Metrology of Viscosity: Have We Learned Enough?

Abstract

Viscosity is one of the most important properties for many technological and scientific applications, and therefore it has been the subject of an enormous effort of measurement, correlation, and interpretation. This effort is completely inconsistent with the fact that it is probably the fluid property with less independent reference values that can be used by most of the everyday users as guidance, calibration, or designing tools. The only accepted standard, the viscosity of pure water at 20 °C, is unsatisfactory because the viscosity among different fluids can vary by a factor of 1014. Its application in the current step-up procedures to produce certified reference materials of higher viscosity, although useful for industrial purposes, degrades the desired small uncertainty of these values. An analysis of the metrology status for Newtonian liquids viscosity, including the best available measurement methods, applicable ranges, existing reference data, uncertainties, and traceability of the measurements to the SI, is made. The discussion assumes in general the internationally accepted definitions of uncertainty.