A thermodynamic approach to viscosity

For use in elastohydrodynamic systems, the ideal lubricant is generally one which forms a thick separating film between the rubbing surfaces over a wide range of operating conditions. This implies a fluid with a low temperature-viscosity coefficient and a high pressure-viscosity coefficient. Unfortunately, there is a braod correlation between these two values for liquids. This paper derives and then verifies, using experimental data, an expression for this correlation based upon the assumption that viscosity is a thermodynamic property of state. From the resultant expression, the factors that contribute to a high ratio of pressure- to temperature-viscosity coefficient are identified and discussed by reference to a range of lubricant structures. Other implications of viscosity being a property of state are also considered. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference In Baltimore, Maryland, October 16–19, 1988

[1]  J. Kotas,et al.  Thermodynamic activation functions of viscous flow of non-polar liquids , 1986 .

[2]  G. Wan,et al.  The Elastohydrodynamic Lubricating Properties of Water-Polyglycol Fire-Resistant Fluids , 1984 .

[3]  E. Kuss,et al.  p, V, T‐Messungen an zwanzig organischen Flüssigkeiten , 1970 .

[4]  M. Fury,et al.  Transport processes in compressed liquid pyridine , 1979 .

[5]  R. B. Dow.  A Note on Viscosity as a Function of Volume and Temperature of Oils , 1935 .

[6]  D. Dowson,et al.  Isothermal Elastohydrodynamic Lubrication of Point Contacts: Part III—Fully Flooded Results , 1976 .

[7]  A. Bondi.  Viscosity and Molecular Structure , 1951 .

[8]  A. Bondi.  Notes on the Rate Process Theory of Flow , 1946 .

[9]  T. Farrar.  Chapter 5 – Fourier Transform NMR , 1971 .

[10]  J. Jonas,et al.  Dense liquids. II. The effect of density and temperature on viscosity of tetramethylsilane and benzene , 1975 .

[11]  J. Jonas,et al.  Dense liquids. I. The effect of density and temperature on self‐diffusion of tetramethylsilane and benzene‐d6 , 1975 .

[12]  D. Hasha,et al.  Self‐diffusion and viscosity of methylcyclohexane in the dense liquid region , 1979 .

[13]  D. J. Wilbur,et al.  Fourier transform NMR in liquids at high pressure. III. Spin–lattice relaxation in toluene‐d8 , 1975 .

[14]  E. Kuss.  pVT-Data and Tait-Equation for 4-trans-(4-alkyl)-Cyclohexyl-Benzonitriles , 1981 .

[15]  E. Kuss.  The Viscosity-Pressure Behavior of Three 4-Trans-(4-Alkyl)-Cyclohexyl-Benzonitriles and of an Eutectic Mixture , 1983 .