Effect of mechanical vibration and its influence on thermal performance of a nanofluid heat exchanger

Many situations involve flowing fluids on nonstationary platforms. For example, moving vehicles undergo vibrations in their transit. The effect of vibration on heat exchangers with nanofluids as working fluids has not been explored systematically, and this study examines the impact of vibrations in these situations. Vibrations having amplitudes in the range of 1-5 mm, and frequencies from 6 to 25 Hz are investigated. A 2% volume fraction Al2O3 solution with water as the base fluid has been utilized as the fluid; Reynolds numbers ranging from 10,000 to 25,000 were considered. The Nusselt number, friction factor, factor of merit, and effective thermal performance have been used to assess the heat transfer augmentation caused by vibration. It is found that the heat transfer characteristics are significantly enhanced by the active vibration provided in the form of a time-dependent sinusoidal velocity perpendicular to the axis of the heat exchanger tube. An increase of up to 70% in the Nusselt number was observed compared to the case without vibration. But, the friction factor was also enhanced; hence, a factor of merit and thermal performance factor was used as a comprehensive measure for changes to the performance. It was found that for a 5 mm amplitude and a 25 Hz frequency, a 30.7% rise in the factor of merit was observed with respect to the case where the tube is static. In addition, the thermal performance factor increased by 1.3.