Local Heat Transfer Characteristics of Flows Induced by Multiple Piezoelectrically Actuated Vibrating Cantilevers

Piezoelectric fans have been shown to provide substantial enhancements in heat transfer over natural convection while consuming very little power. The local heat transfer coefficients induced by multiple piezoelectric fans operating simultaneously in close proximity are determined experimentally. The fans vibrate close to an electrically heated stainless steel foil, and the entire temperature field is observed by means of an infrared camera. A vibration amplitude of 10 mm is considered, with the distance from the heat source to the fan tip chosen to vary from 0.01 to 2.0 times the amplitude, and the distance between the fans, or pitch, varying from 0.5 to 4.0 times the amplitude. The two-dimensional contours of the local heat transfer coefficient are compared to those observed for a single fan under similar conditions. Results show that the benefit of adding a second fan is highest at an intermediate pitch that is equal to the vibration amplitude. Constructive interference is observed under these conditions yielding a local performance increase over isolated fan operation. For a large fan pitch, separate contours surrounding each fan are similar to those of a single fan, but their performance is lower than that of the corresponding single fan. For a small fan pitch the cooling obtained with the fan pair is similar to that with just one fan, suggesting minimal benefit from adding the second fan in this case.