Transport Phenomena Research Articles

Heat and mass transfer in MHD flow of SWCNT and graphene nanoparticles suspension in Casson fluid

AbstractThe exceptional mechanical properties of carbon nanotubes (CNTs) and graphene nanoparticles, particularly their high aspect ratio and flexibility, position them as highly promising materials for the next generation of armor technology. Their incorporation into protective wear, such as bullet‐proof vests, offers the potential for significant improvements in both performance and cost efficiency. By replacing traditional materials with CNTs and graphene, the durability and maintenance of these protective devices could be substantially enhanced, leading to more effective and sustainable solutions for personal safety. This study focuses on the complex phenomena of heat and mass transport within a suspension of CNTs and graphene nanoparticles dispersed in a Casson fluid, particularly under the influence of an applied magnetic field. The analysis begins by reformulating the governing equations using similarity variables to transform them into a dimensionless form to simplify the problem. The resulting dimensionless equations are then solved using the three‐stage Lobatto IIIa finite difference method, a robust numerical technique well‐suited for solving boundary value problems in fluid dynamics. The results of this investigation highlight a significant 78.41% reduction in skin friction when compared with traditional CNT‐water nanofluid systems. This considerable decrease in skin friction not only reveals the superior performance of the CNT‐graphene nanofluid suspension but also opens up new possibilities for the design and development of advanced protective materials. These findings contribute to the growing body of knowledge on nanofluid applications and offer valuable insights for future research in the field of advanced armor technology.

Radiative MHD Casson Non-Newtonian Nanofluid Slip Flow Induced by Stretching Cylinder: A Numerical Approach

Objectives: This article investigates the continuous magnetohydrodynamics slip flow across an extending cylinder, including heat radiation and free stream velocity. The proposed model incorporated the Brownian motion parameter and thermophoresis. Methods: Applying the similarity transformation to a system of partial differential equations yields an ordinary differential equation of first order. Since, there is the nonlinear nature of the modified equations, these ordinary differential equations are addressed by employing mathematical modeling. The shooting process has been embraced to solve changed equations by implementing the following Runge-Kutta Fehlberg method. Findings: Graphical representations are used to show how several fluid factors, such as Casson fluid parameter, free stream velocity, thermophoresis, magnetic parameter, Brownian motion parameter, heat generation parameter, Lewis number, radiation parameter, chemical reaction and curvature parameter affect concentration, temperature and velocity. Results for physical quantity of interest are also computed and reported in tabular form. The study's main findings showed that nanoparticle temperatures rise with greater Brownian motion parameter values, whereas nanoparticle concentration falls with higher heat radiation parameter values. Additionally, it is found that with rise in Lewis number rises as 0.1, 0.4, 0.7, 1.0, 1.3, heat transfer rate falls down by 21.19%. The outcomes are calculated using the MATLAB software. Novelty: This technique's validity is defended by comparing its most recent findings to previously published results and successfully meeting the convergence criteria. The present work emphasizes the analysis of free stream flow in the cylindrical area, specifically in the existence of partial slip and heat radiation, under convective circumstances. This study has significant implications for electronic devices such as processors as well as many businesses and the field of biological and medical sciences. The present investigation aims to support production businesses in achieving the desired level of quality of their products by effectively managing the transport phenomena. Keywords: Stretching cylinder, Heat radiation, Brownian motion, Thermophoresis, Non-Newtonian nanofluid, Shooting technique

Significance of magnetic field and Darcy–Forchheimer law on dynamics of non-Newtonian hybrid nanofluid flow over a spinning disc with Arrhenius activation energy and shape factor

Purpose The purpose of the study is to explore the three-dimensional heat and mass transport dynamics of the magneto-hydrodynamic non-Newtonian (Casson fluid) hybrid nanofluid flow comprised of − as nanoparticles suspended in base liquid water as it passes through a flexible spinning disc. The influence of a magnetic field, rotation parameter, porosity, Darcy−Forchheimer, Arrhenius’s activation energy, chemical reaction, Schmidt number and nanoparticle shape effects are substantial physical features of the investigation. Furthermore, the influence of hybrid nanofluid on Brownian motion and thermophoresis features has been represented using the Buongiorno model. The novelty of the work is intended to contribute to a better understanding of Casson non-Newtonian fluid boundary layer flow. Design/methodology/approach The governing mathematical equations that explain the flow and heat and mass transport phenomena for fluid domains include the Navier−Stokes equation, the thermal energy equation and the solutal concentration equations. The governing equations are expressed as partial differential equations, which are then converted into a suitable set of non-linear ordinary differential equations by using the necessary similarity variables. The ordinary differential equations are computed by combining the shooting operation with the three-stage Lobatto BVP4c technique. Findings Graphs and tables are used in the process of analysing the characteristics of velocity distributions, temperature profiles and solutal curves at varying values of the parameters, along with friction drag, heat transfer rate and Sherwood number. It has been revealed that the radial and axial velocities decrease when the Casson parameter value increases and that the rate of heat transmission is higher in hybrid nanofluids with nanoparticles in the shape of a blade. The increase in Brownian motion and thermophoresis parameters causes a rise in the temperature profile. Also, an increase in the activation energy parameter improves the solutal curve. The use of nanoparticles was shown to improve extrusion properties, the rotary heat process and biofuel generation. Originality/value All results are presented graphically and all physical quantities are computed and tabulated. The current results are compared to previous investigations and found to agree significantly with them.

Asymmetric thermo-electro-osmotic responses in charged conical nanochannels

Nanofluidic thermo-electric and thermo-osmotic responses have attracted increasing attention for their potential in low-grade heat energy recovery. However, the synergistic influence of geometric asymmetry and electrolyte physical properties on these responses is often overlooked. This study investigates asymmetric thermo-electro-osmotic responses by systematically varying parameters such as conicity, Debye length, and surface charge density within conical nanochannels. We employ the numerical model coupling extended Poisson-Nernst-Planck-Navier-Stokes and energy equations to simulate ion transport, fluid flow, and heat transfer. Results demonstrate pronounced asymmetries in thermo-electric and thermo-osmotic responses between forward and backward nanochannel configurations. The short-circuit current strongly depends on conicity, Debye length, and surface charge density, while the Seebeck coefficient is primarily influenced by Debye length, and surface charge density. Thermo-osmotic flow is significantly affected by all parameters, with flow direction reversals observed under specific conditions. The study highlights that Debye length and surface charge density significantly influence both thermo-electric and -osmotic responses, whereas geometric asymmetry predominantly affects thermo-osmotic response. This study provides a valuable framework for understanding fundamental thermal-driven transport phenomena at the nanoscale. The observed synergistic effects between various parameters offer insights for optimizing thermo-electric energy conversion and fluidic control within conical nanochannels, paving the way for innovative applications in nanofluidic technology and energy recovery systems.

DG-IMEX method for a two-moment model for radiation transport in the [formula omitted] limit

We consider neutral particle systems described by moments of a phase-space density and propose a realizability-preserving numerical method to evolve a spectral two-moment model for particles interacting with a background fluid moving with nonrelativistic velocities. The system of nonlinear moment equations, with special relativistic corrections to O(v/c), expresses a balance between phase-space advection and collisions and includes velocity-dependent terms that account for spatial advection, Doppler shift, and angular aberration. The model is conservative for the correct O(v/c) Eulerian-frame number density and is consistent, to O(v/c), with Eulerian-frame energy and momentum conservation. This model is closely related to the one promoted by Lowrie et al. [1] and similar to models currently used to study transport phenomena in large-scale simulations of astrophysical environments. The proposed numerical method is designed to preserve moment realizability, which guarantees that the moments correspond to a nonnegative phase-space density. The realizability-preserving scheme consists of the following key components: (i) a strong stability-preserving implicit-explicit (IMEX) time-integration method; (ii) a discontinuous Galerkin (DG) phase-space discretization with carefully constructed numerical fluxes; (iii) a realizability-preserving implicit collision update; and (iv) a realizability-enforcing limiter. In time integration, nonlinearity of the moment model necessitates solution of nonlinear equations, which we formulate as fixed-point problems and solve with tailored iterative solvers that preserve moment realizability with guaranteed global convergence. We also analyze the simultaneous Eulerian-frame number and energy conservation properties of the semi-discrete DG scheme and propose a “spectral redistribution” scheme that promotes Eulerian-frame energy conservation. Through numerical experiments, we demonstrate the accuracy and robustness of this DG-IMEX method and investigate its Eulerian-frame energy conservation properties.

Pore Network Modeling of Intraparticle Transport Phenomena Accompanied by Chemical Reactions.

In this work, a 3D pore network model (PNM) is introduced for modeling reaction-diffusion phenomena, with and without coupled heat transfer, in a spherical porous catalyst particle. The particle geometry is generated by packing thousands of microspheres inside a large sphere to represent the 3D geometry, porosity, and tortuosity of a spherical catalyst particle. A pore-network representation is extracted from this geometry, and a PNM for diffusion-reaction and heat conduction is constructed. This newly proposed particle-scale PNM allows for the application of realistic 3D nonuniform boundary conditions on the particle's surface, which is commonly encountered in slender packed-bed reactors. Concentration profiles inside the particle, and effectiveness of the reactions, is analyzed.

Non-similar approach for enhanced heat and mass transfer in nanofluid using Keller box algorithm

The nanofluids provide various benefits over pure fluids in heat and mass transport applications; hence, their research is crucial. For instance, they can increase heat transfer rate by enhancing the fluid’s thermal conductivity and may enhance mass transfer rate by changing the surface characteristics. Furthermore, nanofluids are being demonstrated to effectively diminish pressure drops in exchangers for heat, which can lower energy consumption and operating expenses. In the existing literature, the majority of the theoretical studies considered self-similar flows. However, there are certain actual flow situations that do not allow for a self-similar solution. The current study considers such of those situations where the non-similarity of the transport phenomena is unavoidable. The non-similarity of the present problem is caused by the consideration of thermophoretic diffusion or the contribution of viscous dissipation when the wall temperature follows a power-law form. For a pure fluid, the same problem admits a self-similar solution in the absence of viscous dissipation effects. In this problem, the non-similarity is caused by the nature of the thermal transport process and not because of the momentum transport. Therefore, the consideration of viscous dissipation in the boundary layer of nanofluid is an interesting aspect to explore the behavior of thermal and mass transport phenomena. Moreover, the current analysis intends to investigate the transport enhancement in a non-similar flow of a nanofluid by utilizing the Buongiorno model. In the current nonsimilar modeling, possibilities for the existence of a self-similar solution are also highlighted. An implicit finite-difference numerical scheme, the Keller-Box method, is utilized. The problem involves several physical parameters of interest, such as the Eckert number, Lewis number, Brownian motion parameter, and thermophoresis parameter, whose potential impact on the non-similar nature of the problem and on thermal enhancement is analyzed and quantified.

Piezo-viscous micropolar fluid flow between two parallel annular disks

A theoretical analysis of the piezo-viscous dependence of micropolar fluid flow between parallel annular disks has been conducted. It is assumed that viscosity changes exponentially with pressure. Pressure is analytically approximated using a small perturbation method with the viscosity coefficient as the perturbation parameter. Squeeze film time, pressure, and load carrying capacity are calculated and graphically demonstrated across various viscosity–pressure characteristics. The study examines how an increase in cross-viscosity correlates with notable growth in pressure, response time, and bearing load. According to the results, micropolar fluid offers an increase in the load-bearing capacity and therefore lengthens the response time to prevent the contact of parallel annular disks. These observations are useful for bearings, seals, and lubrication systems, where controlling viscosity and pressure is crucial for smooth operation and productivity. As the limiting case of micro-polar fluid when the coupling number tends to zero or the couple stress parameter approaches infinity, without the annular ring, the present derivation agrees well with the Newtonian viscous case of parallel planar squeezing disks described by Bird et al. [Transport Phenomena (John Wiley & Sons, 2006)].

Uncertainty and sensitivity analysis of the fission product behaviour in the Phébus FPT1 test with the system code AC2

The Phèbus FP (Fission Product) research program, conducted by IRSN and CEA, aimed to improve the understanding of the phenomena governing core melt down, fission product release and transport, as well as the fission product behaviour in the containment. The test facility represents a 900 MWe PWR at a 1/5000 scale. The second test, FPT1, was carried out in 1996 and utilised an Ag-In-Cd alloy control rod. There is a growing interest in Best Estimate Plus Uncertainty analysis both in the research, as well as in the licensing. It has a long-standing history in case of thermal–hydraulic system codes focusing on design basis accidents, but its application is limited on the severe accident domain. In recent times however an increasing attention has been paid to evaluating severe accident codes’ uncertainties. This study presents an uncertainty and sensitivity analysis (UaSA) of the FPT1 test, focusing on fission product behavior modeling within the severe accident code system AC2. The detailed application of the coupled codes ATHLET-CD and COCOSYS in this context is novelty. Detailed description of the methodological and practical approach is provided. The uncertain input parameters chosen and quantified are directly related to the phenomena describing the fission product transport and retention phenomena both in the primary circuit, as well as in the containment, while thermal–hydraulic conditions within the primary circuit were kept as much as possible constant. Finally, the study has been complemented by a sensitivity analysis deriving the Spearman's rank correlation coefficient for each uncertain input parameter.

An ion soft-landing apparatus for ion transport study with surface potential measurement.

An apparatus for explorations of ion transport in a medium and across an interface has been constructed. The ion soft-landing technique is used to deposit low-energy ions onto a pre-adsorbed medium layer on a metal substrate. The designed low-energy ion source can produce a mass-filtered ion beam with tens of nanoampere from solid sources such as bulk metals and salts. The kinetic energy of the ion beam can be lower than 1.0eV, enabling the ions to be soft-landed onto the medium at the surface. A Kelvin probe with a resolution of less than 32 mV is incorporated to measure the surface potential (SP) variation of the ion-landed sample to monitor the ion transport process in the medium. Temperature-programmed SP measurements on an Ag+-adsorbed ice film prepared on Pt(111) reveal that the temperature threshold for the Ag+-induced SP change of the ice film is about 110K. The apparatus performance demonstrates its potential in studies of ion transport and related phenomena at both macroscopic and microscopic levels.

Surface roughness analysis of cilia-driven flow for shear-thinning fluid inside a horizontal passage

The underlying investigation reports the impact of surface roughness on the mechanism of ciliary transport of Carreau–Yasuda (C–Y) liquid through a horizontal passage. The considered equations are further simplified with the help of a low Reynolds number and large wavelength approximation. The resulting boundary value problem is numerically tackled with the MATLAB built-in function bvp5c. The impact of sundry parameters on physical quantities is examined through graphical representation. The results indicate that the influence of roughness cannot be ignored during the cilia-driven channel flow, as a significant impact of roughness is observed on velocity, pressure, pressure rise, and streamlines. For several non-Newtonian pumping analysis with rough surface, this evaluation will serve as a benchmark. The current findings will also be applied to the creation of new medical pumps for transportation phenomena.

Scanning glass microelectrode technique for investigating temperature-dependent electrical properties

Abstract Recent progresses in ionic current analyses related to micro- and nano-object sensing, electrochemical sensors, and liquid pollution monitoring have attracted significant attention. Micro- and nanoscale sensors with high spatial resolution and high signal-to-noise ratios are also effective for obtaining detailed understanding of ion transport phenomena. We have developed a glass microelectrode technique for measuring the electrical potential distribution by scanning through liquids. It enables us to directly evaluate electrical properties with a spatial resolution equal to the glass tip diameter, which is less than 1 μm. Herein, we optimize the channel and cell structures for the analysis of temperature-dependent properties, which allows us to measure the temperature dependence of conductivity and viscosity in the range of 303--333 K based on the Stokes--Einstein relation. The proposed method, which directly measures the spatial distribution of electrical potential, is suitable for analyzing conductivity, viscosity, and concentration without preprocessing calibration.

Graph neural network-based multiscale thermal modeling for heterogeneous materials with complex structures

This study presents a novel GNN-based model for multiscale thermal characterization of heterogeneous materials with complex microstructures. It incorporates relationships between composition, structure, and thermal transport across multiple scales, leveraging the structure of GNNs. Results demonstrate enhanced performance of the GNN-based model compared with existing methods. Specifically, the GNN model improved thermal conductivity prediction with a mean absolute error of 0.18 W/mK (15 % improvement over the Bayesian neural network-based model) and provided a 30x speedup in computation time. The model successfully connected atomic-scale interactions to macroscale properties, achieving less than 5 % error in predicting effective thermal conductivity from one scale to another. Furthermore, it demonstrated the ability to capture nonlinear thermal transport phenomena with 92 % accuracy. The model also improved the prediction of the transient thermal responses by 20 %, accurately capturing the time-varying behaviour of materials. This work also proved the model’s ability to handle new material systems with transfer learning, achieving 88 % accuracy. Finally, Bayesian neural networks integrated into the model provided uncertainty quantification, with 95 % of experimental measurements falling within the predicted bounds. This work demonstrated the ability of the framework to handle complex microstructures, nonlinear phenomena, and transient responses while maintaining a computationally efficient model that can enable real-time applications in design and optimization needed in modern materials innovation. It represents a powerful tool for data-driven multiscale mechanics that could accelerate materials research and development for the aerospace, electronics cooling, and additive manufacturing industries.

Statistical analysis on the rate of heat transfer of radiative water‐based hybrid nanofluid flow over an elongating surface due to velocity slip and melting heat condition

AbstractThe performances of the heat transfer due to dissipative heat likely magnetic dissipation is a challenging field of research because of it's diversifies applications in industries and engineering. Particularly, nowadays, in biomedical field of research the implementation of dissipation along with thermal radiation is vital. Based upon the current scenario, the present investigation leading to the role of magnetic dissipation vis‐à‐vis thermal radiation on the water‐based hybrid nanofluid past an electro‐magnetized elongating surface associated with melting boundary conditions. The adaptation of the transformed rule particularly, similarity rules are useful to convert the proposed set of problems in to ordinary. Further, shooting‐based numerical technique is proposed to handle the governing equations. The interesting and novel approach in this topic is the use of robust statistical technique, that is, response surface methodology for the optimizing Nusselt number for the use of various factors. Moreover, the validation is obtained by conducting a hypothetical testing using analysis of variance (ANOVA) which conforms a best output model for appropriate response. Further, the major outcomes of the study are depicted as; the unsteadiness parameter decelerates the velocity profile of the hybrid nanofluid for the interaction. However, the increasing particle concentration favours in enhancing the heat transport phenomenon.

Kinetic model of multi-component polyatomic gas mixture considering internal energy excitation

In this paper, a kinetic Boltzmann model equation with internal degrees of freedom is established for thermodynamic non-equilibrium multi-component polyatomic gas mixture by using continuous energy levels to deal with rotational energy and vibrational energy. The normalization and conservativeness of the kinetic model are analyzed and proved. Then, numerical algorithm and wall boundary conditions for solving the model equation are given. Then, normal shock-wave structure flow problem and pressure/temperature gradient driven micro-channel flow problem for the two-component gas mixture are used to verify the reliability of the model. The simulation results are in good agreement with those obtained by other methods, which verifies the reliability of the model and algorithm in this paper. Finally, taking 25 N attitude control engine two-dimensional profile as the object, the study for two-dimensional profile nozzle internal and external mixed flow problem is carried out, and the influence of different inlet rarefaction levels on the molecular transports of mixed flow field and the molecular transport phenomena of mixed flow field with different number of components are discussed.

A dynamical calo-porosimeter to characterize wetting and drying processes in lyophobic nanometric pores.

Lyophobic heterogeneous systems, based on porous fluids made of ordered nanoporous particles immersed in a non-wetting liquid, constitute systems of interest for exploring wetting, drying, and coupled transport phenomena in nanometric confinement. To date, most experimental studies on the forced filling and spontaneous emptying of lyophobic nanometric pores, at pressures of several tens of MPa, have been conducted in a quasi-static regime. However, some studies have shown that dynamical measurements are essential to shed light on the rich physics of these phenomena. We describe here a dynamical calo-porosimeter that allows for the simultaneous mechanical and calorimetric characterization of filling and emptying cycles over four decades of timescales, ranging from a few milliseconds to 10 seconds. This thermally regulated instrument can be operated between -5 and 70°C. It also enables the study of a given porous material successively with different liquids by switching from one to another. The characterization of wetting dynamics, the study of slow kinetics due to changes in solute concentration, and the rapid measurement of the heat of wetting, among other thermal properties, are presented as examples of the possible applications of this apparatus.

Magnetohydrodynamic Stagnation Point Flow and Heat Transfer of Casson Fluids Over a Stretching Sheet

This research investigates the effects of heat transfer on the stagnation-point flow of a non-Newtonian Casson fluid in a two-dimensional magnetohydrodynamic (MHD) boundary layer over a stretched sheet, considering thermal radiation impacts. By employing similarity transformations, the governing partial differential equations are transformed into nonlinear ordinary differential equations. The obtained self-similar equations are numerically solved using the Optimal Homotopy Analysis Method (OHAM). The numerical results are graphically represented, showcasing the influence of various parameters on fluid flow and heat transfer characteristics. The study uncovers important dynamics in transport phenomena. Examining and illustrating the effects of dimensionless parameters on velocity, temperature, and concentration profiles reveal significant insights. Moreover, skin friction and Nusselt number results for Casson fluids are analyzed and presented. The findings indicate that the Casson parameter and Hartman number act in opposition to fluid momentum, while the thermal conductivity parameter enhances fluid temperature. Thus, this research provides valuable insights into MHD boundary layer flows of non-Newtonian Casson fluids with thermal radiation effects, and the OHAM solution method proves effective in predicting flow transport properties.

Analytic structure of diffusive correlation functions

Diffusion is a dissipative transport phenomenon ubiquitously present in nature. Its details can now be analyzed with modern effective field theory (EFT) techniques that use the closed-time-path (or Schwinger-Keldysh) formalism. We discuss the structure of the diffusive effective action appropriate for the analysis of stochastic or thermal loop effects, responsible for the so-called long-time tails, to all orders. We also elucidate and prove a number of properties of the EFT and use the theory to establish the analytic structure of the n-loop contributions to diffusive retarded two-point functions. Our analysis confirms a previously proposed result by Delacrétaz that used microscopic conformal field theory arguments. Then, we analyze a number of implications of these loop corrections to the dispersion relations of the diffusive mode and new, gapped modes that appear when the EFT is treated as exact. Finally, we discuss certain features of an all-loop model of diffusion that only retains a special subset of n-loop “banana” diagrams. Published by the American Physical Society 2024

Mathematical modelling and performance analysis of an AEM electrolyzer

In this study, an analytical model including electrochemical reactions and mass transfer in an anion-exchange membrane electrolyzer (AEMEL) has been developed by considering water sorption/desorption in electrodes. The model developed was used to investigate the performance of the AEMEL in terms of efficiency, transport phenomena and operating parameters. The numerical results revealed that the voltage losses in the AEMEL are mainly due to activation losses. The effects of important parameters such as membrane thickness, operating pressure on cell performance, and species transport were also investigated. The results also revealed that the AEMEL performance improves with decreasing membrane thickness, but the membrane thickness should be considered together with hydrogen permeability and differential operating pressure to operate the electrolyzer safely.

Electron-Surface Scattering from First-Principles.

Electron-surface scattering is important for many transport phenomena and practical applications. Particularly, the downscaling of microelectronics demands higher electrical conductivity for interconnects, which are currently based on Cu, which suffers from strong surface scattering. However, much is still unclear, such as which surface orientation causes stronger scattering. Existing theories require phenomenological parameters whose values are unknown unless fitted to experimental data or based on assumptions, thereby limiting their accuracy and predictive power. Here we present an accurate, parameter-free approach that enables an accurate calculation of electronic transport with surface scattering. Then we apply it to study the conductivities of Cu films with different surface orientations. Contrary to the common belief that a more compact surface should have higher conductivity, we find that (111) is less conductive than (001). This can be explained by the symmetry of the electronic structure. Furthermore, we propose a phenomenological model that has a better fit to the first-principles results than the conventional one. Our work offers insights into electronic transport and enables accurate calculation, understanding, and prediction for a broad range of systems where surface scattering matters.