Through the latent heat evaporation, flow boiling in microchannels has great potential in achieving high temperature uniformity at a high working heat flux with reduced pumping power, which is critical in cooling high power electronics and photonics and in improving reliability and energy efficiency of micro-heat exchangers and reactors. However, flow boiling in microchannels is stochastic and hampered by several severe constraints such as bubble confinements, viscosity and surface tension force-dominated flows. It is well known that heat and mass transfer are ultimately governed by boundary layers (BLs) during flow boiling in microchannels. It was observed, by disturbing BLs such as creating oscillations, introducing capillary flows along walls, and promoting thin film evaporation, flow boiling in microchannels can be enhanced. However, research to enhance flow boiling by intentionally constructing and optimizing BLs is still lacking. In this study, by directly reconstructing or designing the BLs, the flow boiling in microchannels can be controlled and designed as desired to some extent. This can be achieved by forming innovative hydrophilic nanotip arrays along microchannel walls. After multiple and transitional two-phase regimes are unified by nanotip-induced BLs, in this project, it will be feasible to develop general, physics-based, and robust two-phase models. Equally importantly, the concept developed in this project will be positively utilized to push the limit of flow boiling in microchannels. The specific tasks of this project will be pursued to achieve project goals: construct and optimize BLs by developing hydrophilic nanotip arrays with advanced profiles; achieve an unprecedented flow boiling performance; characterize new flow boiling phenomena with induced BLs in microchannels; and develop understandings of the induced BLs and their critical roles in determining two-phase transport phenomena in nano- and micro-domains.
This project will form the basis for a new research discipline in fluid mechanics with induced BLs, enable new research directions in two-phase transport, and provide fundamental insights pertinent to two-phase transport at the nano- and micro-domains. Drastically enhanced flow boiling in microchannels by controlling BLs can update the two-phase cooling technology and scientific discovery in thermal/fluids. Compatibility with microelectronics will lead to embedded cooling solutions for high power electronics and photonics, which is still a challenging task. This project will also aim to educate next generation scientists and engineers in micro/nano-technologies and providing opportunities to undergraduates, in particular underrepresented minorities, to gain first-hand research experience in micro/nanotechnologies and expand their intellectual horizon by bridging the state-of-the-art micro/nanotechnologies and basic science.
