Determination of derived volumetric properties and heat capacities at high pressures using two density scaling based equations of state. Application to dipentaerythritol hexa(3,5,5-trimethylhexanoate).

Reliable equations of state (EoS) together with heat capacities at atmospheric pressure make it possible to determine properties such as the isobaric thermal expansivity, compressibility, both isothermal and isentropic, high pressure isobaric heat capacities or speed of sound. In this work, we analysed the reliability of two density scaling based EoS, Power-Law Density Scaling (PLDS) and General Density Scaling (GDS), and the Tammann-Tait EoS to determine these quantities. For this aim, dipentaerythritol hexa(3,5,5-trimethylhexanoate), diPEiC9, was chosen because it has been recently proposed as a candidate to fill the gap of reference fluids suitable for high pressure viscometer calibration or their verification. New experimental densities measured between (283.15 and 398.15) K at pressures up to 70 MPa together with isobaric heat capacities between (282.93 and 399.92) K and thermal conductivities between (283 and 333) K at 0.1 MPa of diPEiC9 are reported. Literature relative volumes up to 400 MPa for this compound were also used. The three EoSs give rise to coherent values of the above properties. The most difficult property to describe is isobaric thermal expansivity for which the isobaric curves can present minima and/or maxima and the isotherm curves can cross at different pressures. The loci of the maxima of the isobaric thermal expansivity in p-T diagrams of the GDS and PLDS EoSs are very close.

Heat Transfer Capability of (Ethylene Glycol + Water)-Based Nanofluids Containing Graphene Nanoplatelets: Design and Thermophysical Profile.

This research aims at studying the stability and thermophysical properties of nanofluids designed as dispersions of sulfonic acid-functionalized graphene nanoplatelets in an (ethylene glycol + water) mixture at (10:90)% mass ratio. Nanofluid preparation conditions were defined through a stability analysis based on zeta potential and dynamic light scattering (DLS) measurements. Thermal conductivity, dynamic viscosity, and density were experimentally measured in the temperature range from 283.15 to 343.15 K and nanoparticle mass concentrations of up to 0.50% by using a transient plate source, a rotational rheometer, and a vibrating-tube technique, respectively. Thermal conductivity enhancements reach up to 5% without a clear effect of temperature while rheological tests evidence a Newtonian behavior of the studied nanofluids. Different equations such as the Nan, Vogel-Fulcher-Tamman (VFT), or Maron-Pierce (MP) models were utilized to describe the temperature or nanoparticle concentration dependences of thermal conductivity and viscosity. Finally, different figures of merit based on the experimental values of thermophysical properties were also used to compare the heat transfer capability and pumping power between nanofluids and base fluid.