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In recent years, many researches have investigated nanofluids pool boiling and reported some contradictory results. In this study, the pool boiling heat transfer of water- alumina and TiO2-water nanofluids at saturated temperature was investigated experimentally. The experiments were conducted to investigate the impact of concentration and type of nanofluid on the pool boiling heat transfer of brass surface. Water- alumina and TiO2-water nanofluids with volumetric concentration of 0.0025-1% and 0.0025, 0.01, 0.25 % was used, respectively. An experimental setup with a cylindrical heated test section made of brass and surface roughness of 0.2µm was designed and fabricated. The experimental results showed that, the heat transfer decreases as the nanoparticles added into the pure water base fluid. At a constant heat flux, the heat transfer coefficient decreases as the alumina volumetric concentration increments from 0.0025 to 0.01% and then increases for further addition from 0.01 to 1%. The TiO2-water nanofluids performance with respect to the water-alumina nanofluids was not very promising. That means, the boiling heat transfer decreases while the boiling surface temperature increase at a constant heat flux.

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Increasing heat transfer and preventing sedimentation in equipment have always attracted the attention of engineers. In this work, the variations of salt concentration were effective on bubble diameter, departure frequency and generation points and its sediments acted as a heat transfer resistance. Therefore, first, the effect of ultrasonic waves on salt sedimentations in pool boiling was investigated. The results revealed that the ultrasonic waves had positive effect by suspending the soluble particles in the fluid and preventing them from precipitating on the surface of heat transfer. Increasing turbulences and perturbations due to changes in bubble dynamic and cavitation phenomenium, led to improve the heat transfer coefficient, significantly. The role of roughness on the surface heat transfer in bubble production was other investigation of the work. Bubble production by increasing the roughness with ultrasonic wave’s irradiation had direct and important effects on enhancing the heat transfer. Finally, salt and nanofluid sediments were compared. The nanoparticles precipitate faster and more easily under the bubble layer, but less in the salt solution if its dissolution is maintained. The ultrasonic waves were employed at three powers of 30%, 60% and 90%. Finally, the heat transfer coefficient and bubble departure diameter increased as 8.43% and 7.54%, respectively. In addition, the sedimentation decreased by 37.19%. As a result, the waves reduced their deposition by preserving salt dissolution.