Showing papers on "Viscous liquid published in 2021"

Comprehensive study of thermophoretic diffusion deposition velocity effect on heat and mass transfer of ferromagnetic fluid flow along a stretching cylinder

Abstract: The aim of this current investigation is to discuss the flow of a ferromagnetic viscous liquid with thermophoretic particle deposition over a stretching cylinder on taking account of a uniform heat...

Sparse identification of multiphase turbulence closures for coupled fluid–particle flows

Abstract: In this work, model closures of the multiphase Reynolds-averaged Navier–Stokes (RANS) equations are developed for homogeneous, fully developed gas–particle flows. To date, the majority of RANS closures are based on extensions of single-phase turbulence models, which fail to capture complex two-phase flow dynamics across dilute and dense regimes, especially when two-way coupling between the phases is important. In the present study, particles settle under gravity in an unbounded viscous fluid. At sufficient mass loadings, interphase momentum exchange between the phases results in the spontaneous generation of particle clusters that sustain velocity fluctuations in the fluid. Data generated from Eulerian–Lagrangian simulations are used in a sparse regression method for model closure that ensures form invariance. Particular attention is paid to modelling the unclosed terms unique to the multiphase RANS equations (drag production, drag exchange, pressure strain and viscous dissipation). A minimal set of tensors is presented that serve as the basis for modelling. It is found that sparse regression identifies compact, algebraic models that are accurate across flow conditions and robust to sparse training data.

Shear relaxation governs fusion dynamics of biomolecular condensates

Abstract: Phase-separated biomolecular condensates must respond agilely to biochemical and environmental cues in performing their wide-ranging cellular functions, but our understanding of condensate dynamics is lagging. Ample evidence now indicates biomolecular condensates as viscoelastic fluids, where shear stress relaxes at a finite rate, not instantaneously as in viscous liquids. Yet the fusion dynamics of condensate droplets has only been modeled based on viscous liquids, with fusion time given by the viscocapillary ratio (viscosity over interfacial tension). Here we used optically trapped polystyrene beads to measure the viscous and elastic moduli and the interfacial tensions of four types of droplets. Our results challenge the viscocapillary model, and reveal that the relaxation of shear stress governs fusion dynamics. These findings likely have implications for other dynamic processes such as multiphase organization, assembly and disassembly, and aging.

Numerical simulation for the steady nanofluid boundary layer flow over a moving plate with suction and heat generation

Abstract: In the study, the steady, laminar, incompressible, convective flow of a viscous fluid over a moving plate is investigated theoretically by adopting different types of nanoparticles Radiation, internal heat generation and viscous dissipation effects are considered in the energy modeled equation The governing flow equations for the momentum and temperature are reduced to dimensionless form via similarity transformations The solutions to the resultant equations alongside with the transformed boundary conditions are numerically obtained using MATLAB package bvp4c Validation with earlier studies are done for the non-internal heat generation case for two distinct nanoparticles of type Cu-water and Al-water Extensive visualization of flow rate and heat distributions for various emerging parameters are examined Temperature is consistently enhanced with a rising Eckert number of both types of nanofluids, whereas it is strongly reduced with rising values of radiation term Heat transfer coefficient is consistently increased with a nanoparticle volume fraction of high convective heat in the medium

MHD Flow of Thermally Radiative Maxwell Fluid Past a Heated Stretching Sheet with Cattaneo–Christov Dual Diffusion

Abstract: This study explains the impression of MHD Maxwell fluid with the presence of thermal radiation on a heated surface. The heat and mass transmission analysis is carried out with the available of Cattaneo–Christov dual diffusion. The derived PDE equations are renovated into ODE equations with the use of similarity variables. HAM technique is implemented for finding the solution. The importance of physical parameters of fluid velocity, temperature, concentration, skin friction, and heat and mass transfer rates are illustrated in graphs. We found that the fluid velocity declines with the presence of the magnetic field parameter. On the contrary, the liquid temperature enhances by increasing the radiation parameter. In addition, the fluid velocity is low, and temperature and concentration are high in Maxwell fluid compared to the viscous liquid.

Convective heat transfer for Peristaltic flow of SWCNT inside a sinusoidal elliptic duct

Abstract: A mathematical model is presented to analyse the flow characteristics and heat transfer aspects of a heated Newtonian viscous fluid with single wall carbon nanotubes inside a vertical duct having elliptic cross section and sinusoidally fluctuating walls. Exact mathematical computations are performed to get temperature, velocity and pressure gradient expressions. A polynomial solution technique is utilized to obtain these mathematical solutions. Finally, these computational results are presented graphically and different characteristics of peristaltic flow phenomenon are examined in detail through these graphs. The velocity declines as the volume fraction of carbon nanotubes increases in the base fluid. Since the velocity of fluid is dependent on its temperature in this study case and temperature decreases with increasing volumetric fraction of carbon nanotubes. Thus velocity also declines for increasing volumetric fraction of nanoparticles.

Integral-based spectral method for inextensible slender fibers in Stokes flow

Abstract: Every animal cell is filled with a cytoskeleton, a dynamic gel made of inextensible fibers, such as microtubules, actin fibers, and intermediate filaments, all suspended in a viscous fluid. Numerical simulation of this gel is challenging because the fiber aspect ratios can be as large as $10^4$. We describe a new method for rapidly computing the dynamics of inextensible slender filaments in periodically-sheared Stokes flow. The dynamics of the filaments are governed by a nonlocal slender body theory which we partially reformulate in terms of the Rotne-Prager-Yamakawa hydrodynamic tensor. To enforce inextensibility, we parameterize the space of inextensible fiber motions and strictly confine the dynamics to the manifold of inextensible configurations. To do this, we introduce a set of Lagrange multipliers for the tensile force densities on the filaments and impose the constraint of no virtual work in an $L^2$ weak sense. We augment this approach with a spectral discretization of the local and nonlocal slender body theory operators which is linear in the number of unknowns and gives improved spatial accuracy over approaches based on solving a line tension equation. For dynamics, we develop a second-order semi-implicit temporal integrator which requires at most a few evaluations of nonlocal hydrodynamics and a few block diagonal linear solves per time step. After demonstrating the improved accuracy and robustness of our approach through numerical examples, we apply our formulation to a permanently cross-linked actin mesh in a background oscillatory shear flow. We observe a characteristic frequency at which the network transitions from quasi-static, primarily elastic behavior to dynamic, primarily viscous behavior. We find that nonlocal hydrodynamics increases the viscous modulus by as much as 25%, even for semi-dilute fiber suspensions.

Entropy Analysis on a Three-Dimensional Wavy Flow of Eyring–Powell Nanofluid: A Comparative Study

Abstract: The thermal management of a system needs an accurate and efficient measurement of exergy. For optimal performance, entropy should be minimized. This study explores the enhancement of the thermal exchange and entropy in the stream of Eyring–Powell fluid comprising nanoparticles saturating the vertical oriented dual cylindrical domain with uniform thermal conductivity and viscous dissipation effects. A symmetrical sine wave over the walls is used to induce the flow. The mathematical treatment for the conservation laws are described by a set of PDEs, which are, later on, converted to ordinary differential equations by homotopy deformations and then evaluated on the Mathematica software tool. The expression of the pressure rise term has been handled numerically by using numerical integration by Mathematica through the algorithm of the Newton–Cotes formula. The impact of the various factors on velocity, heat, entropy profile, and the Bejan number are elaborated pictorially and tabularly. The entropy generation is enhanced with the variation of viscous dissipation but reduced in the case of the concentration parameter, but viscous dissipation reveals opposite findings for the Newtonian fluid. From the abovementioned detailed discussion, it can be concluded that Eyring–Powell shows the difference in behavior in the entropy generation and in the presence of nanoparticles due to the significant dissipation effects, and also, it travels faster than the viscous fluid. A comparison between the Eyring-Powell and Newtonian fluid are also made for each pertinent parameter through special cases. This study may be applicable for cancer therapy in biomedicine by nanofluid characteristics in various drugs considered as a non-Newtonian fluid.

Falling balls in a viscous fluid with contact: Comparing numerical simulations with experimental data

Abstract: We evaluate a number of different finite-element approaches for fluid–structure (contact) interaction problems against data from physical experiments. This consists of trajectories of single particles falling through a highly viscous fluid and rebounding off the bottom fluid tank wall. The resulting flow is in the transitional regime between creeping and turbulent flows. This type of configuration is particularly challenging for numerical methods due to the large change in the fluid domain and the contact between the wall and the particle. In the finite-element simulations, we consider both rigid body and linear elasticity models for the falling particles. In the first case, we compare the results obtained with the well-established Arbitrary Lagrangian–Eulerian (ALE) approach and an unfitted moving domain method together with a simple and common approach for contact avoidance. For the full fluid–structure interaction (FSI) problem with contact, we use a fully Eulerian approach in combination with a unified FSI-contact treatment using Nitsche's method. For higher computational efficiency, we use the geometrical symmetry of the experimental setup to reformulate the FSI system into two spatial dimensions. Finally, we show full three-dimensional ALE computations to study the effects of small perturbations in the initial state of the particle to investigate deviations from a perfectly vertical fall observed in the experiment. The methods are implemented in open-source finite element libraries, and the results are made freely available to aid reproducibility.

Viscosity of cohesive granular flows.

Abstract: Cohesive granular materials such as wet sand, snow, and powders can flow like a viscous liquid. However, the elementary mechanisms of momentum transport in such athermal particulate fluids are elusive. As a result, existing models for cohesive granular viscosity remain phenomenological and debated. Here we use discrete element simulations of plane shear flows to measure the viscosity of cohesive granular materials, while tuning the intensity of inter-particle adhesion. We establish that two adhesion-related, dimensionless numbers control their viscosity. These numbers compare the force and energy required to break a bond to the characteristic stress and kinetic energy in the flow. This progresses the commonly accepted view that only one dimensionless number could control the effect of adhesion. The resulting scaling law captures strong, non-Newtonian variations in viscosity, unifying several existing viscosity models. We then directly link these variations in viscosity to adhesion-induced modifications in the flow micro-structure and contact network. This analysis reveals the existence of two modes of momentum transport, involving either grain micro-acceleration or balanced contact forces, and shows that adhesion only affects the latter. This advances our understanding of rheological models for granular materials and other soft materials such as emulsions and suspensions, which may also involve inter-particle adhesive forces.

Properties of assembly of superparamagnetic nanoparticles in viscous liquid.

Abstract: Detailed calculations of the specific absorption rate (SAR) of a dilute assembly of iron oxide nanoparticles with effective uniaxial anisotropy dispersed in a liquid are performed depending on the particle diameters, the alternating (ac) magnetic field amplitude H0 and the liquid viscosity. For small and moderate H0 values with respect to particle anisotropy field Hk the SAR of the assembly as a function of the particle diameter passes through a characteristic maximum and then reaches a plateau, whereas for sufficiently large amplitudes, H0 ~ Hk, the SAR increases monotonically as a function of diameter. The realization of viscous and magnetic oscillation modes for particle unit magnetization vector and director for moderate and sufficiently large H0 values, respectively, explains this behavior. It is found that the SAR of the assembly changes inversely with the viscosity only in a viscous mode, for nanoparticles of sufficiently large diameters. In the magnetic mode the SAR of the assembly is practically independent of the viscosity, since in this case the nanoparticle director only weakly oscillates around the ac magnetic field direction. The conditions for the validity of the linear response theory have been clarified by comparison with the numerical simulation data.

CFD simulation of creeping flows in a novel split-and-recombine multifunctional reactor

Abstract: Various mixing processes deal with the blending of viscous fluids at low Reynolds numbers. Some of the emerging trends rely on the use of either active or passive microstructures to achieve this task when highly viscous or fragile fluids are employed. The compactness of such mixers remains, however, a major challenge due to the long residence times required to achieve the desired outcome. Split-and-Recombine (SAR) mixers are a promising solution since they rely on a multi-lamination process to perform a series of baker’s transforms on the concentration profile. The current work is a numerical study that describes the hydrodynamic and mixing performance of a new topology of SAR mixers. This mixer is characterized by a double separation and recombination aimed at increasing the mixture homogeneity in a shorter distance. For this purpose, a finite element solver is used to compute the pressure drop, friction factor, concentration profile, and segregation scales for a viscous fluid in the creeping flow regime. The results are compared against two commonly used SAR mixers in the open literature. The findings show that the newly proposed mixer exhibits a superior performance through a better mixing quality at a lower energy consumption requirement.

Magnetohydrodynamic flow of viscous fluid between two parallel porous plates with bottom injection and top suction

Abstract: This paper deals with the problem of steady laminar flow of an electrically conducting viscous incompressible fluid flow between two parallel porous plates of a channel in the presence of a transve...

Finite difference simulations for magnetically effected swirling flow of Newtonian liquid induced by porous disk with inclusion of thermophoretic particles diffusion

Abstract: Heat and mass transfer analysis of viscous liquid flow generated by rotation of disk has generated prodigious interest due to promising utilizations in numerous processes such as thermal energy generation systems, turbine rotators, geothermal energy preservations, chemical processing, medicinal instrumentations, computing devices and so forth. In view of such extraordinary utilizations in numerous engineering procedures existent exertion is excogitated to disclose flowing phenomenon over rotating disk. To raise the importance of current analysis influential physical aspects like magnetic field, permeability, Dufour and Soret diffusion phenomenon are also incorporated. Subsequently, flow field distributions are analyzed for suction and injection cases. Modelling is structured via PDE’s by obliging constitutive conservation laws. Boundary layer approach is executed to reduce complexity of attained partial differential system. Transformations developed by Karman are implemented to convert developed differential framework into ODE’s. Implicitly finite differenced technique known as Keller Box is engaged to find solution of coupled intricate high order ordinary differential equations. Influence of flow controlling parameters on associated distributions are revealed through graphical and tabular representations. The related quantities of engineering interest like coefficients of wall drag force, along radial and tangential directions are also computed. Credibility of presently computed results is established by constructing comparison with previously published literature. It is inferred that magnetic strength parameter enhances tangential and radial components of velocity whereas contrary trend is depicted in axially directed velocity. In addition, temperature and momentum distributions show up surging attribute versus magnetic field parameter. All associated profiles have exhibited decrementing aspects against suction parameter. It is also revealed that increment in Soret tends to produce depreciation in temperature profile whereas concentration distribution is enhanced.

Convection heat mass transfer and MHD flow over a vertical plate with chemical reaction, arbitrary shear stress and exponential heating.

Abstract: The present research article is directed to study the heat and mass transference analysis of an incompressible Newtonian viscous fluid. The unsteady MHD natural convection flow over an infinite vertical plate with time dependent arbitrary shear stresses has been investigated. In heat and mass transfer analysis the chemical molecular diffusivity effects have been studied. Moreover, the infinite vertical plate is subjected to the phenomenon of exponential heating. For this study, we formulated the problem into three governing equations along with their corresponding initial and boundary conditions. The Laplace transform method has been used to gain the exact analytical solutions to the problem. Special cases of the obtained solutions are investigated. It is noticed that some well-known results from the published literature are achieved from these special cases. Finally, different physical parameters' responses are investigated graphically through Mathcad software.

Love-Type Wave Propagation in an Inhomogeneous Cracked Porous Medium Loaded by Heterogeneous Viscous Liquid Layer

Abstract: Love-type wave propagation through inhomogeneous dual porous layer has been investigated in this present article. The heterogeneous fluid-saturated dual porous stratum is bounded by a non-homogeneous viscous liquid layer and an isotropic half-space. Impacts of viscosity, inhomogeneity, matrix porosity along with fracture porosity have been calculated in detail. Navier–Stokes equation has been used to acquire the velocity component in heterogeneous viscous liquid layer. Separable variable method has been performed to convert partial differential equations into ordinary differential equations. Elimination of arbitrary constants from boundary conditions leads to complex dispersion relation of Love-type wave propagation. The complex equation consists of Whittaker functions and their derivatives which are expanded up to second term by approximating large parameters. Dispersion and attenuation equations of Love-type wave have been decoupled for implementing several graphs which illustrate reverberations of heterogeneity parameter, porosity, volume fraction of fractures, density on dispersive and damping nature of Love-type wave. Fundamental mode and higher modes of Love-type wave are observed through graphical execution. Effects of inhomogeneity parameters are also portrayed through surface plotting. Correlation of liquid layer and fractured porous layer in crustal region has been established both analytically and graphically which is also validated by applying particular conditions. Heterogeneity parameter, volume fraction of fractures, porosity, density have major impact on dispersion and attenuation of Love-type wave propagating in dual porous medium. This solid–liquid collaborative study unlocks a different area of future research.

Hydrodynamic instabilities in swirling flow under axial magnetic field

Abstract: The present paper investigates numerically the hydrodynamic instabilities occurring in a cylindrical container filled with a conducting viscous fluid and submitted to an axial magnetic field. The axisymmetric swirling flow produced by rotation of the bottom disk, in which a vortex breakdown bubble occurred on the axis of symmetry. This flow structure represents one of the most important instabilities. The governing Navier–Stokes and potential equations are solved by using the finite-volume method. For both steady-state and oscillatory regimes, various combinations of the top, bottom, and side walls conductivity are considered. The effects of the magnetic field and wall electrical conductivities on the position of vortex breakdown and his disappearance is developed. The results obtained showed that the vortex breakdown is suppressed beyond the magnitude of the magnetic field exceeds a critical value. The stability diagram (Ha c r –Re) corresponding to the vortex breakdown disappearance for electrically conducting and insulating walls is obtained.

Immersed granular collapse: from viscous to free-fall unsteady granular flows

Abstract: The collapse of a granular column in a liquid is investigated using numerical simulations. From previous experimental studies, it has been established that the dynamics of the collapse is mostly influenced by the Stokes number St, comparing grain inertia and viscous fluid dissipation, and the initial volume fraction of the granular column φi. However, the full characterization of the collapse in the (St, φi) plane is still missing, restricting its modelling as a physical process for geophysical applications. Only numerical tools can allow the variation over the parameter space (St, φi) that is hardly reachable in experiments as well as a full description of the granular phase that plays a major role in dense granular flows. For this purpose, a dedicated numerical model is used including a discrete element method to resolve the granular phase. The specific objectives of the paper are then twofold: (i) the characterization of the dynamics of the collapse and its final deposit with respect to (St, φi) to complement available experimental data, and (ii) the description of the granular rheology according to these two dimensionless numbers including dilatancy effects. A simple predictive model stems from the obtained results, allowing one to explain the evolution of the final deposit with (St, φi).