Velocity Slip Effects Research Articles

Investigation of Effects of Thermal Radiation, Magnetic Field, Eckert Number, and Thermal Slip on MHD Hiemenz Flow by Optimal Homotopy Asymptotic Method

Analytical investigation of thermal radiation, Prandtl number, Eckert number, permeability parameter, magnetic field, velocity, and thermal slip effects on magnetohydrodynamic Hiemenz flow over a permeable plate with forced convection has been presented. Similarity variable conversion method has been applied to transmute the fundamental governing equations of the fluid dynamics in flow into a pair of nonlinear third-order ordinary differential equations and is analytically solved by the optimal homotopy asymptotic method (OHAM). The influences of several relevant physical parameters in the model on velocity and temperature of the fluid have been studied and analysed profoundly by use of graphs and tables. It is detected that, with mounting value of suction/blowing parameter and magnetic field parameter, the skin friction coefficient enhances. Likewise, it is seen that the Nusselt number increases with enhancing value of magnetic parameter. It is also witnessed that the velocity increases as the Eckert number, blowing/suction parameter, and permeability parameter increase, but it decays against magnetic field and velocity slip parameter. Moreover, the result reveals that the fluid temperature upsurges along with snowballing the radiant heat, magnetic field parameter, and the Eckert number. However, it descends against thermal slip parameter, Prandtl number, wall temperature exponent, and velocity slip parameter. A comparison with previous studies has been made, and the result shows an excellent agreement.

Artificial neural networking (ANN) analysis for heat and entropy generation in flow of non‐Newtonian fluid between two rotating disks

Mixed convection is a mechanism of heat transport in a thermodynamic system in which the motion of fluid particles is produced by gravity as well as external forces like fans, pumps, or any other devices. Such type of heat transport has a fruitful application in daily life due to reliable maintenance. In this regard, numerous researchers and analyst have focused on the importance of mixed convective flow to explore its different aspects, and frequent research articles are published in this area. In this work, mixed convective entropy optimized nanomaterial magnetohydrodynamics (MHD) flow of Ree‐Eyring fluid is discussed between two rotating disks. The effects of porosity and velocity slip are considered. Both the disks are rotating with different angular frequency and stretching rates. Modeling is performed for the energy equation subject to heat generation/absorption, dissipation, radiative heat flux, and Joule heating. Four types of irreversibilities are discussed, and total entropy rate is calculated. The obtained results are compared with past studies and found good agreement with them. The physical curiosity like skin friction and Sherwood and Nusselt numbers are numerically calculated. Series solutions are computed via homotopy method. Our obtained outcomes show that the velocity and temperature fields show contrast behavior against larger magnetic parameter. It is also noticed that the entropy rate and Bejan number have opposite behaviors against higher values of Weissenberg number. The entropy rate increases for higher Weissenberg number while Bejan number decays.

A bubble structure dependent drag model for CFD simulation of bi‐disperse gas‐solid flow in bubbling fluidizations

AbstractIn this work, the bi‐disperse gas‐solid flow system inside a grid cell is decomposed into subsystems, and a bubble structure dependent drag model is proposed. The bi‐disperse drag correlation derived from direct numerical simulation is coupled to calculate the drag coefficient in subsystems. The effects of slip velocity, particle composition concentration, and solid concentration gradient are considered in the novel drag model. Three simulation cases are carried out to validate the effectiveness of the novel drag model. It is found that smaller particles strongly influence the heterogeneity of larger particles. Solids concentration gradient is obvious at the bubble surface, gas inlet, and the bed upper surface, indicating the dramatic change of interphase drag force in these regions. Simulation results predicted by the novel drag model are more accurate than the traditional drag model. The comparison between 2D and 3D simulations for a pseudo‐2D fluidized bed are also presented.

Lift and drag forces acting on a particle moving in the presence of slip and shear near a wall

Abstract

Melting Heat Transfer of MHD Micropolar Fluid Flow Past An Exponentially Stretching Sheet with SLip and Thermal Radiation

The effects of velocity slip and radiation on MHD flow and melting heat transfer of a micropolar fluid due to an exponentially stretched sheet are presented. By means of similarity transformations the leading partial differential equations are changed to a set of ordinary differential equations which are nonlinear. Numerical solutions of the nonlinear system of equations are then obtained by changing the boundary value problem first to an initial value problem. It is observed that the pertaining parameters have significant effects on the flow and heat transfer characteristics, which are presented and talked about in detail through their illustrations. Due to boost in the melting parameter, the fluid velocity, angular velocity and temperature are found to decrease. Fluid velocity and angular velocity both decrease with a rise in slip at the boundary but quite opposite is the effect on the temperature.

HEAT TRANSFER AND SLIP CONSEQUENCES ON PERISTALTIC TRANSPORT OF A CASSON FLUID IN AN AXISYMMETRIC POROUS TUBE

The present study investigates the effects of heat transfer on a Casson fluid flow through a porous axisymmetric tube in the presence of slip effects. The long wavelength and small Reynolds number approximation is used to obtain the closed form solutions. The numerical integration is employed to obtain pressure rise and frictional force. A parametric analysis has been presented to study the effects of Darcy number, velocity slip, yield stress, Prandtl number, Eckert number, and thermal slip on pressure rise, pressure gradient, frictional force, and temperature. The study reveals that the reduction in pressure rise is observed for an increase in the value of porous parameter and an increase in the value of velocity slip parameter enhances the pressure rise in the porous tube. The obtained results are found to be in good agreement with the available literature

Effects of Second-Order Velocity Slip and the Different Spherical Nanoparticles on Nanofluid Flow

The paper theoretically investigates the heat transfer of nanofluids with different nanoparticles inside a parallel-plate channel. Second-order slip condition is adopted due to the microscopic roughness in the microchannels. After proper transformation, nonlinear partial differential systems are converted to ordinary differential equations with unknown constants, and then solved by homotopy analysis method. The residual plot is drawn to verify the convergence of the solution. The semi-analytical expressions between NuB and NBT are acquired. The results show that both first-order slip parameter and second-order slip parameter have positive effects on NuB of the MHD flow. The effect of second-order velocity slip on NuB is obvious, and NuB in the alumina–water nanofluid is higher than that in the titania–water nanofluid. The positive correlation between slip parameters and Ndp is significant for the titania–water nanofluid.

Nonlinear convection flow of dissipative Casson nanofluid through an inclined annular microchannel with a porous medium

AbstractThe nonlinear convection study on the flow of a dissipative Casson nanofluid through a porous medium of an inclined micro‐annular channel is presented. The cylindrical surfaces were conditioned to temperature increase and velocity slip effects. A uniform magnetic field strength was applied perpendicular to the cylinder surface. The heat source and Darcy number influence are explored in the examination of the blood rheological model (Casson) through the annular cylinder. Appropriate dimensionless variables are imposed on the dimensional equations encompassing Casson nanofluid rheology through an annular microchannel. The resulting systems of equations were solved and computed numerically via Chebyshev‐based collocation approach. Thus, the solutions of flow distributions, volumetric flow rate, and other flow characteristics were obtained. The result shows that both nonlinear convection parameters decrease the nanoparticle volume fraction, whereas they increase the energy and momentum distributions. Moreover, the volumetric flow rate is upsurged significantly by a wider porous medium, annular gap, a higher Casson parameter, and nonlinear convection influence.

Velocity and thermal slip effects on two-phase flow of MHD Jeffrey fluid with the suspension of tiny metallic particles

This investigation addresses the mathematical analysis of three fundamental multiphase flows through diverse channels. Jeffrey fluid is taken as the base liquid which suspends with tiny spherical particles of Hafnium (Hf). Owing to the magnetic susceptibility of the metal particles and electrically conducting fluid, the effects of transversely applied magnetic fields have also been taken into account. Thermal slip boundary conditions are imposed on the magnetohydrodynamics (MHD) of multiphase flows which are confined by the lubricated flat walls. The additional contribution of viscous dissipation and thermal radiation. Flow dynamics are modeled with the help of Navier–Stokes equations; which end up in the system of nonlinear and coupled differential equations, then solved exactly. A detailed parametric study is also carried out, which reveals that the momentum of each phase reduces in response to Hartmann number while having an opposite influence on the temperature profile. More energy is added to the system due to an increase in Brinkman number and magnetic field. Finally, the presented theoretical study not only addresses many industrial applications. But, also helps to predict that multiphase flows through a horizontal channel is more prominent when generated by moving wall with the contribution of constant pressure gradient. Moreover, the present work serves as the precedent, for it bridges the missing gap in the existing literature.

Radiative Boundary Layer Flow of Casson Fluid Over an Exponentially Permeable Slippery Riga Plate with Viscous Dissipation

This study is aimed to analyze the steady of stagnation point flow and radiative heat transfer of a non-Newtonian fluid which is Casson fluid passing over an exponentially permeable slippery Riga plate in presence of thermal radiation, magnetic field, velocity slip, thermal slip, and viscous dissipation effects. The governing partial differential equations are transformed into ordinary differential equations by using similarity transformation then solved numerically by boundary value problem solver (BVP4C) in MATLAB software package. The numerical results are evaluated with previous researches to reach an agreement with the parameters of the current study. This study is discussing the behavior of the velocity and temperature profiles as well as skin friction coefficient and local Nusselt number for various physical parameters such as magnetic field, radiation, suction, thermal slip, velocity slip, Prandtl number, Eckert number and modified Hartmann number. Numerical results are shown graphically for each parameter with different values. It is found that the momentum boundary layer thickness increases with increasing the values of Casson parameter. The temperature decreases when the velocity slip parameter and thermal slip parameter are increased.

MHD Hybrid Cu-Al<sub>2</sub>O<sub>3</sub>/ Water Nanofluid Flow with Thermal Radiation and Partial Slip Past a Permeable Stretching Surface: Analytical Solution

The influence of velocity slip and thermal radiation effects on the magnetohydrodynamic hybrid Cu-Al2O3/water nanofluid flow over a permeable stretching sheet is reported in this paper. The similarity transformation is adopted to reduce the partial differential equations to the ordinary differential equations. Exact analytical method is implemented to solve the problem. Maple program is used to facilitate the calculation process. The new additional effects which are the velocity slip and thermal radiation effects are considered towards the model to scrutinize the impacts. The effects of various parameters towards the velocity and temperature profiles are demonstrated through graphs, meanwhile the skin friction coefficient and the local Nusselt number are exhibited through the tabulation of data. The existence of velocity slip reduced the velocity profile but enhanced the temperature profile. The thermal radiation effect has increased the temperature profile. The heat transfer rate are enhanced for the case of hybrid nanofluid compared to the mono nanofluid.

Thermal transport of bio-convection flow of micropolar nanofluid with motile microorganisms and velocity slip effects

The motivation of current research is to explore thermo-bioconvection micropolar liquid flow subject to motile microorganisms and nanomaterials. Rheological model characteristics of Maxwell viscoelasticity-based micropolar nanoliquid are considered for analysis. Slip mechanisms and stratification phenomenon are accounted. Heat and concentration diffusions are characterized by exploiting the Cattaneo-Christov fluxes for heat and mass. Aspects of thermophoresis, thermal radiation and Brownian motion are also accounted. The dimensional non-linear boundary value problems are rendered into the dimensionless ODE’s by utilizing admissible transformations and then tackled numerically by utilizing bvp4c technique via computational commercial software MATLAB. Significance of sundry variables against velocity, temperature, concentration of nanoparticles and microorganism’s concentration are described through graphs and numeric data.

Unsteady Boundary Layer Stagnation Point Flow and Heat Transfer over a Stretching Sheet in a Porous Medium with Slip Effects

Boundary layer flow and heat transfer over a stretching sheet in a porous medium has many applications in industrial processes. The effect of porosity plays a significant role in determining the behaviour of the fluid flow. Based on that, we analyzed the unsteady boundary layer stagnation point flow and heat transfer towards a stretching sheet by considering the porosity. The velocity and thermal slip effects are taken into consideration in the present analysis. The governing non-linear partial differential equations were transformed into a system of nonlinear ordinary differential equations using similarity transformation. The resulting ordinary differential equations were solved numerically using the shooting method in Maple software. Numerical results for the dimensionless velocity profile, temperature profile, skin friction coefficients and the local Nusselt number are presented for various parameters. The effect of dimensionless material parameter, thermal slip effect and velocity slip effect on the flow field is also discussed. It is found that the skin friction coefficients decrease whereas the local Nusselt number increases with the increase in permeability parameter.

Numerical Simulations and Experiments of Ignition of Solid Particles in a Laminar Burner: Effects of Slip Velocity and Particle Swelling

Ignition and combustion of pulverized solid fuel is investigated in a laminar burner. The two-dimensional OH radical field is measured in the experiments, providing information on the first onset of ignition and a detailed characterization of the flame structure for the single particle. In addition, particle velocity and diameter are tracked in time in the experiments. Simulations are carried out with a Lagrangian point-particle approach fully coupled with an Eulerian solver for the gas-phase, which includes detailed chemistry and transport. The numerical simulation results are compared with the experimental measurements in order to investigate the ignition characteristics. The effect of the slip velocity, i.e. the initial velocity difference between the gas-phase and the particle, is investigated numerically. For increasing slip velocity, the ignition delay time decreases. For large slip velocities, the decrease in ignition delay time is found to saturate to a value which is about 40% smaller than the ignition delay time at zero slip velocity. Performing a simulation neglecting the dependency of the Nusselt number on the slip velocity, it is found that this dependency does not play a role. On the contrary, it is found that the decrease of ignition delay time induced by the slip velocity is due to modifications of the temperature field around the particle. In particular, the low-temperature fluid related to the energy sink due to particle heating is transported away from the particle position when the slip velocity is non-zero; therefore, the particle is exposed to larger temperatures. Finally, the effect of particle swell is investigated using a model for the particle swelling based on the CPD framework. With this model, we observed negligible differences in ignition delay time compared to the case in which swelling is not included. This is related to the negligible swelling predicted by this model before ignition. However, this is inconsistent with the experimental measurements of particle diameter, showing a significant increase of diameter even before ignition. In further simulations, the measured swelling was directly prescribed, using an analytical fit at the given conditions. With this approach, it is found that the inclusion of swelling reduces the ignition delay time by about 20% for small particles while it is negligible for large particles.

Impacts of slip in radiative MHD peristaltic flow of fourth grade nanomaterial with chemical reaction

In present study the impacts of thermal radiation and Joule heating for MHD peristaltic motion of fourth-grade nanoliquid in a channel are addressed. Elastic characteristics of channel walls are studied. Velocity, concentration and thermal slip effects are imposed. Furthermore the influences of viscous dissipation, heat source /sink and chemical reaction in modelling are retained. Nanofluid model consisting of thermophoresis and Brownian motion is employed. Mathematical formulation is developed by adopting long wave length and low Reynolds number. Numerical technique is used for finding the solutions of the governing problem. Comprehensive study of emerging flow variables for velocity, temperature, concentration of nanoparticles, heat transfer coefficient and trapping is addressed graphically. Moreover the results for skin friction coefficient and Sherwood number are also examined.

On the relationship between drag and vertical velocity fluctuations in flow over riblets and liquid infused surfaces

Direct numerical simulations (DNS) of flow over triangular and rectangular riblets in a wide range of size and Reynolds number have been carried out. The flow within the grooves is directly resolved by exploiting the immersed-boundary method. It is found that the drag reduction property is primarily associated with the capability of inhibiting vertical velocity fluctuations at the plane of the crests, as in liquid-infused surfaces (LIS) devices. This is mimicked in DNS through artificial suppression of the vertical velocity component, which yields large drag decrease, proportionate to the riblets size. A parametrization of the drag reduction effect in terms of the vertical velocity variance is found to be quite successful in accounting for variation of the controlling parameters. A Moody-like friction diagram is thus introduced which incorporates the effect of slip velocity and a single, geometry-dependent parameter. Reduced drag-reduction efficiency of LIS-like riblets is found as compared to cases with artificially imposed slip velocity. Last, we find that simple wall models of riblets and LIS-like devices are unlikely to provide accurate prediction of the flow phenomenon, and direct resolution of flow within the grooves in necessary.

Simulation of the Slip Velocity Effect in an AC Electrothermal Micropump.

The principal aim of this study was to analyze the effect of slip velocity at the microchannel wall on an alternating current electrothermal (ACET) flow micropump fitted with several pairs of electrodes. Using the finite element method (FEM), the coupled momentum, energy, and Poisson equations with and without slip boundary conditions have been solved to compute the velocity, temperature, and electrical field in the microchannel. The effects of the frequency and the voltage, and the electrical and thermal conductivities, respectively, of the electrolyte solution and the substrate material, have been minutely analyzed in the presence and absence of slip velocity. The slip velocity was simulated along the microchannel walls at different values of slip length. The results revealed that the slip velocity at the wall channel has a significant impact on the flow field. The existence of slip velocity at the wall increases the shear stress and therefore enhances the pumping efficiency. It was observed that higher average pumping velocity was achieved for larger slip length. When a glass substrate was used, the effect of the presence of the slip velocity was more manifest. This study shows also that the effect of slip velocity on the flow field is very important and must be taken into consideration in an ACET micropump.

Reduced-order modelling of concentration polarization with varying permeation: Analysis of electro-osmosis in membranes

Concentration polarization is a major challenge to water desalination process. It affects membrane performances by reducing permeate flux and increasing the risk of fouling. One promising approach to reduce concentration polarization is to use external forces such as electro-osmosis. Previously developed reduced-order model either assumed dissolving wall condition, which does not represent the real process mechanism or does not incorporate the effect of electro-osmotic flow (EOF) slip velocity. In this work, we bridge the research gap by proposing a reduced-order model with permeation for membrane systems by considering the effect of EOF slip velocity. The proposed model is shown to provide accurate prediction when compared with computational fluid dynamics (CFD) results. Additionally, the model can complete simulations in seconds, which is 2 orders of magnitude faster as compared to CFD. Using the validated model, we study the mechanism of mixing caused by the slip velocity. Results show that improved mixing and enhanced mass transfer is concentrated in the region between electrodes. We also propose analytical expressions to determine shear stress and pressure drop, which are linked to mass transfer enhancement and energy requirement respectively. This leads us to obtain an optimal electrode spacing to improve mass transfer.

Effect of nanoparticle shapes on irreversibility analysis of nanofluid in a microchannel with individual effects of radiative heat flux, velocity slip and convective heating

AbstractIn this study, the flow of a nanoliquid in a microchannel is examined. Two distinct metallic nanoparticles, titanium and silver, are used in this study. The slip regime and convective boundary are considered to compute the momentum and energy balance equation. The mathematical expressions are made dimensionless by using nondimensional quantities. A numerical approach called Runge‐Kutta‐Fehlberg scheme is employed to obtain the solution. Effects of the internal heat source and radiative flux on fluid model are examined. The upshots of the pertinent flow parameter and the physical features are visualized through graphical elucidations. The effect of flow constraints on the second law analysis for the described physical phenomenon is predicted. Conclusion indicates that lowering of temperature of the nanofluid is obtained by higher values of nanoparticle volume fraction. The causes of irreversibility in a thermal system is explored in this investigation. The results indicate that nonspherical nanoparticles has higher thermal conductivity ratio as compared with spherical nanoparticles. Minimization of entropy can be attained through increasing volume fraction of titanium and silver nanoparticles. Besides, it is emphasized that entropy generation is high in case of disc‐shaped nanoparticles, followed by needle and sphere shapes.

Non-linear stability analysis of two-layered porous journal bearings with velocity slip and percolation effect of additives of coupled-stress lubricant

In this paper a non-linear stability analysis of the two-layered porous journal bearing under coupled-stress lubricant has been presented with velocity slip phenomenon and additive’s percolation effect. In this non-linear transient analysis, system stability is determined by tracing the locus of the journal center and various trajectories of journal center locus have been represented in graphical form for different operating conditions. Furthermore, stability characteristics in respect of critical mass parameter and whirl ratio have been studied under various parametric conditions and a comparison between the linear and non-linear stability analysis have been demonstrated. To acquire the non-dimensional pressure values, non-dimensional transient Reynolds equation has been solved and with these pressure values, bearing load carrying capacity are derived. Fourth order Runge-Kutta method is used to solve the second order equations of motion for journal bearing system to obtain the stability characteristics. Results of this analysis may be helpful for designing such bearings.