Search Results (26)

The steady low-Reynolds-number rotation of a chain of coaxial soft spheres (each with an impermeable hard core covered by a permeable porous layer) about the axis in a viscous fluid is analyzed. The particles may be unequally spaced, and may differ in the permeability and inner and outer radii of the porous surface layer as well as angular velocity. By using a method of boundary collocation, the Stokes and Brinkman equations for the external fluid flow and flow within the surface layers, respectively, are solved semi-analytically. The particle interaction effect increases as the relative gap thickness between adjacent particles or their permeability decreases, which can be significant as the gap thickness approaches zero. A particle’s hydrodynamic torque is reduced (its rotation is enhanced) when other particles rotate in the same direction at equivalent or greater angular velocities, but increases (its rotation is hindered) when other particles rotate in the opposite direction at arbitrary angular velocities. For particles with different radii or permeabilities, the particle interaction has a greater effect on smaller or more permeable particles than on larger or less permeable particles. For the rotation of three particles, the presence of the third particle can significantly affect the hydrodynamic torques acting on the other two particles. For the rotation of numerous particles, shielding effects between particles can be substantial. When the permeability of porous layers is low, relative fluid motion is barely felt by the hard cores of the soft particles. The insights gained from this analysis on the effects of interactions among rotating soft particles may be of great importance in many physicochemical applications of colloidal suspensions. Full article

In this research, high-performance ZnAl-layered double hydroxides (ZnAl-LDHs) with different Zn²⁺ concentrations were prepared on the surface of an anodized 1060 aluminum alloy using the in situ growth method, and the influence of Zn²⁺ concentration on corrosion resistance and tribological behavior was further explored. The surface morphology, element distribution, phase composition, and mechanical performance of ZnAl-LDHs/anodic aluminum oxide (AAO) composite coatings were tested and analyzed. Subsequently, the investigation of the anti-corrosion properties and tribological behavior of as-prepared composite coatings and AAO were conducted experimentally. The results show that with the increase in Zn²⁺ concentration, the thickness and bonding strength of the coatings gradually increase, and the hardness progressively decreases. The ZnAl-LDHs/AAO composite coating with a Zn²⁺ concentration of 0.3 mol/L exhibits the best anti-corrosion ability, which has the minimum corrosion current density of 2.435 × 10⁻⁹ A/cm². This can be attributed to the uniform and compact ZnAl-LDH films where the porous structure of the AAO is well sealed. Moreover, the excellent friction-reduction and anti-wear properties of ZnAl-LDHs/AAO composite coatings with larger Zn²⁺ concentrations are verified using a ball-on-disc rotating wear tester under dry wear. A reasonable mechanism for improving tribological properties of resulting ZnAl-LDHs/AAO composite coatings is proposed. Full article

The aim of the present study is to investigate magnetohydrodynamic (MHD) time-dependent flow past a vertical slanted plate enclosing heat and mass transmission (HMT), induced magnetic field (IMF), thermal radiation (TR), and viscous and magnetic dissipation characteristics on a chemical reaction fluid flow. A boundary layer estimate is taken to develop a movement that exactly captures the time-dependent equations for continuity, momentum, magnetic induction, energy, concentration, generalized Ohm’s law, and Maxwell’s model. Partial differential equations designate the path occupied by the magnetized fluid as it passes through the porous matrix. In addition, a heat source is included in the model in order to monitor the flow nature in the current study. Because of the nonlinearity in the governing equations, the mathematical models are computed numerically by RK4 method. Further, tables and graphs are depicted to elucidate the physical influence of important factors on the flow characteristics. The novelty of the present work is investigating the irregular heat source and chemical reaction over the porous rotating channel. It is perceived that high thermal radiation occurs with increases in temperature and concentration. It is witnessed that the IMF effect is diminished for large values of magnetic Prandtl number (MPN). It is also analyzed that with increasing the heat source factor, the velocity of the fluid enhances. For stability analysis, the existing effort is compared with the published work and good agreement is found. Moreover, the residue error estimation confirms our solution. Full article

The creeping flow of a viscous fluid around a soft colloidal sphere rotating about a diameter normal to two planar walls at an arbitrary position between them is theoretically investigated in the steady limit of small Reynolds numbers. The fluid velocity outside the particle consists of the general solutions of the Stokes equation in circular cylindrical and spherical coordinates, while the fluid velocity inside the porous surface layer of the particle is expressed by the general solution of the Brinkman equation in spherical coordinates. The boundary conditions are implemented first on the planar walls by means of the Hankel transforms and then at the particle and hard-core surfaces by a collocation technique. The torque exerted on the particle by the fluid is calculated as a function of the ratio of the core-to-particle radii, ratio of the particle radius to the flow penetration length of the porous layer, and relative particle-to-wall spacings over the entire range. The wall effect on the rotating soft particle can be significant. The hydrodynamic torque exerted on the confined soft sphere increases as the relative particle-to-wall spacings decrease and stays finite even when the soft sphere contacts the plane walls. It is smaller than the torque on a hard sphere (or soft one with a reduced thickness or penetration length of the porous layer), holding the other parameters constant. For a given relative wall-to-wall spacing, this torque is minimal when the particle is situated midway between the walls and rises as it locates closer to either wall. Full article

Lightweight blades with high strength are urgently needed in practical rotor engineering. Sandwich structures with porous core and reinforced surfaces are commonly applied to achieve these mechanical performances. Moreover, blades with large aspect ratios are established by the elastic plate models in theory. This paper studies the vibration of a rotating sandwich pre-twist plate with a setting angle reinforced by graphene nanoplatelets (GPLs). Its core is made of foam metal, and GPLs are added into the surface layers. Supposing that nanofillers are perfectly connected with matrix material, the effective mechanical parameters of the surface layers are calculated by the mixing law and the Halpin–Tsai model, while those of the core layers are determined by the open-cell scheme. The governing equation of the rotating plate is derived by employing the Hamilton principle. By comparing with the finite element method obtained by ANSYS, the present model and vibration analysis are verified. The material and structural parameters of the blade, including graphene nanoplatelet (GPL) weight faction, GPL distribution pattern, porosity coefficient, porosity distribution pattern, length-to-thickness ratio, length-to-width ratio, setting angle and pre-twist angle of the plate are discussed in detail. The finds provide important inspiration in the designing of a rotating sandwich blade. Full article

In the present study, the effects of using a corrugated porous layer on the forced convection of a hybrid nanofluid flow over a 3D backward facing step are analyzed under the coupled effects of magnetic field and surface rotation. The thermal analysis is conducted for different values of the Reynolds number (Re between 100 and 500), the rotational Reynolds number (Rew between 0 and 2000), the Hartmann number (Ha between 0 and 15), the permeability of the porous layer (the Darcy number, Da between ${10}^{-5}$ and ${10}^{-2}$) and the amplitude (ax between 0.01 ap and 0.7 ap) and wave number (N between 1 and 16) of the porous layer corrugation. When rotations are activated, the average Nusselt number (Nu) and pressure coefficient values rise, while the increment of the latter is less. The increment in the average Nu is higher for the case with a higher permeability of the layer. When the corrugation amplitude and wave number are increased, favorable impacts of the average Nu are observed, but at the same time pressure coefficients are increased. Successful thermal performance estimations are made by using a neural-based modeling approach with a four input-two output system. Full article

In this paper, the thermal instability of rotating convection in a bidispersive porous layer is analyzed. The linear stability analysis is employed to examine the stability of the system. The neutral curves for different values of the physical parameters are shown graphically. The critical Rayleigh number is evaluated for appropriate values of the other governing parameters. Among the obtained results, we find: the Taylor number has a stabilizing effect on the onset of convection; the Soret number does not show any effect on oscillatory convection, as the oscillatory Rayleigh number is independent of the Soret number; there exists a threshold, $R_c^{*}$ ∈ (0.45, 0.46), for the solute Rayleigh number, such that, if $R_C$ > $R_c^{*}$, then the convection arises via an oscillatory mode; and the oscillatory convection sets in and as soon as the value of the Soret number reaches a critical value, (∈(0.6, 0.7)), and the convection arises via stationary convection. Full article

This article aims to study the effect of the vertical rotation and magnetic field on the dissolution-driven convection in a saturated porous layer with a first-order chemical reaction. The system’s physical parameters depend on the Vadasz number, the Hartmann number, the Taylor number, and the Damkohler number. We analyze them in an in-depth manner. On the other hand, based on an artificial neural network (ANN) technique, the Levenberg–Marquardt backpropagation algorithm is adopted to predict the distribution of the critical Rayleigh number and for the linear stability analysis. The simulated critical Rayleigh numbers obtained by the numerical study and the predicted critical Rayleigh numbers by the ANN are compared and are in good agreement. The system becomes more stable by increasing the Damkohler and Taylor numbers. Full article

The present work studies an axisymmetric rotating truncated cone made of functionally graded (FG) porous materials reinforced by graphene platelets (GPLs) under a thermal loading. The problem is tackled theoretically based on a classical linear thermoelasticity approach. The truncated cone consists of a layered material with a uniform or non-uniform dispersion of GPLs in a metal matrix with open-cell internal pores, whose effective properties are determined according to the extended rule of mixture and modified Halpin–Tsai model. A graded finite element method (FEM) based on Rayleigh–Ritz energy formulation and Crank–Nicolson algorithm is here applied to solve the problem both in time and space domain. The thermo-mechanical response is checked for different porosity distributions (uniform and functionally graded), together with different types of GPL patterns across the cone thickness. A parametric study is performed to analyze the effect of porosity coefficients, weight fractions of GPL, semi-vertex angles of cone, and circular velocity, on the thermal, kinematic, and stress response of the structural member. Full article

In this study, we investigated multilayer coatings fully developed with steady Newtonian and non-Newtonian fluids through parallel inclined plates. The channel was rotating about the $y$-axis with angular velocity $\Omega$. The channel contained three regions; Region 1 and Region 3 were filled with Newtonian fluid, while Region 2 had Jeffrey fluid through a porous medium. The governing equations were formed by using Navier stokes and energy equations. The equations were coupled and were non-linear due to the involvement of Darcy’s dissipation terms. The systems of equations for Region 1 and Region 3 were solved analytically, while the equations of Region 2 were solved by using the regular perturbation method. The effects of governing parameters such as magnetic field, Grashof number, the ratio of heights, angle of inclination, and ratio of viscosities on velocity and temperature were investigated, and the results are presented graphically in this paper. It is noted that the increase in buoyancy force incorporated through the Grashof number and the angle of inclination enhanced the axial and transverse velocities and the temperature for the three layers. We found that the Nusselt number increases by increasing the couple stress parameter and magnetic field parameters, and skin friction decreases at the lower plate. The main observation is that temperature and both velocity profiles increased in Region 2 with the increase in the Jeffrey parameter. Full article

The major finding of this paper is studying the stability of a double diffusive convection using the so-called local thermal non-equilibrium (LTNE) effects. A new combined model that we call it a Brinkmann-Forchheimer model was considered in this inquiry. Using both linear and non-linear stability analysis, a double diffusive convection is used in a saturated rotating porous layer when fluid and solid phases are not in the state of local thermal non-equilibrium. In addition, we discussed several related topics such as the effect of solute Rayleigh number, symmetric properties, Brinkman coefficient, Taylor number, inter-phase heat transfer coefficient on the stability of the system, and porosity modified conductivity ratio. Moreover, two cases were investigated in non-linear theory, the case of the Forchheimer coefficient $\mathcal{F}=0$ and the case of the Taylor-Darcy number $\tau =0$. For the validation of this work, some numerical experiments were made in the non-linear energy stability and the linear instability theories. Full article

Porous hydroxyapatite-biochar composites with layered microstructures (SC–HA/C) were prepared by carbonizing sugarcane stem nodes and then soaking them in lime water and (NH₄)₂HPO₄ solutions in rotation. The surface area of SC–HA/C ranges from 8.52 to 28.44 m²/g, and its microstructure inherits various macro-, meso-, and micro-pores in the cell walls of sugarcane and in the pits of the vessel walls. The maximum removal capacities were 11.50, 14.65, and 19.81 mg/g for the Cu (II) immobilization at 25 °C, 35 °C, and 45 °C with the solution Cu (II) concentration of 10~320 mg/L, respectively, which were in accordance with the copper sorption capacities of synthesized nano-hydroxylapatites. The Cu (II)-removal kinetics and isotherm followed the pseudo-second-order equation and the Langmuir equation very well. The formation of the Cu-containing hydroxylapatite solid solutions ((CuxCa_1−x)₅(PO₄)₃(OH)) through adsorption, ion exchange (x = 0.01~0.04), and dissolution-coprecipitation (x = 0.13~0.35) was the dominant process for the Cu (II) removal by the SC–HA/C composite. Full article

The effect of rotation and cross-diffusion on convection in a horizontal sparsely packed porous layer in a thermally conducting fluid is studied using linear stability theory. The normal mode method is employed to formulate the eigenvalue problem for the given model. One-term Galerkin weighted residual method solves the eigenvalue problem for free-free boundaries. The eigenvalue problem is solved for rigid-free and rigid-rigid boundaries using the BVP4c routine in MATLAB R2020b. The critical values of the Rayleigh number and corresponding wave number for different prescribed values of other physical parameters are analyzed. It is observed that the Taylor number and Solutal Rayleigh number significantly influence the stability characteristics of the system. In contrast, the Soret parameter, Darcy number, Dufour parameter, and Lewis number destabilize the system. The critical values of wave number for different prescribed values of other physical parameters are also analyzed. It is found that critical wave number does not depend on the Soret parameter, Lewis number, Dufour parameter, and solutal Rayleigh number; hence critical wave number has no impact on the size of convection cells. Further critical wave number acts as an increasing function of Taylor number, so the size of convection cells decreases, and the size of convection cells increases because of Darcy number. Full article

The influence of casting centrifugation process parameters, such as a rotation speed (ω), the amount of the film-forming solution (V), and its concentration (C) on transport properties of composite membranes were investigated. A number of composite membranes based on poly (1-trimethylsilylpropyne) (PTMSP) and micro- (MFFK-1) and ultrafiltration (UFFK) membranes were obtained using the spin-coating method. For the first time, an unexpected dependence of permeance and ideal selectivity on rotation speed had been discovered: the thickness of the selective layer decreases from 3.0 to 1.0 μm for MFFK-1 and from 1.7 to 1.1 μm for UFFK with an increase of spin coater rotation speed from 500 to 3000 rpm. However, the gas permeance of composite membranes in the range of 500–2000 rpm was reduced due to an increase of a penetration depth of PTMSP into a support layer porous structure (estimated by the EDX method). The permeance of the PTMSP/UFFK membranes was higher than PTMSP/MFFK-1 membranes due to a thinner selective layer and a lower penetration depth of polymer solution into the pores of the support. The highest CO₂/N₂ selectivity values were achieved as 5.65 ± 0.9 at CO₂ permeance 5600 ± 1000 GPU for PTMSP/UFFK membranes (C_PTMSP = 0.35%, V_solution = 1 mL, ω = 1000 rpm), and 6.1 ± 0.5 at CO₂ permeance 4090 ± 500 GPU for PTMSP/MFFK-1 membranes (C_PTMSP = 0.35%, V_solution = 1 mL, ω = 2000 rpm). Full article

The flow and heat transfer in a rotating vertical porous layer, placed far from the axis of rotation, and subjected to internal heat generation and centrifugal jitter, is considered. The linear stability theory is used to determine the convection threshold, in terms of the critical Rayleigh number. Typical liquids used in engineering applications and heavy liquid metals are used to demonstrate conditions at which the Vadasz number is sufficiently small to warrant the retention of the time derivative in the momentum equation. When considering low amplitude and high frequency approximation, the results show that vibration has a stabilizing effect on the onset of convection. The impact of increasing the Vadasz number is to stabilize the convection, in addition to reducing the transition point from synchronous to subharmonic solutions. In summary, when the Vadasz number is large, centrifugal jitter has no impact on the convection stability criteria. In contrast, when the Vadasz number is small, centrifugal jitter impacts the convection stability criteria. Full article