(Equivalent Test Methods: IP 71-1, SO 3104, DIN 51562, JIS 2283 and AFNOR T60-100)
EXPLANATION
This test method covers the determination of the kinematic viscosity of liquid petroleum products, both transparent and opaque, by measuring the time for a volume of liquid to flow under gravity through a calibrated glass capillary viscometer. The dynamic viscosity can be obtained by multiplying the measured kinematic viscosity by the density of the liquid. This test method is primarily intended for application to liquids for which the shear stress and shear rates are proportional. This test method also includes the determination of the kinematic viscosity of fuel oils which often exhibit non-Newtonian properties.
DEFINITIONS
Kinematic viscosity - a measure of the resistive flow on a fluid under gravity, the pressure head being proportional to the density, ρ, of the fluid: for gravity flow under a given hydrostatic head, the pressure head of a liquid is proportional to its density, ρ. For any particular viscometer, the time of flow of a fixed volume of fluid is directly proportional to its kinematic viscosity, v = n/ρ, where n is the dynamic viscosity coefficient. The kinematic viscosity coefficient has the dimension L(2)/T, where L is a length, and T is a time. The cgsunit of kinematic viscosity is one centimetre squared per second and is called one stokes (symbol St). The SI unit of kinematic viscosity is one metre squared per second and is equivalent to 10(4) ST. Frequently, the centistokes (symbol cSt) is used 1 cSt = 10(-2) St = 1 mm2/s .
TEST SUMMARY
The time is measured in seconds for a fixed volume of liquid to flow under gravity through the capillary of a calibrated viscometer under a reproducible driving head and at a closely controlled temperature. The kinematic viscosity is the product of the measured flow time and the calibration constant of the viscometer.
TEST PRECISION
Where y is the average of determinations being compared; x is the average of results being compared.
The precision for used oils has not been determined but is expected to be poorer than that for formulated oils. Because of the extreme variability of such used oils, it is not anticipated that the precision of used oils will be determined.