Slip Flow Research Articles

Lattice Boltzmann simulation of neutrally buoyant circular slip particle motion in a clockwise double-lid-driven square cavity

This paper is on the motion of a neutrally buoyant but circular slip particle in a clockwise double-lid-driven square cavity. The slip flow at the particle surface is implemented by the lattice Boltzmann method with corrected slip boundary schemes. The effects of slip length (Ls), initial particle position, Reynolds number (Re), and particle size (D) are studied on the migration of the slip particle. The motion of the circular slip particle is dominated by the centrifugal and boundary-repulsion forces. The results show that the cavity center is the unique fixed point, and once the slip particle initially deviates from the cavity center, it is always stabilized at the same limit cycle. With the increase in slip length, the limit cycle of the circular slip particle is closer to the cavity boundaries, which brings a stronger centrifugal force to balance the increased boundary-confinement effect. As the slip length, Ls, exceeds 0.02D, the limit cycle forms more quickly than the circular no-slip particle. When Re increases to within 1000, the limit cycle is squashed along the leading diagonal of the cavity and pushed toward the boundaries; however, when Re increases beyond 1000, two developing secondary vortices confine the limit cycle to shrink toward the cavity center. With the increase in particle size, the enhanced boundary confinements lead to the shrinkage of the limit cycle toward the cavity center.

Navier’s slip and interactive Lorentz force impact on radiative stretched flow of copper–water/methanol nanofluid using a micro-convection model

The present investigation aims at three dimensional slip flow of a variable electrical conducting and radiative nanofluid past an exponential stretching sheet under the action of induced Lorentz force. The novelty of the study is the introduction of Navier’s slip subject to three dimensional stretched flow influneced by Lorentz force. Implementation of micro-convection variable thermal conductivity model. The system of non-dimensionalized governing differential equations is solved numerically by using 4th-order R.K. method cum shooting technique. The effective outcome of current study is that drag force offered by magnetic interaction accounts for the decelerated fluid motion. Non-zero slip leads to the diminution of fluid velocity, surface viscous drag and heat transfer rate from the stretched surface.

Thermo-osmotic slip flows around a thermophoretic microparticle characterized by optical trapping of tracers

Thermo-osmotic slip flows around a thermophoretic microparticle characterized by optical trapping of tracers

Numerical simulation of unsteady MHD bio-convective flow of viscous nanofluid through a stretching surface

The current flow model is prepared to explore the characteristics of heat and mass transfer through a time-dependent bio-convection slip flow of viscous nanofluid moving over a porous radiative stretched surface model. The outset of bio-thermal convection in a suspension comprising gyrotactic microorganisms and nanoparticles is considered along with radiation and velocity slip. The presence of these nanoparticles and their motion within the nanofluid gives rise to thermophoresis as well as the Brownian motion phenomena and the consideration of these aspects in the model gives realistic results. Moreover, the present model includes the collective influence of the aligned magnetic field, heat source, and mass suction on the boundary. The similarity analysis has been carried out to transform the basic model equations into nonlinear dimensionless ordinary differential equations (ODEs) which are solved numerically using the bvp4c technique in MATLAB. Some reasonable values have been assigned to the flow parameters based on the above different conditions which provide various graphical results. Certain finding states that velocity and temperature respectively decrease and increase as the aligned magnetic field angle is scaled up, whereas the nano particles concentration strengthens with the amplifying values of convection diffusion and thermophoresis parameter and slumps with the rising values of Brownian motion parameter and Schmidt number respectively. Moreover, the concentration of microorganism and nano particles diminishes with the rising values of Schmidt number, as well as the improvement of convection diffusion parameter and Schmidt number magnifies the Sherwood number. The local density of motile microorganisms reduces with the improvement of stretching parameter and bio-convection Schmidt respectively. The obtained results have been validated by comparing them with the published literature.

Static performance analysis of gas foil thrust bearings under inclined thrust disc considering the slip flow effect

As one of the important components in air compressors for fuel cell vehicles, the static performance of the gas foil thrust bearings greatly affects the operating stability of the rotor system. In actual operation, thrust disc tilt and the slip flow effect often occur, which will change the characteristics of bearings. Therefore, this paper focuses on the static performance of gas foil thrust bearings under tilting conditions with account of the slip flow effect. Firstly, the gas film thickness equation is established when the thrust disc is inclined, and the Reynolds equation is modified by the boundary slip conditions. Secondly, the load capacity and friction torque of bearings are solved by the finite difference method and successive over-relaxation method. Finally, the sensitivity of rigid and elastic bearings to tilt angles is analyzed by comparing the static characteristics under tilting conditions. The results show that the load capacity will be overestimated without considering the slip flow effect, and the tilting of the thrust disc increases both the load capacity and friction torque. Furthermore, compared with rigid bearings, elastic foil bearings have better adaptability to tilting conditions, which is conducive to the stable operation of the rotor system.

Thermal Characteristics of Dry Gas Seal in Startup Process Considering Microscale Effects

The heat generated during the startup process of dry gas seals, such as the friction heat of the asperities, viscous shear heat, and the expansion heat of the gas film, easily leads to seal failure and endangers the stable operation of turbomachinery. This study combines the statistically modified contact model and the average Reynolds equation by considering the adiabatic index and the microscale effects of dry gas seals to explore the heat generation characteristics of dry gas seals formed in series at multiple times. In particular, the change laws and influencing factors among the components, including the friction heat of asperities and the shear heat and expansion heat of the gas film and total heat, are investigated. A comparative analysis indicates that the slip flow effect increases the total heat during the startup process. The friction heat is much greater than expansion heat and shear heat. Despite constant acceleration, exponential acceleration, or Harrison acceleration, the heat changes are uneven during the startup process. In particular, the heat changes sharply in the early stage and slowly in the later stage. The Harrison acceleration mode is the most conducive to sealing stability.

Analysis of Slip Effects on the Stability and Interactions of Mach 5 Flat-Plate Boundary-Layer Waves

The issue of boundary-layer transition with slight rarefaction for high-speed aircraft has recently received increased attention. In this paper, the stability and resonant interactions of boundary-layer waves for a Mach 5 flat plate under the slip effect are investigated using direct numerical simulation (DNS) and linear stability theory (LST). The slip effect is modelled by slip boundary conditions within the Navier-Stokes (NS) framework, and an LST method considering wall perturbations for both no-slip and slip flows is established. The present numerical results indicate that the slip effect has a consistent impact on the stability of fast and slow modes as obtained from DNS and current LST. In addition, the DNS results show that the slip effect delays the conversion of mode F1 to mode S led by their resonance, and enhances the resonant interactions between fast mode waves and fast acoustic waves.

Significance of Upstream Wall Conditions in Characterizing the Heat Transfer Phenomena of Rarefied Flows

Abstract Slip flows in small-scale flow networks involve simultaneous presence of multiple factors governing the flow field. In addition, conditions of upstream wall need to be clearly defined for quantifying the total heat that fluid receives from the wall. The present work addresses these aspects by analyzing the heat transfer aspects of slip flow of gaseous nitrogen through a circular pipe, undergoing either heating or cooling. The complete form of the governing equations is solved numerically while retaining property variation. The thermal field is found to exhibit two distinct asymptotic regions, with the first one representing fully developed heat transfer and the second one representing isothermal states. The fully developed Nusselt number (Nufd) is found to rise first, before dropping continuously with rise in Knudsen number (Kn). The pair of Kn and maximum Nufd is found to be dependent on Peclet number (Pe) of the system. Local Nu is found to drop to a minimum, lower than Nufd for Kn∼O(10−3) due to a significant radial advection. The presence of an adiabatic upstream wall reveals that heat may propagate up to the inlet for Kn≳0.015. An analytical solution is developed to approximate this limiting value of Kn, and it agrees well with the numerical results. The observed flow behavior leads to the categorization of flow regime into three types: (i) Kn<0.001, possessing dependence on change in Pe only, (ii) 0.001≤Kn<0.01, possessing concurrence of effects due to change in Pe and Kn, and (iii) 0.01≤Kn<0.1, possessing dependence on change in Kn only. Further, Pe is shown to represent Nubulk for the flow, where in the range 0.01≤Kn<0.1, Nutot≈Nubulk as Kn approaches 0.01 and Nutot≈Nuin as Kn approaches 0.1. A convenient approach is proposed to evaluate Nutot for any condition of the upstream wall. These outcomes indicate the necessity to clearly define the condition of the upstream wall and to evaluate the total heat transfer in small-scale heat exchangers, which may be much larger than what fluid carries downstream.

Convective Heat Transfer and Entropy Generation Analysis in Elliptic Microchannels

Abstract In this paper, we investigate analytically the first and the second law characteristics of fully developed gaseous slip flow with the H1 boundary condition through elliptical microchannels. The closed-form solution of temperature distribution was obtained with the separation of variables method. Expressions for the Nusselt number, the nondimensional entropy generation rate, and the Bejan number were further deduced. The influences of crucial factors, including viscous dissipation, rarefaction, aspect ratio, and fluid axial heat conduction, have been carefully evaluated. The results indicated that viscous dissipation has a dramatic impact on heat transfer characteristics. But the rarefaction effect was found to significantly reduce the effect of the viscous dissipation on the Nusselt number, and the former may not deteriorate the heat transfer performance when considering the viscous dissipation. The main source of the entropy generation rate is controlled by fluid axial heat conduction when the Peclet number is less than one. The impacts of the viscous dissipation, the rarefaction, and the aspect ratio on entropy generation are magnified when fluid axial conduction dominates the irreversibility. The analytical solutions of the current study will make it possible to compare, evaluate, and optimize alternative elliptical microchannel heat exchanger design options.

Magneto-convective hybrid nanofluid slip flow over a moving inclined thin needle in a Darcy-Forchheimer porous medium with viscous dissipation

PurposeThe purpose of this study is to provide that porous media and viscous dissipation are crucial considerations when working with hybrid nanofluids in various applications.Recent years have witnessed significant progress in optimizing these fluids for enhanced heat transfer within porous (Darcy–Forchheimer) structures, offering promising solutions for various industries seeking improved thermalmanagement and energy efficiency.Design/methodology/approachThe first step is to transform the original partial differential equations into a system of first-order ordinary differential equations (ODEs). The fourth-order Runge–Kutta method is chosen for its accuracy in solving ODEs. The present study investigates the free convective boundary layer flow of hybrid nanofluids over a moving thin inclined needle with the slip flow brought about by inclined Lorentz force and Darcy–Forchheimer porous matrix, viscous dissipation.FindingsIt is found that slip conditions (velocity and Thermal) exist for a range of the natural convection boundary layer flow. In the hybrid nanofluid flow, which consists of Al2O3 and Fe3O4 are nanoparticles, H2O − C2H6O2 (50:50) are considered as the base fluid. The consequence of the governing parameter on the momentum and temperature profile distribution is graphically depicted. The range of the variables is 1 ≤ M ≤ 4, 1 ≤ d ≤ 2.5, 1 ≤ δ ≤ 4, 1 ≤ Fr ≤ 7, 1 ≤ Kr ≤ 7 and 0.5≤λ ≤ 3.5. The Nusselt number and skin friction factors are used to calculate the numerical values of various parameters, which are displayed in Table 4. These analyses elucidate that upsurges in the value of the Fr noticeably diminish the momentum and temperature. It is investigated to see if the contemporary results are in outstanding promise with the outcomes reported in earlier works.Practical implicationsThe results can be very helpful to improve the energy efficiency of thermal systems.Social implicationsThe hybrid nanofluids in heat transfer have the potential to improve the energy efficiency and performance of a wide range of systems.Originality/valueThis study proposes that in the combined effects of hybrid nanofluid properties, the inclined Lorentz force, the Darcy–Forchheimer model for porous media and viscous dissipation on the boundary layer flow of a conducting fluid over a moving thin inclined needle. Assessing the potential practical applications of the hybrid nanofluids in inclined needles, this could involve areas such as biomedical engineering, drug delivery systems or microfluidic devices. In future should explore the benefits and limitations of using hybrid nanofluids in these applications.

Entropy generation in the ternary nanofluid flow through an atherosclerotic vessel under periodic body acceleration

This article delves into the examination of the entropy generation within the slip flow of a ternary nanofluid flowing through a stenotic blood vessel. To capture the non-Newtonian rheology of blood, the constitutive equation of the Sutterby fluid model is employed. The governing equations are modeled in cylindrical polar coordinates. These equations are made dimensionless by a suitable choice of dimensionless parameters. Additionally, the dimensionless governing equations are simplified by applying the mild stenosis assumption. With the help of prescribed initial and boundary conditions, the numerical solution of the formulated problem is acquired by applying the explicit finite difference scheme. The outcomes of numerous governing parameters on the velocity profile, temperature profile, and entropy generation are explored through graphical forms. The velocity profile rises as the slip parameter and the inclination parameter are increased. The temperature profile rises with the growing values of the source parameter and decreases with enhancing values of the shape size parameter. The increasing strength of the applied magnetic field causes a reduction in the entropy generation. A comparison of the current study with the existing results is also presented. The plot of the Nusselt number shows that the height of stenosis plays an important role in monitoring its temporal variation. The current findings have been refined to provide elasticity-worthy material for researchers in the field of biomedical science who are interested in assessing blood flow under stenosis conditions and developing effective therapies for a wide range of diseases.

Ab initio modelling of transport phenomena in multi-component mixtures of rarefied gases

The direct simulation Monte Carlo method based on ab initio potentials is applied to model transport phenomena in binary, ternary and quaternary mixtures of noble gases. To this end, the Couette and Fourier problems are solved over the whole range of the rarefaction parameter spanning the near free-molecular, transitional, and slip flow regimes. Moreover, analytical solutions are obtained in the limits of the free-molecular and continuous medium regimes of flow. As a result, the shear stress, heat flux through multi-component mixtures, distributions of velocity, temperature, and mole fractions of each species are calculated as a function of the gas rarefaction. An analysis of these data points out the properties which are strongly affected by the chemical composition. It is found that the largest deviations of characteristics of mixtures from those of a single gas are observed for the binary mixture of helium and krypton, while their deviations for the ternary and quaternary mixtures are smaller. A temperature variation in a mixture leads to non-uniform distributions of chemical composition due to the thermal diffusion phenomenon. Such redistributions are analyzed in both problems and their effect on the heat and momentum transfer is evaluated. The reported results can be used to evaluate the main factors determining transport phenomena in practical applications such as vacuum systems, microfluidics, gas separation technology, space research etc.

Bubbles and bed expansion in low pressure fluidization

Fluidization at low pressure has significant benefits over traditional fluidized beds for the fine chemical industry. Yet there is a lack of knowledge of bubbling and bed behaviour under the slip flow regime (low pressure), and this presents a hindrance to the optimization of this process. In this work, the fundamental aspects of gas bubbles and bed expansion are investigated for a wider range of operating pressure, flow rates and bed aspect ratio. Typically, rising individual bubbles undergo a series of breakups and coalesce as they rise in the bed. The lowering of pressure below 14,884 Pa was found to inhibit this behaviour indicating a qualitative indication of the impact of pressure on the bubble dynamics. The bubbles formed at low pressure were larger in average size, greater in number at the inlet and have a higher aspect ratio. All these factors were directly related to the expansion of gas due to the lowering of operating pressure. Under a controlled environment with single rising bubbles, the gas expansion was predictable using the ideal gas equation. However, where the pressure is low enough (≤ 24,231 Pa) the inhomogeneous fluidization impacted the predictability and trend of the bubbling zone and bed expansion. Despite this, the overall consumption of fluidizing mass was magnitudes lower to generate similar sizes of bubbles at atmospheric pressure. This has a direct impact on the usage of fluidizing gas while maintaining similar gas-solid mixing behaviour. Overall, the benefits of low pressure can be obtained at moderate pressure between 49,130 pa and 24,231 Pa at AR 3 with homogeneous fluidization.

Generalized slip impact of Casson nanofluid through cylinder implanted in swimming gyrotactic microorganisms

In this paper, the self-propelled movement on gyrotactic swimming microorganisms into this generalized slip flow by nanoliquid over the stretching cylinder with strong magnetic field is discussed. Constant wall temperature was pretended as well as the Nield conditions of boundary. The intuitive non-Newtonian particulate suspension was included into applying Casson fluid by the base liquid and nanoparticles. This formation on the bio-mathematical model gives the boundary value problem by the nonlinear partial differential equations. Primly, modeled numerical system was converted to nondimensional against this help on acceptable scaling variables and the bvp4c technique was used to acquire the mathematical outcomes on the governing system. This graphical description by significant parameters and their physical performance was widely studied. The Prandtl number has the maximum contribution (112.595%) along the selected physical parameters, whereas the Brownian motion has the least (0.00165%) heat transfer rate. Anyhow, Casson fluid was established for much helpful suspension of this method on fabrication and coatings, etc. Therefore, this magnetic field performs like the resistive force of that fluid motion, and higher energy was enlarged into the structure exhibiting strong thermal radiation.

Impact of melting and radiation on MHD mixed convective heat transfer slip flow through vertical porous embedded micro-channel

Impact of melting and radiation on MHD mixed convective heat transfer slip flow through vertical porous embedded micro-channel

Elastic stability of viscoelastic liquid films flowing on a porous substrate

This paper investigates the linear stability of viscoelastic liquid films flowing down an inclined porous substrate analytically and numerically. It focuses on the Stokes flow of viscoelastic films and uncovers two unstable modes triggered by elasticity. The elastic surface mode with a long wave number is solved analytically and numerically. Our results also indicate elasticity can trigger an elasto-porous mode at small incline angle and ratio of film thickness to substrate thickness. The Oldroyd-B model is used for the constitutive relation between the strain and polymer stress. The classical Beavers–Joseph condition is applied to describe the boundary conditions at the fluid-porous interface (Beavers and Joseph, 1967). This condition represents the linear relationship between velocity gradient of fluid layer and velocity difference between two layers, ∂zu=ακ(u−um), where α is the Beavers–Joseph coefficient, representing slip flow at the interface; κ is the permeability of the porous medium. Effects of porous medium properties, including permeability and depth ratio, as well as the impact of slip flow at the interface on the unstable modes are examined.

Nano‐bioconvective anisotropic slip flow in anisotropic porous medium with Coriolis force effects

AbstractThe present paper examines the impact of the Coriolis force and anisotropic Darcian porous medium on the nonsteady convective flow of bio‐nanofluid along a three‐dimensional stretchable surface. The problem has applications in extrusion processes and the geographical movement of tectonic plates under a moveable ocean. Emphasis is placed on the combined effects of anisotropic porous medium, anisotropic momentum slip and temperature, and microorganism slips at the wall. The pertaining equations are condensed to a set of similarity equations before being simulated using the Keller‐box method, an efficient numerical technique. The study reveals that the friction factor along the y‐axis decreases as the rotation parameter increases. Moreover, the heat and nanoparticle volume fraction movement gradient decrease along the y‐axis when the Darcy number and stretching rate increase. However, these rates increase with a higher velocity slip. In addition, the density of microorganisms in the bio‐nanofluid decreases when there are higher levels of unsteadiness, rotation, and Darcy numbers, as well as with increased bioconvection parameters.

Mathematical model for a thermal cooling system with variable viscosity and thermal conductivity over a rotating disk

Mathematical models involving rotation of the disks and the flow of fluid over these serve as a prototypical representation of electronic devices including rotational components. The rotation results in substantial heat generation and the excessive heat buildup can affect performance and reliability, and can cause failure. Therefore efficient cooling mechanisms are essential to dissipate the generated heat and maintain the devices’ temperature within safe operating limits. In this research paper, the focus is on investigating the magnetohydrodynamic (MHD) slip flow and heat transfer of power-law nanofluid over an infinite rotating disk. The study incorporates numerical methods to analyze the system, considering the variable thermal conductivity and viscosity as a function of velocity gradients, and employing velocity slip conditions at the boundary. To facilitate the analysis, the similarity transformation technique is applied, which effectively reduces the governing boundary value problem to a set of nonlinear ordinary differential equations (ODEs). The research explores the dependence of the velocity and temperature profiles on various parameters, including the nanofluid volume concentration parameter, power-law index, magnetic parameter, and velocity slip parameters. Through the numerical results, the influence of these parameters on the flow and heat transfer characteristics is presented and thoroughly discussed. The outcomes of the study are presented in the form of graphs and tables, providing valuable insights into the behavior of the power-law nanofluid flow and heat transfer over the rotating disk.

Study on the slip behavior of CO2-crude oil on nanopore surfaces with different wettability

Unconventional reservoirs are characterized by a significant amount of micro and nanopores, which pose a critical challenge in accurately assessing the microscopic fluid transport behaviors to enhance oil and gas recovery in such reservoirs. CO2 injection is a promising recovery method for unconventional resources, hence the transport mechanism of CO2-crude oil at the nanoscale deserves further exploration. In this work, the flow and transport behaviors of CO2 and multicomponent crude oil in hydrophilic, neutral, and hydrophobic nanopores were investigated by the molecular dynamics simulation (MD) method. The CO2-crude oil shows a negative slip flow on hydrophilic surfaces, while it has a slip flow on neutral and hydrophobic surfaces. By illustrating the distribution structure of each component in the fluid and the solid-liquid interaction energy, the inherent causes of the slip mechanism of different wettability surfaces were revealed. The transport capacity and permeability of CO2-crude oil in the pores with different wettability were investigated. Modifying the Hagen-Poiseuille equation based on slip characteristics can effectively improve the prediction ability of nanopore permeability. This study is helpful to understand the flow and slip behavior of CO2-crude oil in nanopores of unconventional reservoirs, which provides a theoretical basis for accurately predicting the migration of reservoir fluid in nanopores.

Damage evolution model and failure mechanism of continuous carbon fiber-reinforced thermoplastic resin matrix composite materials

As a new composite material with high strength, toughness, and heat resistance, the continuous fiber-reinforced polyaryl ether sulfone ketone (PPESK) thermoplastic resin matrix composite (CFRP) has a wide temperature range, which is attributed to the complex temperature sensitivity of the matrix. The failure evolution characteristics under different conditions are not clear yet, which significantly limits its development and application to high-precision equipment. In this work, in order to deeply explore the full three-dimensional (3D) multi-scale multi-physics damage evolution mechanism of the CFRP over a wide temperature range, macroscale cross-temperature stretching/bending experiments, computer tomography (CT) scanning, and microscale scanning electron microscopy (SEM) are performed to effectively capture the overall damage morphology and local fiber/matrix damage failure characteristics of the material. The results show that the reinforcement with continuous fibers increases the tensile strength of the CFRP by 14–45 times and its bending strength by 2–6 times compared to those of the PPESK matrix in the cross-temperature domain. Moreover, the main failure mechanism of the CFRP in the cross-temperature domain is matrix crushing and fiber fracture at room temperature and fiber fretting slip and matrix viscous flow at high temperatures. This further explains the deformation mechanism of the CFRP, which can maintain its stability at high temperatures (low elongation at break: 1%–1.2%). The unique trans-temperature regional energy evolution and continuous fiber reinforcement of the material matrix resin PPESK lay the synergic stability of the high temperature performance and damage morphology of the CFRP. In particular, a cell model is constructed to further reveal the damage evolution characteristics of the matrix, fiber, and interface of the CFRP at the micro-scale. Combined with the failure mode theory and the performance degradation mechanism of composite materials, the temperature influence factor is introduced to formulate a multi-scale full 3D temperature-dependent damage evolution constitutive model of the CFRP over a wide temperature range. The constitutive model of the CFRP is incorporated in finite element software, and the simulation results are compared with the experimental ones for validation. The results show that the model developed in this work can effectively characterize the complex mechanical damage morphology and progressive failure characteristics of the CFRP over a wide temperature range.