Coupling zinc oxide nanopatterns with low-power acoustics for synergistic two-phase cooling enhancement

Active and passive heat transfer enhancement strategies have demonstrated promising potential to remarkably augment the heat exchange efficiency of energy system and power electronic devices. Especially, flexible acoustic manipulation and controllable nanopatterns are promising candidates for achieving synergistic enhancement demands. However, existing acoustic approaches typically require bulky transducers operating at high power levels, the fabrication of nanopatterns suffers sophisticated and expensive procedures, which limits their applicability in compact spaces. Moreover, the fundamental heat transfer enhancement mechanisms of acoustics and nanopatterns are not thoroughly understood. This study proposes a synergistic active and passive enhancement strategy coupling low-power acoustics with a zinc oxide nanopattern (n-ZnO) surface within a compact flow channel heat exchanger. n-ZnO surface with abundant nucleation sites and super wettability is prepared via a straightforward chemical synthesis approach. n-ZnO surface results in a significant increase in quenching heat flux, enhancing the heat transfer coefficient (HTC) and substantially reducing the wall superheat (by up to 13.1 °C). When the acoustics is activated on the n-ZnO surface, the strong acoustic radiation force delays the onset of vapor film, increasing critical heat flux (CHF). The mechanism by which the acoustics produce different effects at various heat fluxes is analyzed with bubble behavior and heat flux partitioning model. The coupling of the n-ZnO surface with acoustics achieves a synergistic and significant enhancement of both CHF and HTC at different flow rates by at least 41.9 % and 50.7 %, respectively. These findings not only provide new insights for the development of robust synergistic enhancement strategies but also offer important perspectives on the in-depth understanding of heat transfer mechanisms.