UCLA

Recent developments in electronic and optoelectronic devices, especially in the highly power-sensitive areas of portable and wearable applications, have led to increased challenges in their thermal management. Conventional rotary fans are difficult to scale down and power-inefficient when miniaturized. Piezoelectric fans, which typically consist of flexible blades mechanically fixed to piezoelectric actuators, are promising alternatives to rotary fans because they have simpler structures, produce less noise, and require less power consumption [1]. Although piezoelectric fans have been commercially available for over a decade, systematic study of their power consumption mechanism has been limited. A combined experimental and modeling study is conducted to help elucidate the mechanism of power dissipation in piezoelectric fans, and correlate them with heat transfer performance.

Powers consumed by a commercially available piezoelectric fan and by its piezoelectric actuator (with the fan blade cut off) are measured separately as a function of frequency and bias input voltage. A mechanical model is next developed to theoretically partition the fraction of power transferred to the surrounding air and that portion consumed by the piezoelectric actuator. In parallel, the heat transfer coefficients over a heated flat surface are measured for a set of piezoelectric fans of different blade lengths and thicknesses to obtain insight into piezoelectric fans’ cooling enhancements normalized by power consumptions.

It is observed that the power consumption predicted by the proposed model for a piezoelectric actuator (with the blade cut off) agrees with that measured. In addition, the model estimated flow power (power transferred to surrounding air) matches the difference between the separately measured total power consumption of the piezoelectric fan and that of its piezoelectric actuator, indicating the validity of the proposed model in partitioning the power consumption of a complete piezoelectric fan. It is also confirmed that the heat transfer performance of the piezoelectric fan is closely related to its induced flow power rather than the total power consumed. As will be discussed in following chapters, the “power efficiency of piezoelectric fan cooling” should be characterized by its flow power rather than total power consumption.