Rolling ball viscometer calibration with gas over whole interest range of pressure and temperature improves accuracy of gas viscosity measurement

A practical method for measuring gas viscosity uses gas to calibrate the rolling ball viscometer over the whole interest range of pressure and temperature. It reduces the turbulent effect of gas flow around the ball. The viscometer calibration at only atmospheric pressure yields poor results, because it cannot accommodate the turbulent effect at higher pressures. We used nitrogen to calibrate the viscometer for the pressure up to 8,000 psia and temperature up to 260 °F. Optimal tube inclination angle and also ball/tube diameter ratio ensure the laminar flow around the ball and improve the accuracy of the results. Viscosity measurements of ultrapure CO2 confirmed this technique