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Issue
1, Volume 4, January 2009
Title of the Paper:
Optimization of Thermal Components in a Stirling Engine
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Authors:
Jafar Zarinchang, Amin Yarmahmoudi
Abstract: Stirling engines are known as high efficiency engines. In theory
their efficiency is equal to Carnot efficiency but in practice due to some
reasons their efficiency reduces. One of the most important sources of
efficiency reductions is imperfect heat transfer. In this way, heat exchangers
are key components in the Stirling engines. There may be three or four heat
exchangers in the Stirling engine system, these heat exchangers are Heater,
Regenerator and Cooler which exchange heat to and from the engine. The design
and configuration of these heat exchangers effect on engine performance. The
optimization of these parts for a 20 kw Stirling engine is shown in this
paper.
Keywords:
Stirling Engine, Cooler, Heater, Regenerator, Heat Exchanger, Optimization,
Performance
Title of the Paper:
Thermal Parameters of Heavy-current Lines in the Process of Formulation of
Optimal Design of these Devices
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Authors:
Karol Bednarek
Abstract: The paper presents a mathematical model of calculation of
electrodynamic parameters in the constructions of three-phase heavy-current
lines (power busducts). Particular attention has been paid to determining
temperatures of the system. For purpose of electrodynamic analysis the method
of integral equations has been used. The presented calculation model was used
in the process of optimization of the designs of heavy-current busducts, aimed
at minimization of the investment and operational costs of these devices.
Genetic algorithms were used for the optimization purpose. Thermal calculation
was carried out for a definite physical system. The effect of predefined
electrodynamic parameters on the optimization results has been analyzed.
Keywords:
Thermal calculation, electrodynamical parameters, heavy current lines,
optimization, genetic algorithms, power busducts
Issue
2, Volume 4, April 2009
Title of the Paper:
Unsteady Mixed Convection Heat and Mass Transfer Past an Infinite Porous Plate
with Thermophoresis Effect
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Authors:
Tariq Al-Azab
Abstract: An analysis has been developed in order to study the unsteady mixed
convection flow of an incompressible fluid past an infinite vertical porous
plate with thermophorisis particle deposition effect. The governing equations
are solved numerically using an implicit finite difference technique. The
selected numerical method is validated by comparing the results with the
analytical solutions. Numerical results for the details of the velocity
profiles which are shown on graphs have been presented. It is found that the
steady state values of thermophoretic deposition velocity reached faster as
the thermophoresis constant decreased and the temperature ratio increased.
Keywords:
Mixed convection, Heat and mass transfer, Unsteady, Thermophorisis, Plate
Title of the Paper:
Influence of Key Properties of Pongamia Biodiesel on Performance Combustion
and Emission Characteristics of a DI Diesel Engine
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Authors:
Ch. Satyanarayana, P. V. Rao
Abstract: The purpose of this study is to examine the influence of key
properties of pongamia biodiesel on engine performance, combustion, and
emission characteristics of direct injection diesel engine. The key properties
of the pongamia biodiesel such as viscosity, density, bulk modulus, calorific
value, iodine value, cetane number, saturation% and oxygen% are considered for
this study. Experiments were conducted in a naturally aspirated, single
cylinder, four-stroke, stationary, water cooled, constant rpm, in-line
(pump-high pressure tube-fuel injector) direct injection diesel engine with
pongamia biodiesel (with and without preheating), and petroleum diesel as
fuels. The performance was evaluated in terms of fuel consumption, brake
specific energy consumption, and thermal efficiency. A significant improvement
in thermal efficiency was observed with preheated biodiesel. The peak
pressures and peak heat release rates for biodiesel was slightly higher than
diesel fuel. The high peak pressures of the biodiesel are probably due to
dynamic injection advance caused by its higher bulk modulus. The higher values
of peak heat release rates indicate better premixed combustion with the
biodiesel. However, the peak pressures for preheated biodiesel decreases due
to late injection and faster evaporation of the fuel. It was observed that at
full load the nitric oxide emission of biodiesel is increased by 6 %. The
hydrocarbon emissions of the biodiesel are very low and are reduced up to 32 %
as compared to that of diesel fuel. There is a significant reduction in all
exhaust gaseous emissions. Also a considerable reduction in nitric oxide
emission is observed with preheated biodiesel due to change in premixed
combustion phase. However when the preheated biodiesel is used, the smoke
emission was increased due to prolonged combustion (diffusion) at lower
viscosity. A considerable reduction in carbon monoxide emission as also
observed with the preheated biodiesel.
Keywords:
Pongamia, properties, bulk modulus, preheating, DI diesel engine, combustion,
emissions
Issue
3, Volume 4, July 2009
Title of the Paper:
Analysis of Thermal and Olfactory Comfort in Closed Spaces
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Authors:
Ioan Sarbu, Olga Bancea
Abstract: It is well known that the prediction of comfort in buildings is
performed either by direct measurement of each microclimate parametre, or by
some comfort indices which synthesize the combined influence of more
environmental factors implied. This paper approaches the numerical prediction
of thermal comfort in closed spaces on the basis of PMV – PPD model, and its
testing to asymmetric or nonuniform thermal radiation, as well as the indoor
air quality control. It is developed a computation and testing model of
thermal comfort in buildings, as well as a methodology to determine the
outside airflow rate and to verify the indoor air quality in rooms, according
to the European Standard CEN 1752. Also, it is presented the thermal comfort
criteria for design of heating systems. On the bases of these mathematical
models there were elaborated the COMFORT 1.0 and COMFORT 2.0 computer
programs, implemented on compatible microsystems IBM-PC. The COMFORT 1.0
computer program allows both for the direct computation of the PMV (predicted
mean vote) and PPD (predicted percent dissatisfied) indices in different
points of a room, and their comparative analysis, and the determination of the
mean radiant temperature in isolated points or in a series of points situated
on a straight line. The COMFORT 2.0 program computes the outside airflow rate
for a room ventilation, the number of air exchanges per hour, and the
variation in time of contaminants concentration of room air according to
European and national norms and analyses influence of different parametres on
these sizes. The performance of the developed computational models and the
advantages of the proposed computer programs is illustrated by using some
numerical comparative applications for two constructive types building.
Keywords:
Closed spaces, Thermal comfort prediction, Olfactory comfort analysis, Outside
airflow rate, Indoor air quality control, Mathematical models, Computer
programs, Numerical comparative analysis
Title of the Paper:
Comparison of the Performances of Absorption Refrigeration Cycles
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Authors:
Z. Crepinsek, D. Goricanec, J. Krope
Abstract: This paper compares the performance of absorption refrigeration
cycles that are used for refrigeration temperatures below 0°C. Since the most
common vapor absorption refrigeration systems use ammonia-water solution with
ammonia as the refrigerant and water as the absorbent, research has been
devoted to improvement of the performance of ammonia-water absorption
refrigeration systems in recent years. In this paper the performances of the
ammonia-water and possible alternative cycles as ammonia-lithium nitrate,
ammonia-sodium thiocyanate, monomethylamine-water, R22-DMEU, R32-DMEU,
R124-DMEU, R152a-DMEU, R125-DMEU, R134a-DMEU, trifluoroethanol (TFE)-tetraethylenglycol
dimethylether (TEGDME), methanol-TEGDME and R134a-DMAC are compared in respect
of the coefficient of performance (COP) and circulation ratio (f). The highest
COP and the lowest f, were found as a function of the generator, condenser,
absorber and evaporating temperature.
Keywords:
Absorption, refrigeration, working fluids, COP, circulation ratio, waste heat
Title of the Paper:
Working Characteristics of Small-Scale Absorption Unit with Two-Cylinder
Design
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Authors:
J. Pospisil, M. Balas, M. Baxa, Z. Fortelny
Abstract: This contribution presents operation of the small-scale absorption
units with focus on working stability of the operating parameters. The
contribution discuses the long-term operation of LiBr-H2O absorption units
with consideration of corrosion, slit forming processes and production of
incondensable gases. The onestage experimental absorption chiller with exactly
same design of desorber-condenser and absorber-evaporator was build up at the
Brno University of Technology in 2008. This experimental absorption unit
operates with LiBr-H2O working pair. Design of the unit keeps two-cylinder
conception, which is common for large-scale absorption units. Heat transfer
between the working fluid and the heating/cooling water is realized with
utilizing of falling film cooper pipe registers. The cooling capacity of the
absorption chiller was designed 6 kW on temperature level 9 °C. The
contribution introduces design of the one-stage experimental absorption unit,
building, operation experiences and the results of a carried out measurements.
The measurements were focused on assessment of heat transfer on the falling
film tube bundles and the entire COP evaluation. Four independent pumps
enabled to test the influence of a flow rate change in different loops of the
absorption unit.
Keywords:
Absorption unit, falling film, heat transfer, working stability, tube bundle
Issue
4, Volume 4, October 2009
Title of the Paper:
Improved Transformer Thermal Models
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Authors:
Marius-Constantin Popescu, Aida Bulucea, Liliana Perescu
Abstract: In this paper, on basis of heat transfer mechanism, some models of
transformer thermal and loss of life will be studied. Thermal mechanisms are
complex by their own and even more when applied to a complex system, either
geometrically either physically, such as the transformer is. However, the
required transformer thermal model must be as simple as possible without
loosing representative ness of major phenomena involved; a compromise must
then be achieved between accuracy and complexity. Based on the thermal model
adopted by International Standards, small improvements to increase model
accuracy are presented and a comparative study of resulted accuracy under
different load and ambient temperature profiles is performed.
Keywords:
Loss of life models, Thermal parameters, Transformer thermal
Title of the Paper:
CFD Code Florean for Industrial Boilers Simulations
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Authors:
Heierle Yevgeniya, Leithner Reinhard, Mueller Horst, Askarova Aliya
Abstract: Computational fluid dynamics (CFD) becomes more and more reliable
tool to analyze the furnace operation under different conditions. This paper
provides and overview of the current possibilities of 3D–Finite Volume tool
FLOREAN developed at the Institute for Heat and Fuel technology TU
Braunschweig. This program is used for simulations of combustion processes in
industrial furnaces. Distributions of different parameters such as
temperature, fluid flow properties (velocities, pollutant substances such as
CO, NOx) etc. are simulated. These simulations can be used to design furnaces,
optimize furnace operation and minimize pollutant emissions.
Keywords:
Computational fluid dynamics, Combustion, Pollutant Emission, Furnace design
and operation
Title of the Paper:
Flat-Plate Collector with Solar-Powered Pump and Problem of Boiling on
Downward-Facing Surface
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Authors:
I. G. Shekriladze, E. S. Machavariani, G. I. Gigineishvili, J. G. Rusishvili,
D. I. Shekriladze
Abstract: Conceptual design of flat-plate collector (FPC) with integrated
solar-powered pump (SPP) has been carried out. SPP represents simple heat
engine - membrane pump operating through alternating of processes of
evaporation and condensation in its working chamber. It should provide
circulation of water using part of absorbed by FPC heat returning it finally
to the same heat carrier. Two basic versions of structural layout of FPC have
been considered: the first - with flow-through absorber (with circulation of
water through riser pipes welded to absorbing plate) and the second – with
absorber with gravity-assisted heat pipes (GAHPs). Important role of proper
organization of boiling heat transfer on downward-facing heating surface of
working chamber, in terms of efficient operation of SPP, is stated.
Thermo-hydrodynamic peculiarities of this process are considered. The ways of
improvement of reliability and efficiency of SPP are outlined.
Keywords:
Flat-Plate Collector, Solar-Powered Pump, Boiling, Downward-Facing Surface,
Multifactoring
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