Bubble dangling phenomenon and heat transfer characteristic investigations of printed-nanowires in saturated flow boiling

This study conducted an experimental investigation into the bubble-dangling phenomenon and the heat transfer characteristics of nanowire (NW) substrates under saturated flow boiling conditions. The research considered the influence of NW morphology on bubble behavior, demonstrating that bubbles are more readily trapped by the roughened surfaces of the NWs due to substantial friction compared to unmodified flat substrates. This trapping effect inhibits bubble movement along the flow direction. The extended retention period of bubbles prior to detachment can result in increased flow resistance of the coolant, ultimately impairing liquid replenishment capacity and leading to premature dry-out. Conversely, it was observed that augmenting the roughness of the NW substrate can effectively enhance capillary-driven forces, facilitating a greater recirculated flow towards the heated surface during the nucleate boiling regime. To elucidate the complex impact of NW morphology on bubble dynamics and wicking characteristics, three distinct printed zinc oxide (ZnO) NWs were fabricated on unmodified silicon substrates, each subjected to varying nanoparticle seeding periods, utilizing a combination of microcontact printing and solution growth methods. Based on the experimental outcomes, a modified critical heat flux (CHF) model was proposed, which accounts for the wicking force associated with the ratio of liquid replenishment capacity to vapor evaporation rate. This model aims to predict the CHF of NW substrates operating with deionized (DI) water under saturated flow boiling conditions.