Concentration Polarization Phenomenon Research Articles

Enhancement of Overlimiting Current in a Three-Dimensional Hierarchical Micro/Nanofluidic System by Non-uniform Compartmentalization

AbstractOverlimiting current (OLC) is a non-linear current response that occurs related to an ion concentration polarization (ICP) phenomenon in micro/nanofluidic systems and holds great importance since it represents the rate of selective ion transportation through perm-selective structure. For last two decades, numerous studies of OLC have been reported about understanding the fundamentals of nanoelectrokinetics and enhancing ion transportation through perm-selective membranes. Recent study reported that the alignment of non-uniform microspace near the perm-selective membranes in two-dimensional micro/nanofluidic systems can significantly enhance OLC, i.e., overlimiting conductance (σOLC). This is attributed to recirculation flow induced by combination of unbalanced electroosmosis and induced pressure driven flow among non-uniform microspaces. However, 2D micro/nanofluidic systems have limited practicality due to their small volume and low throughput. Herein, we tested the OLC enhancement using 3D-printed hierarchical micro/nanofluidic systems with respect to the non-uniformity of microspaces. The 3D microspaces were fabricated as a mesh structure using a conventional 3D printer. By comparing current–voltage measurement with each type of mesh, we experimentally confirmed the generation of recirculation flow among non-uniform meshes and ionic current enhancement in 3D hierarchical micro/nanofluidic system. Also, we further investigated the enhancement of overlimiting conductance depending on the mesh pattern. Furthermore, we validated that this effect of microscale non-uniform compartmentalization, both increasing surface area and aligning non-uniform spaces, appears not only at low molar concentration but at high molar concentrations. This demonstration can offer a strategy to design optimal electrochemical systems where a perm-selective ion transportation is crucial.

High performance Zn–Al LDH modified forward osmosis membrane with antibacterial, anti-membrane fouling, and photocatalytic degradation ability

Forward osmosis membrane has shown great potential in the fields of seawater desalination and sewage treatment. However, the concentration polarization phenomenon and membrane fouling in the water treatment process greatly reduce the water treatment performance and restrict its application. To address these challenges, we employed a pre-buried seed-in-situ growth method to facilitate the Zn–Al layered double hydroxide (Zn–Al LDH) growth on the thin nanofiber membrane, and use it as the support layer for the preparation of a Zn–Al LDH modified forward osmosis membrane. Studies have shown that the introduction of Zn–Al LDH significantly improves the water treatment efficiency of the forward osmosis membrane (In Al-DS mode, the water flux increased by 87.5 %, up to 50.50 LMH, with a low specific salt flux of 0.13 g L−1). It also exhibits exceptional antibacterial, anti-membrane fouling, and photocatalytic degradation properties. This research presents a novel approach for the development of advanced high-efficiency forward osmosis membranes.

Optimizing the economic viability of proton exchange membrane fuel cells operated with oxygen-enriched cathode air for residential hydrogen energy storage systems

The recovery and utilization of oxygen in residential hydrogen energy storage systems significantly impact economic factors. This study introduces an algorithm tailored to optimize oxygen concentration (fraction) across varied operational conditions, encompassing considerations for both efficiency (positive aspect) and lifetime (negative aspect). Initially, an enhanced air supply system (ASS), functioning with oxygen-enriched cathode air, is devised following the forefront scheme. Moreover, a dynamic model is formulated based on MATLAB/Simulink® software for the proton exchange membrane fuel cell (PEMFC) system. The model enables quantitative assessment of system gains in relation to various current densities and oxygen fractions, and its accuracy is partially validated through experimental data. Further, a model correlating stack lifetime to oxygen concentration (fraction) is established using experimental data obtained from other researchers. Finally, the optimal oxygen fractions are determined and managed, with a comparison of the effects before and after optimization. The optimized results indicate a 13% improvement in stack net power at rated operating conditions and a 24% improvement at peak operating conditions, and the system efficiency is improved by 24% and 43% at rated and peak operating conditions, respectively. In addition, the minimum value of system efficiency is observed to be 54%, and there is a notable attenuation of the concentration polarization phenomenon. This approach contributes to mitigating the challenge of lower system efficiency in normal PEMFCs for residential hydrogen energy storage systems (RHESSs) attributed to inadequate gas supply pressure.

Optimizing Reverse Osmosis Feed Spacer Design for Enhanced Dimethylphenol Removal from Wastewater: A Study of Hydrodynamics and Performance Indicators

Due to its high pollutant rejection and low energy usage, the spiral wound module of reverse osmosis (RO) process is the most commonly used technology utilised in wastewater treatment. For a spiral wound module, the presence of a feed spacer is important as a key solution to mitigate the concentration polarisation phenomenon, due to disorderly fluid flow, and to improve the mass transfer coefficient. Undoubtedly, improvements in the spiral wound module design, mainly in the symmetrical shape of the feed spacer, can have a significant impact on the cost and probable use of these modules. Despite the wide interest in appraising the impact of feed spacer geometry and orientation on the performance of a spiral wound module for RO process-based water desalination, the hydrodynamics of feed spacers (pressure drop and mass transfer coefficient) and the associated influences of feed spacer design (the height of the feed spacer, the angle of the filaments, and the porosity) on the removal of pollutants from wastewater have not yet been addressed. The current investigation aims to fill this gap by studying the hydrodynamics and design parameters of the selected parallelogram feed spacer type ultrafiltration (UF−3) for the removal of dimethylphenol from wastewater. Using model-based simulation, the impacts of UF−3 feed spacer design parameters, including the height, angle between the filaments (orientation), and porosity on the pressure drop, friction factor, axial flow fluid velocity, mass transfer coefficient, water flux, dimethylphenol rejection, recovery rate, and specific energy consumption are detailed in this study. The study intends to demonstrate the optimum design features of UF−3 feed spacer that should be considered to assure the highest elimination of dimethylphenol from wastewater in addition to the lowest specific energy consumption.

Pengolahan Limbah Cair Laundry Menggunakan Membran Ultrafiltrasi Aliran Cross Flow dengan Variasi Tekanan Transmembran dan Konsentrasi Chemical Cleaning Agent (NaOH)

Ultrafiltration membrane is one of wastewater treatment technologies, but membranes have limitations such as the occurrence of the phenomenon of concentration polarization and fouling. The research objective of this study the effect of variations in transmembrane pressure against the rejection percentage COD, TSS, and the effect of variations in transmembrane pressure, concentration of washing of the efficiency and effectiveness of washing the membrane. The process of ultrafiltration membranes and membrane chemical washing wastewater laundry do with variations in pressure of 1 bar, 2 bar, and 3 bar. Variation of chemical cleaning agent concentration of 1%, 1.5% and 2%, rinsing with distilled water for 30 minutes, filtering wastewater laundry for 120 minutes, and washing using chemical cleaning agent (NaOH) for 30 minutes. Highest rejection percentage for COD parameter 86.6% and 85.7% for TSS parameters in transmembrane pressure of 3 bar. The highest washing efficiency of the value of Flux Recovery (FR) gained 81.9%, and the value of resistance of Removal (RR) gained 82.59% with a concentration of 2% in the transmembrane pressure of 3 bar. The highest leaching effectiveness obtained at 50.21% with a concentration of 2% and a transmembrane pressure of 3 bar.

A numerical study on applying ion concentration polarization in micropump design

This work focuses on applying the phenomenon of ion concentration polarization to design and investigate a micropump model that is a kind of electroosmotic micropump. Numerical study is conducted for ion concentration polarization in the manner that generates electro-osmosis flow and pumping effect. The formation of the extended space charge layer and the actions of the electric field upon this layer is applied to generate electro-osmosis flow to drive flow in the system. It is clarified that pumping effect can be enhanced by improving the geometry configurations. Multiple simulations are conducted to obtain an optimal micropump design.

Process optimization of osmotic membrane distillation for the extraction of valuable resources from water streams

The rising demand for sustainable wastewater management and high-value resource recovery is pressing industries involved in, e.g., textiles, metals, and food production, to adopt energy-efficient and flexible liquid separation methods. The current techniques often fall short in achieving zero liquid discharge and enhancing socio-economic growth sustainably. Osmotic membrane distillation (OMD) has emerged as a low-temperature separation process designed to concentrate valuable elements and substances in dilute feed streams. The efficacy of OMD hinges on the solvent’s migration from the feed to the draw stream through a hydrophobic membrane, driven by the vapor pressure difference induced by both temperature and concentration gradients. However, the intricate interplay of heat and mass processes steering this mechanism is not yet fully comprehended or accurately modeled. In this research, we conducted a combined theoretical and experimental study to explore the capabilities and thermodynamic limitations of OMD. Under diverse operating conditions, the experimental campaign aimed to corroborate our theoretical assertions. We derived a novel equation to govern water flux based on foundational principles and introduced a streamlined version for more straightforward application. Our findings spotlight complex transport-limiting and self-adjusting mechanisms linked with temperature and concentration polarization phenomena. Compared with traditional methods like membrane distillation and osmotic dilution, which are driven by solely temperature or concentration gradients, OMD may provide improved and flexible performance in target applications. For instance, we show that OMD—if properly optimized—can achieve water vapor fluxes 50% higher than osmotic dilution. Notably, OMD operation at reduced feed temperatures can lead to energy savings ranging between 5 and 95%, owing to the use of highly concentrated draw solutions. This study underscores the potential of OMD in real-world applications, such as concentrating lithium in wastewater streams. By enhancing our fundamental understanding of OMD’s potential and constraints, we aim to broaden its adoption as a pivotal liquid separation tool, with focus on sustainable resource recovery.

Concentration polarization around polyelectrolyte-coated electrodes. Model and observations

An investigation on the phenomenon of concentration polarization (CP) in conducting porous particles is presented in this work, considering both bare and polyelectrolyte-coated particles. The conducting nature of the porous structure brings about the induction of a surface (and hence volume) charge distribution by the applied external field. The polymer charge (with its counterions from solution) is superimposed on this field-induced component. From the solution of Poisson’s equation, the concentration and potential profiles are evaluated, and from them, the concentration polarization can be calculated. The results are presented as concentration perturbation as a function of time after application of the field, both for bare and coated particles. Experiments are also performed aimed at measuring the CP using a solution of fluorescent dye (rhodamine B). From the increase or decrease of fluorescence, the concentration perturbations are observed around the particle. Importantly, depletion of concentration is observed on both sides of the particle when this is bare. In contrast, if the particles are coated, the classical pattern of a pole of increased concentration and an opposite one of decreased concentration is found. Dielectric dispersion experiments in suspensions of bare and brush-coated particles confirm this fact.

Modeling non-linear ion transport phenomena in ion-selective membranes: Three simplified models

In electromembrane processes employing the ion concentration polarization phenomenon, such as electrodialysis (ED), ion concentration polarization (ICP) desalination, and reverse electrodialysis, the ion-selective membrane (ISM) has been modeled with an assumption of an ideal ISM permits only the passage of counter-ions with all the co-ions blocked. However, in the works that study the effects of co-ion flux on the response of system, this assumption has been questioned about the adequate answer to the simulation of the characteristic properties of the membrane. In this work, we evaluate the three models which are used widely in modeling ISM including surface-charged, space-charged and nanochannel array model. The results show that the nanochannel array and space-charged models, the alternative model for the model ISM in the case of the studies which consider the effects of co-ion leakage on the performance of the system, sufficiently mimic the key characteristic of the membrane. Their current–voltage response (I-V) curve conforms to a typical one, yet they differ due to the varying co-ion fluxes. The nanochannel array model, which is the direct model of the actual ISM, closely mimics the seed electroconvection vortices near the membrane, which does not appear in the surface-charged and space-charged model. This model is computationally expensive because of resolving the nonlinearity of the variables near the entrance of nanochannels, so it is not the appropriate model to employ in a study that considers the micrometer or millimeter order scale system. Finally, the space-charged model is more appropriate to mimic the ISM but requires more careful consideration of the simplification condition. By investigating the volume charge density of the membrane in the space-charged model, we suggest a value that brings the most similar I-V curve to that of the nanochannel array model.

Control strategy and verification of reducing battery polarization characteristics to improve unmanned aerial vehicles endurance

This study focuses on extending the duration of unmanned aerial vehicles (UAVs) by improving their power systems and introduces an extended endurance system (EES) for UAVs using a combination of lithium-ion batteries (LiBs) and lithium-ion capacitors (LiCs). Subsequently, a novel control strategy is proposed within the EES to enhance the UAV's endurance by improving the LiB's utilization. The EES control strategy incorporates the Lic's utilization to supplement the load with additional energy once the LiB is depleted. This implementation extends the flight duration and surpasses the duration extension resulting from reducing the LiB concentration polarization phenomenon due to the LiC. The hardware experiment and the simulation verify the proposed EES. The results indicate that the extension of UAV's endurance brought about by LiC is limited. Notably, the extension in endurance is primarily attributed to the innovative control strategy implemented within the proposed EES. Due to the LiC, this strategy significantly enhances the LiB's utilization by mitigating the concentration polarization phenomenon associated with it. As a result, the LiB's energy (utilization%) experiences substantial increments of 16.0 %, 25.5 %, and 22.7 % during hovering, altitude variation, and loaded hovering scenarios, respectively.

A 3-dimentinal CFD model for simulation of an O2/N2 separation process using an industrial PIHF membrane module for N2 enrichment

In this research, simulation of an O2/N2 membrane separation process for N2 enrichment using an industrial polyimide hollow fiber (PIHF) membrane module was performed based on finite element method. A 3-dimensional (3D) model was used to simulate the mass transfer, convection and diffusion phenomenon in the membrane module. In order to validate the model, the simulation results were compared with the industrial process data, and good agreement was observed. The effects of feed molar flow rate, feed pressure, and molar flow rate of sweep gas stream on the N2 enrichment percentage were investigated. As discovered, the N2 enrichment percentage is improved by enhancing the feed pressure and sweep gas flow rate, while an increase in feed flow rate promotes a diminish in percentage of N2 enrichment. Besides the operational parameters, the influence of flow patterns (co-current and counter-current) and fiber length on the N2 enrichment in lumen side and gas molecules distribution in the membrane side of PIHF membrane module was investigated respectively. As the fiber length increased, the N2 enrichment percentage augments for both patterns due to membrane surface area increment in the PIHF membrane module, which the percentage of N2 enrichment in the countercurrent pattern was higher than co-current. Moreover, Concentration Polarization Index (CPI) was investigated to show the degree of polarization expansion along the PIHF membrane. The effect of feed molar flow rate on the concentration polarization index was investigated, which showed that concentration polarization phenomenon is reduced when feed molar flow rate enhances.

A numerical study of sample preconcentration using ion concentration polarization in single microfluidic channels with dual ion-selective membranes

In this work, we investigated three single straight microchannel designs for the microfluidic biomolecule concentration device, including one traditional single channel and two innovative channels. These microchannels utilized the ion concentration polarization (ICP) phenomenon to preconcentrate very dilute sample biomolecules. By numerically solving coupled equations, Nernst–Planck, Poisson, and Navier–Stokes with appropriate boundary conditions, we provide insight into the ICP phenomenon and the preconcentration mechanism. From the detailed modeling results, we clarify the influence of important working parameters, including electric potentials, the ion-selective membrane dimensions, the channel dimensions, and the ionic strength of buffer solution on the formation of ICP and the enrichment rate of the charged biomolecules. These modeling results for various working conditions of the preconcentration systems highlight the advantage of generating a stronger electric field to preconcentrate biomolecules of two innovative channel designs over the conventional one. The findings are useful tips for the design and optimization of preconcentration microfluidic devices.

Enhancing of transport parameters and antifouling properties of PVDF membranes modified with Fe3O4 nanoparticles in the process of proteins fractionation

Polyvinylidene fluoride (PVDF) possesses a broad range of applications, including membrane separation used for water and wastewater treatment. However, the natural hydrophobic character of PVDF causes fouling problems which limit the applicability of this material. For that reason, various experimental protocols focused on the PVDF modification are in the spotlight of the recent research.This work focuses on PVDF membranes, modified with iron (II, III) oxide nanoparticles (NPs). The structural and morphological properties of membrane materials have been evaluated using FTIR, SEM, SEM-EDX, AFM, and contact angle (CA) measurements. The modified membrane demonstrated improved hydrophilicity as the contact angle value decreased from 68°± 2° to 51°± 2°. Transport parameters of the obtained membranes were investigated during the dead-end ultrafiltration (UF) process. Compared to the pristine PVDF membrane, the mass transport coefficient of the modified membrane increased twice owing to the ability of Fe3O4 to move in a magnetic field, which allowed to enhance transport parameters and reduce the fouling and concentration polarization phenomena. The modification process improved pure water permeability from 45 L·m−2·h−1·bar−1 for a pristine PVDF membrane to 72 L·m−2·h−1·bar−1 for PVDF with immobilized Fe3O4 NPs. The appropriateness of magnetically active membrane materials in UF of various proteins was also discussed in terms of protein separation and fractionation. The developed magnetoactive PVDF membrane can be used in the process of proteins fractionation owing to its property to prevent the accumulation of lysozyme on the membrane surface at the alkaline medium: the rejection of lysozyme was only 5.3 % at the pH equal to 12.

Forward-Reverse Osmosis Processes for Oily Wastewater Treatment

In this study, the feasibility of Forward–Reverse osmosis processes was investigated for treating the oily wastewater. The first stage was applied forward osmosis process to recover pure water from oily wastewater. Sodium chloride (NaCl) and magnesium chloride (MgCl2) salts were used as draw solutions and the membrane that was used in forward osmosis (FO) process was cellulose triacetate (CTA) membrane. The operating parameters studied were: draw solution concentrations (0.25 – 0.75 M), oil concentration in feed solution (FS) (100-1000 ppm), the temperature of FS and draw solution (DS) (30 - 45 °C), pH of FS (4-10) and the flow rate of both DS and FS (20 - 60 l/h). It was found that the water flux and oil concentration in FS increase by increasing the concentration of draw solutions, the flow rate of FS and the temperature for a limit (40oC), then, the water flux and oil concentration decrease with increasing the temperature because of happening the internal concentration polarization phenomenon. By increasing the oil concentration in FS and the flow rate of the DS, the water flux and oil concentration in FS decreased, while it had a fluctuated behavior with increasing pHof oily wastewater. It was found also that MgCl2 gives water flux higher than NaCl. So the values of resistance to solute diffusion within the membrane porous support layer were 55.93 h/m and 26.21 h/m for NaCl and MgCl2 respectively. The second stage was applied reverse osmosis process using polyamide (thin film composite (TFC)) membrane for separating the fresh water from a diluted (NaCl) solution using different parameters such as draw solution concentration (0.08–0.16 M), feed flow rate (20–40 l/h).

Evaluation of the relevant mass and heat transfer phenomena in a packed bed membrane reactor for the direct conversion of CO2 to dimethyl ether

This study investigates the relevant heat and mass transfer phenomena occurring at the different scales in a packed bed (membrane) reactor for the direct conversion of CO2 to dimethyl ether (DME) via the implementation of 2D heterogeneous reactor models. Intra-particle diffusion limitations were found to be relevant for particle diameters larger than 1 mm and temperature above 220 ⁰C, such that the catalyst efficiency drops down to 50% and 5% for the Cu/ZnO/Al2O3 and the HZSM-5, respectively, in the most critical conditions (i.e., 270 ⁰C and Dp of 10 mm). A component-specific Thiele modulus-efficiency correlation was developed based on the results of the rigorous particle model to account for pore-diffusion limitations without having to solve a complex heterogeneous reactor model. This correlation shows the typical behavior reported in literature for power law kinetics and accurately predicts the reaction performance with deviation of less than 5% for values of the Thiele modulus lower than 2. In the packed bed membrane reactor (PBMR), the concentration polarization (CP) also showed to affect the reactor performance. The concentration of water at the surface of the membrane selective layer was found to be up to 64% lower than the concentration in the bulk phase, hindering the effectiveness of the membrane separation. To account for this phenomenon via a simplified approach, a Sherwood-type correlation was developed to determine a CP mass transfer coefficient, based on the results obtained via the rigorous 2D PBMR model. Such correlation showed to predict with high accuracy (i.e., errors lower than 5%) the effect of the CP on the PBMR performance. Differently from the pore diffusion and CP phenomena, the intra-particle heat transfer, the particle–fluid mass and heat transfer as well as the axial dispersion were found to have a negligible effect on the reactor behavior. Finally, given the relevant mass/heat transfer phenomena, this study proposes further reactor optimization strategies, such as the reduction of the zeolite loading in the bifunctional catalyst bed by ca. 90% with respect to what is reported in literature.

Modeling and optimization of salt and boron removal in reverse osmosis system

Seawater reverse osmosis (SWRO) is a mature technology that has significantly evolved over the past few decades. However, boron removal remains a serious challenge. A new RO transport model was developed by combining the irreversible thermodynamic theory and solution-diffusion theory and considering the solute concentration polarization phenomenon. The developed RO model supplemented by the use of variable solution properties and transport parameters was validated with existing data and, it was then applied to identify the main operation parameters and assess their effect on SWRO performance, with the aim of minimizing specific energy consumption and satisfying water quality requirements. The results showed that the solution-diffusion approach, cannot capture the interaction between transported boron and water species. For high pH, applied feed pressure, and flow rate, the convective transport of boron through the seawater membrane is remarkable and its contribution to the overall boron flux can reach over 20 %. The feed operating conditions have significantly influenced the quality of the water production and the amount of energy used. The results showed that the optimal SEC increased by approximately 40 %, and the recovery ratio decreased by 11.6 % as the feed flow rate increased from 0.002 to 0.005 m3/s.

Predicting Water Flux in Forward Osmosis with Unknown Feed Solution Composition: An Empirical Approach Based on Thermodynamical Properties

This study investigated the predictability of forward osmosis (FO) performance with an unknown feed solution composition, which is important in industrial applications where process solutions are concentrated but their composition is unknown. A fit function of the unknown solution's osmotic pressure was created, correlating it with the recovery rate, limited by solubility. The osmotic concentration was derived and used in the subsequent simulation of the permeate flux in the considered FO membrane. For comparison, magnesium chloride and magnesium sulfate solutions were used since these show a particularly strong deviation from the ideal osmotic pressure according to Van't Hoff and are, thus, characterized by an osmotic coefficient unequal to 1. The simulation is based on the solution-diffusion model with consideration of external and internal concentration polarization phenomena. Here, a membrane module was subdivided into 25 segments of equal membrane area, and the module performance was solved by a numerical differential. Experiments in a laboratory scale for validation confirmed that the simulation gave satisfactory results. The recovery rate in the experimental run could be described for both solutions with a relative error of less than 5%, while the calculated water flux as a mathematical derivative of the recovery rate showed a bigger deviation.

Estrogen adsorption from an aqueous solution on the chitosan nanoparticles

In this research, chitosan nanoparticles as an efficient and reusable adsorbent with adsorption capacity of 5.79 mg/g, surface area of 62 m2/g and pHpzc of 8.07 were applied to remove the ethinylestradiol (as a sample of estrogen) from an aqueous wastewater. The chitosan nanoparticles were characterized by SEM, XRD and FT-IR analyses. Four independent variables involving contact time, adsorbent dosage, pH, and initial concentration of estrogen were applied to design the experiments by Design Expert software (CCD under RSM). In fact, number of experiments was minimized and the operating conditions were optimized for the maximum estrogen removal. The results indicated that three independent variables (contact time, adsorbent dosage, and pH) increment increased the estrogen removal while the estrogen initial concentration enhancement decreased the removal due to the concentration polarization phenomenon. The optimum conditions for the estrogen removal (92.50 %) on the chitosan nanoparticles were found at contact time of 220 min, adsorbent dosage of 1.45 g/l, pH of 7.3 and estrogen initial concentration of 5.7 mg/l. Moreover, the Langmuir isotherm and pseudo-second order models could properly legitimize estrogen adsorption process on the chitosan nanoparticles.

A novel Solution-Diffusion-Flory-Rehner model to predict flux behavior during forward osmosis with thermo-responsive hydrogel as draw agent

Although hydrogels as excellent draw agents have been extensively investigated, the relationship between the driving force of hydrogel and mass transfer behavior during forward osmosis (FO) remains unclear. The hydrogel-driven FO requires a mass transfer model to clarify its driving mechanism, yet no model was available at present. In the current study, a water flux model driven by thermal-responsive hydrogel was first developed by coupling solution-diffusion model and Flory-Rehner model (SDFR). Considering the diffusion characteristics of hydrogel, a redefined parameter DH corresponding to water diffusion coefficient in hydrogel matrix was introduced to the SDFR model. The validity of the model and DH were verified by comparing experimental water flux data for different concentrations of feed solution with the corresponding simulating results from SDFR model. The SDFR model successfully predicted the flux behavior of FO under wide varieties of operating conditions. Furthermore, the existence of internal concentration polarization phenomenon in hydrogel-driven FO was unveiled by modeling the pressure distribution across FO membrane, and its effect on flux behavior was quantified. The SDFR model was also employed to design a novel ionic thermal-responsive hydrogel with better FO performance. The new insights gained from the SDFR model in this study will help to develop more efficient FO applications with hydrogel-based draw agents.

Computational fluid dynamics study on concentration polarization phenomena in silica membrane reactor during methanol steam reforming

In this study, the concentration polarization phenomena occurring during methanol steam reforming carried out in a silica membrane reactor were theoretically investigated using a computational fluid dynamic tool. To our best knowledge, there are no computational fluid dynamics studies applied to the investigation of the concentration polarization phenomena in silica membrane reactors. Therefore, this study represents a first step in analyzing theoretically this phenomenon in such reactors. After developing a two-dimensional model and solving their governing equations by numerical method, the validation of the theoretical results have been carried out by using experimental data published in previous works. The simulation results showed that operational conditions such as temperature, pressure, feed flow rate, and H2O/CH3OH molar ratio are effective on the concentration polarization. Moreover, the impact of the velocity profile on the concentration polarization module in the silica membrane reactor of this work was theoretically discussed. In this regard, increasing temperature and pressure from 470 to 570 K, and from 2 to 10 bar, respectively, better performance in terms of methanol conversion (from 50% to 98%, and from 88% to 91%, respectively) and H2 recovery (from 20% to 21.5%, and from 20% to 22.5%, respectively) were reached, even though it determined a more evident concentration polarization effect. This study pointed out how higher pressures determined a significant increase of the concentration polarization factor, which was responsible for the plateau trend of both conversion and hydrogen recovery above 6 bar.