The flow field and convective heat transfer in the unit structure of heat exchangers by using acoustic waves

Abstract

In this paper, a combination of numerical simulation and experimental investigation is carried out. A study on the effect of low-frequency acoustic waves on the flow field and convective heat transfer in the unit structure of a staggered heat exchanger is presented. Air is considered as background free flow, with a Reynolds number of 200. The range of the pipe pitch ratio is 2.2–5, the frequency range of the sound wave is 50–200 Hz, and the range of the sound pressure level is 115–135 dB. The results highlighted that the reattachment phenomenon on the downstream cylindrical surface gradually disappeared with the addition of external acoustic perturbation. Additionally, the lift coefficient increases with an increase in the sound pressure level, and the larger the pitch ratio, the greater the vortex shedding frequency. At the same time, the drag coefficient also increases. As both the sound frequency and pressure level increase, the array surface localization and average Nusselt number increase. In particular, when S/D = 5, multiple acoustic incidences and reflections occurred on the wall at the array gap. According to the acoustic superposition principle, it is noted that the acoustic energy reinforced the fluid flow at the gap. This leads to an improvement of 75 % in the array surface-averaged convective heat transfer compared to the acoustic perturbation case with no sound. The findings of the experiments demonstrated the ability of acoustic waves to enhance convective heat transfer on the surface of cylindrical arrangements.