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Low temperature fluidity is important for lubricating oil. Viscoelastic
solid transition temperature at atmospheric pressure T"V"E"0 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 T"V"E"0 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' T"V"E"0 and K.
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