Diffusive Mixing Research Articles

The impact of inner air jet on fuel mixing mechanism and mass diffusion of single annular extruded nozzle at supersonic combustion chamber

In this research, the usage of an extruded annular nozzle for mixing fuel through the combustion chamber is fully studied. The chief focus is to reveal the flow of the fuel jet by three-dimensional simulation of the sonic hydrogen jet with two nozzle heights (1 mm and 2 mm). The main novelty of this study is the connection of mass diffusion mechanism on fuel mixing of jet released from the extruded nozzle in combustion chamber. The computational method is developed for modeling of highly compressible airflow with a cross-fuel jet released from an extruded nozzle. Both annular and coaxial fuel and air jet are investigated to find the efficient mechanism of fuel distribution inside the combustor. The flow parameters and vortex structure near the injector are fully analyzed. RANS equations are used for the modeling of the high-velocity flow. Our results show that the injection of fuel through the extruded nozzle improves the performance of fuel mixing in the combustor. Coaxial fuel and air jets released from extruded nozzle is more efficient for fuel injection system due to formation of strong interactions of the fuel with free air stream.

Mix-and-extrude: high-viscosity sample injection towards time-resolved protein crystallography.

Time-resolved crystallography enables the visualization of protein molecular motion during a reaction. Although light is often used to initiate reactions in time-resolved crystallography, only a small number of proteins can be activated by light. However, many biological reactions can be triggered by the interaction between proteins and ligands. The sample delivery method presented here uses a mix-and-extrude approach based on 3D-printed microchannels in conjunction with a micronozzle. The diffusive mixing enables the study of the dynamics of samples in viscous media. The device design allows mixing of the ligands and protein crystals in 2 to 20 s. The device characterization using a model system (fluorescence quenching of iq-mEmerald proteins by copper ions) demonstrated that ligand and protein crystals, each within lipidic cubic phase, can be mixed efficiently. The potential of this approach for time-resolved membrane protein crystallography to support the development of new drugs is discussed.

Uncertainty in parameterized convection remains a key obstacle for estimating surface fluxes of carbon dioxide

Abstract. The analysis of observed atmospheric trace-gas mole fractions to infer surface sources and sinks of chemical species relies heavily on simulated atmospheric transport. The chemical transport models (CTMs) used in flux-inversion models are commonly configured to reproduce the atmospheric transport of a general circulation model (GCM) as closely as possible. CTMs generally have the dual advantages of computational efficiency and improved tracer conservation compared to their parent GCMs, but they usually simplify the representations of important processes. This is especially the case for high-frequency vertical motions associated with diffusion and convection. Using common-flux experiments, we quantify the importance of parameterized vertical processes for explaining systematic differences in tracer transport between two commonly used CTMs. We find that differences in modeled column-average CO2 are strongly correlated with the differences in the models' convection. The parameterization of diffusion is more important near the surface due to its role in representing planetary-boundary-layer (PBL) mixing. Accordingly, simulated near-surface in situ measurements are more strongly impacted by this process than are simulated total-column averages. Both diffusive and convective vertical mixing tend to ventilate the lower atmosphere, so near-surface measurements may only constrain the net vertical mixing and not the balance between these two processes. Remote-sensing-based retrievals of total-column CO2, with their increased sensitivity to convection, may provide important new constraints on parameterized vertical motions.

An alternating direction implicit compact finite difference scheme for the multi-term time-fractional mixed diffusion and diffusion–wave equation

An alternating direction implicit(ADI) compact finite difference scheme for the two-dimensional multi-term time-fractional mixed diffusion and diffusion–wave equation is given in this paper. By using the Riemann–Liouville fractional integral operator on both sides of the original equation, we obtain a time-fractional integro–differential equation with the order of the highest derivative being one. Using the weighted and shifted Grünwald formulas of Riemann–Liouville fractional derivative and fractional integral, and the Crank–Nicolson approximation, a temporal second-order approximation is obtained for the equivalent integrodifferential system. In the spatial direction, a fourth-order compact approximation is employed to give a fully discrete scheme. Using the splitting techniques for higher dimensional problems, we derive the fully discrete ADI Crank–Nicolson scheme. With the positive definiteness of the related time discrete coefficients and spatial operators, the stability and convergence (second-order in time and fourth-order in space) in the discrete L2-norm are proved by using energy method. Two numerical examples are given to demonstrate the efficiency and accuracy of the proposed method.

Variable thermo-physical properties of fluid flow along with exponential stretching; A chemical reaction study

Heat and mass transfer having variable fluid properties has wide range of applications in industrial and engineering processes.The transference of species arises in several processes like oil transport phenomenon, food processing and diffusion of assured medicines in blood (drug delivery). Current research deals with the mixed convection and radiation effects on flow of a non-Newtonian tangent hyperbolic fluid with variable thermo-physical properties and activation energy. Arrhenius kind of chemical reaction is taken along an exponentially stretchable surface. The main focus of the current exploration is to execute shear thinning tangent hyperbolic fluid past an exponentially stretchable surface under the influence of variable viscosity, mixed convection, thermal radiation and activation energy. Transformation approach is opted to attain the non-linear ODE's based on standard conservation laws of mass, linear momentum and energy. Numerical solutions of the governing problem are computed via the shooting technique. Characteristics of the parameters appearing in modeling like radiation parameter, variable viscosity parameter, mixed convection parameter, Williamson parameter, variable conductivity and diffusivity are comprehensively analyzed through graphical behavior.

A Choquard type equation involving mixed local and nonlocal operators

In the present work, we are concerned with an elliptic problem involving a mixed order diffusion operator with both local and nonlocal parts and a critical nonlinearity of Hartree type. We first investigate the corresponding Hardy-Littlewood-Sobolev inequality and establish the optimal constant. Using variational methods and a Pohožaev identity we then show existence and nonexistence results for the corresponding subcritical perturbation problem.

Gas separation properties of PIM-1 films treated by elemental fluorine in liquid perfluorodecalin

Gas transport properties of PIM-1 films treated by elemental fluorine in a liquid perfluorodecalin were investigated. The investigation included an estimation of fluorine content in a fluorinated layer, pure and mixed gas permeability, diffusion and solubility coefficients measurement, ideal selectivity assessment and analysis of fluorination time effect on gas transport properties. An increase of treatment duration resulted in an increase of concentration of fluorine in the fluorinated layer as well as a depth of fluorination. The depths of fluorination linearly increased with square of fluorination time indicating a diffusion of fluorine in the fluorinated layer to be a restrictive stage of kinetics of fluorination. The effect of the drop in gas permeability was demonstrated to be dependent on the kinetic size of the penetrant. The comparison of liquid-phase and gas-phase regimes was performed, and it was shown that sharp decrease in gas permeability is observed for gas-phase regime at short times of fluorination already, whereas this decrease is more gradual for liquid-phase fluorination. According to a Barrie method, the gas transport parameters of the fluorinated layer of the modified PIM-1 films were calculated, which turned out to be much lower than those for the virgin PIM-1 polymer and slightly lower than the gas transport parameters for dry Nafion. The reduction of the gas permeability coefficients is mostly induced by a sharp decrease in the gas diffusion coefficients. According to combination of permeability and selectivity, the fluorinated PIM-1 samples show excellent results exceeding the 2008 Robeson upper bounds for H2/CH4, H2/CO2, H2/N2, He/CH4 and others gas pairs. Mixed gas experiments were also conducted for hydrogen-containing mixtures and fluorinated PIM-1 samples have demonstrated good separation characteristics for the model binary mixtures attaining separation factors as high as 115–143 (H2/CH4), 4.4–6.7 (H2/CO2) and 49–146 (He/CH4), which makes these materials promising for helium recovery from natural gas and hydrogen recovery from various catalytic and biohydrogen production mixtures. Ten-months aging of the PIM-1 sample fluorinated during 30 min showed a decline of permeability by 25 and 40%, respectively and a slight decrease of ideal selectivity.

Numerical Simulation of Granular Flow in Concrete Batching Plant via Discrete Element Method

A new giant concrete batching plant with the production capacity of 270m3/hr was designed, analyzed and fabricated. In this concrete batching plant, the granular materials used for high-quality products must be uniformly mixed to attain a homogenous mixture. For this, the discrete element method (DEM) was utilized to simulate the filling, mixing, and discharging processes. The Hertz-Mindlin, elastic-plastic spring-dashpot and Simplified Johnson-Kendall-Roberts (SJKR) models were used for the interaction rules among granular particles. In the light of the aforementioned models, the first simulation with different particle sizes and the second simulation with monosized particles were realized. In the first simulation, the segregation by percolation and momentum segregation were perceived during the bunker filling stage, as well as the seeded granulation, which occurred in the mixer when the radii of particles were not monosized. Furthermore, in the second simulation, convective, diffusive and shear mixing mechanisms were observed and consequently the quantification of the mixing index was calculated using the lacey and miles statistical methods. At last, the active regions formed in the mixer were investigated by taking the velocity of the particles as reference during the mixing stages as well as the mixture throughput from the transfer chute.

Inclusion Bayes factors for mixed hierarchical diffusion decision models.

Cognitive models provide a substantively meaningful quantitative description of latent cognitive processes. The quantitative formulation of these models supports cumulative theory building and enables strong empirical tests. However, the nonlinearity of these models and pervasive correlations among model parameters pose special challenges when applying cognitive models to data. Firstly, estimating cognitive models typically requires large hierarchical data sets that need to be accommodated by an appropriate statistical structure within the model. Secondly, statistical inference needs to appropriately account for model uncertainty to avoid overconfidence and biased parameter estimates. In the present work, we show how these challenges can be addressed through a combination of Bayesian hierarchical modeling and Bayesian model averaging. To illustrate these techniques, we apply the popular diffusion decision model to data from a collaborative selective influence study. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Origin of the Delayed Fluorescence by Triplet–Triplet Annihilation in Solids with a Power Law Exponent of between −1/2 and −1

Triplet–triplet annihilation (TTA) merges low electronic energies in two molecules to high electronic energy in one molecule, which, following triplet sensitization, allows us to achieve high-efficiency conversion using low-intensity light. Although efficient TTA up-conversion in solutions has been reported, the TTA up-conversion in solid matrixes is preferred for practical applications. However, the emission decay kinetics after pulsed-light excitation is more complex in solids than in liquids, and the process underlying the different TTA kinetics has not yet been elucidated. Herein, we report that the complexity in the TTA kinetics in solid matrixes can originate from processes such as slow mixing of triplet excitons by migration, strong dependence on the initial distribution of triplet excitons, and an anisotropic random walk of excitons. We show theoretically that power-law fluorescence with an exponent of between −1/2 and −1 can originate from the slow diffusional mixing of excitons in one and three dimensions, where the initial exciton generation is uniformly distributed. By analyzing experimental data, we show that rich fluorescence kinetics observed experimentally by varying the temperature in molecular solids can be deeply understood in terms of bulk and nonbulk TTA under dispersive as well as normal diffusion.

A Hybrid Local Radial Basis Function Method for the Numerical Modeling of Mixed Diffusion and Wave-Diffusion Equations of Fractional Order Using Caputo’s Derivatives

This article presents an efficient method for the numerical modeling of time fractional mixed diffusion and wave-diffusion equations with two Caputo derivatives of order 0<α<1, and 1<β<2. The numerical method is based on the Laplace transform technique combined with local radial basis functions. The method consists of three main steps: (i) first, the Laplace transform is used to transform the given time fractional model into an equivalent time-independent inhomogeneous problem in the frequency domain; (ii) in the second step, the local radial basis functions method is utilized to obtain an approximate solution for the reduced problem; (iii) finally, the Stehfest method is employed to convert the obtained solution from the frequency domain back to the time domain. The use of the Laplace transform eliminates the need for classical time-stepping techniques, which often require very small time steps to achieve accuracy. Additionally, the application of local radial basis functions helps overcome issues related to ill-conditioning and sensitivity to shape parameters typically encountered in global radial basis function methods. To validate the efficiency and accuracy of the proposed method, several test problems in regular and irregular domains with uniform and non-uniform nodes are considered.

Chaotic advection mixer for capturing transient states of diverse biological macromolecular systems with time-resolved small-angle X-ray scattering.

Advances in time-resolved structural techniques, mainly in macromolecular crystallography and small-angle X-ray scattering (SAXS), allow for a detailed view of the dynamics of biological macromolecules and reactions between binding partners. Of particular promise, are mix-and-inject techniques, which offer a wide range of experimental possibility as microfluidic mixers are used to rapidly combine two species just prior to data collection. Most mix-and-inject approaches rely on diffusive mixers, which have been effectively used within crystallography and SAXS for a variety of systems, but their success is dependent on a specific set of conditions to facilitate fast diffusion for mixing. The use of a new chaotic advection mixer designed for microfluidic applications helps to further broaden the types of systems compatible with time-resolved mixing experiments. The chaotic advection mixer can create ultra-thin, alternating layers of liquid, enabling faster diffusion so that even more slowly diffusing molecules, like proteins or nucleic acids, can achieve fast mixing on timescales relevant to biological reactions. This mixer was first used in UV-vis absorbance and SAXS experiments with systems of a variety of molecular weights, and thus diffusion speeds. Careful effort was also dedicated to making a loop-loading sample-delivery system that consumes as little sample as possible, enabling the study of precious, laboratory-purified samples. The combination of the versatile mixer with low sample consumption opens the door to many new applications for mix-and-inject studies.

Preparation and performance of Sn-based composite solder joints by solid-liquid low-temperature solder bonding technology

In the era of big data, the advantages of 3D packaging are becoming increasingly significant. In addition, the mismatch between the coefficient of thermal expansion (CTE) of the PCB and BGA components leads to dynamic warpage of the system, and the expansion and innovation of low-temperature soldering have been a new trend. We developed a fully mixed solder joint of a SAC305(Sn-3.0Ag-0.5Cu wt.%) solder ball and Sn–58Bi(wt.%) solder paste by solid-liquid low-temperature solder bonding technology. The mixing degree and diffusion process of the two were calculated and simulated by mathematical calculation and COMSOL Multiphysics. The results show that a completely mixed solder joint can be obtained after reflow at 210 °C for 5 min. The average shear strength of the composite solder joints was 63.68 ± 1.12 MPa, which was about twice that of the single SAC305 and Sn58Bi solder joints, and the shear fracture was a composite mode of brittle and ductile fracture, which appeared in the IMC and the solder, respectively. After complete mixing, the solder wettability angle was less than 26.68°, with outstanding wetting properties. No phase transition occurred after aging, the distribution of each phase remained uniform, and no enrichment of the brittle phase was observed at the interface. The shear strength decreased slightly with aging time, and the reduction value was less than 10 MPa, which has good reliability.

Transition between Different Diffusion Modes of Individual Lipids during the Membrane-Specific Action of As-CATH4 Peptides.

The cell membrane permeabilization ability of immune defense antimicrobial peptides (AMPs) is widely applied in biomedicine. Although the mechanisms of peptide-membrane interactions have been widely investigated, analyses at the molecular level are still lacking. Herein, the membrane-specific action of a native AMP, As-CATH4, is investigated using a single-lipid tracking method in combination with live cell and model membrane assays conducted at different scales. The peptide-membrane interaction process is characterized by analyzing single-lipid diffusion behaviors. As-CATH4 exhibits potent antimicrobial activity through bacterial membrane permeabilization, with moderate cytotoxicity against mammalian cells. In-plane diffusion analyses of individual lipids show that the lipid molecules exhibit non-Gaussian and heterogeneous diffusion behaviors in both pristine and peptide-treated membranes, which can be decomposed into two Gaussian subgroups corresponding to normal- and slow-diffusive lipids. Assessment of the temporal evolution of these two diffusion modes of lipids reveal that the peptide action states of As-CATH4 include surface binding, transmembrane defect formation, and dynamic equilibrium. The action mechanisms of As-CATH4 at varying concentrations and against different membranes are distinguished. This work resolves the simultaneous mixed diffusion mechanisms of single lipids in biomimetic cell membranes, especially during dynamic membrane permeabilization by AMPs.

Magnetohydrodynamic double-diffusive mixed convection in a curvilinear cavity filled with nanofluid and containing conducting fins

This work numerically analyzes the mixed convective double diffusion of Fe3O4-water-based nanofluid in a tilt curvilinear lid-driven cavity studied under the effect of an inclined magnetic field. The horizontal upper wall is at a lower thermal and concentration gradient and moves toward the right. The side vertical walls and bottom walls kept adiabatic. Furthermore, two numbers of conducting fins are affixed to the inclined walls at high temperatures and concentrations. The finite element approach is implemented to analyze the considered variables: Richardson number (Ri), Hartmann number (Ha), Reynolds number (Re), Lewis number (Le), buoyancy ratio (N), magnetic inclination angle (α), nanofluid volume fraction (ϕ) as well as the fins length on the heat and mass transport phenomena. The results showed that the Nuavg and Shavg increase by increasing Reynolds number, the nanoparticles volume concentration, and the fin length, while they decrease by increasing Hartmann number. When Ri is small, Nuavg rises with the increasing magnetic field inclination, but when Ri is high, the inclination angle works adversely. On the other hand, the Shavg increases with the rise of the magnetic field inclination for all Ri values. It can be seen also, when Lewis number increases, the Nuavg and Shavg values increase with increasing Ri and magnetic inclination angles.

СОРБЦИОННАЯ СПОСОБНОСТЬ СЛОИСТЫХ ДВОЙНЫХ ГИДРОКСИДОВ Mg-Al ПО ОТНОШЕНИЮ К ИОНАМ Co (II), Cu (II), Sr (II) и Cs (I)

Mg-Al layered double hydroxides with a hydrotalcite structure have been synthesized. The sorption properties of the synthesized sample with respect to non-ferrous metal ions — Co2+, Cu2+, Sr2+ and Cs+ are investigated. The capacities of the adsorption monolayer of the Mg-Al layered hydroxide sample were calculated, amounting to 2.13, 2.21, 1.88 and 3.48 mmol/g with respect to Co(II), Cu(II), Sr(II) and Cs(I) ions, respectively. It is shown that the sorption process is described by a pseudo-second-order kinetic model and proceeds in a mixed diffusion mode.

Experimental investigations on fuel spatial distribution characteristics of aeroengine afterburner with all typical components

The fuel space distribution is a key factor in the combustion performance of afterburner. We have investigated the fuel space distribution and flow field in afterburner with all typical components. In this study, the complete afterburner test section of the afterburner is composed of a typical mixing diffuser, fuel supply system, flame stabilizer and heat shield. At the same time, we built an experimental system that enables a wide operating range of the afterburner. A temperature measuring rake, a pressure measuring rake, a Particle Image Velocimetry (PIV) system and a laser particle sizer were used to measure the flow field and fuel distribution in the combustor. It was found that the fuel particle size in the combustor space along the flow direction decreases, then increases and then gradually decreases. This is because the fuel particle size is smallest at the vortex nucleus in the recirculation zone after the stabilizer. The increase of the incoming Mach number will lead to an increase in the range of the recirculation zone behind the stabilizer, thus making the fuel distribution in the entire combustor more uniform. When the diffusion ratio is increased from 1.0 to 1.4, a significant asymmetric counter-rotating vortex pair can be formed after the stabilizer. Compared with the blockage ratio of 0.2 and 0.4, when the blockage ratio is 0.3, the fuel particle size will be reduced by 24%–32%. The spatial distribution of the fuel is not sensitive to pressure changes, and under the experimental conditions, the fuel particle size will increase by 9–25 µm with the decrease of pressure. In summary, when the diffusion ratio is 1.4 and the blockage ratio is 0.3, the afterburner has the most reasonable fuel distribution and flow field, which is conducive to the stable and efficient operation of the afterburner..

Mechanisms associated with material deformation, and microstructural evolution during friction stir welding of pure titanium and Al alloy

Aluminium and titanium are important structural metals; however, their joining is difficult because of different microstructural responses and intermetallic compounds (IMCs). The present work underlines the mechanisms associated with friction stir welding of pure Ti and Al alloy. The results show no visible defect, while multiple particles are consolidated in the stirred zone (SZ). Chemical composition across Al-Ti interfaces is different and dependent on location and particle size. This affirms intensive mechanical mixing and thermal diffusion of Al-Ti substrates and IMCs formation. The UTS and ductility of the Al-Ti joint are ∼73% and 37% higher than Al base metal, respectively. Deformation of Ti in SZ is responsible for phase evolution and joint formation with better joint characteristics.

Acid pressure oxidation leaching of arsenopyrite in the presence of pyrite: Oxygen consumption kinetics

In the process of extraction of gold from refractory sulphide ores, arsenopyrite and pyrite represent two of the major hosts for gold in solid solution. In this study, the pressure oxidation of arsenopyrite and arsenopyrite-pyrite mixtures in a H2SO4–O2 system have been investigated, with the aim of using the oxygen consumption kinetics to probe the oxidation mechanisms. The effects of temperature (180–220 °C), acidity (pH 0.5–2.5), dissolved iron concentration (10 and 30 g/L) and molar ratios (0:1–3:1) of pyrite-to-arsenopyrite (Py/Aspy) were evaluated. Kinetic analysis of arsenopyrite dissolution at 180–220 °C via a shrinking core model indicated an activation energy (Ea) of 48.46 kJ/mol, suggesting a mixed interface reaction and diffusion control. The order of the reaction to acidity was 0.16 at 200 °C, suggesting that [H+] is likely not the rate-limiting factor under typical reaction conditions. The addition of Fe(II) ions to the feed enhanced arsenopyrite oxidation, due to the formation of Fe(III) as a surrogate oxidant to drive the reaction.The Ea for Py/Aspy of 1:1 exhibited two behaviours, calculated to be 77.32 kJ/mol below 200 °C and decreasing to 34.59 kJ/mol above 200 °C. The former was attributed to surface control due to the oxidation of elemental sulphur, followed by a switch to mixed control at elevated temperatures. As Py/Aspy was increased to 2:1 and 3:1, a single behaviour was observed, with Ea values of 56.01 kJ/mol and 43.35 kJ/mol respectively. These values imply a mixed control and begin to approximate literature values for pyrite oxidation. A time-to-a-given-fraction method was also used to examine changes in Ea with reaction extent. Arsenopyrite was found to be under mixed control for most of the reaction extent. At increasing pyrite fractions, oxidation was observed to be reaction-limited at the initial stage of reaction, potentially reflecting the kinetics of sulphur oxidation.

Synthesis and physicochemical properties of sodium oleyl sulfate

Abstract In this paper, sodium oleyl sulphate (SOS) was successfully synthesised by reacting octyl alcohol (OA) with gaseous sulphur trioxide (SO3) as a sulphating reagent in a falling film reactor. The structure was determined by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1HNMR) spectroscopy. The dynamic adsorption and aggregation behaviour of SOS was systematically investigated to reveal the relationship between the structure and properties of SOS. The physicochemical properties of SOS were determined by measuring the equilibrium surface tension, dynamic surface tension and dynamic contact angle, respectively. A laser particle size analyser and a transmission electron microscope (TEM) were used to analyse the aggregation behaviour of SOS. Compared to sodium dodecyl sulphate (SDS) and sodium n-octadecyl sulphate (C18H37OSO3Na), which have a similar structure to SOS, the increase in hydrophobic chain size and tighter molecular packing enabled by the polar head conformation caused a decrease in CMC and an increase in surface activity. The efficiency of the surface activity was controlled by a mixed diffusion kinetic adsorption mechanism. Moreover, SOS in aqueous solution showed efficient wettability on the surface of the low-energy paraffin film at concentration above the CMC. In addition, SOS molecules can spontaneously form spheroidal aggregates with increasing concentration, and the size of the aggregates increased with the concentration.