The performance of hydrogen

The significance of the propellant stagnation temperature is further illustrated by the performance of hydrogen as a heat transfer rocket propellant, figure V.C.2. 

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How quickly can we cut the costs and improve the performance of hydrogen production, hydrogen storage, and fuel cells ... 

As discussed previously, in many propulsion systems the recovery of a large fraction of the dissociation energy in the nozzle expansion through recombination is difficult to achieve. While the assumption of frozen flow with respect to recombination reactions appears necessary for many heat transfer rocket nozzle expansions, it is possible that condensation phenomena are sufficiently rapid to provide near equilibrium flow with respect to phase changes. For this special possibility, phase equilibrium in the presence of frozen dissociation, it has been shown theoretically (48) that the performance in terms of specific impulse of propellants containing light metallic elements can exceed the performance of hydrogen. 

The aim of the Greek test site was to study the possibility for hydrogen to become an alternative product for wind-park developers, in case electricity transmission lines are saturated, studying at the same time the performance of hydrogen production and storage technologies under variable power input. 

While it is expected that electrocatalytic reactions on Ru surfaces should be strongly structure-sensitive, the first report on structural effects on hydrogen oxidation and evolution reactions appeared only recently The structural effects in the hydrogen oxidation reaction (HOR) and the hydrogen evolution reaction (HER) may be factors affecting the performance of hydrogen fuel cell anodes. 

Explore effects of fuels, fuel components, additives and impurities on the performance of hydrogen generation technologies... 

Recent developments in DMFCs, including published results of demonstration systems (Gottesfeld, 2002 Dohle et al 2002 and Ren, Zelanay et al 2000) indicate that a power of about 60 mW per square centimeter of electrode area is feasible, but is unlikely to be exceeded in the near fumre. This is considerably lower than the performance of hydrogen fuel cells and considerably constrains the area of application of this type of cell. 

Khorkounov B, Gebert A, Mickel C, Schultz L, Improving the performance of hydrogen storage electrodes based on mechanically alloyed Mgg3Ni3oY9 , Journal of Alloys and Compounds, 2008 458 479-486. 

Many problems with MNDO involve cases where the NDO approximation electron-electron repulsion is most important. AMI is an improvement over MNDO, even though it uses the same basic approximation. It is generally the most accurate semi-empirical method in HyperChem and is the method of choice for most problems. Altering part of the theoretical framework (the function describing repulsion between atomic cores) and assigning new parameters improves the performance of AMI. It deals with hydrogen bonds properly, produces accurate predictions of activation barriers for many reactions, and predicts heats of formation of molecules with an error that is about 40 percent smaller than with MNDO. 

The deterrnination of hydrogen content of an organic compound consists of complete combustion of a known quantity of the material to produce water and carbon dioxide, and deterrnination of the amount of water. The amount of hydrogen present in the initial material is calculated from the amount of water produced. This technique can be performed on macro (0.1—0.2 g), micro (2—10 mg), or submicro (0.02—0.2 mg) scale. Micro deterrninations are the most common. There are many variations of the method of combustion and deterrnination of water (221,222). The oldest and probably most reUable technique for water deterrnination is a gravimetric one where the water is absorbed onto a desiccant, such as magnesium perchlorate. In the macro technique, which is the most accurate, hydrogen content of a compound can be routinely deterrnined to within 0.02%. Instmmental methods, such as gas chromatography (qv) (223) and mass spectrometry (qv) (224), can also be used to determine water of combustion. 

Selectivity of propylene oxide from propylene has been reported as high as 97% (222). Use of a gas cathode where oxygen is the gas, reduces required voltage and eliminates the formation of hydrogen (223). Addition of carbonate and bicarbonate salts to the electrolyte enhances ceU performance and product selectivity (224). Reference 225 shows that use of alternating current results in reduced current efficiencies, especiaHy as the frequency is increased. Electrochemical epoxidation of propylene is also accompHshed by using anolyte-containing silver—pyridine complexes (226) or thallium acetate complexes (227,228). 

SolubiHty of carbon dioxide in ethanolamines is affected by temperature, amine solution strength, and carbon dioxide partial pressure. Information on the performance of amines is available in the Hterature and from amine manufacturers. Values for the solubiHty of carbon dioxide and hydrogen sulfide mixtures in monoethanolamine and for the solubiHty of carbon dioxide in diethanolamine are given (36,37). SolubiHty of carbon dioxide in monoethanolamine is provided (38). The effects of catalysts have been studied to improve the activity of amines and provide absorption data for carbon dioxide in both mono- and diethanolamine solutions with and without sodium arsenite as a catalyst (39). Absorption kinetics over a range of contact times for carbon dioxide in monoethanolamine have also been investigated (40). 

Jaquet and Miller [1985] have studied the transfer of hydrogen atom between neighbouring equilibrium positions on the (100) face of W by using a model two-dimensional chemosorption PES [McGreery and Wolken 1975]. In that calculation, performed for fairly high temperatures (T> rj the flux-flux formalism along with the vibrationally adiabatic approximation (section 3.6) were used. It has been noted that the increase of the coupling to the lattice vibrations and decrease of the frequency of the latter increase the transition probability. 

FRS. 1985. Evaluation of the Performance of an End-of-Line Flame Arrester When Subjected to Unconfmed Hydrogen-Air Explosions. Report of Investigation FRD 184/03 for IMl Amal Limited. Fire Research Station, Borehamwood, Herts., England. 

Run frequenqf calculations on the two vinyl alcohol isomers we considered in the last chapter. Optimize the structures at the RHF level, using the 6-31G(d) basis set, and perform a frequency calculation on each optimized structure. Are both of the forms minima What effect does the change in structure (i.e., the position of hydrogen in the hydroxyl group) have on the frequencies ... 

The recovery of hydrogen chloride as well as the production of hydrochloric acid is effectively performed in... 

Gladysheva, V. P. and Shatalov, A. Ya., Effect of Hydrogen-ion Concentration on the Performance of Differentially Aerated Couples , Izv. Vysshikh. Uchebn. Zavedenii, Khim. i Khim. Tekhnoi., 9, 48 (1966) C.A., 65, 5002a... 

Niobium like tantalum relies for its corrosion resistance on a highly adherent passive oxide film it is however not as resistant as tantalum in the more aggressive media. In no case reported in the literature is niobium inert to corrosives that attack tantalum. Niobium has not therefore been used extensively for corrosion resistant applications and little information is available on its performance in service conditions. It is more susceptible than tantalum to embrittlement by hydrogen and to corrosion by many aqueous corrodants. Although it is possible to prevent hydrogen embrittlement of niobium under some conditions by contacting it with platinum the method does not seem to be broadly effective. Niobium is attacked at room temperature by hydrofluoric acid and at 100°C by concentrated hydrochloric, sulphuric and phosphoric acids. It is embrittled by sodium hydroxide presumably as the result of hydrogen absorption and it is not suited for use with sodium sulphide. 

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