Preparation of Nitrogen-Doped Carbon Catalyst to Oxygen Reduction Reaction and Influence of Protective Gas Flowing on Its Activity

A non-precious metal catalyst MnHMTA/C to oxygen reduction reaction was prepared by py- rolyzing a precursor from manganese chloride, hexamethylenetetramine and acetylene black in nitrogen gas atmosphere. The effect of heat treatment temperature and flowing of nitrogen gas were investigated. A catalyst with the highest activity can be obtained at 700 ℃. Mn（Ⅱ） ion was changed to MnO in heat treatment, which improved the catalytic activity of the catalyst. Hexamethylenetetramine takes part in the formation of active site of the catalyst as its decomposed gases. The flowing of protective gas takes the decomposed gases out of the tube furnace and brings negative effect on the catalytic activity of the MnHMTA/C catalyst.

Criterion of gas and solid dual-phase flow atomization crash in molten metal

A self-invented atomization process, in which molten metal is atomized into powder by a high-velocity gas stream carrying solid particles as the atomization medium, was introduced. The characteristics of powders prepared by common gas atomization and dual-phase flow atomization under similar conditions were compared. The experimental results show that the dual-phase flow-atomized powders have average particle sizes that are one-half that of the common gas-atomized particles;additionally, they possess a finer microstructure and higher cooling rate under the same atomization gas pressure and the same gas flow. The Weber number in the crash criteria of liquid atomization is adopted to measure the crash ability of the atomization media. The Weber number of the dual-phase flow atomization medium is the sum of that of the gas and the solid particles. Furthermore, the critical equation of the crash model in dual-phase flow atomization is established, and the main regularities associated with this process were analyzed.

An integrated approach to study of strata behaviour and gas flow dynamics and its application

This paper presents an advanced and integrated research approach to longwall mining-induced strata move- ment, stress changes, fractures, and gas flow dynamics with actual examples of its application from recent studies for coextraction of coal and methane development at Huainan Mining Group in China, in a deep and multi-seam mining environment. The advanced approach takes advantage of the latest techniques in Australia for mine scale geotechnical characterisation, field measurement, monitoring and numerical modelling. Key techniques described in this paper include coal mine site 3D geotechnical characterisation methods, surface deep downhole multi-point extensometers and piezometers for overburden displacement and pore pressure measurements during mining, tracer gas tests for goal gas flow patterns, and advanced numerical modelling codes for coupled coal mine strata, water and gas simulations, and longwall goaf gas ttow investigations. This integrated approach has resulted in significant insights into the complex dynamic imeraction between strata, groundwater, and gas during mining at Huainan Mining Group in recent years. Based on the lindings from the extensive field monitoring and numerical modelling studies, a three-dimensional annular-shaped over-lying zone along the perimeter of the longwall panel was identified for optimal methane drainage during mining.

Partitioning characteristics of gas channel of coal-rock mass in mining space and gas orientation method

In order to research the influence of coal-rock mass morphology of mining space on the flow law of gas,the laboratory physical model and numerical computation methods were adopted to simulate coal mining activities.The simulation results indicate that,after coal seam mining,the loose rock accumulation body of free caving,ordered rock arrangement body of plate damage rich in longitudinal and transverse fractures and horizontal fissure body formed by rock mass deformation imbalance are formed from bottom to top in the mining space.For these three types of accumulation bodies,there are essential differences in the accumulation state,rock size and gas breakover characteristics.According to this,the coal-rock mass in the mining space is classified into gas turbulence channel area,gas transitional flow channel area and gas seepage channel area.In the turbulence channel area,the gas is distributed transversely and longitudinally and gas diffuses in the form of convection with Reynolds number R_e more than100;in the transitional flow channel area,one-way or two-way gas channels are crisscross and gas is of transitional flow regime with R,.between 10 and 100.In the seepage channel area,there are a few vertical gas channels with R,.less than 10.In this paper,the researches on the gas orientation method in different partitions were further carried out,gas orientation methods of low-level pipe burying,middle-level interception and high-level extraction were determined and an on-site industrial test was conducted,achieving the effective diversion of gas and verifying the reasonableness of gas channel partition.

Numerical simulation of a gas pipeline network using computational fluid dynamics simulators

This article describes numerical simulation of gas pipeline network operation using high-accuracy computational fluid dynamics (CFD) simulators of the modes of gas mixture transmission through long, multi-line pipeline systems (CFD-simulator). The approach used in CFD-simulators for modeling gas mixture transmission through long, branched, multi-section pipelines is based on tailoring the full system of fluid dynamics equations to conditions of unsteady, non-isothermal processes of the gas mixture flow. Identification, in a CFD-simulator, of safe parameters for gas transmission through compressor stations amounts to finding the interior points of admissible sets described by systems of nonlinear algebraic equalities and inequalities. Such systems of equalities and inequalities comprise a formal statement of technological, design, operational and other constraints to which operation of the network equipment is subject. To illustrate the practicability of the method of numerical simulation of a gas transmission network, we compare computation results and gas flow parameters measured on-site at the gas transmission enter-prise.

Gas Flow in Unilateral Opening Pulse Tubes Based on Real Gas Equation of State

The real gas effect is dominant at high pressure and low temperature, and it is modeled by complex equations of state other than perfect gas law. In the vicinity of liquid-vapor critical point, the real gas exhibits unusual gas dynamic behavior. In the present work, a transient wave fields in unilateral opening pulse tube is simulated by solving the Navier-Stokes equations incorporated with the Peng-Robinson thermodynamic model. The computational fluid dynamics （CFD） results show a remarkable deviation between perfect gas model and real gas model for contact interface and shockwave. The wave diagram based on the real gas model can help to solve the problem of offset design point.

Three-dimensional Simulation of Gas/Solid Flow in Spout-fluid Beds with Kinetic Theory of Granular Flow

A three-dimensional Eulerian multiphase model, with closure law according to the kinetic theory of granular flow, was used to study the gas/solid flow behaviors in spout-fluid beds. The influences of the coefficient of restitution due to non-ideal particle collisions on the simulated results were tested. It is demonstrated that the simulated result is strongly affected by the coefficient of restitution. Comparison of simulations with experiments in a small spout-fluid bed showed that an appropriate coefficient of restitution of 0.93 was necessary to simulate the flow characteristics in an underdesigned large size of spout-fluid bed coal gasifier with diameter of lm and height of 6m. The internal jet and gas/solid flow patterns at different operating conditions were obtained. The simulations show that an optimal gas/solid flow pattern for coal gasification is found when the spouting gas flow rate is equal to the fluidizing gas flow rate and the total of them is two and a half times the minimum fluidizing gas flow rate. Besides, the radial distributions of particle velocity and gas velocity show similar tendencies; the radial distributions of particle phase pressure due to particle collisions and the particle pseudo-temperature corresponding to the macroscopic kinetic energy of the random particle motion also show similar tendencies. These indicate that both gas drag force and particle collisions dominate the movement of particles.

Pressure-Driven Gas Flows in Micro Channels with a Slip Boundary:A Numerical Investigation

In this paper,flow of slightly rarefied compressible nitrogen in microchannels has been investigated numerically for low values of Reynolds and Mach numbers.The 2D governing equations were solved using Finite Element Method with first-order slip boundary conditions(Comsol Multiphysics software).A validation was performed by comparing with similar configuration from the literature.It was found that our model can accurately predict the pressure driven flow in microchannels.Several interesting findings are reported about the Relative pressure,longitudinal velocity,Mach number,effect of gas rarefaction and flow rate.

Gas–liquid flow mass transfer in a T-shape microreactor stimulated with 1.7 MHz ultrasound waves

This paper describes the application of ultrasound waves on hydrodynamics and mass transfer characteristics in the gas–liquid flow in a T-shape microreactor with a diameter of 800 μm. A 1.7 MHz piezoelectric transducer(PZT) was employed to induce the vibration in this microreactor. Liquid side volumetric mass transfer coefficients were measured by physical and chemical methods of CO_2 absorption into water and Na OH solution. The approach of absorption of CO_2 into a 1 mol·L^(-1) Na OH solution was used for analysis of interfacial areas. With the help of a photography system, the fluid flow patterns inside the microreactor were analyzed. The effects of superficial liquid velocity, initial concentration of Na OH, superficial CO_2 gas velocity and length of microreactor on the mass transfer rate were investigated. The comparison between sonicated and plain microreactors(microreactor with and without ultrasound) shows that the ultrasound wave irradiation has a significant effect on kLa and interfacial area at various operational conditions. For the microreactor length of 12 cm, ultrasound waves improved kLa and interfacial area about 21% and 22%, respectively. From this study, it can be concluded that ultrasound wave irradiation in microreactor has a great effect on the mass transfer rate. This study suggests a new enhancement technique to establish high interfacial area and kLa in microreactors.

Gas-kinetic numerical method for solving mesoscopic velocity distribution function equation

A gas-kinetic numerical method for directly solving the mesoscopic velocity distribution function equation is presented and applied to the study of three-dimensional complex flows and micro-channel flows covering various flow regimes. The unified velocity distribution function equation describing gas transport phenomena from rarefied transition to continuum flow regimes can be presented on the basis of the kinetic Boltzmann-Shakhov model equation. The gas-kinetic finite-difference schemes for the velocity distribution function are constructed by developing a discrete velocity ordinate method of gas kinetic theory and an unsteady time-splitting technique from computational fluid dynamics. Gas-kinetic boundary conditions and numerical modeling can be established by directly manipulating on the mesoscopic velocity distribution function. A new Gauss-type discrete velocity numerical integra- tion method can be developed and adopted to attack complex flows with different Mach numbers. HPF paral- lel strategy suitable for the gas-kinetic numerical method is investigated and adopted to solve three-dimensional complex problems. High Mach number flows around three-dimensional bodies are computed preliminarilywith massive scale parallel. It is noteworthy and of practical importance that the HPF parallel algorithm for solving three-dimensional complex problems can be effectively developed to cover various flow regimes. On the other hand, the gas-kinetic numerical method is extended and used to study micro-channel gas flows including the classical Couette flow, the Poiseuillechannel flow and pressure-driven gas flows in twodimensional short micro-channels. The numerical experience shows that the gas-kinetic algorithm may be a powerful tool in the numerical simulation of microscale gas flows occuring in the Micro-Electro-Mechanical System （MEMS）.

Propagation law of shock waves and gas flow in cross roadway caused by coal and gas outburst

In order to study the propagation law of shock waves and gas flow during coal and gas outburst,we analyzed the formation process of outburst shock waves and gas flow and established the numerical simulation models of the roadways with 45°intersection and 135°intersection to simulate the propagation of outburst gas flow and the process of gas transport.Based on the analysis of the simulation results,we obtained the qualitative and quantitative conclusions on the characteristics and patterns of propagation and attenuation of outburst shock waves and gas flow.With the experimental models,we investigated the outburst shock waves and gas flow in the roadways with the similar structures to the simulated ones.According to the simulation results,when the angle between the driving roadway and the adjacent roadway increased,the sudden pressure variation range in adjacent roadway and the influencing scope of gas flow increased and the sudden pressure variation duration decreased.The intersection between the driving roadway and the adjacent roadway has no effect on airflow reversal induced by the shock waves and gas flow.

Effects of Gas Flow Field on Clogging Phenomenon in Close-Coupled Vortical Loop Slit Gas Atomization

In order to study the basic characteristics of gas flow field in the atomizing chamber near the nozzle outlet of the vortical loop slit atomizer and its influence mechanism on clogging phenomenon,the computational fluid dynamics(CFD)software Fluent is used to conduct a numerical simulation of the gas flow field in the atomizing chamber near the nozzle outlet of this atomizer under different annular slit widths,different atomization gas pressures and different protrusion lengths of the melt delivery tube. The results show that under atomization gas pressure p=4.5 MPa,the greater the annular slit width D,the lower the static temperature near the central hole outlet at the front end of the melt delivery tube,and the smaller the aspirating pressure at the front end of the melt delivery tube. These features can effectively prevent the occurrence of the clogging phenomenon of metallic melt. Under an annular slit width of D=1.2 mm,when the atomization gas pressure satisfies 1 MPa ≤ p ≤ 2 MPa and increases gradually,the aspirating pressure at the front end of the melt delivery tube will decline rapidly. This can prevent the clogging phenomenon of metallic melt. However,when the atomization gas pressure p >2 MPa,the greater the atomization gas pressure,the lower the static temperature near the central hole outlet at the front end of the melt delivery tube,and the greater the aspirating pressure at the front end of the melt delivery tube. Hence,the effect of preventing the solidification-induced clogging phenomenon of metallic melt is restricted. When atomization gas pressure is p =4.5 MPa and annular slit width is D=1.2 mm,the greater the protrusion length H of the melt delivery tube,and the smaller the aspirating pressure at its front end. The static temperature near the central hole that can be observed in its front end is approximate to effectively prevent the occurrence of clogging phenomenon of metallic melt. However,because of the small aspirating pressure,the metallic melt flows into the atomizing chamber from the central hole at the front end of the melt delivery tube at an increasing speed and the gas-melt ratio in the mass flow rate is reduced,which is not conducive to the improvement of atomization performance.

On the Development of a Model for the Prediction of Liquid Loading in Gas Wells with an Inclined Section

The ability to predict liquid loading in horizontal gas wells is of great importance for determining the time of drainage and optimizing the related production technology.In the present work,we describe the outcomes of experiments conducted using air-water mixtures in a horizontal well.The results show that the configuration with an inclined section is the most susceptible to liquid loading.Laboratory experiments in an inclined pipe were also conducted to analyze the variation of the critical gas flow rate under different angles,pressure and liquid volume(taking the equal liquid volume at inlet and outlet as the criterion for judging on the critical state).According to these results,the related angle of the inclined section ranges from 45°to 60°.Finally,a modified approach based on the Belfroid model has been used to predict the critical gas flow rate for the inclined section.After comparison with field data,this modified model shows an accuracy of 96%,indicating that it has better performances with respect to other models used in the past to predict liquid loading.

Parametric study of gas−liquid two-phase flow field in horizontal stirred tank

Based on Fluent software,the gas−liquid two-phase flow in the horizontal stirred tank was simulated with SST k−ωturbulence model,Eulerian−Eulerian two-fluid model,and multi-reference flame method.The mixing process in the tank was calculated by tracer method.The results show that increasing the rotating speed or gas flow is conducive to a more uniform distribution of the gas phase and accelerates the mixing of the liquid phase.When the rotating speed exceeds 93 r/min,the relative power demand remains basically constant.The change in the inclination angle of the upper impeller has minimal effect on the gas phase distribution.When the inclination angle is 50°,the relative power demand reaches the maximum.An appropriate increase in the impeller distance from the bottom improves the gas holdup and gas phase distribution but increases the liquid phase mixing time.

A Mathematical Model on Vacuum Chamber of a Multifunctional RH-degasser

A 3D-mathematical model was developed for the simulation of gas flow, combustion and heat convection in RH vacuum chamber. Under different conditions, the influences of the Kawasaki Oxygen Top Blowing system (KTB) on the gas flow, chemical reactions and temperature distributions were calculated based on the model. The optimum position of the lance is suggested for the RH-KTB degassing process.

Numerical analysis of gas emission rule from a goaf of tailing roadway

Targeting the problem of large amounts of gas emission from the goaf of the No.14201 working face in the Shaqu coal mine of Huajin Coking Coal Co. Ltd., we used a negative exponential function to describe the attenuation process of gas emission in goaf (the stable source) based on the principle of field flow. Equations of two-component flow (gas and air) and seep- age-diffusion in a heterogeneous goaf flow field are solved by means of numerical simulation and fluid mechanics principles of air movement and gas distribution during gas emission from goaf. The results indicate that the air diversion volume has a negative, exponential relation with the volume of gas emitted from goaf to the working face and is clearly inversely related to gas concentra- tion. We calculated the minimum amount of air diversion and distributed air volume in the tailing roadway required for safe pro- duction.

Temperature influence on macro-mechanics parameter of intact coal sample containing original gas from Baijiao Coal Mine in China

Investigation of temperature effect on mechanical parameters of coal is very important for understanding the mechanical response of coal bed at high temperature.It is especially benefcial for mitigating the thermal-induced disasters occurred in those coal mines suffering from heat hazard.In this work,coal samples,obtained from the No.2442 working face of Baijiao Coal Mine,were subjected to uniaxial compression ranging from 20 to 40℃ with an interval of 5℃.The apparatus used was designed to obtain deformation of a stressed sample,as well as the emission of gases desorbing from coal matrix.The adsorbed gas desorption caused by heating is measured during the entire testing.It is evident that the concentrations of releasing gas(containing methane,carbon dioxide and ethane)slightly rise with increasing temperature.Gas movement observed is closely related to the deformation of coal sample.Both uniaxial compressive strength and elastic modulus of coal samples tend to reduce with temperature.It reveals that increasing temperature can not only result in thermal expansion of coal,but also lead to desorption of preexisting gas in coal which can in turns harden coal due to shrinks of the coal matrix.Even though desorption of adsorbed gas can contribute to the hardening effect for the heated coal,by comparison to the results,it could be inferred that the softening of coal resulted from thermal expansion still predominates changes in mechanical characters of coal sample with temperature at the range from20 to 40℃.

Permeability evolution and gas flow in wet coal under non-equilibrium state:Considering both water swelling and process-based gas swelling

Accurate knowledge of gas flow within the reservoir and related controlling factors will be important for enhancing the production of coal bed methane.At present,most studies focused on the permeability evolution of dry coal under gas adsorption equilibrium,gas flow and gas diffusion within wet coal under the generally non-equilibrium state are often ignored in the process of gas recovery.In this study,an improved apparent permeability model is proposed which accommodates the water and gas adsorption,stress dependence,water film thickness and gas flow regimes.In the process of modeling,the water adsorption is only affected by water content while the gas adsorption is time and water content dependent;based on poroelastic mechanics,the effective fracture aperture and effective pore radius are derived;and then the variation in water film thickness for different pore types under the effect of water content,stress and adsorption swelling are modeled;the flow regimes are considered based on Beskok’s model.Further,after validation with experimental data,the proposed model was applied to numerical simulations to investigate the evolution of permeability-related factors under the effect of different water contents.The gas flow in wet coal under the non-equilibrium state is explicitly revealed.

Gas Flow Distribution in Pelletizing Shaft Furnace

Through thermal test, cold state experiment, analysis and simulation of thermal process, the gas flow distribution in pelletizing shaft furnace （PSF） was discussed. The results show that there are five flowing trends among them, the downward roasting gas and the upward cooling gas are the most unsteady, which influence flow distribution greatly. Among the operating parameters, the ratio of inflow is a key factor affecting the flow distribution. The roasting and cooling gases will entirely flow into the roasting zone and internal vertical air channels （IVAC）, respectively, if the ratio of inflow is critical. From such a critical operating condition increasing roasting gas flow or decreasing cooling gas flow, the roasting gas starts flowing downwards so as to enter the inside of IVAC the greater the ratio of inflow, the larger the downward flowrate. Among constructional parameters, the width of roasting zone b1, width of IVAC b2 and width of cooling zone b3, and the height of roasting zone h1, height of soaking zone h2 and height of cooling zone hs are the main factors affecting flow distribution. In case the ratio of b2/b3, or h3/h2, or h1/h2 is increased, the upward cooling gas tends to decrease while the downward roasting gas tends to increase with a gradual decrease in the ratio of inflow.

“Redistribution” Effect of Lumpy Zone for Gas Flow in BF

The gas flow from tuyere to raceway zone by blasting involves three distributional zones, such as dripping, cohesive, and lumpy zone. The gas flow distribution in lumpy zone directly affects the gas utilization ration and smooth operation in the blast furnace. However, the furnace closeness brings about great difficulty in the study of high-temperature gas flow. The charging and blasting system affecting the gas flow and whether the top gas flow distribution could reflect its inner condition as well as the furnace state, such as hanging or scaffolding, which have become the main problems for the research on gas flow. Recently, several researches overseas studied gas flow distribution using the numerical simulation method; however, such a research was rare amongst the natives. In this study, the flow model of gas in cohesive and lumpy zone was established using the numerical simulation software and the gas flow distributions with uniform distribution of burden permeability, scaffolding of wall, and nonuniform charge level were analyzed. As a result, the effects of cohesive zone and lower parts on the gas flow are very limited and the charge level largely affects the distribution of top gas flow. Therefore, it was found that the distribution of top gas flow could hardly reflect the inner gas flow. The process is called ＂redistribution＂ effect, which means that the gas flow after passing through the raceway, dripping, and cohesive zone is distributed when it flows into the lumpy zone.