The effect of vibration on droplet dynamics and heat transfer of spray cooling

Abstract

The heat transfer mechanism of spray cooling under vibration has yet to be revealed, so it is crucial to deeply analyze the droplet impingement dynamics and heat transfer mechanism under vibration. However, there is still a gap in analyzing how vibration quantitatively affects droplet impingement dynamics and heat transfer performance. To fill this research gap, this paper will employ high-speed cameras to quantitatively analyze droplets' dynamics and heat transfer properties under various vibrational conditions. The results demonstrate that droplet spreading is enhanced at high-frequency conditions, but the enhancement decreases with the reduction in amplitude. Under high amplitude conditions, droplets gain additional inertial forces to overcome adhesive forces, causing oscillation in the three-phase contact line of the droplets, which significantly consumes the kinetic energy of droplet spreading, thereby suppressing droplet spreading. Vibration overall suppresses droplet spreading; at an amplitude of 0.2 mm and frequency of 80 Hz, the spreading enhancement factor is merely 4 %. Moreover, the droplet's heat transfer rate, heat flux, heat transfer coefficient, and cooling efficiency all increase with the rise in vibrational frequency but are all subdued by the amplitude. Compared to a static surface, vibration suppresses droplet heat transfer but can facilitate droplet heat transfer under low amplitude and high-frequency conditions. At an amplitude of 0.2 mm, the maximum heat transfer enhancement factor (HTEF) is 16 %. At an amplitude of 0.8 mm and frequency of 10 Hz, the minimum HTEF is −44 %. This research undoubtedly brings innovative insights into spray droplet impact dynamics and heat transfer and can provide valuable guidance for related industrial applications.