Olivia Fandiño

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.

Compressibilities and viscosities of reference and vegetable oils for their use as hydraulic fluids and lubricants

The use of biodegradable lubricants based on vegetable oils is receiving increasing attention, being an important area of research, in order to promote products with a reduced environmental impact during their entire life cycle. Compressibility is one of the key properties that should be taken into account to develop efficient hydraulic fluids and gear oils. The isothermal compressibility of four reference fluids, a sunflower base oil and a biodegradable oil up to 50 MPa and from 298.15 K to 373.15 K has been determined. For this aim an experimental device based on a vibrating-tube densimeter was used to obtain the density values. The density values at atmospheric pressure were correlated within an absolute average deviation of 0.07% with the Rackett equation whereas a modified Tait equation was used to correlate the experimental data over all temperatures and at higher pressures. The sunflower base oil analyzed in this work has a slightly lower compressibility than those of the reference oils for hydraulic and two stroke engines applications. Moreover, viscosities from 278.15 K to 373.15 K and the viscosity index (VI) were determined for all the analyzed oils using a SVM 3000 Anton Paar rotational Stabinger viscometer.