Mahmut D. Mat

Numerical study of hydrogen absorption in an Lm−Ni5 hydride reactor

Abstract Metal hydride formation in an Lm−Ni5 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. Nomenclature C p specific heat ( J kg −1 K −1 ) E a activation energy ( J mol −1 ) H reactor height (m) K permeability ( m 2 ) m hydrogen mass absorbed ( kg m −3 s −1 ) M moleculer weight ( kg mol −1 ) P pressure (Pa) R universal gas constant ( J mol −1 K −1 ) T temperature (K) t time (s) V gas velocity ( m s −1 ) Greek letters e porosity λ thermal conductivity ( W m −1 K −1 ) μ dynamic viscosity ( kg m −1 s −1 ) ρ density ( kg m −3 ) Subscripts e effective eq equilibrium f cooling fluid g gas s solid ss saturated

A three-dimensional mathematical model for absorption in a metal hydride bed

Heat 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.

Application of a hybrid model of mushy zone to macrosegregation in alloy solidification

Abstract Solidification of an aqueous ammonium chloride (NH 4 Cl–H 2 O) solution inside a two-dimensional cavity is numerically investigated using a continuum mixture mathematical model. The mushy region where solid and liquid phases co-exist is considered a non-Newtonian fluid below a critical solid fraction, and a porous medium thereafter. This critical solid fraction is chosen as that corresponding to the coherency point, where a solid skeleton begins to form. The numerical results show that the solidification of a hypereutectic NH 4 Cl–H 2 O solution is mainly characterized by the rejection of solute at the mushy region and double diffusive convection induced by the opposing solutal and thermal buoyancy forces. The mathematical model agrees satisfactorily with the available experimental and numerical data.

Experimental and numerical investigation of effect of particle size on particle distribution in particulate metal matrix composites

The effect of particle size on particle distribution during the casting of particulate metal matrix composites (PMMC) is experimentally and numerically investigated. Pb20% Sn alloy and Zr2O3 particles are employed as matrix and reinforcing materials respectively. The casting is performed with an inert gas pressure. The final product is sectioned at several locations and particle fraction is determined using image processing software. Particle fraction is numerically determined by following trajectories of selected particles. It is found that particle fraction decreases along the mold and segregation is reduced with larger particles. The numerical results agree reasonable with experimental data

A TWO PHASE MODEL FOR ELECTROCHEMICAL SYSTEMS

Two phase flow is encountered in many electrochemical systems and play vital role on system efficiency, species transport, velocity distribution etc. A two phase flow model which accounts specific nature of liquid and gaseous phase is developed. The model applied to water electrolysis in an electrochemical cell. Transport equations are solved numerically for both phases with allowance for inter — phase mass and momentum Exchange. Liquid and gaseous phase distributions velocities, current density distribution are calculated under various working conditions.

Direct Methanol Solid Oxide Fuel Cell

In this study, performance of membrane electrode assembly (MEA) was studied with hydrogen and methanol/water vapor fed directly to the anode. MEA was prepared by using scandia-stablized zirconia (SSZ) electrolyte and NiO-SSZ and Sr-doped lanthanum ferrite (LSF) as anode and cathode material. A three dimensional model of solid oxide fuel cell (SOFC) has been developed and is used to predict the temperature, fuel concentration distribution across the cell. On the other hand we designed special experimental set up for testing MEA performance. The influence of different operation parameters (temperature, fuel concentration, fuel-air flow rate...) to the MEA performance was examined. The results show the maximum power generation from MEA when fed with methanol and hydrogen. The maximum power output of 1.6 W/cm² was obtained at 750oC with pure hydrogen. When methanol was directly used as fuel the maximum power output was 1.2 W/cm² at same temperature.

Effect of Nano Ion Conductor Infiltration on the Performance of Anode Supported Solid Oxide Fuel Cells

A high performance anode supported solid oxide fuel cell (SOFC) is developed by low-cost tape casting, co-sintering and nano-ion conductor infiltration techniques. A mixture of gadolinium and cerium nitrate solution is infiltrated into both anode and cathode layers and fired at a temperature that gadolinium nitrate and cerium nitrate undergoes a solid state reaction and forms nano ion conductor phase in both electrodes. The effect of molar concentrations and firing temperature of nano ion conductor phase on the cell performance are investigated. The measurements show that nano-sized ion conductor infiltration significantly improves the cell performance. The cell provides 1.718 Wcm -2 maximum power density at an operation temperature of 750°C. The high performance is attributed to increase in the oxide ion conductivity and three phase boundaries of both anode and cathode layers by nano ion-conductor infiltration.