Viscous Dissipation Research Articles

Significance of chemical reaction and viscous dissipation on magnetized-Marangoni convective flow of dusty Casson hybrid (AA7072+AA7075/sodium alginate) nanofluid with Soret and Dufour effects

ABSTRACT In the current study, mass and heat transfer flow of radiated Casson hybrid nanofluid with nanoparticles and dust deferment over sheet are explored. The Soret and Dufour effects, activation energy and microorganisms in the hybrid nanofluid model are described. Marangoni convection, a prominent occurrence in microgravity caused by surface tension gradients. It can be used for many different things, such as the creation of molten crystals, thin-film diffusion, the generation of vapour bubbles during nucleation, and semiconductor manufacturing. In sodium alginate, we wondered about the aluminium alloys AA7072 and AA7075. The aluminium alloys included in this study are specially made materials with improved heat transmission characteristics. aluminium and zinc are combined in AA7072 alloy in the ratios of 98 & 1, respectively, with the addition of silicon, ferrous metals, and copper. Similarly, AA7075 is a blend of aluminium, magnesium, zinc, and copper in the proportions of ~ 90, ~3, ~6, and ~ 1, respectively, with silicon ferrous and magnesium as additional metals. The controlling PDEs are transformed into nonlinear ODEs with the aid of a new set of similarity variables. These ODEs are then numerically solved using the RKF-45th method. The findings show that when the Marangoni convection parameter increases, the concentration, temperature, and microbiological characteristics drop while the velocity profile increases for both the dust and fluid phases.

Peristaltic transport of diethylene glycol-based magnesium aluminate nanofluid under the effects of viscous dissipation and Hall current

ABSTRACT The fundamental importance of peristaltic phenomena in numerous biological systems, including dialysis, heart-lung machines, urine transportation, invertebrate locomotion, and the passage of gallbladder bile into the intestines, persuaded scientists to investigate the different aspects of it over the past few years. In addition, peristaltic pumping is an important consideration in industrial processes including, roller pumps used for the transport of sanitary materials, finger pumps, cell separation, and endoscopes. Keeping such inspirational applications in mind, the present investigation is dedicated to exploring the peristaltic transport of a Cross-magneto nanofluid through a curved geometry in the presence of heat transfer. The inspection of the heat transfer is conducted by utilizing variable viscosity and ohmic heating aspects. This study also retains the characteristics of viscous dissipation, heat generation/absorption, and thermal conductivity of nanofluids. Modeling of the 2D, incompressible Cross nanofluid with peristaltic movement is carried out using a curvilinear coordinate system. The basic equations of the problem are mPodeled in the light of physical laws and then simplified by adopting the lubrication theory. The solutions of the resulting nonlinear system are computed numerically. The outcomes of the related flow parameters on the nanofluid’s temperature, pressure gradient, velocity distribution, heat transfer, streamlines pattern, and stresses at the wall are discussed through graphs. The graphical results depict that the rates of heat transfer are augmented by increasing the curvature parameter, Hartmann number, and nanoparticles’ volume fraction while decreasing the Hall parameter and temperature-dependent viscosity parameter. Moreover, the nanofluid’s temperature increases by improving the values of the heat generation parameter, whereas it decreases for the Hall parameter. Furthermore, a reduction in the axial velocity occurs near the center of the channel, when Hartmann number attains higher values.

Non-similar analysis of bioconvection MHD micropolar nanofluid on a stretching sheet with the influences of Soret and Dufour effects

In this study, we investigate the capabilities of magnetohydrodynamic bioconvective micropolar nanofluids, considering the impact of Soret and Dufour effects using a non-similarity analysis. Our objective is to forecast the complex heat and mass transfer phenomena observed in both biological and industrial systems. In recent years, notable progress in energy applications has spurred our inquiry and exploration. To augment thermal conductivity and explore potential biocompatibility, we utilize blood as the base fluid, incorporating silver Ag\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\left({\ ext{Ag}}\\right)$$\\end{document} and copper oxide (CuO)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\ ext{CuO}})$$\\end{document}. This distinctive configuration offers improved control over thermal properties and supports the exploration of advanced applications across various domains. In our analysis, we also consider factors such as viscous dissipation, the influences of Soret and Dufour effects, the existence of a magnetic field, and the occurrence of heat generation. The governing PDEs and their corresponding boundary conditions are transformed into dimensionless form through the use of suitable non-similar transformations. The outcomes generated by the modified model are obtained through the application of a local non-similarity approach, extended up to the second degree of truncation, and integrated with a finite difference code (bvp4c). Furthermore, the effects of different factors on fluid flow, micro-rotation, heat transfer, volume fraction, and microorganism properties in the analyzed flow scenarios are demonstrated and examined through visual representations, following the attainment of satisfactory agreement between the obtained results and those reported in prior studies. The tables are designed to present numerical variations for the drag coefficient and Nusselt number. A comparative analysis is conducted on previously published work, despite certain limitations, in order to evaluate the accuracy of the numerical scheme. It can be shown that the material parameter K\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K$$\\end{document} has two effects on micropolar fluid dynamics: it increases the micro-rotation profile, which leads to higher fluid stiffness, and it reduces the velocity profile in response to an angled magnetic field. Furthermore, in bio-convective micropolar fluid, greater K\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$K$$\\end{document} values are correlated with an elevated temperature profile, showing enhanced heat transfer efficiency via increased fluid speed and kinetic energy production. The velocity profiles in bioconvective micropolar fluids rise with higher magnetic field values (M)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(M)$$\\end{document}, highlighting the significance of magnetic field orientations for a thorough comprehension of the behavior of fluids in these systems. Increasing the Dufour effect (Du)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\ ext{Du}})$$\\end{document} raises the temperature profile, whereas increasing the Soret effect (Sr)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\ ext{Sr}})$$\\end{document} lowers the concentration profile. Furthermore, increasing the bio-convective Lewis numbers (Le)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\ ext{Le}})$$\\end{document} results in larger concentrations of moving microorganisms, but increasing the Peclet number (Pe)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$({\ ext{Pe}})$$\\end{document} results in a drop in microbe concentrations. The main focus of our study is to devise unique transformations customized to address the intricacies of the specific problem under investigation. These transformations aim to produce precise and efficient outcomes, offering valuable insights for future research in the realm of nanofluid flows, particularly concerning pressure ulcer problems.

Numerical analysis of the MHD Williamson nanofluid flow over a nonlinear stretching sheet through a Darcy porous medium: Modeling and simulation

Abstract In the current study, we delve into examining the movement of a nanofluid within a Williamson boundary layer, focusing on the analysis of heat and mass transfer (HMT) processes. This particular flow occurs over a sheet that undergoes nonlinear stretching. A significant facet of this investigation involves the incorporation of both the magnetic field and the influence of viscous dissipation within the model. The sheet is situated within a porous medium, and this medium conforms to the Darcy model. Since more precise outcomes are still required, the model assumes that both fluid conductivity and viscosity change with temperature. In this research, we encounter a system of extremely nonlinear ordinary differential equations that are treated through a numerical technique, specifically by employing the spectral collocation method. Graphical representations are used to illustrate how the relevant parameters impact the nanoparticle volume fraction, velocity, and temperature profiles. The study involves the computation and analysis of the effect of physical parameters on the local Sherwood number, skin friction coefficient, and local Nusselt number. Specific significant findings emerging from the present study highlight that the rate of mass transfer is particularly influenced by the thermophoresis factor, porous parameter, and Williamson parameter, showing heightened effects, while conversely, the Brownian motion parameter demonstrates an opposing pattern. The results were computed and subjected to a comparison with earlier research, indicating a notable degree of conformity and accord.

Contact-angle hysteresis on rough surfaces: mechanical energy balance framework

Using as a starting point conservation of momentum, a multiphase mechanical energy balance equation is derived that accounts for multiple material phases and interfaces present within a moving control volume. This balance is applied to a control volume that is anchored to a three-phase contact line as it advances continuously over the surface of a rough and chemically homogeneous and inert solid. Using semi-quantitative models for the material behaviour occurring within the control volume, an order of magnitude analysis is performed to neglect insignificant terms, producing an equation for predicting contact-angle hysteresis from a knowledge of the interface dynamics occurring around the three-phase contact line. It is shown that the viscous energy dissipation that occurs during the ‘stick–slip’ motion of the three-phase contact line, being the cause of contact-angle hysteresis on rough surfaces, can be calculated from changes in intermediate equilibrium interface states. The balance is applied to the Wenzel, Cassie–Baxter and Fakir (super-hydrophobic) wetting states, showing for the Fakir case that significant dissipation occurs during both interface advance and recede, and relating these dissipations to interfacial area changes that occur around the ‘stick–slip’ events.

Capillarity Constructed Open Siphon for Sustainable Drainage.

Siphon is an effective method to transfer liquid from a higher to a lower level, which has many applications in hygienic design, clinical apparatus, and hydraulic engineering. Traditional operation requires energy to overcome gravity and establish flow in a closed system. Achieving sustainable high flux siphon drainage without energy input remains a challenge due to viscous dissipation. Here, an unexpected open siphon behavior on the South American pitcher plant Heliamphora minor consisting of trichomes covered pitcher and a wedge-shaped sheath is examined. Exploiting the concept of Digital Twin, a new biomimetic research method by transforming the biological sample to a virtual 3D model is proposed and unveiled that maintained connection of wicking on sub-millimeter long trichomes due to asymmetric pressure distribution and ascending in wedge sheath under unbalanced pressure forms continuous surface flow. Exploring this mechanism, a biomimetic siphon device achieving continuous high flux exposed to ambient air is constructed. Besides, particles floating on the meniscus in the outside wedge move under a curvature gradient as water ascends, which implies a biological nutrient capture method and new dust collection manner in the drainage system. Applying the underlying principle enhances the siphon efficiency of floor drains and has the potential for other liquid transfer device design improvements.

Examining the potential of Sigma-Thermic heat transfer fluid and its nanofluid in a natural circulation loop through CFD studies

Abstract This study investigates the impact of hot heat exchanger (HHX) inlet temperature on Sigma-thermic heat transfer fluid (STHF or STF) performance in a natural circulation loop. Various fluids, including STHF and STHF-based nanofluids, with volumetric concentrations ranging from 0.5% to 3%, are employed in the loop. The primary objective is to analyze the thermal performance of the loop under different conditions, focusing on temperature distribution, Nusselt number, friction factor, effectiveness, and mass flow rate. 3D numerical simulations are conducted, and the numerical model is validated against existing literature. The developed model incorporates considerations for viscous dissipation and axial conduction to predict the heat transfer potential of the loop. As the HHX inlet temperature increases, the mass flow rate rises. Notably, STHF/CuO nanofluids exhibit a more substantial enhancement than other nanofluids. At a 1 vol% concentration, the mass flow rate increases by 9.5%, 4%, and 2.7% for STHF/CuO, STHF/Al2O3, and hybrid nanofluids, respectively, compared to pure STHF. The study reveals significant improvements in mass flow rates and heat transfer efficiency with increasing HHX inlet temperatures, especially with STHF/CuO nanofluids. The total entropy generation reduction is notable, with percentages ranging from 2% to 18.5% for various nanofluids compared to pure STHF

What Rayleigh numbers are achievable under Oberbeck–Boussinesq conditions?

The validity of the Oberbeck–Boussinesq (OB) approximation in Rayleigh–Bénard (RB) convection is studied using the Gray & Giorgini (Intl J. Heat Mass Transfer, vol. 19, 1976, pp. 545–551) criterion that requires that the residuals, i.e. the terms that distinguish the full governing equations from their OB approximations, are kept below a certain small threshold $\hat {\sigma }$ . This gives constraints on the temperature and pressure variations of the fluid properties (density, absolute viscosity, specific heat at constant pressure $c_p$ , thermal expansion coefficient and thermal conductivity) and on the magnitudes of the pressure work and viscous dissipation terms in the heat equation, which all can be formulated as bounds regarding the maximum temperature difference in the system, $\varDelta$ , and the container height, $L$ . Thus for any given fluid and $\hat {\sigma }$ , one can calculate the OB-validity region (in terms of $\varDelta$ and $L$ ) and also the maximum achievable Rayleigh number ${{Ra}}_{max,\hat {\sigma }}$ , and we did so for fluids water, air, helium and pressurized SF $_6$ at room temperature, and cryogenic helium, for $\hat {\sigma }=5\,\%$ , $10\,\%$ and $20\,\%$ . For the most popular fluids in high- ${{Ra}}$ RB measurements, which are cryogenic helium and pressurized SF $_6$ , we have identified the most critical residual, which is associated with the temperature dependence of $c_p$ . Our direct numerical simulations (DNS) showed, however, that even when the values of $c_p$ can differ almost twice within the convection cell, this feature alone cannot explain a sudden and strong enhancement in the heat transport in the system, compared with its OB analogue.

Investigation of convective peristaltic flow of non-Newtonian fluids through a non-uniform tapered porous conduit with Ohmic heating and viscous dissipation

ABSTRACT The study of convective magnetohydrodynamic (MHD) biofluid transport through a non-uniform duct is of interest due to its applications to biomedical devices and equipment. Because of this, a comparative study of free convective peristaltic flow of non-Newtonian (Casson and Jeffrey) fluids in a tapered porous symmetric duct with Hall current and viscous dissipation effects is carried out. The proposed dimensional governing equations are converted into a system of non-dimensional partial differential equations by invoking adequate non-dimensional parameters. Furthermore, a long-wavelength approximation is used to reduce the complexity of the system. Then the reduced system of partial differential equations is solved analytically using the regular perturbation method. The fascinating features of the influential parameters on the flow characteristics are demonstrated and analyzed in depth through graphs and tables. The results demonstrate that the velocity and temperature in the Jeffrey fluid flow are larger compared to those in the Casson fluid flow. The thermal Grashof number and the Hall current parameter enhanced the pressure rise profile. This research has significant implications in biomedical devices (MRI, vitamins A and D injections, heart-lung machines, etc.) and pharmaceutical fluid preparation in biomedical sciences.

Mixed convective flow of engine oil-based non-Newtonian tri-hybrid nanofluid across a porous rotating disk

Purpose Flow induced by rotating disks is of great practical importance in several engineering applications such as rotating heat exchangers, turbine disks, pumps and many more. The present research has been freshly displayed regarding the implementation of an engine oil-based Casson tri-hybrid nanofluid across a rotating disk in mass and heat transferal developments. The purpose of this study is to contemplate the attributes of the flowing tri-hybrid nanofluid by incorporating porosity effects and magnetization and velocity slip effects, viscous dissipation, radiating flux, temperature slip, chemical reaction and activation energy. Design/methodology/approach The articulated fluid flow is described by a set of partial differential equations which are converted into one set of higher-order ordinary differential equations (ODEs) by using convenient conversions. The numerical solution of this transformed set of ODEs has been spearheaded by using the effectual bvp4c scheme. Findings The acquired results show that the heat transmission rate for the Casson tri-hybrid nanofluid is intensified by, respectively, 9.54% and 11.93% when compared to the Casson hybrid nanofluid and Casson nanofluid. Also, the mass transmission rate for the Casson tri-hybrid nanofluid is augmented by 1.09% and 2.14%, respectively, when compared to the Casson hybrid nanofluid and Casson nanofluid. Originality/value The current investigation presents an educative response on how the flow profiles vary with changes in the inevitable flow parameters. As per authors’ knowledge, no such scrutinization has been carried out previously; therefore, our results are novel and unique.

Williamson MHD Nanofluid Flow via a Porous Exponentially Stretching Sheet with Bioconvective Fluxes

The recent study concentrates on magnetohydrodynamics (MHD). Williamson fluid drifts over an exponentially extending sheet. The porous medium is also crucial to improving thermal efficiency. The flow pattern model considers the inspirations of Joule heating, heat generation, viscous dissipation, and thermal radiation. This study also comprises the activation energy, bio-convectional, and gyrotactic microorganism phenomena. Furthermore, the Brownian and thermophoresis effects of nanoparticles are taken into consideration. Using proper similarity transformation, PDEs of the impetus, temperature, concentricity, motility microbe density, and boundary constraints upgrade into a non-linearly ordinary differential equations (ODEs) mode. Using MATLAB, transformed non-dimensional ODEs are dealt with using shooting procedures and results of significant physical strictures using a built-in bvp4c solver. Finally, it is elaborated and briefly explored numerically and visually can find interesting physical strictures versus the velocity gradient, temperature gradient, solutal gradient of species, and microbes' gradient. Incorporating microorganisms and nanoparticles into Williamson fluids can create novel materials with tailored properties for diverse applications. However, it's crucial to consider stability, biocompatibility, and environmental impact when designing these advanced fluid systems.

New insights into MHD squeezing flows of reacting-radiating Maxwell nanofluids via Wakif's–Buongiorno point of view

AbstractThis work presents a computational investigation of a squeezing nanofluid flow under the influence of thermal radiation, magnetohydrodynamics (MHD), and chemical process in a constrained parallel-wall geometry. In this study, the non-Newtonian behavior of a rate-type (Maxwell) nanofluid is captured by rheological expressions that serve as the foundation for the flow formulation. This kind of thinking makes it possible to simulate the intricate nanofluid behavior that incorporates the elastic and viscous responses, which are useful in a variety of situations related to nanofluid dynamics, rheology, and materials science. Additionally, the transport equations are modeled properly using Wakif's–Buongiorno nanofluid model. The equations reflecting the dynamics of the nanofluid and heat-mass transport are developed based on admissible physical assumptions, such as the negligible viscous dissipation as well as the lower magnetic Reynolds number. After that, several similarity variables are introduced in these equations to get the dimensionless formulation form. Akbari–Ganji's method is used to carry out extensive computational simulations. Our results show that the increased squeezing parameters lead to larger horizontal and vertical velocities. On the other hand, the temperature showed a reverse relationship with the increasing squeezing parameters and exhibiting a cooling impact.

Entropy production on mixed convection stagnation point flow of nonlinear radiative fourth-grade hybrid nanofluid through a stretchable Riga surface

The purpose of the current study is to inspect entropy generation, mixed convective stagnation point flow, and thermal transfer features of nonlinear radiative fourth-grade hybrid nanofluid (NF) confined by a convectively heated Riga surface. The heat transport is examined with the existence of two disparate heat source modulations, variable thermal conductivity, and viscous dissipation. The original flow equations are first transmuted using appropriate transformations into non-dimensional ordinary differential equations, which are then solved via an overlapping grid-based spectral collocation scheme. The upshots of various pertinent parameters on velocity, temperature, entropy generation, and valuable engineering quantities are deliberated. Pivotal results obtained reveal that speedily flow of fluid and skin friction can be accelerated by strong magnetic force, rising mixed convection, and material parameters. Also, convective boundary conditions, along with nonlinear radiation and fluctuating thermal conductivity, are recommended for boosting fluid temperature, rates of entropy generation and heat transport. Thermal mechanism in hybrid NF is dominant over simple NF, which implies that performance of hybrid NF is better than that of simple NF. The outcomes of this study can be useful in enriching thermal performance of the working fluid, assisting in diagnosing causes of incompetency in thermal systems, and discovering suitable means of minimizing entropy generation with the intention of mitigating the loss of useful and scarce energy resources.

Pulsatile flow of blood and Cattaneo Christov heat flux model in diseased arteries with variable properties

ABSTRACT The current effort is executed to interpret the heat transmission of combined stenosis and aneurysm in an artery, taking into account variable properties such as viscous dissipation and thermal radiation. We reduced the two directional energy and momentum equations to unidirectional flow by normalizing them under the mild stenotic assumption. After that, a mathematical framework for the physical problem is developed. An intricate nonlinear set of partial differential equations results from this formulation. A suitable numerical method of finite difference is employed on consequent equations to solve them. Afterward, graphical results predict the region of flow and the influence of involved parameters is shown in pictorial form. Furthermore, these solutions are employed to test how certain parameters, like streamlines, flow rate, and wall shear stress, affect blood flow. Using streamlines, we will also observe the general behavior of blood flow patterns.

Transportation of melting heat in stratified Jeffrey fluid flow with heat generation and magnetic field

In current years, storage of energy is a challenging task for the scientists and researchers. So, they are interested to develop some extra ordinary techniques of energy storage. Thus, our main theme here is to focus on the latent heat energy (melting heat) which is more economical and sustainable. Transportation of melting heat in quadratic stratified Jeffrey fluid flow in the vicinity of stagnation point is scrutinized. The flow is deformed by linear stretchable sheet. Characteristics of heat transportation are scrutinized through viscous dissipation and heat generation or absorption. Constant magnetic field is implemented to electrically conducting fluid in vertical direction. The arising governing equations are converted in the non-dimensional state through suitable transformations. Homotopic technique is utilized for simulation of solutions. Graphical behavior of velocity and temperature fields is investigated corresponding to relevant parameters. As a conclusion, higher amount of energy can be achieved as melting phenomenon enhances, and also results in low temperature. Further, dominant stratification decays the temperature field. Current study will play key role in industrial liquids like polymer solutions to make high quality fiberglass, paints, silicone heat valves etc. This study will also deliberate efficiently for the storage of energy through phase change procedure i.e., melting phenomenon.

Heat transport analysis of nanoliquid in a microchannel with aggregation kinematics: a modified Buongiorno model approach

ABSTRACT Convective heat transmission of Ti O 2 − EG nanoliquid under slip and convective regime in a microchannel is examined using a modified Buongiorno model. The fractal-based approach is employed to describe the aggregation of nanoparticles. The impact of molecular dynamics, particularly on dynamic viscosity and thermal conductivity due to the aggregation of nano-sized particles, is simulated with the help of two significant models: namely, the Krieger-Dougherty model and the Maxwell-Bruggeman model, respectively. The aspect of the interfacial layer enables us to get a realistic nanoliquid model. The solutions for the designed nondimensional mathematical model are obtained numerically. The variation in flow and thermal distribution for pertinent parameters are visualized graphically. The study reveals that the thermophysical characteristics sturdily depend on nanoparticle concentration and cluster formation. It is emphasized that the viscous dissipation and radiative heat transfer contribute towards magnifying the irreversibilities in a microchannel. The findings are useful in bioconvection and various heat transfer applications.

Integral methods for friction decomposition and their extensions to rough-wall flows

A primary objective of integral methods, such as the momentum integral method, is to discern the physical processes contributing to skin friction. These methods encompass the momentum, kinetic energy and angular momentum integrals. This paper reformulates existing integrals based on the double-averaged Navier–Stokes equations, and extends their application to flows over rough walls. Our derivation yields distinct decompositions for the bottom-wall viscous friction coefficient, denoted as $C_S$ , and the roughness element drag coefficient $C_R$ . The decompositions comprise three terms: a viscous term, a turbulent term and a roughness (dispersive) term – regardless of the flow configuration, be it channel or boundary layer. Notably, when these integrals are evaluated for laminar flow scenarios, only the viscous term remains significant. In addition, we elucidate the spatial distributions of the terms within these decompositions. To demonstrate the practicality of our formulations, we apply them to analyse data from direct numerical simulations of turbulent half-channel flows. These flows feature aligned and staggered cubical roughness at various packing densities. Our analyses, based on kinetic-energy-oriented decompositions, reveal that when the surface coverage density $\lambda _p$ is small, the dominant terms within the decompositions are the viscous and turbulent terms. With increasing $\lambda _p$ , the viscous dissipation term decreases, while the turbulent production term increases and then decreases. These variations arise from a subdued near-wall cycle and the development of a shear layer at the height of the cubes.

Mixing, heating and ion-neutral decoupling induced by Rayleigh-Taylor instability in prominence-corona transition regions.

This study explores nonlinear development of the magnetized Rayleigh-Taylor instability (RTI) in a prominence-corona transition region. Using a two-fluid model of a partially ionized plasma, we compare RTI simulations for several different magnetic field configurations. We follow prior descriptions of the numerical prominence model (Popescu Braileanu et al. 2021 Astron. Astrophys. 646, A93(doi:10.1051/0004-6361/202039053),Popescu Braileanu et al. 2021 Astron. Astrophys. 650, A181 (doi:10.1051/0004-6361/202140425)and Popescu Braileanu et al. 2023 Astron. Astrophys. 670, A31(doi:10.1051/0004-6361/202142996)) and explore the charged-neutral fluid coupling and plasma heating in a two-dimensional mixing layer for different magnetic field configurations. We also investigate how the shear in magnetic field surrounding a prominence may impact the release of the gravitational potential energy of the prominence material. We show that the flow decoupling is strongest in the plane normal to the direction of the magnetic field, where neutral pressure gradients drive ion-neutral drifts and frictional heating is balanced by adiabatic cooling of the expanding prominence material. We also show that magnetic field within the mixing plane can lead to faster nonlinear release of the gravitational energy driving the RTI, while more efficiently heating the plasma via viscous dissipation of associated plasma flows. We relate the computational results to potential observables by highlighting how integrating over under-resolved two-fluid sub-structure may lead to misinterpretation of observational data. This article is part of the theme issue 'Partially ionized plasma of the solar atmosphere: recent advances and future pathways'.

Numerical analysis of velocity slip and magnetic Soret effect on dissipative Maxwell liquid motion about a stretching wall with heat source/sink

The main aim of present numerical analysis is to explore the effects of viscous dissipation and velocity slip on the two-dimensional steady-state viscous incompressible flow of Maxwell fluid over a stretching sheet under the infleunce of magnetic field. Novel collective effects of heat source/sink and Soret impacts have been included in the governing equations to explore the salient features of heat and mass transport mechanism. Further, the velocity slip is introduced into the boundary conditions to depict the momentum transport behavior in the flow region. A typical Maxwell fluid model is deployed to separate the non-Newtonian flow behavior from that of classical Newtonian fluids. However, the visco-elastic Maxwell fluid finds its abundant applications in various fields of engineering and medicine such as plastic sheet drawing, metallurgy, polymer sheet extrusion, chemical engineering, electronic cooling, injection molding and nuclear cooling and many others. Inspired by these applications, authors have made an attempt to disclose the magneto-thermo salient features of slip flow of Maxwell fluid over stretching wall under Soret effect. The current physical situation results the highly nonlinear coupled two-dimensional steady-state partial differential equations and which are not amenable to any of the direct techniques. Due to this, the suitable similarity transformations are deployed to reduce the dimensional complexity of the constructed partial differential equations. A robust Matlab-based bvp4c scheme is utilized as a basic tool to produce the similarity solutions of the governing equations. The computer generated numerical data is presented in view of flow, temperature and concentration profiles including physical quantities of interest like skin-friction coefficient, heat and mass transport rates for the various values of physical parameters range such as, 0 ≤ M ≤ 1 , 0 ≤ β ≤ 1 , − 0.3 ≤ λ ≤ 0.6 , − 0.2 ≤ Q ≤ 0.2 , 0 ≤ Ec ≤ 2.2 , 1.2 ≤ Pr ≤ 2.2 , 0 ≤ Sr ≤ 0.5 and 1.2 ≤ Sc ≤ 2.2 . Accordingly, it is noticed that, enhancing magnetic parameter decreases the Maxwell fluid flow and amplifies the temperature and concentration fields. Enlarging Maxwell fluid parameter decreases the velocity field and increases the temperature and concentration profiles. Amplified slip parameter diminished the Maxwell flow inside the flow regime. Increasing heat source/sink parameter amplifies the temperature field. Further, magnifying Soret number amplifies the concentration field. Magnitude of skin-friction coeffiecient enlarged with amplified magnetic and Maxwell fluid parameters. Heat and mass transport rates decayed with enhancement in heat source/sink and Soret parameters. Finally, it is described that, the present similarity solutions showing good agreement with the previously reported solutions in the literature and this fact confirms the accurateness of the used numerical method and the generated similarity solutions.

Finite difference analyses of bioconvective Williamson nanofluids stream over irregular plates with effects of nonlinear radiation and viscous dissipation

The purpose of this work is to provide a comprehensive analysis of the bioconvective Williamson nanofluid stream while considering the effects of radiation flux and viscous dissipation. The two-phase nanofluids model is applied where the impacts of the Brownian motion and thermophores are significant. This study starts with introducing the governing system in case of the irregular plane then it transforms to the regular plane. The solution methodology is based on the fully implicit finite difference method. The major results disclosed that maximizing the amplitude parameter causes a diminishing in the velocity and skin-friction coefficients. Also, lower behaviors are noted for the velocity in the case of Williamson nanofluids compared to a Newtonian nanofluid case (We = 0). Furthermore, the considered range of Biot number (1 ≤ Bi ≤ 5)causes an improvement in the surface temperature up to 71.59%.