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Issue
1, Volume 3, January 2008
Title of the Paper: Conservative
Averaging and Finite Difference Methods for Transient Heat Conduction in 3D
Fuse
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Authors: Raimonds
Vilums, Andris Buikis
Abstract: Three-dimensional mathematical model of the automotive fuse is
considered in this paper. Initially, partial differential equations of the
transient heat conduction are given to describe heat-up process in the fuse.
Conservative averaging method is used to obtain analytical approximation of
these equations by the system of three ordinary differential equations.
Finite difference scheme is given if conservative averaging procedure is
stopped one step before, i.e., after 1D problem of partial differential
equations is obtained.
Keywords:
Heat conduction, Quasi-linear, Transient process, Three-dimensional,
Analytical reduction, Conservative averaging, Finite difference scheme.
Title of the Paper: Heat
Exchanger Exergetic Lifecycle Cost Optimization using Evolutionary Algorithms
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Authors: Liaquat Ali
Khan, Ali El-Ghalban
Abstract: Considering lifecycle cost analysis during the design phase of
thermal systems gives the design effort more worth. Furthermore thermodynamic
exergetic optimization is a proven useful method for determining the most
lifecycle cost optimal design of thermal systems for given thermodynamic
constraints. The most thermodynamic efficient heat exchanger design basing on
first law analysis may not be the better method for economic lifecycle cost
estimation of a heat exchanger. Nevertheless, including the second law
(exergetic) analysis in the lifecycle cost optimization technique will
definitely result in a thermodynamic efficient and heat exchanger design. In
this study lifecycle cost optimization procedure for shell and tube heat
exchanger has developed. The total cost includes capital and operating costs,
which are the components of objective function. The study searches for the
optimum cost if they exist, by doing the optimum first the parametric study
based on both sizing and rating problems. The study also searches for the
optimum (minimum cost) using the evolutionary method of optimization, and
results are confirmed using genetic optimization method, direct search method
and simplex method. Evolutionary Optimization has recently experienced a
remarkable growth. New concepts, methods and applications are being
continually proposed and exploited to provide efficient tools for solving a
variety of optimization problems. These techniques include Genetic
Algorithms, Genetic Programming, Evolutionary Programming and Evolution
Strategies among others, all of which have inspired by restricted models of
natural evolution. Cost of the heat exchanger has been optimized basing on
different constraints, like length, shell diameter, tube pitch etc.
Keywords:
heat exchanger, operating cost, optimization, entropy generation, exergy
destruction, thermodynamics, evolutionary method.
Title of the Paper: Computational
Fluid Dynamic Modeling of Nickel/Metal Hydride (Ni/MH) Battery during Charge
Cycle
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Authors: Nabi Jahantigh,
Ebrahim Afshari
Abstract: A three-dimensional mathematical model containing temporal and
spatial coordinates with variable heat generation rates and temperature
gradients across the battery is presented for analyzing the thermal behavior
and obtaining the internal temperature profile of cylindrical Ni/MH battery.
This model is performed to investigate the effects of thermal environment on
battery electrochemical and thermal behaviors under various charging
conditions. The governing equations are discretized using a finite volume
based finite difference method and solved using a computational fluid dynamic
code. Results shown that under the forced convection, the increase of the
heat transfer coefficient can decrease the battery temperature, however, lead
seriously to the less uniform temperature profile across the battery. The
cell temperature rise is significant when the cell is charged at high rates
and under poor cooling conditions, primarily due to the oxygen reactions
occurring near the end of full charge. Overcharge can result in an
increasingly higher temperature rise and a steeper temperature gradient
within a battery.
Keywords:
Ni/MH Battery; Thermal Analysis; Heat Transfer Coefficient, Charge, CFD.
Issue
2, Volume 3, April 2008
Title of the Paper: Computer Simulation of Heat and
Mass Transfer in Permeable Media
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Authors: Marcel Rosca,
Miklos Antics, Kostas Karytsas
Abstract: The University of Oradea had a research program on power generation
from low enthalpy geothermal energy, before it became a partner in the
LOW-BIN project, in which it is intended to build two demonstration units for
power generation using geothermal water with about 85°C and slightly over
100°C. For this reason, it was considered interesting to built a numerical
model of the well and surrounding rock to simulate the heat and mass
transfer. The paper briefly presents the model setup, its calibration, and
some simulation results.
Keywords:
geothermal, modeling, simulation, TOUGH2.
Issue
3, Volume 3, July 2008
Title of the Paper: The
Stability of the Operating Parameters of Rocket Engine with Solid Propellant
for Low Pressure
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Authors:
Teodor-Viorel Chelaru,
Adrian-Viorel Coman
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 engine with solid
propellant (RESP). The model results will be compared with experimental
results and the quality of the model will be evaluated. The study of
operating stability RESP 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 eigenvalue of the stability
matrix. The results are analyzed for a functional rocket engine at low
pressure, which has the combustion chamber made of cardboard, engine used for
anti-hailstone rocket. Two representatives cases will be take in to
consideration and analyzed from the point de view of burn parameters, one of
them for stable conditions and other for instable conditions. For both cases
a complete analysis will be done and the results will be compared. The
novelty of the work lies in the technique to tackle the stability problem for
the operation of rocket engines at low pressure, many of them representing
specific applications for civil destination.
Key-Words:
- Rocket, Engine, Solid propellant, Stability, Liapunov theory, Low pressure,
Anti-hailstone.
Title of the Paper: Numerical
Analysis of Coupled Radiation and Laminar Forced Convection in the Entrance
Region of a Circular Duct for Non-Grey Media: Entropy Generation
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Authors: Akram
Mazgar, Faycal Ben Nejma, Kamel Charrada
Abstract: The current study
analyses entropy generation
induced by coupled
forced convection and
thermal radiation heat
transfer, in circular tubes and for non-grey media. A laminar flow of over
heated water vapour in the entrance
region of the duct was investigated. A specially developed numerical model,
based on the finite- volume
technique, is used
for the solutions
of the governing
differential equations. The
radiative transfer coefficients
are deduced by
use of the
“Ray Tracing” method
through S4 directions, in
combination with the ″statistical narrow
band correlated-k″
(SNBCK) model. The
local entropy generation
distributions as well
as the overall
entropy generation in
the whole flow
fields are analyzed.
The developing of
velocity and temperature fields is also presented in this
study.
Keywords:
Entropy generation, Coupled convection and radiation, SNBCK model, non-grey
gas.
Title of the Paper: Heat
Capacity of Vertical Ground Heat Exchangers with Single U-Tube Installation in
the Function of Time
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Authors: Laszlo
Garbai, Szabolcs Mehes
Abstract: - One of the major problems of ensuring optimal working of ground
source heat pump systems is a heat transfer around vertical ground heat
exchanger. The working of vertical U-tube can be understood as a heat
exchanger between the ground and the heat carrying medium. In our case this
heat carrying medium is fluid, which transfers the extracted heat from the
ground to the heat pump. In winter we extract heat from the ground and in
summer we transfer heat to the ground. In our paper we propose a simple
calculation model to calculate the temperature change and the thermal
resistance in vertical ground heat exchangers with single U-tube
installation. We made calculations to obtain the amount of extractable heat
from the U-tube in the function of different mass flow. We did these
calculations for several periods of time, 1 day, 1 year, 10 years. We found
that the amount of extractable heat in winter and in summer is between 10 –
80 % in the function of mass flow, and with elapsing time its values decline.
Key-words:
- heat pump, U-tube, heat transfer, heat flow, thermal resistance, system
theory.
Title of the Paper: Research
on Static and Dynamic Heat Balance of the Human Body
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Authors:
H. C. Laszlo Banhidi, Laszlo
Garbai, Imrich Bartal
Abstract: This paper attempts to give a brief summary of the concept,
objectives and research methodology of comfort theory and, in particular,
thermal comfort for international building service engineers. It also
provides an overview of the findings of international research and the goals
of ongoing Hungarian projects (mainly carried out at the Department of
Building Service Engineering and Process Engineering at the Budapest
University of Technology and Economics). Moreover, the importance of comfort
theory and its application by engineers will be highlighted. We intend to
present the basic equations of the classical comfort theory, the equations of
the human body’s static heat balance, and the so called comfort equation as
well as its sensitivity depending on the thermic parameters of the microclimate.
The PMV expression describing the thermal comfort of the human body and its
sensitivity, derivatives and cross-derivatives is emphasized, too. The
concept of dynamic thermal sensation and the possibilities of its research is
going to be introduced, which is possible only through the presentation of
system theory, system dynamics and regulation theory.
Keywords:
Thermal Comfort, Static and Dynamic Heat Balance, Thermal Sensation, Human
Body.
Issue
4, Volume 3, October 2008
Title of the Paper: Comparison
of Calculation Methods and Models in Software for Computer Graphics and
Radioactive Heat Exchange
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Authors: Konrad
Domke
Abstract: The paper describes the physical backgrounds for modeling in visualization
using computer graphics software and in programs of radiative heat exchange.
Physical phenomena in both cases (generation, propagation, reflection and
absorption of light and radioactive heat flux) are quite similar, provided
with basic equations, typical simplification assumptions and the most
frequently applied methods of resolving such issues. Various models applied
in radioactive heat transfer and computer graphics software are compared. The
similarity and differences of algorithms for both tasks are determined and
replaceability conditions are enumerated. Formulas are provided to convert
thermal boundary values (temperature and power density) into luminous or radiant
quantities (luminance) and vice versa. A possible scope of shared
computations is also outlined.
Keywords:
computer graphics, radiative heat transfer, rendering, modeling, radiosity,
ray tracing, boundary conditions.
Title of the Paper: Temperature Determination in
Hydrotechnical Works as a Variable of the Energy Change Between Air and
Environment
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Authors: Dan
Codrut Petrilean, Florin Dumitru Popescu
Abstract: Hydro energetic works represent the major climate and ventilation
problems in the rooms where they are made. The air temperature of these rooms
is determined by two elements: the warmth that emanates from the massif,
especially in great depths, and the humidity of air, which is seldom close to
saturation. This paper studies these two elements solving the problem of
parameter interaction (temperature - humidity) from an analytical point of
view. The analytically obtained equations are experimentally validated
through a case study.
Key
words: - mass transfer coefficient, humidity balance, temperature variation
on lineal meter per hydro technical work, hydro-energetically installations,
real gases, convection coefficient.
Title of the Paper: Investigation
and Influence of Indoor Air Quality on Energy Demand of Office Buildings
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Authors: Dan
Laszlo Kajtar, Tamas Hrustinszky
Abstract: - In office buildings occupants do high intensity intellectual work
in eight hours. Quality and quantity of completed tasks are elementary
influenced by indoor comfort, particularly thermal environment and indoor air
quality. Investigation of indoor air quality has brief history, although it
is getting more important issue nowadays. At Department of Building Service
Engineering and Process Engineering, research work has been carried out as
industrial assignments as well as tenders, sponsored by Hungarian Scientific
Research Fund. For indoor air quality examination a laboratory state has been
developed. Several materials have been evaluated concerning emission rate and
its effect on indoor air quality. In the course of research, naive panels
have been adopted, using Fanger (-1;+1) and Hedonic scale. Improved indoor
air quality require increased fresh air rate, hereby energy demand of
building become higher. Therefore we have dealt with energy demand influenced
by indoor air quality as well.
Key-Words:
- Indoor air quality, fresh airflow rate, HVAC system.
Title of the Paper: Investigation of Combined Effects
for the Modelling of Thermal Comfort Conditions in Buildings
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Authors: Lajos
Barna, Edit Barna
Abstract: - The purpose of HVAC appliances is to provide a comfortable
environment and set the conditions for efficient work. The enhancement of
buildings’ energy performance puts emphasis on meeting the comfort
requirements indoors, as the acceptable environments have to be provided from
less energy. The comfort of the occupant is determined by the heat exchange
between his body and his indoor environment. There are four local discomfort
parameters that may cause discomfort on certain body parts even if whole body
thermal comfort conditions are met. To help the modelling of thermal comfort
conditions in buildings, on one hand we investigated, through human subject
experiments, the combined effect of two discomfort parameters that are
simultaneously present in the indoor space. Another modeling method is
introduced in the second part of the paper where we show the results of CFD modeling
of possible discomfort caused by natural ventilation required for air supply
of gas appliances.
Key-Words: - Air supply, CFD method,
Numerical modeling, Human subject experiment, Local discomfort.
Title of the Paper: A Mathematical Approach to Estimate
Air Rate in a Heating Furnace.
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Authors: Minea
Alina Adriana
Abstract: - Heat transfer is extremely important in a wide range of materials
processing techniques. Therefore, it is important to understand these flows
and develop methods to minimize or control their effects. The transport in
furnaces and ovens used for heat treatment strongly influence the quality of
the product. However, quantitative information on the dependence of product
quality, process control and optimization on the thermal transport is often
unavailable. Research in thermal materials processing is largely directed at
the basic processes and underlying mechanisms, physical understanding,
effects of different transport mechanisms and physical parameters, general
behavior and characteristics, and the thermal process undergone by the
material. It is usually a longterm effort, which leads to a better
quantitative understanding of the process under consideration. However, it can
also provide inputs, which can be used for design and development. In order
to develop an appropriate mathematical model for a given materials processing
system, several idealizations and simplifications were made to make the
problem amenable to an analytical solution. A general procedure, which
includes considerations of transient versus steady-state transport, number of
spatial dimensions needed, neglecting of relatively small effects,
idealizations such as isothermal or uniform heat flux conditions, and
characterization of material properties, may be adopted to obtain the usual
simplifications in analysis. In addition, the simplifications and
approximations that lead to a mathematical model also indicate the dominant
variables in a problem. This helps in developing efficient physical or
experimental models. This paper focuses on the link between basic research on
the underlying transport mechanisms and the engineering aspects associated
with the process and the system. The results are focused on mathematical interpretation
of the heat transfer processes that occur in industrial heating equipments.
These are the bases for future researches regarding simulation and
experimental models.
Key-words: - Air rate, Convection, Furnace,
Heating, Mathematical model, Materials processing
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