Thermodynamics Research Center / ThermoML | Journal of Chemical Thermodynamics

ABSTRACT

The thermal conductivity of the heat transfer fluids commonly used in industrial processes is a major concern in the continuous searching of their performance improvement. During last decades, dispersions of high thermal conductivity nanoparticles in conventional fluids, nanofluids, have received increasingly attention to achieve this aim. The thermophysical properties, not commonly available in the literature, are necessary to describe their thermo-fluid behaviour. Thus, characterization studies become necessary to evaluate the potential heat transfer enhancements. This work presents the thermophysical profile according to the properties with a noticeable influence on the heat transfer capability of different functionalized graphene nanoplatelet dispersions (0.25, 0.50, 0.75 and 1.0) wt% in a propylene glycol-water mixture at (30:70)% mass ratio, usually employed in thermal facilities. Initially, nanofluid stability was investigated optimizing the pH value by analysing zeta potential measurements. Then, densities, heat capacities, thermal conductivities, and dynamic viscosities were experimentally determined throughout the temperature range from (293.15 to 323.15) K. Density was studied by using a pycnometric technique and results were used to analyze the isobaric thermal expansivity behaviour. A differential scanning calorimeter was utilized to obtain heat capacities and thermal conductivities were measured for the nanopowder, base fluid and nanofluids through devices based on the guarded heat flow meter method and the transient hot wire technique. Furthermore, rheological behaviour was analysed by means of a rotational rheometer with cone-plate geometry. Conductivity enhancements up to 16% with respect to base fluid were achieved. Finally, potential enhancements of heat transfer performance in laminar and turbulent flow were investigated through an analysis of different figures of merit based on the experimental results.