VIBRATING-WIRE VISCOMETRY ON LIQUIDS AT HIGH-PRESSURE

The paper describes the design and operation of vibrating-wire viscometers for liquids which have a precision in viscosity measurement of +/-0.1% over the temperature range 30 to 75-degrees-C at pressures up to 300 MPa. Attention is concentrated upon the details of the mechanical support of the wire which proves to be vital in order to ensure that the instrument operates in accordance with the theoretical model of it. The accuracy of viscosity measurements made with the present instruments in an absolute manner is no better than +/- 3% owing to the uncertainties in the characteristics of the vibrating-wire. When operated in a relative manner the accuracy pan be improved to one of +/- 0.5% but is then limited by the uncertainty in the standard reference values for the viscosity of liquids under ambient conditions. It is argued that further absolute viscosity measurements of high accuracy under ambient conditions are essential to further progress in viscometry.