Mass Transport Research Articles

Inward motion of diamond nanoparticles inside an iron crystal

In the absence of externally applied mechanical loading, it would seem counterintuitive that a solid particle sitting on the surface of another solid could not only sink into the latter, but also continue its rigid-body motion towards the interior, reaching a depth as distant as thousands of times the particle diameter. Here, we demonstrate such a case using in situ microscopic as well as bulk experiments, in which diamond nanoparticles ~100 nm in size move into iron up to millimeter depth, at a temperature about half of the melting point of iron. Each diamond nanoparticle is nudged as a whole, in a displacive motion towards the iron interior, due to a local stress induced by the accumulation of iron atoms diffusing around the particle via a short and easy interfacial channel. Our discovery underscores an unusual mass transport mode in solids, in addition to the familiar diffusion of individual atoms.

Kebijakan Trans Metro Deli sebagai Upaya Meningkatkan Layanan Transportasi Umum di Kota Medan

The Trans Metro Deli policy in Medan City is an effort to improve public transportation services. First, this policy provides an integrated and efficient mass transportation system through a special bus network with routes that cross strategic points in the city of Medan. Second, the adoption of information technology in the operational management of Trans Metro Deli allows users to obtain the latest information regarding bus schedules, routes and conditions in real-time, increasing reliability and user comfort. Apart from that, implementing affordable fares is also an important point in this policy, expanding transportation accessibility for people from various economic layers. Third, the Trans Metro Deli policy also prioritizes safety and security aspects in the use of public transportation by establishing operational standards and strict supervision of the bus fleet and personnel. This has a positive impact on public perception and trust in the service. Furthermore, efforts to improve infrastructure including the development of special bus stops and lanes are also an important part of this policy, ensuring accessibility and efficiency in daily operations. In conclusion, the Trans Metro Deli policy in Medan City is a significant step in improving public transportation services by integrating various aspects such as operational efficiency, use of technology, safety, comfort and accessibility. In this way, it is hoped that it can have a broad positive impact on the mobility and quality of life of city residents.

Critical role of transport phenomena in the performance of a catalytic fixed bed reactor for the CO2 hydrogenation to CH4 evaluated by modeling and simulation

CO2 hydrogenation with renewable hydrogen enables the production of CH4 to be used as energy carrier (CO2 + 4H2 ⇆ CH4 + 2H2O). Steady state 1D pseudo-homogeneous and heterogeneous models, in the absence or presence of mass and energy transport in the axial direction of the reactor and inside the solid phase, are considered to simulate a non-isothermal fix bed reactor. Numerical strategies for solving these models in Matlab R2022b are discussed. The pseudo-homogeneous plug-flow model is not able to describe the experimental results irrespective of the global heat transfer coefficient considered. The inclusion of mass and energy transport in the reactor axial direction is crucial for describing the experimental data. The inclusion of mass and heat transport inside the solid phase by the heterogeneous model enables the best fitting. This work provides a valuable modeling tool for future industrial-scale reactor design.

Artificial neural computing and statistical analysis of heat and mass transport of nanofluid flow with melting heat and thermal stratification

The melting heat phenomenon in viscous nanofluid MHD flow over a stretching sheet with variable porosity and permeability was utilized. The behavior of magneto-viscous nanofluid flow was scrutinized using the concepts of machine learning and statistics. Thermal stratification, heat source, and activation energy in the solution of tween-20 nanoparticles and an ethyl-acetate base-type fluid are examined. Brownian and thermophoretic phenomena are included. Non-linear partial differential equations (PDEs) are converted into non-linear ordinary differential equations (ODEs) via von Karman similarity variables. Dataset is generated by the 4th-order Runge-Kutta numerical method for the artificial neural network. The ratio parameter and melting parameter enhance the velocity outline, while the melting parameter and thermal stratification parameter reduce the temperature outline. An increase in the concentration outline is seen with the activation energy parameter and Brownian motion parameter both increase the concentration outline. The system's performance using metrics like regression analysis, mean squared error, and error histograms is evaluated. The impact of these factors on significant results, such as the drag coefficient and heat transfer rate, is statistically investigated using multiple linear regressions. The integration of statistical and machine learning methods is deemed crucial for enhancing understanding of complex fluid dynamics in magnetic nanofluid flows.

Linker-induced hollow MOF embedded into arginine-modified montmorillonite for efficient urea removal: Adsorption behavior and mechanism analysis

The precise regulation of hollow metal–organic framework (HMOF) and the effective assembly with excellent guest materials present limitless potential for pollutant removal. In this work, the arginine-modified montmorillonite (AMMT) was preferentially prepared via room temperature impregnation approach, and then the AMMT-HMOF composite was effectively constructed through a one-pot method. During this process, linker-induced MOF to MOF route was proposed, i.e., solid ZIF-67 transformed into hollow MOF-74 (thicknesses: ∼25 nm). Of note, this route involves the transition from solid to hollow structures, as well as the change between different topologies. Next, the AMMT-HMOF composite was evaluated for adsorption experiments with urea in aqueous solution as the target molecule. Further speaking, the optimization experiments were conducted to analyze the impact of pH, contact time, adsorbent mass and original urea concentration towards the adsorption process. The as-fabricated absorbent presented a maximum adsorption capacity of 298.5 mg/g within 1 h, demonstrating adherence to pseudo-second-order kinetics and the Langmuir model. The excellent adsorption performance can be ascribed to the enlarged layer spacing of AMMT, as well as the fast mass transport and abundant diffusion channels in HMOF. Additionally, the mechanistic analyses revealed the existence of hydrogen bonding interactions between the adsorbent and urea. Meanwhile, the adsorbent displayed the outstanding morphological and structural stability after usage. According to our survey, this is the first time to use this linker-induced MOF-to-MOF strategy and predictably assemble with functionalized montmorillonite to construct the hollow MOF composite for urea adsorption.

On the support of measures with fixed marginals with applications in optimal mass transportation

On the support of measures with fixed marginals with applications in optimal mass transportation

Implications of homogeneous–heterogeneous reactions, Hall current, and dissipative radiative heat transfer on MHD Casson fluid flow over a bi-directional stretching sheet

This consideration highlights a numerical analysis of the unsteady three-dimensional flow of a Casson fluid over a stretching surface extending in its plane considering the effects of Hall current, thermal radiation, homogeneous–heterogeneous reactions, viscous dissipations, and an external magnetic field. The fluid flow in the region is developed due to the stretching of the sheet along the two directions in its plane. Two different species are present in the flow region which are taking part in homogeneous and heterogeneous reactions. Fluid velocity, thermal, and mass transportation are expressed mathematically using a set of nonlinear partial differential equations ( PDEs ) along with suitable boundary conditions. By using the appropriate similarity transformations, these equations ( PDEs ) that reflect the mathematical model are transformed into a set of nonlinear ordinary differential equations ( ODEs ) . The transformed equations ( ODEs ) were further solved numerically utilizing the bvp 4 c solver. The comprehensive study regarding the impacts of flow parameters on velocities, temperature, and concentration is also presented with graphs. It is observed that the thermal boundary layer is enhanced with an increment in the Hall current parameter, magnetic parameter, and thermal radiation. Moreover, with an increase in homogeneous-heterogeneous reaction parameters, mass transportation decreases. The physical quantities such as the coefficient of skin friction and coefficient of heat and mass transfer are also obtained numerically. Moreover, an appropriate agreement is obtained on comparing the current results with previously published results.

Assessment of Sustainable Mobility Patterns of University Students: Case of Cameroon

The transition to sustainable mobility is a recognized socio-economic and environmental challenge, particularly among young adults. In addressing the gap in the literature on young adults’ travel behaviors, especially in Cameroon, this paper investigates the transport mode choices, influencing factors, and barriers to sustainable mobility of students at the National Advanced School of Public Works, Yaoundé (NASPW). Data were collected through online questionnaires with 360 valid responses. Findings revealed that most students used multiple modes of transport for commuting, with moto-taxis being the most common. Accessibility, vehicle speed, and flexibility appeared as the most important reasons for the preferred transport modes, while driver’s license possession, safety perceptions, speed, and proximity were significant predictors for mode choice. Demographic factors were found to influence transport preferences, with distinct clusters prioritizing different aspects. Barriers to public transport were primarily long waiting times and congestion, while active mobility was hindered by distance, infrastructure, and weather. The usage of public transportation was encouraged by its affordability and reduced travel time, whilst active options were preferred due to cost savings and health benefits. To promote sustainable mobility for campus travel, it is crucial to encourage active modes, develop mass transport systems, and raise awareness through symposia and conferences among students and staff.

Study on Confined Water in Flexible Graphene/GO Nanochannels.

The structural evolution of flexible nanochannels within a 2D material membrane, influenced by the ingress of water molecules, plays a crucial role in the membrane's filtration and structural stability. However, the experimental observation of nanoscale water is challenging, and current studies mostly focus on rigid nanochannels. Further investigation on the nanoconfined water is urgently needed, considering the flexibility and deformation of the channel. In this work, MD simulations and theoretical analyses are conducted to investigate the water structure and thermodynamic properties when confined within both rigid and flexible graphene/graphene oxide (GO) nanochannels. In free rigid graphene nanochannels, the interlayer distance exhibits a quantized increase with the number of water molecules, along with sudden changes in entropy, potential energy, and free energy of the water molecules. Meanwhile, in flexible graphene nanochannels, the average interlayer space increases linearly with the number of water molecules. In free rigid GO nanochannels, with the increase of oxidation concentration, the quantized increase in the interlayer space gradually diminishes, accompanied by a decrease in both potential energy and free energy. This work provides insights into the configurational evolution of flexible nanochannels within water, offering guidance in fields such as desalination and mass transport of 2D material membranes.

Second-order water wave properties over Roseau’s three-parameter bottom topography

Summary In his book Asymptotic Wave Theory (North-Holland 1976), Roseau develops the only known exact solution for linear wave propagation over a shoal. Remarkably, almost half a century later, the only properties of that solution which appear to have been used to validate more wide-ranging models are the limiting values of wave height in the far field. The primary aim of this work is to remedy this situation by providing a robust computational setting where the solution may be fully evaluated randomly both on the surface and the interior, speedily and to a high degree of accuracy. Such ‘benchmark’ solutions will facilitate a much more rigorous approach to validation of more general alternative approximation models. One such has some of its numerical results here examined and subsequently largely vindicated by the present calculations. Computation of the absolutely convergent solution integrals is supported by cubic spline approximation of an integrand component which satisfies a certain difference equation and the work is extended to cover bottom profiles with overhang including the extreme case where the overhang degenerates to a semi-infinite flat plate. The further development of solutions at second-order reveals details of mean Eulerian current and the attendant Stokes drift enabling mass transport computations; all illustrated through the entire depth with a range of contouring and arrows plots. The force field that drives a second harmonic component is calculated and shows excellent agreement with its equivalent in the more general modal expansion model applied to a non-identical but somewhat similar profile. This further validates the modelling approach and application described in that work.

Designing Nanofluidic Channels of Boron Nitride Nanosheets/Aramid Nanofibers/Covalent Organic Frameworks Nanofiltration Membrane for Ultrafast Mass Transport.

2D lamellar nanofiltration membrane is considered to be a promising approach for desalinating seawater/brackish water and recycling sewage. However, its practical feasibility is severely constrained by the lack of durability and stability. Herein, a ternary nanofiltration membrane via a mixed-dimensional assembly of 2D boron nitride nanosheets (BNNS) is fabricated, 1D aramid nanofibers (ANF), and 2D covalent organic frameworks (COF). The abundant 2D and 1D nanofluid channels endow the BNNS/ANF/COF membrane with a high flux of 194 L·m‒2·h‒1. By the synergies of the size sieving and Donnan effect, the BNNS/ANF/COF membrane demonstrates high rejection (among 98%) for those dyes whose size exceeds 1.0nm. Moreover, the BNNS/ANF/COF membrane also exhibits remarkable durability and mechanical stability, which are attributed to the strong adhesion and interactions between BNNS, ANF, and COF, as well as the superior mechanical robustness of ANF. This work provides a novel strategy to develop robust and durable 2D lamellar nanofiltration membranes with high permeance and selectivity simultaneously.

Heat and mass transfer analysis of Casson-based hybrid nanofluid flow in the presence of an aligned magnetic field: An application toward mechanical engineering

This examination explores the flow of a hybridized nanofluid (HyNf) containing silica and tin oxide nanoparticles mixed with engine oil (EO/SnO2-SiO2). The flowing occurs via a permeable material constrained by a semi-infinite flat plate. The study takes into account various factors such as convective heat and mass transference, chemical reactions, the Dufour effect, the Lorentz force, thermal radiative fluxing, and radiative absorbing. The research involves converting the managing formulas of the flowing model into a dimensionless form and applying the regular perturbation procedure to find solutions for the rate of fluid flow, temperature, and species diffusion. The surface frictional factor, Nusselt quantity, and Sherwood quantity reflect the shearing stress, rates of heat transference, and rates of mass transport at the plate, respectively. An analysis is conducted on the impact of several factors, including the suction variable, magnetic variable, radiation-absorbing factor, Casson parameter, and Dufour number, on the flow and related quantities. This analysis is based on an examination of graphs and tables. The findings suggest that the heat transference rate in the Casson hybridized nanofluid is better than that in the mono nanofluid. It is exposed that the temperature reduces at the plate having improved frequency of oscillation and also fluid velocity declines for improving values of aligned magnetized field [Formula: see text], but it shows the reverse phenomenon with Gr1 and Gc1.

Effects of temperature and pressure on the limiting current density of PEM electrolysis cells based on a theoretical prediction model and experiments

Operation at high current density of polymer electrolyte membrane electrolysis cell (PEMEC) can reduce its electrode area and capital expense. The high current density operation is limited by the limiting current density (LCD), where electrolysis voltage abruptly increases. Effects of operating temperature and pressure on the LCD were evaluated in a lab-scale PEMEC within a range from 70 to 90 °C and from 0.1 to 0.3 MPa. Also, a theoretical model was developed to predict the LCD, and to clarify what determines LCD and how the operating conditions influence the LCD. The theoretical analysis suggests that when current density is close to the LCD, water mass transport at anode reaches a limitation, which indicates that water saturation reaches almost zero at anodic catalyst layer. The analysis also finds that lower operating temperature and higher operating pressure can reduce oxygen gas saturation and raise the water saturation in porous transport layer at anode, and finally enlarge the LCD.

The varying viscosity impact in an inclined peristaltic channel with diffusion‐thermo and thermo‐diffusion

AbstractA mathematical model is constructed to investigate the behavior of peristaltic flow of Jeffrey fluid in an inclined tapered asymmetric porous channel. The fluid viscosity is taken as space dependent variable quantity. Heat absorption, Soret and Dufour effects are also retained in the current scrutiny. These preferences have broad applications in engineering, biology and industry. We began our investigation by taking into account the two‐dimensional inclined asymmetric porous channel. In the context of mathematical modeling, the appropriate dimensional nonlinear equations for momentum, heat and mass transport are simplified into dimensionless equations by applying the essential estimation of long wavelength and low Reynolds number. The solution of the governing equations is executed numerically. A graphical depiction of many crucial physical characteristics on velocity, temperature, concentration, heat transfer rate, Nusselt number and Streamlines have been reported in ending section. Temperature profile exhibits an escalation with the augmentation of Brinkman number and Dufour number . For the growing values of Prandtl number , an increment in temperature profile is observed whilst a reverse tendency is captured for concentration profile. It is noted that concentration profile falls down owing to the enhancement in Soret number and Schmidt number . An oscillatory outlook is noticed for heat transfer rate and Nusselt number. The novelty of this proposed model in the research domain specifically depends on considerations of the combined study of the Variable viscosity, Darcy resistance, Viscous dissipation, Mixed convention, Heat absorption, Soret and Dufour effects in peristaltic flow of non‐ Newtonian Jeffrey fluid in an inclined Asymmetric tapered channel under the influence of convective boundary conditions.

Oxygen-enriching triphase platform for reliable sensing of femtomolar Alzheimer’s neurofilament lights

Accurate quantification of neurofilament lights (NfLs), a prognostic blood biomarker, is highly required to predict neurodegeneration in the presymptomatic stages of Alzheimer’s disease. Here, we report self-oxygen-enriching coral structures with triphase interfaces for the label-free photocathodic detection of NfLs in blood plasma with femtomolar sensitivities and high reliability. In conventional photocathodic immunoassays, the poor solubility and sluggish diffusion rate of the dissolved oxygen serving as electron acceptors have necessitated the incorporation of additional electron acceptors or aeration procedures. To address the challenge, we designed the coral-like copper bismuth oxides (CBO) with robust solid–liquid–air contact boundaries that enrich the interfacial oxygen levels without an external aeration source. By optimally assembling the perfluorododecyltrichlorosilane (FTCS) and platinum (Pt) co-catalysts into the silver-doped CBO (Ag:CBO), the stable solid–liquid–air contact boundaries were formed within the sensor interfaces, which allowed for the abundant supply of air phase oxygen through an air pocket connected to the atmosphere. The Pt/FTCS-Ag:CBO exhibited the stable background signals independent of the dissolved oxygen fluctuations and amplified photocurrent signals by 1.76-fold, which were attributed to the elevated interfacial oxygen levels and 11.15 times-lowered mass transport resistance. Under the illumination of white light-emitting diode, the oxygen-enriching photocathodic sensor composed of Pt/FTCS-Ag:CBO conjugated with NfLs-specific antibodies precisely quantified the NfLs in plasma with a low coefficient of variation (≤2.97%), a high degree of recovery (>97.0%), and a limit of detection of 40.38 fg/mL, which was 140 times lower than the typical photocathodic sensor with diphase interfaces.

Molecular Electrocatalysis under Finite Diffusive Mass Transport Conditions. An Analytical Approach

AbstractMolecular electrocatalysis has emerged as a crucial branch of molecular electrochemistry, finding applications across various fields such as energy generation, electroanalysis, and electrosynthesis. In recent years, the study of these processes within confined spatial domains, has been increasingly frequent. However, a significant gap exists in the theoretical understanding of the interplay between different kinetics (redox and chemical) and mass transport under these conditions, and how their combined effects influence the electrochemical response. As a first step to address the aforementioned gap, this manuscript presents a theoretical expression for the current‐potential‐time response of a catalytic reaction occurring under finite diffusive conditions. The results indicate that, when the chemical kinetics is not fast, there are significant differences in electrochemical responses due to mass transport influences. Thus, in the case of bounded finite diffusion, a loss of efficiency in the process is observed, resulting in lower currents compared to those corresponding to semi‐infinite diffusive conditions. The validity of well‐known methods, such as the analysis of the current plateau or the foot of the wave under stationary conditions, is discussed. Experimental validation of these results is also provided through the study of the oxidation of Solketal mediated by the oxidation of TEMPO radical.

Examining stagnation-point flow impinging on a deforming cylinder in Reiner-Rivlin fluid with integrated heat and mass transfer

Here the Reiner-Rivlin model is applied to explore non-Newtonian flow in stagnation-point region around a stretching cylinder. Under the influence of viscous heating and thermos-diffusion, the phenomena of combined heat and mass transport are investigated. To explore the intrinsic irreversible nature of transport phenomena, the current work incorporates an analysis of entropy generation. Additionally, prescribed wall temperature and concentration are taken into consideration when developing the computational framework, and it will be shown later that these assumptions are essential to achieving self-similar analysis. Numerical computations are developed by the MATLAB tool “bvp4c” while analytical solutions are found by the optimal homotopy approach embedded in the routine “BVPh 2.0” of MATHEMATICA. For a reasonable choice of embedded parameters, both techniques produce the same numerical results. For various regulating parameters, the importance of curvature effects on the boundary layers is explained. Flow visualization utilizing streamlines and isotherms reveals interesting patterns for both Newtonian and non-Newtonian flows. The force required by the stretching cylinder is analyzed by evaluating skin friction coefficient, in the case of Reiner-Rivlin fluid. Furthermore, surface cooling rate and mass flux are scrutinized graphically and in tabular form. The cooling rate of the cylindrical boundary is higher than that of the flat plate boundary. Furthermore, a noticeable reduction in surface cooling rate is found for increasing values of Reiner-Rivlin fluid parameter.

Simultaneous quantification of terpenes and cannabinoids by reversed-phase LC-APCI-MS/MS in Cannabis sativa L. samples combined with a subsequent chemometric analysis

Cannabis sativa L. has been the most discussed medicinal plant in recent years. In particular, the dynamic shift from a formerly illicit and tightly controlled substance to a plant recognized for both medicinal and recreational purposes has brought C. sativa into the global spotlight. Due to the ongoing international legalization processes, fast and convenient analytical methods for the quality control of C. sativa flowers for medicinal and recreational purposes are of tremendous interest. In this study, we report the development and validation of a liquid chromatography-tandem mass spectrometry (LC–MS/MS)-based method applying atmospheric pressure chemical ionization (APCI) to fully quantify 16 terpenes and 7 cannabinoids including their acidic forms by a single chromatographic method. The method presented here is unique and simple, as it eliminates the need for derivatization reactions and includes the unconventional analysis of volatile compounds by liquid chromatography. Samples were prepared by a simple and fast ethanolic extraction. Separation was accomplished within 25 min on a reversed-phase C18 column. Method validation was conducted according to international guidelines regarding selectivity, accuracy, precision, robustness, and linearity. Detection was done in multiple reaction monitoring, which allowed the simultaneous quantification of co-eluting analytes applying two selective mass transitions. In addition, due to reproducible in-source decarboxylation, the acidic forms of cannabinoids were reliably quantified using mass transitions of the neutral forms. The accuracy given as the bias was below 15% for all analytes. Matrix effects for cannabinoids were studied by spiking Humulus lupulus extracts with the analytes at varying concentrations. APCI did not show susceptibility toward ion suppression or enhancement. In addition, the recovery effect after spiking was between 80 and 120% for terpenes. Further, 55 authentic C. sativa extracts were fully quantified, and the obtained results for the terpene profiles were compared to state-of-the-art gas chromatography coupled to flame ionization detection. Comparable results were achieved, emphasizing the method’s applicability for cannabinoids and terpenes. Further, acquired metabolite patterns for C. sativa samples were studied, identifying a relationship between cannabinoid and terpene patterns, as well as the abundance of myrcene in CBD-dominant C. sativa strains.Graphical

Enhancing Flow Batteries: Topology Optimization of Electrode Porosity and Shape Optimization of Cell Design

This research focuses on the improvement of porosity distribution within the electrode of an all‐vanadium redox flow battery (VRFB) and on optimizing novel cell designs. A half‐cell model, coupled with topology and shape optimization framework, is introduced. The multiobjective functional in both cases aims to minimize pressure drop while maximizing reaction rate within the cell. Topology optimization results reveal dependencies on initial value, porosity constraint, and flow rate. The distribution with lower porosity is preferred downstream of the inlet manifold. This design enhances active surface area, thus facilitating more effective conversion of incoming educts and improving mass transport of products. Compared to homogeneous electrodes, two‐part design demonstrates superior performance at specific porosity values. For combined porosities of 0.7 and 0.95, optimized distribution results in 81 % reduction in pressure drop, while conversion rate decreases by 7%. As regards various cell designs, optimization suggests a need to reconsider the vertical format of a rectangular cell. Horizontal cells are favored for nearly all porosities and flow rates. Trapezoidal and radial designs characterized by reduced downstream cross sections lead to higher pressure drops and are not preferred. This work provides further valuable insight into optimizing VRFB electrodes and challenges conventional cell design assumptions.

Highlighting the operating regimes of microchannel electrodes under laminar flow: Mapping of photoluminescence and electrochemiluminescence through semi-transparent electrodes

Semi-transparent platinum electrodes were designed and optimized to implement photoluminescence (PL) and electrochemiluminescence (ECL) in microchannels under flow conditions. The luminescence properties of tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)32+) were used to map steady-state emitted light through semi-transparent microchannel electrodes. Several diffusive-convective regimes were thus imposed in order to experimentally highlight the operating conditions of the electrodes, in particular the active zones at their upstream edges contributing to the Faradaic current. PL and ECL profiles were established on the electrode surfaces as a function of flow rate. The PL profiles confirmed the control of the process by mass transport. The data were validated by numerical simulations within the limits of experimental accuracy. ECL emission in presence of the co-reactant tri-n-propylamine (TPA) was also limited by mass transport. However, in comparison the characteristics of the ECL profiles demonstrated the complexity of the underlying mechanism involving Ru(bpy)32+ regeneration and TPA consumption.