structure. In 1988
began the thermal production of the new Heating Station/Plant, and only for
hot water. After 1990 the finances for 2?120/150 MW groups were stopped and
their construction also. As the hot water prepared in 2?100 Gcal/h hot water
boilers was not enough for district heating of the town, the steam pressure
was reduced from 15 to 6 bar, its temperature also and using heat exchangers
the Heating Plant could deliver more hot water for district heating of the
town. So other 225 Gcal/h (261 MW) were produced. The paper presents the
solution for Heating Plant in order to produce enough hot water, electric
energy for inner consumption being assured in the same time. Also, the effects
on environmental protection and on the heat market in system are analized.
Keywords:
Heat and power cogeneration, Turbine, Steam, Hot water, Heat exchanger,
Electric energy, Thermal energy, Energy savings, Environmental protection,
Heat market
Title of the Paper:
Energy Analysis of Low Temperature Heating Systems
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Authors:
Ioan Sarbu
Abstract: The assurance of the heat demand for millions of buildings equipped
with centralized heating systems imposes equipment with high performances not
only in the heat generation but also in the distribution of thermal energy.
One way to obtain higher efficiency of the heating systems is to work on
reduced temperature, which means that the temperatures throughout the system
are lowered as much as possible. In this system the heat losses will decrease,
the consumers will benefit a higher thermal comfort and it is possible to use
with higher efficiency the renewable energy sources. The system must be
controlled and optimized in correspondence with the ever-changed heat demand.
In this paper are analysed the energy savings in heating systems with reduced
forward temperature, for different types of radiators taking into account the
thermal insulation of the distribution pipes. In this purpose are developed
some calculation models and the effects of thermal agent temperature variation
on the energy saving are illustrated by a numerical example.
Keywords:
Central heating systems, Low forward temperature, System control, Radiator
heating, Floor heating, Energetical analysis, Energy saving, Computation
models
Title of the Paper: Study
Regarding the Influence of the Plate Heat Exchanger Configuration on its
Performance
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Authors:
Roxana Grigore, Sorin Popa, Aneta Hazi, Gheorghe Hazi
Abstract: The paper presents an analysis related to the correlation between
the performance of plate heat exchanger and its number of plates. There are
take in consideration eight different cases obtained by changing the plate’s
number of a heat exchanger and using finite element method are performed
numerical simulations of fluid flow distribution. Numerical results are
presented for 1 pass -1pass counter-flow plate heat exchanger. These results
are shown in terms of cold water temperature at the outlet, hot water
temperature at the outlet, exchanger effectiveness and log – mean temperature
difference as functions of the heat capacity ratio and the number of plates.
Keywords:
Plate heat exchanger, finite element method, mesh, fluid flow, number of
plates, heat exchanger effectiveness, log mean temperature difference
Title of the Paper:
Research Regarding the Variation of the Cost of Fluido-Dynamic Lost Energy on
a Pneumatic Network of Compressed Air
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Authors:
Nan Marin Silviu, Petrilean Dan Codrut, Marian Dumitru
Abstract: This paper provides an in-depth theoretical and practical
presentation of the energy cost variation and it is about the fluido-dynamic
lost energy during an hour on a meter of pneumatic network. This study follows
two steps. First, we calculate the value matrix of the cost of fluido-dynamic
lost energy for two extreme values of the coefficient of proportionality
depending on the diameter of the compressed air pipe and also we determine the
dependency of the cost of fluido-dynamic lost energy for extreme values of the
coefficient of proportionality on the diameter of the network. Then, on the
second step of the study, we will present the dependency of the cost of
fluido-dynamic lost energy for the extreme values of the coefficient of
proportionality on the volumetric flow of compressed air.
Keywords:
Energy saving, cost, fluido-dynamic lost energy, network, pressure loss,
determination application
Title of the Paper:
Biogas Production through Anaerobic Fermentation, based on Different Waste
Biomass
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Authors:
Adrian Eugen Cioabla, Ioana Ionel
Abstract: The paper presents a comparative experimental analysis between
different types of biomass residues used for biogas production, during their
behavior along the anaerobic fermentation process. The comparison is achieved
using as parameter the biogas quality and quantity which are produced, using
different available agricultural and wood residues: beech dust, linden dust,
corn waste and a mixture composed by corn and mix of maize and corn waste. All
the measurements were made on a lab scale pilot installation.
Keywords:
Biomass residues, anaerobic fermentation, pilot installation, biogas, RES
Title of the Paper:
Dufour and Soret Effects on Heat and Mass Transfer in a Micropolar Fluid in a
Horizontal Channel
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Authors:
Faiz Awad, Precious Sibanda
Abstract: The problem of free convection of heat and mass in micropolar fluid
in a channel subject to cross diffusion (namely the Soret and Dufour effects)
is presented. The effect of small and large Peclet numbers on the temperature
and concentration profiles is determined while the effects of various
parameters such as the Reynolds number, the coupling parameter and the spin
gradient viscosity parameter on the fluid properties are determined and shown
graphically. The study uses the homotopy analysis method to find approximate
analytical series solutions for the governing system of nonlinear differential
equations. The analytical results are validated using the Matlab bvp4c
numerical routine.
Keywords:
Micropolar fluid, heat transfer, mass transfer, Peclet numbers, homotopy
analysis method
Title of the Paper:
Blow-up Solutions for a Degenerate Parabolic Problem with a Localized
Nonlinear Term
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Authors:
P. Sawangtong, B. Novaprateep, W. Jumpen
Abstract: In this article, we establish a blow-up solution and the blow-up set
of such a solution of the degenerate parabolic problem with a localized
nonlinear term: 0txx where and are given functions and 0 is a fixed point in
the domain of In order to ensure the occurrence for blow-up in finite time,
the sufficient condition to blow-up in finite time is shown. We furthermore
study the particular problem of the previous problem: 0 quxβ where andq are
specified constants. Under suitable assumptions on we obtain the same results
as before.
Keywords:
Blow-up in finite time, Blow-up set, Complete blow-up, Localized nonlinear
terms, Semilinear parabolic problems
Issue
4, Volume 5, October 2010
Title of the Paper:
Theoretical and Numerical Analysis of Fuel Droplet Vaporisation at High
Temperatures
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Authors:
Habib Merouane, Abdelhamid Bounif
Abstract: In our work we present a theoretical analysis and numerical solution
of fuels droplets vaporisation n-alkaline (n-heptane, n-octane, n-nonane and
n-decane) that evaporate slowly in air to stagnant conditions, ambient
temperature and pressure and at different temperatures. The results show that
liquid fuel droplets which have the lowest molar mass vaporize quickly.
Vaporisation rate becomes more significant when environment temperature
increases. This is confirmed by the experimental results of M.Birouk (1996)
and C.Morin (1999). Average and instantaneous vaporisation rates have been
estimated from D2 law at temperatures varying from 473 to 673 K and at
atmospheric pressure.. The main objective of our study is to better understand
the process of vaporizing droplets sprays, to better prepare the gas mixture
in the combustion chambers and improve the combustion efficiency to reduce
pollutant formation and of such as unburned carbon monoxide and NOx.
Keywords:
Droplets vaporisation, fuel droplet, droplets
Title of the Paper:
Radon-222 Accumulation in Air Confined by Phosphogypsum-Bearing Boundaries:
Simulation for Distinct Exhaling Scenarios
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Authors:
Jose A. Rabi, Nivaldo C. Silva
Abstract: Understanding radon-222 exhalation from phosphogypsum-bearing
materials and its accumulation in confined air is fundamental for radiation
exposure assessment and radiological protection design based on human health
risks. Despite evoking time dependence, zero-order models with respect to
space assume uniform distribution of radon-222 activity. If detailed
description is desired, one must consider spatial dependence as well.
Accordingly, this work proposes a time-varying two-dimensional
diffusion-dominant model where radon- 222 self-decay is accounted as a sink
term in the governing differential equation while its exhalation from
boundaries is modelled as Neumann-type boundary condition. By adapting an
existing academic simulator for transport phenomena, distinct exhaling
scenarios are numerically simulated and discussed bearing in mind the failure
of the aforesaid homogeneous distribution hypothesis as well as future
extensions of the simulator.
Keywords:
Mass transfer, modelling, simulation, phosphogypsum, radon-222, radiological
protection
Title of the Paper:
Modeling of a Thermoelement with Segmented Legs for RTG Applications
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Authors:
M. Lazard, J. P. Roux, A. A. Pustovalov, H. Scherrer
Abstract: This study deals with the modelling of segmented thermoelements for
Radioisotopic Thermoelectric Generator. One of the more important quantities
for a thermoelement as well as for any device is its efficiency. As far as a
thermoelement with segmented legs is concerned, it is not an easy task to
evaluate its efficiency. In a first step, approximations are made and the
values of the thermophysical and thermoelectrical parameters are assumed to be
constant (mean values are used to perform calculi). Then a more complete
modelling is proposed: the thermo dependence of the parameters is taken into
account. The compatibility of the thermoelectric materials is checked and an
optimization is be made in order to determine the value of the relative
current density that allows to maximize the efficiency of the thermoelement.
Keywords:
Modelling, Radioisotopic Thermoelectric Generator, segmented legs, efficiency
Title of the Paper:
Volumetric and Wall Non Grey Gas Entropy Creation in a Cylindrical Enclosure
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Authors:
Faycal Ben Nejma, Akram Mazgar, Kamel Charrada
Abstract: We analyse a numerical computation of entropy generation by
radiative heat transfer through an emitting-absorbing non-grey gas, confined
in a cylindrical enclosure. The “statistical narrow band correlated-k” model
is associated to the “Ray Tracing” method to deduce the radiative properties
of the gas and to solve the radiative transfer equation. We present the impact
of boundary conditions and cylinder dimensions on the entropy generation.
Keywords:
Entropy, Emission, Absorption, Non-grey gas, Ray tracing, SNBCK model
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