The development of an absolute viscometer for use at elevated conditions, with particular reference to the viscosity of water

• Main Author: Wonham, Jon
• Published: University of Glasgow 1967
• Subjects: T Technology (General)
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.761820

This thesis forms a report of the progress made by the author in developing a rotating cylinder viscometer for measurement at elevated temperature and pressure. Initially, some proposals of Whitelaw (5) were tested in a preliminary design of viscometer. Experience gained with this instrument made possible the construction of a viscometer from which the viscosity of liquid water has been obtained in the range 12° to 116°C and at pressures up to 230 Kgf/cm2. Important features of this design, which have been successfully applied, include a null technique for measuring the angular deflection of the stationary cylinder and the use of a high pressure mechanical face seal for the shaft driving the rotating cylinder. A vacuum rig was constructed for measuring the torsional properties of suspension wires used in the viscometer. The temperature of this rig could be varied which allowed the torsional stiffness of tungsten wire to be determined experimentally up to 150°C. Viscosity measurements at 1 atm. pressure were fitted to a modified Arrhenius equation of the form η = AeB/T-T0 The standard deviation of experimental values from this equqtion was 7 x 10-3 cP which, at 20°C, amounts to approximately 0.7% of the measured viscosity. The absolute value of viscosity given by this equation was approximately higher than the presently accepted standard value at this temperature. At temperatures above 50°C the results obtained appear to be slightly low, the possible reasons for which have been explained. Results at elevated pressure were made over a similar temperature range although the majority of determinations were made at temperatures below 20°C. These low temperature measurements lend support to the findings of Bett and Cappi (48) rather than those of Home and Johnson (52) who have made the most recent experimental investigations in this field. The results obtained are regarded as preliminary in so far as a systematic coverage of the whole range has not yet been made. A second, partially completed, instrument is described which will extend the rsinge of measurement to 400°C and 1000 Kgf/cm2. A system of radial diffraction gratings producing moire fringes has been incorporated which, it is expected, will improve the precision with which the deflection of the inner cylinder may be obtained. Since the dynamic method of measuring the torsional stiffness of the wire has been used a number of tests were performed to investigate the effect of varying the mass, inertia and amplitude of a torsional pendulum. The results of these tests are described in a number of Appendices, the main conclusion being that the amplitude effect is significant and a correction factor may be derived which can be applied to the angular deflection of the wire when it is used statically.