Showing papers by "Scott Bair published in 2017"

In Pursuit of a High-Temperature, High-Pressure, High-Viscosity Standard: The Case of Tris(2-ethylhexyl) Trimellitate

Abstract: This paper presents a reference correlation for the viscosity of tris(2-ethylhexyl) trimellitate designed to serve in industrial applications for the calibration of viscometers at elevated temperatures and pressures such as those encountered in the exploration of oil reservoirs and in lubrication. Tris(2-ethylhexyl) trimellitate has been examined with respect to the criteria necessary for an industrial standard reference material such as toxicity, thermal stability, and variability among manufactured lots. The viscosity correlation has been based upon all of the data collected in a multinational project and is supported by careful measurements and analysis of all the supporting thermophysical property data that are needed to apply the standard for calibration to a wide variety of viscometers. The standard reference viscosity data cover temperatures from 303 to 473 K, pressures from 0.1 to 200 MPa, and viscosities from approximately 1.6 to 755 mPa s. The uncertainty in the data provided is of the order of ...

Elastohydrodynamic performance of a bio-based, non-corrosive ionic liquid

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 l ...

Viscosity Measurements of R32 and R410A to 350 MPa

Abstract: Viscosity measurements were performed with a falling cylinder viscometer on difluoromethane (R32) and the refrigerant blend R410A (R32 + R125 with 50% by mass) at the temperatures 313.15 K, 348.15 K, and 393.15 K with pressures of 350 MPa. The measurement results are compared with literature data and with data calculated using an extended corresponding states (ECS) model. The agreement with literature data is closer for R410A than for R32 while the deviations from the ECS model are higher for R410A than for R32. Correlations that represent the new results as functions of temperature and pressure within their uncertainty are also reported.

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

Abstract: 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 that 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–pressure–viscosity correlations are applied to all materials for use in modeling. Correlations are provided for the temperature and pressure dependencies of the viscosity of the oils, refrigerant, and mixtures. The definition of pressure–viscosity coefficient is a pressing problem for elastohydrodynamics.

Effect of lubricant rheology on friction in coated elastohydrodynamic lubricated contacts

Abstract: This work investigates the effect of lubricant rheology on friction in coated elastohydrodynamic contacts. Two lubricants with relatively different properties are selected and two coating configura...

Comment on “The Relationship Between Friction and Film Thickness in EHD Point Contacts in the Presence of Longitudinal Roughness” by Guegan, Kadiric, Gabelli, & Spikes

Abstract: Guegan and coworkers have addressed the important problem of friction of elastohydrodynamic contacts in the mixed regime. Any attempt at understanding friction in the mixed regime must address the friction in the full-film regime. To analyze fiction for the full film, they used a common, but unsupported, assumption that the friction curve is a rheological flow curve. The inconsistency can be demonstrated by integration over the contact with the assumed Eyring equation employing the known pressure dependence of the viscosity and also by a full numerical simulation which yields the same sinh friction curve without using the Eyring assumption.

The high-pressure viscosity of refrigerant/oil systems

Abstract: Application of the new quantitative elastohydrodynamics to the concentrated contacts operating within refrigerant compressors will require the accurate description of the viscosity of the lubricant that is diluted by the refrigerant. This article presents extensive viscosity measurements on polyolester and polyvinylether oils and their mixtures with low mass fractions (2–23%) of refrigerants R134a and R410a. Pressures up to 400 MPa and temperatures to 100°C were reached. Correlations are presented to predict the viscosity and pressure–viscosity coefficients at arbitrary temperatures and pressures and concentrations. Pressure–viscosity coefficients are compared with those derived from film thickness measurements using one of the popular definitions for the coefficient. Where comparisons can be made, the film-derived pressure–viscosity coefficients were mostly inaccurate. Part of the problem has been the lack of a single well-accepted and rigorous definition of the pressure–viscosity coefficient and the lack of an accurate film thickness formula that employs that definition. Copyright © 2017 John Wiley & Sons, Ltd.

Purported fragile-to-Arrhenius crossover in squalane

Abstract: Jadhao and Robbins (1) claim to have discovered a crossover from Vogel–Fulcher–Tammann (VFT) to Arrhenius in squalane occurring at a viscosity of μ = 1,000 Pa⋅s using extrapolation of the simple Eyring equation to the limiting low-shear viscosity from nonequilibrium molecular dynamic simulation at high shear rates. Stickel et al. (2) introduced a non–model-specific derivative analysis of relaxation time and viscosity data. The Stickel … [↵][1]1Email: scott.bair{at}me.gatech.edu. [1]: #xref-corresp-1-1