Slip Coefficient Research Articles

Effect of Surface Coating Condition on High‐friction Organic Zinc‐rich Paints for HSFB Joints

AbstractWith the development of paints, high‐friction organic zinc‐rich paints with slip coefficients more than 0.45 have been advanced, making it possible to obtain more sophisticated and higher quality high strength bolted friction joints. Moreover, comparing to the inorganic zinc‐rich paints used at present, organic zinc‐rich paints are more appropriate for using in situ construction. However, since the application conditions of organic coatings have not been specified, it is recommended that a slip test should be carried out separately for each surface preparation to confirm the slip coefficient. In this study, slip tests were carried out on high strength bolted friction joint specimens to investigate the influence of high‐friction organic zinc rich paint film thickness and surface preparation on the slip coefficient. Furthermore, based on the experimental results, a surface preparation that can consistently produce a high slip coefficient is proposed.

Laboratory investigation on gas slippage phenomenon in coal sample and its research significance

The gas slippage effect (GSE) of coal is associated with the coalbed methane (CBM) wells' productivity. Through the helium permeability experiment of five coal samples with different vitrinite reflectance, characteristics of gas permeability variations in coal samples with different coalification degrees are analyzed, the influence of coalification degrees, coal pore structures, and different gases on GSE is revealed, and the impact of GSE on the CBM wells productivity is discussed. It indicatess that the gas permeability of coal varies with the pore pressure in a negative power function and a gas slippage coefficient of coals declines with the rise of Klinkenberg permeability by a negative power function. With the ascend of vitrinite reflectance of coal, there is an asymmetric “U-shaped” change trend in GSE. The GSE in coal with different vitrinite reflectance is mostly govern by the pore diameter distribution of coal. The slippage parameter of gas is consistent with the evolution law of coal pore structures during coal metamorphism. The slippage coefficient of different gases is obtained. On this basis, the prediction model of CBM well production considering GSE is established, and the impact degree of GSE on CBM well productivity is revealed.

Parametric study on lateral behavior of totally precast RC shear wall with horizontal bolted connection

Dry-type connections have gained considerable popularity worldwide due to their superior construction efficiency and quality. However, a significant drawback of most conventional dry-type connections is the direct embedding of connectors in the concrete wall panel, consequently causing stress concentration in the connections and leading to extensive spalling of concrete. This study introduces an innovative high-strength bolted connection as a solution to address the problem of stress concentration in concrete. To evaluate the seismic performance of the high-strength bolted connection, monotonic lateral loading tests were conducted. In this study, a finite element (FE) model was developed using ABAQUS software, and validated through experimental results. Furthermore, a parametric study was conducted using the FE model to assess the influence of several key design parameters on the lateral response and anti-slip capacity of the bolted connection in the precast shear wall. These parameters include bolt specifications, anti-slip coefficient, flange thickness of the H-connector, widths of the initial gap, axial compression ratio, and connection arrangement. The results indicate that the anti-slip capacity is not significantly influenced by the flange thickness of H-connectors and initial gap width, but it increases with an increase in bolt specification, slip coefficient, and axial compression ratio. Additionally, the ultimate bearing capacity of the precast shear wall remains unaffected by both the anti-slip coefficient and the initial gap width. Moreover, the high-stress area of the H-connector is concentrated at the ends. Finally, the design parameters are recommended according to the numerical analysis results.

Investigation of non-Newtonian Fluid Flow and Heat Transfer in Microchannel with Hydrophobic Surface

Forced convection in microchannel for power law fluid was investigated by Lattice Boltzmann method in which term of viscose dissipation and slip condition on the wall are considered. The problem was studied for various Reynolds number, Prandtl number and slip coefficients. In this study, contours of velocity, temperature profile, local friction factor and average Nusselt number are presented. Average Nusselt number with respect to power law index is greater for shear-thinning fluid (n<1) than Newtonian (n=1) and shear-thickening fluid (n>1). For Re=30 enhancing slip coefficient raises the average Nusselt number. The results have shown that the friction factor is decreasing along the channel because of changing in velocity gradient. Slip coefficient improves the convection heat transfer mechanism for Non-Newtonian fluids.

Drag on a sphere in a slow flow of a binary mixture of rarefied gases

The drag force on a sphere in an isothermal binary mixture of rarefied gases is calculated on the basis of the McCormack model for the linearized Boltzmann equation. The diffuse scattering of the gas–surface interaction law is assumed as the boundary condition. The rigid-spheres model of interatomic interaction potential is used as well as ab initio potentials for helium, argon, and krypton gases. The force is obtained in a wide range of the gas rarefaction, which covers the free molecular, transition, and slip regimes of the gas flow. In the free molecular and slip flow regimes, the problem is solved analytically, while in the transition regime, the system of kinetic equations is solved numerically via the discrete velocity method optimized to overcome the problem of discontinuity of the distribution function of molecular velocities on the convex surface. The calculations are carried out for the mixtures helium–argon and helium–krypton at 300 K. In the slip flow regime, the data available in the literature for the viscous slip coefficient of the helium–argon mixture are used, while for the mixture helium–krypton, it is calculated. The influence of the interatomic interaction potential, molar fraction, and ratio of atomic mass of species in the mixture on the drag force is analyzed.

Modeling the wetting behavior of grinding wheels

Helical flute grinding is an important process step in the manufacturing of cylindrical cemented carbide tools where the use of cooling lubricants is a defining factor determining process performance. Finding optimal parameters and cooling conditions for the efficient use of lubricant is essential in reducing energy consumption and in controlling properties of the boundary zone like residual stresses. Any mathematical model describing the interactions between grinding wheel, lubricant and workpiece during the process has to account for the complex microstructure of the wheel; however, this renders the identification of parameters like slip or heat exchange coefficients numerically prohibitively expensive. In this paper, results from grinding oil droplet experiments are compared with simulation results for the wetting behavior of grinding wheels. More specifically, finite element simulations of the thin-film equation are used to identify slip parameters for different grinding wheel specifications (grain size, bonding structure, wetting status). Our results show that both the bonding and the grain size have an influence on the wetting behavior. The slip parameters that we identified account for the fluid-microstructure interactions and will be used to effectively model those interactions in more complex 3D fluid-dynamic simulations via the Beavers-Joseph condition.

Global sensitivity analysis using multi-resolution polynomial chaos expansion for coupled Stokes–Darcy flow problems

Determination of relevant model parameters is crucial for accurate mathematical modelling and efficient numerical simulation of a wide spectrum of applications in geosciences. The conventional method of choice is the global sensitivity analysis (GSA). Unfortunately, at least the classical Monte-Carlo based GSA requires a high number of model runs. Response surfaces based techniques, e.g. arbitrary Polynomial Chaos (aPC) expansion, can reduce computational effort, however, they suffer from the Gibbs phenomena and high hardware requirements for higher accuracy. We introduce GSA for arbitrary Multi-Resolution Polynomial Chaos (aMR-PC) which is a localized aPC based data-driven polynomial discretization. The aMR-PC allows to reduce the Gibbs phenomena by construction and to achieve higher accuracy by means of localization also for lower polynomial degrees. We apply these techniques to perform the sensitivity analysis for the Stokes–Darcy problem which describes fluid flow in coupled free-flow and porous-medium systems. We consider the Stokes equations in the free-flow region, Darcy’s law in the porous-medium domain and the classical interface conditions across the fluid–porous interface including the conservation of mass, the balance of normal forces and the Beavers–Joseph condition for the tangential velocity. This coupled problem formulation contains four uncertain parameters: the exact location of the interface, the permeability, the Beavers–Joseph slip coefficient and the uncertainty in the boundary conditions. We carry out the sensitivity analysis of the coupled model with respect to these parameters using the Sobol indices on the aMR-PC expansion and conduct the corresponding numerical simulations.

Numerical exploration of slip effects on second-grade fluid motion over a porous revolving disk with heat and mass transfer

Revolving-disk systems are employed in various industrial settings including turbine engineering, chemical and food processing industries and others. The current article scrutinizes a second-grade fluid motion generated by an infinite porous disk having partial slip character. Heat transfer induced by heating of the disk surface and by viscous and ohmic heating effects is modeled and analyzed under thermal slip condition. Accompanying mass transfer process with thermophoretic diffusion is also formulated. A self-similar system is obtained akin to the case of no-slip case discussed in a previously published study. The adoption of velocity slip assumption induces non-linearity in the boundary conditions in velocity components. Computational procedure embedded in MATLAB bvp4c platform is opted to simulate the system for full range of slip parameters. In contrast to a previously published work pertaining to the no-slip case, present numerical methodology gives accurate results for wide ranges of Prandtl number and elasticity parameter. Boundary layer formations above the disk are examined under various controlling parameters. A comparative assessment of slip and no-slip cases is presented through both graphical illustrations and tabulated results for the resisting torque, the Nusselt number and the Sherwood number. Current numerical findings match very well with the existing homotopy solutions for the no-slip case. The presence of a wall slip mechanism leads to a clear suppression of all the velocity components. Furthermore, an augmentation in the thermal/concentration slip coefficient significantly reduces the thermal/solutal penetration depth. Additionally, we observe a noticeable increase in the driving torque as the elasticity parameter enhances. The slip action of the surface is also predicted to raise the torque required by the disk.

Corrosion-induced mechanical properties of shear bolted connections in high-strength weathering steel

There have existed numerous experimental and analytical investigations about how bolted connections made of high-strength steel behave under corrosion conditions. However, the corrosion-induced mechanical properties are much less attentively scrutinized for bolted connections consisting of high-strength weathering steel. Accordingly, this paper presents an experimental investigation of load-bearing performance regarding shear bolted connections made of high-strength weathering steel subjected to corrosion. The corrosion tests were initially performed for nine specimens subjected to accelerated corrosion by copper salt spray, after which mechanical properties of these connections under different levels of corrosion were then investigated by static tensile tests to formulate the mathematical relation between mass loss rate and corrosion time, and to analyze the mathematical relationships between mass loss rate and mechanical index including slip coefficient, bolt preload, slip load or ultimate load. The results indicate that the corrosion that the specimens underwent primarily impacted the non-contact surfaces, and the relationship between the corrosion rate and the corrosion time conforms to the power function model for high-strength weathering steel. It is concluded that the corrosion environment has a significant impact on the slip load, slip coefficient and bolt preload of bolted connections.

Influence of nozzle structure and process parameters for 3D printing HTPB-based propellant

This paper studies the influence of nozzle structure and process parameters on the solid propellant 3D printing process, so as to better guide nozzle structure optimization and process improvement, and realize continuous extrusion and molding of solid propellant. Four characteristic parameters such as nozzle diameter, nozzle shrinkage angle, process temperature, and wall slip coefficient are selected, and the influence of these four parameters on the extrusion speed and pressure of solid propellant slurry in the nozzle is discussed by using the orthogonal test principle and ANSYS/POLYFLOW. The results show that the most significant factor affecting the outlet velocity uniformity index and outlet pressure is the wall slip coefficient, followed by the nozzle diameter, and the influence of temperature and contraction angle is small.

Numerical investigation of pseudoplastic fluid flow and heat transfer in a microchannel under velocity slip effect

This study uses the lattice Boltzmann method to research the heat transfer features of Pseudoplastic fluid in a microchannel. The Power law model is intended to simulate non-Newtonian fluids. The fluid slip on the surface is applied to the hydrophobic surfaces, and also the viscose dissipation term is considered in the governing equations. The problem is presented for Reynolds numbers 20 and 30, slip coefficients 0.01, 0.02, and 0.03, and Prandtl numbers 1 and 6.2. Results reveal that the average Nusselt number in the microchannel with a power index of 0.5 of non-Newtonian fluid is more significant than Newtonian fluid. It was seen that viscose dissipation impact on the average Nusselt number is insignificant.

Slip and non-slip flows of MHD nanofluid through microchannel to cool discrete heat sources in presence and absence of viscous dissipation

This paper investigates heat transfer (HTR) and fluid flows of a magnetohydrodynamic (MHD) nanofluid (NFD) in a two-parallel-plate microchannel with three isothermal heat sources and under temperature jump and slip (0 < B* < 0.1) and non-slip regimes. The flow is subjected to a magnetic field (0 < Ha < 60) in three zones in the presence and absence of viscous dissipation (VDS) (0 < Br < 0.1). Using SIMPLE algorithm, it is found that a rise in the Re (0 < Re < 100) increases HTR under both slip and non-slip conditions. VDS decreases HTR from the isothermal heat source to the NFD flow. An increase in the slip coefficient raises the Nu, particularly at higher Ha. A rise in the Ha leads to greater HTR under the slip boundary condition. An increase in the slip coefficient raises the Nu by 52.52% in the presence of VDS and by 1.16% in the absence of VDS.

Nonlinear free convective with longitudinal slits in the presence of super-hydrophobic and non-hydrophobic microchannels in a suspension of nanoparticles: Multi-Linear Regression Analysis

Super hydrophobic microchannels have extremely high water repellency, and such a property is reliant on a set of factors, namely the surface construction and the surface energy. The surface energy can be depressed either by exhausting a chemical film that is coated or stuck to the surface or by adjusting the existing surface interaction or by producing micro- and nanotextures. Further, due to the latter reason of inducing super hydrophobic properties, a study of manufacturing processes to produce surface textures becomes critical to the understanding of the area. The latest generative manufacturing techniques, such as 3-D (three-dimensional) printing, laser machining, and so on are new-generation processes that can be used to write over surfaces at different resolutions. Viewing into this, the natural convection of conductive nanofluids in vertical slot micro-channels with super-hydrophobic slips and temperature jumps, the non-linear Boussinesq approximation approach provides an accurate solution. One inner surface of the microchannel surface has been physically modified to exhibit temperature jumps and super-hydrophobic velocity slips. The transverse magnetic field indicates the direction of flow. In two different physical situations, it is possible to get a single answer. Type I involves heating the super-hydrophobic surface without heating the non-slip surface, and Type II involves heating the non-slip surface without heating the super-hydrophobic surface. Velocity slip reduces the Type I Nusselt number and increases the Type II Nusselt number in both situations. The temperature jump factor has the opposite effect. In contrast to the change in linear density with temperature, the non-linear density change with temperature causes an increase in flow and velocity. It is observed that more slip coefficient corresponds to less Nusselt number and more slip velocity, especially at larger magnetic parameter values to increase the heat transfer rate from the microchannel walls. It is recommended to use Al2O3-water nanofluid the nanofluid composed of nanoparticles with higher thermal conductivity. Applications of the subject include anti-wetting micro technology, electrolytic cell maintenance, micro-hydraulic devices, and micro-electronic heat dissipation.

Influence of slippage on thermocapillary flow induced by a Gaussian temperature distribution on small-scale water droplets driven by surface acoustic waves

In the present work, we theoretically analyze the influence of thermocapillary flow on the atomization by surface acoustic waves (SAWs) of a sessile water droplet exposed to a high-frequency acoustic field and placed over a substrate with slippage at the wall. Thermocapillary flow is induced by imposing a Gaussian temperature profile along the free surface of the droplet. Such fluid flow in conjunction with the acoustically-driven capillary waves at the free surface prior to atomization under the influence of the slip phenomenon is analyzed by applying the lubrication theory to the flow field governing equations, leading to the derivation of an evolution equation written in terms of the acoustic capillary number, the Marangoni number, and the substrate slip coefficient. The numerical solution of the evolution equation has led us to propose the combined influence of thermocapillary and slip phenomena as a valuable means of assisting in the regulation of aerosol diameter in SAW atomization, capable of exerting a significant influence on the interfacial dynamics of droplets prior to atomization.

The inner and outer solutions to the inertial flow over a rolling circular cylinder

This paper proposes a new approach for evaluating numerically the forces and moments applied to a circular cylinder that is immersed in a fluid and which translates and rotates near a plane wall. Under the proposed approach, the flow is decomposed into inner and outer flows. The inner flow represents the flow in the thin interstice between the cylinder and the wall, and is obtained as an analytic expression using lubrication theory. The outer flow represents the flow far from the interstice, which does not depend on the magnitude of the gap between the cylinder and the wall, when the gap is small. The outer flow is obtained using numerical simulation as a function of both the Reynolds number and the slip coefficient. The force and moment coefficients are then obtained, as functions of the Reynolds number, slip coefficient and gap-to-diameter ratio, by combining the inner and outer solutions. Importantly, since the outer flow does not depend on the gap-to-diameter ratio, the parameter space to be explored by numerical simulations is greatly reduced compared to using finite gap ratio simulations. Moreover, the numerical difficulties associated with resolving the interstitial flow are avoided. The proposed approach can be extended to a wide range of rolling bodies, including spherical particles and wheels, and should significantly reduce the computational expense required to model the hydrodynamic forces and predict the subsequent motion of such bodies.

Anisotropy of nanoindentation in copper single crystals under different orientations

The anisotropy of nanoindentation in copper single crystals is studied through experiments and simulations. Nanoindentation tests with different orientations were carried out, and the depth was 20nm-500nm. Simulations were carried out using crystal plasticity finite element method. The results show that sample with different orientations present anisotropic with increase of indentation depth. The accumulated plastic strains of the samples with different orientations are different due to the different angle between the loading direct and the normal to the slip surface. The cumulative plastic strain of oriented samples is the smallest, and orientation is the largest. The amount of slip coefficients initiated simultaneously for samples with different orientations is responsible for the differences in nanoindentation properties.

A Modification of the Beavers–Joseph Condition for Arbitrary Flows to the Fluid–porous Interface

Physically consistent coupling conditions at the fluid–porous interface with correctly determined effective parameters are necessary for accurate modeling and simulation of various applications. To describe single-fluid-phase flows in coupled free-flow and porous-medium systems, the Stokes/Darcy equations are typically used together with the conservation of mass across the interface, the balance of normal forces and the Beavers–Joseph condition on the tangential velocity. The latter condition is suitable for flows parallel to the interface but not applicable for arbitrary flow directions. Moreover, the value of the Beavers–Joseph slip coefficient is uncertain. In the literature, it is routinely set equal to one that is not correct for many applications, even if the flow is parallel to the porous layer. In this paper, we reformulate the generalized interface condition on the tangential velocity component, recently developed for arbitrary flows in Stokes/Darcy systems, such that it has the same analytical form as the Beavers–Joseph condition. We compute the effective coefficients appearing in this modified condition using theory of homogenization with boundary layers. We demonstrate that the modified Beavers–Joseph condition is applicable for arbitrary flow directions to the fluid–porous interface. In addition, we propose an efficient two-level numerical algorithm based on simulated annealing to compute the optimal Beavers–Joseph parameter.Article HighlightsA modification of the Beavers–Joseph condition is proposed based on recently developed generalized coupling conditions.The Beavers-Joseph parameter can be found only for unidirectional flows.An efficient numerical algorithm to determine the optimal Beavers-Joseph parameter is developed.

Advanced design of a small-scale mini gerotor pump in a high-temperature and high-viscosity fluid thermal system

In this research, the development of a small-scale heat transfer gerotor pump with an advanced arrangement for high-viscosity and high-temperature fluids is described comprehensively. The small-scale pump design aims to meet the needs of modular components for industry and research, especially for small-scale heat transfer applications such as residential heating systems. VDI 2221 approach was used to construct an advanced gerotor pump with an internal reservoir unit that can generate additional pressure and minimize the slip factor, thereby increasing its volumetric efficiency. The developed small-scale pump was designed in a smart arrangement, which required fewer components than a typical heat transfer pump. This helps to reduce the maintenance of the pump and its components. Experimental tests were performed using a testing apparatus equipped with a heater, a control system using Pulse Width Modulation (PWM) adjustment, valves, pressure, and temperature gauges. The instruments in the apparatus test were used to control the flow rate and pump speed and monitor the temperature of the working fluid. The results of the experiment show that the advanced gerotor pump was able to deliver fluid with a viscosity of 307 ml/min and a temperature of up to 230 °C. The components arrangement minimizes the slip factor, which is mostly the main challenge of positive displacement pumps. The maximum slip coefficient of the advanced gerotor pump design is 0.095. The volumetric efficiency was in the range of 0.803–0.905 when the pump operated at 2,100 RPM and 230 °C. The experiment and analysis results show that the pump can be implemented for the actual application of the thermal system, for research and industry

Обобщённый закон внешнего трения скольжения твёрдых тел

A mathematical model describing the law of contact gliding friction, taking into account changes in the sliding contact states, is proposed for consideration. The generalization of classical linear models of contact friction is carried out by putting in more additive components allowing for new state transitions of frictional interaction.&#x0D; The developed mathematical model makes it possible to give analytic description of the schematic diagram of classical slip coefficient change depending on the load of B.I. Kostetsky and allows adding to

Slip boundary conditions for rough surfaces

The velocity slip and temperature jump for a two-dimensional rough plate under hypersonic conditions were analyzed using the Direct Simulation Monte Carlo (DSMC) method. Surface roughness was explicitly modeled by introducing various structures on the flat plate. The influences of relative roughness height, which involves the roughness height, roughness spacing, incoming velocity, and the degree of rarefaction, were analyzed and discussed. It is found that with the increase of the relative roughness height, the jump temperature increases, while the slip velocity decreases gradually. The effects of surface roughness on the slip coefficients can be attributed to the change of accommodation coefficients. A new slip model for rough surfaces was established in this paper, which accounts for the coupling effects of gas rarefaction and surface roughness, without the effort to model the surface roughness explicitly. The nitrogen flows in the microchannel, and flows over a blunt cone and an axisymmetric bi-conic body, were simulated under the modified and conventional slip boundary conditions, respectively. The numerical solutions were validated with experimental data. It can be safely concluded that compared with the traditional first-order slip boundary conditions, the modified slip model improves the accuracy of macroscopic properties, especially the heat transfer coefficient.