Mechanism model for shale gas transport considering diffusion, adsorption/desorption and Darcy flow

To improve the understanding of the transport mechanism in shale gas reservoirs and build a theoretical basic for further researches on productivity evaluation and efficient exploitation, various gas transport mechanisms within a shale gas reservoir exploited by a horizontal well were thoroughly investigated, which took diffusion, adsorption/desorption and Darcy flow into account. The characteristics of diffusion in nano-scale pores in matrix and desorption on the matrix surface were both considered in the improved differential equations for seepage flow. By integrating the Langmuir isotherm desorption items into the new total dimensionless compression coefficient in matrix, the transport function and seepage flow could be formalized, simplified and consistent with the conventional form of diffusion equation. Furthermore, by utilizing the Laplace change and Sethfest inversion changes, the calculated results were obtained and further discussions indicated that transfer mechanisms were influenced by diffusion, adsorption/desorption. The research shows that when the matrix permeability is closed to magnitude of 10^-9D, the matrix flow only occurs near the surfacial matrix; as to the actual production, the central matrix blocks are barely involved in the production; the closer to the surface of matrix, the lower the pressure is and the more obvious the diffusion effect is; the behavior of adsorption/desorption can increase the matrix flow rate significantly and slow down the pressure of horizontal well obviously.

Research on attenuation characteristic of sound wave in coal or rock body

In order to using power sound wave increase permeability of coal, rules of attenuation of sound wave in coal should be studied. In this paper, characteristic and mechanism of attenuation of sound wave in coal was researched according to acoustic theory and attenuation coefficients was estimated by acoustic parameter of coal. The research results show that the main attenuation mechanism of sound wave in coal is absorption attenuation and scattering attenuation. The absorption attenuation includes viscous absorption, thermal conduction absorption and relaxation absorption. Attenuation coefficient of sound wave in gaseous coal is 38.5 Np/m. Researches on attenuation characteristic of sound wave will provide the theoretical basis for power sound wave improving permeability of coal and accelerating desorption of coal bed gas.

Mixing in Shallow Waters: Measurements, Processing, and Applications

Microstructure profiling measurements taken on a shallow Black Sea shelf and in Lake Banyoles and Boadella reservoir （Both in Spain） are analyzed to investigate the influence of boundary-layer-induced turbulence of various sources on mixing in the water interior. The state of turbulence in shallow waters is examined and details of microstructure data processing and error analysis are discussed. The dependence between averaged activity parameter A6 and buoyancy Reynolds number Reb for the shelf turbulence indicates that for Reb 〈 1 the state of turbulence can be described by the fossil turbulence model, which postulates AG - Re b^1/2. For Reb 〉 1, however, the influence of Reb on Ao is weak, signifying that the buoyancy Reynolds number can no longer serve as the governing parameter for active turbulent mixing. The generation of turbulence by a one-minute long wind bursts （the Boadella reservoir） increases the averaged dissipation rate （ε） of the surface mixed layer by more than 5 times （up to 3 × 10^-6 W kg^-1）. The influence of the wind bursts was also traced below the thermocline, where turbulent patches with （ε） = （10^-7 - 10^-6） W kg^-1 were generated. It is shown that the geothermal convection in Lake Banyoles produces intermittent turbulent patches with characteristic dissipation rate （ε） = （2 × 10^-8- 3 × 10^-7） W kg^-1, which influences the overall vertical mixing in the basin.

A coupled DEM and LBM model for simulation of outbursts of coal and gas

An outburst of coal and gas is a major hazard in underground coal mining. It is generally accepted that an outburst occurs when certain conditions of stress, coal gassiness and physical-mechanical properties of coal are met. Outbursting is recognized as a two-step process, i.e., initiation and development. In this paper, we present a fully-coupled solid and fluid code to model the entire process of an outburst. The deformation, failure and fracture of solid （coal） are modeled with the discrete element method, and the flow of fluid （gas and water） such as free flow and Darcy flow are modeled with the lattice Boltzmann method. These two methods are coupled in a two-way process, i.e., the solid part provides a moving boundary condition and transfers momentum to the fluid, while the fluid exerts a dragging force upon the solid. Gas desorption from coal occurs at the solid-fluid boundary, and gas diffusion is implemented in the solid code where particles are assumed to be porous. A simple 2D example to simulate the process of an outburst with the model is also presented in this paper to demonstrate the capability of the coupled model.

Collision Statistics of Driven Polydisperse Granular Gases

We present a dynamical model of two-dimensional polydisperse granular gases with fractal size distribution, in which the disks are subject to inelastic mutual collisions and driven by standard white noise. The inhomogeneity of the disk size distribution can be measured by a fractal dimension df. By Monte Carlo simulations, we have mainly investigated the effect of the inhomogeneity on the statistical properties of the system in the same inelasticity case. Some novel results are found that the average energy of the system decays exponentially with a tendency to achieve a stable asymptotic value, and the system finally reaches a nonequilibrium steady state after a long evolution time. Furthermore, the inhomogeneity has great influence on the steady-state statistical properties. With the increase of the fractal dimension df, the distributions of path lengths and free times between collisions deviate more obviously from expected theoretical forms for elastic spheres and have an overpopulation of short distances and time bins. The collision rate increases with df, but it is independent of time. Meanwhile, the velocity distribution deviates more strongly from the Gaussian one, but does not demonstrate any apparent universal behavior.

Effect of protective coal seam mining and gas extraction on gas transport in a coal seam

A gas–solid coupling model involving coal seam deformation,gas diffusion and seepage,gas adsorption and desorption was built to study the gas transport rule under the effect of protective coal seam mining.The research results indicate:(1) The depressurization effect changes the stress state of an overlying coal seam and causes its permeability to increase,thus gas in the protected coal seam will be desorbed and transported under the effect of a gas pressure gradient,which will cause a decrease in gas pressure.(2) Gas pressure can be further decreased by setting out gas extraction boreholes in the overlying coal seam,which can effectively reduce the coal and gas outburst risk.The research is of important engineering significance for studying the gas transport rule in protected coal seam and providing important reference for controlling coal and gas outbursts in deep mining in China.

Direct Numerical Simulation of Particle Dispersion in Gas-Solid Compressible Turbulent Jets

A numerical method was developed to directly simulate the compressible, particle-laden turbulent jets.The fourth order compact finite difference schemes were used to discretize the space derivatives. The Lagrangian method was adopted to simulate the particle motion based on one-way coupling. It is found that the turbulent intensity profiles attain self-similar status in the jet downstream regions. At the Stokes number of 1, particles are concentrated largely in the outer boundaries of the large-scale vortex structures with the most uneven distribution and the widest dispersion in the lateral direction. Particles at the much smaller Stokes numbers are distributed evenly in the flow field, and the lateral dispersion is also considerable. Distribution of particles at much larger Stokes numbers is more uniform and the lateral dispersion becomes small. In addition, the inflow conditions have different effects on the particle dispersion. The direct numerical simulation (DNS) results accord with the previous experiments and numerical studies.

Influence of impeller diameter on overall gas dispersion properties in a sparged multi-impeller stirred tank

The impeller configuration with a six parabolic blade disk turbine below two down-pumping hydrofoil propellers, identified as PDT + 2CBY, was used in this study. The effect of the impeller diameter D, ranging from0.30 T to 0.40T(T as the tank diameter), on gas dispersion in a stirred tank of 0.48 m diameter was investigated by experimental and CFD simulation methods. Power consumption and total gas holdup were measured for the same impeller configuration PDT + 2CBY with four different D/T. Results show that with D/T increases from 0.30 to 0.40, the relative power demand(RPD) in a gas–liquid system decreases slightly. At low superficial gas velocity VSof 0.0078 m·s-1, the gas holdup increases evidently with the increase of D/T. However, at high superficial gas velocity, the system with D/T = 0.33 gets a good balance between the gas recirculation and liquid shearing rate, which resulted in the highest gas holdup among four different D/T. CFD simulation based on the two-fluid model along with the Population Balance Model(PBM) was used to investigate the effect of impeller diameter on the gas dispersion. The power consumption and total gas holdup predicted by CFD simulation were in reasonable agreement with the experimental data.

Calculation of Transport Properties of CF4＋Noble Gas Mixtures

The present work is concerned with determining the viscosity,diffusion,thermal diffusion factor and thermal conductivity of five equimolar binary gas mixtures including:CF4-He,CF4-Ne,CF4-Ar,CF4-Kr,CF4-Xe from the principle of corresponding states of viscosity by the inversion technique.The Lennard-Jones (12-6) model potential is used as the initial model potential.The calculated interaction potential energies obtained from the inversion procedure is employed to reproduce the viscosities,diffusions,thermal diffusion factors,and thermal conductivities.The accuracies of the calculated viscosity and diffusion coefficients were 1% and 4%,respectively.

Overview of flowline bundle technology from concept selection to offshore installation

Flowline bundle system consisting of carrier pipe,sleeve pipe and internal flowlines offers innovative solution for the infield transportation of oil and gas. Due to its features,flowline bundle offers a couple of advantages over conventional flowline in particular for cases where multi-flowlines and high thermal performance is of great interest. The main benefits and advantages of such system include excellent thermal performance to prevent wax formation and hydrates,multiple bundled flowlines,mechanical and corrosion protection,potential reuse, etc. With the developments of offshore oil and gas industries,more and more hydrocarbon resources are being explored and discovered from shallow to deep water. Pipeline bundle system can be a smart solution for certain applications,which can be safe and cost effective solution. The objective of this paper is to overview pipeline bundle technology,outline detailed engineering design issue and procedure. Focus is given to its potential application in offshore for infield transportation. Engineering design principles and procedures for pipeline bundle system are highlighted. Construction methods of flowline bundle onshore are reviewed. Offshore towing and installation of pipeline bundle procedure is outlined.

Enhancement of Proton Exchange Membrane Fuel Cell Performance Using a Novel Tapered Gas Channel

Based on use of multi-dimensional models,this investigation simulates the performance of a proton exchange membrane fuel cell by varying the channel pattern.In the one-dimensional model,the porosity of the gas diffusion layer is 0.3.The model reveals the water vapor distribution of the fuel cell and demonstrates that the amount of water vapor increases linearly with the reduction reaction adjacent to the gas channel and the gas diffusion layer.Secondly,four novel tapered gas channels are simulated by a two-dimensional model.The model considers the distributions of oxygen,the pressure drop,the amount of water vapor distribution and the polarization curves.The results indicate that as the channel depth decreases,the oxygen in the tapered gas channel can be accel-erated and forced into the gas diffusion layer to improve the cell performance.The three-dimensional model is employed to simulate the phenomenon associated with four novel tapered gas channels.The results also show that the best performance is realized in the least tapered gas channel.Finally,an experimentally determined mechanism is found to be consistent with the results of the simulation.

Kinetic characteristics of coal gas desorption based on the pulsating injection

In order to understand the kinetic characteristics of coal gas desorption based on the pulsating injection （PI）, the research experimentally studied the kinetic process of methane desorption in terms of the PI and hydrostatic injection （HI）. The results show that the kinetic curves of methane desorption based on PI and HI are consistent with each other, and the diffusion model can best describe the characteristics of meth- ane desorption. Initial velocity, diffusion capacity and ultimate desorption amount of methane desorption after P! are greater than those after HI, and the ultimate desorption amount increases by 16.7-39.7%. Methane decay rate over the time is less than that of the HI. The PI influences the diffusion model param- eters, and it makes the mass transfer Biot number B＇_i decrease and the mass transfer Fourier series F＇_0 increase. As a result, PI makes the methane diffusion resistance in the coal smaller, methane diffusion rate greater, mass transfer velocity faster and the disturbance range of methane concentration wider than HI. Therefore, the effect of methane desorption based on PI is better than that of HI.

Axial Liquid Dispersion in Gas-Liquid-Solid Circulating Fluidized Bed

The effects of liquid viscosities, solid circulating rates, liquid and gas velocities and phase holdups on the axial dispersion coefficient, Dax, were investigated in a gas-liquid-solid circulating fluidized bed (GLSCFB).Liquid viscosity promotes the axial liquid backmixing when solid particles and gas bubbles are present. Increases in gas velocities and solid circulating rates lead to higher Dax. The effects of liquid velocity on Dax are associated with liquid viscosity. Compared with conventional expanded beds, the GLSCFBs hold less axial liquid dispersion,approaching ideal plug-flow reactors.

Influence of preload discreteness on air-operated separation process of low-shock separation device

To investigate the influence of design parameters on the performance of separation device,the structure and air-operated test of a low-shock separation device are introduced and analyzed in this paper.According to the law of energy conservation and aerodynamics,a mathematical model is built.Because the preload used to ensure the connection reliability has the discreteness,which will influence the separation process,the influence of preload discreteness on the air-operated separation process is simulated and tested.Simulation results are consistent with the experimental results.It is shown that the change of preload has an obvious influence on the separation process.The study is useful for the design and optimization of separation device.

Chemical Composition of Summertime PM_(2.5) and Its Relationship to Aerosol Optical Properties in Guangzhou,China

Urban aerosols have a large effect on the deterioration of air quality and the degradation of atmospheric visibility.Characterization of the chemical composition of PM 2.5 and in situ measurements of the optical properties of aerosols were conducted in July 2008 at an urban site in Guangzhou,Southern China.The mean PM 2.5 concentration for the entire period was 53.7±23.2 μg m 3.The mean PM 2.5 concentration (82.7±25.4 μg m 3) on hazy days was roughly two times higher than that on clear days (38.8±8.7 μg m 3).The total water-soluble ion species and the total average carbon accounted for 47.9%±4.3% and 35.2%±4.5%,respectively,of the major components of PM 2.5.The increase of secondary and carbonaceous aerosols,in particular ammonium sulfate,played an important role in the formation of haze pollution.The mean absorption and scattering coefficients and the single scattering albedo over the whole period were 53±20 M m 1,226±111 M m 1,and 0.80±0.04,respectively.PM 2.5 had a high linear correlation with the aerosol extinction coefficient,elemental carbon (EC) was correlated with aerosol absorption,and organic carbon (OC) and SO 4 2 were tightly linked to aerosol scattering.

Enhancement of Electrical Performance of c-Si Solar Cells with New Texturization and Diffusion Process

Improving cell efficiency and increasing throughput in solar cell industry efforts were put on uniform texturization and optimum diffusion process. To reduce reflectivity, NaOH/KOH （sodium hydroxide/potassium hydroxide） and IPA （isopropyl alcohol） are widely used in standard alkaline texturization of mono c-Si （crystalline silicon） （〈100〉 crystal orientation） wafers, where IPA promotes formation of uniform pyramidal structure but leads to unstable process. In this work, carbohydrates have been investigated as an additive in etchant solution. Moreover uniform phosphorus diffusion process for B2B （back to back） diffusion （loading two wafers in one single slot of quartz boat） has been investigated with single and multiple temperature plateaus. Impact of pre-oxygen step on phosphorus diffusion is investigated in which number of inactive phosphorus at the PSG （phosphosilicate glass）-Si interface is reduced. A batch of 156 PSQ （pseudo square） mono c-Si solar cells with 18%-18.20% efficiency was fabricated which is -0.3% higher than the standard process. The EL （electroluminescence image）, reff （carrier effective life time）, Voc （open circuit voltage）, Isc （short circuit current）, Pvk （peak power） and r/ （efficiency） have been examined and compared with standard.

Flame Stretch Analysis in Diffusion Flames with Inert Gas

Experimental investigations of impinging flame with fuel mixed with non-reaction gas were conducted. According to the observations of combustion test and temperature measurement, the non-reaction gas might dilute the local concentration of fuel in the diffusion process. The shape of the flame was symmetrical due to the flame stretch force. Results show that the conical flame might be de-structured by the addition of inert gas in pure methane fuel. The impinging flame became shorter and bluer as nitrogen was added to the fuel. The conditions of N2/CH4 equal to 1/2 and ill show a wider plane in the YZ plane. The effect of inert gas overcomes the flame stretch and destroys the symmetrical column flame as well as the cold flow. Nitrogen addition also enhances the diffusion rate and combustion efficiency.

Thermal stability of luminous YAG: Ce bulk ceramic as a remote phosphor prepared through silica-stabilizing valence of activator in air

Aprototype of YAG： Ce （Y3Al5O12） luminous bulk ceramic as a remote phosphor for white LED illumination was fabricated in air through a strategy of silica addition. With increasing the amount of silica in a specific range, the opaque sample turns to be semi-transparent. The precipitation of crystals is verified to be in pure YAG phase by X-ray diffraction （XRD）. Beyond the limit of silica amount, the dominant phase of YAG crystal is found to coexist with a small amount of newly-formed Y2Si2O7, Al2O3 and the amorphous phase. The YAG crystals are with a grain size of approximately 2 μm and distribute evenly. The YAG hosts after structural modification via addition of silica result in yellow band emission of 5d → 4f transition peaked around 535 nm as excited by a blue LED, owing to the self-reduction of Ce^4＋ to Ce^3＋ even in the absence ofreductive atmosphere.

Effect of Diffuser Vane Shape on the Performance of a Centrifugal Compressor Stage

The present paper reports the results of experimental investigations on the effect of diffuser vane shape on the performance of a centrifugal compressor stage. These studies were conducted on the chosen stage having a back- ward curved impeller of 500 turn tip diameter and 24.5 mm width and its design flow coefficient is Фd=0.0535. Three different low solidity diffuser vane shapes namely uncarnbered aerofoil, constant thickness flat plate and circular arc cambered constant thickness plate were chosen as the variants for diffuser vane shape and all the three shapes have the same thickness to chord ratio （t/c=0.1）. Flow coefficient, polytropic efficiency, total head coeffi- cient, power coefficient and static pressure recovery coefficient were chosen as the parameters for evaluating the effect of diffuser vane shape on the stage performance. The results show that there is reasonable improvement in stage efficiency and total head coefficient with the use of the chosen diffuser vane shapes as compared to conven- tional vaneless diffuser. It is also noticed that the aero foil shaped LSD has shown better performance when com- pared to flat plate and circular arc profiles. The aerofoil vane shape of the diffuser blade is seen to be tolerant over a considerable range of incidence.