Enhancing forced-convection heat transfer of a channel surface with synthetic jet impingements

Abstract

A transient numerical simulation was carried out to investigate the convection heat transfer enhancement of a heated surface in an airflow channel using a synthetic jet. The study was performed with a channel-flow average velocity varying up to 3 m/s, which has the corresponding channel Reynolds number of 3,616. The peak-to-peak amplitude of a jet diaphragm was varied from 0.4 to 1.2 mm to investigate its effects on the heat transfer enhancement. The synthetic jet was operated at three different locations relative to the heated surface in the streamwise direction with an operating frequency increased up to 200 Hz. The heat transfer of the heated surface was characterized by evaluating a phase-averaged convection heat transfer coefficient over ten operational cycles of the synthetic jet after the flow and thermal fields reached a quasi-steady state. In addition, the helicity flow visualization was conducted to observe the dynamic and transport characteristics of vortex packets generated by the synthetic jet and their interaction with the heated surface. It was found that the vortex packets represent high-momentum zones with strong swirling motions in the streamwise direction, and their direct impingement or sweeping on the heated surface was highly responsible for the heat transfer enhancement.