Effects of blade shape on convective heat transfer induced by a piezoelectrically actuated vibrating fan

An experimental and numerical investigation is performed to explore the effects of blade shape on the convective heat transfer performance induced by piezoelectric fans. Five blade types are taken into consideration corresponding to the ones presented by Lin et al. [28], including one baseline type with a rectangular shape (Type-A), two rectangular shapes with wider widths (Type-B and Type-C), and two trapezoidal shapes in divergent (Type-D) and convergent (Type-E). All the blades are attached to the same piezoelectric patch and have the same exposed length. The vibration tests show that the blade shape has a significant influence on the vibrating characteristics of piezoelectric fan. Related to the baseline Type-A, Type-B and Type-C make the first-order resonance frequency a little descent. Type-D makes its first-order resonance frequency far less than the baseline type but Type-E is opposite. From the numerical simulations, the vortical structures induced by different blades vibrating at their respective resonance frequencies are illustrated. It is found that Type-B and Type-C produce stronger vortical flow although they have a little less vibrating frequency than the baseline Type-A. For Type-E, as its vibration frequency is obviously larger than Type-A, the scale of vortex shedding from the vibrating fan seems much stronger. In comparison with baseline type of piezoelectric fan, the location of highly local heat transfer zone moves from the center to both edges of fan-tip vibration envelope of fan-tip vibration envelope with the increase of blade width. In general, the blade types like Type-C and Type-E are suggested to be the favorable shapes for achieving better convective heat transfer performance. However, a little larger power consumption for actuating the piezoelectric fan is paid in relative to the baseline blade shape.