Mass Transfer Direction Research Articles

Experimental study of rotating direction for dual-axial swirlers on the flow field and combustion characteristics of aero-engine combustor

The flow field structure for aero-engine combustor is one of the most important factors for combustion performance. To investigate how the rotating direction of dual-axial swirlers affects the flow field and combustion characteristics, particle image velocimetry (PIV) experiments were conducted in the primary combustion and intermediate zones. Additionally, planar laser induced fluorescence (PLIF) was used to map the distribution of kerosene and OH in the primary combustion zone. The results show that the swirling jets in co-swirl exhibit greater jet momentum, resulting in a longer primary recirculation zone and a larger deflection angle of the primary jets. This ultimately leads to a higher recirculation rate compared to counter-swirl. The primary jets define the boundary of the flow field structure. The rotating direction primarily affects the flow field structure upstream of the primary jets, exerts a relatively weaker influence on the intermediate zone, which is mainly affected by the deflection direction of the primary jets, and essentially has no impact on the dilution jets. Co-swirl has a relatively stable flow field than counter-swirl, whereas the flow field in counter-swirl is more chaotic, featuring a greater number of vortex cores in the primary recirculation zone. The coupling between the primary and swirling jets affects the mass transfer direction in the intermediate zone, which is reflected in the fact that the mass transfer is from top-left to bottom-right in co-swirl, while it is in the opposite direction in counter-swirl. OH is predominantly found in the swirling shear layers, the primary and secondary combustion zones, whereas kerosene is mainly concentrated in the shear layers of swirling jets. The kerosene distribution in co-swirl shows a larger and more concentrated expansion angle compared to counter-swirl. In contrast, the OH distribution downstream of counter-swirl is broader, with more intense combustion due to enhanced kerosene decomposition and fuel-air mixing. The smaller primary recirculation zone in counter-swirl forces the primary combustion zone to extend downstream, leading to a more intense reaction in the secondary recirculation zone.

Mathematical modeling of multi-component aerosol droplet evaporation and growth in indoor environments

Multi-component droplets from daily activities and production processes severely degrade indoor air quality. Their health hazards and removal efficiency depend on size and composition, significantly affected by evaporation and growth. The phase transition process is complex, involving a broad spectrum of droplet sizes with diverse heat and mass transfer characteristics. Components within the droplets experience simultaneous phase transitions at differing rates and mass transfer directions. This study aims to refine the existing evaporation model of single-component droplets in continuous flows by theoretically integrating the effects of varying droplet sizes and multiple components. A multi-component droplet evaporation/growth model that spans the entire range of droplet sizes has been developed, and predictions have been made based on this model. Utilizing MATLAB, this model accurately predicts the indoor dynamics of multi-component droplets, with deviations under 16 % from experiments. It improves accuracy by over 25 % across droplet sizes via dimensionless transfer coefficients and boosts precision by over 24 % for multi-component droplets with zero-diffusion transport. The radius of the droplet after phase change can reach 8.42 × 10−6 m and remains suspended in the air for an extended period. This study establishes a solid theoretical foundation for accurately predicting the indoor distribution of multi-component droplets.

Beyond Symmetry: Exploring Asymmetric Electrospun Nanofiber Membranes for Liquid Separation

AbstractComposite membranes with asymmetric traits have gained attention in liquid separation, featuring gradient chemical and physical attributes that align or oppose mass transfer direction. Chemically asymmetric configurations harness internal driving forces to heighten separation efficiency, rendering them an appealing option for heightened separation efficiency and fouling prevention. Concurrently, the internal hierarchical structure differences within composite membranes—such as fiber‐based structural adjustments and the gradient density of functional layers—yield the dual benefits of effective liquid repelling and heightened transport efficiency. Unlike conventional phase‐change methods, electrospinning technology possesses advantages in constructing and governing composite fibrous membrane materials with asymmetric chemistry and hierarchical structures, driven by its adaptable stacking methodologies. Notably, the inherent pore structure of electrospun nanofibrous membranes emerges as a proven solution for minimizing transport resistance. In recent times, interest has surged in electrospun nanofibrous membranes endowed with internal asymmetric properties. However, the spotlight has predominantly graced Janus membranes, spotlighting opposite wettability on different sides, leaving other facets of asymmetric membrane enhancement somewhat underexplored. This comprehensive work unveils recent strides in design, fabrication, facilitated transport mechanisms, and real‐world liquid separation applications, all under the aegis of electrospun nanofiber membranes, each endowed with distinct asymmetric properties.

Polyethylene-derived radical mediated hydrogen atom transfer synergizes with conjugated dual size effect of core-shell particles to enhance BTEX formation

Aromatic hydrocarbons (AHs) production from in-situ catalytic co-pyrolysis (CCP) of biomass and plastics is a promising technology. However, the combined effects of the mixing mode and proportion of raw materials in catalytic co-pyrolysis and the double-size effect of micro-mesoporous core-shell catalysts on AHs production remain questionable. The formation characteristics and mechanism of AHs in CCP process were studied from mass transfer and free radial direction. The results showed that the yield of BTEX (benzene, toluene, ethylbenzene, and xylene) was 20.44 wt% when the mass ratio of cellulose/polyethylene/cellulose (C-P-C) was 0.5:1:0.5 at 500 ℃. The free radicals generated during the breaking of polyethylene bonds can promote the transfer of hydrogen atoms to cellulose pyrolysis intermediates, which results in mass transfer effect. The C-P-C loading mode makes hydrogen atoms always pass through the cellulose without escaping, and the increase of polyethylene ratio makes the number of hydrogen free radicals increase significantly, both of which jointly regulate the hydrogen free radical mass transfer efficiency. However, the high concentration of hydrogen free radicals can quench the pyrolysis of cellulose. The conjugated double size effect of ZSM-5 @MCM-41 leads to their greater catalytic capacity for free radical carrying co-pyrolysis products compared to ZSM-5. With the increase of mesoporous shell, the yield of BTEX increases first and then decreases, but the yield of coke is opposite. The BTEX yield of 1.0SH-Z5 @ M41 is 3.15 times that of ZSM-5, and the coke yield is only 14.70% that of ZSM-5. The reaction pathway of promoting cellulose pyrolysis by polyethylene and the mechanism of hydrogen free radical - mass transfer co-pyrolysis involved were put forward.

The Effect of Non-Solvent Nature on the Rheological Properties of Cellulose Solution in Diluted Ionic Liquid and Performance of Nanofiltration Membranes.

The weak point of ionic liquids is their high viscosity, limiting the maximum polymer concentration in the forming solutions. A low-viscous co-solvent can reduce viscosity, but cellulose has none. This study demonstrates that dimethyl sulfoxide (DMSO), being non-solvent for cellulose, can act as a nominal co-solvent to improve its processing into a nanofiltration membrane by phase inversion. A study of the rheology of cellulose solutions in diluted ionic liquids ([EMIM]Ac, [EMIM]Cl, and [BMIM]Ac) containing up to 75% DMSO showed the possibility of decreasing the viscosity by up to 50 times while keeping the same cellulose concentration. Surprisingly, typical cellulose non-solvents (water, methanol, ethanol, and isopropanol) behave similarly, reducing the viscosity at low doses but causing structuring of the cellulose solution and its phase separation at high concentrations. According to laser interferometry, the nature of these non-solvents affects the mass transfer direction relative to the forming membrane and the substance interdiffusion rate, which increases by four-fold when passing from isopropanol to methanol or water. Examination of the nanofiltration characteristics of the obtained membranes showed that the dilution of ionic liquid enhances the rejection without changing the permeability, while the transition to alcohols increases the permeability while maintaining the rejection.

CO2 storage in porous media unsteady thermosolutal natural convection -Application in deep saline aquifer reservoirs

In this paper, the storage of CO2 is investigated numerically under supercritical conditions in deep saline aquifer reservoirs. The simulations were performed on a non-deformable, saturated porous material inside a vertical enclosure that was assumed to be impermeable and insulated on three sides. The porous medium is homogeneous and isotropic with constant thermo-physical properties except for the fluid density, which varies according to Boussinesq approximations. A dynamic model assumes that flow is two-dimensional and obeys Darcy's motion law. The thermal equilibrium assumption (LTE) is also considered. The set of conservation equations and the appropriate initial and boundary conditions have been resolved numerically by the classical finite volume method. Spatio-temporal variations of different state variables such as pressure, velocity, temperature, and concentration were numerically simulated and plotted versus controlling parameters, particularly the thermal and solutal Rayleigh numbers, RaT and RaS; the Lewis number, Le; and the reservoir's aspect ratio, A. According to regulating factors, and physical and geological qualities, we could predict the behavior of CO2 that would be stored in a geologic reservoir that is thought to be porous media. We could also estimate the time and direction of CO2 mass transfer based on the abovementioned factors. Great attention was paid to examining the sensitivity of fluid flow, heat, and mass transfer rates according to the reservoir form and the operating conditions.

Turbulent One-dimensional Interfacial Scalar Transport: Statistical Random Square Waves Solution

In this study the mass transport through free turbulent liquid surfaces, or gas/liquid interfaces, is considered. The main direction of mass transfer is perpendicular to the interface, so that a one-dimensional point of view is followed. The equations for the interfacial gas/liquid transport are presented using the random square waves method (RSW), a statistical tool that models the fluctuations of physical variables as ideal signals. The method defines three statistical functions (partition, reduction, and superposition), related to fluctuations of concentration and velocity, which were introduced into the mass advection-diffusion equation generating a set of differential equations adequate for boundary layer problems. Solution profiles of the partition and reduction functions, and of turbulent fluxes across the boundary layer were obtained for transient situations. The solutions use Taylor series centered at the immersed border of the concentration boundary layer. For practical applications, the series were truncated and the coefficients were calculated in order to satisfy adequate physical conditions. The proposed procedure substitutes coefficients of the higher order parcels of the truncated series, enabling them to satisfy boundary conditions in the two borders of the domain of interest, which is the region of variation of the mass concentration. The theoretical profiles for concentration and turbulent fluxes close to the interface agree with measurements and predictions found in the literature.

Electron-induced effects in Ge-Se films studied by Kelvin probe force microscopy

The processes of surface relief formation on GexSe100-x films under their point irradiation by an electron beam have been studied. Electron-induced effects in GexSe100-x films are interpreted in framework of a two-layer charge model. The distribution of the surface potential in the locally irradiated regions of the GexSe100-x film have been established using the Kelvin probe force microscopy (KFPM). The KPFM measurements reveal that the driving force behind mass transfer is not localized charge in the film itself, but rather the gradient of the electric field created by the charge. The potential distribution derived from the measured KPFM illustrates the distribution of gradient of the electric field. We find that the direction of the field gradient sets the direction of mass transfer during point exposure with electron beam.

Computational model for predicting the dynamic dissolution and evolution behaviors of gases in liquids

Dynamic gas–liquid mass transfer behaviors are widely encountered in the chemical, environmental, and engineering fields. Referring to the Singhal full cavitation model, Henry's law, and Zhou's experiments, we innovatively developed a computational model for dissolved and released mass-transfer to revolutionize the independent unidirectional gas-to-liquid or liquid-to-gas theory. From a new perspective, coupled dissolution and evolution mechanisms were defined similar to how condensation and evaporation were redefined, where dissolution and release mass-transfer prediction methods that can be applied to three-dimensional calculations were integrated for the first time. The dissolved gas saturation concentration was the criterion for determining the direction of mass transfer. According to the theoretical derivation, the driving forces behind the dissolution and evolution are the remaining undissolved gas and real-time solution concentration, respectively. We confirmed the validity of the proposed dynamic model using an unsteady simulation after a grid independence study and an experimental verification of dissolved oxygen concentration in plug-discharge flow. The difference in dissolved oxygen concentration between simulations of this computational model and experiments could be low as 2.0%. A higher dissolved oxygen concentration was distributed in the flow separation and throat gas–liquid blocking zones, indicating that a surge in the flow velocity led to an increased mass transfer rate. In addition, a parametric study was conducted to consider the impact of the oxygen volume fraction and initial dissolved oxygen concentration on the real-time concentration.

Scaling analysis of large pressure jump driven adsorption of water vapour in columnar porous silica gel bed

Adsorption process can be initiated either by Large Temperature Jump (LTJ) or Large Pressure Jump (LPJ). In this study, a theoretical analysis of coupled heat and mass transfer process during LPJ driven adsorption has been carried out using scaling principles of the governing conservation equations. A columnar domain consisting of silica gel (adsorbent) and water vapour (adsorbate) pair has been considered with heat and mass transfer directions orthogonal to each other. This domain is subjected to a sudden LPJ with isothermal boundary condition. Adsorption process has been divided into three phases for scaling analysis viz. i) pressure equalization ii) adsorption accompanied by heat generation and iii) heat removal phase. From order of magnitude arguments, various important physical scales for each phase have been derived and validated with a 2-dimensional computational fluid dynamics (CFD) study. The temperature rise in the adsorber bed is found to be 14.5 K, and the time scale to attain peak temperature is ~100 s from the initiation of adsorption. This justifies the short cycle time deployed in practical PSA systems to operate near isothermal condition. The outcomes of this investigation serve as a fundamental insight into LPJ driven adsorption process and help identify the various factors which practically effect this mode of adsorption.

Photochemically assisted patterning: An interfacial hydrodynamic model perspective

Photoresponsive organic liquids and polymers may undergo reversible photochemical reactions with accompanying change in chemical structure upon exposure to a suitable wavelength of light. Spatial variations in chemical structure can cause surface tension gradients along thin films of such materials, resulting in Marangoni flows when the material is in its fluid state. Consequently the fluid film can self-organize into topographical patterns. Here, we provide a hydrodynamic model perspective of photochemically assisted patterning in thin fluid films using principles of momentum and mass transfer. Photochemical reaction occuring simultaneously along with hydrodynamic flow is modelled. Dynamical variation of the photoproduct concentration, accounting for first order chemical reaction kinetics, is considered. Our simulations highlight the counteracting effects of reaction kinetics and Marangoni flow as the mechanism responsible for pattern evolution. We capture various pillar and hole array morphologies obtained by controlling the direction of Marangoni flow and reaction-induced mass transfer. The resolution and timescales of pattern formation are computed as function of experimental control parameters such as the reaction rate coefficient (K0), Marangoni number (M), and distance between the film and light source. A process map comparing feature sizes on a photomask (w) with those of the patterns evolved in the material is developed. It reveals optimum w − M and w − K0 combinations required for faithful reproduction of photomask feature sizes and deviation from ideally templated patterns.

Mechanism study on magnitude of mass transfer coefficients in liquid desiccant dehumidification and regeneration

• Mass transfer coefficients of regeneration are much lower than dehumidification. • Lower mass transfer coefficients of regeneration are decided by transfer direction. • Water release has a huge free energy barrier but water absorption has not. • Correlations considering parameters of aqueous solution show higher accuracy. Liquid desiccant systems have attracted extensive attention due to huge energy-saving and environmental potential. Mass transfer coefficients are key parameters for system design and performance evaluation. Contrast experiments between liquid desiccant dehumidification and regeneration were conducted here to investigate the magnitude of mass transfer coefficients by using LiBr aqueous solutions. Mass transfer coefficients of dehumidification were found to be much higher than regeneration even under the condition that the mass transfer driving force and inlet parameters except solution temperatures were kept the same. To obtain microscopic explanation, free energy curves of water transport were simulated by molecular dynamics based on umbrella sampling. Results show that large energy obstacle should be overcome for water moving into air, which is unnecessary for water transported into aqueous solution. Lower mass transfer coefficients of regeneration should be attributed to the mass transfer direction rather than higher solution temperatures of regeneration than dehumidification. Dimensionless correlations of mass transfer coefficients using water diffusivity in LiBr aqueous solution and correlations using surface tensions show better prediction performance than dimensionless correlations using water diffusivity in air. This study discloses changing mechanism of mass transfer coefficients and helps develop correlations with high accuracy.

Experimental investigation on drop size distribution and mean drop size in an L-shape pulsed packed extraction column

In this study, the mean drop diameter and drop size distribution have been investigated in a pilot plant of a new type of extraction column entitled “L-shaped pulsed packed extraction column” by using two liquid systems of toluene/acetone/water and n-butyl/acetone/water in the presence of mass transfer in two directions. The effects of operational variables, physical properties and mass transfer direction have been considered on the dispersed drop size. It is found that the mean drop diameter and drop size distribution is significantly affected by the pulsation intensity and interfacial tension of liquid system. However, the phases flow rates and mass transfer direction have a weaker impact. Furthermore, it is observed that the mean drops diameter in the horizontal and vertical sections of the used column have mostly the same size and it is considered as a significant advantage. Finally, new correlations are proposed to accurately predict the mean drop size and drop size distribution. Good agreement between predictions and experiments was found for all operating conditions, chemical systems and mass transfer direction that were investigated.

First photometric investigation of two short-period eclipsing binaries ASAS J105115-6032.1 and GDS J1056047-604149

ASAS J105115-6032.1 (hereafter ASAS J1051) and GDS J1056047-604149 (hereafter GDS J1056) are two short-period contact binaries close to each other in the Antarctica sky area. By analyzing the light curves from AST3-1, the first photometric solutions are presented using the Wilson–Devinney (W–D) method. It is detected that both systems are W-type contact binaries with mass ratios of q = 3.2621(0.0083) and q = 4.843(0.014), respectively. Both of them have a moderate degree of contact factor of f = 46.9(1.2)% and f = 43.9(1.2)%. The asymmetries in the light curve of the intermediate-contact system GDS J1056 (strong O’Connell effect) are interpreted by a dark spot on the more massive component. For the first time, we carried out the O−C diagram analysis based on many photometric data. The results indicate an orbital period increase at a rate of dP/dt=+5.28×10−7d⋅yr−1 for ASAS J10511. As for GDS J1056, a period decrease of dP/dt=−5.41×10−7d⋅yr−1, superimposed with a cyclic period change with a semi-amplitude of 0.00744 d and a period of 11.97 yr, is discovered. The cyclic period change may be caused by the light travel-time effect via the presence of a tertiary companion with a lowest mass of M3 = 0.35(0.03)M⊙. The period increase in ASAS J1051 can be explained by the mass transfer from the less massive component to its companion. In contrast, the period decrease in GDS J1056 reveals an opposite direction of mass transfer. The facts suggest that these two intermediate-contact binaries will evolve into shallow- and deep-contact binary systems.

Dynamics of liquid mass transfer in a water bridge

The paper presents experimental results of the dynamics of mass transfer through a water bridge arising between two dielectric cups with distilled water under the action of a constant high voltage between cylindrical electrodes. It is established that, depending on the ratio of the electrode diameters, the total fluid flow in the water bridge can be directed both to the cathode and to the anode. It is shown that the inversion of the direction of mass transfer of liquid through the bridge is due to the redistribution of volume charges. Keywords: water bridge, EHD flow, anode, cathode.

Динамика массопереноса жидкости в водном мостике

The paper presents experimental results of the dynamics of mass transfer through a water bridge arising between two dielectric cups with distilled water under the action of a constant high-voltage voltage between cylindrical electrodes. It is established that, depending on the ratio of the electrode diameters, the total fluid flow in the water bridge can be directed both to the cathode and to the anode.It is shown that the inversion of the direction of mass transfer of liquid through the bridge is due to the redistribution of volume charges.

Experimental investigation on dispersed phase holdup in an L-shape pulsed packed extraction column

In this study, the dispersed phase hold-up has been investigated in a pilot plant of a new type of extraction column entitled “L-shaped pulsed packed extraction column” by using two liquid systems of toluene/acetone/water and n-butyl/acetone/water in the presence of mass transfer in two directions. The effects of operational variables, physical properties and mass transfer direction have been considered on the dispersed phase hold-up. It is found that the dispersed phase hold-up is significantly affected by the pulsation intensity, dispersed phase flow rate and interfacial tension of liquid system. However, the continuous phase flow rate and mass transfer direction have a weaker impact. Furthermore, it is observed that the behavior of hold-up in the horizontal and vertical sections of the used column is distinctive in some case. Such that any factor which reduces the dispersed drop size, leads to an increase in hold-up in the vertical section of the column and a decrease in hold-up in the horizontal section of the column. Finally, new correlation is proposed to accurately predict the dispersed phase hold-up. Good agreement between predictions and experiments was found for all operating conditions, chemical systems and mass transfer direction that were investigated.

Assessment of population balance approach and maximum entropy on drop size behavior of vanadium extraction from sulfate solution in continuous pilot plant column

The present study develops comprehensive drop size distribution by coupling numerical modeling with experimental data to optimize the heavy metal extraction in a modified rotating disc contactor column. Droplet behavior was illustrated based on the maximum entropy principle, population balance model, normal and log-normal functions. For case studies, the vanadium extraction from sulfate solution by mixtures of D2EHPA and TBP extractants and metal stripping from the loaded organic phase by ammonium solution was employed as the reactive agents to generate chemical reactions. The modeling results indicated that the agitation speed and mass transfer direction have more profound influences on the drop size distribution, whereas only partially associated with the phase flow rates. Mathematical optimizations based on the Lagrange multipliers method are conducted to formulate the new correlations in terms of the maximum entropy principle (MEP). The population balance model (PBM) was utilized to characterize the distribution internal coordinate with main parameters in the breakage and coalescence of drops. From output results for drop size distribution, the population balance approach validated significantly with the experimental data for reactive systems in an MRDC column.

Parametric and algebraic study of an isolated pore shape in solid after unidirectional solidification

This study applies algebraic polynomials to investigate the effects of independent dimensionless parameters on the shape of an isolated pore resulting from a bubble completely entrapped by a solidification front. The pore shape in solid is contemporarily challenging in controlling directional properties of natural or functional materials in MEMS, packaging, manufacturing and medical and micro-or nano-technologies. In this work, polynomials with different degrees are provided by extending previous work, accounting for conservation of total solute content in the pore and boundary layer on the bubble cap, on which solute transport in different directions, balance of pressures and physico-chemical equilibrium are satisfied. Dimensionless independent parameters include product of Bond number with initial liquid concentration, solidification rate, mass transfer coefficient, Henry’s law constant, atmospheric pressure, and initial contact angle. By comparison with numerical solutions of thermal fluid and concentration equations, it is found that Cases 1 and 2 referred to different mass transfer coefficients and directions of solute transport from the pore to surrounding liquid in the early stage are relevant, rather than available Cases 3 and 4 with different modeling of solute transfer rates. Polynomials with 4 and 5 degrees to predict shapes of the isolated pore are in good agreement with numerical solution of simultaneous first-order unsteady ordinary equations governing solute gas pressure and geometry of the pore and experimental data.

Modeling of mass transfer coefficient using response surface methodology in a horizontal-vertical pulsed sieve-plate extraction column

The effects of various parameters and their interactions on the mass transfer behavior of toluene-acetone-water, n-butyl acetate-acetone-water systems in a horizontal-vertical (L-shaped) pulsed sieve-plate column were investigated using the response surface methodology (RSM). The studied parameters included pulsation intensity, interfacial tension, and dispersed and continuous phase velocities. The volumetric overall mass transfer coefficient was determined using the axial dispersion model. According to the empirical data and the results of analysis of variance (ANOVA), new correlations were presented to predict the overall mass transfer coefficient in the two sections of the column. The correlation coefficient (R2) was achieved as 0.995 and 0.986 for the horizontal and vertical sections, respectively, proving that the models fit the data well. The modeling results showed that the values of the volumetric overall mass transfer coefficient in the horizontal section were higher than those of the vertical section. This can be attributed to the direction of mass transfer (d→c) and the entry of solvent (dispersed phase) from the horizontal section of the column that creates the maximum concentration gradient and the driving force of mass transfer in the horizontal section. The optimum overall mass transfer coefficients were obtained as 0.925 × 10−3 and 0.530 × 10−3 1/s for the horizontal and vertical sections, respectively.