High-frequency alternating nucleate boiling of water enabled by microslot arrays in microchannels

Abstract Flow boiling in parallel and isolated microchannels has been extensively studied. In this study, five parallel microchannels (W = 200 µm, H = 250 µm, L = 10 mm) are interconnected by 28 micro-slots (20 µm wide and 250 µm deep) starting from the outlet. These micro-slots serve as nucleation sites to greatly enhance nucleate boiling. More importantly, the alternating and enhanced nucleate boiling in neighboring microchannels can generate additional pressure drop during the bubble growth-departure cycle and hence enable highly desirable periodic rewetting inside channels, particularly near outlet regions. This new microchannel configuration can substantially enhance nucleate boiling during flow boiling processes. Coupling with the enhanced nucleate boiling and the induced thin film evaporation, heat transfer coefficient (HTC) in present microchannel configuration can be enhanced up to ~107.6% at mass flux 250 kg/m2∙s with a ~17% higher critical heat flux (CHF) compared to the plain-wall microchannels with inlet restrictors (IRs). In addition, we achieve a CHF value of 810 W/cm2 at a moderate mass flux of 430 kg/m2∙s. All these enhancements are realized without compromising two-phase pressure drop compared to plain wall microchannels with inlet restrictors (IRs). Two-phase flow instabilities in terms of temperature and pressure drop fluctuations are also significantly suppressed.