EHL simulation using the free-volume viscosity model

Abstract

The free-volume viscosity model can accurately predict the temperature-pressure-viscosity relationship of lubricants. However, it is seldom used in elastohydrodynamic lubrication (EHL) simulation. This paper presents the application of the free-volume viscosity model in a Newtonian EHL simulation of a squalane-lubricated circular contact. Good agreement is observed between available experimental data and simulation results. The pressure-viscosity coefficients fit from viscometer data are also discussed. A recently developed definition of the coefficient is used to compare the coefficient value extracted from EHL film thickness interference measurements. Results indicate that the coefficient values from the curve fitting and EHL film thickness extraction agree well which has not been previously observed. Two factors help achieve this agreement: the new coefficient definition and smaller prediction error when using the Hamrock-Dowson formula in the cases studied. The effects of different pressure-viscosity relationships, including the exponential model, the Roelands model and the free-volume model, are investigated through an example with bright stock mineral oil. It is found that the real pressure-viscosity behavior predicted by the free-volume model yields a higher viscosity at the low-pressure area which results in a larger central film thickness. Therefore, due to use of the freevolume model, the present results are more consistent with experimental observations than previously reported numerical results.

New Experimental Data and Reference Models for the Viscosity and Density of Squalane

“…[43][44][45][46][47][48][49][50][51][52] In cases where an existing experimental data set was repeated (or it appeared that the same point was not re-measured) in subsequent articles, only the original data set was included in the regression data set: 64 , where there was a very limited data set available for the development of a reference model, the abundance of experimental data for squalane made it unnecessary to include molecular simulations in this work. 37,[65][66][67][68][69][70][71][72][73] Two points from Whitmore et al (1966) 8 were not included due to the inability of converting kinematic viscosities of sub-cooled squalane (219 and 233) K.…”

A Quantitative Solution for the Full Shear-Thinning EHL Point Contact Problem Including Traction

“…Recently [11], the film thickness in point contact for squalane was accurately calculated from the coupled Reynolds and elasticity equations. Squalane is a monodisperse, low-molecular-weight liquid, known to possess a sufficiently large Newtonian limit, G& 6 MPa [12], that the behavior within the inlet zone, which determines film thickness, may be assumed to be Newtonian.…”

High Pressure Rheological Behavior of 1-Ethyl-3-methylimidazolium n-Hexylsulfate and Trihexyl(tetradecyl)phosphonium Tris(pentafluoroethyl)trifluorophosphate

“…Several definitions of the pressure-viscosity coefficients 66 were used for this aim: the local pressure-viscosity coefficient at different pressure conditions (0.1 MPa or another pressure) or the piezoviscous coefficient highest, among others. Bair et al 66 and Liu et al 68 showed that the definition of film given by equation (16) In order to analyze the effect of the lubricant in the central thickness (hc), we have used the following equation 64 proposed by the American Gear Manufactures Association (AGMA) for calculation of hc:…”