Gas Layer Research Articles

Review on hydrodynamic instabilities of a shocked gas layer

Review on hydrodynamic instabilities of a shocked gas layer

Near-Wall Cavitation Effect: A Molecular Dynamics Study.

Cavitation has been the subject of abundant studies, but the internal mechanism of cavitation is less well known. In this article, a microlevel near-wall model was established by using LAMMPS to present the process of cavitation effect. The results of molecular dynamics simulation revealed the fluctuation process of the liquid near the wall with the change in pressure. Molecular dynamics was also used to evaluate the void volume fraction and density distribution of the system. The results exhibited that the cavitation process can be divided into two stages: the initial cavitation stage and the rapid growth stage. Based on these results, the effects of wettability and initial system temperature on the near-wall cavitation effect were demonstrated. The results indicated that the hydrophobic near-wall forms a gas layer to weaken the density fluctuation, while the hydrophilic wall is opposite. Increasing the temperature could positively affect molecular motion and cavitation. This work provides a theoretical basis for further exploration of the cavitation effect.

Numerical study on natural gas hydrate production by hot water injection combined with depressurization

The low efficiency and unstable gas production of hydrate exploitation have become the difficulties restricting the commercial development of combustible ice. In this work, based on the existing geological conditions, this paper establishes a low-permeability hydrate heterogeneous reservoir model to analyze the effects of hot water injection on well and reservoir. The results show that the greater the wasted heat from the produced water and some injected water migrating to the gaseous hydrocarbon layer and the underlying at the middle and late stage of hydrate production as the hot water injection rate. Moreover, the gas and water production will suddenly appear surge phenomenon during the hydrate production due to the disappearance of the water lock effect affected by thermal-hydraulic-chemical multi-field coupling, which depends on the hot fluid properties. Therefore, the new technology of slow hot water injection after depressurization or different injection rates at different stages in the injection well is proposed in this paper. And it is also necessary to optimize the vertical position of the injection well or add a thin layer with low permeability at the bottom of the gaseous hydrocarbon layer. Finally, the hot water injection temperature should be controlled above 50 °C.

The extremely sharp transition between molecular and ionized gas in the Horsehead nebula

Massive stars can determine the evolution of molecular clouds by eroding and photo-evaporating their surfaces with strong ultraviolet (UV) radiation fields. Moreover, UV radiation is relevant in setting the thermal gas pressure in star-forming clouds, whose influence can extend across various spatial scales, from the rims of molecular clouds to entire star-forming galaxies. Probing the fundamental structure of nearby molecular clouds is therefore crucial to understand how massive stars shape their surrounding medium and how fast molecular clouds are destroyed, specifically at their UV-illuminated edges, where models predict an intermediate zone of neutral atomic gas between the molecular cloud and the surrounding ionized gas whose size is directly related to the exposed physical conditions. We present the highest angular resolution (~0.″5, corresponding to 207 au) and velocity-resolved images of the molecular gas emission in the Horsehead nebula, using CO J = 3–2 and HCO+ J = 4−3 observations with the Atacama Large Millimeter/submillimeter Array (ALMA). We find that CO and HCO+ are present at the edge of the cloud, very close to the ionization (H+/H) and dissociation fronts (H/H2), suggesting a very thin layer of neutral atomic gas (<650 au) and a small amount of CO-dark gas (AV = 0.006–0.26 mag) for stellar UV illumination conditions typical of molecular clouds in the Milky Way. The new ALMA observations reveal a web of molecular gas filaments with an estimated thermal gas pressure of Pth = (2.3 – 4.0) × 106 K cm−3, and the presence of a steep density gradient at the cloud edge that can be well explained by stationary isobaric photo-dissociation region (PDR) models with pressures consistent with our estimations. However, in the H II region and PDR interface, we find Pth,PDR > Pth,H II suggesting the gas is slightly compressed. Therefore, dynamical effects cannot be completely ruled out and even higher angular observations will be needed to unveil their role.

Study on water and oxygen transfer characteristics of HT-PEM fuel cells

In this study, a steady-state model is developed by combining mechanical, Navier–Stokes, Maxwell–Stefan, and Butler–Volmer equations. This model is then used to investigate the influences of diffusion layer thickness deformation under a specific assembly force on the porosity distribution as an indicator of fuel cell performance. The HT-PEM (high temperature proton exchange membrane) fuel cell model is built using COMSOL Multiphysics software, simulating the changes in diffusion layer porosity under different thicknesses of the diffusion layer, thus analyzing the trends in variation of water and oxygen concentration in the cathode diffusion layer. The battery has different current densities at different operating potentials. The influence of the working potential on the mass transfer concentration and the variation in the mass transfer concentration of the diffusion layer under the different areas of flow channel and flow ridge is discussed. The simulation results have a certain reference value for the optimization of mass transfer in a diffusion layer. The results reveal the combined effect of the assembly force and flow field, which makes the porosity distribution uneven and results in remarkable lateral current in the gas diffusion layer (GDL). The thicker the diffusion layer, the less oxygen consumed, and a large amount of oxygen is retained in the gaseous diffusion layer. It can be concluded that thicker diffusion layer is conducive to more uniform mass transfer and diffusion. These results can potentially be used to promote the performance and application of HT-PEMFC.

Looking for evidence of high-mass star formation at core scale in a massive molecular clump

Context. High-mass stars are formed as a result of the fragmentation of massive molecular clumps. However, what it is not clear is whether this fragmentation gives rise to stable prestellar cores massive enough to directly form high-mass stars or leads to prestellar cores of low masses that, by acquiring material from the environment, generate high-mass stars. Several recent observational studies focused on the characterisation of prestellar massive clump candidates. Nevertheless, studies of active massive clumps at different evolutionary stages are still needed to gain a complete understanding of how high-mass stars form. Aims. We present a comprehensive physical and chemical study of the fragmentation and star formation activity towards the massive clump AGAL G338.9188+0.5494, which harbours the extended green object EGO 338.92+0.55(b). The presence of an EGO embedded in a massive clump suggests that high-mass star formation is occurring at clump scale. The main goal of this work is to find evidence of such high-mass star formation, but at core scale. Methods. Using millimetre observations of continuum and molecular lines obtained from the Atacama Large Millimeter Array database at Bands 6 and 7, we study the substructure of the massive clump AGAL G338.9188+0.5494. The angular resolution of the data at Band 7 is about 0″.5, which allows us to resolve structures of about 0.01 pc (~2000 au) at the distance of 4.4 kpc. Results. The continuum emission at 340 GHz reveals that the molecular clump is fragmented into five cores, labelled C1 to C5. The 12CO J = 3−2 emission shows the presence of molecular outflows related to three of them. The molecular outflow related to core C1 is among the most massive (from 0.25 to 0.77 M⊙) and energetic (from 0.4 × 1046 to 1.2 × 1046 erg), considering studies carried out with similar observations towards this type of source. Rotational diagrams for the CH3CN and CH3CCH yield temperatures of about 340 and 72 K, respectively, for the core C1. The different temperatures show that the methyl cyanide would trace a gas layer closer to the protostar than the methyl acetylene, which would trace outermost layers. Using a range of temperatures going from 120 K (about the typical molecular desorption temperature in hot cores) to the temperature derived from CH3CN (about 340 K), the mass of core C1 ranges from 3 to 10 M⊙. The mid-IR 4.5 µm extended emission related to the EGO coincides in position and inclination with the discovered molecular outflow arising from core C1, which indicates that it should be the main source responsible for the 4.5 µm brightness. The average mass and energy of such a molecular outflow is about 0.5 M⊙ and 1046 erg, respectively, which suggest that 10 M⊙ is the most likely mass value for core C1. Additionally, we find that the region is chemically very rich with several complex molecular species. In particular, from an analysis of the CN emission, we find strong evidence that this radical is indirectly tracing the molecular outflows, or, more precisely, the border of the cavity walls carved out by such outflows, and therefore we point out that this is probably one of the first clear detection of CN as a tracer of molecular outflows in star-forming regions.

Numerical simulation of coupling behavior in coaxial hybrid arc welding apparatus

Double-layer coaxial hybrid arcing technology has been developed based on an inner constraint arc and an outer ring arc; the heat and pressure properties of the arc source are supposed to be decoupled and leading to improved controllability of the weld pool thermal-force state. But, the coupling state between the two arcs is not uncovered, and the process window for stable hybrid arc is narrow. In this study, a numerical model of the coaxial hybrid arc system is established, the influence of the water-cooled nozzle on the arc is considered, and the model's accuracy is verified by the measured arc pressure. The physical fields, such as temperature, velocity, and current density distribution, of the hybrid arc are calculated, and the influence of the inner constraint arc current or outer ring arc current on arc pressure and the coupling state in the hybrid arc are uncovered. It was found that (1) at the center of the stable hybrid arc, the current density, magnetic flux intensity, Lorentz force, and arc pressure with a rise in constraint arc current are higher than with a rise in outer arc current; (2) given the total current, adjust the proportion of the inner or outer arc currents, the total heat input basically remains unchanged; and (3) the cause of the arc collapse phenomenon, which is challenging to explain experimentally: the non-ionized gas layer in the orifice throat is broken through.

Steady states of the Parker instability

ABSTRACT We study the linear properties, non-linear saturation, and a steady, strongly non-linear state of the Parker instability in galaxies. We consider magnetic buoyancy and its consequences with and without cosmic rays. Cosmic rays are described using the fluid approximation with anisotropic, non-Fickian diffusion. To avoid unphysical constraints on the instability (such as boundary conditions often used to specify an unstable background state), non-ideal magnetohydrodynamic equations are solved for deviations from a background state representing an unstable magnetohydrostatic equilibrium. We consider isothermal gas and neglect rotation. The linear evolution of the instability is in broad agreement with earlier analytical and numerical models; but we show that most of the simplifying assumptions of the earlier work do not hold, such that they provide only a qualitative rather than quantitative picture. In its non-linear stage the instability has significantly altered the background state from its initial state. Vertical distributions of both magnetic field and cosmic rays are much wider, the gas layer is thinner, and the energy densities of both magnetic field and cosmic rays are much reduced. The spatial structure of the non-linear state differs from that of any linear modes. A transient gas outflow is driven by the weakly non-linear instability as it approaches saturation.

Effects of Fire Source Conditions on Vent Flow Velocity and Hot Gas Layer Characteristics in Two Rooms Connected by Vertical Opening

In this study, the effects of fire source conditions on the vent flow velocity and hot gas layer characteristics in two rooms (ROOM-I and ROOM-II) connected by a vertical opening (VO-I) were investigated experimentally. In ROOM-II, the vertical opening (VO-II) connected to the outside was installed. The fire sources were located at the centers of ROOM-I and ROOM-II, and the heat release rates were 1.32, 3.32, and 5.21 kW. Regarding the vent flow velocity, when the fire source was located in ROOM-I, the outflow of the hot gas and inflow of cold air occurred in the upper and lower parts of VO-I and VO-II, respectively, which were the same as those of VO-II when the fire source was located in ROOM-II. However, when the fire source was located in ROOM-II, the hot gas in the upper part of VO-I flowed out to ROOM-I and flowed again into ROOM-II. Additionally, the hot gas layer thickness and temperature rise in the fire and adjacent rooms were compared. In the fire room, the case where the fire source was placed in ROOM-I showed a thicker hot gas layer and a higher hot gas layer temperature rise than the case where the fire source was placed in ROOM-II. In the adjacent room, the case where the fire source was placed in ROOM-I showed a thinner hot gas layer and a higher hot gas layer temperature rise than the case where the fire source was placed in ROOM-II. The dependence of the hot gas layer temperature rise on the heat release rate was higher than that of the hot gas layer thickness.

Symmetry Energy in the Inner Crust Region of Neutron Stars: A Study Around the Neutron Drip Density Point using the Compressed Liquid Drop Model

The properties of neutron star’s inner crust have been investigated using the Compressible Liquid Drop Model, particularly around the neutron drip density region, which is the boundary between the outer and inner crust. Symmetry energy in the equations of state SLy4 and BSk3 was calculated to determine the density data between the outer and inner crusts. The properties of the inner crust can be understood through parameters such as the change in the number of nucleons in the atomic nucleus, the asymmetry parameter in surface energy, and volume energy. It was shown that the choice of the symmetry energy expansion coefficient (L) of order-1 results in a distinct energy range of 9-11 MeV within the neutron drip region. This contrasts significantly with the energy symmetry observed around saturation density, which reaches (30 ± 4) MeV in the reference models used. Furthermore, it was found that symmetry energy affects the neutron composition in the inner crust. As the density increases, neutron numbers rise, while proton counts exhibit relative stability within the range of 40 to 50 for each atomic nucleus. Importantly, we observe a marked decrease in proton fraction at the onset of the neutron drip region, where ???? ≅10 MeV, suggesting electron capture processes transforming protons into neutrons. This phenomenon contributes to the presence of neutron and free neutron gas layers within the inner crust.

Plastron restoration for underwater superhydrophobic surface by porous material and gas injection

Restoring and maintaining the gas layer (plastron) on underwater superhydrophobic surface (SHS) is critical for the real-world application of SHS, such as reducing friction drag in high-Reynolds number turbulent flows. In this work, we experimentally investigated the capability of a technology based on porous material and gas injection to restore the plastron on an underwater SHS from a fully wetted state. The SHS was created by sprayed coating a commercial superhydrophobic coating on a porous steel plate. In the experiments, the SHS was immersed in stationary liquid, the gas injection pressure and gas injection duration were independently controlled. The status of gas layer on SHS was examined by a high-speed camera. We found that the surface area being restored with a plastron increased with increasing gas injection pressure and gas injection duration, and that the plastron restoration process involved bubble formation, merging and detachment. A layer of gas was left on the surface after bubble detachment. The size of the detached bubble increased with time due to bubble merging, and became stable when there was no more bubble merging. Increasing gas injection pressure led to higher gas flow rates, larger detached bubble sizes and faster plastron restorations. A plastron restoration within 0.3 s was achieved at the highest pressure, faster than the in-situ gas generation methods. Furthermore, we found that the gas flow rate through the underwater SHS can be described by a modified Darcy’s law. Our results highlighted the potential of using porous material and gas injection to restore the plastron and made possible the real-world implementation of SHS.

An Analytical Model Coupled with Orthogonal Experimental Design Is Used to Analyze the Main Controlling Factors of Multi-Layer Commingled Gas Reservoirs

The majority of China’s multi-layer low permeability tight gas reservoirs are currently being extracted through the method of multi-layer co-production. However, due to the significant disparity in physical properties and varying degrees of pressure depletion among the production layers, elucidating the primary factors influencing the productivity contribution of each gas layer remains challenging. A multi-factor analytical model is proposed for commingled gas wells with multiple layers. An unstable model is established for the production of commingled layers, and the problem of flow distribution is addressed using the Duhamel convolution principle. The Laplace transform is subsequently employed to derive the solution in the Laplace domain, which can be inverted utilizing the Stehfest inversion algorithm to obtain a real-time domain solution. The influence of reservoir factors on the stratification contribution rate has been comprehensively analyzed, encompassing permeability, porosity, initial pressure, drainage radius, and layer thickness. The orthogonal test design was employed to conduct range analysis and variance analysis separately, yielding the primary and secondary order as well as influence weight of the five factors. The findings demonstrate that, within this gas reservoir, the discharge radius, thickness, and porosity are identified as the primary factors influencing gas well productivity. Furthermore, seven horizontal flow charts illustrating the double-layer gas reservoir and five horizontal flow charts depicting single-factor variations in the double-layer gas reservoir were constructed. These charts provide a clear visualization of the impact of each reservoir factor on stratification’s contribution rate. In contrast to previous studies, this novel approach presents a comprehensive optimization framework that ranks the influence weights of individual factors and identifies the most significant factors impacting multi-layer gas reservoirs. The presented method also serves as a foundation for the subsequent selection of multi-layer gas reservoirs, formulation of gas well stimulation measures, and efficient development.

Driving Forces of Natural Gas Flow and Gas–Water Distribution Patterns in Tight Gas Reservoirs: A Case Study of NX Gas Field in the Offshore Xihu Depression, East China

The driving forces behind gas flow and migration, as well as the associated gas–water distribution patterns in tight gas reservoirs, are not only closely related to the formation mechanisms of “sweet spots”, but also serve as crucial geological foundations for the development of efficient modes and optimal well placement. In this work, three methods, namely, critical gas column height driven by buoyancy, critical pore throat radius driven by buoyancy, and gas–water distribution attitude, were used to quantitatively evaluate the critical conditions for buoyancy and overpressure to get gas flowing in the tight sandstone gas field. In light of the geological background, the driving forces of gas flow/migration and gas–water distribution patterns were comprehensively analyzed. On this basis of the origins of overpressure driving gas flow/migration were identified by using multiple empirical methods, the evolution of overpressure and characteristics of gas–water distribution driven by overpressure were studied by using PetroMod_2014 simulation software. The results show that the four main gas-bearing layers in the NX tight sandstone gas reservoir differ widely in gas flow/migration dynamics and gas–water distribution patterns. Gas accumulation in the H3b layer is influenced by both buoyancy and overpressure. Subsequently, buoyancy leads to the differentiation of gas from water based on density and the formation of edge water. Furthermore, the distribution area of the gas reservoir is determined by the presence of an anticline trap. In contrast, in H3a, H4b and H5a gas layers, buoyancy is not sufficient to overcome the capillary force to make the gas migrate during and after accumulation, and the driving force of gas flow is the overpressure formed by fluid volume expansion during hydrocarbon generation of Pinghu Formation source rocks. Because buoyancy is not the driving force of natural gas flow, H3a, H4b and H5a layers have gas and water in the same layer and produced together, and no boundary and bottom water, where the anticlinal trap does not control the distribution of gas and water, and gas source faults control the boundary of the gas reservoir. These understandings not only significantly expand the gas-bearing target of H3a, H4b and H5a gas layers delineated in the buoyancy driving pattern but also provide an important geological basis for the formulation of an efficient development plan by class and grade for the NX tight sandstone gas field.

MSW pyro-gasification using high-temperature CO2 as gasifying agent: Influence of contact mode between CO2, char and volatiles on final products

The volatiles and char derived from municipal solid waste (MSW) pyrolysis can be catalytically reformed and gasified using high-temperature CO2 (HT-CO2) as gasifying agent and char as a catalyst simultaneously to obtain high quality synthesis gas, but the reactor's design for this purpose is still a question. In this research, the contact configuration between the HT-CO2, the volatile compounds, and the char from MSW pyrolysis were studied to understand the relevant reaction behaviors and to establish guidelines for the reactor’s design. Three contact modes were designed, including: M1, where volatiles and HT-CO2 contact first, then contact the char; M2, where volatiles, CO2, and char contact simultaneously at the bottom of the char layer; and M3, where CO2 contacts with the char first, then the volatiles contact in the middle of the char layer. The temperature evolution in the char layer, the yields and properties of the resultant combustible gases, used char, and tar were investigated. Experimental results revealed that the contact mode significantly affected the levels of char gasification and volatiles' reforming. For M1, intense thermal cracking of volatiles occurred and 65.41% of the input heat of HT-CO2 was consumed for thermal cracking, resulting in substantial carbon deposition and limited energy transfer from char to the synthesis gas. While, the char contacting HT-CO2 firstly in M3 improved its catalytic activity, causing 73.33 % of the input heat utilized for gasification and reforming; as a result, the maximum synthesis gas yield of 0.71 Nm3/kgMSW and gas energy ratio of 76.3 % were obtained respectively in M3 with the lowest tar yield of 5.45 %; additionally, the used char corresponded to the highest specific surface area of 10.12 m2/g. Ultimately, M3 is constructive and recommended, and the findings of this study offer helpful guidance for the design of pyro-gasification reactors.

Impact of surface physisorption on gas scattering dynamics

Engineering flow systems operating under low pressures and/or at the micro/nano scale generally include a physically adsorbed gas layer next to the surface. In this paper, we develop a scattering kernel that accounts for the effect of adsorption, arising from van der Waals interactions, on the dynamics of molecules impinging on solid smooth surfaces. In the limit of low bulk density, surface adsorption becomes negligible and the scattering kernel recovers consistently the Cercignani–Lampis model, which best describes molecular collisions with a clean, smooth surface. In the limit of high bulk density, a dense adsorbed molecular layer forms next to the surface and its presence is picked up by the Maxwell model with complete diffuse reflection, which better captures the multiple collisions suffered by molecules. A weight coefficient based on the Langmuir adsorption isotherm is incorporated into the modelling to handle the transition between these two limiting conditions of low and high densities. The proposed model is validated against high-fidelity molecular dynamics simulations that are performed for a variety of gas–surface combinations and adsorbed molecular layers with different densities. It is shown that the proposed model very well captures the scattering patterns of beams of gas molecules at different velocities impinging on surfaces, as well as momentum and energy accommodation coefficients in the entire range of explored conditions.

Numerical Simulation of Improved Gas Production from Oceanic Gas Hydrate Accumulation by Permeability Enhancement Associated with Geomechanical Response

In the Shenhu Area of the South China Sea, although some numerical studies are conducted on the gas production at well SHSC-4, the geomechanical responses have not been taken into account, and the associated impact of permeability enhancement on gas production has not been thoroughly investigated. In this study, pTOUGH+HYDRATE V1.5 coupled with the RGMS is applied to account for geomechanical responses. Based on actual geological conditions, the reservoir model has five layers: the hydrate-bearing layer (HBL), the three-phase layer (TPL), the free gas layer (FGL), the overburden, and the underburden. The numerical results match the trial production data, validating the numerical model. The analysis shows that gas production from the FGL contributed the most (72.17%) to the cumulative gas production (Vg), followed by the TPL (23.54%) and the HBL (4.29%). The cumulative water-to-gas ratio (RwgT) gradually decreased during gas production, with the HBL exhibiting the highest value. Permeability enhancement can improve gas production, with the FGL being the most responsive to such enhancement. It increased Vg by 87% and reduced RwgT to 85%. To achieve more realistic production schemes and better enhance energy recovery, it is advisable to conduct numerical investigations that incorporate geomechanical considerations due to the intricate nature of hydrate-bearing sediments.

Energetic characterization during plasma electrolytic polishing of cemented tungsten carbide

Electrical and thermal measurements were conducted during the plasma electrolytic polishing (PEP) of cemented tungsten carbide (WC-Co) materials to characterize energetic aspects of the process in relation to the temporal development of the gaseous layer near the workpiece. The power transferred to the workpiece is determined using a calorimetric probe and employing the time derivative of the temperature curve. It shows distinct heating phases due to the generation of the gaseous layer. At the beginning of the process, a typical power of 367 ± 17 W is transferred to the workpiece of a surface area of 14 cm2. At longer process times, a stabilized gaseous layer limits the power transferred to the workpiece to 183 ± 3 W. In an attempt to describe the heat transferred to the electrolyte, the electrolyte temperature was measured using a thermocouple situated 15 mm away from the workpiece. The local electrolyte temperature increases from 70 to 81 °C for an immersion depth of 20 mm. Moreover, the spatiotemporal development of the electrolyte temperature was obtained by 2D-hydrodynamic modeling using COMSOL Multiphysics®. The modeling results for the local temporal temperature development are in excellent agreement with the experimental values when the turbulent model is applied up to t = 65 s. Afterward, the laminar model leads to a better agreement. Furthermore, line scan x-ray photoelectron spectroscopy revealed that aliphatic carbon was preferentially removed. Only a slight compositional gradient in the vertical direction after the PEP process was observed.

Femtosecond Laser Preparation of Terracotta Warrior-like Pit Superhydrophobic Structure on Magnesium Alloy with Mechanical Durability and Corrosion Resistance.

Magnesium alloys are among the most promising materials for medical implants, and by preparing a superhydrophobic surface, the rate of corrosion can be effectively slowed down and durability be improved. However, the anticorrosion surfaces are inevitable to be damaged for the conventional micro-nanostructured superhydrophobic magnesium alloys, which highly limits their application prospects. This work proposes the development of a Terracotta Warrior pit superhydrophobic structure (TWPSS), consisting of a wall structure with a Terracotta Warrior-like pit and a lotus-like surface papillae structure within the wall. For the first time, top-down laser ablation of the pits to prepare the lotus-like surface papilla structure is used in conjunction with a bottom-up laser-guided melt stacking of the raised wall structure to achieve rapid fabrication of a TWPSS on a magnesium alloy surface. The Cassie-Baxter-based design of the wall structure spacing effectively protects the internal lotus-like surface papillae from damage and the disappearance of low surface energy material, and the results show that the superhydrophobic surfaces of magnesium alloys have excellent mechanical durability and repairability. In addition, it was found that the recast layer and laser melting stacked layers produced on the surface of the alloy during femtosecond laser processing refined the grain size of the magnesium alloy and effectively suppressed the corrosion rate. The combination of the superhydrophobic gas layer and the resulting grain refinement slowed down the corrosion of the magnesium alloy. Thus, the rapid preparation of TWPSS structures with mechanical durability and corrosion resistance by femtosecond lasers expands the clinical applications of superhydrophobic surface magnesium alloys in medical devices.

Improving biogas yield via poultry droppings doped with plantain peels

This research work investigates biogas production from poultry droppings mixed with plantain peels and poultry droppings without plantain peels and its statistical analysis using Microsoft excel and a four factor response surface methodology (RSM). Chemical and proximate compositions of digestate were carried out with the aids to determine the potential use for agricultural purposes. Result obtained from poultry droppings mixed with plantain peels and poultry droppings without mixing with plantain peels indicates the maximum biogas yield as 3.06 x 10-2 and 2.42 x 10-2 m3/day respectively. Analysis of variance of regression equation shows the coefficient of determination (R2) of 99.67% and 99.98% respectively. Ambient, slurry, gas layer and interface between slurry and gas layer temperatures were measured during the fermentation process and were found to be within the mesophilic temperature range. Chemical and proximate compositions of the digestates show that it could be used as replacement for biological fertilizers. Therefore, it can be concluded that mixing plantain peels with poultry droppings increased the biogas volume.

New insights into pore fractal dimension from mercury injection capillary pressure in tight sandstone

Mercury injection capillary pressure (MICP) has been widely used for pore fractal dimension determination and thus leads to a variety of calculation models with different results. Here, taking the tight sandstone gas reservoir of Shaximiao Formation in Jinhua-Zhongtaishan area, central Sichuan Basin as the object, the theory, method and application of pore fractal dimension determination from MICP are explored. Based on Yu-Xia model and Washburn equation, rigorous analytical expressions on fractal dimension, capillary pressure and mercury saturation are deduced. After pre-processing including validation, consistency correction and shape-preserving interpolation, the fractal turning point is located with the local maximum of the front-back moving variance ratio of mercury saturation, and then the global, macropore and micropore fractal dimensions are determined respectively by nonlinear fitting. As suggested by the data processing results of the 39 MICP samples, there is no significant direct correlation between pore fractal dimensions and petrophysical properties represented by permeability. However, the combination of fractal model related parameters, especially global fractal dimension and entry pressure, can identify effectively reservoir quality ranks. Meanwhile, for gas layers with relatively high permeability, larger global fractal dimensions may imply roughly more favorable pore structure and better reservoir quality, while the total quality of the relatively low-permeability gas layers is poor and nearly independent of the fractal dimensions. The representative MICP-based pore fractal models, He-Hua and Shen-Li, are critically reviewed. The theoretical simplification and calculative approximate of these two models lead to some degree of error in pore fractal dimension determination, despite their slight correlation in the fitting results with those of the present model. This study may improve the understanding of the pore fractal dimension determined from MICP and provide reference for pore structure evaluation, reservoir quality classification and capillary pressure modeling.