Facile Fabrication of Nanostructured Microchannels for Flow Boiling Heat Transfer Enhancement

Flow boiling in microchannels promises high heat transfer due to the combined effect of latent heat of vaporization and forced convection in confined spaces. However, flow boiling based miniaturized thermal management devices are limited due to instability induced dryout. While several efforts have been made to delay instabilities via advanced surface modification techniques, there is a need to expand the scope of applications by developing low-cost and scalable fabrication technologies for commonly used heat exchanger materials. In this paper, we use a facile and self-limiting chemical oxidation technique for fabricating sharp needle-like superhydrophilic CuO nanostructures within six parallel 500 x 250 mu m(2) microchannels spread uniformly over a 1 x 1 cm(2) area in a copper heat sink. We demonstrate heat transfer enhancement with nanostructured microchannels (NSM) without any appreciable change either in the average pressure drop or the fluctuations in comparison to baseline plain wall microchannels (PWM). Analysis of the high-speed images was performed to attribute the enhancement with NSM to the presence of a capillarity-fed thin-film evaporation regime, which otherwise was absent in PWM. We believe that these results are encouraging and suggest that the heat sink geometry can be optimized to investigate the true potential of nanostructured microchannels.