Mass Transport Phenomena Research Articles

Clarification of the Reaction Mechanism of the Photoassisted Anodic Oxidation of SiC in a Newly Developed Inverted Rotating Disk Electrode Cell Setup

Due to the distinctive chemical and physical properties of silicon carbide (SiC), interest in the material as a substrate for semiconductor industry has risen significantly during the past two decades. As a wide bandgap semiconductor SiC is known to be highly chemically inert. Still, under specific conditions SiC takes part in a number of electrochemical reactions that lead to a rapid oxidation of the surface. The goal of this work is to understand the fundamental factors driving this process for n-type SiC crystals in aqueous electrolytes.In alkaline solutions, the photoelectrochemical behaviour of n-type SiC is determined by two partial reactions (oxidation/dissolution) 1 :(1a) SiC + 6h+ (hν) + 6OH- → SiO2 + CO + 3H2O(1b) SiC + 8h+ (hν) + 8OH- → SiO2 + CO2 + 4H2O(2) SiO2 + 2OH- → [Si(OH)2O2]2- For the investigation of such photoassisted or photoelectrochemical reaction mechanisms involving mass transfer, we specifically developed a new inverted rotating disk electrode (IRDE) cell setup 2 that allows to control the most essential experimental parameters (i.e. potential, diffusion conditions and light intensity).In this setup, rotation of the disk electrode is achieved by magnetic coupling between a driver magnet (i.e. a magnetic stirrer) and the follower magnet included in the sample holder. The cell allows a homogeneous illumination and removal of gaseous reaction products, while still providing leak tightness. The surface of the semiconductor electrode is illuminated with UV light (λ = 365 nm) from a high-power LED. The distance between light source and sample is minimized to achieve maximum surface illumination of the sample.To investigate mass transport phenomena, electrolytes with relatively low solubility of SiO2 are preferable. Therefore, we used potassium hydroxide solutions in a concentration range where mass transport of hydroxide ions plays a major role.Performing cyclic voltammetry in this newly developed IRDE cell allows to distinguish different reaction regimes that are either limited by mass transport, photon flux or hole transport. For low light intensities (either through a large distance between the sample and the LED or through low driving currents through the LED) the number of photon-induced holes is limiting. At low electrolyte concentrations, the transport of hydroxyl ions and the dissolution of the oxidation products determine the reaction rate. At low potentials, hole transport limits the overall current flow. Each of these reaction regimes was studied individually to conduct a potential reaction mechanism.[1] D. H. van Dorp und J. J. Kelly, „Photoelectrochemistry of 4H–SiC in KOH solutions,“ Journal of Electroanalytical Chemistry, Bd. 599, Nr. 2, pp. 260-266, 2007.[2] K. Mairhofer, P. Mayr, S. Radl, M. Nelhiebel, S. Larisegger, G. Fafilek, „An Inherently Leakage-Free Inverted Rotating Disk Electrode Setup“, 2022. Figure 1

The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors

Biogas upgrading uniquely requires pressurisation of hollow fibre membrane contactors (HFMC) to be competitive with classical water absorption, and when complemented with an ambient industrial temperature range, these conditions will determine CO2 mass transport phenomena that are distinct dependent upon whether microporous or nonporous membranes are used. This study therefore examines the independent and concomitant role of temperature and pressure in determining CO2 mass transport, and selectivity, within microporous and nonporous HFMC. At low solvent temperatures, higher CO2 flux was achieved which indicates that solvent solubility is more critical than CO2 diffusivity to enhancing mass transport. Low temperatures also favoured mass transfer within the microporous membrane, explained by the reduction in solvent vapour pressure which limited pore wetting by condensation. In contrast, the nonporous membrane exhibited poorer mass transfer at low temperatures due to a decline in dense polymer permeability. Crucially in this study, neither wetting of the microporous membrane or plasticisation of the nonporous membrane were observed following pressurisation. Consequently, CO2 flux increased in proportion to the applied pressure for both membrane types, emphasising the critical role of pressurisation in augmenting process intensification for biogas upgrading which is typically facilitated at pressures of 7–10 bar. Resistance-in-series analysis illustrated how pressurisation reduced gas-phase resistance, and subsequently enhanced selectivity. Consequently, an outlet gas quality of 98% methane could be achieved within a single microporous module at 4.5 bar, meeting the industrial standard for biomethane whilst reducing solvent requirements, separation energy and methane losses. Comparable behaviour was observed during pressurisation of the nonporous membrane, but with a less significant benefit to CO2 mass transfer and selectivity, ostensibly due to the resistance imparted by the dense polymer. When considered collectively, low solvent temperature and high gas pressure enhance process intensification subsequently reducing process size (e.g., membrane area) and separation energy, while also advancing selectivity to deliver a gas product at the composition required for biomethane with minimum methane losses, which are critical factors in demonstrating microporous HFMC as an industrially competitive solution for biogas upgrading.

Elastic deformation resulting from internal mass loading: semi-analytical solution

SUMMARY Numerous physical processes are responsible for mass exchange between the surface and the interior of the Earth, including but not limited to the conversion of surface water and groundwater, volcanic eruptions and the consequent outflow of magma to the surface, and underground mining of mineral resources, among others. These mass transport phenomena influence the deformation of the Earth's crust. In this study, we extend the conventional loading theory to analyse the extent of crustal deformation by obtaining Green's functions due to internal mass loading in a layered elastic spherical earth model. For the surface source and internal source, the displacement and gravity change show significant differences within a specific horizontal range several times the source depth. Compared with other physical quantities, horizontal displacement is more sensitive to source depth. Furthermore, the utilization of a disc-like load example serves to illustrate the distinctions in displacement deformation between internal and surface loadings. We also published the code for calculating Green's function for internal mass loading in the public repository GitHub.

Role of localized magnetic field in vortex generation in tri-hybrid nanofluid flow: A numerical approach

Abstract Tri-hybrid nanofluid (THNF) can achieve a higher heat transfer rate than conventional hybrid nanofluid by combining three different nanoparticles with synergistic effects. It can have more diverse physical and thermal properties by choosing different combinations of nanoparticles. That is why it has more potential applications in various fields such as solar thermal, biomedical, and industrial processes. On the other hand, vortices are circular motions of liquid or gas that occur when there is a velocity difference. They are important for understanding how fluids mix and transport mass. They can be found in nature, such as in tornadoes and hurricanes. The aim of the current study is to mainly investigate the complex interaction of Lorentz force with the tri-hybrid nanoparticles inside a lid-driven square cavity. It can be seen that the magnetic field has caused the evolution of new vortices (which are very important while analyzing any flow model due to their importance in interpreting fluid mixing and mass transport phenomena) in the flow field, thus adding much more significance to our work. Most of the scientific literature is enriched with investigations dealing with the problems assuming a uniform magnetic field occupying the flow field, but in this research, a vertical strip of magnetism within the flow field will be introduced. It may be the first effort to interpret the role of the applied magnetic field in the formation of the new vortices in the flow field. A single-phase model is utilized to describe THNF whereas a numerical solution to the governing differential equations has been obtained by employing an algorithm based on the central difference discretization and the alternating direction implicit method. The analysis reveals that the magnetic field intensity may result in up to 13 and 119% increase in the skin friction and Nusselt number, respectively. Similarly, a remarkable change in the Nusselt number and the skin friction is also observed by raising the Reynolds number Re. Moreover, the localization or confinement of the magnetic field does not always increase or decrease the Nusselt number. Thus, it is concluded that there will be a certain width of the magnetic corridor for which the Nusselt number would be optimal. Further, the THNF containing Al2O3, Ag, and TiO2 outperforms in terms of enhancing the average Nusselt number, compared to the simple nanofluid containing the abovementioned particles.

Analysys of the performance a PEM-type electrolyzer in variable energy supply conditions

In this article, the main variables related to the performance of a proton exchange membrane-type electrolyzer are analyzed along with the risk of explosion for different operating conditions, notably when the electrolyzer works with a variable solar energy power supply and at high pressure. A novel mathematical model was developed that considers all mass transport phenomena through the membrane electrode assembly (MEA) for water, hydrogen, and oxygen, as well as the water evaporation in the anode and cathode channels. The main findings of this work are that for a solar energy supply operating at high pressure, the electrolyzer cannot function safely throughout the day, since in the hours when solar irradiation is lower, low current densities favor high hydrogen concentrations at the anode. Finally, it was found that greater thicknesses of the membrane increased the explosion risk due to the increase in the MEA temperature and therefore the hydrogen solubility.

A modern study on peristaltically induced flow of Maxwell fluid considering modified Darcy’s law and Hall effect with slip condition

The current investigation is designed to scrutinize the Peristalsis of Magneto-hydrodynamics viscous-elastic (Maxwell) fluid with slip condition. The present article is beneficial in a way to understand the Hemodynamics through the arteries, and capillaries by considering the Hall current characteristics. Since the wall shear stress of Maxwell fluid is less as compared to Newtonian fluid hence it exhibits blood flow characteristics. Moreover, modified Darcy’s law is also taken into consideration. The phenomena of heat and mass transport are developed in the light of the thermal conduction mechanism given by Fourier along with viscous-dissipation. The governing system of ODEs is found to be non-linear. To achieve the series solution for considered flow problem, perturbation scheme is used by considering small wavenumber. The graphical impact of influential parameters is discussed exhaustively and graphically. The key outcome of this study is that the Hall current and slip both alter the flow fields. Additionally, it has been observed that temperature and velocity profiles show comparable behaviours for various parameters. The slip parameter has an increasing effect on fluid motion and temperature. The bolus’s size gradually becomes larger as we increase the values of both velocity slip and hall parameter. According to the author's knowledge, no research had previously been done in the literature that specifically addressed the peristalsis of viscoelastic fluid considering the Hall and porosity effect with slip conditions. The current investigation fills the breach in this area of research.

Mathematical modeling of breakthrough curves for 8-hydroxyquinoline removal from fundamental equilibrium and adsorption rate studies

The mathematical modeling of the dynamic adsorption of 8-Hydroxyquinoline on activated carbon (AC) in batch and fixed-bed adsorbers is outlined in this study. The model is centered on the mass transport phenomena occurring in the solution and inside the adsorbent and considers the axial dispersion, convective transport, intraparticle diffusion mechanisms, and adsorption on the active site. Moreover, this work proposes a methodology to solve the model based on basic studies of adsorption equilibrium and rate; therefore, the prediction of the breakthrough curves by fitting the mass transport parameters is not considered, which is a significant advance in the design of fixed-bed columns. The equilibrium results demonstrated that 8-HQ adsorbs on AC by dispersive π-π and hydrophobic interactions with a mass 8-HQ adsorbed of 454 mg g−1. The kinetic study revealed that the time to achieve equilibrium diminished by up to 200 min upon establishing a turbulent stirring regime. In addition, it was found that intraparticle transport is governed by surface diffusion. Finally, using the information obtained in the batch regime, it was possible to interpret and predict the packed bed behavior in a broad range of operational conditions with an error of 10.6 % in the prediction of the breakthrough point.

Effects of Cooling Rate and Emulsifier Combination on the Colloidal Stability of Crystalline Dispersions Stabilized by Phospholipids and β-Lactoglobulin

A lot of applications for (semi-)crystalline triacylglycerol (TAG)-in-water dispersions exist in the life science and pharmaceutical industries. Unfortunately, during storage, these dispersions are often prone to changes in particle size due to unforeseen crystallization and recrystallization events. This results in the alterations of important product properties, such as viscosity and mouthfeel, or the premature release of encapsulated material. In this study, we investigated the effects and interplay of formulation, i.e., emulsifier combination, and processing parameters, i.e., cooling rate, on the colloidal stability of dispersed TAGs and aimed to improve their colloidal stability. We chose phospholipids (PLs) and β-lactoglobulin (β-lg) as the emulsifiers for our model systems, which are commonly applied in many food systems. When dispersions were characterized directly after cooling, we obtained smaller particles and narrower size distributions after fast cooling. Over the course of eleven weeks, the creaming behavior, particle size, melting behavior and polymorphism were characterized. The dispersions stabilized with solely β-lg exhibited a slight increase in particle size, whereas a decrease in size was found when PLs were added. Our results indicate that mass transport phenomena between TAG droplets and particles took place during storage. This migration of TAG molecules changed the composition and size distribution of the dispersed phase, especially at higher PL concentration (0.1 wt%). In our case, this could be prevented by using a lower concentration of PLs, i.e., 0.05 wt%.

Transport Phenomena in a Banded Solid Oxide Fuel Cell Stack—Part 2: Numerical Analysis

Solid oxide fuel cells are recognized as a promising energy conversion technology. Crucial to the field is the opportunity to reduce the costs of prototyping methodology. Due to the difficulty of conducting direct measurements inside the electrodes and fuel cell’s channels, numerical modeling remains the primary tool for improving the understanding and analyzing a fuel cell operation. Here, a computational fluid dynamic simulation of a banded solid oxide fuel cell’s stack, applied to enhance the geometrical design, is shown. A mathematical model, which includes momentum, heat, mass, and charge transport phenomena, was developed and used for the numerical simulation. The model was validated against the experimental study and confirmed its accuracy. The gas flow rate influence on the performance was investigated in details. Various arrangements of fuel and air channels were simulated and analyzed, including extending the system into a short stack. The proposed design modifications led to an increase in the volumetric power density of the stack compared to the existing prototype design. The proposed mathematical and numerical models were shown to be useful for testing further design modifications to the stack, including performance analysis, by changing the operating parameters of the system or applying new materials.

Considerations for Electrochemical Phosphorus Precipitation: A Figures of Merit Approach

Electrochemical phosphorus precipitation (EPP) from wastewater is a promising emerging technology for recovering valuable nutrients. While there are significant advantages of EPP compared to traditional phosphorus recovery, large gaps in reported performance exist between EPP methods and between EPP and industrial methods. Herein we discuss Figures of Merit (FOM) to normalize and report EPP performance at low-to-intermediate technology readiness levels (TRLs). The appropriate use of FOM in electrochemical engineering enables better comparison between technologies, enhanced understanding of electrochemical and mass transport phenomena, and faster scale-up and adoption of nascent technologies.¬ FOM specific to EPP are discussed along with important considerations and adaptations from traditional electrochemical engineering FOM. Importantly, this FOM approach may be adapted for many different electrochemical processes and technologies, aiding in the push toward and adoption of electrification in chemical processing.

Heat and mass transfer analysis for magnetized flow of {mathrm{ZnO}-SAE50} nanolubricant with variable properties: an application of Cattaneo–Christov model

The current study scrutinizes heat and mass transfer features of magnetized flow of {mathrm{ZnO}-SAE50} nanolubricant over Riga plate in a Darcy Forchheimer medium. The effects of variable viscosity, thermal radiation, variable thermal conductivity, viscous dissipation and uniform heat source/sink are examined in this study. The diffusion model presented by Cattaneo–Christov is incorporated in this study to enclose heat and mass transport phenomenon. Additionally, the mass transfer rate is inspected subjected to the effects of variable solutal diffusivity and higher order chemical reaction. Heat and mass transfer phenomena have significant applications in the disciplines of science and technology that can be seen everywhere in nature. This simultaneous transportation phenomenon indicates a variety of applications in manufacturing processes, aerodynamics, cooling systems, environmental sciences, oceanography, food industries, biological disciplines, and energy transport systems etc. The modeled system of PDEs is metamorphosed to nonlinear ODEs with the introduction of appropriate transformations. An eminent bvp4c method in MATLAB has been incorporated to execute the resulting system of ODEs numerically. The outcomes of velocity, temperature and concentration profiles corresponding to various emerging parameters have been exposed graphically. The motion of {mathrm{ZnO}-SAE50} nanolubricant tends to enhance significantly with larger modified Hartmann number, whereas converse behavior is reported by increasing porosity parameter and variable viscosity parameter. The greater heat transfer rate is observed for variable thermal conductivity parameter. The rates of heat and mass transfer slow down for thermal and solutal time relaxation parameters respectively. The concentration profile gets enriched by growing the order of the chemical reaction and variable mass diffusivity parameter. It is concluded that by increasing solid volume fraction up to 1.5%, the viscosity of the nanolubricant enhances up to 12% which consequently slows down motion of the nanolubricant but increases temperature and concentration profiles.

A case study of different magnetic strength fields and thermal energy effects in vortex generation of Ag-TiO2 hybrid nanofluid flow

Vortices grab the attention of many scientists while analyzing any flow model due to their importance in interpreting fluid mixing and mass transport phenomena. Since vortices exist in the natural environment, so researchers need to investigate them whenever they are encountered. Solar collectors, automobile cooling, engine applications, thermal management, and machine cutting, are just a few of the major areas in which most hybrid nanofluids could help to improve overall performance. The goal of this study is to demonstrate the highly complex dynamics of a Lorentz force, which governs the rotation of nanoparticles and the composition of the complex configuration of eddies inside the fluid flow of the hybrid fluid carrying Silver (Ag), and Titanium dioxide (TiO2) nanoparticles. The existing research offers an innovative analysis that investigates the isotherms and streamlines around the magnetic strips in the flow regime and thermal hydrogen energy bonds. The alternating direction implicit (ADI) methodology combined with central differences has been incorporated to determine the numerical solution of the problem. Confined Lorentz force is noticed to be a root of nano-sized hybrid particle's spinning, resulting in the complex structure of vortices in the flow field and the thermal hydrogen energy. The fixed values of the parameters that have been used in the simulation process are: Mn=5, Re=5, φ1 = 0.05, and φ2 = 0.02 unless otherwise mentioned. The findings reveal that, as the magnetic fields are strengthened, the degeneracy of both primary vortices can be seen immediately, which gives rise to two new relatively small vortices squeezed along the two vertical walls. However, as the Reynolds number increases, new vortices of different strengths and rotational directions in the flow regime can be noticed. It is found that the Reynolds number is responsible for increasing the Nussselt number along the lower horizontal wall. The magnetic parameter, on the other hand, adds a zigzag behavior to the Nusselt number. Finally, as Ag-TiO2 concentration increases, the Nusselt number becomes more sensitive.

Modeling High-Power Density Ceria-Based Direct Ammonia Fueled SOFC Stacks for Mobile Applications

SOFCs can be directly run with ammonia (NH3), which is anticipated to play a major role in future renewable energy systems due to its superior conditioning and storage characteristics. Here, we numerically investigate the performance of NH3-fueled SOFC stacks based on a high-power density ceria-based cell design by means of detailed multi-scale simulations on 1D-button cell and 3D-stack level. The model is validated based on electrochemical performance data collected on a Ni-GDC/GDC/SSC-GDC button cell at 500-650 °C. While the decomposition of NH3 at the surface of the Ni-particles is modeled by employing an elementary kinetic framework, a physically-based distributed charge-transfer model is consulted to account for the leakage current across the GDC electrolyte as a function of operation conditions. In this way, the intricate coupling between the mass, heat and charge transport phenomena, as well as the electrochemistry and thermo-catalytic chemistry can be studied on the industrially relevant scale to assist integration into a hybridized power generation system. Model predictions indicate the 120-cell stack running on NH3 to reach a very promising performance in the intermediate-temperature range.

Highly Porous Iridium Thin Electrodes with Low Loading and Improved Reaction Kinetics for Hydrogen Generation in PEM Electrolyzer Cells

Highly efficient electrodes with simplified fabrication and low cost are highly desired for the commercialization of proton exchange membrane electrolyzer cells (PEMECs). Herein, highly porous Ir-coated thin/tunable liquid/gas diffusion layers with honeycomb-structured catalyst layers were fabricated as anode electrodes for PEMECs via integrating a facile and fast electroplating process with efficient template removal. Combined with a Nafion 117 membrane, a low cell voltage of 1.842 V at 2000 mA/cm2 and a high mass activity of 4.16 A/mgIr at 1.7 V were achieved with a low Ir loading of 0.27 mg/cm2, outperforming most of the recently reported anode catalysts. Moreover, the thin electrode shows outstanding stability at a high current density of 1800 mA/cm2 in the practical PEMEC. Moreover, with in-situ high-speed visualizations in PEMECs, the catalyst layer structure's impact on real-time electrochemical reactions and mass transport phenomena was investigated for the first time. Increased active sites and improved multiphase transport properties with favorable bubble detachment and water diffusion for the honeycomb-structured electrode are revealed. Overall, the significantly simplified ionomer-free honeycomb thin electrode with low catalyst loading and remarkable performance could efficiently accelerate the industrial application of PEMECs.

A Methodological Sustainability Assessment to Process Intensification (MSAtoPI) by reactive-separation systems

To produce clean and cheap power by eliminating the economic and energy penalties, it is necessary to develop new technologies or improve the existing processes based on sustainability criteria and alternative fuels. Integration of sustainability into process design contributes to the achievement of this target by eliminating or minimizing negative effects. However, measuring sustainability performance and decision-making are crucial and challenging steps for the development of sustainable industrial processes. The framework for Methodological Sustainability Assessment to Process Intensification (MSAtoPI) is thus introduced in this study as a methodological approach with appropriate sustainability indicators that ensures the capability of gathering and abstracting the complex process operations (energy, mass, and momentum transport phenomena), and that offers clear analysis and communication. The main concepts are demonstrated in practice by using a biomass-based, highly efficient, and ultra-compact process to produce H2 while simultaneously capturing CO2 in an IGCC (Integrated Gasification Combined Cycle) power plant, which is intensified by reactive-separation systems (a hybrid membrane reactor (MR)/adsorptive reactor (AR) system). MSAtoPI clearly concretizes that the proposed intensified reactive-separation systems have huge potential to produce clean and cheap power by eliminating the economic and energy penalties by having more sustainable natures (minimum: ∼18%, average: ∼75%, maximum: ∼140% improvement in sustainability).

Thermal case study and generated vortices by dipole magnetic field in hybridized nanofluid flowing: Alternating direction implicit solution

A vortex is a location in a fluid where the flow revolves around an axis line, which may be flat or curved. Researchers must look at vortices whenever and wherever they are found since they are present in natural systems. The purpose of this investigation is to present an understanding of how the nanofluid flow (driven by an external mechanism) interacts with the magnetic field produced by a nearby paced magnetic source. While most of the scientific literature is enriched with investigations dealing with the problems assuming a uniform magnetic field occupying the flow field, the current analysis is devoted to studying the complex interaction of the spatially varying magneto force with the nanofluid flow. We have noticed that the magnetic field has caused the evolution of new vortices (which are very important while analyzing any flow model due to their importance in interpreting fluid mixing and mass transport phenomena) in the flow field, thus adding much more significance to our work. The single-phase model (SPM) has been used to describe the hybrid nanofluid whereas the numerical solution to the governing differential equations has been obtained by employing an algorithm based on the central difference discretization and the alternating direction implicit method. The governing factors for the current examination are the Reynolds number, the magneto variable, and the volumetric concentration of the nanoparticles, with the ranges, considered being 1≤Re≤150, 0≤Mn≤150 and 0≤ϕ≤0.2, respectively. The analysis reveals that the Nusselt number (Nu) steepens noticeably at the enclosure's upper left corner. 20% increment in nanoparticle volume fraction may result in up to 72% boost in the Nusselt quantity whilst causing an up to 33% decrease in skin friction. Furthermore, compared to copper, iron oxide nanoparticles are shown to be more dependent on drag force. The flow field is dominated by two almost similar main vortices while there is no magnetic source, but as the magnetic source gets stronger, the bottom vortex gets stronger. It enlarges and constricts the top vortex, breaking it down while creating two new, weaker vortices. As it produces three vortices at comparatively lower values of the pertinent parameters, the Reynolds number functions as a catalyst for the action of the magneto force variable. Finally, the Nusselt quantity and frictional factor both significantly alter once the nanostructure is incorporated into the base fluid.

SiC-based structured catalysts for a high-efficiency electrified dry reforming of methane

The process of dry reforming of methane (DRM) can allow the conversion of methane and carbon dioxide, the two main greenhouse gases (GHG), into syngas which can be either used as feedstock for chemicals production or it can undergo through separation step for H2 recovery. However, the heat required for the reaction is obtained by combustion of fossil fuels, so CO2 footprint of the process is significant. Another problematic aspect of the process concerns the heat transfer to the catalytic volume: for allowing the catalytic bed to reach and maintain the reaction temperature, the heating medium outside the tubes containing the catalyst must have a temperature higher than 1000 °C. A process intensification could be performed by combining two innovative technologies: (i) the use of electrification for the energy supply (microwave heating and direct electrification) and (ii) the adoption of structured catalysts with high thermal conductivity.This work proposed the study of electrified DRM process using two Ni-based structured catalysts prepared starting by different carriers, a Silicon carbide (SiC) honeycomb monolith and a Si–SiC open-cell foam. The electrification of the DRM process has been realized by using either microwave heating or electrification through Joule (or ohmic) heating, and the experimental tests have been performed at different space velocity values. The configuration of the carriers has been carefully chosen in order to enhance the heat and mass transport phenomena, allowing to assure a flat temperature profile along the entire catalytic bed.The results have shown that the SiC monolith is more suitable than the Si–SiC foam for a microwave-assisted catalytic test. In fact, the higher fraction of void in the foam determines a lower heat absorption, and a consequently higher energy consumption (8.29 kWh/Nm3 H2 and 4.2 kWh/Nm3 H2, for the foam and the monolith respectively). Moreover, the monolith-based catalyst approached the thermodynamic equilibrium values in terms of CH4 conversion in all the investigated temperature range, while in the same tests the foam-based catalyst reached these values only at the higher temperatures. Conversely, the foam-based catalyst has shown the best performance in the electrification tests through Joule heating: the CH4 conversion approached the equilibrium values in the investigated temperature range and, more important, the energy consumption value was of 2.6 kWh/Nm3 H2, very close to the theoretical one (1.90 kWh/Nm3 H2) and equal to about ¼ of that obtained with microwaves.

Magnetohydrodynamic double-diffusive mixed convection in a curvilinear cavity filled with nanofluid and containing conducting fins

This work numerically analyzes the mixed convective double diffusion of Fe3O4-water-based nanofluid in a tilt curvilinear lid-driven cavity studied under the effect of an inclined magnetic field. The horizontal upper wall is at a lower thermal and concentration gradient and moves toward the right. The side vertical walls and bottom walls kept adiabatic. Furthermore, two numbers of conducting fins are affixed to the inclined walls at high temperatures and concentrations. The finite element approach is implemented to analyze the considered variables: Richardson number (Ri), Hartmann number (Ha), Reynolds number (Re), Lewis number (Le), buoyancy ratio (N), magnetic inclination angle (α), nanofluid volume fraction (ϕ) as well as the fins length on the heat and mass transport phenomena. The results showed that the Nuavg and Shavg increase by increasing Reynolds number, the nanoparticles volume concentration, and the fin length, while they decrease by increasing Hartmann number. When Ri is small, Nuavg rises with the increasing magnetic field inclination, but when Ri is high, the inclination angle works adversely. On the other hand, the Shavg increases with the rise of the magnetic field inclination for all Ri values. It can be seen also, when Lewis number increases, the Nuavg and Shavg values increase with increasing Ri and magnetic inclination angles.

Numerical simulation of mass and heat transport phenomena of hydromagnetic flow of Casson fluid with sinusoidal boundary conditions

AbstractA magnetic field might interact with its surroundings, influencing chemical and physical processes in materials processing, heat exchangers, and other scientific study. Therefore, a computational study of non‐Newtonian (Casson) free convective MHD unsteady fluid flow has been highlighted in this article with mass and heat transit property through a vertical infinite porous plate. A sinusoidal boundary conditions as well as chemical reaction and thermal radiation have been considered. Using a collection of nondimensional variables, the flow related equations are also turned into nondimensional form. The EFDM algorithm is employed in order to arrive at a numerical solution via Compaq Visual Fortran. The reliability of the numerical solution has been confirmed using stability testing and convergence analysis. The whole system is convergent when the values of Prandtl number and Lewis number are greater than or equals to 0.075 and 0.025, respectively. A visual depiction of the impact of the pertinent factors on dimensionless velocity, temperature, and concentration profiles are displayed through graphical representation as well as with tabular representation. It has been inspected that when the magnetic component is regarded, it greatly affects the heat transfer factors of Casson nanofluid and the heat also rises when Eckert number, heat source and radiation parameter accelerate. It is also found that the Sherwood number is increased as the impact of chemical reaction parameter and the Lewis number, also the skin friction is decreased as the influence of porosity term got accelerated. The comparison of the current findings with the data that were previously published serves as the final stage in validating the present study.

Phase-Field Study of the History-Effect of Remelted Microstructures on Nucleation During Additive Manufacturing of Ni-Based Superalloys

In the current work we employ multi-phase-field simulations to understand the effect of remelting on microstructure evolution, especially on nucleation of new grains during selective electron beam melting (SEBM) of Ni-based super alloy. The phase-field model is coupled to both mass and heat transport phenomena including release of latent heat of solidification. We run remelting simulations in both as cast and homogenized conditions. Experimental observations show that remelting triggers the nucleation of new grains at the melt pool border. The simulation results shed more light on the local conditions at the melt pool border thereby enhancing our understanding of the mechanisms responsible for the nucleation. The simulation results are validated with experimental results obtained for the Ni–20.5 mol pct Al model binary alloy.