Validated high-pressure vibrating tube densimeter for accurate fluid density data at pressures up to 600 bar

Abstract

Vibrating tube densimeters (VTDs) have been widely used over the past fifty years for accurate density measurements of gases and liquids. This study presents an in-house designed and built support system for the Anton Paar DMA HP densimeter, a commercial high-pressure VTD capable of measuring densities from 0 to 3 000 kgm⁻³ at pressures up to 700 bar and temperatures ranging from −10 to 200 ^oC. While the device includes internal temperature control via a Peltier thermal block, pressure must be externally generated and controlled. For this purpose, a high-pressure sampling system was developed. Given that density measurements are highly sensitive to temperature, particular attention was paid to accurate temperature monitoring using an external Pt100 thermometer connected to a precision thermometry bridge. To prevent air humidity condensation during experiments, the VTD was enclosed in a dry box of own design. We describe the technical details of the setup, including the calibration of pressure and temperature sensors. Density results at pressures up to 600 bar are presented for several reference liquids–water, ethanol, and ethylene glycol – and compared with standard reference data. Calibration of the U-tube cell at high pressure was performed using vacuum, dry nitrogen and ultrapure water. To relate density to the period of oscillation, several calibration models were considered such as the Anton Paar manufacturer model, polynominal model by Outcalt, or a physically-based model considering material and mechanical properties of a Hastelloy cell by May et al.