Development of a rolling ball viscometer for simultaneous measurement of viscosity, density, bubble-point pressure of CO ₂ -expanded liquids

In this work, a rolling ball viscometer was developed that makes it possible to measure viscosity, density, and phase equilibria simultaneously. The cell is mounted inside a high-pressure vessel and can be used at pressures up to 30 MPa and temperatures up to 200 °C. Calibration of the viscometer was carried out by using water at inclined angles from 10° to 30° at temperatures of 40 °C and 80 °C and at pressures up to 20 MPa with toluene viscosity being used for confirmation; viscosity measurements of toluene were found to agree with literature data to within 0.66% in average relative deviation. Viscosity, density, and bubble-point pressure of ethanol + CO ₂ systems were measured at 40 °C; bubble-point pressures for the ethanol + CO ₂ system agreed to within 2.2% of the literature. Viscosity of the ethanol + CO ₂ system were measured at saturated and pressurized liquid states and viscosity values decreased with increasing CO ₂ composition, and decreased to about half the value of pure ethanol for 0.32 mol fraction of CO ₂ .