Relation between low temperature fluidity and sound velocity of lubricating oil

Low temperature fluidity is important for lubricating oil. Viscoelastic solid transition temperature at atmospheric pressure TVE0 represents the low temperature fluidity of lubricating oil, which is estimated from the occurrence of photo elastic effect by lowering the temperature using liquid nitrogen. Sound velocity in lubricating oil is measured using Sing around technique. Then the adiabatic Bulk modulus K is calculated from the measured sound velocity. A relation is found between the adiabatic bulk modulus and the viscoelastic solid transition temperature of lubricating oil. The relation depends on the molecular structure of lubricating oil. The oils of a group belong to almost same molecular structure, follows the same relation. For same molecular structure TVE0 decreases as decreasing the adiabatic bulk modulus of lubricating oil. It is also found that, the viscoelastic solid transition temperature of blend oils can be predicted from the base oils’ TVE0 and K.