Mass Transfer Effects Research Articles

MHD Casson Fluid Flow over a Stretching Surface with Suction, Double Stratification, and Heat and Mass Transfer Effects

Abstract In this article, we investigated the flow of a magnetohydrodynamic Casson fluid across an extending surface with exponential permeability in a double-stratified medium. Thermal radiation, suction, heat sources, viscous dissipation, and chemical reactions drive the stream field. We converted the flow describing partial differential equations into terms of ordinary differential equations by applying appropriate transformations. Next, we utilised the bvp4c package in Matlab to obtain numerical solutions for these equations. We explored and graphically showed the implications of different non-dimensional governing parameters for temperature, concentration, and velocity profiles. After analysis, we provide a tabular presentation of the friction factor, Nusselt, and Sherwood numbers. The Casson fluid temperature shows a rising trend for the solutal stratification parameter and a decreasing trend for the thermal stratification parameter, while the Casson fluid velocity shows a declining trend towards both of these parameters. The Casson fluid concentration also behaves differently depending on the stratification parameter; for example, it increases for thermal stratification and decreases for solutal stratification. We notice that an increase in the Casson parameter's value suppresses the velocity field. However, as the Casson parameter increases, both the temperature and the concentration improve. Furthermore, comparisons with previously published findings also support the current results. \sethlcolor{yellow}\hl{The study of MHD Casson fluid flow that includes suction, dual stratification, and the effects of heat and mass transfer is very useful in many areas, such as polymer processing, metallurgical engineering, biomedical applications, environmental sciences, and advanced cooling technologies.

Deep Eutectic Solvent and Molten Salt-Assisted Construction of Wheat Straw-Derived N/O Co-Doped Porous Carbon for Flexible Zinc-Air Batteries.

As a common biomass resource, wheat straw is gradually being derived as carbon materials for oxygen reduction reaction (ORR) in zinc-air batteries (ZABs). Herein, the wheat straw-derived carbon was prepared by ball milling and pyrolysis using deep eutectic solvent (DES) as the medium, which avoided the cumbersome procedures. The hydrogen bond of DES was utilized to reconstructed into a hydrogen bond network structure between DES and lignin/cellulose/hemicellulose of wheat straw. The hydrogen bond network structure was converted into N/O co-doped porous carbon (N/O-WSPC) with abundant N/O co-doped sites after high-temperature pyrolysis. Meanwhile, KHCO3 was employed to further generate hierarchical pore structures and increase the specific surface area of the N/O-WSPC. The N/O co-doped sites provided intrinsic ORR activity, while the porous structure facilitates the mass transfer effect. Therefore, the N/O-WSPC exhibited a half-wave potential of 0.87 V (vs. RHE) and a limiting current density of 5.98 mA cm-2 for ORR. The N/O-WSPC-based flexible ZAB displayed an energy density of 652.23 Wh kg-1 and a charging-discharging cycle duration for over 19 h. The DES-assisted strategy facilitates the sustainable and efficient application of wheat straw-derived carbon materials in energy storage and conversion devices.

Differentiation of adsorption and degradation in steroid hormone micropollutants removal using electrochemical carbon nanotube membrane

The growing concern over micropollutants in aquatic ecosystems motivates the development of electrochemical membrane reactors (EMRs) as a sustainable water treatment solution. Nevertheless, the intricate interplay among adsorption/desorption, electrochemical reactions, and byproduct formation within EMR complicates the understanding of their mechanisms. Herein, the degradation of micropollutants using an EMR equipped with carbon nanotube membrane are investigated, employing isotope-labeled steroid hormone micropollutant. The integration of high-performance liquid chromatography with a flow scintillator analyzer and liquid scintillation counting techniques allows to differentiate hormone removal by concurrent adsorption and degradation. Pre-adsorption of hormone is found not to limit its subsequent degradation, attributed to the rapid adsorption kinetics and effective mass transfer of EMR. This analytical approach facilitates determining the limiting factors affecting the hormone degradation under variable conditions. Increasing the voltage from 0.6 to 1.2 V causes the degradation dynamics to transition from being controlled by electron transfer rates to an adsorption-rate-limited regime. These findings unravels some underlying mechanisms of EMR, providing valuable insights for designing electrochemical strategies for micropollutant control.

Kinetics of hydrothermal reactions of n-butanol over Pt/Al2O3 catalyst for biopropane fuel gas production

Energy defossilisation using drop-in biofuels is an important step towards Net Zero. Producing low-carbon clean-burning propane fuel from biomass provides such additional sustainability benefits. In this work, kinetics of hydrothermal reactions of n-butanol, a biomass-derived feedstock, to produce propane over 5 wt% Pt/Al2O3 catalyst have been studied from 523- 573 K. Experimental data revealed negligible internal and external mass transfer effects and, when fitted to an integral power-rate law equation, gave activation energy of 70 kJ mol−1 (n-butanol reaction order = 1). Furthermore, an appropriate Langmuir-Hinshelwood model was developed, which predicted similar activation energy 62 kJ mol−1. Low adsorption enthalpies for n-butanol (–33.51 kJ mol−1) and water (−18.16 kJ mol−1) indicated weak interactions on the catalyst surface. These agreed with the fast reaction rate of ≈1.0 x 10-5 mol gcat-1 s−1 obtained at ≥ 548 K. As a new research area, generation of such accurate kinetics data will contribute to process development for large-scale biopropane production.

Progress in the Effect of Mass Transfer in the Lacunar-Canalicular System on Aging Osteoporosis

Progress in the Effect of Mass Transfer in the Lacunar-Canalicular System on Aging Osteoporosis

Five definitions of adsorption and their relevance to the formulation of dynamic mass balances in gas adsorption columns

Numerous dynamic mass balances in the literature that describe the adsorption of gases in a column are written in terms of actual or absolute adsorption, while unwittingly and incorrectly utilizing excess adsorption isotherms. Perhaps this is because the actual and absolute adsorption isotherms cannot be experimentally measured nor predicted without making uncertain assumptions. The objective here was to derive unambiguous relationships between actual, absolute, excess, net and column amounts adsorbed that provide a straightforward understanding of the subtle differences between these quantities and that provide a simple means for incorporating them into dynamic mass balances. For this purpose, the actual, absolute, excess, net and column amounts adsorbed (loadings) were clearly defined, along with various volumes, porosities and densities that exist inside and outside an adsorbent contained in a column with a gaseous adsorbate. These adsorption definitions and quantities were used to derive four interconversion relationships for each type of adsorption in terms of the actual loading. The resulting expressions, based on intensive properties, can be used to relate any adsorption definition to any other adsorption definition. These relationships were also used to derive five dynamic mass balances, one for each type of adsorption. The similarities and differences in the terms between each of these five dynamic mass balances were discussed, along with their applicability to real world problems. In some cases at low pressure where the isotherms do not differ appreciably, it may be approximately correct to use excess or net adsorption isotherms in a dynamic mass balance written in terms of actual or absolute adsorption. However, the extent of the incorrectness is unknown due to mass transfer effects. So, it is recommended to use the dynamic mass balance with its specific type of adsorption, most likely excess adsorption. Then, when certain assumptions are made about the adsorbing and non-adsorbing void fractions, these expressions can be readily used in adsorption process simulation.

Flexible Hybrid Membrane with Synergistic Exciton Dynamics for Excessive 280 h of Durably Piezo-Photocatalytic H2O-to-H2 Conversion.

Solar-driven H2O-to-H2 conversion is a feasible artificial photoconversion technology for clean energy production. However, low photon utilization efficiency has become a major obstacle limiting the practical application of this technology. Herein, a metal atomic replacement (Sb→Ni) is conducted to disintegrate bulk Sb2S3 nanorods and synchronously grow the NiS nanolayers, and a flower-like Sb2S3-NiS nanocomposite with high BET specific surface area and synergistic exciton dynamics is constructed for simulated solar (SSL)-driven H2O-to-H2 conversion. The optimal Sb2S3-NiS nanocomposite is compounded with polyvinylidene fluoride (PVDF) to prepare a flexible PVDF/Sb2S3-NiS (PSN) hybrid membrane with stable structure and excellent recyclability via an electrospinning method. Due to the synergistically interacted organic-inorganic interface and high porosity, it is conducive to the exposure of effective active sites, exciton conduction and mass transfer and exchange, thereby an outstanding alkaline (Ph=13.0) H2O-to-H2 conversion activity with a 0.06% of solar-to-hydrogen efficiency and over 280 h (70 cycles) of durable recycling is achieved under the collaborative drives of SSL and weak ultrasound (40 Hz). This study raises a state-of-the-art membrane material for solar-driven panel reaction technology.

Heat and mass transfer analysis on peristaltic transport of PTT fluid with wall properties

The current study is intended to examine the effect of heat and mass transfer on the peristaltic propulsion of the Pan-Thien-Tanner fluid in a cylindrical tube with wall properties. The complexity of the system is reduced by long wavelength and low Reynolds number strategy. The physical behavior of the peristaltic motion of the PTT fluid is explained and elucidated graphically for several values of various parameters connected with this flow problem. It has been revealed that raising the Source/Sink parameter values and the Weissenberg number results in a higher velocity profile. The outcomes embrace the key to understanding the human organs' physiological fluid motion, such as the chime moment in the small intestine and esophagus.

Application of a Film Model to Mass Transfer and Chemical Reaction at a Plasma-Liquid Interface

Abstract Plasma electrodes provide novel ways of conducting electrochemical processes in liquids, in particular because of the ability to generate unique reactive radical species. However, the radicals injected into the liquid and their ensuing reactions are often confined to a narrow region near the interface of the plasma and the liquid. Thus, mass transfer has been found to play an important role in the observed kinetics and a modeling framework that includes both transport and kinetics is required to interpret experimental data. Here, we apply the idea of a film model for interphase mass transfer to plasma-liquid electrochemical processes, whereby transport is described by a stagnant film that is inherently linked to the concentration boundary layer and the mass transfer coefficient. Equations that govern the transport and reaction of radicals and substrates within the film are solved assuming a quasi-steady state approximation. The model is applied to specific case studies from the literature to estimate important parameters that cannot easily be measured in experiments, such as the mass transfer coefficient. Our study shows that a film model can elucidate the effect of mass transfer on observed conversion rates and allow the intrinsic kinetics to be unraveled.

Heat and mass transfer effects on an unsteady MHD boundary layer flow of fractionalized fluid

This research investigates the transient magnetohydrodynamic (MHD) flow of a non-integer Maxwell fluid over a vertical plate, taking into account the effect of diffusion-thermo and parameter of heat absorption. The fractional derivative Caputo-Fabrizio is employed to model the problem. Using the Laplace integral transform technique, we solve the dimensionless governing equations to obtain the profiles of velocity, concentration, and temperature, which are then presented in graphical form for easy comparison and interpretation. The influence of several parameters—specifically, the fractional parameter and heat absorption is thoroughly analyzed and illustrated through a series of graphical representations. Furthermore, a comparison between traditional as well as fractionalized velocity fields is provided. The results show that chemical reactions and magnetic fields reduce the velocity profile, while diffusion-thermo and mass Grashof number increase the fluid velocity.

Novel stationary basket reactor for effective biomass delignification with deep eutectic solvent

Biomass pretreatment and conversion are crucial for sustainable development, but lack information on equipment that ensures effective mass transfer and easy biomass separation post-process. This work introduces a novel basket reactor with a stationary bed (StatBioChem) for biomass processing using deep eutectic solvents (DESs). We compared the delignification efficiencies of soft and hard biomass samples processed in the StatBioChem reactor, a stirred tank reactor (STR), and a commercial SpinChem® reactor. The StatBioChem design allowed DES to flow evenly through biomass in the basket, achieving the highest delignification degree, particularly for hard biomass. This effect was not observed in the SpinChem® basket reactor. High delignification led to increased glucose yields in subsequent enzymatic hydrolysis. The StatBioChem effectively combines the simplicity and efficiency of an STR with the ease of solvent recovery typical of basket reactors.

Highly Dispersed Pd‐CeOx Nanoparticles in Zeolite Nanosheets for Efficient CO2‐Mediated Hydrogen Storage and Release

AbstractFormic acid (FA) dehydrogenation and CO2 hydrogenation to FA/formate represent promising methodologies for the efficient and clean storage and release of hydrogen, forming a CO2‐neutral energy cycle. Here, we report the synthesis of highly dispersed and stable bimetallic Pd‐based nanoparticles, immobilized on self‐pillared silicalite‐1 (SP‐S‐1) zeolite nanosheets using an incipient wetness co‐impregnation technique. Owing to the highly accessible active sites, effective mass transfer, exceptional hydrophilicity, and the synergistic effect of the bimetallic species, the optimized PdCe0.2/SP‐S‐1 catalyst demonstrated unparalleled catalytic performance in both FA dehydrogenation and CO2 hydrogenation to formate. Remarkably, it achieved a hydrogen generation rate of 5974 molH2 molPd−1 h−1 and a formate production rate of 536 molformate molPd−1 h−1 at 50 °C, surpassing most previously reported heterogeneous catalysts under similar conditions. Density functional theory calculations reveal that the interfacial effect between Pd and cerium oxide clusters substantially reduces the activation barriers for both reactions, thereby increasing the catalytic performance. Our research not only showcases a compelling application of zeolite nanosheet‐supported bimetallic nanocatalysts in CO2‐mediated hydrogen storage and release but also contributes valuable insights towards the development of safe, efficient, and sustainable hydrogen technologies.

Highly Dispersed Pd-CeOx Nanoparticles in Zeolite Nanosheets for Efficient CO2-Mediated Hydrogen Storage and Release.

Formic acid (FA) dehydrogenation and CO2 hydrogenation to FA/formate represent promising methodologies for the efficient and clean storage and release of hydrogen, forming a CO2-neutral energy cycle. Here, we report the synthesis of highly dispersed and stable bimetallic Pd-based nanoparticles, immobilized on self-pillared silicalite-1 (SP-S-1) zeolite nanosheets using an incipient wetness co-impregnation technique. Owing to the highly accessible active sites, effective mass transfer, exceptional hydrophilicity, and the synergistic effect of the bimetallic species, the optimized PdCe0.2/SP-S-1 catalyst demonstrated unparalleled catalytic performance in both FA dehydrogenation and CO2 hydrogenation to formate. Remarkably, it achieved a hydrogen generation rate of 5974 molH2 molPd -1 h-1 and a formate production rate of 536 molformate molPd -1 h-1 at 50 °C, surpassing most previously reported heterogeneous catalysts under similar conditions. Density functional theory calculations reveal that the interfacial effect between Pd and cerium oxide clusters substantially reduces the activation barriers for both reactions, thereby increasing the catalytic performance. Our research not only showcases a compelling application of zeolite nanosheet-supported bimetallic nanocatalysts in CO2-mediated hydrogen storage and release but also contributes valuable insights towards the development of safe, efficient, and sustainable hydrogen technologies.

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.

Effect of multi-component gas on removal of trace hydrogen sulfide activity from blast furnace gas using activated carbon adsorbent

Abstract In the steel industry, blast furnace gas (BFG) is huge with complex components. The existence of hydrogen sulfide (H2S) in the BFG can produce sulfur dioxide (SO2) after combustion, which will increase the source of SO2 pollution and make the desulphurization more difficult, to be threat to people health. At present, the removal of H2S by dry adsorption with modified activated carbon adsorbent is a high-precision and low-cost desulphurization method. However, the effect of complex gas components in BFG on the adsorption of H2S by activated carbon adsorbent is not sufficient. Based on the fixed bed adsorbent evaluation system, a new type of highly efficient copper-cerium oxide (Cu–Ce–O) modified activated carbon H2S adsorbent was developed. And the effects of carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), oxygen (O2), sulfur dioxide and hydrogen chloride (HCl) in BFG on the desulfurization activity of adsorbents were investigated. The results showed that the performance of H2S removal decreased in the presence of CO, CO2, HCl and SO2, and improved in the presence of H2 and O2. Other parameters were also studied which might influence the process. The application of modified activated carbon adsorbent in simulated BFG is basically stable. According to the fitting results of adsorption kinetics for the five adsorption models, as the atmosphere becomes BFG from N2, pore diffusion becomes the main adsorption form. However, the effects of internal diffusion, chemical adsorption and external mass transfer decreased. The Bangham model is the most suitable model to describe H2S adsorption process.

Vacancies engineering in ultrathin porous g-C3N4 tubes for enhanced photocatalytic PMS activation for imidacloprid degradation

Precise morphology and vacancy engineering is a promising strategy to enhance the degradation performance of refractory contaminants in photocatalysis coupling peroxymonosulfate activation (PC-PMS) systems. In this context, we developed ultrathin porous g-C3N4 tubes with three-coordinated nitrogen (Nb) vacancies between the heptazine units through hydrogen intercalated exfoliation and selective nitrogen removal at high temperatures. The ultrathin porous tubular architecture provides an ultrahigh-specific surface area with abundant exposed active sites, ensures effective mass transfer, and shortens the diffusion distance of photogenerated carriers. The Nb vacancies act as unsaturated sites, inhibiting the photogenerated carrier’s recombination and facilitating the adsorption/activation of O2 and its conversion to ∙O2– via photogenerated electrons. Then, the PMS is subsequently oxidated by photogenerated holes selectively producing 1O2. Together, these continuously released free radicals unlock the complete degradation of imidacloprid within 20 min in the PC-PMS system, with a degradation rate about 350 % higher than conventional g-C3N4 tubes and 10-fold that of pristine g-C3N4. This study provides a novel insight into the efficient utilization of photogenerated electron-hole pairs conversion to ∙O2– and 1O2 for the removal of pesticide contaminants through the rational design of photocatalysts in the PC-PMS system.

Efficient numerical modeling of time-fractal tangent hyperbolic fluid flow with heat and mass transfer

This paper introduces a precise method for solving time-fractal parabolic equations specifically designed to represent complex physical phenomena using fractal calculus. The suggested technique attains third-order accuracy by utilizing the fractal Taylor series and implements a concise scheme for spatial discretization. Stability and convergence analyses are offered for scalar and system fractal parabolic equations. The mathematical model analyzes fluid flow over both flat and oscillatory surfaces, considering the effects of heat and mass transfer. This involves transforming the governing equations into dimensionless partial differential equations, which are then solved using the suggested method. From the calculated results, it can be verified that the proposed scheme produces less error than the existing two schemes. This study enhances computational techniques for fractal calculus and introduces novel opportunities for comprehending non-Newtonian fluids in diverse physical contexts.

Effect of heat and bubble mass transfer on the efficiency of alkaline electrolysis hydrogen production

Effect of heat and bubble mass transfer on the efficiency of alkaline electrolysis hydrogen production

Enhancing performance and durability of PVDF-ceramic composite membranes in microbial fuel cells using natural rhamnolipids

Ceramic membranes are widely used in microbial fuel cells (MFCs) owing to their cost-effectiveness and availability. However, these membranes often face challenges such as biofouling and negative mass-transfer effects. This study explored the use of a polymer layer to mitigate these issues, focusing on a polyvinylidene fluoride (PVDF) nanofibre membrane with various surface modifications. The modifications included alkaline treatment (PVDF-OH), rhamnolipids treatment (PVDF/BS), and a combination of both (PVDF-OH/BS). The ceramic membrane integrated with PVDF-OH/BS achieved the highest power density of 13.8 W m−3, which was 38 % higher than that of the unmodified ceramic membrane. Additionally, during the long-term study (days 90–101), the Ceramic + PVDF-OH/BS maintained a 64 % higher power performance compared to the unmodified ceramic membrane, indicating superior antifouling properties. Electrochemical and surface characterisation revealed that rhamnolipid-modified PVDF nanofibers enhanced fouling resistance. The findings demonstrate that natural biosurfactants which can be produced in situ within MFCs, can form a protective layer over membranes and significantly enhance their long-term power performance. This study represents the first instance of using natural microbial biosurfactants to improve membrane efficiency in a bioelectrochemical system.

Effect of fluid direction and reactor structure on heat storage performance of Ca(OH)2/CaO based on shell-tube thermochemical energy storage device

The flow direction of the heat transfer fluid (HTF) and reactor structure inside the shell-tube heat exchanger has a significant impact on the heat transfer performance of the shell-tube reaction device. In this study, a comprehensive 3D multi-physics coupled model of a shell-tube fixed bed thermochemical energy storage (TCES) device is developed. The investigation delves into the influence of HTF flow direction and reactor structural design on a plethora of critical parameters including temperature distribution, steam pressure distribution, reaction extent, reaction time, heat transfer power, heat transfer efficiency, and heat storage efficiency within the reactor. The result indicates that the flow direction of HTF has an impact on the homogeneity of the reaction in the tube, and the countercurrent and concurrent flow can realize the gradient and homogeneous occurrence of the reaction in the tube, respectively. Both lessening the outer diameter of the device and increasing the diameter of the heat storage material filling tube can improve the average heat exchange efficiency and the average heat storage efficiency. Compared with the basic case (Basic case A), the optimized (Case D) heat storage device volume decreased by 13.38 %, the energy stored amount increased by 24.14 %, heat storage time shortened by 8.04 %, and heat storage efficiency increased by 32.14 %. Additionally, the inlet temperature and velocity still have an obvious influence on the thermal performance of the reactor after structural optimization. These research findings guide for improving the heat and mass transfer effect and working performance of the shell-tube fixed bed Ca(OH)2/CaO reactor.