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 Volume 5, 2010
Print ISSN: 1790-5044
E-ISSN: 2224-3461








Issue 1, Volume 5, January 2010

Title of the Paper: Stabilization Operation Region and Operational Variables Effect on a Reciprocal Flow Burner


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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


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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