Showing papers on "Transport phenomena published in 2021"

A machine learning approach to the prediction of transport and thermodynamic processes in multiphysics systems - heat transfer in a hybrid nanofluid flow in porous media

Abstract: Comprehensive analyses of transport phenomena and thermodynamics of complex multiphysics systems are laborious and computationally intensive. Yet, such analyses are often required during the design of thermal and process equipment. As a remedy, this paper puts forward a novel approach to the prediction of transport behaviours of multiphysics systems, offering significant reductions in the computational time and cost. This is based on machine learning techniques that utilize the data generated by computational fluid dynamics for training purposes. The physical system under investigation includes a stagnation-point flow of a hybrid nanofluid (Cu−Al2O3/Water) over a blunt object embedded in porous media. The problem further involves mixed convection, entropy generation, local thermal non-equilibrium and non-linear thermal radiation within the porous medium. The SVR (Support Machine Vector) model is employed to approximate velocity, temperature, Nusselt number and shear-stress as well as entropy generation and Bejan number functions. Further, PSO meta-heuristic algorithm is applied to propose correlations for Nusselt number and shear stress. The effects of Nusselt number, temperature fields and shear stress on the surface of the blunt-body as well as thermal and frictional entropy generation are analysed over a wide range of parameters. Further, it is shown that the generated correlations allow a quantitative evaluation of the contribution of a large number of variables to Nusselt number and shear stress. This makes the combined computational and artificial intelligence (AI) approach most suitable for design purposes.

Non-Fourier phonon heat conduction at the microscale and nanoscale

Abstract: The description of phonon heat conduction has typically been based on Fourier diffusion theory. However, over the past three decades, a host of interesting phonon transport phenomena beyond the Fourier diffusion picture have drawn much attention. Although most of the studies focused on classical size effects that lead to reduced thermal conductivity, other phenomena have been observed, often at the microscale and nanoscale, that are either completely novel or appear only at elevated temperatures. Examples are the prediction and observation of phonon second sound at high temperatures, quantized heat conduction and Anderson localization. These developments reveal rich phonon heat conduction phenomena analogous to those of electrical conduction. This Review discusses different non-Fourier heat conduction regimes (including the Casimir–Knudsen classical size effect regime), phonon hydrodynamics, the coherent phonon transport regimes (including localization and quantization of heat conduction) and the possibility of divergent heat conduction in low dimensions. Phonon heat conduction at the microscale and the nanoscale exhibits rich phenomena beyond the predictions of Fourier’s law, rivalling the phenomena of electrons. This Review discusses phonon heat conduction regimes, including the Casimir–Knudsen size effect, hydrodynamic transport, coherent transport (from quantization and localization) and divergence.

Significance of Joule heating and viscous heating on heat transport of MoS2–Ag hybrid nanofluid past an isothermal wedge

Abstract: The problem of flow and heat transport of magneto-composite nanofluid over an isothermal wedge has not been addressed in the literature up to yet. Thus, this article features the laminar transport of Newtonian composite nanomaterial (C2H6O2–H2O hybrid base liquid + MoS2–Ag hybrid nanoparticles) in the presence of exponential space- and temperature-dependent heat source past an isothermal wedge. An incompressible and electrically conducting fluid is assumed. The effects of Joule heating and viscous heating are also accounted. Single-phase nanofluid model and boundary layer approximation are utilized to govern the equations of flow and heat transport phenomena. The solution of the simplified coupled system of dimensionless constraints is obtained by using the Runge–Kutta–Fehlberg method based on the shooting technique. Detailed analysis of active quantities of interest has been presented and discussed. The interesting physical quantities (friction factors and Nusselt number) are estimated. Also, the slope of the data point is calculated in order to estimate the amount of decrease/increase in physical quantities.

Cattaneo–Christov heat flux theory on transverse MHD Oldroyd-B liquid over nonlinear stretched flow

Abstract: A hydromagnetic transverse flow of an Oldroyd-B-type liquid with a heat flux of the Cattaneo–Christov model with variable thickness has been analyzed. Consider additional impacts of thermal conductivity as well as heat generation. Governing equations were transmitted into a set of nonlinear ordinary differential equations using similarity conversion, and then, numerical solution was evaluated using the procedure Runge–Kutta–Fehlberg. The physical response related to velocity and temperature is investigated computationally. The outcomes also show that the momentum boundary-layer thickness increases the values of magnetic field strength, but the reverse trend is observed for the thermal boundary layer. Impacts of retardation and relaxation time effects are quite the opposite of the temperature field. The obtained computations are useful in transport phenomena which are involving hydromagnetic rheological fluids.

Ion Correlations and Their Impact on Transport in Polymer-Based Electrolytes

Abstract: Author(s): Fong, KD; Self, J; McCloskey, BD; Persson, KA | Abstract: The development of next-generation polymer-based electrolytes for energy storage applications would greatly benefit from a deeper understanding of transport phenomena in these systems. In this Perspective, we argue that the Onsager transport equations provide an intuitive but underutilized framework for analyzing transport in polymer-based electrolytes. Unlike the ubiquitous Stefan-Maxwell equations, the Onsager framework generates transport coefficients with clear physical interpretation at the atomistic level and can be computed easily from molecular simulations using Green-Kubo relations. Herein we present an overview of the Onsager transport theory as it applies to polymer-based electrolytes and discuss its relation to experimentally measurable transport properties and the Stefan-Maxwell equations. Using case studies from recent computational work, we demonstrate how this framework can clarify nonintuitive phenomena such as negative cation transference number, anticorrelated cation-anion motion, and the dramatic failure of the Nernst-Einstein approximation. We discuss how insights from such analysis can inform design rules for improved systems.

Impact of oxytactic microorganisms and variable species diffusivity on blood-gold Reiner–Philippoff nanofluid

Abstract: Currently, researchers across the world achieved theoretical and experimental works to investigate the significance of nanofluid due to their diverse application in heat transport phenomena. Nanofluids are actually the suspension of nanoparticles in the base liquid. Embedding nanoparticles in the base fluid enhances thermal conductivity and heat transfer rate. The present article shed light on the influence of gold nanoparticles along with oxytactic microorganisms on radiative Reiner–philippoff fluid due to extendable sheet. Suitable transformation convert the partial differential equations (PDEs) are renovated into nonlinear ordinary differential equations (ODEs) and furthermore tackled these equations numerically via bvp4c Matlab builtin scheme. Further the investigations are carried out in the presence of molecular diffusivity, oxytactic microorganisms and nonlinear thermal radiation. The effect of influential parameters on heat transfer, mass transfer, motile density of microorganisms profile are investigated with the assistance of tables and graphs. Embedding the nanoparticles and nonlinear thermal radiation amplifies the heat transfer process and motile density profile depreciates owing to an augmentation in Peclet number. The novel outcomes of this investigation will advance the field of nanomaterials.

A review on the theory of stable dendritic growth

Abstract: This review article summarizes the main outcomes following from recently developed theories of stable dendritic growth in undercooled one-component and binary melts. The nonlinear heat and mass transfer mechanisms that control the crystal growth process are connected with hydrodynamic flows (forced and natural convection), as well as with the non-local diffusion transport of dissolved impurities in the undercooled liquid phase. The main conclusions following from stability analysis, solvability and selection theories are presented. The sharp interface model and stability criteria for various crystallization conditions and crystalline symmetries met in actual practice are formulated and discussed. The review is also focused on the determination of the main process parameters-the tip velocity and diameter of dendritic crystals as functions of the melt undercooling, which define the structural states and transitions in materials science (e.g. monocrystalline-polycrystalline structures). Selection criteria of stable dendritic growth mode for conductive and convective heat and mass fluxes at the crystal surface are stitched together into a single criterion valid for an arbitrary undercooling. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

Advances in modeling transport phenomena in material-extrusion additive manufacturing: Coupling momentum, heat, and mass transfer

Abstract: Material-extrusion (MatEx) additive manufacturing involves layer-by-layer assembly of extruded material onto a printer bed and has found applications in rapid prototyping. Both material and machining limitations lead to poor mechanical properties of printed parts. Such problems may be addressed via an improved understanding of the complex transport processes and multiphysics associated with the MatEx technique. Thereby, this review paper describes the current (last 5 years) state of the art modeling approaches based on momentum, heat and mass transfer that are employed in an effort to achieve this understanding. We describe how specific details regarding polymer chain orientation, viscoelastic behavior, and crystallization are often neglected and demonstrate that there is a key need to couple the transport phenomena. Such a combined modeling approach can expand MatEx applicability to broader application space, thus we present prospective avenues to provide more comprehensive modeling and therefore new insights into enhancing MatEx performance.

A Review on the Hydrodynamics of Taylor Flow in Microchannels: Experimental and Computational Studies

Abstract: Taylor flow is a strategy-aimed flow to transfer conventional single-phase into a more efficient two-phase flow resulting in an enhanced momentum/heat/mass transfer rate, as well as a multitude of other advantages. To date, Taylor flow has focused on the processes involving gas–liquid and liquid–liquid two-phase systems in microchannels over a wide range of applications in biomedical, pharmaceutical, industrial, and commercial sectors. Appropriately micro-structured design is, therefore, a key consideration for equipment dealing with transport phenomena. This review paper highlights the hydrodynamic aspects of gas–liquid and liquid–liquid two-phase flows in microchannels. It covers state-of-the-art experimental and numerical methods in the literature for analyzing and simulating slug flows in circular and non-circular microchannels. The review’s main objective is to identify the considerable opportunity for further development of microflows and provide suggestions for researchers in the field. Available correlations proposed for the transition of flow patterns are presented. A review of the literature of flow regime, slug length, and pressure drop is also carried out.

Phase-field modeling of multicomponent and multiphase flows in microfluidic systems: a review

Abstract: The purpose of this study is to perform a detailed review on the numerical modeling of multiphase and multicomponent flows in microfluidic system using phase-field method. The phase-field method is of emerging importance in numerical computation of transport phenomena involving multiple phases and/or components. This method is not only used to model interfacial phenomena typical to multiphase flows encountered in engineering and nature but also turns out to be a promising tool in modeling the dynamics of complex fluid-fluid interfaces encountered in physiological systems such as dynamics of vesicles and red blood cells). Intrinsically, a priori unknown topological evolution of interfaces offers to be the most concerning challenge toward accurate modeling of moving boundary problems. However, the numerical difficulties can be tackled simultaneously with numerical convenience and thermodynamic rigor in the paradigm of the phase field method.,The phase-field method replaces the macroscopically sharp interfaces separating the fluids by a diffuse transition layer where the interfacial forces are smoothly distributed. As against the moving mesh methods (Lagrangian) for the explicit tracking of interfaces, the phase-field method implicitly captures the same through the evolution of a phase-field function (Eulerian). In contrast to the deployment of an artificially smoothing function for the interface as used in the volume of a fluid or level set method, however, the phase-field method uses mixing free energy for describing the interface. This needs the consideration of an additional equation for an order parameter. The dynamic evolution of the system (equation for order parameter) can be described by Allen–Cahn or Cahn–Hilliard formulation, which couples with the Navier–Stokes equation with the aid of a forcing function that depends on the chemical potential and the gradient of the order parameter.,In this review, first, the authors discuss the broad motivation and the fundamental theoretical foundation associated with phase-field modeling from the perspective of computational microfluidics. They subsequently pinpoint the outstanding numerical challenges, including estimations of the model-free parameters. They outline some numerical examples, including electrohydrodynamic flows, to demonstrate the efficacy of the method. Finally, they pinpoint various emerging issues and futuristic perspectives connecting the phase-field method and computational microfluidics.,This paper gives unique perspectives to future directions of research on this topic.

Review of Transport Phenomena and Popular Modelling Approaches in Membrane Distillation.

Abstract: In this paper, the transport phenomena in four common membrane distillation (MD) configurations and three popular modelling approaches are introduced The mechanism of heat transfer on the feed side of all configurations are the same but are distinctive from each other from the membrane interface to the bulk permeate in each configuration Based on the features of MD configurations, the mechanisms of mass and heat transfers for four configurations are reviewed together from the bulk feed to the membrane interface on the permeate but reviewed separately from the interface to the bulk permeate Since the temperature polarisation coefficient cannot be used to quantify the driving force polarisation in Sweeping Gas MD and Vacuum MD, the rate of driving force polarisation is proposed in this paper The three popular modelling approaches introduced are modelling by conventional methods, computational fluid dynamics (CFD) and response surface methodology (RSM), which are based on classic transport mechanism, computer science and mathematical statistics, respectively The default assumptions, area for applications, advantages and disadvantages of those modelling approaches are summarised Assessment and comparison were also conducted based on the review Since there are only a couple of full-scale plants operating worldwide, the modelling of operational cost of MD was only briefly reviewed Gaps and future studies were also proposed based on the current research trends, such as the emergence of new membranes, which possess the characteristics of selectivity, anti-wetting, multilayer and incorporation of inorganic particles

A comprehensive three-dimensional model coupling channel multi-phase flow and electrochemical reactions in proton exchange membrane fuel cell

Abstract: As a clean electrochemical energy conversion device, proton exchange membrane (PEM) fuel cell will play great effect in the carbon neutral society. It is widely recognized as a challenge to couple the multi-phase flow in gas flow channel and the electrochemical activities in the electrodes in PEM fuel cell modeling. In this study, a two-fluid model is developed to describe the multi-phase flow in the whole cell, in conjunction with the transport phenomena and electrochemical reaction kinetics. We assume the analogy between micro channel and porous media, and derive the gas/liquid velocity ratio for multi-phase flow in channel through Darcy's law for two-phase flow, which is expressed as a function of gas/liquid viscosity ratio and liquid saturation. Integration of the two-fluid model makes it able to predict the two-phase pressure drop and local liquid saturation in gas flow channels in an operating fuel cell. A sub-model of liquid water coverage at the GDL (gas diffusion layer) surface is also developed and incorporated into the model to study the impact of various contact angles at GDL surface on cell performance. The liquid saturation profiles along the flow direction are compared with literature data with reasonable agreement achieved. The model is employed to study a flow field of five parallel channels connected with an inlet/outlet manifold. It shows that multi-phase flow in the gas flow channel leads to more non-uniform flow and oxygen distributions, and hence a larger concentration loss under high current densities than the single-phase channel flow model.

Computation of radiative Marangoni (thermocapillary) magnetohydrodynamic convection in a Cu-water based nanofluid flow from a disk in porous media: Smart coating simulation

Abstract: With emerging applications for smart and intelligent coating systems in energy, there has been increasing activity in researching magnetic nano nanomaterial coating flows. Surface tension features significantly in such regimes, and in presence of heat transfer, Marangoni (thermocapillary) convection arises. Motivated by elaborating deeper the intrinsic transport phenomena in such systems, in this paper, a mathematical model is developed for steady radiative heat transfer and Marangoni magnetohydrodynamic (MHD) flow of Cu-water nanofluid under strong magnetic field from a disk adjacent to a porous medium. The semi-analytical Adomain Decomposition Method (ADM) is employed to solve the governing equations which are reduced into ordinary differential equation form via the Von Karman similarity transformation. Validation with a GDQ (Generalized Differential Quadrature) algorithm is included. The response in dimensionless velocity, temperature, wall heat transfer rate and shear stress is investigated for various values of the control parameters. Temperature is reduced with increasing Marangoni parameter whereas the flow is accelerated. With increasing permeability parameter temperatures are elevated. Increasing radiative flux boosts temperatures further from the disk surface. Increasing magnetic parameter strongly damps the boundary layer flow and elevates the temperatures, also eliminating temperature oscillations at lower magnetic field strengths.

Constructing many-body dissipative particle dynamics models of fluids from bottom-up coarse-graining

Abstract: Since their emergence in the 1990s, mesoscopic models of fluids have been widely used to study complex organization and transport phenomena beyond the molecular scale. Even though these models are designed based on results from physics at the meso- and macroscale, such as fluid mechanics and statistical field theory, the underlying microscopic foundation of these models is not as well defined. This paper aims to build such a systematic connection using bottom-up coarse-graining methods. From the recently developed dynamic coarse-graining scheme, we introduce a statistical inference framework of explicit many-body conservative interaction that quantitatively recapitulates the mesoscopic structure of the underlying fluid. To further consider the dissipative and fluctuation forces, we design a novel algorithm that parameterizes these forces. By utilizing this algorithm, we derive pairwise decomposable friction kernels under both non-Markovian and Markovian limits where both short- and long-time features of the coarse-grained dynamics are reproduced. Finally, through these new developments, the many-body dissipative particle dynamics type of equations of motion are successfully derived. The methodologies developed in this work thus open a new avenue for the construction of direct bottom-up mesoscopic models that naturally bridge the meso- and macroscopic physics.

Control of dusty nanofluid due to the interaction on dust particles in a conducting medium: Numerical investigation

Abstract: With ultra-high thermal significances, the nano-materials present some fundamental applications in many thermal engineering eras, mechanical and chemical engineering and modern technology. For sustainable development of industrial growth of a country, the enhancement in energy production and resources become one of the most fundamental challenges for scientists. This analysis presents the thermal aspects of dust nanoparticles in a dusty nano-material for the interaction of transverse magnetic field come across an expanding surface. The conjunction of Maxwell model thermal conductivity influences the characteristic of thermal properties that is helpful to enrich the heat transport phenomena. A mathematical model is prepared by considering metal nano-material (copper and silver) in association with the conventional fluid water. The numerical treatment is deployed for the solution of the complex nonlinear problem characterized by dust phase material and fluid transformed governing equations. The transport of heat energy is affected by the transient behavior of the volume fraction, dust particle number density in conjunction with magnetic field. However, the key features of the outcomes for the characterizing parameters are lubricated through graphs and simulated numerical values for the rate coefficients are presented in table that leads to the validation work with the earlier investigation. An increment in heat transfer rate is noted with suspension of copper nanoparticles in the dusty fluid while heat transfer reduces in case of silver nanoparticles. The nanoparticles temperature enhanced with interaction parameter and specific heat ratio. The current analysis has a greater impact in bio-medical since i.e. the blood flow within the artery as well as several industrial and engineering applications. All these aspects depend upon the nanoparticles particle size therefore the dust and nanoparticles proposed here are spherical.

Electromagnetic Hybrid Nano-Blood Pumping via Peristalsis Through an Endoscope Having Blood Clotting in Presence of Hall and Ion Slip Currents

Abstract: This article refers to an investigation of peristaltic transport of hybrid nanoparticle suspended blood through an endoscopic annulus with elastic walls in the existence of blood clotting under electromagnetic forces (EMF). The dual effects of Hall and ion-slip currents are accounted for. The energy equation is formulated invoking internal heat source and viscous-Ohmic dissipation terms. Blood is used as a base fluid, and silver and aluminum oxide nanoparticles are dispersed in order to have a hybrid blood suspension. The impacts of the geometrical shape of nanoparticles are examined. The governing partial differential equations (PDEs) for the proposed flow model are simplified under the assumption of long wavelength and low Reynolds number. The transformed non-linear coupled PDEs are solved analytically by employing the homotopy perturbation method (HPM) with Mathematica computational software. The graphical illustrations are presented to interpret various flow constraints of interest. Outcomes reflect that the Hall and ion slip parameters have diminishing behavior on the blood flow while the opposite fashion prevails on it for increasing Hartmann number. Augmenting Hall and ion slip parameters result in an upsurge in the blood temperature. Expanding the volume fraction of nanoparticles enhances the blood temperature. Hall and ion slip effects are to reduce the wall shear stress (WSS) at the peristaltic wall. The maximum amplitude of the heat transfer coefficient is computed for the brick shape of nanoparticles when compared to the other shapes of nanoparticles. The streamlines are configured with trapping ed bolus phenomena to outline the blood flow pattern in the endoscope. Our model may be pertinent to physiological systems, medical simulation devices, transport phenomena in pharmacology, nano-pharmacological delivery systems, surgical procedures, etc. In endoscopy, a magnetic force field is used in order to detect or treat diseases.