Heat transfer enhancement by the fluttering phenomenon

Abstract

The fast-developing 5G technology requires superior heat transfer technology while the carbon neutralization action requires improving the energy efficiency of the current techniques. Therefore, it is necessary to develop a heat transfer technique with high heat dissipation ability as well as high energy efficiency. The dynamics of the fluttering flag has been widely explored and the potential of its application in heat sinks has been demonstrated. However, there are some challenges, especially the energy efficiency issue, hindering the commercialization of this technique to the industry. We provide our insight to tackle those issues. The increased pressure drop induced by the flag-fluttering motion can be addressed by splitting the flag, so that the energy efficiency can be improved by about 30%. The high critical flow velocity to actuate flag fluttering can be decreased by the inverted flag configuration and is further tuned by the flag thickness, and finally we reduce the critical velocity to be as low as 1.5 m/s, so as to make this technology more feasible to the industry. The energy efficiency of this fluttering-based heat transfer enhancement could be substantially increased by substituting the air-driven flag with a piezoelectric fan, and we utilize the geometrical arrangement to improve the cooling effect of the piezoelectric fan by about 70%. All these strategies not only increase the energy efficiency, but also improve the heat transfer performance. Both numerical and experimental approaches were used. Flag motion investigated by high-speed camera, flow visualization by smoke, and vorticity analysis have been performed. The performance characterization and the mechanism analysis were studied and given in detail. Our study demonstrates that the fluttering-based heat transfer technique is of great potential to meet the requirement of both high heat dissipation ability and energy saving. Besides, our work provides solutions to tackle those problems when applying this technique to industry, which paves the way for future electronic cooling.