NEW RECOMMENDED VISCOSITY VALUES FOR WATER AS THE METROLOGICAL BASIS OF VISCOMETRY

In order to update with a reduced uncertainty the water viscosity valu es used as the metrological basis for viscosity measurements, a critic al evaluation of the results of water viscosity measurements published over the past fifty years has been carried out. The temperature depen dence determined in relative measurements based on she viscosity of wa ter at 20 degrees C can be characterized by a polynomial that describe s the measured values with a relative standard deviation of 4,6.10(-4) . From five investigations of the direct, absolute determination of th e viscosity Of water over a temperature range from 19, 75 degrees C to 25,5 degrees C, a value of (1,0020+/-0,0014) mPa . s was determined f ar the viscosity at 20 degrees C applying this temperature dependence. This value deviates by 3.10(-4) from the previous base value converte d to the ITS-90, and the uncertainty is smaller by approximately 40 %. Recommended viscosity values are given for selected temperatures betw een 15 degrees C and 40 degrees C.