New experimental densities are reported for squalane and for branched pentaerythritol tetra(2ethylhexanoate), PEB8, in the compressed liquid state over the temperature range from (278.15 to 353.15) K and for pressures up to 45 MPa. The reliability of the technique and the procedure up to 25 MPa has been verified in our previous works, and in the present work they were checked up to 45 MPa by comparing our experimental densities for heptane with literature data. A total of 297 density values have been measured with a high-pressure vibrating tube densimeter. The correction factor for density due to the sample viscosity has been considered. This factor ranges from 1 × 10 -4 to 1 × 10 -3 g‚cm -3 for PEB8 and from 4 × 10 -5 to 6 × 10 -4 g‚cm -3 for squalane over the entire Tp interval. The pressure and temperature dependencies of squalane and PEB8 densities could be accurately represented by the Tammann-Tait equation with standard deviations of 3 × 10 -5 g‚cm -3 for squalane and 9 × 10 -5 g‚cm -3 for PEB8. These density data were used to analyze the isothermal compressibility, the isobaric thermal expansivity, and the internal pressure of squalane and PEB8.

One of the potential applications of the ionic liquids (ILs) is their use as lubricants or lubricant additives. The choice of the cation and the anion of the ILs, as well as the side chain design, determine their fundamental properties, which permits us to create tailor-made lubricants and lubricant additives among other functional fluids. In this work we have studied 10 ILs for which we report densities and viscosities from 283.15 K (and for some ILs at lower temperatures) up to 373.15 K. The viscosities of the ILs fall in the range of the applications of hydraulic fluid or lubricants. Four of these ILs were composed by the anion tris(pentafluoroethyl)trifluorophosphate [(C 2 F 5 ) 3 PF 3 ] À and one of the following cations:and trihexyl(tetradecyl)phosphonium [P 6,6,6,14 ] + . Furthermore, three of the ILs contain the anion bis(trifloromethylsulfonyl)imide [NTf 2 ] À and one of the following cations [C 4 C 1 C 1 mim] + , [C 4 C 1 Pyrr] + , or [C 1 OC 2 C 1 Pyrr] + . Two other ILs contain the 1-ethyl-3-methylimidazolium cation [C 2 C 1 mim] + and an alkyl sulfate anion (ethylsulfate [C 2 SO 4 ] À or n-hexylsulfate [C 6 SO 4 ] À ). The last one is composed by [C 4 C 1 Pyrr] + and trifluoromethanesulfonate [CF 3 SO 3 ] À . The experimental values were used to determine the glass-transition temperature and fragility of these ILs and to analyze the capability of two group contribution methods recently proposed by Gardas and Coutinho for the density and viscosity prediction of ILs.

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The experimental measurements of dynamic viscosity for squalane, pentaerythritol tetra-2-ethylhexanoate (PEB8), and pentaerythritol tetranonanoate (PEC9) have been performed using a Ruska rolling-ball viscometer over the temperature range of 303.15−353.15 K and a pressure range of 0.1−60 MPa. A total of 2016 experimental measurements of the rolling time have been obtained for the determination of 252 dynamic viscosity data. The available literature viscosity data for squalane at high pressures have been compared with the new measurements, and an average deviation of 1.5% has been obtained, which is within the experimental uncertainty (±3%). The higher viscosity values are reached for PEB8, followed by PEC9. For the pentaerythritol esters, it has been observed that the dynamic viscosity increases with the branching degree of the molecule. The relative change in viscosity with temperature is biggest for PEB8 and, consequently, the poorer viscosity index (VI) values and higher temperature coefficients have been obtained for this fluid. The lowest pressure−viscosity coefficient and the highest VI have been obtained for PEC9.

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.

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The dispersion and stability of nanofluids obtained by dispersing Al2O3 nanoparticles in ethylene glycol have been analyzed at several concentrations up to 25% in mass fraction. The thermal conductivity and viscosity were experimentally determined at temperatures ranging from 283.15 K to 323.15 K using an apparatus based on the hot-wire method and a rotational viscometer, respectively. It has been found that both thermal conductivity and viscosity increase with the concentration of nanoparticles, whereas when the temperature increases the viscosity diminishes and the thermal conductivity rises. Measured enhancements on thermal conductivity (up to 19%) compare well with literature values when available. New viscosity experimental data yield values more than twice larger than the base fluid. The influence of particle size on viscosity has been also studied, finding large differences that must be taken into account for any practical application. These experimental results were compared with some theoretical models, as those of Maxwell-Hamilton and Crosser for thermal conductivity and Krieger and Dougherty for viscosity.

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