Hydrogen diffusion coefficient in liquid metals evaluated by solid-gas eutectic unidirectional solidification

Based on the solid-gas eutectic unidirectional solidification technique and the principle of unidirectional solidification of single-phase alloy, a new method for evaluating the diffusion coefficient of hydrogen in liquid metals was proposed. Taking Cu-H2 system for example, the influences of argon partial pressure and superheat degree of melt on the diffusion coefficient of hydrogen in liquid metal were studied and the predicted values were similar to each other. The obtained temperature-dependent equation for diffusion coefficient of hydrogen in liquid copper is comparable with experimental data in literature, which validates the effectiveness of this method. The temperature-dependent equations for diffusion coefficient of hydrogen in liquid Mg, Si and Cu-34.6%Mn alloy were also evaluated by this method, along with the values at the melting point of each metal and alloy.

A novel solid-gas process to synthesize LaMnO_3 perovskite with high surface area and excellent activity for methane combustion

A novel solid-gas route to prepare LaMnO3 perovskite catalysts for methane combustion has been developed. The method was carried out using a polyvinylpyrrolidone-metal complex as precursor via a solid-gas process to obtain the target materials. The structure and properties of the precursor and the catalysts were characterized by FT-IR, TG-DSC, XRD and N2 adsorption-desorption techniques. The results indicate that the catalysts synthesized via the solid-gas process possess higher surface areas, better thermal resistance and catalytic activity as compared to those prepared with the conventional sol-gel citrate method.

Solid-gas interface thermal conductance for the thermal barrier coating with surface roughness:The confinement effect

The yttria-stabilized zirconia(YSZ)is a famous thermal barrier coating material to protect hot-end components of an engine.As a characteristic feature of the YSZ,the surface roughness shall play an important role in the interface thermal conductance between the YSZ and gas,considering that the gas is typically at an extremely high temperature.We investigate the effect of the surface roughness on the thermal conductance of the YSZ-gas interface with surface roughness described by nanoscale pores on the surface of the YSZ.We reveal two competitive mechanisms related to the microstructure of the pore,i.e.,the actual contact area effect and the confinement effect.The increase of the pore depth will enlarge the actual contact area between the YSZ and gas,leading to enhancement of the solid-gas interface thermal conductance.In contrast to the positive actual contact area effect,the geometry-induced confinement effect greatly reduces the interface thermal conductance.These findings shall offer some fundamental understandings for the microscopic mechanisms of the YSZ-gas interface thermal conductance.

Solid-gas Phase Preparation Method for Porous Molybdenum Trioxide

A novel solid-gas reaction preparation technology was used to adjust the composition and microstructure of the composite crystal materials by changing the preparation parameters. Compared with the commonly used sol-gel method, acid base neutralization sedimentation method, hydrothermal method, and gas phase deposition method, the technology was relatively simplified and the elemental composition was controllable, without the use of openings and additives. A kind of multi-element composite porous metal oxide was obtained by pre-intercalation and decarburization. In order to increase the porosity of MoO3 material and promote the adsorption and diffusion of reactant molecules, the microstructure of MoO3 was studied. The preparation process of porous molybdenum trioxide by solid gas combination process was discussed, which provides an innovative idea for the design and preparation of new materials with a large specific surface area and other desirable properties.

Dynamic modeling framework for solid-gas sorption systems

A dynamic modeling framework based on an intelligent approach is proposed to identify the complex behaviors of solid-gas sorption systems.An experimental system was built and tested to assist in developing a model of the system performance during the adsorption and desorption processes.The variations in the thermal effects and gaseous environment accompanying the reactions were considered when designing the model.An optimization platform based on a multi-population genetic algorithm and artificial criteria was established to identify the mod-eling coefficients and quantify the effects of condition changes on the reactions.The calibration of the simulation results against the tested data showed good accuracy,where the coefficient of determination was greater than 0.988.The outcome of this study could provide a modeling basis for the optimization of solid-gas sorption systems and contribute a potential tool for uncovering key characteristics associated with materials and components.

Constructal optimization for a solid-gas reactor based on triangular element

Entropy generation minimization for heat and mass transfer process in a solid-gas reactor is carried out based on constructal theory by using triangular elemental area. The aspect ratio of the triangular elemental area is optimized under constraint conditions. A number of optimal triangular elements are assembled to a new large rectangular area, which is optimised again. The procedure is repeated until the control-volume is covered, and the complete analytical results are obtained. The effects of some parameters on minimum entropy generation are analysed by nu-merical examples. The results show that smaller entropy generation can be ob-tained when the optimization for a given volume is carried out on the basis of tri-angular elements than those obtained on the basis of rectangular elements.

Flow characteristics and Shannon entropy analysis of dense-phase pneumatic conveying under high pressure

Experiments of dense-phase pneumatic conveying of pulverized coal using nitrogen are carded out in an experimental test facility with the conveying pressure up to 4. 0 MPa and the gas-solid ratio up to 450 kg/m^3. The influences of different conveying differential pressures, coal moisture contents, gas volume flow rates and superficial velocities on the solid-gas ratios are investigated. Shannon entropy analysis of pressure fluctuation time series is developed to reveal the flow characteristics. Through investigation of the distribution of the Shannon entropy under different conditions, the flow stability and the evolutional tendency of the Shannon entropy in different regimes and regime transition processes are discovered, and the relationship between the Shannon entropy and the flow regimes is also established. The results indicate that the solid-gas ratio and the Shannon entropy rise with the increase in conveying differential pressure. The solid-gas ratio and the Shannon entropy reveal preferable regularity with gas volume flow rates. The Shannon entropy is different for different flow regimes, and can be used to identify the flow regimes. Both mass flow rate and the Shannon entropy decrease with the increase in moisture contents. The Shannon entropy analysis is a feasible approach for researching the characteristics of flow regimes, flow stability and flow regime transitions in dense-phase pneumatic conveying under high pressure.

A new numerical approach of coupled modeling for solid deformation and gas leak flow in multi-coal-seams

From the viewpoint of interaction mechanics for solid and gas, a coupled mathematical model was presented for solid coal/rock deformation and gas leak flow in parallel deformable coal seams. Numerical solutions using the SIP (Strong Implicit Proce- dure) method to the coupled mathematical model for double parallel coal seams were also developed in detail. Numerical simulations for the prediction of the safety range using protection layer mining were performed with experimental data from a mine with potential danger of coal/gas outbursts. Analyses show that the numerical simulation results are consistent with the measured data in situ.

Numerical simulation of powder transport behavior in laser cladding with coaxial powder feeding

Laser cladding with coaxial powder feeding is one of the new ponent to improve performance of its surface. In the process, processes applied to produce well bonding coating on the com- the clad material is transported by the carrying gas through the coaxial nozzle, generating gas-powder flow. The powder feeding process in the coaxial laser cladding has important influence on the clad qualities. A 3D numerical model was developed to study the powder stream structure of a coaxial feeding nozzle. The predicted powder stream structure was well agreed with the experimental one. The validated model was used to explore the collision behavior of particles in the coaxial nozzle, as well as powder concentration distribution. It was found that the par- ticle diameter and restitution coefficient greatly affect the velocity vector at outlet of nozzle due to the collisions, as well as the powder stream convergence characteristics below the nozzle. The results indicated a practical approach to optimize the powder stream for the coaxial laser cladding.

Mass and Heat Transfer Enhancement of Chemical Heat Pumps

An inert additive, expanded graphite (EG), has been prepared and used to enhance the heat and mass transfer process of chemical heat pumps. The effects of mixing ratio and mixing method on the chemical reaction time are investigated.