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 suith 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 bused 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. © 1990 Taylor & Francis Group, LLC.