Abstract
This paper is focused on ultrasonic properties of Al2O3 and TiO2 nanoparticles dispersed in distilled water by ultrasonification. In order to study the effect of ultrasonic wave quality on stability of sonificated nanofluid, two types of ultrasonic pulse were used to prepare nanofluids: continuous and discontinues pulses. It was found that discontinues pulses cannot break all of the clusters and some large aggregates can be seen in nanofluid and sedimentation occurs after 48h. It seems obvious that the attenuation is directly proportional to the thermal conductivity. In addition, the ultrasonic velocity and attenuation were measured for temperatures ranging from 20 to 75°C and for different concentrations. The results show, no similarity with previous studies in micrometer or millimeter size of particles, the solid nanoparticles do not reduce the ultrasonic velocity for some concentrations and velocity in nanofluids has a maximum, which is higher than the base fluid. Moreover, the attenuation coefficient of nanofluids increases in diluted nanofluids, especially, when the temperature is higher than 45°C.
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