• Tribology and Lubricants
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• v.28 no.2
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• pp.47-55
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• 2012

Generally, to product multi-grade oil like engine oil, a sort of mineral base oil is mixed with a fundamental additive package liquid and a polymer liquid as viscosity index improver in order to improve the lubricating property of base oil. That is, engine oil is the mixture of more than two fluids. Specially, a polymeric type liquid cannot be seen as the linear viscosity like Newtonian fluids. In this research, by using the governing equation describing non-Newtonian hydrodynamic lubrication related with the mixture of incompressible fluids based on the principle of continuum mechanics, it will be compared the bearing performance between the mixture of each liquid to be blended and multi-grade engine oil as a single fluid in a high speed hydrodynamic journal bearing. Further, it is to be found the way estimating the performance of the blended multi-grade engine lubricant in a journal bearing in advance before blending by using the physical properties of mineral base oil, fundamental additive liquid and polymer liquid of viscosity index improver. So, it can be reduced the number of trial and error to get the wanted lubricant by selecting the proper volume fraction of each liquid to satisfy the expected performance and estimating in advance the performance of various multi-grade oils before blending. Therefore, it can be shorten the developing time and saved the developing cost.

• Tunnel and Underground Space
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• v.12 no.4
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• pp.277-283
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• 2002

This experimental study concerns the characteristics of a helical flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. The pressure losses and skin friction coefficients have been measured for the fully developed flow of Non-Newtonian fluid, aqueous solution of sodium carbomethyl cellulose (CMC) and bentonite with inner cylinder rotational speed of 0~400 prm. Also, the visualization of helical flows has been performed to observe the unstable waves. The results of present study reveal the relation of the Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The pressure losses increase as the rotational speed increases, but the gradient of pressure losses decreases as the Reynolds number increases in the regime of transition and turbulence. And the increase of flow disturbance by Taylor vortex in a concentric annulus with rotating inner cylinder results in the decrease of the critical Reynolds number with the increase of skin friction coefficient.

• Journal of applied mathematics & informatics
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• v.25 no.1_2
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• pp.51-66
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• 2007

A layer of compressible, rotating, elastica-viscous fluid heated & soluted from below is considered in the presence of vertical magnetic field to include the effect of Hall currents. Dispersion relation governing the effect of viscoelasticity, salinity gradient, rotation, magnetic field and Hall currents is derived. For the case of stationary convection, the Rivlin-Erickson fluid behaves like an ordinary Newtonian fluid. The compressibility, stable solute gradient, rotation and magnetic field postpone the onset of thermosolutal instability whereas Hall currents are found to hasten the onset of thermosolutal instability in the absence of rotation. In the presence of rotation, Hall currents postpone/hasten the onset of instability depending upon the value of wavenumbers. Again, the dispersion relation is analyzed numerically & the results depicted graphically. The stable solute gradient and magnetic field (and corresponding Hall currents) introduce oscillatory modes in the system which were non-existent in their absence. The case of overstability is discussed & sufficient conditions for non-existence of overstability are derived.

• Tribology and Lubricants
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• v.14 no.1
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• pp.54-63
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• 1998

In many practical lubricated contacts such as a rough concentrated contact on the sliding of nominally flat surfaces, the fluid may be of molecular (nanometer) scale owing to the asperity interactions on the surfaces. Under this condition, there is insufficient lubricant on the concentrated contact spot to maintain a realistic continuum. Rheological behavior for this kind of concentrated contact has been studied extensively to know whether the application of viscous fluid model is appropriate. The interaction of two rough surfaces is simplified as perfectly flat-rough surfaces contact under certain conditions by "composite topography" and for a nanometer scale fluid film, three kinds of rheological fluid behavior are analyzed in elastohydrodynamic asperity point contact.t contact.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.3
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• pp.194-200
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• 2009

Suspension of a single solid particle in a channel flow with a constant pressure gradient is studied numerically. The interaction of a circular particle with a surrounding Newtonian fluid is formulated using a combined formulation. Numerical results are presented using two dimensionless variables: the sedimentation Reynolds number and the generalized Froude number. From the present results, it has been shown that a solid particle is suspended at a smaller generalized Froude number as the viscosity of the surrounding fluid increases. The time taken for equilibrium position is found to be smaller as fluid viscosity increases when both : the sedimentation Reynolds number and the generalized Froude number are the same while, at the same situation, the dimensionless time taken for equilibrium position is to be nearly the same regardless of fluid viscosity when a dimensionless time variable is introduced

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.10a
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• pp.173-182
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• 1997

In many practical lubricated contacts such as a rough concentrated contact on the sliding of nominally flat surfaces, the fluid may be of molecular (nanometer) scale owing to the asperity interactions on the surfaces. Under this condition, there is insufficient lubricant on the concentrated contact spot to maintain a realistic continuum. Rheological behavior for this kind of concentrated contact was studied to know whether the application of viscous fluid model is appropriate. The interaction of two rough surfaces is simplified as perfectly flat-rough surfaces contact under certain conditions by "composite topography" and for a nanometer scale fluid film, three kinds of rheological fluid behavior are analyzed in elastohydrodynamic asperity point contact.t contact.

• Journal of computational fluids engineering
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• v.4 no.2
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• pp.9-16
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• 1999

The present study investigates flow character and heat transfer behaviors of viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. An axially-constant heat flux on bottom wall and peripherally constant temperature boundary condition(H1) was adopted. The Reiner-Rivlin fluid model is used as the normal stress model for the viscoelastic fluid and temperature-dependent viscosity model is adopted. The present results show a signifiant change of the main flow field which causes a large heat transfer enhancement. This phenomena can be explained by the combined effect of buoyancy, temperature-dependent viscosity and viscoelastic property on the flow.

• Journal of the Korean Society of Safety
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• v.18 no.3
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• pp.8-13
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• 2003

Equivalent Reynolds equation of truncated cone type SFD bearing using nonnewtonian EV fluid is derived. The 3 nondimensional oil film pressures and its forces are obtained with axial and circumferential pressure gradient of bearing respectively, and dynamic characteristics for the stability of rotor-bearing system are obtaind through the governing equation for an elastic rotational shaft. It is shown that EV fluid is less sensitive to the changes of oil-film than newtonian fluids for dynamic characteristics. Therefore, results show that it is better to use an EV fluid with truncated cone type SFD bearing for the vibration control of rotational machines.

• Korea-Australia Rheology Journal
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• v.18 no.2
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• pp.51-65
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• 2006

Of concern in the present theoretical investigation is the study of blood flow and convection-dominated diffusion processes in a model bifurcated artery under stenotic conditions. The geometry of the bifurcated arterial segment having constrictions in both the parent and its daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is constructed mathematically with the introduction of suitable curvatures at the lateral junction and the flow divider. The streaming blood contained in the bifurcated artery is treated to be Newtonian. The flow dynamical analysis applies the two-dimensional unsteady incompressible nonlinear Wavier-Stokes equations for Newtonian fluid while the mass transport phenomenon is governed by the convection diffusion equation. The motion of the arterial wall and its effect on local fluid mechanics is, however, not ruled out from the present model. The main objective of this study is to demonstrate the effects of constricted flow characteristics and the wall motion on the wall shear stress, the concentration profile and on the mass transfer. The ultimate numerical solutions of the coupled flow and diffusion processes following a radial coordinate transformation are based on an appropriate finite difference technique which attain appreciable stability in both the flow phenomena and the convection-dominated diffusion processes.

• Journal of Biomedical Engineering Research
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• v.11 no.2
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• pp.233-242
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• 1990

In the current flow visualization studies, the role of non-Newtonian characteristics (such as shearra to dependent viscosity and viscoelasticity ) on flow behavior across the sudden ex- pansion step in a circular pipe as a model for blood flow experiments is investigated over a wide range of Reynolds numbers. The expansion ratios tested are 2.000 and 2.667 and the range of the Reynolds number covered in the current flow visualization tests are 10~35, 000 based on the inlet. diameter. The reattachment longuEs for the viscoelastic fluids in the lami- nar flow regime are found to be much shorter than those for the Newtonian fluid. In addition it decreases significantly with increasing concentration of viscoelastic fluids at the same Reynolds number. However, in the turbulent flow regime, the reattachment length for the viscoelastic fluids Is two or three times longer than those for water, and gradually increases with increasing concentration of viscoelastic solutions, resulting In 25 and 28 step-height dis- tances for 500 and 1, 000 lpm ployacrylamide solutions, respectively. This may be due to the fact that the elasticity in pobacrylamide solutions suppresses the eddy motion and controls separation and reattachment behavior in the sudden expansion pips flow.