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Öğe A three-dimensional mathematical model for absorption in a metal hydride bed(PERGAMON-ELSEVIER SCIENCE LTD, 2002) Aldas, K; Mat, MD; Kaplan, YHeat and mass transfer, fluid flow and chemical reactions in a hydride bed are numerically investigated with a general purpose PHOENICS code. Hydride formation takes place faster near the cooled boundary walls and slower around the core region of the bed. It is found that fluid flow affects the temperature distribution in the system, however, it does not significantly improve the amount of hydrogen absorbed. (C) 2002 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.Öğe An improved correlation for heat transfer coefficient of two-phase flow in a vertical tube(BEGELL HOUSE, INC, 1999) Altinisik, K; Mat, MD; Aldas, K; Kaplan, Y; Karakoc, F; Dincer, I; Ayhan, TA correlation is developed using Lockhard-Martinelli parameters for predicting the heat transfer coefficient during the two phase flow of water-vapor system. An upward flow in a vertical circular pipe at atmospheric conditions is considered. The constants in the correlation have been obtained after 2800 measurements. The accuracy of correlation is found to be 96.5 using t test. Delta T-h(tp) and h(tp) variations are also investigated using measured data.Öğe Experimental and theoretical analysis of hydrogen absorption in LaNi5-H-2 reactors(PERGAMON-ELSEVIER SCIENCE LTD, 2005) Demircan, A; Demiralp, M; Kaplan, Y; Mat, MD; Veziroglu, TNHydrogen 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. 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 numerical results are compared with the measured data to validate the mathematical model. A reasonable agreement between the numerical results and experimental data is obtained. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.Öğe Experimental and theoretical study of metal-hydride reactors(SPRINGER, 2005) Kaplan, Y; Demiralp, M; Veziroglu, TN; Sammes, N; Smirnova, A; Vasylyev, OHydrogen absorption in LaNi5-H-2 reactor is experimentally and theoretically investigated. Two different reactors were designed and hydrogen gas was charged at constant temperature at constant pressure. Temperature changes in the tanks during the hydrogen charge were measured at several locations and readings of the data were continued until the temperature has stabilized. In the theoretical program, a two dimensional mathematical model, which considers complex heat and mass transfer during this process is developed and numerically solved. The numerical results are compared with the measured data to validate the mathematical model. A reasonable agreement between the numerical results and experimental data is obtained.Öğe Hydrogen as burner fuel: modelling of hydrogen-hydrocarbon composite fuel combustion and NOx formation in a small burner(JOHN WILEY & SONS LTD, 2005) Ilbas, M; Yilmaz, I; Veziroglu, TN; Kaplan, YThe objective of this work is to investigate numerically the turbulent non-premixed hydrogen (H-2) and hydrogen-hydrocarbon flames in a small burner. Numerical studies using Fluent code were carried out for air-staged and non-staged cases. The effects of fuel composition from pure hydrogen to natural gas (100% H-2, 70% H-2 + 30% CH4, 10% H-2 + 90% CH4, and 100% CH4) were also investigated. The predictions are validated and compared against the experimental results previously obtained and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation equations and reaction equations governing the problem. Although, three different turbulence models were tested, the standard k-epsilon model was used for the modelling of the turbulence phenomena in the burner. The temperature and major pollutant concentrations (CO and NOx) distributions are in good agreement with the existing experimental results. Air staging causes rich and lean combustion regions thus lower NOx emissions through the combustor exit. Blending hydrogen with methane causes considerable reduction in temperature levels and thus NO emissions. Increasing the mixture ratio from stoichiometric to leaner mixtures also decreases the temperature and thus NO emissions. Hydrogen may be considered a good alternative fuel for burners, as its use reduces the emission of pollutants; and as it is a renewable synthetic fuel. Copyright (c) 2005 John Wiley & Sons, Ltd.Öğe Investigation of three-dimensional heat and mass transfer in a metal hydride reactor(JOHN WILEY & SONS LTD, 2002) Mat, MD; Kaplan, Y; Aldas, KA mathematical model for three-dimensional heat and mass transfer in metal-hydrogen reactor is presented. The model considers three-dimensional complex heat, and mass transfer and chemical reaction in the reactor. The main parameter in hydriding processes is found to be the equilibrium pressure, which strongly depends on temperature. Hydride formation enhanced at regions with lower equilibrium pressure. Hydriding processes are shown to be two dimensional for the system considered in this study. Effects of heat transfer rate and R/H (radius to height) ratio on hydride formation are investigated. Hydride formation increases significantly with larger heat transfer rate from the boundary walls, however after a certain heat transfer rate, the increase in formation rate is found to be not significant, due to the low thermal conductivity of the metal-hydride systems. The estimated results agree satisfactorily with the experimental data in the literature. Copyright (C) 2002 John Wiley Sons, Ltd.Öğe Investigations of hydrogen and hydrogen-hydrocarbon composite fuel combustion and NOx emission characteristics in a model combustor(PERGAMON-ELSEVIER SCIENCE LTD, 2005) Ilbas, M; Yilmaza, I; Kaplan, YIn this paper, the numerical simulation of a turbulent non-premixed hydrogen (H-2) diffusion flame has been performed in a model combustor. CFD studies using Fluent code were carried out changing fuel composition from pure hydrogen to natural gas (100% H-2, 70% H-2+ 30% CH4, 10% H-2 + 90% CH4, and 100% CH4). The model prediction studies have been extended to combustion air staging. Air 25% was staged and introduced through the two tangential inlets. The predictions are validated and compared against the experimental results obtained in this study and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation and reaction equations governing the problem. The standard k-epsilon model is used for modelling of turbulent flow as the model was far enough for the turbulence phenomena in the combustor. The chemical combustion reactions are described by seven species and three steps. A NOx post-processor has been used for predicting NO, emissions from the combustor. The temperature and major pollutant concentration (CO and NOx) distributions are in good agreement with the experimental measurements. The overall flame temperature increases as hydrogen is added or decreases as methane is added to the fuel mixture. The addition of methane to hydrogen decreases the flame temperature and thus NOx emissions considerably. Air staging causes rich and lean combustion regions and thus lower NOx emissions through the combustor exit. (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.Öğe Mathematical modelling of hydrogen storage in a LaNi5 hydride bed(JOHN WILEY & SONS LTD, 2003) Kaplan, Y; Veziroglu, TNThis paper presents a numerical investigation of hydrogen storage in a metal hydrid bed. For this Purpose, a two-dimensional mathematical model which considers complex heat and mass transfer and fluid flow during the hydriding process is accomplished ill this study. The coupled differential equations are solved with numerical method based on integrations Of equation over finite control volumes. The driving force for fluid flow is considered to be pressure difference due to the temperature distribution in the system. It is found that fluid flow enhances the local hydriding rate in the system by driving the hot fluid to the colder regions. The numerical results were found to agree satisfactorily with the experimental data available in the literature. Copyright (C) 2003 John Wiley Sons, Ltd.Öğe Numerical investigation of heat and mass transfer in a metal hydride bed(ELSEVIER SCIENCE INC, 2004) Dogan, A; Kaplan, Y; Veziroglu, TNThis paper presents a mathematical model for hydrogen storage in a metal hydride bed. For this purpose, a two-dimensional mathematical model which considers complex heat and mass transfer during the hydriding process is developed. The coupled differential equations are solved with a numerical method based on integrations of governing equation over finite control volumes. The driving force is considered to be pressure difference because of the temperature distribution in the system. The numerical results showed that the hydriding performance depends on the temperature distribution in the hydride bed. Fluid flow enhances the hydriding rate in the system by driving the hot fluid to the colder regions. The numerical results were found to agree satisfactorily with the experimental data available in the literature. (C) 2003 Elsevier Inc. All rights reserved.Öğe Numerical study of hydrogen absorption in an Lm-Ni-5 hydride reactor(PERGAMON-ELSEVIER SCIENCE LTD, 2001) Mat, MD; Kaplan, YMetal hydride formation in an Lm - Ni-5 storage tank is numerically studied with a continuum mathematical model. The model considers complex heat, and mass transfer and chemical reaction in the reaction bed. It is found that hydride formation enhances at regions with lower equilibrium pressure. The adsorbed hydrogen mass increases faster at the initial times of the hydriding process and slows down after the temperature of reaction bed increases due to the heat of the reaction. Numerical results agree satisfactorily with the experimental data in the literature. (C) 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.
