In this study we present the experimental investigation of the thermal behavior of nanofluids. A tremendous interest has been developed in this new generation of heat transfer fluid for cooling applications in industrial processes, because of their excellent thermal performance. A colloidal mixture of nano-sized (<100 nm) TiO_2 (p-25) particles dispersed in a base fluid propylene glycol was formulated by the two-step method. The volume fractions of nanoparticles used were 0.1% and 0.50% for preparing the nanofluids. The average sizes, size distribution and surface morphology for the characterization of nanoparticles at different magnification have been determined using FESEM. The thermal conductivity, thermal diffusivity and ultrasonic velocity of the prepared nanofluids at different concentration were experimentally studied in the temperature range of 20-80°C. This however, has not been addressed in literature so far. Results show that thermal conductivity increases whereas the ultrasonic velocity decreases with increasing temperature. The ultrasonic investigation confirms the enhancement of thermal conductivity of nanofluids as reported in literature.
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