Papers by Keyword: Hydrogen

Abstract: The two-phase united anaerobic fermentation has been paid more and more attention in recent years. But how to increase the biogas production yield and the degradation rate of organic matter needs more research. The batch anaerobic fermentation studies demonstrated the feasibility of H2 and CH4 generation utilizing kitchen wastewater as substrate, and the vaccination rate, dilution rate, substrate concentration were optimized. The conclusion showed that dilution rate is the most important factor, following by kitchen wastewater concentration and inoculum volume. The most excellent program of the organic load, the inoculation volume and the dilution volume are 150 +300 ml, 135 ml, 225 ml, respectively. Under these conditions the hydrogen and methane production rate were the highest of 4.15 ml/ml，2.55 ml/ml (calculated as the wastewater volume), respectively. The acid-forming pathways of kitchen wastewater was typical butyric- propionic acid mixed fermentation type. The appropriate dilution could decrease the concentration of the total acids and increase the biogas production yield.

Abstract: Hydrogen is an important chemical commodity. Fluidized bed oxygen permeable membrane reactor is a novel technology for hydrogen production from natural gas reforming. An Aspen model is built for this novel reactor. Influences of reaction pressure, oxygen to carbon ratio, and steam to carbon ratio on the hydrogen concentration in syn-gas, hydrogen yield, and reaction temperature and methane conversion are studied. The results are compared with the ordinary fluidized bed reactor. It shows that the fluidized bed oxygen permeable membrane reactor has a higher methane conversion and a hydrogen yield and a higher hydrogen concentration in the syngas, due to its in-situ oxygen separation from air.

Abstract: Electrochemical Chloride Extraction (ECE) is a new method to halt the corrosion of steel in concrete contaminated by chloride. The bond strength between steel and concrete with and without ECE were tested through steel pull-out test, and the effects of current density and total charge passed during ECE on it were analyzed. A demo device was designed to analyze the hydrogen evolution during ECE by dividing the cathode reactions and anode reactions into two sealed bottles. The relation between hydrogen content and electrons passed in the circuit and the adverse effects of the hydrogen on steel reinforced concrete was conducted. Through drilling appropriate number of holes from concrete surface into the steel, some hydrogen can be released and its adverse effects can be mitigated in a certain degree.

Abstract: Hydrogen-induced defects of ZnO single crystals electrochemically charged with hydrogen have been investigated by positron beam-based Doppler broadening spectroscopy, X-ray diffraction (XRD) and optical microscopy (OM). XRD and OM results indicated that a deformation layer was formed due to hydrogen-induced structural change at the subsurface of ZnO single crystal. Slow positron beam measurements showed that this deformation layer contained many defects, such as dislocations and Zn vacancies, which led to increase of S parameter.

Abstract: In the present work hydrothermally grown ZnO single crystals were electrochemically charged with hydrogen. The influence of hydrogen on ZnO microstructure was investigated by positron annihilation spectroscopy (PAS) combined with X-ray diffraction (XRD) using synchrotron radiation. Hydrogen concentration in the samples was determined by nuclear reaction analysis (NRA). It was found that a high concentration of hydrogen can be introduced into ZnO by electrochemical loading. At low concentrations, absorbed hydrogen causes elastic volume expansion of ZnO crystal. At higher concentration, hydrogen-induced stresses exceed the yield stress in ZnO and plastic deformation of the crystal takes place leading to formation of a defected subsurface layer in the crystals.

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.

Abstract: Hydrogen absorption in Pd causes a significant volume expansion. In free-standing bulk Pd, the hydrogen-induced volume expansion is isotropic. However, the situation becomes more complicated in thin Pd films. Contrary to bulk samples, thin films are clamped to an elastically stiff substrate, which prevents in-plane expansion. Hence, the volume expansion of a thin film is strongly anisotropic because it expands in the out-of-plane direction only. Internal stresses introduced by absorbed hydrogen may become so high that detachment of a film from the substrate is energetically favorable and buckles of various morphologies are formed. In the present work, we studied hydrogen-induced buckling in a nanocrystalline thin Pd film deposited on a sapphire substrate. Slow positron implantation spectroscopy (SPIS) was employed as a principal tool for the characterization of defects and investigation of defect interactions with hydrogen. SPIS studies were combined with X-ray diffraction and direct observations of buckling by light microscopy. It was found that buckling of thin Pd film occurs at hydrogen concentrations x_H > 0.1 and is accompanied by a strong increase of dislocation density.

Abstract: Nominally undoped, hydrothermally grown ZnO single crystals have been investigated before and after exposure to remote H-plasma. Defect characterization has been made by two complementary techniques of positron annihilation: positron lifetime spectroscopy and coincidence Doppler broadening. The high-momentum parts of the annihilation photon momentum distribution have been calculated from first principles in order to assist in defect identification. The positron annihilation results are supplemented by Atomic Force Microscopy for characterization of the crystal surface. It was found that virgin ZnO crystal contains Zn-vacancies associated with hydrogen. H-plasma treatment causes a significant reduction in concentration of these complexes. Physical mechanism of this effect is discussed in the paper.

Abstract: The powder metallurgy (PM) approach is widely used for cost-effective production of titanium alloys and articles. In the PM approach the large specific surface of starting powders heightens the risk of excessive impurity presence and, hence, degradation of final alloy properties. The present study analyzes the opportunity to produce sintered commercially pure titanium (CP-Ti) with acceptable impurity content from powder materials. Starting titanium and titanium hydride powders were comparatively examined. The impurity elements (oxygen, chlorine, carbon) and their conditions on the powder particle surface, as well as the surface processes and gases emitted from powders upon heating, have been analyzed by means of surface science techniques. The role of hydrogen emitted from titanium hydride in material purification has been discussed. The opportunity to produce titanium materials with final admissible content of interstitials (O, C, Cl, and H) using starting titanium hydride powder has been demonstrated.

Abstract: Tin Brass Heat Exchanger Tube Was Hydrogen-Charged under Various Cathodic Charging Conditions. the Introduction of Charged Hydrogen into Tin Brass Tube Was Found to Induce Hardening of its Surface. the Severity and the Depth of the Hardened Region Was Observed to Increase with either Cathodic Current Density or Charging Time. Ageing after Charging Results in either Complete or Partial Recovery of Hardness, Depending upon the Charging Conditions Applied to the Heat Exchanger Tube.