M.S. Theses
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Browsing M.S. Theses by Author "Aksan, Emre."
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Item 2-D mathematical modelling of hydrogen storage in metal hydrides(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2009., 2009.) Küçük, Gülşad.; Aksan, Emre.In this study a numerical model which simulates heat and mass transfer processes of hydrogen absorption in LaNi5 is studied. Energy balance method is used for discretizing the heat equation. Transient heat conduction with convective boundary conditions is evaluated with explicit scheme. The analyses are conducted using MATLAB. Evaluation of temperature profiles and hydrogen mass that is being absorbed during hydriding are shown to be correlated with the experimental data and with the previous numerical studies. Since the hydriding reaction is exothermic, the rate of removal of heat released is critical in time needed to reach saturation in metal-hydride reactor. The effects of bed geometry, inlet hydrogen pressure, and metal porosity, initial bed temperature and the temperature of cooling fluid are investigated. Different cases are compared with the base case which is chosen to have similarities with conventional metal hydride tanks in reactor geometry and in thermophysical properties.Item Design of a 150 kw solar power plant in Cihanbeyli(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1981., 1981.) Sürmen, Ali.; Aksan, Emre.This study is devoted to the modeling of the performance of solar concentrators for central receiver power plants. A continuum field representation of ideal heliostat arrays is adopted in the formulation of the modeling. This representation accounts for two governing factors: the law of reflection of light rays imposes steering constraints on mirror orientations; the proximity of mirrors creates shadow effects by blocking the incident and/or reflected solar radiation.The results of a steering analysis which develops the space-time characteristics of heliostats and of a shadow analysis which determines the local effectiveness of mirrors in reflecting solar energy to a central point are combined to obtain in closed analytical form the global characteristics of circular concentrators. These charasteristics appear as time profiles for mirror orientations and for effective concentrator areas. A 150kw actual solar power plant is designed for Cihanbeyli by introduction of suitable derating factors by moving from the upper limits of performance established by these characteristics.Item Design realization and field testing of a vertical-axis wind turbine(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1981., 1981.) Yazgaç, Erdal.; Aksan, Emre.The purpose of this invertigation is to set up an experimental system for the field testing of the performance characteristics and practical serviceability of a vertical axis wind turbine. Based on previous research work, a Savonius Wind turbine prototype was manufactured in the ideal dimensions. With the caupling of the necessary apparatus, it was tested on the roof of the engineering building of the campus under natural conditions. According to the experimental results, 1/ The efficiency of the prototype is much higher than the models tesced in a wind tunnel. It varies between 34-53%, and does not fall below 34% of the power in the wind in relatively lower and higher speeds. 2/ The efficiency reaches its peak value of 53% as the outer rim of the turbine reaches a velocity equal to that of the wind. At high wind speeds, the rotational velocity of the rotor rim is about twice the wind speed. 3/ In a region of similar wind regime as the testing region, a 1m2 area turbine when reinforced with the necessary flywheel system and control circuitry, is found powerful enough to charge a car battery continuously. 4/ For two regions of annual averages 10-15 mph any size prototype turbine of the same diameter as that tested is found to have a generating capacity of about 95 kw-hr / YEAR-m2 and 220 kw-hr / YEAR-m2 for constant torque operation.Item Laminar force convection heat transfer in some noncircular pipes(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1982., 1982.) Ergen, Mehmet Murat.; Aksan, Emre.In this study, solutions to forced, convection heat transfer problems in fully developed laminar flow are obtained for Newtonian fluids with constant properties. Internal flow for square, triangular and elliptical cross-sections have been solved. In addition, an approximate solution is presented for conduits with internal flow given by X4+ y4= a 4 . To solve the aformentioned problems, Complex Variable Techniques, Biharmonic Solutions, Variational and Finite Element Methods have been used. Biharmonic Solutions are directly applied to square and triangular pipes using the available solutions, in the plate theory. The Variational formulation of the governing equations are obtained. Based on this formulation velocity and temperature distributions are found in square pipes using the Ritz Method. Variational formulation is further used in corporation with the Finite Element Technique to determine approximate solutions for noncircular pipes. The Complex Variable Method is very suitable when applied to parallel plates, circular, triangular and elliptical pipes. It also gives considerable knowledge of heat transfer for the cross-section given by X4+ y4= a 4. Theoretical solutions for each of these geometries are then compared numerically by Finite Element Method.Item Mixed convection about a rotating sphere(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1986., 1986.) Ecder, Ali.; Aksan, Emre.This report presents a theoretical analysis of flow and heat transfer characteristics of the effects of rotational speed, buoyancy force and the Prandtl number on laminar boundary layer over a rotating sphere in forced flow. Applying the finite difference method, numerical computations are carried out for various values of the above parameters. Both assisting and opposing flows are considered. Although the heating condition of uniform wall tempeuture is used in the analysis, the case of uniform surface heat flux is also studied in the formulation. After an introduction to the subject and an examination of the previous works, the theoretical background chapter supplies a general formulation. In the seotion which follows, the problem is specified. Then the results of the numerical solution are displayed in graphical form. Finally, the results are discussed and conclusions are arrived at. The computer program is also supplied.Item Solar brine evaporation process(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1984., 1984.) Kora, A. Halûk.; Aksan, Emre.The use of "Solar Brine Evaporators" in the production of natural sodium sulfate has been investigated. Three types of evaporators were used; "open" , "closed" and "closed with suction". Evaporation efficiencies for all three types of evaporatorshave been determined. Experimental results based on small scale evaporators using thin film evaporation, have succeeded in in creasing brine concentrations from 5% to 30%. As a result crystal production capacity increased by 55%. For large scale applications due to ease of operation "open" type evaporators must also be considered although their evaporation efficiencies were not as high as the other two types.Item Temperature distribution for rotating solid cylinders heated by radiation(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1981., 1981.) Eskin, Nurdil.; Aksan, Emre.The temperature distribution in rotating circular cylinders heated.by radiation has been studied in this thesis. Analytical solutions have been obtained for solid cylinders rotating with constant angular velocity, with incoming radiation taken perpendicular to the axis of rotation and incident on one side. Thermal equilibrium has been achieved by means of reradiation to the surrounding opposite half-space. The treatment employed makes use of the method of separation of variables with linearized boundary conditions. Results of the study agree very well with works cited where similar problems have been treated employing different mathematical techniques.Item The solar-assisted heat pump systems for space and water heating(Thesis (M.S.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 1986., 1986.) Aşçıoğlu, İffet Naz.; Aksan, Emre.In this study, solar-assisted heat pump systems, their contribution to reduce the consumption of non-renewable energy and their compensation for some of the shortcomings of the individual systems are considered. The base solar systems and base heat pump systems are also covered, before going into the hybrid systems. Three special types of solar-assisted heat pump systems such as parallel, series and dual systems are included,and closely examined in various aspects. Their advantages over the base solar energy systems and the base heat pump systems and also over one another are stated. The efficiency of each system and the ways to improve the efficiency is discussed.Item Thermodynamic feasibility of solar-assisted absorption cooling(Thesis (M.S.)- Bogazici University. Institute for Graduate Studies in Science and Engineering, 1987., 1987.) Olcay, Dilek.; Aksan, Emre.Solar cooling is probably among the most promising ways for solar energy utilization in near future. The purpose of the present study is to investigate the thermodynamic feasibility of operating the solar absorption system for space cooling. The thermodynamic analysis is performed for various ranges of the operation parameters selected to conform to typical climatic conditions of Turkey. At the beginning of the study, both ammonia-water and lithium-bromide-water absorption systems have been considered. The lithium-bromide-water system is preferred since it has become more popular for air conditioning applications. The most important advantage of lithium-bromide-water absorption system is that,it operates satisfactorily at generator temperatures of 85 to 90°C, achievable by a flat plate collector. A theoratical model is developed to investigate the characteristics of a lithium-bromide-water absorption type refrigeration cycle. A computer program is developed to find the design conditions of this system. Another computer program is developed to calculate the amount of useful heat energy that can be obtained from flat plate solar collectors. Combined system consists of a flat plate solar collector, generator, condensor, evaporator, absorber and economizer. The results indicate that the lithium-bromide-water absorption system combined with flat plate solar collectors may provide energy savings in considerable amounts.