Technical Brief

Revisiting the Compressibility of Oil/Refrigerant Lubricants

[+] Author and Article Information
Scott Bair

Georgia Institute of Technology,
Center for High-Pressure Rheology,
George W. Woodruff School of Mechanical Engineering,
Atlanta, GA 30332-0405
e-mail: scott.bair@me.gatech.edu

Mark Baker

CPI Fluid Engineering,
a Division of the Lubrizol Corporation,
2300 James Savage Road,
Midland, MI 48642
e-mail: MRBA@CPIfluideng.com

David M. Pallister

CPI Fluid Engineering,
a Division of the Lubrizol Corporation,
2300 James Savage Road,
Midland, MI 48642
e-mail: DAPAL@CPIfluideng.com

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received February 19, 2016; final manuscript received March 10, 2016; published online August 11, 2016. Assoc. Editor: Ning Ren.

J. Tribol 139(2), 024501 (Aug 11, 2016) (4 pages) Paper No: TRIB-16-1060; doi: 10.1115/1.4033335 History: Received February 19, 2016; Revised March 10, 2016

A fixture was fabricated for the purpose of restraining the expansion of an existing metal bellows piezometer so that a refrigerant and oil mixture can be admitted under pressure. Measurements on a polyol ester (POE) with 9.2 wt.% of R134a show that the addition of refrigerant slightly increases compressibility. The previously reported reduction in compressibility (increase in bulk modulus) by Tuomas and Isaksson (2006, “Compressibility of Oil/Refrigerant Lubricants in Elasto-Hydrodynamic Contacts,” ASME J. Tribol., 128(1), pp. 218–220) of an ISO 68 POE when mixed with R134a cannot be supported by precise measurements of the volume compression. The increased compressibility found by Comuñas and co-workers (2002, “High-Pressure Volumetric Behavior of x 1, 1, 1, 2-Tetrafluoroethane + (1 − x) 2, 5, 8, 11, 14-Pentaoxapentadecane (TEGDME) Mixtures,” J. Chem. Eng. Data, 47(2), pp. 233–238) is the correct trend. The Tait equation of state (EoS) has been fitted to the data for both the neat POE and its 9.2% by weight mixture with refrigerant. The usual problem was encountered for the mixture with the Tait EoS at low pressure where the compressibility becomes greater than predicted due to proximity to the vapor dome. The measured relative volumes of the mixture can be used to collapse the viscosity to a master curve when plotted against the Ashurst–Hoover thermodynamic scaling parameter. The thermodynamic scaling interaction parameter is approximately the same as for the neat oil.

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Grahic Jump Location
Fig. 1

The relative volume of the oil, RL68H, and the fit to the Tait EoS

Grahic Jump Location
Fig. 3

The Grunberg–Nissan mixing law fitted to the data points by adjusting g and adjusting m to the values given in the text

Grahic Jump Location
Fig. 2

The relative volume of RL68H + 9.2 wt.% R134a compared with the Tait EoS for the neat oil

Grahic Jump Location
Fig. 4

Master curve derived from the measured relative volumes of the oil/refrigerant mixture in Table 2



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