Numerical Simulation of Erosion Characteristics for Solid-Air Particles in Liquid Hydrogen Elbow Pipe

The crystalline solid-air in the liquid hydrogen will cause erosion or friction on the elbow, which is directly related to the safety of liquid hydrogen transportation. The CFD-DPM model was used to study the erosion characteristics of solid-air to liquid hydrogen pipelines. Results show that the outer wall of the cryogenic liquid hydrogen elbow has serious erosion in the range of 60–90°, which is different from the general elbow. The erosion rate is linearly positively correlated with the mass flow of solid-air particles, and the erosion rate has a power function relationship with the liquid hydrogen flow rate. The fitted relationship curve can be used to predict the characteristics and range of the elbow erosion. The structure of the liquid hydrogen elbow also has an important influence on the solid-cavity erosion characteristics. The increase of the radius of curvature is conducive to the reduction of the maximum erosion rate, while the average erosion rate undergoes a process of increasing and then decreasing. The radius of curvature is 60 mm, which is the inflection point of the average erosion rate of the 90° elbow. The research results are expected to provide a theoretical basis for the prevention of liquid hydrogen pipeline erosion.

Variation of the Number of Heat Sources in Methane Dry Reforming: A Computational Fluid Dynamics Study

To overcome the weak point of the gas type heating (failure in heating uniformly and persistently), liquid type molten salt as a concentration of solar energy was considered as a heat source for dry reforming. This high-temperature molten salt flowing through the center of the tubular reactor supplies necessary heat. The dependence on the number of heat source of the hydrogen production was investigated under the assumption of the fixed volume of the catalyst bed. By changing these numbers, we numerically investigated the methane conversion and hydrogen flow rate to find the best performance. The results showed that the methane conversion performance and hydrogen flow rate improved in proportion to the number of heating tubes. For the one heat source, the reactor surrounded by a heat source rather than that located in the center is the best in terms of hydrogen yield. In addition, this study considered the case in which the system is divided into several smaller reactors of equal sizes and a constant amount of catalyst. In these reactors, we saw that the methane conversion and hydrogen flow rate were reduced. The results indicate that the installation of as many heating tubes as possible is preferable.

Evolution of Unidirectional Solidification Microstructure and Hydrogenated Treatment of Nb-Ti-Co Quasiperitectic Alloys

Titanium alloys have a wide range of applications, and the internal placement of hydrogen into them can modulate the microstructure of the alloys and thus have great potential for further development. However, few studies have been reported on the application of this technique to Nb-Ti-Co ternary alloys, which needs to be urgently investigated. In this paper, four types of alloys (Nb10Ti61Co29, Nb15Ti55Co30, Nb20Ti50Co30, and Nb25Ti50Co25) are selected near the eutectic point of the phase diagram to study their placement of hydrogen by both static and dynamic processes of hydrogen’s placements, focusing on the effects of the temperature, time, and hydrogen-flow rate of such processes on the amount of hydrogen placements. The relationship between the hydrogen replacement parameters and the mechanical properties of the alloys is constructed. The results show that the placed-hydrogen amount of Nb-Ti-Co as-cast alloy grows with the increase of hydrogen-flow rate and soaking (or holding) time, with an upper limit of the placed-hydrogen amount, and the pattern of the directionally- solidified alloys is similar to that of the as-cast alloys; however, at a certain soaking time and hydrogen- flow rate, although the placed hydrogen amount of both alloys rises with the increase of temperature, the placed-hydrogen amount of Nb-Ti-Co directionally-solidified alloys is always larger than that of the as-cast alloys. However, the amount of hydrogen placement in the Nb-Ti-Co directionally-solidified alloys is always larger than that in the as-cast alloys, and the amount of hydrogen placement decreases significantly as the growth rate of the alloys increases. In addition, the microhardness decreases with increasing growth rate in the directionally-solidified specimens, and the amount of hydrogen placement and microhardness increase with growing Nb content.

Amorphous-to-nanocrystalline transition in silicon thin films by hydrogen diluted silane using PE-CVD method

: Herein, we report effect of variation of hydrogen flow rate on properties of Si:H films synthesized using PE-CVD method. Raman spectroscopy analysis show increase in crystalline volume fraction and crystallite size implying that hydrogen flow in PECVD promote the growth of crystallinity in nc-Si:H films with an expense of reduction in deposition rate. FTIR spectroscopy analysis indicates that hydrogen content in the film increases with increase in hydrogen flow rate and hydrogen is predominantly incorporated in Si-H2 and (Si-H2)n bonding configuration. The optical band gap determined using E04 method and Tauc method (ETauc) show increasing trend with increase in hydrogen flow rate and E04 is found higher than ETauc over the entire range of hydrogen flow rate studied. We also found that the defect density and Urbach energy also increases with increase in hydrogen flow rate. Photosensitivity (Photo /Dark) decreases from  103 to  1 when hydrogen flow rate increased from 30 sccm to 100 sccm and can attributed to amorphous-to-nanocrystallization transition in Si:H films. The results obtained from the present study demonstrated that hydrogen flow rate is an important deposition parameter in PE-CVD to synthesize nc-Si:H films.

Structure of Diamond Films Grown Using High-Speed Flow of a Thermally Activated CH4-H2 Gas Mixture

Diamond films are advanced engineering materials for various industrial applications requiring a coating material with extremely high thermal conductivity and low electrical conductivity. An approach for the synthesis of diamond films via high-speed jet deposition of thermally activated gas has been applied. In this method, spatially separated high-speed flows of methane and hydrogen were thermally activated, and methyl and hydrogen radicals were deposited on heated molybdenum substrates. The morphology and structure of three diamond films were studied, which were synthesized at a heating power of 900, 1700, or 1800 W, methane flow rate of 10 or 30 sccm, hydrogen flow rate of 1500 or 3500 sccm, and duration of the synthesis from 1.5 to 3 h.The morphology and electronic state of the carbon on the surface and in the bulk of the obtained films were analyzed by scanning electron microscopy, Raman scattering, X-ray photoelectron, and near-edge X-ray absorption fine structure spectroscopies. The diamond micro-crystals with a thick oxidized amorphous sp2-carbon coating were grown at a heating power of 900 W and a hydrogen flow rate of 1500 sccm. The quality of the crystals was improved, and the growth rate of the diamond film was increased seven times when the heating power was 1700–1800 W and the methane and hydrogen flow rates were 30 and 3500 sccm, respectively. Defective octahedral diamond crystals of 30 μm in size with a thin sp2-carbon surface layer were synthesized on a Mo substrate heated at 1273 K for 1.5 h. When the synthesis duration was doubled, and the substrate temperature was decreased to 1073 K, the denser film with rhombic-dodecahedron diamond crystals was grown. In this case, the thinnest hydrogenated sp2-carbon coating was detected on the surface of the diamond crystals.