Study on wall-slip effect of magnetorheological fluid and its influencing factors

2021 ◽  
pp. 1045389X2110149
Author(s):  
Rongyu Wu ◽  
Hongjian Tang ◽  
Yunshan Fu ◽  
Jinan Zheng ◽  
Honglei Lin ◽  
...  
Keyword(s):  
Wall Slip ◽  
Solid Particles ◽  
Rheological Parameters ◽  
Fluid Viscosity ◽  
Slip Effect ◽  
Working Surface ◽  
Braking Torque ◽  
Rotor Surface ◽  
Conventional Models ◽  
Slip Layer

The wall-slip effect is observed in areas with magnetorheological fluids (MRFs). A slip layer is formed, which reduces the friction between the solid particles and working surface that causes relative movement of the particles. This leads to errors in the measurement of rheological parameters and an inaccurate braking torque model. Thus, here, a rheometer with a sandpaper on the rotor is used to change the working surface roughness to analyze the wall-slip effect of the MRFs. Based on the experimental results, the influence patterns of wall-slip effect on fluid viscosity and yield stress are obtained. Furthermore, a MRF model is established that considers wall-slip effect, which is different from the conventional models. The model is employed to establish a magnetorheological (MR) braking torque model. To verify the braking torque model, a prototype was manufactured, and its mechanical properties were tested. When compared with a smooth rotor, the braking torque of MR brakes with rectangular grooves is increased. This confirms the existence of the wall-slip effect and shows that the wall-slip effect of MRF can be effectively suppressed by incorporating grooves on the rotor surface.

scholarly journals Simulating Fracture Sealing by Granular LCM Particles in Geothermal Drilling

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4878
Author(s):  
Lu Lee ◽  
Arash Dahi Taleghani
Keyword(s):  
Elevated Temperatures ◽  
Solid Particles ◽  
Fluid Viscosity ◽  
Lost Circulation ◽  
Fracture Sealing ◽  
Typical Treatment ◽  
Well Abandonment ◽  
Fracture Apertures ◽  
Geothermal Drilling ◽  
Lost Circulation Materials

Lost circulation occurs when the returned fluid is less than what is pumped into the well due to loss of fluid to pores or fractures. A lost-circulation event is a common occurrence in a geothermal well. Typical geothermal reservoirs are often under-pressured and have larger fracture apertures. A severe lost-circulation event is costly and may lead to stuck pipe, well instability, and well abandonment. One typical treatment is adding lost-circulation materials (LCMs) to seal fractures. Conventional LCMs fail to properly seal fractures because their mechanical limit is exceeded at elevated temperatures. In this paper, parametric studies in numerical simulations are conducted to better understand different thermal effects on the sealing mechanisms of LCMs. The computational fluid dynamics (CFDs) and the discrete element method (DEM) are coupled to accurately capture the true physics of sealing by granular materials. Due to computational limits, the traditional Eulerian–Eulerian approach treats solid particles as a group of continuum matter. With the advance of modern computational power, particle bridging is achievable with DEM to track individual particles by modeling their interactive forces between each other. Particle–fluid interactions can be modeled by coupling CFD algorithms. Fracture sealing capability is investigated by studying the effect of four individual properties including fluid viscosity, particle size, friction coefficient, and Young’s modulus. It is found that thermally degraded properties lead to inefficient fracture sealing.

Determining the Effective Thermal Conductivity of a Nanofluid Using Brownian Dynamics Simulation

2003 ◽  
Author(s):  
P. Bhattacharya ◽  
S. K. Saha ◽  
A. Yadav ◽  
P. E. Phelan ◽  
R. S. Prasher
Keyword(s):  
Thermal Conductivity ◽  
Brownian Motion ◽  
Effective Thermal Conductivity ◽  
Brownian Dynamics ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Solid Particles ◽  
Dynamics Simulation ◽  
Fluid Viscosity ◽  
Brownian Dynamics Simulation

A nanofluid is a fluid containing suspended solid particles, with sizes of the order of nanometers. Normally the fluid has a low thermal conductivity compared to the suspended particles. Therefore introduction of these particles into the fluid increases the effective thermal conductivity of the system. It is of interest to predict the effective thermal conductivity of such a nanofluid under different conditions like varying particle volume fraction, varying particle size, changing fluid conductivity or changing fluid viscosity, especially since only limited experimental data are available. Also, some controversy exists about the role of Brownian motion in enhancing the nanofluid’s thermal conductivity. We have developed a novel technique to compute the effective thermal conductivity of a nanofluid using Brownian dynamics simulation, which has the advantage of being computationally less expensive than molecular dynamics. We obtain the contribution of the nanoparticles towards the effective thermal conductivity using the equilibrium Green-Kubo method. Then we combine that with the thermal conductivity of the base fluid to obtain the effective thermal conductivity of the nanofluid, and thus are able to show that the Brownian motion contributes greatly to the thermal conductivity.

Wall Slip Effect in Couette Rheometers

2012 ◽  
Vol 192-193 ◽  
pp. 353-358 ◽  
Author(s):  
Siri Harboe ◽  
Michael Modigell ◽  
Annalisa Pola
Keyword(s):  
Wall Slip ◽  
Casting Process ◽  
Subject Area ◽  
Slip Effect ◽  
Suspension Parameters ◽  
Glass Spheres ◽  
Die Filling ◽  
Experimental Parameters ◽  
Semi Solid ◽  
Solid Form

Wall slip of suspensions in confined flow is caused by segregation of a thin layer of liquid phase adjacent to the walls. This causes the bulk phase to slide along the walls, which means that the fluid flow velocities respective to the walls are not zero. In rheometers this affects the evaluation of the rheological properties. Despite the importance of understanding and controlling segregation effects, little research has been done on this subject area. Indeed in industrial casting, the die filling behaviour, and therefore the product quality, may depend on the segregation phenomena. It is important to understand the wall slip phenomenon’s correlation with experimental parameters, as a step towards casting process optimization. Two issues are handled in the present work, the first is the evaluation of different methods to investigate the wall slip effect, the second is the investigation of the wall slip effect dependency on the suspension parameters particle size and solid fraction, respectively. The suspensions employed for the investigations were the aluminium alloy A356 in semi-solid form and a “synthetic suspension” built up of glass spheres in silicon oil. As a result of the above described investigations, influence of suspension parameters are found, and a validated method to avoid the wall slip effect is suggested.

scholarly journals Flow Induced By A Rotating Microchannel-A Numerical Study

2021 ◽  
Author(s):  
Kashif Ali ◽  
Shahzad Ahmad ◽  
Anique Ahmad ◽  
Faisal Ali
Keyword(s):  
Power Law ◽  
Hartmann Number ◽  
Stokes Equations ◽  
Numerical Study ◽  
Wall Slip ◽  
Future Generation ◽  
Fluid Viscosity ◽  
Power Law Fluid ◽  
Fluid Behavior ◽  
Behavior Index

Abstract In this paper, a mathematical foundation has been developed for the primary understanding of complex interaction of the wall slip with the Coriolis and Lorentz forces acting orthogonally on the Electromagnetohydrodynamic (EMHD) flow of a power-law fluid in a microchannel. Modified Navier Stokes equations are solved numerically by incorporating the fully implicit computational scheme with suitable initial and boundary conditions, which generates numerical results in excellent comparison with the literature for a certain limiting case. An extensive effort has been made to understand how the Hartmann number, fluid behavior index, rotating Reynolds number, and slip parameter affects the flow. Results show the velocity of the power-law fluid depends strongly on flow parameters. Critical Hartmann number can be obtained for the power-law fluid in presence of uniform electric and magnetic fields. As a promising phenomenon, existence of a cross over point (which depends upon the fluid behavior index) for the centerline flow velocity, has also been predicted. Reduction in the shear stress and fluid viscosity can be controlled effectively by incorporating a slippery film of lubricant on the periphery of the microchannel. This work is useful to meet the upcoming challenges of future generation, like improvement in bio-magnetic-sensor technologies as well as electrical and mechanical mechanisms.

Diffusion-Layer Theory for Flows Under Apparent Wall Slip

1998 ◽  
Vol 63 (1) ◽  
pp. 132-140 ◽  
Author(s):  
Ondřej Wein
Keyword(s):  
Mass Transfer ◽  
Velocity Profile ◽  
Solid Surface ◽  
Diffusion Layer ◽  
Analytical Formula ◽  
Wall Slip ◽  
Slip Effect ◽  
Local Power ◽  
Overall Mass Transfer Coefficient ◽  
Apparent Wall Slip

An explicit analytical formula is given for the overall mass transfer coefficient between the bulk of flowing microdisperse liquid and a small but finite active part of a solid surface. The apparent wall slip effect inside a diffusion layer is reflected through the local power-law velocity profile, vx(z) = Bzp, and a distribution B = B(x,y) over the solid surface.

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