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 Volume 3, 2008
Print ISSN: 1790-5044
E-ISSN: 2224-3461








Issue 1, Volume 3, January 2008

Title of the Paper: Conservative Averaging and Finite Difference Methods for Transient Heat Conduction in 3D Fuse


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


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


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


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


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


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


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


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


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


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


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


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.


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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