The equation of state of a polydimethylsiloxane fluid

Abstract

AbstractExperimental data for the dependence of the specific volume on temperature and pressure (PVT data) of a polydimethylsiloxane fluid with 100 cS viscosity are presented. The temperature range covered is 30–344°C and the pressure range is 0–200 MPa (0–29,000 psi). Coefficients for an empirical equation of state are reported. This equation of state is based on a polynomial fit to the zero‐pressure isobar, combined with the Tait equation. The maximum deviation in specific volume between the data and the fitted empirical equation of state is less than 0.006 cm3/g, or less than 0.05% of the volume, except at the highest temperature, where sample degradation is likely to occur. The isothermal compressibility and thermal expansivity are derived from the empirical equation of state, and both show a strong temperature and pressure dependence. Reducing parameters for the Simha–Somcynsky theoretical equation of state were found to be P* = 502 MPa, V* = 0.9765 cm3/g, and T* = 8175 K. A comparison between theory and experimental data at temperatures to 245°C (recommended upper use temperature) revealed volume deviations comparable to those obtained using the Tait equation.