Pressure–viscosity response in the inlet zone for quantitative elastohydrodynamics

Bair, Scott

doi:10.1016/j.triboint.2016.01.037

Cited by 11 publications

(16 citation statements)

References 38 publications

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“…Where η0 is the low-shear viscosity at reference (ambient) pressure, *  is the reciprocal asymptotic isoviscous pressure coefficient and q is the McEwen exponent. This is equivalent to the Tait pressure-viscosity equation [68] for low (ambient [69]) reference pressures. The parameters that were used for the fits to the McEwen equation in Figure 9 and 10 are given in Table 3.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Evaluation of Methods for Viscosity Simulations of Lubricants at Different Temperatures and Pressures: A Case Study on PAO-2

Mathas

Holweger

Wolf

et al. 2021

Tribology Transactions

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The behavior of lubricants at operational conditions, such as at high pressures, is a topic of great industrial interest. In particular, viscosity and the viscosity-pressure relation are especially important for applications and their determination by computational simulations is very desirable. In this study we evaluate methods to compute these quantities based on fully atomistic molecular dynamics simulations which are computationally demanding but also have the potential to be most accurate. We used the 9,10dimethyloctadecane molecule, main component of PAO-2 base oil as the lubricant for our tests. The methods used for the viscosity simulations are the Green-Kubo equilibrium molecular dynamics (EMD-GK) and non-equilibrium molecular dynamics (NEMD), at pressures of up to 1.0 GPa and various temperatures (40-150 degrees Celsius). We present the theory behind these methods and investigate how the simulation parameters affect the results obtained, to ensure viscosity convergence with respect to the A c c e p t e d M a n u s c r i p t simulation intervals and all other parameters. We show that by using each method in its regime of applicability, we can achieve good agreement between simulated and measured values. NEMD simulations at high pressures captured zero shear viscosity successfully, while at 40 degrees Celsius EMD-GK is only applicable to pressures up to 0.3 GPa, where the viscosity is lower. In NEMD, longer and multiply repeated simulations improve the confidence interval of viscosity, which is essential at lower pressures. Another aspect of these methods is the choice of the utilized force field for the atomic interactions. This was investigated by selecting two different commonly used force fields.

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Section: Accepted Manuscriptmentioning

confidence: 99%

Evaluation of Methods for Viscosity Simulations of Lubricants at Different Temperatures and Pressures: A Case Study on PAO-2

Mathas

Holweger

Wolf

et al. 2021

Tribology Transactions

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“…The parameters for the improved Yasutomi correlation can be seen in Table 2. Based on these pressure-viscosity measurements, pressure-viscosity coefficients by three different definitions were calculated based on the McEwen model [25]. The results are shown in Table 3.…”

Section: Resultsmentioning

confidence: 99%

“…The pressure-viscosity coefficients based on the measured limiting-low-shear viscosities of the [choline] [L-proline] IL were calculated with the use of the McEwen model [24,25] for the following pressure-viscosity definitions: The conventional pressure-viscosity coefficient, α 0 the reciprocal asymptotic isoviscous pressure coefficient, α * employed in Hamrock & Dowson film thickness formulas [26], and finally the general film-forming pressure-viscosity coefficient α f ilm . A more complete description of the different definitions of pressure-viscosity coefficients can be found elsewhere [27].…”

Section: Limiting Low Shear Measurements and Pressure-viscosity Calcumentioning

confidence: 99%

Elastohydrodynamic Performance of a Bio-Based, Non-Corrosive Ionic Liquid

Björling

Bair

et al. 2017

Applied Sciences

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Abstract: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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“…The McEwen model, equation (3), describes the data very well and has the advantage of providing analytical expression for some pressure-viscosity coefficients [8]. The thin curves through the data points are the McEwen equation for the mixtures and the parameters are listed in Table 2.…”

Section: Preliminary Resultsmentioning

confidence: 99%

“…First, the compressibility is much greater for refrigerants than for oils and this compressibility influences the oil/refrigerant solution [7]. Second, the classical film thickness formulas define the various pressure-viscosity coefficients according to pressure-viscosity models which are only accurate for very viscous oils [8,9].…”

Section: Introductionmentioning

confidence: 99%

A New High-Pressure Viscometer for Oil/Refrigerant Solutions and Preliminary Results

Bair

2016

Tribology Transactions

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The reliability and efficiency of refrigeration compressors is dependent on the lubricating effectiveness of the refrigeration oil which is necessarily a solution of oil and refrigerant. In this article, the development of a high pressure viscometer, which can operate at elastohydrodynamic lubrication (EHL) inlet pressures for oil/refrigerant solutions, is explained in detail. New viscosity measurements are presented for two compressor oils to 1.2 GPa. Preliminary results are given for a polyol ester with two concentrations of R134a refrigerant to 0.35 GPa. These are the first measurements of oil/refrigerant solutions to such high pressure. Temperature-pressureviscosity correlations are applied to all materials for use in modeling. Correlations are provided for the temperature and pressure dependences of the viscosity of the oils, the refrigerant and for the mixtures. The definition of -pressure-viscosity coefficient‖ is a pressing problem for elastohydrodynamics.

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Pressure–viscosity response in the inlet zone for quantitative elastohydrodynamics

Cited by 11 publications

References 38 publications

Evaluation of Methods for Viscosity Simulations of Lubricants at Different Temperatures and Pressures: A Case Study on PAO-2

Evaluation of Methods for Viscosity Simulations of Lubricants at Different Temperatures and Pressures: A Case Study on PAO-2

Elastohydrodynamic Performance of a Bio-Based, Non-Corrosive Ionic Liquid

A New High-Pressure Viscometer for Oil/Refrigerant Solutions and Preliminary Results

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