Numerical simulation of flow and heat transfer induced by periodic motion of dual piezoelectric fans in confined volume

Piezoelectric (PE) fan is a novel type of active cooling device which enhance heat transfer with less power consumption. In order to achieve the theoretical limit of heat transfer performance of multiple PE fans system in confined volume, the blade location effects on that were investigated in detail by conducting three-dimensional simulations. Here, the blade pitch ranges from 1.6 to 4.2 times the fan width, and the optimal values of blade pitch with respect to four typical vibration phase angles (0 degrees, 60 degrees, 120 degrees, 180 degrees) were obtained, respectively. For all vibration modes, the air volume variation curve follows a parabola trend with blade pitch. The largest air volume is obtained when fans operating in-phase mode (phi = 0 degrees), a conclusion that differs from that in infinite space. We attribute this to the vortex action, and its formation is determined by two effects. The positive one is the attenuation of counteracting effect from normal forces with the increasing blade pitch, where the force was exerted by two blades onto their inner fluid. The negative one is weakening of the coupling effect of two jets formed by the blade tips when spacing of dual fans is gradually increased. In addition, the local hot spot phenomenon was observed in both in-phase and counter-phase mode. It was observed that the distance between local hot spots broadens with the increasing blade pitch for in-phase mode while remains substantially constant for counter-phase mode. Our work provides a design principle for heat transfer optimization of dual PE fans in confined volume and will benefit both theoretical understanding and application in thermal management of PE fan system.