압전소자의 진동을 받는 유체의 열전달 특성에 관한 연구

Abstract

The present study was investigated on characteristics of heat transfer when the piezoelectric vibration was applied in a fluid. This study was to investigate the characteristics of heat transfer in a medium for the cases: one without piezoelectric vibration and the other with piezoelectric vibration. Also, in order to find out the effect on enhancement of heat transfer, ultrasonic vibrator and piezoelectric actuator which consisted of the piezoelectric module was used in a phase change material (PCM) and an air cooling region in thermoelectric cooling system, respectively. In this study, the heat flow was measured in the absence of and in the presence of acoustic streaming. The streaming created by ultrasonic vibrations was visually by a particle image velocimetry (PIV), an infrared thermal camera and a CCD camera. The experimental results revealed that convection state was activated with ultrasonic vibration and the melting of a PCM was accelerated from the dimensionless time, FoSte*=0.9×10^5 and 1.2×10^5 when the heat flux q"=11517.43W/m^2 and 6436.21W/m^2 was applied, respectively. Also, the acoustic streaming created by ultrasonic vibration could accelerate the melting process of a PCM as much as 2.5 times. In addition, the profiles of the augmentation ratio of heat transfer coefficient were experimentally measured and were compared with those of the acoustic pressure obtained by numerical prediction using a coupled finite element-boundary element method (Coupled FE-BEM). The acoustic pressure induced by acoustic streaming in a medium has improved the enhancement of heat transfer about 1.5 times. Also, when the piezoelectric actuator was applied to the heat transfer process of thermoelectric cooling system, acoustic streaming was occurred in an air cooling region. And, the temperature distributions in an air cooling region were uniformly maintained about 15℃ ± 0.5℃ because the natural convection flow was changed to the locally forced convection flow happened by acoustic streaming. In the end, the results clearly show that the enhancement of heat transfer is closely related to variations in the acoustic pressure and the acoustic streaming is one of the prime effects to enhance the convection heat transfer.