Measurement Method of Coefficient of Thermal Expansion and Compressive Elastic Modulus of Highly Viscous Liquids

The coefficient of thermal expansion and the modulus of elasticity in compression are important physical parameters for the temperature and compressive behavior of the density of liquid lubricants. Changes in the coefficient of thermal expansion and the modulus of elasticity in the compression of lubricants affect the accuracy of theoretical analyses of problems such as sealing and lubrication failures under actual operating conditions. Existing commercial vibrating string densitometers can measure the temperature and pressure characteristics of low-viscosity liquid density with high accuracy, but the damping effect of high-viscosity lubricants seriously affects the vibrating string excitation, and the measurement error is large. In this paper, a device was designed to measure the coefficient of thermal expansion and compressive elastic modulus of high-viscosity lubricating oils using Invar alloy as the tank material and a small internal diameter capillary metering expansion volume, with an accuracy of ±0.05% for density measurement and ±3% for coefficient of thermal expansion and compressive elastic modulus measurement. PAO8, PAO10 and PAO65 were selected as the base oils for the determination of the coefficient of thermal expansion from room temperature to 80 ℃ and the compressive elastic modulus at room temperature. The coefficient of thermal expansion of base oil from room temperature to 80 ℃ was about 7×10⁻⁴~10×10⁻⁴/℃, which increased by nearly 30%. The compressive elastic modulus of the base oil was about 1.28~1.45 GPa, which decreased slightly with the increase in temperature. The device designed in this study for the determination of the coefficient of thermal expansion and compressive elastic modulus of lubricating oil filled the gap in the accurate determination of the coefficient of thermal expansion and compressive elastic modulus of high viscosity lubricating oil, and it could provide support for the theoretical analysis of lubricating oils to calculate the required parameters.