On the measurement of physical properties in high pressure systems using acoustic levitation

Knowledge of thermophysical properties of liquids in phase equilibrium with a dense gas is inevitable for high pressure spray processes or extraction. Nevertheless, the existing data sets are scarce and sometimes incongruent, because measurements are tedious and time consuming. Therefore, this work records the development of measurement procedures for density, surface tension and viscosity based on acoustic levitation. To determine density, the forces required to acoustically position a drop of an unknown liquid and a reference material with known density are compared. Surface tension and viscosity are simultaneously determined using the free decay of drop shape oscillations. To develop these measurement methods, experiments using different liquids with viscosities from 2 mPa·s to 30 mPa·s and interfacial tensions between 18 mN/m and 28 mN/m are carried out under ambient pressure. Influences of the sound field or the amplitude of oscillation on the results are analyzed. After validating the method under ambient pressure, interfacial tension and viscosity of squalane and polyethylene glycol 400 saturated with CO2 under pressure are measured. The results are compared to literature data for these systems. Concluding the results, acoustic levitation emerges as a promising method for physical property measurement under both ambient and high pressure, since it allows simultaneous interfacial tension and viscosity determination using only microliter samples.