Heat transfer enhancement in laminar flow heat exchangers due to flapping flags

Heat transfer enhancement due to flapping flags in a heated duct flow is studied using three-dimensional (3D) fully coupled fluid-structure-thermal simulations. Following prior work, which was limited to two-dimensional models, we examine the mechanisms and the heat transfer performance for a more realistic, 3D model of a flag in a rectangular duct heat exchanger. We then examine the role of the flag aspect-ratio and spanwise confinement, which are key design parameters for this device. We find that the narrow flags do not exhibit sufficiently energetic flapping to generate any meaningful heat transfer enhancement. We also find that the wide flags significantly increase heat flux and an increase in the width of the flag can further increase the thermal enhancement factor.