Heat transfer capability of functionalized graphene nanoplatelet dispersions in propylene glycol + water (30 : 70 wt.%)

Abstract

One of the most restricting factors in the performance of industrial heat transfer processes is the low thermal conductivity of the thermal fluids commonly used. Hence, dispersions of nanoparticles with high thermal conductivity in conventional fluids, nanofluids, have received increasingly interest over last decades in order to obtain improvements in heat transfer processes. The thermophysical properties are necessary to their flow behaviour characterization and they are not commonly available in the literature. Therefore, laboratories with wide experience in thermophysical characterization should call attention to this issue. This study aims to determine those properties with a noticeable influence on the heat transfer capability for dispersions of functionalized graphene nanoplatelets in a propylene glycol:water mixture at (30:70) % mass ratio, usually employed in thermal facilities. Initially, nanofluid stabilities were investigated analyzing zeta potential measurements, optimizing the pH value. Tests for obtaining densities, heat capacities, thermal conductivities and dynamic viscosities were developed for different nanoadditive mass concentrations (0.25, 0.50, 0.75 and 1.0) wt.% over throughout the temperature range from (293.15 to 323.15) K. Thus, density values were obtained by using a pycnometric technique, a differential scanning calorimeter was utilized to measure heat capacities, thermal conductivities were determined with a transient hot wire technique while rheological tests were carried out by means of a rotational rheometer with cone-plate geometry. Secondly, thermal conductivity focused our attention due to its important role in the heat transfer process. Remarkable increases, up to 16 %, were found in this property.