Parallel Gas Research Articles

Structure design and mechanism research of combined cyclone plate separator based on particle separation

Although there has been much research on the gas–solid separation equipment of cyclone plate, there is still a lot of research space for miniaturization, low resistance, and easy maintenance. In this paper, parallel gas–solid separation equipment is designed based on computational fluid dynamics and experimental verification methods to address the practical problems faced by the fresh air system of the enterprise plant. The internal flow field of the separator is studied by numerical simulation, and the structural parameters of the separator are optimized according to the performance indicators provided by the enterprise. The optimal structure that meets the performance requirements and has the best effect is determined. Subsequently, the actual performance of the optimal structure was verified by wind tunnel experiments, and the deviation between the experimental results and the numerical simulation results was compared. The results show that increasing the number of blades, adjusting the blade angle, and increasing the height of the outer cylinder are beneficial in improving the internal flow field of the separator. Among them, the blade angle significantly affects the tangential velocity and axial velocity of the separator. When these three parameters are increased, the filtration efficiency increases first and then decreases. Finally, when the number of blades is 8, the blade angle is 50°, and the height of the outer cylinder is 0.63 m, the separation efficiency is the highest, and the pressure drop is the lowest. This structure satisfies all performance indicators. The experimental results show that the minimum filtration efficiency is 92.4%, and the maximum pressure drop does not exceed 500 Pa. Compared with the numerical simulation results, the experimental value is 0.29% lower, which shows that the structure has good separation performance and has a significant reference value for the fresh air system of the industrial workshop.

A model reduction framework of flow maldistribution and mitigation strategy for parallel flow field based polymer exchange membrane fuel cell

Mitigating flow maldistribution plays a crucial role in next-generation industry-used parallel-based flow field design for polymer exchange membrane fuel cells (PEMFCs), especially for larger-size cells and higher current density. In this study, a model reduction framework is proposed to alleviate flow maldistribution among parallel gas flow channels and associated computational burden. The gas flow features and electrochemical kinetics of four mitigation strategies including expanded manifold, partially porous media, dot matrix, and partially narrow structures are investigated in detail. The results indicate that the fuel cell model and a fluid flow model without the reactions show similar maldistribution features among parallel channels. The observed flow maldistribution can be effectively reduced by mitigating designs. Expanding the manifold space significantly alleviates the vortex impeding the gas entry to individual channel inlet, and the inlet exhibits better flow uniformity and pressure drop in the direction perpendicular to the channel than in the parallel to. The fully-inserted and manifold-inserted porous media methods present symmetrical quadratic-shaped flow patterns among channels, while that of the partially-inserted porous media inside channels is unsymmetrical. Additionally, the concentration loss with a partially narrowed design decreases by 44.7%, 12.9%, and 24.2% compared with the expanded manifold, partial porous media, and dot matrix designs at 1.8 A cm−2 owing to better flow uniformity and mass transport. These model framework and mitigation strategies are valuable for designing future high-performance industrial PEMFCs.

Absorption in a pseudo-first-order regime with two irreversible reactions: Influence of the second reaction on the transfer rate

Gas-absorbing liquids such as CO2 often undergo two reactions: a main reaction and a secondary reaction. The solute flux transferred is a result of both reactions. Kinetics is one of the most important properties in the design of an absorber. To access the rate constant of the main reaction, the assumption of a pseudo-first-order (PFO) regime is often made, but the criteria for the system to be in a pseudo-first-order regime change between researchers. Furthermore, the impact of the secondary reaction is either neglected or overestimated. Recently, some researchers carried out simulations of multiple parallel gas–liquid reactions in the instantaneous regime and developed generalized criteria for this regime. In this study, to estimate the impact of the secondary reaction in a PFO regime, hundreds of simulations were carried out with two irreversible reactions within the framework of the film theory. This work proves that for Ha1 > 10, Ha2 > 10, Ha1/E∞,1 < 0.5, Ha2/E∞,2 < 0.5, normalized concentration profiles depend only on three factors: Ha1/ E∞,1, Ha2/ E∞,2, and Ha1/Ha2. Curves and generalized equations are provided enabling the estimation of the concentrations of reactants at the interface, the enhancement factor, and the influence of each reaction on the gas transfer flux (average absolute relative deviation ≤ 0.50 %). New criteria for determining whether the system can be considered in a pseudo-first-order regime are defined, giving accurate predictions with a success rate of 96.2 %.

Impact of deodorisation time and temperature on the removal of different MOAH structures: a lab-scale study on spiked coconut oil

Vegetable fats and oils are prone to contamination by mineral oil hydrocarbons due to the lipophilic and ubiquitous character of the latter. As the aromatic fraction of these hydrocarbons, MOAH, is associated with carcinogenicity, mutagenicity, and detrimental effects on foetal development, finding strategies to limit or reduce their contamination is highly relevant. Deodorisation (i.e. a refining step) has shown the ability to remove MOAH < C25 in vegetable fats and oils, but there is little information about the structures removed. Therefore, the present study investigated the impact of deodorisation conditions on the removal of different structures of MOAH in spiked coconut oil. An inscribed central composite design was built with time and temperature as variables (0.5-4h, 150-240 °C), while pressure (3 mbar) and steam flow (1 g water/g oil per hour) were kept constant. The analysis of MOAH in the oil was performed using a fully automated liquid chromatography coupled with two parallel comprehensive two-dimensional gas chromatography systems with flame ionisation and time-of-flight mass spectrometric detection. Response surfaces plotting the MOAH loss according to time and temperature were built for different MOAH fractions. The latter were defined based on the number of aromatic rings (>3 or ≤3) and the number of carbon atoms present (C16-C20, C20-C24, C24-C35, C35-C40). It was found that at 200 °C, compounds < C24, including weakly alkylated triaromatics, could be reduced to below the limit of quantification, while at 230 °C, it was possible to remove >60% of the C24-C35 fraction, including pentaromatics of low alkylation.

Interface‐Confined Assembly of Layered Molecular Crystal Arrays Toward Wearable UV‐Radiation Monitor

AbstractOrganic semiconductors have significant potential for wearable optoelectronics due to their designable molecular structures, tunable photoelectronic properties, and flexibility. For their integration into optoelectronic devices, organic semiconductors need to be assembled into single‐crystalline arrays with both precise alignment of micro‐/nanostructures and long‐range order of molecules. In this study, an interface‐confined lithography technique is developed for fabricating organic single‐crystalline microwire arrays with layered molecular stacking and ordered crystallographic orientation toward wearable UV radiation monitor. This interface‐confined strategy introduces parallel gas–liquid–solid three‐phase contact line (TPCL) arrays to suppress the lateral growth of single crystals. Meanwhile, TPCLs with controlled dewetting direction promote longitudinal growth, thus universally yielding 1D arrays based on various organic semiconducting small molecules. These 1D single‐crystalline arrays exhibit high average mobility of 12.5 cm2 V−1 s−1 with uniform electronic properties of 9.3% variation, and good mechanical stability after 1000 bending times. Based on organic 1D arrays, wearable devices with robust photoresponsivity of 8.26 × 103 A W−1 and high mechanical flexibility achieve real‐time monitoring of UV radiation to prevent skin disease. This confined‐assembly strategy opens a new avenue to construct wearable optoelectronic devices for health monitoring.

Coagulation pretreatment coupled with indigenous microalgal-bacterial consortium system for on-site treatment of rural black wastewater

Improper treatment of rural black wastewater (RBW) presents substantial challenges, including the wastage of resource, environmental contamination, and economic consequences. This study proposed an integrated process for RBW treatment, consisting of coagulation/flocculation (C/F) pretreatment and subsequent inoculation of indigenous microalgal-bacterial consortium (IMBC) for nitrogen recovery, namely C/F-IMBC process. Specifically, the optimal C/F conditions (polyaluminium chloride of 4 g/l, polyacrylamide of 50 mg/l, and pH of 6) were determined through a series of single-factor experiments, considering CN, turbidity, and dissolved organic matter (DOM) removal, economic cost, and potential influence on the water environment. Compared to the sole IMBC system for RBW treatment, the proposed C/F-IMBC process exhibited a remarkable 1.23-fold increase in microalgal growth and a substantial 17.6–22.6 % boost in nitrogen recovery. The altered RBW characteristic induced by C/F pretreatment was supposed to be responsible for the improved system performance. In particular, the abundance of DOM was decreased and its composition was simplified after C/F pretreatment, based on the analysis for excitation-emission matrices with parallel factor and gas chromatography–mass spectrometry, thus eliminating the potential impacts of toxic DOM components (e.g., Bis(2-ethylhexyl) phthalate) on IMBC activity. It should also be noted that C/F pretreatment modified microbial community structure as well, thereby regulating the expression of nitrogen-related genes and enhancing the system nitrogen recovery capacity. For instance, the functional Cyanobacteria responsible for nutrient recovery was enriched by 1.95-fold and genes involved in the assimilatory nitrate reduction to ammonia pathway were increased by 1.52-fold. These fundamental findings are expected to offer insights into the improvement of DOM removal and nitrogen recovery for IMBC-based wastewater treatment system, and provide valuable guidance for the development of sustainable on-site RBW treatment technologies.

Bayesian 13C-Metabolic Flux Analysis of Parallel Tracer Experiments in Granulocytes: A Directional Shift within the Non-Oxidative Pentose Phosphate Pathway Supports Phagocytosis.

The pentose phosphate pathway (PPP) plays a key role in the cellular regulation of immune function; however, little is known about the interplay of metabolic adjustments in granulocytes, especially regarding the non-oxidative PPP. For the determination of metabolic mechanisms within glucose metabolism, we propose a novel set of measures for 13C-metabolic flux analysis based on ex vivo parallel tracer experiments ([1,2-13C]glucose, [U-13C]glucose, [4,5,6-13C]glucose) and gas chromatography-mass spectrometry labeling measurements of intracellular metabolites, such as sugar phosphates and their fragments. A detailed constraint analysis showed that the permission range for net and irreversible fluxes was limited to a three-dimensional space. The overall workflow, including its Bayesian flux estimation, resulted in precise flux distributions and pairwise confidence intervals, some of which could be represented as a line due to the strength of their correlation. The principal component analysis that was enabled by these behaviors comprised three components that explained 99.6% of the data variance. It showed that phagocytic stimulation reversed the direction of non-oxidative PPP net fluxes from ribose-5-phosphate biosynthesis toward glycolytic pathways. This process was closely associated with the up-regulation of the oxidative PPP to promote the oxidative burst.

Dimensionless Moduli Governing Under-Rib Transport Phenomenon in Polymer Electrolyte Fuel Cell

Introduction The performance of polymer electrolyte fuel cell (PEFC) can be considerably improved by promoting the under-rib convection or cross flow between adjacent gas channels, e.g., applying the serpentine and staggered partially narrowed flow fields[1]. Although a lot of efforts have been devoted to analyze the under-rib transport phenomenon, an analytical model which quantitively demonstrates the dominant factors of the under-rib processes has not been established. In this study, a theoretical analysis of the relations between oxygen reduction reaction (ORR) and mass transfer capacity is carried out. The dimensionless moduli which combine physical properties, flow field dimensions and operating conditions are derived, which provides a theory for optimization of flow field and operating condition design for PEFC. Theoretical Analysis The water is assumed to only exist in vapor phase in a steady-state isothermal cell. The gas diffusion layer (GDL) is considered as uniform porous medium, in which Darcy’s law is applicable. The even velocity and oxygen mass fraction profiles in through-plane direction inside GDL is considered. The ORR was experimentally proven as a first order reaction of oxygen partial pressure according to our previous study,[2] and is regarded as a surface reaction, so that the oxygen consumption rate can be expressed as Eq. (1). The ORR rate constant, which is the function of the cathode overpotential or electromotive force, is assumed to be fixed across the rib.The theoretical model was derived from one-dimensioned mass balance of oxygen, which exhibits that the under-rib process is dominated by 3 dimensionless moduli, Péclet number Pe, Thiele number φ and the ratio of oxygen mass fractions θ at two sides of the under-rib GDL, which were defined by Eqs. (2)–(4). Péclet number represents the ratio of oxygen convection rate to oxygen diffusion rate, which is determined by the pressure difference between adjacent channels. Thiele number represents the ratio of oxygen diffusion resistance to reaction resistance. The average oxygen mass fraction can thus be calculated from Eq. (5). Results and Discussion The theoretical model was compared with the computational fluid dynamics (CFD) simulation in the computational domain shown in Fig. 1, where the GDL was placed between two parallel gas channels, instead of being laid under the gas channel, and the active area was only located under the rib. In the CFD simulation, the velocity and pressure distributions were calculated by solving Navier-Stokes equations, and the component distribution dependencies on density, diffusivity and viscosity were also considered. Fig. 2 shows the under-rib average current density at different geometries and operating conditions. The dimensionless moduli calculated from the inlet conditions offer an accurate current density prediction, which demonstrates these moduli dominate the under-rib transport phenomenon.The typical operating condition gives φ = 1.5 and Pe = 4, where the model provides the average current density with high confidence. The model provides lower oxygen mass fraction than the CFD results especially in case of θ = 1, which exists in the staggered partially narrowed flow field. The reason can be attributed to the interface between gas channel and GDL, where the low velocity cannot eliminate the mass transport resistance, so that the model overestimated the oxygen mass fraction at rib boundaries, as shown in Fig. 3.The effects of dimensionless moduli on the current density are exhibited in Fig. 4. In case of θ = 1, when Pe is lower than 5, the under-rib convection cannot obviously boost the under-rib oxygen concentration, which was also reported in our previous study[1]. On the other hand, in case of θ< 1 and Pe > 0, although little increase on Pe remarkably improves the under-rib mass transfer which explains the good performance of serpentine flow field, the benefits from the under-rib convection reduces when Pe is high. Additionally, since oxygen cannot be supplied sufficiently from the gas channel, higher φ gives lower under-rib oxygen concentration. Conclusions The theoretical model for describing the under-rib transport phenomenon was established and verified by CFD calculation, which was found to be dominated by 3 dimensionless moduli. The model demonstrates that the Péclet number is required to be large enough in partially narrowed flow fields to maximize the profits from the under-rib convection. Acknowledgment This work was supported by the FC-Platform Program: Development of design-for-purpose numerical simulators for attaining long life and high performance project (FY 2020–FY 2023) conducted by the New Energy and Industrial Technology Development Organization (NEDO), Japan. Reference [1] Y. Ma et al., ECS Trans., 109 (9), 171–197 (2022).[2] M. Kawase et al., ECS Trans., 75(14), 147–156 (2016). Figure 1

Source of two-dimensional electron gas in unintentionally doped AlGaN/GaN multichannel high-electron-mobility transistor heterostructures—Experimental evidence of the hole trap state

Multichannel high electron mobility transistor (MC-HEMT) heterostructures are one of the choices for improved power performance of GaN HEMTs. By comparing the experimentally obtained two-dimensional electron gas (2DEG) concentration of unintentionally doped (UID) AlGaN/GaN MC-HEMTs with simulated 2DEG concentration, we hypothesized that hole trap(s) exist at the buried GaN/AlGaN interfaces, which act as sources of 2DEG in UID MC-HEMT heterostructures. Furthermore, these hole traps stop the Fermi level from cutting the valence band at GaN/AlGaN interfaces, which in turn precludes the generation of parallel two-dimensional hole gas (2DHG) in the MC-HEMT. However, no experimental report is present as a proof for the existence of such a hole trap in MC-HEMT heterostructures. In this study, a capacitance–conductance method on single and dual channel HEMTs revealed traps with higher time constant of 19–28.7 μs exclusively for the dual channel HEMT heterostructure. These traps are observed at the buried GaN/AlGaN interface of the dual channel HEMT; hence, they are attributed to possible hole traps at this interface. By conducting systematic deep level transient spectroscopy measurements, the existence of hole traps is confirmed at the buried GaN/AlGaN interface with an activation energy of 717 meV and a capture cross section of 1.3 × 10−14 cm2. This experimental evidence of the existence of hole traps at the GaN channel/AlGaN interface further supports our claim that these hole traps act as the source of 2DEG in UID MC-HEMTs and that buried parallel 2DHG channels do not exist in MC-HEMTs.

Interactions between two parallel gas jets on the surface of an underwater vertical moving body

In the present study, interactions between two parallel bubbles after the gas jets inject into a liquid cross flow are studied experimentally. For bubble coalescence on the surface of a moving body, the water layer between the twin parallel bubbles possesses initial momentum and bubble coalescence is difficult to conduct. Based on the verification of the repeatability of the experiments, the coalescence mechanism of the twin parallel bubbles subjected to a cross-flow is studied and the effect of re-entrant jet is analyzed, which can reduce the initial momentum of the water layer and promote the coalescence of bubbles. After that, the influences of the initial pressure inside the air chamber and motion speed of the body have been analyzed. The bubble length and its growth rate are proportional to the motion speed of the body and the initial pressure inside the air chamber has little influence on the growth rate of the bubble length. Moreover, only after the stream-wise length of the water layer reaches critical value, bubble coalescence can occur. According to parametric studies, the critical value of stream-wise length of the water layer depends on the motion speed of the body and a correlation has been estimated.

Effects of Gas Macromixing in Polymer Electrolyte Fuel Cell

For PEFCs’ grand-scale commercialization, their performance should be further improved. The performance of PEFC is results of the distributions of local current density and materials concentration, especially oxygen and water. In addition, the in-plane transport of reactant gas in the gas diffusion layer (GDL), which is difficult to measure, affects the distribution of oxygen partial pressure and relative humidity (RH) by mixing the gas with different residence time. In this study, the PEFC was regarded as a reactor, the gas macromixing in which was evaluated by residence time distribution (RTD) in the perspective of chemical engineering. The cell performance with different active area and gas flow rate in parallel and serpentine gas channels was measured experimentally and predicted by the compartment models. According to the model, the gas macromixing in the 1 mm-manifold parallel channel is more obvious than that in the serpentine model, and has better performance at low oxygen conversion, since appropriate water humidification is beneficial to the cell performance. The results also indicate that the gas macromixing should be promoted to improve the water humidification and the cell performance at low oxygen conversion. The computationally inexpensive compartment model is potentially applicable for system simulator and design procedure.

Time-Lapse Observation of Crevice Corrosion in Grade 2205 Duplex Stainless Steel.

The objective of this study was to investigate and visualize the initiation and propagation of crevice corrosion in grade 2205 duplex stainless steel by means of time-lapse imaging. Transparent Poly-Methyl-Meth-Acrylate washer and disk were coupled with duplex stainless steel to create an artificial crevice, with electrochemical monitoring applied to obtain information about the nucleation and propagation characteristics. All nucleation sites and corroding areas inside crevices were recorded in situ using a digital microscope set-up. Localized corrosion initiated close to the edge of the washer, where the crevice gap was very tight, with active corrosion sites then propagating underneath the disk into areas with wider gaps, towards the crevice mouth. The growth was associated with a rise in anodic current interlaced with sudden current drops, with parallel hydrogen gas evolution also observed within the crevice. The current drops were associated with a sudden change in growth direction, and once corrosion reached the crevice mouth, the propagation continued circumferentially and in depth. This allowed different corrosion regions to develop, showing selective dissolution of austenite, a region with dissolution of both phases, followed by a region where only ferrite dissolved. The effect of applied electrochemical potential, combined with time-lapse imaging, provides a powerful tool for in situ corrosion studies.

Domestic cat nose functions as a highly efficient coiled parallel gas chromatograph.

The peripheral structures of mammalian sensory organs often serve to support their functionality, such as alignment of hair cells to the mechanical properties of the inner ear. Here, we examined the structure-function relationship for mammalian olfaction by creating an anatomically accurate computational nasal model for the domestic cat (Felis catus) based on high resolution microCT and sequential histological sections. Our results showed a distinct separation of respiratory and olfactory flow regimes, featuring a high-speed dorsal medial stream that increases odor delivery speed and efficiency to the ethmoid olfactory region without compromising the filtration and conditioning purpose of the nose. These results corroborated previous findings in other mammalian species, which implicates a common theme to deal with the physical size limitation of the head that confines the nasal airway from increasing in length infinitely as a straight tube. We thus hypothesized that these ethmoid olfactory channels function as parallel coiled chromatograph channels, and further showed that the theoretical plate number, a widely-used indicator of gas chromatograph efficiency, is more than 100 times higher in the cat nose than an "amphibian-like" straight channel fitting the similar skull space, at restful breathing state. The parallel feature also reduces airflow speed within each coil, which is critical to achieve the high plate number, while feeding collectively from the high-speed dorsal medial stream so that total odor sampling speed is not sacrificed. The occurrence of ethmoid turbinates is an important step in the evolution of mammalian species that correlates to their expansive olfactory function and brain development. Our findings reveal novel mechanisms on how such structure may facilitate better olfactory performance, furthering our understanding of the successful adaptation of mammalian species, including F. catus, a popular pet, to diverse environments.

Study on numerical simulation of leakage and diffusion law of parallel buried gas pipelines in tunnels

Parallel buried gas pipelines in tunnels are located in a confined space environment, where natural gas is vulnerable to accumulating to the minimum explosion limit concentration after a leakage accident. Therefore, to reduce the time for locating the leakage source after an accident and compensate for the loss of emergency response, an experimental model for scaling parallel gas transmission pipelines in tunnels was established and the dispersion characteristics and influencing factors of continuous leakage of natural gas within buried soil and in tunnel space were investigated numerically, and the correlation between the volume of the explosion range of natural gas within the tunnel space and each influencing factor was explored using gray correlation analysis. The research shows that the leakage dispersion process of parallel buried gas pipelines in tunnels includes seepage leakage in the soil region and diffusion transport in the tunnel air region. In the soil region, natural gas from the pipeline leak forms a circular shape and tends to percolate upward due to the combined effect of pressure and concentration gradients.In the tunnel air region, the spatial dispersion of natural gas concentration obeys a multivariate Gaussian distribution, and the temporal dimension is divided into three phases: the initial phase of leakage, the spreading phase and the stable phase of leakage. The diffusion speed of natural gas is positively correlated with the operating pressure of pipeline. The concentration peak value (ymax) at the leakage orifice position and the leakage aperture (dx) approximately meet the linear relationship: ymax= 7.62dx. The diffusion path of natural gas is greatly influenced by the orientation of the pipeline perforations, and the tunnel walls have a directional effect on the diffusion of natural gas. The main factors affecting the volume of the explosion range of natural gas within the tunnel space are parallel pipeline leakage pressure, pipeline leakage aperture, parallel pipeline leakage position, pipeline operating pressure, and pipeline leakage direction, with grey correlation coefficients of 0.76, 0.675, 0.662, 0.553, and 0.55. The proposed model was demonstrated be able to simulate and predict the diffusion of natural gas under the accidental leakage of buried gas pipelines in tunnels. And the results of this study can guide the installation of buried gas pipelines crossing mountain tunnels to prevent accidents.

Novel fully automated and parallel gas assisted dynamic accelerated solvent extractor and parallel solvent evaporator for analysis of solid and semi-solid samples

The extraction of non-volatile and semi-volatile analytes from solid and semisolid samples has been primarily carried out via heated and/or pressurized liquid extraction mechanisms. Although analyte extraction and concentration processes have significantly evolved and currently several automated solutions are commercially available, these two steps are carried out independently. To the best of our knowledge, human intervention is always required throughout the entire process for sample extract manipulation/transportation among instruments/processes. Expectedly, excessive sample handling throughout the analytical workflow contributes to an increase in the analysis cost, the loss of analyte (s), and numerous potential analytical errors. Herein, we present the first fully automated sample-to-vial solution for analysis of non-volatile and semi-volatile compounds from solid and semisolid samples. This technological development, which is based on gas assisted dynamic accelerated solvent extraction (GA-dASE) and an integrated level-sensing system that controls the endpoint of the evaporation step, allows for fully automated analyte extraction and analyte enrichment. As a proof of concept, we applied this fully automatic extraction and enrichment system towards the quantitative determination of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs) in soil samples. Our results showed that GA-dASE not only matched the performance of the legacy accelerated solvent extraction (ASE), in terms of analyte recovery and reproducibility, but also delivered nearly 3-time reduction in labor per sample. Furthermore, our experiments demonstrated the capability of the instrument to perform fully automated extraction and evaporation steps without human intervention and with no impact on data quality (Relative Standard Deviation, RSD, ≤ 20%). In terms of interlaboratory reproducibility (n = 2), our results showed comparable results for the determination of PAHs using either 10- or 100-mL sample cells.

Identification of gas diffusion phenomena on highly active Ni–ceramic anodes using the DRT technique

Nickel–ceramic composites are conventional and basic materials for anodes of solid oxide fuel cells. Usually, nickel–cermets have insufficient electrochemical activity due to the fact that the hydrogen oxidation reaction is limited by the triple phase boundary (TPB) length. The electrochemical activity of nickel–cermets can be improved by increasing the TPB length or through the wet impregnation with ceria. A distinctive feature of the electrochemical impedance spectra of highly active nickel–ceramic anodes impregnated with ceria is the response from gas diffusion phenomena in the low frequency range. Under certain conditions, the resistance of gas diffusion phenomena cannot be determined by conventional approaches to the analysis of impedance spectra. A tremendous assistance in the analysis of impedance spectra over the past few years has become the method of distribution of relaxation times (DRT). This paper presents the results of studies of highly active nickel–ceramic electrodes made from NiO and Zr0.84Sc0.16O1.92 powders of various dispersion and impregnated with ceria. Using the DRT method was found that in the case of electrode with low porosity the hydrogen oxidation rate is limited by the rates of two parallel gas diffusion processes relaxing in almost the same frequency range.

Multiple upscaling procedures for gas transfer in tight shale matrix-fracture systems

Multiple upscaling schemes for gas transfer in nanoporous media, microporous matrix, core-scale matrix, and centimeter-scale matrix-fracture systems are investigated. An Open Multi-Processing (OpenMP)-based parallelized multi-scale numerical solver for micro-gaseous flow in composite microporous media is developed by coupling the pore-scale multiple-relaxation-time lattice Boltzmann method (MRT-LBM) and representative elementary volume (REV)-scale LBM model. The permeability of the microporous matrix is calculated through hundreds of pore-scale simulations for gas transfer in nanoporous media, before being imported into the REV-scale LBM to predict the core-scale matrix permeability. It is followed by the investigations of the variations of core-scale permeability with the heterogeneous spatial distribution of organic matter aggregates, mineral aggregates, interparticle pores, and microfractures. The parallel and sequential gas transfer processes in a larger shale system containing the tight matrix and hydraulic fractures are studied and analyzed. The results reveal several new insights: 1) the microscale spatial distribution of multiple constituents has relatively little effect on the core-scale permeability; 2) an ultra-large local pressure gradient occurs in a thin boundary layer of tight shale matrix, which is shown to be proportional to the square root of the permeability ratio, resulting in considerable flow characteristic velocity in the matrix; 3) the in-situ matrix-fracture transfer satisfies a sequential transport process due to a long equilibration time delay between the tight matrix and fractures; 4) the observed high production rate for tight shale may be caused by the ultra-large local pressure gradient in the matrix (and not by a large apparent permeability as commonly assumed). The results also reveal some anomalous phenomena for multiscale gas transfer in tight shale formations.

Study on oxygen transport and titanium oxidation in coating cracks under parallel gas flow based on LBM modelling

The oxygen transportation from surrounding air to coating cracks is an important factor in the oxidation and ignition of titanium alloy. In this work, the oxygen transport and surface oxidation of titanium in inclined cracks of coating under parallel airflow are studied with the lattice Boltzmann method. A boundary scheme of LBM about surface reaction is developed. The conversion factors are utilized to build the relationship between the physical scale and the lattice scale. The reliability of the LBM model is validated by the FEM method. The results show that the convective mass transport driven by the surrounding airflow and the vortex structure formed inside the crack are the two significant factors that influence the oxygen transport in cracks. The convective mass transfer plays a major role in oxygen transport when the inclination angle of the crack is small. For the cases with a large inclination angle, the oxygen transfer from the top to the bottom of the crack is mainly controlled by mass diffusion mechanism. The oxygen concentration in inclined cracks is generally less than that in vertical cracks, and oxidation and ignition of the substrate titanium might be more likely to occur in relatively vertical cracks.

Variety of flow patterns in a liquid bridge subjected to a gas stream.

We present an experimental and two-phase computational study of convection in a liquid bridge ([Formula: see text]) that develops under the action of a parallel gas flow. The study focuses on tracking the evolution of hydrothermal waves by increasing the applied temperature difference [Formula: see text] and the temperature of gas moving at the velocity [Formula: see text]. Our experiments revealed certain regularity in the change of oscillatory states with an increase in the control parameters. Above the instability threshold, the nonlinear dynamics passes through three oscillatory regimes, which are repeated in a somewhat similar way at higher values of the control parameters. They are periodic, quasi-periodic with two or three frequencies and multi-frequency state when the Fourier spectrum is filled with clusters of duplex, triplex or higher numbers of frequencies. Three-dimensional numerical simulation, complemented by a deep spectral analysis, sheds light on the evolution of the flow pattern observed in experiments. The developed methodology identified conditions for the existence of a multi-frequency regime such as the presence of a weak low-frequency mode that can modulate strong high-frequency modes, the existence of strong azimuthal modes with different wavenumbers and the [Formula: see text] mode, and the structured combination of peaks in the Fourier spectrum. This article is part of the theme issue 'New trends in pattern formation and nonlinear dynamics of extended systems'.

Energy Consumption Optimization Model of Large Parallel Natural Gas Pipeline Network: Using Compressors with Multiple Operating Modes

In long-distance parallel pipelines, compressor stations are built together, and connecting pipes and cut-off valves are arranged between pipelines, which makes it possible for different stations to operate jointly or independently. In order to reduce pipeline energy consumption, this paper considers the valve switch state, deeply analyzes the station operation mode, and establishes the optimal model of minimum energy consumption of a parallel pipeline. Taking the second and third parallel pipelines of China’s west-east gas transmission as an example, the phasor particle swarm optimization algorithm is used to solve the model. The results show that after optimization, the internal flow was redistributed and energy consumption was reduced by 15.54%.