Determination of the effective thermal diffusivity of nanofluids by the double hot-wire technique

This paper introduces a new transient double hot-wire technique for the direct measurement of the thermal diffusivity of nanofluids. A correlation to be used with the double hot-wire technique to calculate the effective thermal diffusivity of nanofluids is also developed. Several types of nanofluids were prepared by suspending different volume percentages (1-5%) of titanium dioxide (TiO2), aluminium oxide (Al2O3) and aluminium (Al) nanoparticles in ethylene glycol and engine oil. The thermal diffusivities of these nanofluids determined directly by this technique were found to increase substantially with the increased volume fraction of nanoparticles in base fluids. Based on the calibration results obtained for the base fluids, ethylene glycol and engine oil, the measurement error is estimated to be within 1.2%. The measured thermal diffusivities of nanofluids were found to be significantly higher than those calculated from the thermal diffusivity expression (i.e. alpha(eff) = k(eff)/(rho c(p))(eff)) by using the effective thermal conductivities and volumetric specific heats obtained from the conventional hot-wire method and from the volume fraction mixture rule, respectively.