Flux Stability Research Articles

Numerical Study on Combustion and Atomization Characteristics of Coaxial Injectors for LOX/Methane Engine

The LOX/methane engine has an admirable performance under a supercritical state. However, the properties of methane change drastically with varying injection temperature. Because the injector can greatly affect the atomization and combustion, this study performed a three-dimensional numerical simulation of atomization, combustion, and heat transfer in a subscale LOX/methane engine to evaluate the effect of the main fluid parameters with different methane injection temperatures and different injectors on atomization performance and combustion performance. The results show that the larger propellant momentum ratio and Weber number can improve the heat flux and combustion stability in shear coaxial injector, while the influence in swirl coaxial injector is relatively small. Moreover, in shear coaxial injector and in swirl coaxial injector, the larger propellant momentum ratio and Weber number can reduce the droplet size, enhance atomization performance, and improve the combustion efficiency. The numerical model provides an economical method to evaluate the main fluid parameters and proposes new design principles of injectors in LOX/methane engine.

Air superhydrophilic-superoleophobic SiO2-based coatings for recoverable oil/water separation mesh with high flux and mechanical stability

Due to the inherent differences in surface tension between water and oil, it is a challenge to fabricate air superhydrophilic-superoleophobic materials despite their promising potential in the field of oil/water separation. Herein, a facile approach is developed to fabricate air superhydrophilic-superoleophobic SiO2 coating by combination of controllable modifying SiO2 nanoparticle surface by both hydrophilic groups (i.e., –OH groups) and oleophobic groups (i.e., fluorinated groups) with constructing porous and hierarchical structures. Hydroxyl-modified SiO2 nanoparticles (NPs) are synthesized using a base-catalysed procedure in the presence of ammonia or NaOH. Chitosan quaternary ammonium salt (HACC) is introduced to bind SiO2 by forming a unique hydrogen bond between HACC and –OH, followed by adding pentadecafluorooctanoic acid (PFOA) to complex with HACC to form fluorinated groups. The SiO2 coatings are fabricated on various substrates (e.g., glass, foam and Cu mesh) by spraying procedure and characterized using SEM, FTIR, XPS, etc. The contact angles of oils (e.g., pump oil, castor oil, corn oil, hexadecane and bean oil) and water on the coatings are over 150° and close to 0°, respectively. By optimization, the representative SiO2-coated Cu mesh displayed high-efficiency of 99.2% in separating water from mixture of water/pump oil, and high penetration flux of 1.41 × 104 L·m−2 ·h−1. Besides, the coating maintains its superhydrophilic-superoleophobic properties even after 110 cycles of sandpaper abrasion or after being immersed in water for 3 h. After 20 cycles of oil/water separation, the coating retains separation efficiency up to 97.93%. This study provides a new and universal protocol to fabricate unique superwetting surfaces with effective oil/water separation performance, long-term durability and outstanding reusability.

Investigation of flux stability and fouling mechanism during simultaneous treatment of different produced water streams using forward osmosis and membrane distillation

Forward osmosis-membrane distillation (FO-MD) hybrids were recently found suitable for produced water treatment. Exclusion of synthetic chemical draw solutions, typically used for FO, can reduce FO-MD operational costs and ease its onsite application. This study experimentally validates a novel concept for the simultaneous treatment of different produced water streams available at the same industrial site using an FO-MD hybrid system. The water oil separator outlet (WO) stream was selected as FO draw solution and it generated average fluxes ranging between 8.30 LMH and 26.78 LMH with four different feed streams. FO fluxes were found to be governed by the complex composition of the feed streams. On the other hand, with WO stream as MD feed, an average flux of 14.41 LMH was achieved. Calcium ions were found as a main reason for MD flux decline in the form of CaSO4 scaling and stimulating the interaction between the membrane and humic acid molecules to form scale layer causing reduction in heat transfer and decline in MD flux (6%). Emulsified oil solution was responsible for partial pore clogging resulting in further 2% flux decline. Ethylenediaminetetraaceticacid (EDTA) was able to mask a portion of calcium ions and resulted in a complete recovery of the original MD flux. Under hybrid FO-MD experiments MD fluxes between 5.62 LMH and 11.12 LMH were achieved. Therefore, the novel concept is validated to produce fairly stable FO and MD fluxes, with few streams, without severe fouling and producing excellent product water quality.

Increasing the Thermostability of Optoelectronic Devices on Semiconductor Radiators

The article proposes a scheme for thermal stabilization of the radiation flux of mid-IR LEDs in the temperature range + 20 ° C + 80 ° C. It is shown that the relevance of mid-IR LEDs for solving problems of gas analysis, environmental monitoring, moisture measurement and medical diagnostics. It was revealed that the guarantee of the measurement accuracy and sensitivity of optoelectronic devices is the correct spectral matching of the photodetector, LED and absorption of the investigated substance. The disadvantages of emitting diodes associated with time and temperature instability during operation are considered. A study of the spectral characteristics of mid-IR LEDs at various temperatures showed that the wavelength at the maximum the emission spectrum increases almost linearly with increasing temperature, which leads to additional errors and lowers the measurement accuracy of optoelectronic devices. A schematic diagram is proposed for stabilizing the radiation flux of mid-IR LEDs in the temperature range + 20 ° C + 80 ° C..

Hydrogen isotope permeation through yttria coatings on Eurofer in the diffusion limited regime

In fusion power plants a tritium permeation barrier is required in order to prevent the loss of the fuel. Moreover, the tritium permeation barrier is necessary to avoid that the radioactive tritium accumulates in the first wall, the cooling system, and other parts of the power plant. Oxide thin films, e.g. Al2O3, Er2O3 and Y2O3, are promising candidates as tritium permeation barrier layers. With regard to the application, this is especially true for yttrium due to its favorably short decay time after neutron activation compared to the other candidates. The Y2O3 layers with thicknesses from 100 nm to 500 nm are deposited on both sides of Eurofer substrates by RF magnetron sputter deposition. Some of the samples are additionally deposited with palladium thin films to analyse the limited regime. During the annealing in the experiments the palladium layers do not show any crack formation or delamination, verified by scanning electron microscopy. After annealing the cubic crystal structure of the Y2O3 layers is verified by X-ray diffraction. The cubic phase contains a small amount of a monoclinic phase, which is eliminated after the permeation measurements. The permeation reduction factors of the samples are determined in gas-driven deuterium permeation experiments. A permeation reduction of 5000 of the yttria thin film is verified. The diffusion limited regime is identified by the pressure dependence of the permeation measurement and by permeation experiments with the palladium top layers on the Y2O3 thin films. Furthermore, the activation energy of the permeation through the yttria thin films is determined. Pre-annealing times for more than 70 h of the Y2O3 thin films and permeation measurements with temperature cycles for 20 days are performed to show the stability of the permeation flux and hence the microstructure of the barrier layers. Measurement times at each constant temperature level of more than 25 h are required for the stabilization of each permeation flux to a constant value. The permeation measurement setup is enhanced to enable a continuously running equipment for these measurement times.

An anti-oil-fouling and robust superhydrophilic MnCo2O4 coated stainless steel mesh for ultrafast oil/water mixtures separation

Developing novel superhydrophilic/underwater superoleophobic oil/water separation membrane with ultra-high flux and high separation efficiency has important theoretical and practical significance for oily wastewater treatment. In this work, a completely inorganic MnCo2O4 coated stainless steel mesh (MnCo2O4-SSM) was fabricated via a facile hydrothermal-annealing method. The microstructures and strong water affinity of MnCo2O4 endow the stainless steel mesh excellent superhydrophilicity/underwater superoleophobicity and oil/water separation performance. The MnCo2O4-SSM exhibits superior anti-oil-fouling property, high-efficiency oil/water separation ability (>99.9%), ultrahigh flux (>63 L·m−2·s−1) and excellent recycling stability. Furthermore, the mesh shows excellent mechanical and chemical stabilities and long-term durability.

Effects of predator movement patterns on the biofouling layer during gravity-driven membrane filtration in treating surface water

Biological predation has a significant effect on biofouling layers in gravity-driven membrane (GDM) filtration systems. However, the detailed process of predatory activities is still not well known. This study explored the effects of predator movement patterns on the biofouling layer at different temperatures and the factors affecting the stable flux level. The results indicated that Demospongiae, Spirotrichea and Saccharomycetes were the main species, with the body contracting or rotating in one position at 5 °C, and Litostomatea accounted for 55.1% at 10 °C. The weak agility of these species resulted in a less porous biofouling layer with a high extracellular polymeric substance (EPS) concentration, which was responsible for the low permeate flux and the time to reach flux stability. Bdelloidea was dominant at 20 and 30 °C, and the more heterogeneous biofouling layer with a lower EPS concentration was related to their intense creeping and swimming movements and their ability to create current in the water. The grazing of spongy flocs by predators affected the GDM system performance, and a high stable flux was obtained with large and loose flocs. In addition, the diversity of the eukaryotic community decreased after the flux stabilized due to the particular predominance of Bdelloidea at high temperatures, corresponding to a high stable flux. Pollutant removal was less affected by eukaryotes, and decreased ammonia nitrogen removal rates were related to the lower activity of nitrifying bacteria. Moreover, the reliable linear correlation between the temperature and the stable flux implied that the stable flux could be well predicted in the GDM system. The findings are beneficial for developing new strategies for regulating flocs and the biofouling layer to improve the performance of GDM systems.

Competing aerosol effects in triggering deep convection over the Indian Region

Contrasting direct and feedback effects of aerosols on deep convection in the Gangetic Plain of Indian subcontinent have been analyzed by employing observation and modeling framework during the Ganges Valley Aerosol Experiment conducted in 2011. The key question addressed in the current investigation is: while the aerosol direct radiative effect leads to reduced surface shortwave flux and possible stabilization of the lower atmosphere, how is the deep convection favored in a heavily polluted atmosphere? The composites of aerosol, cloud and meteorological parameters during the formation of deep convective clouds (DCCs) under both light- and heavy- pollution conditions are contrasted to elucidate the aerosol effects. An enhanced low-level warming is discernible due to the presence of heavily polluting absorbing aerosols. A seminal role of aerosols in increasing the moist static energy (MSE) through enhancement of internal energy is identified as a primary feature that increases the convection potential of the lower atmosphere. Concomitantly, the greater moisture convergence facilitated by dynamical feedback of enhanced low-level heating destabilizes the atmospheric stratification. Additionally, the microphysical invigoration is examined for any possible role, nevertheless, only a weakened invigoration could be observed possibly due to dominance of meteorology. The observed results are well supported by model simulation of a deep convective event under high- and low-aerosol backgrounds. Besides highlighting the dominance of radiative processes over microphysical processes under heavily polluted environment, the significant correlation between aerosol and high clouds observed during DCC formation under such conditions suggests that the aerosol direct effect in weakening convection could be overcome primarily through enhancement in MSE and concomitant moisture convergence.

G4 flux, algebraic cycles and complex structure moduli stabilization

We construct G4 fluxes that stabilize all of the 426 complex structure moduli of the sextic Calabi-Yau fourfold at the Fermat point. Studying flux stabilization usually requires solving Picard-Fuchs equations, which becomes unfeasible for models with many moduli. Here, we instead start by considering a specific point in the complex structure moduli space, and look for a flux that fixes us there. We show how to construct such fluxes by using algebraic cycles and analyze flat directions. This is discussed in detail for the sextic Calabi-Yau fourfold at the Fermat point, and we observe that there appears to be tension between M2-tadpole cancellation and the requirement of stabilizing all moduli. Finally, we apply our results to show that even though symmetric fluxes allow to automatically solve several F-term equations, they typically lead to flat directions.

Self-assembling of NCQDs-TiO2 nanocomposite on poly(acrylic acid)-grafted polyethersulfone membrane for photocatalytic removal and membrane filtration

Considering the tedious post-reaction recovery of nano-sized phototcatalysts and the critical fouling problem faced in membrane separation, incorporation of photocatalyst with polymeric membrane has been developed to alleviate these issues. In this study, polyethersulfone (PES) membrane was synthesized by phase inversion method and poly-acrylic acid (PAA) was later grafted onto the PES surface via UV-induced graft polymerization technique. The PAA film has introduced –COOH functional groups for the surface immobilization of green nitrogen-doped carbon quantum dots-titanium dioxide (NCQDs-TiO2) photocatalyst via a self-assembly approach. The PAA-modified supporting layer and the NCQDs-TiO2 functional layer were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR). The characterization results evidenced that PAA chains were successfully polymerized on PES support while the nanocomposite was firmly deposited on the PAA-grafted membrane. The novel NCQDs-TiO2/PAA/PES composite membrane demonstrated excellent photocatalytic capability, wherein 94.41% of methylene blue (MB) was removed under 1 h of visible-light irradiation. The antifouling property of the modified membrane was proven by the rapid flux stabilization and the high flux recovery ratio of 83.92%. The current research work proposed the synergistic use of visible-light responsive photocatalytic membrane in the degradation and filtration of wastewater, which is more energy-efficient and could reduce secondary pollution.

How Real-Time Evaluation of Slugging Severity Can Help Maximize Production

In recent years, Aker BP has explored and developed a number of digital improvements to optimize production. The underlying business drivers are meant to improve efficiency, increase production and reserves, decrease costs, and reduce the carbon footprint from operations. The example described in this article has innovative elements of digitalization and automation of workflows which provide a new approach for better handling of slugging in subsea developments with long tiebacks. The new solution has a potential for optimizing production and limiting the amount of flaring. Flow Instabilities in the Vilje Field The Aker BP-operated Vilje field in the Norwegian Continental Shelf has occasionally experienced production-flow instabilities in the production pipelines and risers due to slugging. The company worked with Turbulent Flux to develop a software solution, the FLUX Stability Adviser, to continuously and precisely monitor production in real time. Field Description and Outline of Problem The Vilje field is a subsea development with three horizontal producers tied back to the Alvheim floating production, storage, and offloading (FPSO) facility through a production line longer than 20 km. The inlet separator at Alvheim is shared with other third-party developments. After an initial period of dry-oil production at the field, which started production in 2008, the oil rate has gradually decreased as a result of increased water cuts (WC) over time. Gas lift has been used to sustain production. The occasional slugging at the inlet separator had been controlled by increasing the backpressure to the production line and/or shutting in one of the producers. However, this practice affects production potential and may lead to production losses or deferral. Explanation of the Solution The two companies developed a Stability Adviser application to advise operators of the settings to optimize production in real time while lowering the risks related to slugging at any point in time. The developed solution runs on a cloud infrastructure with an interactive web-user interface. The main user interface contains a 3D heat map which is based on output from a series of pre-run transient simulations and a statistical analysis of the associated slugging severity. The model quality of the pre-run simulations was benchmarked with field data, and a similarity index was introduced to evaluate the degree of matching. Transient multiphase flow simulations represent the state of the art in the prediction and analysis of slugging behavior in multiphase transport pipelines (both terrain-induced and hydrodynamic slugging). These simulators capture and follow slugs as they are forming along the pipeline. That said, these simulations are time consuming, which limits their usefulness in a real-time operational context.

Integrating granular activated carbon (GAC) to gravity-driven membrane (GDM) to improve its flux stabilization: Respective roles of adsorption and biodegradation by GAC

As a low-maintenance and cost-effective process, gravity-driven membrane (GDM) filtration is a promising alternative for decentralized drinking water supply, while the low flux impedes its extensive application. In order to address such issue, an integrated process consisting of granular activated carbon (GAC) layer and GDM was developed. The performance of virgin (fresh GAC) or preloaded GAC (saturated GAC) was compared. Flux stabilization was observed both in the fresh and saturated GAC/GDM process during long-term filtration and their stable fluxes were both improved by approximately 50% relative to the GDM control. Moreover, integrating GAC with GDM contributed to efficient removals for dissolved organic compounds (DOC), assimilable organic carbon (AOC) and low molecular weight substances both in fresh and saturated GAC/GDM filtration. Compared to GDM control, coupling GAC to GDM could significantly reduce the concentrations of extracellular polymeric substances (EPS) and total cell counts (TCC) within the biofouling layer, and engineer highly heterogeneous structures of biofouling layer on the membrane surface. In the fresh GAC/GDM process, the improved flux obtained was mainly related to less coverage of biofouling layer and lower EPS concentrations due to efficient removals of membrane foulants by GAC adsorption. The achieved higher stable flux can be maintained during long-term filtration (after GAC saturation) owing to the combined effects of EPS reduction and formation of highly heterogeneous structures of biofouling layer in the saturated GAC/GDM system. Overall, the integrated GAC/GDM process can hopefully facilitate improvements both in the stabilized flux and permeate quality, with practical relevance for GDM applications in decentralized drinking water supply.

Can ultrafiltration singly treat the iron- and manganese-containing groundwater?

The presence of Fe2+ and Mn2+ would cause severe ultrafiltration (UF) membrane fouling and limited its extensive application in treating the groundwater. A pilot-scale gravity-driven membrane (GDM) process which coupled the dual roles of biocake layer and UF membrane was introduced to treat the groundwater under high Mn2+concentrations and low temperature conditions. The results indicated that flux stabilization was observed during long-term GDM filtration with average stabilized fluxes of 3.6–5.7 L m−2 h−1. GDM process conferred efficient removals of Fe2+ and Mn2+ with both average removals > 95%. Pre-adding manganese oxides (MnOx) could effectively shorten the ripening period of manganese removal from 50 to 30 days, and simultaneously contribute to the Mn2+ removal and flux improvements. The presence of Mn2+ facilitated the formation of heterogeneous structures of biocake layer to primarily determine the flux stabilization of GDM, while the influence of extracellular polymeric substances (EPS) concentrations was nearly negligible. Besides, the Mn2+ removal was primarily attributed to the biocake layer other than UF membrane itself, and the chemically auto-catalytic oxidation by MnOx particles played the pivotal role. Therefore, these findings provide relevance for establishing new strategies in treating the iron-and manganese-containing groundwater.

High flux photocatalytic self-cleaning nanosheet C3N4 membrane supported by cellulose nanofibers for dye wastewater purification

Hazardous dye substances discharged from the textile and dyestuff industries not only threaten local the surrounding ecosystems but are also hard to degraded. We report the preparation of process for a photocatalytic membrane device that can degrade dye pollution under visible light. This filtration membrane, with a well-organized multilayer structure, simultaneously achieves continuous and flow-through separation of degradation products. Cellulose nanofibers (CNFs) were used as a template for nanosheet C3N4 (NS C3N4) preparation; the performance for the photocatalytic degradation of dyes improved as the morphology changed from bulking to nanosheet. NS C3N4 was then attached to the surface of a prepared CNF membrane via vacuum filtration. This device exhibited high efficiency (the degradation rates of both Rhodamine B and Methylene blue both reached 96%), high flux (above 160 L·h−1·m−2·bar−1) and excellent stability (maintaining steady flux and high separation were maintained after 4 h). This easy-preparation, easy-scale-up, and low-cost process provides a new method of fabricating photocatalytic membrane devices for dye wastewater treatment.

Performance Evaluation and Fouling Propensity of Forward Osmosis (FO) Membrane for Reuse of Spent Dialysate.

The number of chronic renal disease patients has shown a significant increase in recent decades over the globe. Hemodialysis is the most commonly used treatment for renal replacement therapy (RRT) and dominates the global dialysis market. As one of the most water-consuming treatments in medical procedures, hemodialysis has room for improvement in reducing wastewater effluent. In this study, we investigated the technological feasibility of introducing the forward osmosis (FO) process for spent dialysate reuse. A 30 LMH of average water flux has been achieved using a commercial TFC membrane with high water permeability and salt removal. The water flux increased up to 23% with increasing flowrate from 100 mL/min to 500 mL/min. During 1 h spent dialysate treatment, the active layer facing feed solution (AL-FS) mode showed relatively higher flux stability with a 4–6 LMH of water flux reduction while the water flux decreased significantly at the active layer facing draw solution (AL-DS) mode with a 10–12 LMH reduction. In the pressure-assisted forward osmosis (PAFO) condition, high reverse salt flux was observed due to membrane deformation. During the membrane filtration process, scaling occurred due to the influence of polyvalent ions remaining on the membrane surface. Membrane fouling exacerbated the flux and was mainly caused by organic substances such as urea and creatinine. The results of this experiment provide an important basis for future research as a preliminary experiment for the introduction of the FO technique to hemodialysis.

Respective role of iron and manganese in direct ultrafiltration: from membrane fouling to flux improvements

Manganese contamination in the surface water has captured ever-increasing attention in the drinking water supply, especially in the fields of membrane filtration. In the present study, an innovative gravity-driven membrane (GDM) process, combining the supplementary effects between the bio-cake layer and ultrafiltration (UF) membrane, has been constructed with expects to treat the iron-and manganese-containing surface water. The results indicated that iron and manganese were deeply eliminated by GDM process with both concentrations of less than 0.05 mg/L in the membrane permeate, and the presence of iron and manganese would also measurably contribute to the removals of organic foulants. Furthermore, little impacts of the presence of iron and manganese on the occurrence of flux stabilization were observed. During the treatments of iron- and manganese-containing surface water, the stable fluxes of GDM process were substantially attributed to the coverage and porosities of bio-cake layer on the membrane surface, regardless of the limited effects of EPS accumulation. The generated manganese oxides would improve the roughness and porosities of bio-cake layer, as well as reduce its coverage and the thickness of basal layer, facilitating flux improvements by approximately 18%. Instead, the iron involvement would engineer a thicker basal layer, increase the coverage and reduce the porosities of bio-cake layer, leading to a flux reduction (~17%). Therefore, GDM process is a cost-effective strategy for decentralized water supply, especially for the treatments of iron- and manganese-containing surface water.

Convective Turbulence in a Cubic Cavity under Nonuniform Heating of a Lower Boundary

The problem of heat transfer intensification using spatially nonuniform boundary conditions is of great interest. In this paper, the influence of a nonuniform, nonperiodic distribution of heating on the flow structure and convective heat flux for developed turbulent regimes (Ra = 1.1 × 109) is studied. The numerical simulation of convective turbulence in a cubic cavity is performed for a nonuniform heating distribution at the lower boundary using open-source software the OpenFoam 4.1. Calculations were carried out for three types of the temperature distribution: localized heating at the center of the lower boundary; nine heaters of the same size, equidistant from each other; and fractal heating. The heating area is the same in all of these distributions. It is shown that in all cases of a nonuniform heating distribution in the cavity a large-scale circulation is formed. The dynamics and structure of large-scale circulation depend on the temperature distribution at the lower boundary of the cavity. Spontaneous reorientations of the large-scale circulation plane by angles of ±45° or ±90° are revealed. A comparison of the intensity of the heat flux through the layer (cavity) at a fixed temperature difference at horizontal boundaries is made. It is shown that the heat transfer intensity weakly depends on the temperature distribution on the lower boundary. The maximum difference in the Nusselt numbers for three types of the nonuniform temperature distribution did not exceed 5%. Comparison of numerical simulation results for the uniform and nonuniform heating distributions at Ra = 1.1 × 109 shows that a decrease in the heating area by 70% leads to a decrease in the Nusselt number by 10%. It is shown that the heat flux also decreases with decreasing heating area, at fixed temperatures in the heating and cooling regions, not proportionally to the change in the area. For practical applications, an important role is played by the stability of the heat flux, which is characterized by the absence of pulsations. It is shown that the use of fractal heating can significantly reduce the level of heat flux pulsations without losses in the efficiency of heat transfer.

Construction of graphene oxide membrane through non-covalent cross-linking by sulfonated cyclodextrin for ultra-permeable butanol dehydration

Two-dimensional (2D) lamellar graphene oxide (GO) membranes represent promising porous materials in alcohol dehydration. The separation performance can be manipulated by the physicochemical properties of interlayer channels. The relatively low flux and poor stability of GO-based membranes in aqueous environment are the major drawbacks. Herein, we intercalated a supramolecular compound, sulfobutyl-β-cyclodextrin (SCD), into the interlayer pores/channels of GO membranes. The sulfonic acid groups on SCD molecules are able to cross-link adjacent GO nanosheets throughnon-covalent interactions. The GO-SCD membranes possess excellent water affinity due to the presence of high hydrophilic sulfonic acid groups. For the n-butanol dehydration, the GO-SCD/PTFE membranes with well-defined interlayer pores exhibited ultrahigh permeation flux of 12955 g m-2 h-1 and separation factor of 1299 under 80 oC. The membranes remained stable in 144 h separation performance evaluation test and exhibited obviously enhanced thermal stability.

Microstructural Investigation and On-Site Repair of Thin Pd-Ag Alloy Membranes.

Pd membranes act in an important role in H2 purification and H2 production in membrane reactors. Pd-Ag alloy membranes fabricated by consecutive electroless- and electroplating process on alumina tubes exhibited good stability under stringent heating/cooling cycles at a ramp rate of 10 K/min, imitating practical fast initiation or emergency shutdown conditions. Bilayer Pd-Ag membranes can form dense and uniform alloy after thermal treatment for 24 h at 823 K under H2 atmosphere, despite a porous structure due to the development of liquid-like properties above Tamman temperature to enforce the migrativity. On the contrary, alloying under N2 atmosphere resulted in a Pd-enriched layer. This led to a lower H2 flux but superior thermal stability compared to that alloying under H2 atmosphere. The trilayer approach of electroless-plated Pd, electro-polated Ag and electroless-plated Pd is not suitable to achieve homogeneous Pd-Ag alloys, which, on the other hand, presented the occurrence of a small gap between top Pd layer and middle Ag layer, probably due to insufficient wetting during plating process. An on-site repair treatment in analogous to MOCVD (Metal-organic Chemical Vapor Deposition) process was first proposed to extend the lifetime of Pd-Ag membrane, i.e., by vaporizing, and subsequent decomposition of Ag(OOCC2F5) powders to “preferentially” block the pinholes under vacuum and at working temperature of ca. 473–673 K, which effectively reduced the N2 flux by 57.4% compared to the initial value. The H2 flux, however, declined by 16.7% due to carbon deposition on the membrane surface, which requires further investigation. This approach shows some potential for on-site repair without disassembly or cooling to room temperature.

A mass-momentum consistent, Volume-of-Fluid method for incompressible flow on staggered grids

The computation of flows with large density contrasts is notoriously difficult. To alleviate the difficulty we consider a discretization of the Navier-Stokes equation that advects mass and momentum in a consistent manner. Incompressible flow with capillary forces is modeled and the discretization is performed on a staggered grid of Marker and Cell type. The Volume-of-Fluid method is used to track the interface and a Height-Function method is used to compute surface tension. The advection of the volume fraction is performed using either the Lagrangian-Explicit / CIAM (Calcul d’Interface Affine par Morceaux) method or the Weymouth and Yue (WY) Eulerian-Implicit method. The WY method conserves fluid mass to machine accuracy provided incompressibility is satisfied. To improve the stability of these methods momentum fluxes are advected in a manner “consistent” with the volume-fraction fluxes, that is a discontinuity of the momentum is advected at the same speed as a discontinuity of the density. To find the density on the staggered cells on which the velocity is centered, an auxiliary reconstruction of the density is performed. The method is tested for a droplet without surface tension in uniform flow, for a droplet suddenly accelerated in a carrying gas at rest at very large density ratio without viscosity or surface tension, for the Kelvin-Helmholtz instability, for a 3mm-diameter falling raindrop and for an atomizing flow in air-water conditions.