Yazar "Mat M.D." seçeneğine göre listele
Listeleniyor 1 - 8 / 8
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe A mathematical model for hydrogen evolution in an electrochemical cell and experimental validation(2006) Mat M.D.; Kaplan Y.; Ibrahimoglu B.; Veziroglu N.; Alibeyli R.; Kuliyev S.Electrochemical reaction is largely employed in various industrial areas such as hydrogen production, chlorate process, electroplating, metal purification etc. Most of these processes often take place with gas evaluation on the electrodes. Presence of gas phase in the liquid phase makes the problem two-phase flow which is much knowledge available from heat transfer and fluid mechanics studies. The motivation of this study is to investigate hydrogen release in an electrolysis processes from two-phase flow point of view and investigate effect of gas release on the electrolysis process. Hydrogen evolution, flow field and current density distribution in an electrochemical cell are investigated with a two-phase flow model. The mathematical model involves solutions of transport equations for the variables of each phase with allowance for inter phase transfer of mass and momentum. An experimental set-up is established to collect data to validate and improve the mathematical model. Void fraction is determined from measurement of resistivity changes in the system due to the presence of bubbles. A good agreement is obtained between numerical results and experimental data. Copyright © (2006) by AFHYPAC.Öğe Application of a bubble-induced turbulence model to subcooled boiling in a vertical pipe(ASME, Fairfield, NJ, United States, 1999) Mat M.D.; Kaplan Y.; Ilegbusi O.J.Subcooled boiling of water in a vertical pipe is numerically investigated. The mathematical model involves solution of transport equations for vapor and liquid phase separately. Turbulence model considers the turbulence production and dissipation by the motion of the bubbles. The radial and axial void fractions, temperature and velocity profiles in the pipe are calculated. The estimated results are compared to experimental data available in the literature. It is found that while present study satisfactorily agrees with experimental data in the literature, it improves the prediction at lower void fractions.Öğe Application of an internal variable model to the mushy zone in alloy solidification(2001) Mat M.D.; Aydemir G.; Kaplan Y.In this study, the solidification of a generic binary alloy in a two-dimensional cavity is numerically investigated. The mushy region that is formed during solidification is considered a non-Newtonian fluid, then a critical solid fraction and a porous medium thereafter. An internal variable which represents the agglomeration and disagglomeration of grains is used in the model. The solidification problem is also solved using a porous model, which is employed generally in the literature and the results are compared with those obtained with the new model. The new model is found to predict an irregular interface morphology between the mushy region and the liquid region.Öğe Effect of grinding time of synthesized gadolinium doped ceria (GDC10) powders on the performance of solid oxide fuel cell(Elsevier B.V., 2014) Aydin F.; Demir I.; Mat M.D.Ceria-based materials are prospective electrolytes for low and intermediate temperature solid oxide fuel cells. In the present work, fully dense CeO2 ceramics doped with 10 mol% gadolinium (Gd0.1Ce0.9O1.95) were prepared with a sol–gel method and commercially purchased GDC10 electrolyte powders were processed. Particle sizes of synthesized electrolyte powders were minimized by ball-milling method. Grinding of the samples were performed in different times intervals (12 h, 15 h, 18 h, 20 h, 25 h, 30 h, 35 h, 40 h and 45 h). Then, these powders were prepared to obtain of solid oxide fuel cells (SOFCs). Performances of these cells having an active area of 1 cm2 were tested using a fuel cell test station that measured in different temperatures (650 and 700 °C). In the present study, gadolinium doped ceria (GDC10) synthesiszed powders were investigated by using XRD and SEM images. Performance values of synthesized GDC10's in different temperature were compared to by commercial GDC10. Commercial GDC10's performance at 650 °C were tested, and maximum current density of 0.413 W/cm2 and maximum current density of 0.949 A/cm2 were obtained. Commercial GDC10 at 650 °C has better result. However, synthesized GDC10's performance at 700 °C demonstrated better results than commercial GDC10's. The performance tests of samples which are 20 h mill showed that they have the maximum power density of was obtained as 0.480 W/cm2 and maximum current density of as 1.231 A/cm2. © 2014 Karabuk UniversityÖğe Heat and mass transfer of hydrogen storage in metal-hydrogen Reactors(2006) Kaplan Y.; Mat M.D.; Ibrahimoglu B.; Veziroglu N.; Alibeyli R.; Kuliyev S.Hydrogen energy is the best alternative to fossil fuels due to its high calorific value and being environmentally friendly. Hydrogen also produces more energy per unit weight than any other fuel. However, storage problem of hydrogen prevents its wide usage and commercialization. Hydrogen absorption in two LaNi5-H2 reactors is experimentally and theoretically investigated. In the experimental program, two tanks are filled with LaNi5 alloy and hydrogen is charged with a constant pressure. The temperature changes in the tanks are measured at several locations and recorded in a computer. Hydriding process is identified from measured temperature histories. An experimental set up is designed to study main characteristics of hydriding process and effect of bed geometry and heat transfer on the hydriding process. Hydriding process is characterized by exothermic reaction between LaNi5 and H2 and rapid temperature increase due the heat release. Hydriding time mainly depend on the successful heat removal from the bed. A bed geometry which provides more heat transfer area significantly reduces hydriding time In the theoretical program, a two dimensional mathematical model, which considers complex heat and mass transfer and fluid flow is developed and numerically solved. The governing equations are numerically solved and calculated results are compared with experimental data. It is found that mathematical model adequately captures the main physics of the hydriding process and can be employed for a better hydride bed design to reduce hydriding time. A reasonable agreement between the numerical results and experimental data is obtained. Copyright © (2006) by AFHYPAC.Öğe Investigation of thermal aspects of hydrogen storage in a LaNi5-H2 reactor(2006) Kaplan Y.; Ilbas M.; Mat M.D.; Demiralp M.; Veziroglu T.N.In this work, hydrogen absorption in a LaNi5-H2 reactor is investigated experimentally and numerically. Experimental measurements were carried out on a cylindrical metal-hydride reactor filled with LaNi5 alloy. During the experiments hydrogen was charged at a constant pressure. The performance of the reactor during hydriding process was obtained at different fluid temperatures and hydriding process was identified from measured temperature histories. The temperature changes in the reactor were measured at several locations and recorded in a computer. The numerical simulation of the reactor was also performed. A two-dimensional mathematical model has been established and solved numerically by the method of finite volume for the simulation. The numerical results are compared with the measured data to validate the mathematical model. The predicted results are in good agreement with the experimental measurements. Copyright © 2005 John Wiley & Sons, Ltd.Öğe Numerical analysis of hydrogen storage in metal-hydride beds [Metal-Hidrid Yataklarda Hidrojen Depolanmasinin Sayisal Analizi](2002) Aldaş K.; Mat M.D.In this study, hydrogen absorption in a metal-hydride bed is numerically investigated. The mathematical model considers the heat and mass transfer and the chemical reaction that take place during the absorption. The hydride bed heats up due to the exothermic reaction. Numerical results show that hydrogen absorption is completed faster near the cooled wall, while it takes longer at the center. Hydriding processes are investigated with the temperature histories, H/M ratio and temperature distributions at several locations in the tank. The estimated H/M ratio is found to agree satisfactorily with the experimental data in the literature.Öğe Prediction of phase segregation during mold filling of semi-solid slurries(ASME, Fairfield, NJ, United States, 1999) Mat M.D.; Ilegbusi O.J.Phase segregation during the mold filling of semi-solid slurry (Sn-15%Pb) is numerically investigated under non-isothermal conditions. The effects of operating parameters on the phase segregation including inlet velocity, initial solid fraction, heat transfer rate, mold geometry are considered. The semi-solid slurry is considered a non-Newtonian fluid below a critical solid fraction (fcr) and a viscoplastic medium saturated with liquid phase above the critical solid fraction. A group of particles are introduced at the mold inlet and phase segregation is studied by following the trajectories of these particles. The sharp property change at the slurry air interface is resolved with Van Leer numerical method. It is found that phase segregation is significantly affected by processing parameter. The segregation decreases with high inlet velocity, low heat transfer rate from the mold wall and cylindrical mold geometry.
