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
1. Scope
1.1 This test method covers the measurement of high-temperature high-shear viscosity at 150°C. The shear rate for this test method corresponds to an apparent shear rate at the wall of 10(6)s(-1). This is the shear rate at the wall calculated for a Newtonian oil. For non-Newtonian oils, the actural shear rate at the wall will vary from this value.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
D1217 Test Method for Density and Relative Density (Specific Gravity) of Liquids by Bingham Pycnometer
D4683 Test Method for Measuring Viscosity at High Temperature and High Shear Rate by Tapered Bearing Simulator
D4741 Test Method for Measuring Viscosity at High Temperature and High Shear Rate by Tapered Plug Viscometer
3. Terminology
3.1 Definitions:
3.1.1 viscosity - the ratio between shear stress and shear rate at the same location. It is sometimes called the coefficient of viscosity, or the dynamic viscosity. It is a measure of a fluid's resistance to flow. In the SI, the unit of viscosity is a pascal second (Pa•s); for practical use a submultiple (millipascal second, mPa•s) is more convenient. The centipoise (cP) is 1 mPa•s and is often used.
3.1.2 apparent viscosity - the determined viscosity obtained by this test method.
3.1.3 kinematic viscosity - the ratio of the viscosity to the density of the fluid. It is a measure of a fluid's resistance to flow under the force of gravity. In the SI, the unit of kinematic viscosity is the metre squared per second (m2/s); for practical use, a submultiple (millimetre squared per second, mm2/s) is more convenient. The centistoke (cSt) is 1 mm2/s and is often used.
3.1.4 Newtonian oil or fluid - an oil or fluid that exhibits a constant viscosity at all shear rates or shear stresses.
3.1.5 non-Newtonian oil or fluid - an oil or fluid that exhibits a viscosity that varies with changing shear rate or shear stress.
3.1.6 shear rate - the spatial gradient of velocity in laminar flow; the derivative of velocity with respect to distance in a direction perpendicular to the direction of flow. The derived unit of shear rate is velocity divided by length. With time in seconds and with consistent units of length, shear rate becomes reciprocal seconds, or s(-1). In a capillary, the significant shear rate for a Newtonian fluid is as follows:
S = 4Q/πR3
where:
S = shear rate, s(-1),
Q = flow rate, and
R = capillary radius in consistent units.
3.1.7 shear stress - force per area of fluid in the direction of flow. In a capillary viscometer, the significant shear stress is the maximum shear stress at the wall, that is, the total force acting on the cross section of the capillary divided by the area of the inside surface of the capillary. The SI unit for shear stress is the pascal (Pa); for practical use in this application, a submultiple, the millipascal (mPa), may be used. Mathematically, the shear stress in a capillary viscometer is as follows:
Z = PR/2L
where:
Z = shear stress, Pa,
P = pressure drop, Pa,
R = capillary radius, and
L = capillary length in consistent units.
3.1.8 density - the mass per unit volume. In the SI, the unit of density is the kilogram per metre cubed (kg/m3); the gram per cubic centimetre is often used. Density in units of g/cm3 is multiplied by 1000 to get density in units of kg/m3.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 apparent shear rate at the wall - shear rate at the wall of the capillary calculated for a Newtonian fluid. The actual shear rate at the wall will differ for a non-Newtonian fluid.
3.2.2 calibration oils - those oils used for establishing the instrument's reference framework of apparent viscosity versus pressure drop from which the apparent viscosities of the test oils are determined. Calibration oils, which are Newtonian fluids, are available commercially or can be blended by the user.
3.2.3 test oil - any oil for which the apparent viscosity is to be determined by following the test method described.
