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Van Hj Harry Leeuwen - One of the best experts on this subject based on the ideXlab platform.
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the determination of the pressure viscosity Coefficient of a lubricant through an accurate film thickness formula and accurate film thickness measurements part 2 high l values
Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 2011Co-Authors: Van Hj Harry LeeuwenAbstract:The pressure–viscosity Coefficient of a traction fluid is determined by fitting calculation results on accurate film thickness measurements, obtained at different speeds, loads, and temperatures. T...
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the determination of the pressure viscosity Coefficient of a lubricant through an accurate film thickness formula and accurate film thickness measurements
Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 2009Co-Authors: Van Hj Harry LeeuwenAbstract:AbstractThe pressure—viscosity Coefficient is an indispensable property in the elastohydrodynamic (EHD) lubrication of hard contacts, but often not known. A guess will easily lead to enormous errors in the film thickness. This article describes a method to deduct this Coefficient by adapting the value of the pressure—viscosity Coefficient until the differences between accurate film thickness approxi-mation values and accurate film thickness measurements over a wide range of values are at a minimum. Eleven film thickness approximation formulas are compared in describing the film thickness of a test fluid with known value of the pressure—viscosity Coefficient. The measurement method is based on spacer layer interferometry. It is concluded that for circular contacts the newer more versatile expressions are not better than some older approximations, which are limited to a smaller region of conditions, and that the older fits are as least as appropriate to find the pressure—viscosity Coefficient of fluids, in ...
Brajendra Kumar Sharma - One of the best experts on this subject based on the ideXlab platform.
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pulsed field gradient nmr spectroscopy applications in determining the pressure viscosity Coefficient and low temperature flow properties of lubricant base oils
Industrial & Engineering Chemistry Research, 2003Co-Authors: Brajendra Kumar Sharma, Arthur J StipanovicAbstract:The pulsed field gradient (PFG) NMR technique was employed to measure the self-diffusion Coefficients (D) of hydrocarbon lubricant base fluids under ambient pressure conditions. This parameter was then related to various rheological properties, including the kinematic viscosity and the pressure viscosity Coefficient (PVC). The results demonstrate that D varies inversely with the fluid viscosity and PVC. This relationship was then used to predict PVC from D for a series of compositionally diverse base oils, providing an R2 value of 0.86. PFG NMR spectroscopy was also used to study the molecular dynamics of the liquid−solid transitions of the oils at low temperatures ranging from +40 to −40 °C. The self-diffusion Coefficient decreased linearly with decreasing temperature to 0 °C and then “leveled off” at lower temperatures. This observation can be explained, using spatially heterogeneous dynamics and other mechanistic models, by the onset of wax crystallization.
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Pressure Viscosity Coefficient of Lubricant Base Oils As Estimated by Nuclear Magnetic Resonance Spectroscopy
Industrial & Engineering Chemistry Research, 2002Co-Authors: Brajendra Kumar Sharma, A. StipanovicAbstract:The pressure viscosity Coefficient (PVC) is an important parameter for base oils in defining their lubricating capacity because it reflects the extent of “thickening” that occurs under high hydrodynamic loads. In this study, spin−lattice relaxation times (T1) derived from NMR experiments are used to probe the dynamic motional environment for a series of compositionally different base oils to better understand the relationship between chemical structure and bulk physical properties such as viscosity and PVC. Using a multivariable statistical analysis, it was demonstrated that the T1 times for certain 13C NMR resonances combined with the viscosity index can accurately predict the PVC of a base oil (R2 = 0.99). Further, 13C NMR-derived “average structural parameters” including certain paraffin, isoparaffin, and naphthenic structures, also predicted PVC very accurately (R2 = 0.99). Collectively, these results illustrate that the “energy-conserving” and “traction” properties of lubricants can be predicted from...
Scott Bair - One of the best experts on this subject based on the ideXlab platform.
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Elastohydrodynamic Performance of a Bio-Based, Non-Corrosive Ionic Liquid
MDPI AG, 2017Co-Authors: Marcus Björling, Scott Bair, Jiahua Zhu, Yijun ShiAbstract:To improve performance of machine components, lubrication is one of the most important factors. Especially for use in extreme environments, researchers look for other solutions rather than common lubricant base stocks like mineral oils or vegetable oils. One such example is ionic liquids. Ionic liquids have been defined as molten salts with melting points below 100 ∘ C that are entirely ionic in nature, comprising both cationic and anionic species. The industrial use of ionic liquids is mostly as solvents, electrolytes, extractants and catalysts. In tribological applications, ionic liquids are mainly studied in boundary lubrication and in pure sliding contacts. In this work, the elastohydrodynamic performance of a bio-based, non-corrosive, [choline][l-proline] ionic liquid is evaluated in terms of Pressure-Viscosity response, film forming capability and friction. The results show a Pressure-Viscosity Coefficient of below 8 GPa − 1 at 25 ∘ C, among the lowest reported for any ionic liquid. The ionic liquid generated up to 70% lower friction than a reference paraffin oil with a calculated difference in film thickness of 11%. It was also shown that this ionic liquid is very hygroscopic, which is believed to explain part of the low friction results, but also has to be considered in practical applications since the water content will influence the properties and thus the performance of the lubricant
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comments on pressure viscosity Coefficient of vegetable oils by biresaw and bantchev
Tribology Letters, 2013Co-Authors: Scott BairAbstract:The classical study of elastohydrodynamic lubrication has not employed a consistent definition of the pressure–viscosity Coefficient (PVC) or alpha of the liquid. This has likely been the result of the inaccurate film thickness formulas that require a value of alpha and of inaccurate film thickness measurements. Practitioners have found it possible to reconcile formula with measurement, when viscosity has been measured in a viscometer, by choosing a definition of alpha from the extensive menu of definitions that have been used. The problem for tribology is that the term, PVC, has become largely meaningless because there is no generally accepted definition.
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high pressure rheology for quantitative elastohydrodynamics
2007Co-Authors: Scott BairAbstract:Chapter 1. An Introduction to Elastohydrodynamic Lubrication 1.1 Lubrication 1.2 Concentrated Contact Lubrication 1.3 Full Elastohydrodynamic Lubrication 1.4 Experimental Elastohydrodynamics 1.5 Conclusion Chapter 2. An Introduction to the Rheology of Polymeric Liquids 2.1 Background 2.2 The Newtonian Model 2.3 Material Functions for Polymeric Liquids 2.4 Rheological Models 2.5 Time-Temperature-Pressure Superposition 2.6 Liquid Failure Chapter 3. General High-Pressure Experimental Techniques 3.1 Background 3.2 Pressure Containment 3.3 Closures 3.4 Feed-throughs 3.5 Pressure Generation and Measurement 3.6 Hydrostatic Media and Volume Compensation Chapter 4. Compressibility and the Equation of State 4.1 Background 4.2 PVT Measurement Techniques and Results 4.3 Empirical Equations of State Chapter 5. The Pressure and Temperature Dependence of the Low-Shear Viscosity 5.1 Background 5.2 High-Pressure Viscometers 5.3 General Pressure-Viscosity Response and Results for Pure Organic Liquids and Lubricants Chapter 6. Models for the Temperature and Pressure Dependence of the Low-Shear Viscosity 6.1 Introduction 6.2 Models for the Temperature-Viscosity Response 6.3 Pressure Fragility and Empirical Models for High Pressure Behavior 6.4 The Pressure-Viscosity Coefficient and Empirical Models for Low Pressure Behavior 6.5 Empirical Models for Large Pressure Intervals 6.6 Models Based on Free Volume Theory 6.7 Generalized Temperature-Pressure-Viscosity Models 6.8 Multi Component Systems Chapter 7. Measurement Techniques for the Shear Dependence of Viscosity at Elevated Pressure 7.1 Introduction 7.2 Phenomena Producing Behavior Similar to Shear-Thinning 7.3 Rheometers for High Pressure Chapter 8. The Shear Dependence of Viscosity at Elevated Pressure 8.1 Introduction 8.2 Normal Stress Differences at Elevated Pressures 8.3 The Origin of Non-Newtonian Behavior in Low-Molecular-Weight Liquids at Elevated Pressures 8.4 Time-Temperature-Pressure Superposition 8.5 The Competition between Thermal Softening and Shear-Thinning 8.6 Multi Component Systems 8.7 The Power-Law Exponent and the Second Newtonian Viscosity Chapter 9. Glass Transition and Related Transitions in Liquids under Pressure 9.1 Measurements of Glass Transition at Elevated Pressure 9.2 Measurements of Dielectric Transition at Elevated Pressure 9.3 The Transitions as Isoviscous States 9.4 The Pressure Variation of Viscosity across the Transition Chapter 10. Shear Localization, Slip and the Limiting Stress 10.1 Introduction 10.2 Measurements of Rate Independent Shear Stress 10.3 Flow Visualization of Shear Bands 10.4 Mohr-Coulomb Failure Criterion 10.5 Change of Character of the Piezoviscous Navier-Stokes Equations 10.6 Thermal Localization, Adiabatic Shear Bands 10.7 Interfacial Slip Chapter 11. The Reynolds Equation 11.1 Background 11.2 Reynolds Equations for Generalized Newtonian Fluids Chapter 12. Applications to Elastohydrodynamics 12.1 Introduction 12.2 Film Thickness for Shear Thinning Liquids 12.3
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the pressure viscosity Coefficient for newtonian ehl film thickness with general piezoviscous response
Journal of Tribology-transactions of The Asme, 2006Co-Authors: Scott Bair, Yuchuan Liu, Jane Q WangAbstract:There has been a long-standing need for a piezoviscous parameter, αfilm , that together with the ambient viscosity, μ0 , will completely quantify the Newtonian rheology so that the film thickness for liquids that do not shear-thin in the inlet may be calculated as h = h(μ0 , αfilm , ...) regardless of the details of the Pressure-Viscosity response. It seems that Blok’s reciprocal asymptotic isoviscous pressure, α*, has certain advantages over the conventional Pressure-Viscosity Coefficient that is poorly suited for this purpose. The first detailed review of piezoviscous models for low pressures is provided. A simulation code that is apparently stable for all realistic Pressure-Viscosity response was utilized with diverse piezoviscous models and model liquids to develop a satisfactory definition of αfilm that reads αfilm = [1 − exp(−3)]/03/α*μ (0) dpμ (p);1/α* = 0∞ μ (0) dp / μ (p). In the case of μ = μ0 exp(αp), αfilm = α and formulas are provided for other models.Copyright © 2006 by ASME
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the pressure viscosity Coefficient of a perfluorinated polyether over a wide temperature range
Journal of Tribology-transactions of The Asme, 2001Co-Authors: Scott BairAbstract:An unbranched perfluoropolyether is the current ball bearing lubricant for deep space flight. We report measurements of viscosity to moderate pressures for the calculation of Pressure-Viscosity Coefficients to temperatures as low as -40°C. A free volume model predicts that a minimum Pressure-Viscosity Coefficient exists at higher temperature. The existence of a minimun α 0 (T) is confirmed by viscometry at temperatures to 180°C.
Jane Q Wang - One of the best experts on this subject based on the ideXlab platform.
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correlation between pressure viscosity Coefficient and traction Coefficient of the base stocks in traction lubricants a molecular dynamic approach
Tribology International, 2019Co-Authors: Jane Q Wang, Ning Ren, Frances E LockwoodAbstract:Abstract The lubricants for traction-continuously variable transmissions (t-CVT) could generate high traction under a high pressure, which requires the design of a special class of base stock molecules. This paper reports the development of a model, based on non-equilibrium molecular dynamics (NEMD) simulations, for estimating traction Coefficients to facilitate the design of base stock molecules prior to their synthesis. The Pressure-Viscosity Coefficients (α) of a number of base stocks in traction lubricants are calculated and the results are correlated with the corresponding traction Coefficient τ. A linear α - τ correlation is obtained with a Coefficient of determination of as high as 0.85.
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pressure viscosity Coefficient of hydrocarbon base oil through molecular dynamics simulations
Tribology Letters, 2015Co-Authors: Pinzhi Liu, Ning Ren, Frances E Lockwood, Jane Q WangAbstract:The pressure–viscosity Coefficient (the α value), which represents the variation of viscosity as a function of pressure, is an important parameter for elastohydrodynamic lubrication analyses. The properties of hydrocarbons in the C20–C40 mass range are of fundamental importance as they are basic constituents of synthetic- and mineral-based lubricant stocks. The conventional acquisition of the α value requires preparation of lubricant samples and experimental testing by means of a high-pressure viscometer. In this paper, we present a method to obtain the α value of a typical base oil (1-Decene trimer) based solely on the molecular dynamics simulations. Non-equilibrium molecular dynamics (NEMD) simulations were performed to calculate the shear viscosity of the lubricant at various temperatures and pressures up to 1 GPa. Elevated temperatures and time–temperature superposition (TTS)-based extrapolations were applied to further extend the ability of the NEMD simulations, and the rotational relaxation time was calculated and used to determine the validity of the NEMD calculations. The α value at 100 °C was calculated and compared with experimental results. Effectiveness of the extrapolation was evaluated with a 95 % confidence interval.
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the pressure viscosity Coefficient for newtonian ehl film thickness with general piezoviscous response
Journal of Tribology-transactions of The Asme, 2006Co-Authors: Scott Bair, Yuchuan Liu, Jane Q WangAbstract:There has been a long-standing need for a piezoviscous parameter, αfilm , that together with the ambient viscosity, μ0 , will completely quantify the Newtonian rheology so that the film thickness for liquids that do not shear-thin in the inlet may be calculated as h = h(μ0 , αfilm , ...) regardless of the details of the Pressure-Viscosity response. It seems that Blok’s reciprocal asymptotic isoviscous pressure, α*, has certain advantages over the conventional Pressure-Viscosity Coefficient that is poorly suited for this purpose. The first detailed review of piezoviscous models for low pressures is provided. A simulation code that is apparently stable for all realistic Pressure-Viscosity response was utilized with diverse piezoviscous models and model liquids to develop a satisfactory definition of αfilm that reads αfilm = [1 − exp(−3)]/03/α*μ (0) dpμ (p);1/α* = 0∞ μ (0) dp / μ (p). In the case of μ = μ0 exp(αp), αfilm = α and formulas are provided for other models.Copyright © 2006 by ASME
Frances E Lockwood - One of the best experts on this subject based on the ideXlab platform.
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correlation between pressure viscosity Coefficient and traction Coefficient of the base stocks in traction lubricants a molecular dynamic approach
Tribology International, 2019Co-Authors: Jane Q Wang, Ning Ren, Frances E LockwoodAbstract:Abstract The lubricants for traction-continuously variable transmissions (t-CVT) could generate high traction under a high pressure, which requires the design of a special class of base stock molecules. This paper reports the development of a model, based on non-equilibrium molecular dynamics (NEMD) simulations, for estimating traction Coefficients to facilitate the design of base stock molecules prior to their synthesis. The Pressure-Viscosity Coefficients (α) of a number of base stocks in traction lubricants are calculated and the results are correlated with the corresponding traction Coefficient τ. A linear α - τ correlation is obtained with a Coefficient of determination of as high as 0.85.
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pressure viscosity Coefficient of hydrocarbon base oil through molecular dynamics simulations
Tribology Letters, 2015Co-Authors: Pinzhi Liu, Ning Ren, Frances E Lockwood, Jane Q WangAbstract:The pressure–viscosity Coefficient (the α value), which represents the variation of viscosity as a function of pressure, is an important parameter for elastohydrodynamic lubrication analyses. The properties of hydrocarbons in the C20–C40 mass range are of fundamental importance as they are basic constituents of synthetic- and mineral-based lubricant stocks. The conventional acquisition of the α value requires preparation of lubricant samples and experimental testing by means of a high-pressure viscometer. In this paper, we present a method to obtain the α value of a typical base oil (1-Decene trimer) based solely on the molecular dynamics simulations. Non-equilibrium molecular dynamics (NEMD) simulations were performed to calculate the shear viscosity of the lubricant at various temperatures and pressures up to 1 GPa. Elevated temperatures and time–temperature superposition (TTS)-based extrapolations were applied to further extend the ability of the NEMD simulations, and the rotational relaxation time was calculated and used to determine the validity of the NEMD calculations. The α value at 100 °C was calculated and compared with experimental results. Effectiveness of the extrapolation was evaluated with a 95 % confidence interval.