Pressure and Flow Rate Performance of Piezoelectric Fans

A piezoelectric fan is a flexible cantilever beam whose vibration is actuated by means of a piezoelectric material. Such fans have been employed for the enhancement of heat transfer by increasing the fluid circulation in regions which are otherwise stagnant. The main focus of past studies has been to predict and describe the heat transfer achievable using these devices, as well as the flow field generated by vibrating cantilevers. In order to directly compare these fans with their traditional counterparts such as small axial fans, the present work casts the performance of piezofans in terms of a characteristic often used to represent conventional fans, namely the fan curve. The primary focus of this paper is to determine the relationship between the pressure and the flow rate generated by miniature piezoelectric fans. Experimental measurements are obtained for fans with operating frequencies of 60 and 113 Hz. The maximum flow rate conditions yield nearly 30 l/min, while the greatest static pressure generated is found to be 6 Pa. The performance is highly dependent on both the vibration amplitude and frequency. Predictive relationships are developed to describe the experimental trends and provide insight into the sensitivity of pressure and flow rate to these operating parameters. These fans are directly compared to two commercially available axial fans, both in terms of overall performance and efficiency with which energy is imparted to the fluid. Piezoelectric fans are found to compare quite favorably using either of these performance metrics with a nearly order-of-magnitude increase in fan efficiency. A secondary focus of this paper is to explore the effects of fan installation details on fan performance. The proximity of surrounding walls is considered through the use of three different enclosures within which the fan is mounted. Effective inlet areas from which the air enters the fan are also identified. This paper provides a practical framework for determining the optimal placement and configuration for these fans in prototypical applications.