SIMULTANEOUS MEASUREMENT OF THE EFFECTIVE THERMAL CONDUCTIVITY AND EFFECTIVE THERMAL DIFFUSIVITY OF NANOFLUIDS

摘要

A transient double hot-wire technique was developed for precise and simultaneous measurement of the effective thermal conductivity and effective thermal diffusivity of nanofluids. The measured effective thermal conductivities and effective thermal diffusivities of nanofluids were found to be higher than those of base fluids and they increase significantly with increasing volume fraction of nanoparticles. The increments of the thermal diffusivities were found to be slightly larger compared to the thermal conductivity values. For example, at 5% volumetric loading of TiO_2 nanoparticles of 15 nm and 10 × 40 nm in ethylene glycol, the maximum increase in effective thermal conductivity was found to be 17% and 20%, whereas the maximum increase in effective thermal diffusivity was 25% and 29%, respectively. Besides particle volume fraction, particle material, particle size and the nature of the base fluid were found to have influence on the effective thermal conductivity and diffusivity of nanofluids. Based on the calibration results obtained for the base fluids the measurement error was estimated to be within 1.2 to 2%.