Mass Transfer Distribution Research Articles

Insights into the pore structure effect on the mass transfer of fuel cell catalyst layer via combining machine learning and multiphysics simulation

Analysis of the catalytic layer (CL) pore structure and three-phase (electron phase, proton phase, and reactant phase) mass transfer in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) is critical for improving concentration polarization and optimizing performance. However, there is a lack of studies on the pore structure’s impact on the catalytic layer three-phase mass transfer. In this work, the influence of pore structure on catalytic layer three-phase mass transfer and multiphysics distribution was investigated by combining machine learning and multiphysics simulation. Among many key factors investigated by machine learning that impact the performance of catalytic layer, porosity emerges as the primary influencing factor. Porosity accounts for 32.7 % of the electric potential drop, with macro/micro porosity contributing 27.6 % and 5.1 %, and 32.8 % of the current density, with macro/micro porosity contributing 15.6 % and 17.2 %. Furthermore, the macropore structure has a much greater influence on the performance of the catalytic layer compared to the micropore structure. Moreover, the simulation results demonstrated that porosity has a great influence on three-phase mass transfer, the oxygen molarity increases with increasing porosity. The electric potential difference increases exponentially as porosity increases. The relationship between current density and porosity is a volcanic relationship, which can be expressed as a quadratic polynomial function. The mesoscopic pore-scale model (PSM) with an εeff of 0.502 (εmic of 0.2 and εmac of 0.378) exhibits the highest mean current density at 619.526 mA/cm2@0.5 V, attributed to a more uniform and efficient three-phase transfer path. The accuracy of the mesoscopic pore-scale model and the polynomial equation is further confirmed through corresponding experiments. The experiment results show that the current density decreased as the εeff increased from 0.682 to 0.702, which aligns with the theoretical predictions of the PSM model and polynomial equation. These studies are valuable for comprehending the internal three-phase mass transfer behavior and optimizing the catalytic layer pore structure to enhance HT-PEMFC performance.

The Phase Distribution Characteristics and Interphase Mass Transfer Behaviors of the CO2-Water/Saline System under Gathering and Transportation Conditions: Insights on Molecular Dynamics.

In order to investigate the interphase mass transfer and component distribution characteristics of the CO2-water system under micro-scale and nano-scale transport conditions, a micro-scale kinetic model representing interphase mass transfer in the CO2-water/saline system is developed in this paper. The molecular dynamics method is employed to delineate the diffusion and mass transfer processes of the system's components, revealing the extent of the effects of variations in temperature, pressure, and salt ion concentration on interphase mass transfer and component distribution characteristics. The interphase mass transfer process in the CO2-water system under transport conditions can be categorized into three stages: approach, adsorption, and entrance. As the system temperature rises and pressure decreases, the peak density of CO2 molecules at the gas-liquid interface markedly drops, with their aggregation reducing and their diffusion capability enhancing. The specific hydration structures between salt ions and water molecules hinder the entry of CO2 into the aqueous phase. Additionally, as the salt concentration in water increases, the density peak of CO2 molecules at the gas-liquid interface slightly increases, while the density value in the water phase region significantly decreases.

Experimental study on the mass transfer and microscopic distribution characteristics of remaining oil and CO2 during water-miscible CO2 flooding

Accurate understanding and quantitative characterization of the microscopic distribution and mobilization mechanisms of remaining oil are crucial for further enhancing oil recovery during CO2 flooding. In this study, miscible CO2 flooding experiments after water flooding were performed to investigate the mass transfer and microscopic distribution characteristics of remaining oil and CO2 using micro-computed tomography technique. Additionally, the distribution characteristics of multiphase fluids (oil, water and CO2) in the pores were comprehensively investigated. Furthermore, the mass transfer effects during the miscible CO2 flooding process, as well as the CO2 sequestration ratio (SR) and sequestration factor (SF) were systematically examined. The experimental results show that the ultimate oil recovery factor after miscible CO2 flooding were 80.9 %, 70.7 %, and 64.7 %, respectively. During the water flooding stage, the produced oil mainly consisted of light hydrocarbons (C5–C16), followed by medium hydrocarbons (C17–C27). The remaining oil was mainly in cluster and network pattern, followed by multiple and oil film pattern. After miscible CO2 flooding, the produced gas mainly consisted of CO2 and CH4, with a significant increase in the mass fraction of light hydrocarbons (C5–C16) in the produced oil. The remaining oil was mainly in multiple and singlet pattern, followed by network and film pattern, with a small portion in cluster pattern. The higher the displacement rate, the smaller the SR, but most of the injected CO2 (SR > 70 %) was retained in the porous media, demonstrating the feasibility of CO2 geological sequestration during the miscible flooding process.

A CFD Study on Optimization of Mass Transfer and Light Distribution in a Photocatalytic Reactor with Immobilized Photocatalyst on Spheres

A CFD Study on Optimization of Mass Transfer and Light Distribution in a Photocatalytic Reactor with Immobilized Photocatalyst on Spheres

Stirred-electrodeposition construction of porous Fe-doped NiSe nanoclusters as a bifunctional catalyst for water splitting

The electrodeposition method is commonly used for fabricating water splitting catalysts. Traditional methods assume a static precursor solution, ignoring the effects of solution dynamics. We theorized that stirring the solution during electrodeposition could improve mass transfer and current distribution, thereby enhancing electrochemical kinetics and nucleation. Consequently, we developed a novel electrodeposition technique to synthesize Fe-doped NiSe, an effective catalyst for alkaline water hydrolysis, demonstrating exceptional performance and stability. This catalyst notably decreases the overpotentials for OER and HER to 185/266 mV and 101/271 mV at 10 and 300 mA cm−2, respectively. At the same time, the overall water splitting system comprising this catalyst requires only a low potential of 1.48 V to stably catalyze water splitting for over 60 hours. Electrochemical tests indicate that stirred deposition endows the catalyst with a larger electrochemically active area. In-situ Raman spectroscopy reveals NiOOH as an active phase, and Fe doping facilitates NiOOH formation at lower overpotentials, enhancing OER performance. First-principles calculations suggest that Fe doping optimizes the rate-determining step, lowers the activation energy for the OER process, and boosts conductivity. This study presents a method to improve OER efficiency in Ni-based catalysts, offering insights into mechanism control.

CFD-population balance modelling for a flat sheet membrane-assisted antisolvent crystallization

A comprehensive model has been developed to couple CFD with the population balance equation (PBE) for a flat sheet membrane-assisted antisolvent crystallization (FS-MAAC) process. The model accurately depicts the fluid dynamics, mass transfer, heat transfer and crystal size distribution (CSD) in the FS-MAAC crystallizer. The crystallization system considered was to produce α-form crystals of glycine. The model investigates the effects of different parameters, such as the velocities of the crystallizing and antisolvent solutions, antisolvent composition, temperature, and gravity. A good agreement was observed between the simulation results and experimental data for the α-form crystals of glycine. The simulation results show a steady-state antisolvent concentration profile in the liquid layer and varied only in the z-direction. Regardless of the variations in the velocity of either the antisolvent solution or the crystallizing solution, the CSD remained narrow, with mean crystal sizes ranging from 27 to 40 μm. Furthermore, increasing mass transfer through the antisolvent transmembrane flux leads to a narrower CSD. Slower antisolvent permeation rates at higher temperatures also promote crystal growth. Also, a narrow CSD is maintained regardless of the initial circulation position of the antisolvent solution. In conclusion, membrane antisolvent crystallization provides a reliable and consistent solution for obtaining crystals with desired CSD under optimal operating conditions.

Membrane role in heat and mass transfer resistance distribution and performance of hollow fiber membrane contactor for SGMD desalination

Hollow fiber membrane contactor (HFMC) is the core device of heat mass exchange between seawater solution and sweeping air in sweeping gas membrane distillation (SGMD) desalination. In order to reveal the distribution of heat and mass transfer resistance on feed solution side, porous membrane side and sweeping air side, a mathematical model considering the simultaneous heat mass transfer and water vapor diffusion mechanism in the membrane pores was established for the cross-flow HFMC. The simulation results of the model were compared with experimental results and literature results. Comparison shows that the deviation of simulation results of the model is less than 13.4 %, which verifies the accuracy and reliability of the simulation results. Influences of the main structural characteristics of porous membrane on the resistance distribution of heat and mass transfer, efficiency and membrane flux were explored. Air side dominates the heat transfer process, while the membrane side accounts for less than 39 % of the total heat transfer resistance for the main range of membrane microstructure parameters investigated. The mass transfer is controlled by the porous membrane except for thin membrane with a thickness of less than 100 μm. Membranes with porosity above 0.8 and as thin as possible can achieve better mass transfer efficiency and freshwater flux. Increasing mean pore diameter has a strong promotion effect on the increase of membrane flux before it reaches 150 nm, and beyond this critical value, the water vapor diffusion mechanism changes from Knudsen collision to molecular collision. Effects of different operating parameters and membrane microstructure parameters on air temperature distribution and humidity distribution were also analyzed.

Influence of liquid film shape on evaporation performance of agitated thin film evaporator

Abstract The agitated thin film evaporator (ATFE), which is known for its high efficiency, force the material to form a film through the scraping process of a scraper, followed by evaporation and purification. The complex shape of the liquid film inside the evaporator can significantly affect its evaporation capability. This work explores how change in shape of the liquid films affect the evaporation of the materials with non-Newtonian characteristics, achieved by changing the structure of the scraper. Examining the distribution of circumferential temperature, viscosity, and mass transfer of the flat liquid film shows that the film evaporates rapidly in shear-thinning region. Various wavy liquid films are developed by using shear-thinning theory, emphasizing the flow condition in the thinning area and the factors contributing to the exceptional evaporation capability. Further exploration is conducted on the spread patterns of the wavy liquid film and flat liquid film on the evaporation wall throughout the process. It is noted that breaking the wavy liquid film on the evaporating wall during evaporation is challenging due to its film-forming condition. For which the fundamental causes are demonstrated by acquiring the data regarding the flow rate and temperature of the liquid film. The definitive findings of the analysis reveal a significant improvement in the evaporation capability of the wavy liquid film. This enhancement is attributed to increasing the shear-thinning areas and maintaining the overall shape of the film throughout the entire evaporation process.

Erratum to: Heat and Mass Transfer and Gas Distribution in a Steam-Water Volume with Noncondensable Gas

Erratum to: Heat and Mass Transfer and Gas Distribution in a Steam-Water Volume with Noncondensable Gas

Non-uniform heat source or sink on the radiated and thermophoretic flow of slender body of paraboloid and cone revolutions in a saturated medium with Brownian motion

Heat and mass transfer acquired the attention of investigators and experts because of massive uses in the field of medicine, manufacturing of modern aircrafts, uses in advanced water filtration plants, distillation process of water, more efficient electronic instruments, more efficient batteries, textile industry, uses as manufacturer in cosmetics industry and modern defense equipment. By viewing this, we considered the numerical study of Fourier flux and buoyancy driven forces on the flow of thermal and diffusion transmission of body revolutions (Paraboloid and cone), situated in a water-logged Darcy medium by allowing the radiation, Brownian motion, time-space dependent heat source or sink, and thermopheretic. Later on, the governing system is solved via Runge–Kutta method. Properties of convoluted governing measures of the organisms on local Nusselt and Sherwood numbers along with velocity, thermal and diffusion shapes are described with the aid of graphically and tabular form. It is stimulating to declare that the non-uniform heat source or sink is highly dominated in cone form of revolution as associated to paraboloid form of flow due to more distribution of mass transfer. From this, one can draw the conclusion that wherever there are higher mass transportation phenomena, cone-shaped body of revolution can be used. It is found that the time- and space-dependent heat source or sink performs as a regulating factor of the transmission of flow phenomena.

Modeling and multiphysics analysis for electrochemical CO2 reduction in solid-electrolyte reactors

Mass transfer and overportential distribution of solid-electrolyte reactors, an electrochemical CO2 conversion equipment, are analyzed by a multiphysics model. It shows that the ohmic loss caused by charge transport in porous solid electrolytes (usually thought to be a major bottleneck of solid-electrolyte reactors) begins to show its significantly negative effect on reactor performance till current densities reach 400 mA/cm2, much higher than that required for relevant commercial operation (∼200 mA/cm2). Thus, we suggest much attention should still be put on how to decrease thermodynamics (∼1.46 V) and activation losses (>1.4 V) of reactors, rather than developing elaborate structures and materials of porous solid electrolytes to decrease ohmic losses.

Heat and Mass Transfer and Gas Distribution in a Steam-Water Volume with Noncondensable Gas

Heat and Mass Transfer and Gas Distribution in a Steam-Water Volume with Noncondensable Gas

A cyclone reactor of electrochemical advanced oxidation processes using PbO2 anode and H2O2 electrosynthesis cathode

Electrochemical advanced oxidation processes are promising tools for pollution abatement but most still lack practical engineering attempts and devices. A type of process intensification reactor for the electrochemical advanced oxidation processes is developed here. The cyclone continuous flow electrochemical reactor adopts a PbO2 anode and H2O2 electrosynthesis cathode together. A lab-scale cyclone continuous flow electrochemical reactor is fabricated and simulated, which is evaluated using the H-acid wastewater. The contributions of the PbO2 anode and H2O2 electrosynthesis cathode to pollutant degradation are discussed particularly. A 3-D model is developed to provide a visualized perspective on the reactor performances, including flow distribution, mass transfer, and current distribution. Pronounced signals of powerful radicals can be detected for the PbO2H2O2 cyclone reactor, including •OH, SO4•−, and 1O2. It exhibits excellent performances on mass transfer, electrical properties, organic degradation, and space-time yield. Such a strategy presents a promising engineering solution for scale-up and further development toward industrial application.

Effect of Ion Mass Transfer and Electric Field Distribution on the Formation of Void Defect in Electroformed Nickel Microcolumns

Effect of Ion Mass Transfer and Electric Field Distribution on the Formation of Void Defect in Electroformed Nickel Microcolumns

CFD modeling of double-partition divided-wall column for mass transfer characteristics

In this study, a coupled two-fluid computational fluid dynamics (CFD)–component transfer (CT) model was constructed to investigate the mass transfer behavior and distribution of component concentration fields on trays within the two-staggered wall regions of a double-partition divided-wall column (DPDWC). By comparing the simulation results of the coupled CFD-CT model with the height-dependent calculation of the clear-liquid layer, this study validated the model, and then proceeded to analyse its effect on mass transfer in multiple zones of the tower under varying gas velocity conditions. The results showed that the mass-transfer efficiency increased initially, but then decreased with an increase in gas velocity within the studied gas velocity range. In addition, the evaporative condensation effect of the component mass transfer cause temperature variations across different regions of the tower.

Novel materials and crystallizer design for freeze concentration

When wastewater streams or seawater are desalinated, the waste product is a hypersaline brine stream which is usually disposed of or stored in evaporation ponds. Eutectic Freeze Crystallization (EFC) is a novel treatment technology for these hypersaline brines that can recover both water and dissolved salts. It works by cooling the stream to the Eutectic temperature, at which point both ice and salt will crystallize. The ice, being less dense than the solution, floats, and the salt, being denser, will sink – thus effecting a gravity separation.Theoretically, EFC can result in zero liquid discharge (ZLD) and has several advantages over conventional separation techniques, including low energy consumption; high quality products and it requires no additional chemicals. It can also be combined with other separation technologies to optimise the separation process.Although it sounds simple, an EFC process can be difficult to design and operate effectively, since each of the elements has its own complexity. Specifically, the issue of ice scaling is one of the major challenges in implementing EFC.Therefore, in this study, we focussed on ice scaling in a freeze concentration system i.e ice crystallization only; without the salt crystallization component that would define the process as an EFC process.We investigated two approaches to scaling reduction:The first was modification of the heat exchanger surface, where we investigated the effect of three different heat exchanger surfaces on ice scaling: a novel polypropylene graphite (PP GR) material, Stainless Steel 316 (SS316) and Aluminium. These three materials were tested in a small-scale Column Crystallizer (CC).The second method was by designing a Continuously Stirred Column Crystallizer (CSCC), which aimed to improve the hydrodynamics independent of pumping, to improve on the heat and mass transfer distribution across the crystallizer and to improve product purity by providing a larger product separation zone. The focus was on producing an efficient crystallizer design, bearing current industrial implementation hurdles in mind.This study confirmed that using materials of low surface energy has the potential to increase the scaling induction times and reduce the severity of ice scaling, hence improving process efficiency. The outcome of the initial, small-scale study provided the required evidence to support scaling up the column crystallizer using PP GR as an HX material of choice.The study also showed that the unique multicompartment mixing system of the novel CSCC led to high supercoolings and long induction times being attained. The column design provides a larger disengagement zone than a conventional column, which has the potential to improve the separation efficiency, and hence the product purity.In summary, with the correct choice of heat exchanger material and appropriate crystallizer design, we have shown that one of the major challenges i.e. ice scaling, can be overcome. This paves the way for EFC being able to be used for the treatment of hypersaline brines, not only at laboratory scale, but also at larger, commercial scales.

Simulation of A Solar Drier for Iroko Wood (Chlorophora Excelsa) in A Tropical Environment

In a previous study conducted by Simo Tagne to designing a solar dryer based on mathematical equations for iroko wood in Cameroon, Africa. However, there is no complete simulation of the drying process on the tool, resulting in the lack of detailed elaboration of the iroko wood drying process. The purpose of this study is to simulate in detail the drying process on the tool using an ANSYS simulation. The model used in this simulation still uses the same mathematical model that has been studied before. This research begins by setting up the ANSYS application with the previous mathematical model, environmental conditions, and tool specifications. Furthermore, simulations are carried out using the ANSYS application with measurements of pressure, temperature, velocity and mass transfer. From this simulation obtained results for the distribution of pressure, temperature, velocity, and mass transfer. From all these distributions, it is sufficient to describe the drying process of the tool according to the mathematical model that has been studied previously.

Three-Dimensional Numerical Simulation of the Performance and Transport Phenomena of Oxygen Evolution Reactions in a Proton Exchange Membrane Water Electrolyzer.

Proton exchange membrane (PEM) water electrolysis, which is one of methods of hydrogen production with the most potential, has attracted more attention due to its energy conversion and storage potential. In this paper, a steady state, three-dimensional mathematical model coupled with the electrochemical and mass transfer physical fields for a PEM water electrolyzer was established. The influence of the different operation parameters on the cell performance was discussed. Moreover, the different patterns of the flow field, such as parallel, serpentine, multi-serpentine, and interdigitate flow fields, were simulated to reveal their influence on the mass transfer and current distribution and how they consequently affected the cell performance. The results of the numerical modeling were in good agreement with the experimental data. The results demonstrated that a higher temperature led to a better mass transfer, current distribution, and cell performance. By comparing the polarization curve, current, velocity, and pressure distribution, the results also indicated that the PEM water electrolyzer with a parallel flow field had the best performance. The results in this study can help in optimizing the design of PEM water electrolyzers.

The effect of fluid dynamics conditions and combustion reactions on the performance and heat and mass transfer distribution of dual-phase oxygen transport membranes

A 3-D model based on CFD approach was developed to explore the effect of fluid dynamic conditions and combustion reactions on oxygen transport, in which the distribution of parameters such as oxygen partial pressure, temperature, velocity, and oxygen permeability were considered. After meshing the geometric model with poly-hexcore method, a series of user defined functions written in C++ were compiled and hooked to FLUENT to solve for oxygen permeation of dual-phase oxygen transport membranes. The results showed that oxygen permeability can be improved by pressurizing the feed side or vacuuming the permeate side, and the increased kinetic effect under evacuation conditions can increase the oxygen permeability by 69.85% at a vacuum pressure of 10 kPa and by 270.94% at 90 kPa. Due to the phenomenon of differential concentration polarization, the effect of oxygen concentration on oxygen permeability is more significant when the oxygen concentration on the feed side is lower than 0.17. Combustion reaction of CH4 promotes oxygen permeation, and the effect of the gap height between the fuel inlet and membrane is determined by several trade-off factors including momentum effects, reaction rate and temperature, and optimal oxygen permeability is achieved with a gap height of 3 mm.

Liquid holdup modeling analysis in horizontal gas–liquid slug flow

In slug flow, the wetted wall fraction and liquid holdup of the liquid film section are key parameters affecting the mass transfer and radial velocity distribution of the liquid film, the friction pressure drop, the momentum transfer between the two phases, and heat transfer characteristics. A modified wetted wall fraction and liquid holdup model based on the modified apparent rough surface (MARS) model is proposed in this study, which considers the friction coefficient and shear stress on the gas–wall, liquid–wall and gas–liquid interfaces and introduced the modified average interface velocity of the liquid film. Air–water slug flow experiments were in a 50 mm diameter acrylic glass pipe equipped with a high-speed camera. The edge detection operator was optimized to obtain the wetted wall fraction and liquid holdup at the liquid film section based on image analysis technology. A comparative analysis of the model performance shows that the mean absolute percentage error (MAPE) of the wetted wall fraction model is 9.4%, and the 96.1% relative deviations are within the ±20% error band. The MAPE of the liquid holdup model is 8.04%, and 93.4% relative error is within the ±25% error band. The modified MARS model has good prediction ability for the wetted wall fraction and liquid holdup of the gas–liquid slug flow.