Volumetric behaviour of the environmentally compatible lubricants pentaerythritol tetraheptanoate and pentaerythritol tetranonanoate at high pressures

Knowledge of proper lubricant selection and its handling can substantially influence the reliability of a refrigeration system. In this sense the awareness of several thermophysical properties of refrigerants, lubricants, and their mixtures under different conditions of pressure and temperature is highly important for designing refrigeration systems. Polyol ester oils have been proposed as lubricant candidates for refrigeration systems. In this work, we have studied the density of two polyol esters, pentaerythritol tetraheptanoate and pentaerythritol tetranonanoate, in the range 278.15 <= T/ K <= 353.15 and 0.1 <= p/MPa <= 45. In addition, the behaviour of two other essential volumetric properties, namely the thermal expansion coefficient and the isothermal compressibility coefficient, as well as the internal pressure have been analysed.