Steady Zone Research Articles

Influence of gas migration on permeability of soft coalbed methane reservoirs under true triaxial stress conditions.

The permeability of the coal body is the key parameter restricting the efficient extraction of coalbed methane, and scholars have analysed it from two angles of the change of stress state and porosity of the coal body. However, there is still a lack of study on the mechanism of gas migration and movement in soft coalbed methane reservoir under the coupling between the true triaxial stress field (maximum principal stress σ1 > intermediate principal stress σ2 > minimum principal stress σ3) and the gas pressure field. In this paper, the coal gas adsorption and seepage experiments are conducted through the self-developed true triaxial ‘gas–solid’ coupled coal mass seepage system with gas as the adsorption and seepage medium and coal briquette taking the place of soft coalbed methane reservoirs. Furthermore, the coal gas adsorption deformation model and the permeability evolution model taking gas adsorption into account are developed. Through analysis of both experimental and theoretic results, the main conclusions are drawn as follows: (i) With the increase in gas pressure, the adsorption deformation variation of coal mass is divided into a slow growth zone, a stable growth zone and a rapid growth zone. (ii) The gas adsorption deformation model developed can predict the variation trend of coal mass adsorption volumetric strains for different types of soft coalbeds, and the fitting variance of experimental and theoretical volumetric strains is above 98%. (iii) With the increase in maximum principal stress difference, the coal permeability variation curve shows two obvious turning points, which can be divided into a slow reduction zone, a rapid reduction zone and a steady reduction zone. (iv) The permeability model of coal mass considering the gas adsorption effect can reflect the variation characteristics of permeability in the rapid reduction zone, and the overall fitting variance of experimental and theoretical permeabilities is above 91%. The above results could provide a reliable experimental and theoretical basis for improving coalbed methane extraction rates.

The evolution from an unsteady to a steady mixing zone between two groundwater flow systems with different concentrations

Heat and mass transport through porous media is governed by the advection-dispersion equation. Near the forward moving mixing front the longitudinal and transversal dispersion lengths are non-zero; only dispersion by molecular diffusion remains. The present paper presents mathematical-physical arguments why in steady transport the dispersion lengths are equal to zero. In conventional models the dispersion lengths are generally assumed to be process-independent. To interpolate between the relatively large dispersion lengths near time-dependent moving front and the steady transport conditions far away from the front, a mathematical model is proposed to describe the process-dependent time-evolution of the dispersion lengths. In this model, the dispersion lengths near the forward moving front are equal to the well-established conventional dispersion lengths that correctly represent the mixing near the front. However, further behind the moving front, where the mass transport has become (almost) steady, the process-dependent model results in vanishing dispersion lengths and, consequently, in a substantially smaller transversal mixing zone.

Water flow in unsaturated soils subjected to multiple infiltration events

In this paper, water flow in a 4 m height column with an unsaturated soil that is subjected to multiple infiltration events for a 62 day period is investigated. One-dimensional (1D) numerical analysis is also undertaken to analyze the flow, extending the seepage theory for unsaturated soils. Results highlight the formation of two wetting fronts; namely, wetting front I and wetting front II that are induced by the first and subsequent infiltration events, respectively. There is a stable zone where the water content is approximately constant; it forms between the two fronts. A conceptual model of the suction profile is proposed for interpreting in situ water flow by dividing the unsaturated zone into four distinct zones; namely, active, steady, transition, and capillary fringe zones. This division is helpful for providing a rational explanation of water flow in different zones. Novel contributions from this study include a relationship between the hydraulic properties in the steady zone and the flow velocity, which is determined by an average influx rate. In addition, the rate of groundwater recharge can also be estimated using the average influx rate. Results of the present study are useful to understand and interpret the relationship between water infiltration and suction or water content profile in the unsaturated zone as well as variation of groundwater table level.

A study of α variant selection in laser solid forming Ti-6Al-4V

The α variant selection of integral as-deposited Ti-6Al-4V prepared by laser solid forming (LSF) has been investigated by Electron Backscattered Diffraction (EBSD). Six types of α variants exist all areas in the deposited cuboid although its microstructure varies from basket-weave to Widmanstätten (and undeveloped basket-weave) to ultrafine basket-weave along building direction. Clusters of three α variants always dominate in medium steady zone until the columnar to equiaxed transition (CET transition) occurs. α variant selection causes strong alteration of high angle grain boundaries (HAGBs), which might be correlated with self-accommodation of shape strains.

Water percolation in a thick unsaturated loess layer considering the ground‐atmosphere interaction

AbstractThe key objective of this paper is to advance our present understanding of how surface water infiltrates in thick unsaturated loess, which is found in arid and semiarid regions of the world, considering the ground‐atmosphere interaction. In situ data for a period of 1 year in thick loess layer at a site in the Loess Plateau of China that has groundwater table at 97.5 m depth were collected for achieving this objective. Climate factors, mainly rainfall and actual evaporation, were measured. In addition, variations of soil temperature and water content at different depths in the unsaturated zone were also measured. The data were used to interpret the water percolation characteristics by dividing the thick unsaturated zone into three zones; namely, (i) surface zone, which constitutes the top 1.0 m, (ii) unsteady zone, which is from 1.0 to 7.0 m, and (iii) steady zone, which is below 7.0 m. In the surface zone, soil temperature and water content are sensitive to climate factors. There is a variation of water content associated with the cumulative influence of infiltration and evaporation in the precipitation and nonprecipitation periods, respectively. In the unsteady zone, the water content is relatively constant; however, temperature varies in different seasons. Water percolation in this zone is both in liquid and vapour phases. In the steady zone, both soil temperature and water content are constant during the entire investigation period. The percolation velocity in this zone is approximately 1.23 × 10−8 m/s or 0.39 m/year, which suggests that it will take approximately 230.8 years for surface water to pass through the thick unsaturated zone and recharge the groundwater.

Chloride Diffusion-Convection into Unsaturated RC Hollow Cylinder Piles in Marine Tidal Zones

Chloride penetration into reinforced concrete (RC) hollow cylinder piles has been identified as one of major factors to cause corrosion of reinforcing steel and to affect the performance and serviceability of piles. Chloride penetration into unsaturated RC hollow cylinder piles in marine tidal zones involves the coupling of diffusion and convection mechanisms. The goal of this study is to investigate the chloride diffusion-convection behavior into unsaturated RC hollow cylinder piles in marine tidal zones through numerical modeling. The governing equation to model the chloride diffusion-convection mechanism was derived and solved numerically using the finite difference method. An illustrative example was demonstrated to predict the chloride concentration distributions in unsaturated RC hollow cylinder piles in the marine tidal zones. Parametric analysis was performed to examine the influence of the main parameters on the chloride concentration distributions in unsaturated RC hollow cylinder piles. The analysis results indicated that the convection action had an obvious effect on the chloride penetration in the convection zone. Chloride diffusion-convection resulted in an increase in the chloride concentration, and the increase in the convection zone was more significant compared to that in the steady diffusion zone at a fixed exposure depth. The influence of the convection zone depth on the chloride concentration distributions was not as significant as the effects of chloride diffusion coefficient and convection velocity in unsaturated RC hollow cylinder piles.

Assessing the Analytical Solution of One-Dimensional Gravity Wave Model Equations Using Dam-Break Experimental Measurements

The one-dimensional gravity wave model (GWM) is the result of ignoring the convection term in the Saint-Venant Equations (SVEs), and has the characteristics of fast numerical calculation and low stability requirements. To study its performances and limitations in 1D dam-break flood, this paper verifies the model using a dam-break experiment. The experiment was carried out in a large-scale flume with depth ratios (initial downstream water depth divided by upstream water depth) divided into 0 and 0.1~0.4. The data were collected by image processing technology, and the hydraulic parameters, such as water depth, flow discharge, and wave velocity, were selected for comparison. The experimental results show that the 1D GWM performs an area with constant hydraulic parameters, which is quite different from the experimental results in the dry downstream case. For a depth ratio of 0.1, the second weak discontinuity point, which is connected to the steady zone in the 1D GWM, moves upstream, which is contrary to the experimental situation. For depth ratios of 0.2~0.4, the moving velocity of the second weak discontinuity point is faster than the experimental value, while the velocity of the shock wave is slower. However, as the water depth ratio increases, the hydraulic parameters calculated by 1D GWM in the steady zone gradually approach the experimental value.

Corrosion and corrosion-friction properties of plasma cladding wear-resistant layer on Fe-based alloy

Plasma cladding technology is used to prepare a plasma cladding gradient wear-resistant layer, and the corrosion and corrosion-friction properties of the plasma cladding wear-resistant layer are analyzed. The results indicate that under pure immersion corrosion, the plasma gradient cladding wear-resisting layer has better corrosion resistance compared with that of single cladding specimen. No obvious corrosion traces occur on the corrosion surface. Under corrosion-friction conditions, the variety law of friction coefficient can be divided into four stages: rapid decline zone, slight increase zone, fluctuation zone and steady zone. The fluctuation ranges of friction coefficient and wear loss greatly reduce compared with those of dry friction. Furthermore, the wear scar has no obvious corrosion traces. The wear mechanism of the substrate is corrosion wear, adhesive wear, abrasive wear and fatigue wear, while the plasma cladding gradient wear-resistant layer is given priority to with adhesive wear and abrasive wear.

Interface structure and contact melting in AgCu eutectic. A molecular dynamics study

Molecular dynamics simulations of the interface structure in binary AgCu eutectic were performed by using the realistic EAM potential. In simulations, we examined the time dependence of the total energy in the process of equilibration, the probability distributions, the composition profiles for the components, and the component diffusivities within the interface zone. It is shown that the relaxation to the equilibrium in the solid state is accompanied by the formation of the steady disordered diffusion zone at the boundary between the crystalline components. At higher temperatures, closer to the eutectic point, the increase in the width of the steady diffusion zone is observed. The particle diffusivities grow therewith to the numbers typical for the liquid metals. Above the eutectic point, the steady zone does not form, instead, the complete contact melting in the system occurs. The results of simulations indicate that during the temperature increase the phenomenon of contact melting is preceded by the similar process spatially localized in the vicinity of the interface.

Directional solidification and growth characteristics of Al2O3/Er3Al5O12/ZrO2 ternary eutectic ceramic by laser floating zone melting

Directionally solidified Al2O3/Er3Al5O12/ZrO2 ternary eutectic ceramic in situ composite rods with length of 110 mm have been fabricated by laser floating zone melting. The microstructural characteristics of steady growth zone, initial growth zone and solid/liquid interface are investigated under high temperature gradient. In the steady growth zone, the eutectic spacing (λ) is rapidly decreased as increasing the growth rate (V), and the corresponding relationship between growth rate and eutectic spacing is determined to be λ = 11.14 × V −1/2. The temperature gradient has been measured to be about 5.3 × 103 K/cm. In the initial growth zone, the melting process and temperature distribution are recorded by infrared thermal imager, and several unstable complex microstructures are observed. In the quenched zone, the regular eutectics with minimum eutectic spacing of 200 nm are obtained. Moreover, the solid/liquid interface during solidification shows convex interface morphology and the interface height is gradually decreased as increasing the growth rate. The eutectic growth behaviors at the center and edge of the as-grown rod are compared and discussed.

Numerical analysis of laminar and transitional flow in a planar sudden expansion

Abstract The laminar and transitional flow through a planar sudden expansion with various expansion ratios is studied using two-dimensional direct numerical simulations at flow Reynolds numbers up to 5000 and expansion ratios in the range of 1.33 to 4.00. Results show the relationship between the reattachment length and the flow Reynolds number and expansion ratio. Correlations are developed for the non-dimensional reattachment length and the maximum velocity magnitude in the reverse-flow region in terms of Reynolds numbers and expansion ratios. The correlations and computed results achieve excellent agreement with published literature. Bifurcation phenomena resulting in the loss of flow symmetry downstream of the sudden expansion is observed and critical Reynolds numbers for the onset of bifurcation for various expansion ratios are identified. The initiation mechanism for bifurcation is attributed to the amplification of streamwise velocity disturbances at a spatial location that depends on the flow Reynolds number. For Reynolds numbers near the critical value for bifurcation onset, the disturbances grow from the sudden expansion, while for Reynolds numbers well above the critical value, the disturbances grow from the location of flow reattachment that occurred in the symmetric condition prior to bifurcation. Finally, the effect of the bifurcation phenomena on the development of flow unsteadiness and transition to turbulence downstream of the sudden expansion is linked to the successive formation of smaller-scale, steady recirculation zones. Transition is initiated by inviscid instability of the inflectional velocity profiles associated with these smaller-scale zones.

Optimum processing parameters for equal channel angular pressing

This study aims to explore the optimum processing parameters for minimum strain coefficient of variance in equal channel angular pressing based on the analysis of whole steady zone. In order to design the die correctly, it is important to understand the effect of die geometry and processing parameters on the deformation behavior, strain distribution and punch load. The influences of channel angle, corner angle and friction coefficient are analyzed using finite element modeling. Analytical models are also used to validate the obtained computational solutions. Results showed that channel angle, corner angle and friction coefficient have significant influences on deformation behavior, strain coefficient of variance and punch load evolution. Among all the combinations of 7 corner angles, 6 channel angles and 6 friction coefficients (set of 252 study cases), it is found that the optimum parameters for maximum strain homogeneity correspond to channel angle ϕ=90o, corner angle ψ=15o and friction coefficient μ=0.3. The influence of friction coefficient on punch load is more pronounced than the influence of die geometry.

Computation of Supersonic Branching Flow with Aerosol Particle Separation

Supersonic branching flows are commonly found in industrial processes like the supersonic aerosol particle separation process and the supersonic inlet of combined aeroengines. In this research, we carry out a numerical study on the supersonic branching flow to reveal its features and its effects on aerosol particle separation. It is found that there are four flow regimes and a critical state in the supersonic branching flow in terms of the shock wave positions, which are determined by the backpressures of the two outlets. The gas flow rate ratio and the particle separation ratio are closely related to the flow regimes. There is a steady working zone where the gas flow rate ratio and the particle separation ratio maintain as constant as the two backpressures vary. In swirling flows, there is a drift of the critical state. In the range of particle sizes studied here, the particle motion is not sensitive to the variations of the particle size in the absence of swirl, but it is not the case for swirling flows. Finally, some features of the steady working zone are discussed. This work is a preliminary research into supersonic branching flow and provides a foundation for the design of relevant devices.

Combustion characteristics of diesel and Jet-A droplets blended with polymeric additive

Recent experimental research has shown that the addition of long chain polymers to hydrocarbon fuel imparts non-Newtonian characteristics to the fuel which results in suppressed splashing behavior upon spilling over a surface and consequently improves fire safety. In this study, combustion of stationary fuel droplets of Diesel and Jet-A doped with different percentages of a long chain polymer (Polybutadiene) was examined and compared with the normal hydrocarbon behavior. In contrast with hydrocarbon droplets with no polymer addition, several zones of combustion including a slow and steady burning zone, a strong swelling zone and two fast and fairly steady combustion zone were also detected. It was found that combustion of polymer added fuel is controlled by the boiling point of more volatile component, i.e. base fuel. Therefore, initially the base fuel is transported to the droplet surface and evaporates. However, polymer addition turned out to slightly decrease burning rate in this stage. Viscosity was found to be the dominating factor that suppresses diffusion of volatile species to the surface and hence reduces evaporation rate at early stages of combustion. Increasing polymer content also resulted in stronger swelling behaviors as well as reduced burning time for both diesel and jet fuel droplets.

Simulation of the Effective of Friction on the Deformation in Equal Channel Angular Pressing (ECAP)

A influence of friction on the deformation behavior and strain homogeneity during ECAP has been studied by conducting 2D and 3D finite element simulations for a range of friction conditions m = 0 – 0.2. The deformation was more uniform in central steady zone as compared to the ends of the sample. The calculated ram load was higher in 3D simulations than 2D simulations. For a frictionless condition, the ram load was similar in both 2D and 3D simulations. Keywords: ECAP, SPD, FEM, Coulomb friction model, friction condition, ram load.

Effect of Direct Current on Microstructure Evolution of Directionally Solidified Sn-70 wt pct Bi Alloy at Different Pulling Rates

The effect of direct current (DC) on the solidification behaviors of Sn-70 wt pct Bi alloy was studied using the directional solidification method. All the microstructures obtained at different pulling rates with DC treatment consisted of two typical structures, i.e., the transitional and steady ones. It was found that the transitional microstructures were two-phase structures under a positive DC, whose morphologies and the corresponding lengths of transitional zone were independent of the pulling rate. However, the transitional microstructures upon DC reversal, which were different from those under a positive DC, strongly depended on the pulling rate. The formation and difference of the transitional microstructures upon DC reversal were mainly attributed to Joule heating and concentration-dependent electromigration. The primary nubby Bi phase and dendritic β-Sn phase, caused by composition fluctuation due to the difference of Lorentz force subjected to Sn and Bi, precipitated in the steady zone regardless of the current polarity.

Hydrodynamics of suspended canopies with limited length and width

Experimental measurements and numerical simulations are carried out to determine the hydrodynamics induced by suspended canopies of limited width and height for canopies with six different densities and canopy element arrangements and two different upstream velocities. Measurements of velocity are obtained using acoustic Doppler velocimetry and the drag force via a load cell. Numerical simulation results using OpenFOAM agree very well with the experimental data and are used to investigate the generated flow fields in detail. The bulk features of the flow are similar to those of other canopies, including emergent and submerged canopies, but the finite dimensions of the canopy results in flow patterns that differ from suspended canopies of essentially infinite width. The detailed hydrodynamics of the flow are controlled by the blockage of the suspended canopy which depends both on the canopy density and the lateral spacing between consecutive longitudinal rows of canopy elements. Increased flow blockage results in increases in the drag coefficient from 0.72 to 1.4, reduction in the flow rate inside the canopy from 58 to 98 % (of the diverted flow, 20–43 % is diverted below the canopy) and increases in the steady wake zone length from 0.6 to 4 times the canopy length. Flow blockage has relatively little effect on the length of the upstream adjustment and total wake zones at 1.09 and 7 times the canopy length respectively. The flow also depends only weakly on the upstream velocity.

Thermal Conductivity of Moulding Sand with Chemical Binders, Attempts of its Increasing

Abstract The investigation results of the thermal conductivity of the selected group of moulding sands with chemical binders, mainly organic, are presented in the hereby paper. Studies encompassed also moulding sands into which additions improving the thermal conductivity were introduced. Two testing methods were applied, i.e. investigations at a steady and unsteady temperature zone. For investigations at a steady temperature zone the new original experimental stand was designed and built, adapted also for testing moulding sands with binders undergoing destruction at relatively low temperatures.

Putting Theory to the Test: Which Regulatory Mechanisms Can Drive Realistic Growth of a Root?

In recent years there has been a strong development of computational approaches to mechanistically understand organ growth regulation in plants. In this study, simulation methods were used to explore which regulatory mechanisms can lead to realistic output at the cell and whole organ scale and which other possibilities must be discarded as they result in cellular patterns and kinematic characteristics that are not consistent with experimental observations for the Arabidopsis thaliana primary root. To aid in this analysis, a ‘Uniform Longitudinal Strain Rule’ (ULSR) was formulated as a necessary condition for stable, unidirectional, symplastic growth. Our simulations indicate that symplastic structures are robust to differences in longitudinal strain rates along the growth axis only if these differences are small and short-lived. Whereas simple cell-autonomous regulatory rules based on counters and timers can produce stable growth, it was found that steady developmental zones and smooth transitions in cell lengths are not feasible. By introducing spatial cues into growth regulation, those inadequacies could be avoided and experimental data could be faithfully reproduced. Nevertheless, a root growth model based on previous polar auxin-transport mechanisms violates the proposed ULSR due to the presence of lateral gradients. Models with layer-specific regulation or layer-driven growth offer potential solutions. Alternatively, a model representing the known cross-talk between auxin, as the cell proliferation promoting factor, and cytokinin, as the cell differentiation promoting factor, predicts the effect of hormone-perturbations on meristem size. By down-regulating PIN-mediated transport through the transcription factor SHY2, cytokinin effectively flattens the lateral auxin gradient, at the basal boundary of the division zone, (thereby imposing the ULSR) to signal the exit of proliferation and start of elongation. This model exploration underlines the value of generating virtual root growth kinematics to dissect and understand the mechanisms controlling this biological system.

Distribution of Cotton in Rectangular Pipeline for Horizontal Foreign Fiber Removed Device

A numerical simulation method using the model of the gas-cotton two-phase is used to analyze the distribution of the cotton in the rectangular pipeline for a horizontal foreign fiber removed device. According to the motion characteristics of the cotton, the optimum length of the rectangular pipeline is found and the distribution of the cotton in the pipeline is obtained. The simulation results show that the optimum length is for the cross-section pipeline. At the same time, in the range of the cotton mainly flows in the middle of the pipeline bottom and the maximum volume fraction of the cotton is 4.5%, at the both sides of the pipeline bottom the cotton is less and the average volume fraction of the cotton is 1%, and there is no the cotton in the middle and upper part of the pipeline; in the range of , the cotton increases rapidly in the middle and upper part of the pipeline and the volume fraction is about 2.7% at ; in the range of , the cotton flows steadily and the volume fractions of the cotton are the same in the middle and upper part of the pipeline, about 2.7% but 1.5% in the lower part of the one. In addition, for the level centers of the cross-sections perpendicular to the cotton flow direction, in the unsteady zone the volume fraction curves of the cotton are symmetrical like a saddle, and in the steady zone the cotton is evenly distributed and its volume fraction curves are horizontal lines.