Experimental study on ONB of flow boiling in microchannel within an ultrasonic field

Flow boiling in the microchannel with the ultrasound is regarded as a promising method for confronting the challenge posed by heat dissipation in microelectronic devices. During this process, the nucleation is vital for the thermal performance, but the nucleation mechanism with the interplay of ultrasonic, thermal, and flow fields remains inadequately explored. This study first endeavors to reveal the nucleation mechanism of flow boiling within the ultrasonic field through the experimental inquiry into the impact of ultrasound on the onset of nucleate boiling (ONB). It is ascertained that ultrasound plays a pivotal role in promotion of the nucleation. An evident decrease of the wall superheat at ONB, specifically 20.7 %, is achieved by activating abundant vapor embryos at a relatively low wall superheat. Meanwhile, associated bubble generation rate increases by approximately two orders of magnitude, owing to the noteworthy reduction in the temporal requisites within the ultrasonic field for the generation of an equivalent number of bubbles. Furthermore, the elevation in ultrasonic power and operating time lead to a substantial reduction of 18.6 % and 16.7 %, respectively, in the wall superheat required to ONB. Concomitant with the rise in mass flux, the heat flux at ONB exhibits a remarkable ascent of 52.1 %.