bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulation of porous burners and hole plate surface burners
Authors: Nemoda Stevan , Trimis Dimosthenis , Zivkovic Goran
Published: July 2007

In comparison to the free flame burners the porous medium burners, especially those with flame stabilization within the porous material, are characterized by a reduction of the combustion zone temperatures and high combustion efficiency, so that emissions of pollutants are minimized. In the paper the finite-volume numerical tool for calculations of the non-isothermal laminar steady-state flow, with chemical reactions in laminar gas flow as well as within porous media is presented. For the porous regions the momentum and energy equations have appropriate corrections. In the momentum equations for the porous region an additional pressure drop has to be considered, which depends on the properties of the porous medium. For the heat transfer within the porous matrix description a heterogeneous model is considered. It treats the solid and gas phase separately, but the phases are coupled via a convective heat exchange term. For the modeling of the reaction of the methane laminar combustion the chemical reaction scheme with 164 reactions and 20 chemical species was used. The proposed numerical tool is applied for the analyses of the combustion and heat transfer processes which take place in porous and surface burners. The numerical experiments are accomplished for different powers of the porous and surface burners, as well as for different heat conductivity character is tics of the porous regions.
Implementation of discrete transfer radiation method into swift computational fluid dynamics code
Authors: Baburic Mario , Raulot Alexandre , Duic Neven
Published: July 2007

The Computational Fluid Dynamics (CFD) has developed into a powerful tool widely used in science, technology and industrial design applications, when ever fluid flow, heat transfer, combustion, or other complicated physical processes, are involved. During decades of development of CFD codes scientists were writing their own codes, that had to include not only the model of processes that were of interest, but also a whole spectrum of necessary CFD procedures, numerical techniques, pre-processing and post-processing. That has arrested much of the scientist effort in work that has been copied many times over, and was not actually producing the added value. The arrival of commercial CFD codes brought relief to many engineers that could now use the user-function approach for mod el ling purposes, en trusting the application to do the rest of the work. This pa per shows the implementation of Discrete Transfer Radiation Method into AVL?s commercial CFD code SWIFT with the help of user defined functions. Few standard verification test cases were per formed first, and in order to check the implementation of the radiation method it self, where the comparisons with available analytic solution could be performed. After wards, the validation was done by simulating the combustion in the experimental furnace at IJmuiden (Netherlands), for which the experimental measurements were available. The importance of radiation prediction in such real-size furnaces is proved again to be substantial, where radiation itself takes the major fraction of over all heat transfer. The oil-combustion model used in simulations was the semi-empirical one that has been developed at the Power Engineering Department, and which is suit able for a wide range of typical oil flames.
The state of biomass energy in Serbia
Authors: Ilic Mladen , Grubor Borislav , Tesic Milos
Published: July 2007

The paper presents a review of the energy potential of different types of biomass residues in agriculture and forestry, and actual state of biomass energy utilization in Serbia. The estimated values of annual energy potential are: about 1.7?10 6 toe (ton of oil equivalent) in biomass residues in agriculture, comprising crop farming, fruit growing, viniculture and stock breeding, and about 1 million toe of biomass from forestry, including different biomass residues and fuel wood. The total annual biomass energy potential of about 2.7?10 6 toe represents 40% of the total coal energy production in Serbia. Towns located in agricultural regions and in regions rich in forest can satisfy their energy demand for centralized heading systems with biomass residues from the territory of their own municipality. With appropriate energy policy, information campaign, research activities and general regulation in the field of biomass energy utilization, the share of biomass energy consumption in total energy balance can be significantly increased.
Behavior of carbohydrate-based material in black liquor during heating
Authors: Louhelainen Jarmo , Raimo Alén
Published: July 2007

One industrial softwood Kraft black liquor was heat-treated (at 175 ?C and 190 ?C for 15-60 min) together with laboratory-made soda-AQ (wheat straw and reed canary grass) and Kraft (reed canary grass) black liquors (at 190 ?C for 30 min). The feedstock black liquors were characterized with respect to their polysaccharide (mainly xylem) and aliphatic carboxylic acid contents before and after the heat treatments. It was noted that, due to the higher amount of polysaccharides in the non-wood black liquors (8.2-16.6% of d.s) compared to that in the softwood black liquor (1.4% of d.s), the heat treatment in the former case resulted in a 5-30% increase in the amount of aliphatic acids formed by various alkali-catalyzed degradation reactions of the liquor polysaccharides. In addition, in each case detailed gas chromatographic studies revealed that as a general trend the content of higher-molecular-mass acids decreased on heating with the subsequent increase in the content of lower-molecular-mass acids.
The veining structure method, the finite element method in thermal deformation determination for the main spindle at numerical control lathes
Authors: But Adrian , Luminosu Ioan
Published: July 2007

In the determination of the process accuracy on computer numerical control (CNC) lathe [1] it is very important to know the thermal deformations. This article presents a new solution to obtain the thermal deformations at the principal arbor (the most important part of a principal actuation for a CNC lathe) by using the element finite method. The first part of the theoretical aspect presents the steps of this method used especially for the principal arbor. The experimental part presents how this method was used to measure and process the signals. The experimental tests were applied in two different situations: (a) when material was catch only in principal arbor, and (b) when material was catch in principal arbor and chuck. The NASTRANMSC program was used, which has the possibility to determine the temperature values in the whole mass of the principal arbor and later the deformation temperature of every point of the ensemble was obtained. In order to analyze the thermal strain influence on the main spindle, the finite element method, the veining structure of a body was used. This is a method through which the "mother" (complex) structure was split in composing parts considered as independent (substructures). The link between different substructures in which the complex structure was split, is made on the common contour of substructures. The substructure becomes this way an independent structure with edge condition, constraint by assembly continuity of initial structure.
Paradox of von Engel-Steenbeck and channel model of the electric arc
Authors: Gerasimov Alexander , Kirpichnikov Alexander , Rachevskiy Leonid
Published: July 2007

It is offered simple algorithm with which help it is possible to estimate heat flux., average temperature, and temperature profile in the channel of the electro arc plasma generator, and also the shape of the positive arc column depending on the rate afflux scavenged of plasma-forming gas through a plasma generator.
On generalized hydromagnetic thermosolutal convection: The Dufour-effect
Authors: Mohan Hari , Kumar Pardeep , Singh Pawittar
Published: July 2007

The effect of uniform magnetic field on the Dufour-driven thermosolutal convection of an electrically conducting fluid completely confined in an arbitrary region bounded by rigid walls is considered. Some general qualitative results concerning the character of marginal state, stability of oscillatory motions and limitations on the oscillatory motions of growing amplitude, are derived. The results for the horizontal layer geometry in the present case follow as a consequence.
Modeling of energy system sustainability index
Authors: Afgan Nairn , Carvalho Maria , Hovanov Nikolai
Published: July 2007

Sustainability comprise complex system approach in the evaluation of energy system state. By its definition sustainability include definition of quality merits without compromising among different aspect of system complexity. It is of paramount importance for any energy system as the complex system to quantify elements of complexity taking into a consideration various degree of complexity. Energy conversion process is characterized by the entropy production as the measure of the irreversibility of the processes within the energy system. So, the complexity element of the energy system reflecting internal parameter interaction can be defined by the entropy production in the system. Complexity elements of the economic indicators are structured in different levels are intrinsic to the specific levels and are measured in different scale. The economic quality is reflecting the finale energy cost. There are a number of parameters which are of interest to be taken into a consideration in the mathematical model for the determination of the optimized values of required for its evaluation. Mutual interaction between the energy system and its surrounding is immanent for any life support system. As it is known every energy system is taking energy sources from the surrounding and disposing residual to the environment. In the social aspect of the energy system are included risk of environmental changes, health and nuclear hazards and may have to deal with a compounding of complexity at different level.
Reliable simple zonal method of the furnace thermal calculation
Authors: Ivanovic Vladan
Published: July 2007

The calculation of the furnace in the industrial and power boilers is the most important and the most responsible part of the thermal calculation, and it has important influence on the rationalization of energy consumption. In the paper one-dimensional zonal method of the furnace thermal calculation of steam boilers is presented. It can successfully define disposition of flue gas temperature and specific thermal load of screen walls with height of the furnace in case of uneven deposits distribution which vary in size and quality. Its greatest use is for comparing furnace performance under various operating conditions.
Modeling of pulverized coal combustion stabilization by means of plasma torches
Authors: Sijercic Miroslav , Belosevic Srdjan , Stefanovic Predrag
Published: July 2007

Application of plasma-system for pulverized coal ignition and combustion stabilization in utility boiler furnaces promises to achieve certain savings compared to the use of heavy oil burners. Plasma torches are built in air-coal dust mixture ducts between coal mills and burners. Characteristics of processes in the ducts with plasma-system for pulverized coal combustion stabilization are analyzed in the paper, with respect to the modeling and numerical simulation of mass, momentum and heat transfer in two-phase turbulent gas-particle flow. The simulations have been performed for three different geometries of the air-coal dust mixture ducts with plasma torches, for TENTAI utility boiler and pulverized lignite Kolubara-Field "D". Selected results of numerical simulation of processes are presented. The plasma-system thermal effect is discussed regarding corresponding savings of liquid fuel. The results of numerical simulations have been analyzed with respect to the processes in the duct and especially with respect to the influence of the duct shape to a temperature field at the outlet cross section, as a basis for the duct geometry optimization. It has been emphasized that numerical simulation of processes can be applied in analysis and optimization of pulverized coal ignition and combustion stabilization and enables efficient and cost-effective scaling-up procedure from laboratory to industrial level.
Potential utilization of renewable energy resources for electricity generation in Bosnia and Herzegovina
Authors: Begic Fajik , Kazagic Anes
Published: July 2007

Along with the current processes of restructuring of Energy power system of Bosnia and Herzegovina, liberalization of the electricity market, and modernization of the existing power plants, Bosnia and Herzegovina must turn to the utilization of renewable resources in reason able dynamics as well. Respecting this policy, the initial Valuation of the potential of renewable erg resources in Bosnia and Herzegovina is per formed. The methodology of evaluation of wind energy utilization is presented in this paper, as well as some other aspects of utilization of the renewable energy resources in Bosnia and Herzegovina. Implementation of selected projects should improve sustainability of energy power production in Bosnia and Herzegovina, by reducing the total emission of carbon dioxide originated from energy power system of Bosnia and Herzegovina.
Modeling of energy and environmental costs for sustainability of urban areas
Authors: Aranda Alfonso , Zabalza Ignacio , Scarpellini Sabina
Published: July 2007

The principal aim of this paper is to present the results achieved by the practical application of energy modeling to urban areas based on two inter related concepts: energy costs and environmental costs. The analysis has-been carried out in three standard Municipalities located in a Mediterranean Zone (Spain) selected based on their different size and socio-economic activities in order to facilitate the extrapolation of results. Energy flows of the chosen areas have been quantified and classified. In addition, energy and environmental costs have been agree gated for each productive sector. Using the methodology proposed in this paper innovative solutions could be specially de signed for different areas in order to ensure the sustainable development of urban areas. Finally, the basis for changing the present development model in the Municipalities set out by means of the application of sustainability principles set in Agenda 21.
Analysis of sustainable HVAC system in tourism facilities on the Adriatic coast
Authors: Zanki-Alujevic Vlasta , Galaso Ivan
Published: July 2007

The world and Mediterranean trends in tourism growth are followed by energy consumption growth. Since heating and air-conditioning accounts forenames half of the energy consumption of many hotels, necessary infrastructure to meet growing demands with minimal impact on natural resources and environment should be provided. This paper deals with sustainable solutions for cooling and heating tourist accommodation facilities on the Adriatic coast. The analysis of the two systems for an apartment complex, the first utilizing sea-water as "free source" of cold energy, and the second as an absorption system utilizing solar thermal energy are compared with conventional vapor compression system. It was shown that significant savings in energy consumption and CO2 emissions could be achieved. At the same time the systems are environ mentally friendly and ensure water conservation with negligible visual and noise pollution.
Comparative analysis of the solar dish electricity production
Authors: Firak Mihajlo
Published: July 2007

Round parabolic solar mirror is of ten called the solar or sun dish. Even when the dish is faceted into several smaller dishes (facets) which are all focusing the sunlight in the single point (focus), it is called a solar dish. When solar radiation to electricity converter is mounted into the dish focus and the sun-tracking system is provided, it could be named solar dish/converter system. Depending on the sort of the converter, two promising systems which are approaching the commercialization could be mentioned. These are solar dish/Sterling system and solar dish/photo voltaic system. In this paper, majority of the technical and economical aspects of the two systems are examined and compared. Two systems are chosen to represent this: SAIC/STM Sun Dish TM, solar dish with Sterling heat engine/generator, and Solar Systems SS20TM representing solar dish with concentrating photovoltaic converter. It is concluded that solar dish with concentrated photovoltaic converter can have much better cost/performance ratio. It is also concluded that recently introduced thermo acoustical converter and photovoltaic cavity converter, probably des ignites future development of the solar dish systems. World?s potential of in stalling solar dish systems according to geographic and climate conditions wisest mated. Also, the number of solar dishes which could, in stalled in Croatia cover yearly state?s electricity consumption was calculated.
Slagging and fouling in biomass co-combustion
Authors: Tortosa-Masiá Abel , Ahnert Falk , Spliethoff Harmut , Loux Claude , Hein Klaus
Published: July 2007

Deposits formation on heat transfer surfaces, namely slagging and fouling, is one of the main problems associated to biomass combustion. Reducing deposits formation can optimize plant operation. Literature review and experience show a clear research demand to wards methods for on line detection of deposits in large-scale boilers. A system consisting of a monitoring model and an on-line measurement method is presented. Results of testing campaigns show the appropriateness of the model to visualize deposit tendencies, and the possibility to determine the influence of ash deposits on heat transfer using the measurement method.
Scaling of permeabilities and friction factors of homogeneously expanding gas-solids fluidized beds: Geldart’s A powders and magnetically stabilized beds
Authors: Hristov Jordan
Published: July 2007

The concept of a variable friction factor of fluid-driven de form able powder beds undergoing fluidization is discussed. The special problem discussed addresses the friction factor and bed permeability relationships of Geldart?s A powders and magnetically stabilized beds in axial fields. Governing equations and scaling relation ships are developed through three approaches (1) Minimization of the pressure drop with respect to the fluid velocity employing the Darcy-Forchheimer equation together with the Richardson-Zaki scaling law, (2) Minimization of the pres sure drop across an equivalent-channel replacing the actual packed beds by a straight pipe with bed-equivalent obstacle of a simple geometry, and (3) Entropy minimization method applied in cases of the Darcy-Forchheimer equation and the equivalent-channel model. Bed-to-surface heat transfer coefficients are commented in the context of the porosity/length scale relationships developed. Both the pressure drop curves developments and phase diagram de signs are illustrated by applications of the intersection of asymptotes technique to beds exhibiting certain degree of cohesion.
Influence of the degree of irreversibility of thermal and mechanical treatment regime on the final qualities of a reacting-system
Authors: Grigorova Veneta , Roussev Dimitar
Published: July 2007

The final qualities of interest (such as grain size, chemical purity, degree of stability, transition order) of new compounds, synthesized in solid state transformation processes (chemical reactions, phase transitions) can be controlled through the evaluation of the entropy generation in the system. Thermally activated chemical reaction (LiCoPO4 synthesis) and mechanically activated phase transition (PdSe2 transformation) are discussed as examples. The LiCoPO4 qualities of interest are grain size (less that 0.5 ?m) and chemical purity (up to 98%). The pyrite structured PdSe2 qualities of interest are: transition-order and degree of stability. The requirements are first-order transition and as higher as possible degree of stability. The grain size of LiCoPO4 and degree of stability of PdSe2 have been de scribed by the calculation of the entropy generation in the treatment process; the chemical purity of LiCoPO4 ? by the reaction co-ordinate and the transition order of PdSe2 ? by the behavior of the thermodynamic potential ? first partial derivative in the transition point. To compute the thermodynamic functions under request, the behavior of the treated system has been investigated by measuring the driving force of its conversion process. In the case of thermal treatment (LiCoPO4) the absorbed heat flux has been measured whereas for the case of mechanical treatment (PdSe2) the applied pres sure and its corresponding material?s specific volume have been measured. Experiments and calculations have been carried out for LiCoPO4 to establish empirical equations, giving the relation ship between the heating regime parameters and final product grain size. For PdSe2, the relation ships between the compression regime parameters and thermodynamic potential and the degree of stability have been received by numerical calculations.
Micro channels in macro thermal management solutions
Authors: Kosoy Boris
Published: July 2007

Modern progress in electronics is associated with increase in computing ability and processing speed, as well as decrease in size. Future applications of electronic devices in aviation, aero space and high performance consumer products? industry demand on very stringent specifications concerning miniaturization, component density, power density and reliability. Excess heat produces stresses on internal components inside the electronic device, thus creating reliability problems. Thus, a problem of heat generation and its efficient removal arises and it has led to the development of advanced thermal control systems. Present research analyses a thermodynamic feasibility of micro capillary heat pumped net works in thermal management of electronic systems, considers basic technological constrains and de sign availability, and identifies perspective directions for the further studies. Computer Fluid Dynamics studies have been per formed on the laminar convective heat transfer and pressure drop of working fluid in silicon micro channels. Surface roughness is simulated via regular constructal, and stochastic models. Three-dimensional numerical solution shows significant effects of surface roughness in terms of the rough element geometry such as height, size, spacing and the channel height on the velocity and pressure fields.
Thermodynamic analysis of air refrigerator on exergy graph
Authors: Nikulshin Vladimir , Bailey Margaret , Nikulshina Viktoria
Published: July 2007

Improving mechanical system efficiency is the goal of many engineers and scientists. Commonly, the solutions to these types of problems are uncovered using thermodynamic analysis and optimization. An innovative method for the thermodynamic analysis of a complex energy-intensive system with an arbitrary structure is described in this paper. The method is based on a novel general equation to calculate the total system exergy efficiency using an exergy flow graph proposed by the authors. Discuss in this paper exergy efficiency and exergy loss models as well this approach allows a user to obtain not only the exergy losses and efficiency of the total system, but also to show the relationship between the exergy efficiency of an individual element and that of the entire system. An example is provided that employs this method to the thermodynamic analysis of an air refrigerator.
High activity carbon sorbents for mercury capture
Authors: Stavropoulos George , Diamantopoulou Irene , Skodras George , Sakellaropoulos George
Published: July 2007

High efficiency activated carbons have been prepared for removing mercury from gas streams. Starting materials used were petroleum coke, lignite, charcoal and olive seed waste, and were chemically activated with KOH. Produced adsorbents were primarily characterized for their porosity by N2 adsorption at 77 K. Their mercury retention capacity was characterized based on the breakthrough curves. Compared with typical commercial carbons, they have exhibited considerably enhanced mercury adsorption capacity. An attempt has been made to correlate mercury entrapment and pore structure. It has been shown that physical surface area is increased during activation in contrast to the mercury adsorption capacity that initially increases and tends to decrease at latter stages. Desorption of active sites may be responsible for this behavior.
Removal of pollutants from poor quality coals by pyrolysis
Authors: Natas Panagiotis , Basinas Panagiotis , Sakellaropoulos George
Published: July 2007

Combustion of poor quality coals and wastes is used today worldwide for energy production. However, this entails significant environmental risks due to the presence of polluting compounds in them, i. e. S, N, Hg, and Cl. In the complex environment of combustion these substances are forming conventional (i. e. SOx, NOx) and toxic (PCDD/Fs) pollutants, while, the highly toxic Hg is volatilized in the gas phase mainly as elemental mercury. Aiming to meet the recently adopted strict environmental standards, and the need of affordable in cost clean power production, a preventive fuels pre-treatment technique, based on low temperature carbonization, has been tested. Clean coals were produced from two poor quality Greek coals (Ptolemais and Megalopolis) and an Australian coal sample, in a lab-scale fixed bed reactor under helium atmosphere and ambient pressure. The effect of carbonization temperature (200-900 ?C) and residence time (5-120 minutes) on the properties of the chars, obtained after pyrolysis, was investigated. Special attention was paid to the removal of pollutants such as S, N, Hg, and Cl. To account for possible mineral matter effects, mainly on sulphur removal, tests were also performed with demineralized coal. Reactivity variation of produced clean coals was evaluated by performing non-isothermal combustion tests in a TA Q600 thermo gravimetric analyzer. Results showed that the low temperature carbonization technique might contribute to clean coal production by effectively removing the major part of the existing polluting compounds contained in coal. Therefore, depending on coal type, nitrogen, mercury, and chlorine abatement continuously increases with temperature, while sulphur removal seems to reach a plateau above 500-600 ?C. More-over, the prolongation of carbonization time above 20 minutes does not affect the elemental conversion of the pollutants and carbonization at 500-600 ?C for ~20 minutes may be considered sufficient for clean coal production from poor quality coals. Clean coal production at higher pyrolysis temperatures results in observed higher initial combustion temperature, mainly due to lower volatile content in produced chars.
Prospects for co-firing of clean coal and creosote-treated waste wood at small-scale power stations
Authors: Zandersons Janis , Zhurinsh Aivars , Someus Edward
Published: July 2007

If a small-scale clean coal fueled power plant is co-fueled with 5% of creosote-treated used-up sleeper wood, the decontamination by carbonisation at 500 ?C in an indirectly heated rotary kiln with the diameter 1.7 m and effective length 10 m can be realized. It should be included in the "3R Clean Coal Carbonisation Plant" system, which processes coal. It will improve the heat balance of the system, since the carbonisation of wood will deliver a lot of high caloricity pyroligneous vapour to the joint furnace of the "3R Clean Coal Carbonisation Plant". Pine wood sleeper sapwood contains 0.25% of sulphur, but the average pine sleeper wood (sapwood and heartwood) 0.05% of sulphur. Most of the sulphur is lost with the pyroligneous vapour and burned in the furnace. Since the "3R Clean Coal Carbonisation Plant" is equipped with a flue gases cleaning system, the SO2 emission level will not exceed 5 mg/m3. The charcoal of the sapwood portion of sleepers and that of the average sleeper wood will contain 0.22% and 0.035% of sulphur, respectively. The increase of the carbonisation temperature does not substantially decrease the sulphur content in charcoal, although it is sufficiently low, and the charcoal can be co-fired with clean coal. The considered process is suitable for small power plants, if the biomass input in the common energy balance is 5 to 10%. If the mean distance of sleepers transportation for Central and Eastern Europe is estimated not to exceed 200 km, the co-combustion of clean coal and carbonized sleepers would be an acceptable option from the environmental and economic points of view.
Gas pollutant cleaning by a membrane reactor
Authors: Kaldis Sotiris , Topis Savas , Koutsonikolas Dimitris
Published: July 2007

An alternative technology for the removal of gas pollutants at the integrated gasification combined cycle process for power generation is the use of a catalytic membrane reactor. In the present study, ammonia decomposition in a catalytic reactor, with a simultaneous removal of hydrogen through a ceramic membrane, was investigated. A Ni/Al2O3 catalyst was prepared by the dry and wet impregnation method and characterized by the inductively coupled plasma method, scanning electron microscopy, X-ray diffraction, and N2 adsorption before and after activation. Commercially available a-Al2O3 membranes were also characterized and the permeabilities and permselectivities of H2, N2, and CO2 were measured by the variable volume method. In parallel with the experimental analysis, the necessary mathematical models were developed to describe the operation of the catalytic membrane reactor and to compare its performance with the conventional reactor. .
Production and characterization of bio-oil from catalytic biomass pyrolysis
Authors: Antonakou Eleni , Dimitropoulos Vasilios , Lappas Angelos
Published: July 2007

Biomass flash pyrolysis is a very promising thermochemical process for the production of bio-fuels and/or chemicals. However, large-scale applications are still under careful consideration, because of the high bio-liquid upgrading cost. In this paper the production of bio-liquids from biomass flash pyrolysis in a single stage catalytic process is being investigated using a novel once through fluid bed reactor. This biomass pyrolysis unit was constructed in Chemical Process Engineering Research Institute and comprises of a catalyst regenerator, a biomass-vibrating hopper, a fluidization reactor (that consists of an injector and a riser reactor), a product stripper along with a hot cyclone and a filter housing and finally a product condensation/recovery section. The unit can process up to 20 g/min. of biomass (50-800 mm) and can circulate up to 300 g/min. of catalyst or inert material. The experiments performed in the pilot plant showed that the unit operates without problems and with satisfactory mass balances in a wide range of experimental conditions both in the absence and presence of catalyst. With the incorporation of an FCC catalyst in the pyrolysis, the physical properties of the bio-oil produced changed, while more stable bio-oil was produced. .
Lignite chemical conversion in an indirect heat rotary kiln gasifier
Authors: Hatzilyberis Kostas , Androutsopoulos George
Published: July 2007

The results on the gasification of Greek lignite using two indirect heat (allothermal) pilot rotary kiln gasifiers are reported in the present work. The development of this new reactor-gasifier concept intended for solid fuels chemical conversion exploits data and experience gained from the following two pilot plants. The first unit A (about 100 kg/h raw lignite) demonstrated the production of a medium heating value gas (12-13 MJ/Nm3) with quite high DAF (dry ash free) coal conversions, in an indirect heat rotary gasifier under mild temperature and pressure conditions. The second unit B is a small pilot size unit (about 10 kg/h raw lignite) comprises an electrically heated rotary kiln, is an operation flexible and exhibits effective phase mixing and enhanced heat transfer characteristics. Greek lignite pyrolysis and gasification data were produced from experiments performed with pilot plant B and the results are compared with those of a theoretical model. The model assumes a scheme of three consecutive-partly parallel processes (i. e. drying, pyrolysis, and gasification) and predicts DAF lignite conversion and gas composition in relatively good agreement with the pertinent experimental data typical of the rotary kiln gasifier performance. Pilot plant B is currently being employed in lime-enhanced gasification studies aiming at the production of hydrogen enriched synthesis gas. Presented herein are two typical gas compositions obtain from lignite gasification runs in the presence or not of lime. .
Performance of falling film plate evaporators in reconstructed multiple-effect evaporation station in sugar factory
Authors: Zavargo Zoltan , Jokic Aleksandar , Prodanic Bojana , Grbic Jasna , Jeftic-Mucibabic Rada
Published: July 2007

General trend of free trade in regional level as well as in the direction of European Union has motivated sugar factories located in Serbia to invest into technologies that are more efficient in order to make their products more competitive at the markets in Europe. The aim of this work was to evaluate effects of falling film plate evaporators on the energy consumption of evaporation plant, as well as to validate performance of this type of evaporators. It was found that this type of evaporator decreased energy requirements and in the same time evaporation process was more effective due to high values of heat transfer coefficients. .
New concept of electrical drives for paper and board machines based on energy efficiency principles
Authors: Jeftenic Borislav , Statkic Sasa , Bebic Milan , Ristic Leposava
Published: July 2007

In this paper, it is described how the reconstruction of the facility of paper machine has been conducted, at the press and drying part of the machine in June 2001, as well as the expansion of the Paper Machine with the "third coating" introducing, that has been done in July 2002, in the board factory "Umka". The existing old drive of the press and the drive of drying groups were established as a Line Shaft Drive, 76 m long. The novel drive is developed on the basis of conventional squirrel cage induction motor application, with frequency converter. The system control is carried out with the programmable controller, and the communication between controllers, converters, and control boards is accomplished trough profibus. Reconstruction of the coating part of the machine, during technological reconstruction of this part of the machine, was being conducted with a purpose to improve performance of the machine by adding device for spreading "third coating". The demands for the power facility were to replace existing facility with the new one, based on energy efficiency principles and to provide adequate facility for new technological sections. Also, new part of the facility had to be connected with the remaining part of the machine, i.e. with the press and drying part, which have been reconstructed in 2001. It has to be stressed that energy efficiency principles means to realize new, modernized drive with better performances and greater capacity for the as small as possible amount of increased installed power of separate drives. In the paper are also, graphically presented achieved energy savings results, based on measurements performed on separate parts of paper machine, before and after reconstruction. .
Description of pelletizing facility
Authors: Cokorilo Vojin , Knezevic Dinko , Milisavljevic Vladimir
Published: July 2007

A lot of electrical energy in Serbia was used for heating, mainly for domes- tics. As it is the most expensive source for heating the government announced a National Program of Energy Efficiency with only one aim, to reduce the consumption of electric energy for the heating. One of the contributions to mentioned reduction is production of coal pellets from the fine coal and its use for domestic heating but also for heating of schools, hospitals, military barracks, etc. Annual production of fine coal in Serbia is 300,000 tons. The stacks of fine coal make a lot difficulties to the each mine because of environmental pollution, spontaneous combustion, low price, smaller market, etc. To prevent the difficulties and to give the contribution to National Program of Energy Efficiency researchers from the Department of Mining Engineering, University of Belgrade, designed and realized the project of fine coal pelletizing. This paper describes technical aspect of this project.
Vlasina wind project: Results and perspectives
Authors: Rakovic Radoslav
Published: July 2007

This paper describes activities and main results of investigation for the Vlasina Wind Project, implemented within National Energy Efficiency Program, segment that deals with alternative and renewable energy sources. The main objective of the project was investigation of possibilities of wind energy generation in mountain areas of the Republic of Serbia. Problems of choice of location, measurement of wind energy potential, choice of type and unit size of wind turbine generators, as well as the interconnection of wind turbine generators and wind power plants to power system are considered. .
Development and investigation of solar collectors for conversion of solar radiation into heat and/or electricity
Authors: Stefanovic Velimir , Bojic Milorad
Published: July 2007

This article describes work on two projects of the National Energy Efficiency Program NEEP 709300036 and NPEE 271003 titled "The model of solar collector for middle temperature conversion of solar radiation in heat" and "Development and investigation on hybrid solar collector for heat and electricity generation", respectively. This first project deals with solar collector that transfers solar radiation in heat in area of middle temperature conversion (at temperatures above 100 ?C). During entire year it can realize significant saving of electric energy used for preparation of warm water and in central and district heating. During work on the second project, two hybrid solar collectors, their installation, mathematical model, software, and experimental set-up were designed and realized. The first collector had the photovoltaic panel located above the absorber and the second collector had the panel located on the absorber. For both collectors, the results show that efficiency of fossil fuel replacement is 85%. .
Efficiency and emission of crop residues combustion facilities in Serbia: Status and needed measures for improvement
Authors: Martinov Milan , Tesic Milos , Brkic Miladin
Published: July 2007

Use of crop residues as fuel has a long tradition in rural areas of Serbia. Numerous biomass-fueled facilities were built during the 80s. Among those were small facilities for household heating, with thermal power from 5 to 50 kW, medium-size facilities for farm and greenhouses, with thermal power 50 to 1000 kW, and large facilities for processing of agricultural products, with thermal powers higher than 1000 kW. The results showed that the level of biomass combustion facilities is in general very low. This is especially the case for heating facilities used for house-hold heating. The measures for improvement were proposed. .
Using geothermal water for greenhouse heating
Authors: Milojevic Svetomir , Djurovic-Petrovic Maja , Radosavljevic Dragana , Glisic Sandra , Stamenic Marko
Published: July 2007

On construction with dimensions 15 x 5 x 2 m, conditions of temperature transmission and vegetables growth are examined. We have been cultivating pepper, cucumber, small cucumber, tomato, and lattice. Over ground heating has been used, consisting of one bent pipe with radius of 10 mm, in the shape of hairpin along the both sides of the construction. Underground heating consists of six pipes with radius of 20 mm on the depth of 350-400 mm. There have been measured the temperature inside construction, the temperature outside construction, the waterflow, and water temperature flowing into and out of the construction. The approximate heating flow factor K is determined by both the equation: heating balance equation and basic equation for temperature transmition. Vegetable growth has been watching during the period of time from March to November 2005.
Atmospheric fluidized bed gasification of promising biomass fuels in southern European regions
Authors: Panopoulos Kyriakos , Fryda Lydia , Kakaras Emmanuel
Published: July 2007

Three promising biomass fuels from southern European regions were gasified atmospherically with air in a lab-scale fluidized bed reactor with quartz or olivine as bed material. The fuels used were an agro-industrial residue (olive bagasse) and the energy crops giant reed and sweet sorghum bagasse. Varying air ratios and temperatures were tested to study the impact on the product gas composition and tar load. Tars were higher in the case of olive bagasse, attributed to its higher lignin content compared to the other two biomasses with higher cellulose. Giant reed gasification causes agglomeration and defluidisation problems at 790?C while olive bagasse shows the least agglomeration tendency. The particular olivine material promoted the destruction of tars, but to a lesser level than other reported works; this was attributed to its limited iron content. It also promoted the H2 and CO2 production while CO content decreased. Methane yield was slightly affected (decreased) with olivine, higher temperatures, and air ratios. Air ratio increase decreased the tar load but at the same time the gas quality deteriorated. .
Laminar air flow free convective heat transfer inside a vertical circular pipe with different inlet configurations
Authors: Mohammed Hussein , Salman Yasin
Published: July 2007

Free convection heat transfer has been experimentally investigated for laminar air flow in a vertical circular pipe by using the boundary condition of constant wall heat flux in the ranges of local Rayleight number (RaL) from 1.1?109 to 4.7?109. The experimental setup was designed for determining the effect of different configurations placed at the inlet of a vertical heated pipe, on the surface temperature, the local and average heat transfer coefficients. The apparatus was made with an electrically heated aluminum pipe with length of 900 mm and inside diameter 30 mm. The inlet configurations included two circular pipes having the same diameter as the heated pipe but with lengths of 600 and 1200 mm, sharp-edge and bell-mouth. It was found that the surface temperature along the pipe surface for same heat flux would be higher values for inlet condition with length of 1200 mm and would be lower values for bell-mouth inlet condition. The results show that the local Nusselt number Nux and average Nusselt number (NuL) values would be higher for bell-mouth inlet condition and lower values for 1200 mm inlet condition. For all inlet configurations, the results reveal that the Nu increases as the heat flux increases. Empirical correlations have been proposed in a form of log NuL vs. log RaL for each case investigated and a general correlation for all cases has been obtained which reveals the effect of inlet conditions existence on the free convection heat transfer process in a vertical circular pipe. .
A novel method for estimating the entropy generation rate in a human body
Authors: Rahman Azizur
Published: July 2007

The main objective of this study is to show a method for calculating entropy generation (Sgen) in a human body under various environmental and physiological conditions. The Sgen in a human body is a measure of activeness of motions, reactions, and irreversibility of processes occurring in a body and is a kind of holistic and thermodynamic index, which characterizes a human body as a whole. Human body at healthier and normal condition generates the least amount of Sgen. Heat transfer over a human body, activity (at rest, Sgen = 0.21J/sK or exercise, Sgen=2.19 J/sK or at death, Sgen = 0J/sK), ambient, body and mean radiant temperatures, emissivity and absorbity of human skin, internal heat elimination, body weight and height, and air speed effect much more on the Sgen in a human body compared to the effects of mass exchange into and out of the body, internal heat production, cross-sectional area of human body, clothing, altitude, and relative humidity of the surrounding air. Among these factors entropy production due to heat transfer over a human body plays a significant role in the total entropy generation rate. .
Instability of two rotating viscoelastic (Walters B') superposed fluids with suspended particles in porous medium
Authors: Kumar Pardeep , Singh Mahinder
Published: July 2007

The instability of the plane interface between two Walters B' viscoelastic superposed fluids permeated with suspended particles and uniform rotation in porous medium is considered following the linearized perturbation theory and normal mode analysis. For the stable configuration the system is found to be stable or unstable if ?' < or > k1/?, depending on kinematic viscoelasticity, permeability of the medium and porosity of the medium. However, the system is found to be unstable for the potentially unstable configuration. .
Thermo elastic-plastic transition in a thin rotating disc with inclusion
Authors: Gupta Kumar , Pankaj P
Published: July 2007

Stresses for the elastic-plastic transition and fully plastic state have been derived for a thin rotating disc with shaft at different temperatures and results have been discussed and depicted graphically. It has been observed that the rotating disc with inclusion and made of compressible material requires lesser angular speed to yield at the internal surface and higher percentage increase in angular speed to become fully plastic as compare to disc made of incompressible material. With the introduction of thermal effect the rotating disc with inclusion required lesser angular speed to yield at the internal surface. Rotating disc made of compressible material with inclusion requires higher percentage increase in angular speed to become fully-plastic as compare to disc made of incompressible material. Thermal effect also increases the values of radial and circumferential stresses at the internal surface for fully-plastic state. .
Optimal parameterization in the measurements of the thermal diffusivity of thermal barrier coatings
Authors: Milosevic Nenad
Published: July 2007

The paper presents an estimation procedure for the measurement of the thermal diffusivity of thermal barrier coatings deposited on thermal conductive substrates using the laser flash method when the thermal contact resistance between the coating and substrate is unknown. The procedure is based on the application of the optimal parameterization technique and Gauss minimization algorithm. It has been applied on the experimental data obtained by using two different samples, one made of PTFE (polytetrafluoroethylene) coating deposited on a stainless steel substrate and the other made of PVC (polyvinylchloride) deposited on a copper substrate. .