ASTM D4624 Measuring Apparent Viscosity by Capillary Viscometer
ASTM D4624 Standard Test Method for Measuring Apparent Viscosity by Capillary Viscometer at High-Temperature and High-Shear Rates
9. Procedure
9.1 Because of the diversity of viscometers that have proven satisfactory for this application, no specific test procedure can be set forth. However, certain aspects of the procedure are common to all viscometer designs and can be prescribed in general terms.
9.1.1 Flushing - Before the viscosity of an oil is measured, the system must be free of contamination from a previous oil tested. Every test procedure must have a provision to accomplish this and that flushing technique must be evaluated to assure its effectiveness.
9.1.2 Effectiveness of the flushing technique is checked by making a series of viscosity measurements with two oils of widely different viscosity. Typically, the sequence of the test is L L H H L L H H, where L is a low-viscosity oil and H is a high-viscosity oil. Carryover of the previous test oil is indicated by a systematic increase in viscosity between the first and second test of a back-to-back pair of tests with the high-viscosity oil, and, similarly, a systematic decrease in viscosity between the first, and second measurement in a pair of back-to-back measurements with the low-viscosity oil.
9.2 Temperature Measurement and Control - Close control and accurate measurement of the test oil temperature at the entrance to the capillary is essential for accurate viscosity measurements. For typical multigrade engine oils at 150°C, a 1°C temperature difference corresponds to about 1.5 % viscosity difference.
9.3 Reynolds Number Limitation - For any set of capillary dimensions, operating conditions should be chosen to keep the flow in the laminar regime throughout the operating range of the instrument, both for Newtonian and for nonNewtonian oils. Laminar flow is characterized by a Reynolds Number smaller than about 2000.
Reynolds Number = (D x V x d)/π
where:
D = diameter of capillary, mm,
V = velocity of flow through capillary, m/s,
d = density of fluid, kg/m3, and
π = viscosity, mPa•s (1 mPa•s = 1 cP).
10. Calculation of Results
10.1 Enter the appropriate calibration curve with the observed value of the dependent variable (pressure in a constant flow rate viscometer and flow rate (or time) in a constant pressure viscometer), and read or calculate the corresponding viscosity.
