Effect of temperature and sonication time on nanofluid thermal conductivity measurements by nano-flash method

• Evaluation of thermal conductivity of nanofluids by Nano-Flash Method is presented.
• Nano-flash technique is a fast and accurate method for measuring thermal conductivity of nanofluids.
• An estimation of the optimal supplied energy and time for sonication is suggested.
• Stability and thermal conductivity of nanofluids depend on sonication time and energy supplied for fluid preparation.
• Thermal conductivity improves for low volumetric concentrations (<0.2%) and high temperatures (>50 °C).

A detailed procedure is presented for the implementation and evaluation, by Nano-Flash Method, of thermal conductivity of nanofluids with water as base fluid and at different volume concentrations of Al2O3. The main advantages of this measurement technique are short measurement times, easy sample preparation and high accuracy. The ultra-sonication technique was employed for preparing the mixture and results showed that the stability and thermal conductivity enhancements of Al2O3–H2O nanofluids are highly dependent on sonication time and the energy supplied to the fluid for its preparation. An estimation of the optimal supplied energy and time for sonication was suggested, while temperature and volumetric concentration effects on thermal conductivity are evaluated by measurements. An enhancement of thermal conductivity with respect to temperature and volumetric concentration is found, as expected. Comparisons with data from literature confirmed the validity and the suitability of the nanoflash technique applied to thermal conductivity evaluation.