Introduction
Polyol esters (POEs) have being used as lubricants for commercial applications because of their characteristic properties and their environmentally safe usage.0 POEs lubricants have favorable properties as refrigeration oils compared to those of polyalkylene glycols. They are less hygroscopic, have higher miscibilities with HFCs and CO0 refrigerants, and are miscible with mineral oils.0,0 Lubricants based on polyol esters represent one of the most important types of synthetic lubricants.0,0 Their high thermal stability and good lubricating properties have
resulted in a wide range of applications from the textile industry to gas turbine motors.0 To minimize costly experimentation, new models that can predict the thermodynamic and transport properties of POEs would be very useful,0 but for this purpose a more complete database of
thermophysical properties over wide temperature and
pressure ranges is needed. One of the goals of our present project is to provide the thermophysical properties over wide temperature and pressure ranges for one type of POE with known structure, namely, pentaerythritol tetraalkyl esters (PEs),0,0 which consist of an isopentane nucleus linked to four identical alkyl ester chains (branched or linear). With this aim, in the present work the volumetric properties of pentaerythritol tetra(0-ethylhexanoate), PEB0, have been studied. To our knowledge, only Wahlstro¨m and Vamling0 have reported density measurements for PEB0 over the temperature interval of (000.00 to 000.00) K and only at atmospheric pressure. Shobha and Kishore0 have published the densities at 0.0 MPa from (000 to 000) K for pentaerythritol tetraoctanoate, which is isomeric with PEB0.