Interfacial Mass Research Articles

Two-group interfacial area transport equation coupled with void transport equation in adiabatic steam water flows

The two-group coupled model with IATE is benchmarked with the recently available adiabatic phase-change flow datasets. The current state of adiabatic phase-change data is extensively discussed, followed by a thorough review of the two-group two-fluid model and the two-group IATE. The interfacial mass generation models from RELAP5/MOD3.3 are benchmarked and are observed to underpredict the group-2 interfacial mass generation rate which then causes underprediction of void fraction under flashing conditions. A new group-2 interfacial mass generation model is proposed using the mass-energy balance approach where slug bubbles are assumed as a cylinder with a constant width that only grows in the lengthwise direction. The proposed model is implemented to the two-group coupled model with IATE and benchmarked with the flashing datasets where the accuracy of the predicted values is significantly improved. Similar benchmark is carried out for flashing conditions with a near-zero initial void faction and adiabatic phase-change flows with an initial condensing phase followed by a flashing phase. It is observed that due to the lack of interfacial area concentration, the interfacial mass generation model is unable to produce a significant enough interfacial mass generation rate to allow the growth of bubbles. Bubble generation models are implemented to the simulations at flashing inception where improved results are obtained.

Influence of solvent polarity on reactive extraction of fumaric acid with Amberlite LA-2 from viscous solutions

ABSTRACT Current studies on the reactive extraction of fumaric acid with Amberlite LA-2 from aqueous phases with different viscosities using three solvents highlighted the influences of rheological properties of the fermentation medium on the efficiency of the extraction system. The obtained results showed that increasing the viscosity of the aqueous phase influences both the efficiency of the reactive extraction and the magnitude of the diffusional and kinetic resistances. The negative effect of increasing the viscosity of fumaric acid solutions on the interfacial mass flow of the product resulting from the reaction between acid and extractant was described by the reduction factor. For dichloromethane, by increasing the speed from 200 to 1000 rpm, the R factor increases 1.05 times for 8 cP and 3.56 times for 64 cP, while for n-heptane R factor increases 1.11 times for 8 cP and 9 times for 64 cP. The positive effect of alcohol was quantified using the amplification factor, which reached maximum values for n-heptane, under similar experimental conditions. The influences of studied factors on interfacial mass flow of the complex formed by reaction of fumaric acid with amine extractant have been quantified by mathematical expressions, proposed for extraction system without and with 1-octanol.

Numerical simulation of continuum scale electrochemical hydrogen bubble evolution

One of the important aspects in improving the efficiency of electrochemical processes, such as water electrolysis, is the efficient removal of bubbles which evolve from the electrodes. Numerical modelling based on Computational Fluid Dynamics (CFD) can describe the process, provide insights into its complexity, elucidate the underlying mechanisms of how bubbles evolve and their effect as well as aid in developing strategies to reduce the impact of the bubble.In this paper, a Volume of Fluid (VOF) based simulation framework to study the evolution of hydrogen bubbles in the order of few hundred micrometers, refered to as continuum scale bubbles, is proposed. The framework accounts for the multiphase nature of the process, electrochemical reactions, dissolved gas transport, charge transport, interfacial mass transfer and associated bubble growth. The proposed solver is verified, for two-dimensional cases, by comparison to analytical solution of bubble growth in supersaturated solutions, stationary bubble, rising bubbles and qualitative analysis based on experimental observations of the variations in current based on static simulations. The proposed solver is used to simulate the evolution of a single bubble under various wetting conditions of the electrode as well as the coalescence driven evolution of two bubbles. The results show that as the bubbles detach, its surface oscillates and the shape of the rising bubble is determined by the balance between drag force and surface tension. These surface oscillations, which causes the bubble to get flattened and elongated, results in temporal variation of the electrical current. The reduction of current due to bubble growth is visible only when these surface oscillations have reduced. The simulations also show the current as a function of the position of the bubble in the interelectrode gap. The framework also predicts the increase in current as a result of bubbles leaving the surface which is larger when the process is coalescence driven. The simulations indicate that bubble coalescence is the underlying mechanism for continuum scale bubble detachment.

On interplay of surface tension and inertial stabilization mechanisms in the stable and unstable interface dynamics with the interfacial mass flux

Non-equilibrium dynamics of interfaces and mixing are omnipresent in fluids, plasmas and materials, in nature and technology, at astrophysical and at molecular scales. This work investigates dynamics of an interface separating fluids of different densities and having interfacial mass flux, and being influenced by the acceleration and the surface tension. We derive solutions for the interface dynamics conserving mass, momentum and energy, find the critical acceleration values separating stable and unstable regimes, and reveal the macroscopic inertial mechanism as primary mechanism of the interface stabilization. We show that while the surface tension influences only the interface, its presence leads to formation of vortical structures in the bulk. For large accelerations the conservative dynamics is unstable, leading to the growth of interface perturbations and the growth of the interface velocity. This new instability can be unambiguously discerned from other instabilities; for strong accelerations it has the fastest growth-rate and the largest stabilizing surface tension value when compared to Landau-Darrieus and Rayleigh-Taylor instabilities. We further find the values of initial perturbation wavelengths at which the conservative dynamics can be stabilized and at which it has the fastest growth. Our results agree with existing observations, identify extensive theory benchmarks for future experiments and simulations, and outline perspectives for application problems in nature and technology.

Molecular Insights into Water Vapor Adsorption and Interfacial Moisture Stability of Hybrid Perovskites for Robust Optoelectronics

• Grand canonical Monte Carlo predicts BET vapor adsorption isotherms on perovskites. • Vapor-induced degradation cannot be simply correlated with surface hydrophilicity. • Humidity affects ion dissociation rates rather than degradation energy barriers. • Coupled water adsorption and diffusion mechanism leads to perovskite ion solvation. • Material loss rates of 5.8 ~ 13.1 μm/s are estimated at 30 ~ 80% relative humidity. Understanding interfacial mass transfer processes, such as the water vapor adsorption-induced degradation of hybrid perovskites, is vital for improving the durability and performance of their optoelectronic devices in the ambient atmosphere with humidity. In this paper, vapor adsorption on prototypical MAPbI 3 , terminated by [MAI] 0 and [PbI 2 ] 0 surface, at different relative humidity (RH) levels is studied using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The resulting vapor adsorption isotherms match the Brunauer-Emmett-Teller (BET) adsorption model with heats of adsorption of 0.510 and 0.609 eV, respectively, for water monolayers on [MAI] 0 and [PbI 2 ] 0 . The formation of water monolayer on [MAI] 0 (for RH ≥ 30%) is consistent with its lower hydrophilicity compared to [PbI 2 ] 0 (for RH ≥ 10%), reflected from the larger water contact angle predicted. Based on predicted water surface coverages at various RHs, the moisture-induced surface degradation kinetics is studied using MD simulations and transition-state theory. Humidity has a minor impact on the degradation energy barriers due to the similar ion removal pathway by water solvation, but strongly affects the ion dissociation rates through the frequency of attempts to attack surface ions. [MAI] 0 is more vulnerable against water than [PbI 2 ] 0 , despite its lower hydrophilicity, implying that long-term exposed MAPbI 3 are mostly terminated by [PbI 2 ] 0 . Furtherly, averaged degradation material loss rates of 5.8 ~ 13.1 μm/s are estimated at 30 ~ 80% RH levels and 300 K, which is consistent with experiment observations. Finally, we offer a picture for the water-diffusion-based degradation mechanism and elucidate interesting hydrogen-bonding features at the vapor-MAPbI 3 interface. This research provides quantitative insights into the inherent vapor-perovskite interactions and addresses the moisture instability mechanisms in metal halide perovskites towards the rational design of water-resistant, long term stable and efficient optoelectronic devices.

Using Liquid Crystals for In Situ Optical Mapping of Interfacial Mobility and Surfactant Concentrations at Flowing Aqueous-Oil Interfaces.

Flow-induced states of fluid interfaces decorated with amphiphiles underlie phenomena such as emulsification, foaming, and spreading. While past studies have shown that interfacial mass transfer, the kinetics of surfactant adsorption and desorption, interfacial mobility, and surfactant reorganization regulate the dynamic properties of surfactant-laden interfaces, few simple methods permit simultaneous monitoring of this interplay. Here, we explore the optical responses of micrometer-thick films of oils (4-cyano-4'-pentylbiphenyl, 5CB) with a liquid crystalline order in contact with flowing aqueous phases of soluble [e.g., sodium dodecyl sulfate (SDS)] or insoluble (e.g., 1,2-dilauroyl-sn-glycero-3-phosphocholine) amphiphiles. We observe the onset of flow of 0.5 mM SDS solutions within a millifluidic channel (area-average velocity of 200 mm/s) to transform a liquid crystal (LC) film with an alignment along the interface normal into a bright birefringent state (average LC tilt angle of 30°), consistent with an initially mobile interface that shears and thus tilts the LC along the flow direction. Subsequently, we observed the LC film to evolve to a steady state (over ∼10 s) with position-dependent optical retardance controlled by gradients in surfactant concentration and thus Marangoni stresses. For 0.5 mM SDS solutions, by using particle tracking and a simple hydrodynamic model, we reveal that the dominant role of the flow-induced interfacial surfactant concentration gradient is to change the mobility of the interface (and thus shear rate of LC) and not to change the easy axis (equilibrium orientation) or anchoring energy (orientation-dependent interfacial energy) of the LC. At lower surfactant concentrations (0.015 mM SDS), however, we show that the LC directly maps flow-induced interfacial surfactant concentration gradients via a change in the local easy axis of the LC. When combined with additional measurements obtained with simple salts and insoluble amphiphiles, these results hint that LC oils may offer the basis of general and facile methods that permit mapping of both interfacial mobilities and surfactant distributions at flowing interfaces.

In-situ plasmonic tracking oxygen evolution reveals multistage oxygen diffusion and accumulating inhibition

Understanding mass transfer processes concomitant with electrochemical conversion for gas evolution reactions at the electrode-electrolyte interface plays a key role in advancing renewable energy storage and conversion. However, due to the complicated diffusion behavior of gas at the dynamic catalytic interfaces, it is still a great challenge to accurately portray mass transfer of gas during electrocatalysis process. Here, we track the diffusion of dissolved oxygen on Cu nanostructured plasmonic interface, which reveals multistage oxygen diffusion behaviors, including premature oxygen accumulation, spontaneous diffusion and accelerated oxygen dissipation. This work uncovers an accumulating inhibition effect on oxygen evolution arising from interfacial dissolved oxygen. With these knowledges, we develop a programmable potential scan strategy to eliminate interfacial gas products, which alleviates the concentration polarization, releases accessible actives sites and promotes electrocatalytic performance. Our findings provide a direct observation of the interfacial mass transfer processes that governs the kinetics of gas-involved multiphases catalysis.

Numerical modeling of reactive bubbly flows based on Euler-Lagrange approach

In this paper, the Euler-Lagrange approach was employed to simulate the gas–liquid reaction system in a rectangular bubble column by combining hydrodynamics, interfacial mass transfer and reaction kinetics. According to the satisfactory agreement with the experiment results, the detailed characteristics of the hydrodynamics were accurately reflected. For the chemisorption process of CO2 in aqueous NaOH, the results were more similar to the experimental values than those reported in the literature. Moreover, further improvements were successfully implemented: A visible inflection point, owing to which the shape of the curve was highly consistent with the experimental data, could be easily observed when taking into account the auto-dissociation of water. A relatively exact slope for the distribution curve of the mean Sauter diameter could be attained in the flow region below z/H = 0.3. In addition, an in-depth assessment was performed by comparing a series of typical mass transfer and enhancement factor models.

Macroscopic and microscopic stabilization mechanisms of unstable interface with interfacial mass flux

Unstable interfaces are omnipresent in plasma processes in nature and technology at astrophysical and at molecular scales. This work investigates the interface dynamics with interfacial mass flux and focuses on the interplay of macroscopic and microscopic stabilization mechanisms, due to the inertial effect and the surface tension, respectively, with the destabilizing acceleration. We derive solutions for the interfacial dynamics conserving mass, momentum, and energy and find the critical values of the acceleration, density ratio, and surface tension separating the stable and unstable regimes. While the surface tension influences only the interface, its presence leads to the formation of vortical structures in the bulk. The vortical structures are energetic in nature, and the velocity field is shear free at the interface. We find that the conservative dynamics is unstable only when it is accelerated and when the acceleration value exceeds a threshold combining the contributions of macroscopic and microscopic mechanisms. In the unstable regime, the interface dynamics corresponds to the standing wave with the growing amplitude and has the growing interface velocity. For strong accelerations and weak surface tensions typical for high energy density plasmas, the unstable conservative dynamics is the fastest when compared to other instabilities; it has finite values of the initial perturbation wavelength at which the interface is stabilized and at which its growth is the fastest. We elaborate extensive theory benchmarks for experiments and simulations and outline its outcomes for application problems in nature and technology.

Effect of nanoparticles on interfacial mass transfer characteristics and mechanisms in liquid-liquid extraction by molecular dynamics simulation

The addition of nanoparticles is a promising strategy to intensify interfacial mass transfer, which possess a wide array of potential applications in considerable industrial processes. In order to elucidate interfacial mass transfer characteristics and mechanisms, the effects of functional group, particle size and volume fraction of silica nanoparticle on dimethyl sulfoxide (DMSO) transfer across the water/hexane interface were investigated by molecular dynamics simulation. The results manifested that hydrophilic nanoparticles are beneficial to mass transfer enhancement. Due to the increase of mass transfer path and steric hindrance of nanoparticles at the liquid-liquid interface, however, hydrophobic and amphiphilic nanoparticles inhibit solute mass transfer. Moreover, the smallest size nanoparticle at the maximum concentration of 10 vol% leads to the highest enhancement, namely the decrease of mass transfer resistance by 36%. By analyzing the mean square displacement and size effect of nanoparticle, it is found that Brownian motion rather than micro-convection is probably the dominant mechanism.

Shining New Light on the Kinetics of Water Uptake by Organic Aerosol Particles.

The uptake of water vapor by various organic aerosols is important in a number of applications ranging from medical delivery of pharmaceutical aerosols to cloud formation in the atmosphere. The coefficient that describes the probability that the impinging gas-phase molecule sticks to the surface of interest is called the mass accommodation coefficient, αM. Despite the importance of this coefficient for the description of water uptake kinetics, accurate values are still lacking for many systems. In this Feature Article, we present various experimental techniques that have been evoked in the literature to study the interfacial transport of water and discuss the corresponding strengths and limitations. This includes our recently developed technique called photothermal single-particle spectroscopy (PSPS). The PSPS technique allows for a retrieval of αM values from three independent, yet simultaneous measurements operating close to equilibrium, providing a robust assessment of interfacial mass transport. We review the currently available data for αM for water on various organics and discuss the few studies that address the temperature and relative humidity dependence of αM for water on organics. The knowledge of the latter, for example, is crucial to assess the water uptake kinetics of organic aerosols in the Earth's atmosphere. Finally, we argue that PSPS might also be a viable method to better restrict the αM value for water on liquid water.

Coupling VOF interfacial mass transfer model with RSM approach in LLE systems: Developing the new correlations for mass transfer, aspect ratio and terminal velocity

The performance of liquid-liquid extraction (LLE) systems is determined by terminal velocity and extraction fraction. Several parameters and their interactive effects influence the performance. In the present study, the response surface methodology(RSM) approach has been used to investigate the parameters' effects and their complicated interactions in hydrodynamics and mass transfer. Hydrodynamic and mass transfer simulations of a single droplet system have been carried out using the VOF method and close agreements have been attained in comparison with experimental data. Subsequently, the RSM and central composite design methods were employed in terminal velocity, aspect ratio, and extraction fraction modeling. The drop diameter, density ratio, and viscosity ratio have been chosen as the effective hydrodynamic parameters in the terminal velocity and aspect ratio. The mentioned hydrodynamic parameters, partition coefficient, and diffusivity ratio have been chosen as the mass transfer variables. The suggested quadratic models of terminal velocity(R2 = 0.99) gives accurate predictions in high Re numbers, while the previous correlations could not. The new general quadratic model of aspect ratio having included the viscosity ratio as an effective parameter, can be used in the wide range of material properties with high accuracy (R2 = 0.95), while the previous correlations have not included the viscosity ratio. The new quadratic model of mass transfer with high accuracy (R2 = 0.99), includes partition coefficient and its interactive effects with diffusivity ratio and hydrodynamic parameters which have not been considered yet. More additionally, the developed model could be applied in every LLE system regardless of the mass transfer resistance existence in the drop/continuous phase or both. Finally, the ANOVA showed that the partition coefficient and viscosity ratio are the most effective parameters in mass transfer, hence the reduction in the partition coefficient along with the reduction in viscosity ratio would help to reach the better mass transfer performance. At the final stage, the optimized conditions have been presented.

Simulation of interfacial mass transfer process accompanied by Rayleigh convection in NaCl solution

Rayleigh convection caused by dissolved CO2 is critical for CO2 capture and storage technology in saline aquifers. However, the poor experimental measurements of theoretical model parameters limit a further analysis of the interfacial mass transfer process after the convection occurring. In this study, a two-dimensional lattice Boltzmann method (LBM) including electrostatic and volume forces is used to simulate Rayleigh convection for CO2 in a NaCl solution at 293.15 K, 1.00 atm. Through calculating the key parameter of the simulated onset time, it indicates that the CO2 interfacial concentration is only 15–20% of the saturated concentration at the true gas–liquid mass transfer interface. Besides, the simulated convective onset time would be delayed by increasing the salt concentration. The average instantaneous mass transfer factor is also decreased with the increased concentration and when the concentration of the NaCl solution is less than 3 mol L−1 (M), the mass transfer rate can be accelerated by more than 3.2 times. We propose a new method to obtain surface renewal time which is determined according to the concentration and velocity field simulated by LBM and find that changes in mass transfer rate follow the penetration theory in the molecular diffusion stage while abiding by the surface renewal theory in the interfacial convection stage. Our results can provide a valuable guide for relevant economic evaluation and appropriate geological sequestrated sites.

Interfacial mass transfer intensification with highly viscous mixture

Many investigations find that mass transfer efficiency decreases dramatically with increasing viscosity, which poses challenges to the industrial processes with the highly viscous mixture. We use liquid films on a vertical plate with windows to address this problem. The hybrid twin-liquid films combine the motility of free-falling films with the stability of wall-bounded films. In this study, the film thickness distributions are measured experimentally, and the detailed hydrodynamics and mass transfer process are studied with numerical simulations. The results reveal the hydrodynamic and mass transfer behaviors of highly viscous twin-liquid films. Due to gravity acceleration inside the window, the maximum velocity of liquid films increases by 2.5–16 times, and the maximum local mass transfer rate increases by 2–6.5 times in our simulations. We conclude that compared with conventional methods, open windows significantly enhance mass transfer in viscous liquid films without additional cost.

Dynamics of hygroscopic aqueous solution droplets undergoing evaporation or vapour absorption

Abstract

Predicting the effective diffusivity across the sediment–water interface in rivers

Abstract Hyporheic exchange directly controls and regulates the transport of nutrients, heat, and organic matter across the sediment–water interface (SWI), thereby affecting the biochemical processes in rivers, which is critical for maintaining the health of aquatic ecosystems. The interface exchange is controlled by multiple processes, including physical, chemical, and biological processes, which can be modeled by the effective diffusion model using an effective diffusion coefficient, Deff, to quantify the hyporheic exchange rate. In this study, genetic programming (GP), a machine learning (ML) technique based on natural selection, is adopted to search for a robust relationship between the effective diffusion coefficient and surface flow conditions, bedforms, and sediment characteristics on the basis of published broad interfacial mass exchange flux measurements. By utilizing a data set covering a wide range of environmental condition parameters, the effective diffusion coefficient prediction models for the SWI with and without bedforms are developed. Results show that the dimensionless effective diffusion coefficient is not only related to the permeability Reynolds number, ReK, but also to the channel Reynolds number, Re. Compared with the flat bed, ReK has a greater effect on the hyporheic exchange when bedforms present at the SWI by affecting the pumping advection strength. The new Deff predictor with a relatively concise form exhibits considerable improvements with regard to prediction ability and is physically sound relative to the existing predictors.

Research on falling film dehumidification performance of microencapsulated phase change materials slurry

In the process of liquid desiccant dehumidification, the temperature-rise of the desiccant solution caused by moisture absorption will seriously affect the dehumidification capacity and performance. It is expected that the temperature rise of solution can be restrained by adding microencapsulated phase change materials (MicroPCMs) into the liquid desiccant solution. In this paper, based on computational fluid dynamics (CFD) method, two-dimensional models of flat plate and corrugated plate falling film dehumidification of the microencapsulated phase change material slurry (MPCMS) were developed and validated. The dynamic boundary method was used to determine the interfacial mass transfer coefficient. The influences of several factors on the dehumidification performance, including the concentration of MicroPCMs, the inlet temperature of the MPCMS and the falling film plate configuration, were investigated. The results show that, adding MicroPCMs into the liquid desiccant solution is beneficial to the dehumidification performance improvement. The inlet temperature of MPCMS is a very critical variable. When the inlet temperature of the slurry is in the phase transformation temperature range of MicroPCMs, with the adding of the microcapsule, the temperature rise in dehumidification process can be restrained, and the moisture removal performance can be improved significantly. When the MPCMS inlet temperature is at the phase transformation onset point, and the concentration of MicroPCMs is 5%, the water condensation rate is 14.2% higher than that of the base solution. Moreover, it’s not that the more microcapsules added, the larger mass transfer coefficient is. There is an optimum concentration of MicroPCMs to achieve the maximum interfacial mass transfer coefficient. The corrugated plate configuration is more conducive to the dehumidification enhancement by the MPCMS.

Predictable interfacial mass transfer intensification of Sn–N doped multichannel hollow carbon nanofibers for the CO2 electro-reduction reaction

Construction of controllable multichannel and mesoporous structures on Sn and N co-doped carbon nanofibers enables intensified interfacial CO2 transfer and stabilized high-loading CO2,ads, enhancing CO2 electro-reduction performance.

Novel hydrophobic catalysts to promote hydration at the water-oil interface.

The limitation of the cyclohexene hydration reaction is that it is a three-phase immiscible reaction. We have described a strategy to overcome this interfacial mass transfer limitation by grafting an organosilane surfactant ((octyl)-trimethoxysilane (OTS)) onto the HZSM-5 zeolite surface. The characterization of the OTS-HZSM-5 zeolite was performed by FTIR, CA, BET, TPD, pyridine-IR, XPS, TGA and XRD techniques. The functionalization of the HZSM-5 zeolite could increase hydrophobicity without significantly reducing the density of acid sites. As a result, the OTS-HZSM-5 zeolite had high catalytic activity (20.87% conversion) compared with HZSM-5 (4.15% conversion) at 130 °C after 4 h. The high catalytic activity makes it a promising candidate for other acid-catalyzed two-phase reactions.

Visual dynamical measurement of the solute-induced Marangoni effect of a growing drop with a PLIF method

We present a visualized measurement of the transient Marangoni effect occurring in interfacial mass transfer processes by using a planner laser-induced fluorescence (PLIF) technique. Since acidity increased remarkably and linearly the fluorescent intensity of Rhodamine B, the concentration distribution of acidic solute inside a drop was obtained by PLIF. Thus, based on the concentration contours of solute, we could probe into the bulk flow and occurrence of the Marangoni effect. The Marangoni effect has been known to be affected by the physical properties of the test system, initial solute concentration, the operating conditions and device configurations. With existence of neutralization reaction in the extraction system, the Marangoni effect was declined as for the acetic acid being consumed rapidly. Last, we found that the density effect of solute coupled with Marangoni effect, which further affected the distribution of solute and then influenced the location and evolution of Marangoni effect.