The Generalized Newtonian Fluid Model and Elastohydrodynamic Film Thickness

2002 ◽  
Vol 125 (1) ◽  
pp. 70-75 ◽  
Author(s):  
Scott Bair ◽  
Farrukh Qureshi
Keyword(s):  
Molecular Weight ◽  
Film Thickness ◽  
Fluid Model ◽  
Shear Thinning ◽  
Nonequilibrium Molecular Dynamics ◽  
Generalized Newtonian Fluid ◽  
Flow Curves ◽  
Liquid Behavior ◽  
Inlet Zone ◽  
Film Thinning

The nature of real shear-thinning in elastohydrodynamic contacts is well-known from both experimental measurement and nonequilibrium molecular dynamics to follow a power-law. Shear-thinning will affect the film thickness when the Newtonian limit is low enough to occur in the inlet zone (less than about 1 MPa shear stress). Then kinetic theory tells us that film thinning should occur for molecular weight greater than 2000 kg/kmol. We present a review of generalized Newtonian models, flow curves for real lubricants and comparison of calculated and measured film thickness. The calculations utilize measurable liquid behavior, in contrast to most previous work.

Scale Effects in Generalized Newtonian Elastohydrodynamic Films

2008 ◽  
Author(s):  
I. I. Kudish ◽  
P. Kumar ◽  
M. M. Khonsary ◽  
S. Bair
Keyword(s):  
Film Thickness ◽  
Scale Effects ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Effective Pressure ◽  
Practical Advantage ◽  
Inlet Zone ◽  
Real Machine

The prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the properties have been obtained from a measurement of the central film thickness in an optical EHL point contact simulator and the assumption of a classical Newtonian film thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient which compensates for shear-thinning. We have shown by a perturbation analysis and by a full EHL numerical solution that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact within a real machine may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning in the inlet zone.

Scale Effects in Generalized Newtonian Elastohydrodynamic Films

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Ilya I. Kudish ◽  
P. Kumar ◽  
M. M. Khonsari ◽  
Scott Bair
Keyword(s):  
Film Thickness ◽  
Scale Effects ◽  
Elastohydrodynamic Lubrication ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Effective Pressure ◽  
Carreau Fluid ◽  
Practical Advantage ◽  
Inlet Zone ◽  
Real Machine

The estimation or prediction of elastohydrodynamic lubrication (EHL) film thickness requires knowledge of the lubricant properties. Today, in many instances, the lubricant properties have been obtained from a measurement of the central film thickness and the assumption of a classical Newtonian film-thickness formula. This technique has the practical advantage of using an effective pressure-viscosity coefficient, which compensates for shear-thinning. We have shown by a perturbation analysis of limiting cases for fluid with Carreau rheology (represented by Newtonian and power fluid) and by a full EHL numerical solution for Carreau fluid that the practice of extrapolating from a laboratory scale measurement of film thickness to the film thickness of an operating contact may substantially overestimate the film thickness in the real machine if the machine scale is smaller and the lubricant is shear-thinning within the inlet zone. The intention here is to show that errors result from extrapolation of Newtonian formulas to different scale and not to provide advice regarding quantitative engineering calculations.

Combined Effects of Shear Thinning and Viscous Heating on EHL Characteristics of Rolling/Sliding Line Contacts

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Punit Kumar ◽  
M. M. Khonsari
Keyword(s):  
Film Thickness ◽  
Thermal Effect ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
Viscous Heating ◽  
Shear Thinning Fluids ◽  
Line Contacts ◽  
Power Law Index ◽  
Good Agreement

The combined influence of shear thinning and viscous heating on the behavior of film thickness and friction in elastohydrodynamic lubrication (EHL) rolling/sliding line contacts is investigated numerically. The constitutive equation put forward by Carreau is incorporated into the model to describe shear thinning. An extensive set of numerical simulations is presented. Comparison of the film thickness predictions with published experiments reveals good agreement, and it is shown that thermal effect plays an important role in the precise estimation of EHL film thickness and friction coefficient. Parametric simulations show that thermal effect in shear-thinning fluids is strongly affected by the power-law index used in the Carreau equation. Comparisons of prediction of the Newtonian fluid model are presented to quantify the degree to which it overestimates the film thickness.

The High Pressure Rheology of Mixtures

2004 ◽  
Vol 126 (4) ◽  
pp. 697-702 ◽  
Author(s):  
Scott Bair
Keyword(s):  
Molecular Weight ◽  
High Pressure ◽  
Binary Systems ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Newtonian Viscosity ◽  
Double Shear ◽  
Ideal Mixing ◽  
Viscosity Behavior ◽  
Single Flow

The Newtonian mixing rules for several binary systems have been experimentally investigated. Some systems show non-ideal mixing response and for some systems the non-ideal response is pressure-dependent, yielding an opportunity for manipulation of the pressure-viscosity behavior to advantage. The mixing of differing molecular weight “straight cuts” can produce very different pressure-viscosity response. This behavior underscores the difficulty in predicting the pressure-viscosity coefficient based upon chemical structure and ambient viscosity since the molecular weight distribution is also important, but it also provides another opportunity to control the high-pressure response by blending. The first experimental observation of double shear-thinning within a single flow curve is reported. Blending then provides the capability of adjusting not only the Newtonian viscosity but also the non-Newtonian shear-thinning response as well.

scholarly journals Analysis of misaligned journal bearing lubrication performance considering the effect of lubricant couple stress and shear thinning

2021 ◽  
Vol 37 ◽  
pp. 282-290
Author(s):  
Junchao Zhu ◽  
Haiyu Qian ◽  
Huabing Wen ◽  
Liangyan Zheng ◽  
Hanhua Zhu
Keyword(s):  
Film Thickness ◽  
Couple Stress ◽  
Journal Bearing ◽  
Shear Thinning ◽  
Inlet Temperature ◽  
Stress Effect ◽  
Misalignment Angle ◽  
Oil Film ◽  
Stress Coefficient ◽  
Lubrication Performance

ABSTRACT This paper investigates journal bearings, and builds a lubrication model taking into account misalignment, the lubricant couple stress effect and shear thinning. In order to explore the sensitivity of couple stress fluid lubrication performance to oil film thickness, we introduce the critical oil film thickness coefficient. The results show that the sensitivity increases with the increase of the couple stress coefficient, and it is highest in the area of minimum oil film thickness. Compared with a parallel journal, increases in the misalignment angle strengthen the effect of couple stress. Shear thinning also plays an important role in bearing lubrication performance. For a low oil inlet temperature, the effect of shear thinning increases with the increase of the couple stress parameter. For a high oil inlet temperature, the influence is negligible. An increase in the misalignment angle will not further enhance the effect of shear thinning.

scholarly journals Effect of 1,4-Napthaquinone (NQ) and benzophenone (BPH)on the photodegradation and biodegradation of methyl cellulose film

2010 ◽  
Vol 7 (1) ◽  
pp. 737-744
Author(s):  
Baghdad Science Journal
Keyword(s):  
Molecular Weight ◽  
Film Thickness ◽  
Carbonyl Compounds ◽  
Methyl Cellulose ◽  
Chain Scission ◽  
Cellulose Derivative ◽  
Accelerated Weathering ◽  
Cellulose Derivatives ◽  
Photodegradation Rate ◽  
Aromatic Carbonyl Compounds

The induced photodegradation of methyl cellulose (MC) films in air was investigated in the absence and presence of aromatic carbonyl compounds(photosenssitizers): 1,4-naphthaquinone (NQ) and benzophenone (BPH) by accelerated weathering tester. The addition of (0.01 wt %) of low molecular weight aromatic carbonyl compounds to cellulose derivatives films(25µm in thickness) enhanced the photodegradation of the polymer films.The photodegradation rate was measured by the increase in carbonyl absorbance. Decreases in solution viscosity and reduction of molecular weight were also observed in the irradiated samples. Changes in the number-average chain scission, the degree of deterioration and in the quantum yield of chain scission values are also observed, and it was concluded that branching or cross-linking has occurred for cellulose derivative with NQ and BPH. Findings from all analytical techniques indicated that the 1,4-naphthaquinone (NQ) photosensitizer enhance the photodegradation of methyl cellulose more than benzophenone (BPH). The effect of the photosensitizer concentration, (ranging from 0.01 to 0.1 %), on the rate of photodegradation was also monitored for MC films. The rates are increased with increasing the photosensitizer concentration. The effect of film thickness is also studied at fixed sensitizer concentration (0.05%), and results show that the rate of cellulose derivative photodegradation decreases with increasing film thickness. The rate constants of the photodegradation of the photosensitizers deduced in cellulose derivatives films, [at concentration of (0.1%)by weight and thickness (25µm)]. Biodegradation of irradiated cellulose derivatives films was conclusively established with bacteria type Pseudomonas aeuroginosa Rb-19 isolated from crude oil. The amount of bacteria growth on MC after 30 days was lower, while there was no growth observed in MC with BPH

The Effect of Polymers on Ceramic Suspension Rheology and Green Component Properties

1992 ◽  
Vol 289 ◽  
Author(s):  
Jennifer A. Lewis ◽  
Andrea L. Ogden ◽  
David Schroeder ◽  
Kirk J. Duchow
Keyword(s):  
Molecular Weight ◽  
Polymer System ◽  
Polyvinyl Butyral ◽  
Shear Thinning ◽  
Suspension Rheology ◽  
Low Molecular Weight ◽  
Polymer Molecular Weight ◽  
Green Component ◽  
Ceramic Suspensions ◽  
Packing Efficiency

AbstractCeramic suspensions were formulated based on an alumina/plasticized-polymer system. The total polymer volume in suspension was held constant, while the relative amount of high-to-low molecular weight polyvinyl butyral (PVB) in suspension was varied. Experiments were performed to elucidate the effects of polymer molecular weight and distribution on the rheological properties of these casting suspensions as well as on the green microstructure of tape-cast components. The polymer properties affected not only the suspension viscosity at a given shear rate as expected, but also the shear thinning behavior of each suspension. Tapes (thickness ≈ 250 μm) were cast from these suspensions and their properties were evaluated. Pore volume, a measure of the packing efficiency, was found to depend strongly on the polymer molecular weight and distribution. In addition, preliminary lamination studies revealed that dimensional stability and anisotropy were also affected by the relative amount of high-to-low molecular weight PVB. A direct correlation was shown to exist between the shear thinning behavior of these suspensions and the resulting dimensional anisotropy exhibited by the tapes cast from each of them. These results demonstrate that polymeric aids influence not only the suspension rheology, but the green component microstructure as well, and, hence, are an integral aspect of ceramic processing.

An Investigation Into the Influence of Fluid Viscoelasticity in a Squeeze Film Bearing

1978 ◽  
Vol 100 (1) ◽  
pp. 56-64 ◽  
Author(s):  
John A. Tichy ◽  
Ward O. Winer
Keyword(s):  
Molecular Weight ◽  
Film Thickness ◽  
High Molecular Weight ◽  
Hydrodynamic Lubrication ◽  
Load Capacity ◽  
Surface Film ◽  
Free Fall ◽  
Squeeze Film ◽  
Delayed Response ◽  
High Molecular Weight Polymers

This investigation concerns a prediction of the behavior of viscoelastic fluids in a parallel circular squeeze film with a constant approach velocity, and a comparison to experimental results. The squeeze film geometry has direct application to unsteady hydrodynamic lubrication. The analysis predicts that load capacity of a viscoelastic fluid may be increased due to normal stress effects or decreased due to a delayed response of shear stress to a change in shear rate. Ten tested fluids include Newtonian control fluids, silicone fluids, high molecular weight polymers in petroleum oils, and extremely high molecular weight polymers in water and glycerin. The experimental squeezing is accomplished by the free fall of a cylindrical steel rod along its axis toward a stationary opposing surface. Film thickness, velocity of approach and load are measured. The velocity of approach is essentially constant in the range of film thickness considered. The water-glycerin-polymer solutions exhibited load capacity increases up to 33 percent, while the petroleum-polymer and silicone fluids showed decreases to 23 percent. It appears that viscoelastic effects cannot account for the reported improved bearing performance of polymer-additive lubricants.

Thermal Conductivity of Amorphous and Crystalline SiO2 Nano-Films from Molecular Dynamics Simulations

2012 ◽  
Vol 501 ◽  
pp. 64-69 ◽  
Author(s):  
Yan He ◽  
Yuan Zheng Tang ◽  
Man Ding ◽  
Lian Xiang Ma
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Film Thickness ◽  
Molecular Dynamics Simulations ◽  
Grain Morphology ◽  
Nonequilibrium Molecular Dynamics ◽  
Calculated Temperature ◽  
Dynamics Simulations ◽  
Different Thickness ◽  
Good Agreement

Normal thermal conductivity of amorphous and crystalline SiO2nano-films is calculated by nonequilibrium molecular dynamics (NEMD) simulations in the temperature range from 100 to 700K and thicknesses from 2 to 6nm. The calculated temperature and thickness dependences of thermal conductivity are in good agreement with previous literatures. In the same thickness, higher thermal conductivity is obtained for crystalline SiO2nano-films. And more importantly, for amorphous SiO2nano-films, thickness can be any direction of x, y, z-axis without effect on the normal thermal conductivity, for crystalline SiO2nano-films, the different thickness directions obtain different thermal conductivity results. The different results of amorphous and crystalline SiO2nano-films simply show that film thickness and grain morphology will cause different effects on thermal conductivity.

New Central Film Thickness Equation for Shear Thinning Lubricants in Elastohydrodynamic Lubricated Rolling/Sliding Point Contact Conditions

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Puneet Katyal ◽  
Punit Kumar
Keyword(s):  
High Pressure ◽  
Equation Of State ◽  
Film Thickness ◽  
Point Contact ◽  
Viscosity Coefficient ◽  
Shear Thinning ◽  
Numerical Approach ◽  
Present Formulation ◽  
Contact Conditions ◽  
Doolittle Equation

This paper offers central film thickness formula pertaining to shear-thinning lubricants under rolling/sliding point contact conditions. The shear-thinning behavior of the lubricants is modeled using Carreau viscosity equation and the piezo-viscous response employed herein is the free-volume based Doolittle equation in conjunction with Tait's equation of state for lubricant compressibility. The present formulation is based on reciprocal asymptotic isoviscous piezo-viscous coefficient as it is a more accurate measure of the high pressure piezo-viscous response of elastohydrodynamic lubricated (EHL) lubricants compared to the conventional pressure–viscosity coefficient. Comparisons between simulated, curve-fitted values, and experimental results validate both the employed numerical approach and rheological model.

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