Papers by Keyword: Hydrogen

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Authors: A.Y. Hudeish, C.K. Tan, Azlan Abdul Aziz, Hassan Zainuriah
Abstract: There is a particular interest in the development of wide band gap semiconductor gas sensor because of their potential for high temperature operation and the ability to integrate them with power or microwave electrodes or with UV solar-blind detector and emitters fabricated in the same materials. AlGaN based devices are attractive for gas sensing in automotive exhausts and flow-gas, because of strong spontaneous polarization of AlGaN (free carrier concentration profiles inside this material that is very sensitive to any manipulation of surface change). In this report, we characterized the Ni/AlGaN/Sapphire Schottky barriers as hydrogen gas sensor at temperature range of 25°C to 500°C. A change in forward current was obtained in response to a change in ambient from pure N2 to 2% H2/ 98% N2, higher than the change in forward current obtained in Ni/GaN or Ni/Si Schottky diodes measured under the same conditions. The sensor response time was independent on the rate of mass transport of gas into the test chamber, while at high temperature, dissociation of gas controlled by the diffusion of atomic hydrogen through the metal/AlGaN surface, increased the sensor response time.
Authors: John Dunlop, Yves Bréchet, Laurent Legras
Abstract: During transport of spent Zircaloy-4 fuel rods, cladding temperatures can be expected to rise well over 400°C for transportation periods longer than 10 days. The kinetics of creep under these conditions will be controlled by both strain hardening and the softening effect of static annealing of cold work and irradiation defects. This paper will focus on the development of a coupled recovery/recrystallisation model for Zircaloy-4 from 400 – 520°C.
Authors: Hong Yun Ma, Li He Yin, Jun Zhang, Jin Ting Huang, Xiao yong Wang, Jia Qiu Dong
Abstract: Isotopic fractionation is the basic study of isotope tracer method. The most common fractionation of water in the natural is diffusion controlled kinetic fractionation in the process of evaporation. This process is now commonly represented by Cappa equation. In Cappa’s concept model, the atmosphere was divided into two layers, the free atmosphere and the laminar layer above the surface of evaporating water. In this article, a modified three layer model was used to represent experiments of Cappa (2003). It was shown that there was a third layer between free atmosphere and the laminar layer, the mixing layer. The simulated results also indicate that: (1) in test one, in which dry air was used as the inlet air, all vapor in the free air was from evaporating. Cappa Model can represents the experiment as well as the three layer model; (2) in test two, in which 50% humidity of air was used as the inlet air, results calculated by Cappa Model showed apparent depleted deviation from measured data; (3) the best fit result of test two supports the exist of the third layer, the mixed layer. It was also indicates that the vapor of mixed layer is made up of partial vapor from free atmosphere and all vapor from laminar layer. The modified Cappa model can represent all tests. Key words: Evaporation process, Hydrogen and oxygen stable isotopes, the factor of fractionation, Cappa Model
Authors: M. Johari Roudi, T. Mahmoodi
Abstract: Graphene is a 2D lattice of Carbon atoms which has a high potential to use it for hydrogen storage. In this paper we have studied theoretically the adsorption of hydrogen molecules on a single-layer graphene and we obtained the adsorption energy including optimized position and orientation of the hydrogen molecule with respect to the graphene surface in different points of the graphene lattice. We have done our calculations using Quantum-ESPRESSO code and applying pseudo-potential method in the framework of Density Functional Theory (DFT). We have used Local Density Approximation (LDA) for exchange correlation energy. Our result shows that adsorption energy is increased with decreasing the density of . However the maximum adsorption energy is occurred on the hollow position and for the surface homogenous arrangement.
Authors: X. Zhou, G.D. Watkins, K.M. McNamara Rutledge
Authors: Fabrizio Reale, Raffaela Calabria, Fabio Chiariello, Rocco Pagliara, Patrizio Massoli
Abstract: The combustion efficiency and the gaseous emission of a 100 kWe MGT, designed for working with natural gas but fuelled with blends containing up to 10% of hydrogen is investigated. A critical comparison between experimental data and results of the CFD analysis of the combustor is discussed. The k-epsilon RANS turbulence model and the Finite Rate – Eddy Dissipation combustion model were used in the numerical computations. The chemical kinetic mechanisms embedded were the 2-step Westbrook and Dryer for methane oxidation, 1-step Westbrook and Dryer for hydrogen oxidation and the Zeldovich mechanism for NO formation. The experimental data and numerical computations are in agreement within the experimental accuracy for NO emissions. Regarding CO, there is a significant deviation between experimental and computational data due to the scarce predictive capability of the simple two steps kinetic mechanism was adopted. From a practical point of view, the possibility of using fuels with a similar Wobbe index was confirmed. In particular the addiction of 10 % of hydrogen to pure methane doesn’t affect the behavior of the micro gas turbine either in terms of NO or CO emissions.
Authors: Zhi Guo Tang, P.Y. Ma, J.P. Cheng, Y.L. Li, Q.Z. Lin
Abstract: Hydrogen from biomass gasification is reviewed as one of the promising clean energies approaches in the future for fuel cell. However, the syngas from biomass gasification usually contains a certain amount of tar, which could not only decrease the efficiency of gasification process and hydrogen production, but also condense as a dense mixture and impose a series of serious problems. So “Excess Enthalpy Gasification (EEG)” is put forward and applied into biomass gasification and a novel biomass gasifier is presented for the purpose of tar-free and hydrogen-rich syngas in this work. The structure characteristic of the gasifier and tar conversion characteristic are analyzed detailedly to prove the feasibility and excellence performance for producing tar-free and hydrogen-rich syngas from biomass gasification.
Authors: Mikhail A. Bubenchikov, Alexander I. Potekaev, Alexey M. Bubenchikov
Abstract: We discuss one of the schemes of hydrogen evolution from a natural gas mixture. The scheme relies on the use of membranes formed by graphene plates containing calibrated pores in the crystalline structure. We provide the description scheme and the technology for calculating interaction between gas environment molecules and nanosized molecular structures. As an example, we consider mechanisms of hydrogen atoms penetration through defects in a graphene plate.
Authors: Yun Xue, Hai Quan Cao, Xue Cheng Lu
Abstract: Review is made of research on LPG engine and hydrogen fueled or enriched engine. Based on the positive features of hydrogen and the current limitations associated with the LPG intake liquid injection engine, a hydrogen enriched LPG intake liquid injection engine was developed, and its performance and exhaust emission characteristics are investigated.
Authors: Ervin Tal-Gutelmacher, Ryota Gemma, Eugen Nikitin, Astrid Pundt, Reiner Kirchheim
Abstract: Titanium and its conventional alloys reveal a high affinity for hydrogen, being capable to absorb up to 60 at.% hydrogen at 600°C, and even higher contents can be alloyed with titanium at lower temperatures. Hydrogen exhibits a low solubility in the low-temperature hexagonal closed-packed (hcp) α phase and a very high solubility (up to 50 at.%) in the high temperature body-centered cubic (bcc) β phase. The presence of hydrogen in the amount exceeding 200 ppm leads to formation of hydrides in α and α + β titanium alloys. While the aforementioned hydrogen behavior within bulk titanium has been well-established and reviewed, this is not the case with titanium thin films. The interpretation of results in these nanosized systems is complicated because the exact determination of the hydrogen concentration is difficult. However, using electrochemical hydrogen loading technique under the proper conditions, the hydrogen concentration can be accurately determined via Faraday’s law. In this study the thermodynamics of the titanium films during hydrogen absorption were investigated by electromotive force (EMF) measurements. Titanium films of different thicknesses were prepared on sapphire substrates in an UHV chamber with a base pressure of 10-8 mbar, using ion beam sputter deposition under Ar-atmosphere at the pressure of 1,5ּ10-4 mbar. The crystal structure was investigated by means of X-Ray diffraction using a Co-Kα radiation. For electrochemical hydrogen loading, the films were covered by a 30 nm thick layer of Pd in order to prevent oxidation and facilitate hydrogen absorption. The samples were step-by-step loaded with hydrogen by electrochemical charging, which was carried out in a mixed electrolyte of phosphoric acid and glycerin (1:2 in volume). An Ag/AgCl (sat.) and Pt wires were used as the reference and the counter electrode, respectively. XRD measurements were performed before and after hydrogenation in order to investigate the effect of hydrogen loading on the films microstructure. The role of varying thicknesses on the main characteristics of hydrogen's absorption behavior, as well as hydrogen-induced microstructural changes in titanium thin films, are discussed in detail.
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