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 Volume 4, 2009
Print ISSN: 1790-5044
E-ISSN: 2224-3461








Issue 1, Volume 4, January 2009

Title of the Paper: Optimization of Thermal Components in a Stirling Engine


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


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


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


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


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


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


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


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


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


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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