Abstract:
In order to investigate the effect of nanoparticle volume fraction, nanoparticle size and temperature on
the thermal conductivity of glycerol based alumina (α-Al2O3) nanofluids, a set of experiments were
carried out for temperature ranging from 20 ˚C to 45 ˚C. The nanofluids contained α-Al2O3
nanoparticles of three different sizes (31 nm, 55 nm and 134 nm) were prepared by two-step method at
volume fractions ranging from 0.5% to 4%. The experimental results show that α-Al2O3-glycerol
nanofluids have substantially higher thermal conductivity than the base fluid and the maximum
enhancement of the relative thermal conductivity was 19.5% for the case of 31 nm at 4% volume
fraction. The data analyses indicated that the volume fraction and size of the nanoparticles have
significant effects on the thermal conductivity ratio (TCR) of Al2O3-glycerol nanofluids, while the
temperature has almost no significant effect on the data for range of this study. At room temperature,
the effective thermal conductivity remains almost constant for 50 hours at 4% volume fractions. The
comparison of the obtained experimental data and predictions from some existing theoretical and
empirical models reveals that the thermal conductivity ratio and its trend could not be accurately
explained by the models in open literature. Consequently, a new empirical correlation based on the
experimental data has been developed in this study.
