Heat transfer enhancement of turbulent channel flow using a piezoelectric fan

Abstract

This study experimentally investigated the flapping dynamics of a piezoelectric (PE) fan in channel flow and the resultant wall heat-removal performance enhancement. The PE fan consisted of a rigid PZT (Lead zirconate titanate) actuator and a flexible PET (Polyethylene terephthalate) blade. The PE fan in absence of electric excitation or air flow was chosen as the baseline data configuration. The mid-span of the PE fan was illuminated by a laser sheet, and the instantaneous profiles of the PE fan were captured by a high-speed camera system; the structure boundary detection algorithm and fast Fourier transform algorithm were used to identify the flapping amplitude and frequency. The time-averaged heat transfer performance across the channel wall with constant heat flux boundary condition was spatially resolved by the temperature sensitive paint measurement. The piezoelectric fan displayed the largest flapping amplitude at the fundamental resonant frequency of 43 Hz. The amplified flapping amplitude and the increased frequency were achieved with the elevation of the Reynolds number, and correspondingly the resultant heat transfer performances were improved. At a low Reynolds number of 1.37×104, the piezoelectric fan blade flapped synchronously with the PZT actuator, while the flapping amplitude was considerably intensified to 0.72 times the blade length under excitation voltage of fundamental resonant frequency, resulting in a 30% augmentation in the local Nusselt number. At a high Reynolds number of 1.91×104, the flapping frequency was locked to its flutter frequency 64.5 Hz, regardless of the excitation voltage frequency. The flapping amplitude and the resultant heat transfer performance were found to be insensitive to the excitation voltage frequency at a Reynolds number of 1.91×104, although the maximum local heat transfer was enhanced by 46% at an excitation voltage frequency 43 Hz.