Enhanced Flow Boiling in Microchannels Integrated with Hierarchical Structures of Micro-Pinfin Fences and Nanowires

Abstract

Two-phase flows in microchannels have been extensively investigated due to their wide range of applications including the fluid process and thermal management in electronic devices. In this study, silicon nanowires (SiNWs) were directly integrated with all the inner microchannel surfaces including walls and micro-pinfins (μ-pinfin) to form SiNW-pinfin hierarchical structures. The objective of this study is to explore if the SiNW-decorated surfaces can further enhance flow boiling through promoting local capillary flows with a better managed pressure drop. Experimental results illustrate that the critical heat flux in the proposed SiNW-pinfin microchannels can be promoted up to 483, 71.7, and 25.5% at a mass flux of 303 kg/m2 s compared with the traditional plain-wall, SiNW-coated plain-wall, and plain-wall with inlet orifice microchannels, respectively. Moreover, the heat-transfer rate of the flow boiling can be enhanced up to 122% at a mass flux of 303 kg/m2 s compared to that of inlet orifice microchannels with an effectively managed pressure drop. The capillary-induced periodic and rapid liquid wetting is believed to be the primary enhancement mechanism.

Advances in micro and nanoengineered surfaces for enhancing boiling and condensation heat transfer: a review

“…171 Building on this work, silicon nanowire pin n fences enable even better performance when compared to micro-pin n fences due to higher capillary pressure. 172 This is seen in the exit vapor quality being 15% higher than that of micro-pin n fence boiling for constant temperature boundary conditions. Furthermore, a 43% reduction in pressure drop was also been reported due to enhanced rewetting.…”

Micro‐/Nanohierarchical Structures Physically Engineered on Surfaces: Analysis and Perspective

“…To take advantage of the fiber-based hierarchical structure, researchers have also attempted to imitate natural fiber structures (e.g., gecko's paws and tree frog's toes). To this end, various fabrication processes for fiber-based hierarchical structures have been developed, such as the formation of additional nanofiber structures using nanoscale molds on rationally de-signed micropatterns, [10] mechanical transfer of nanofibers (such as vertically aligned CNTs, [15] metal nanowires, [103] and polymer-based nanofibers [104] ) on the microstructure, and combination of prefabricated nanofibers in micropatterns by post-treatment using mechanical shear forces. [13,21] Physical engineering methods of fabricating fiber-based hierarchical structures have limitations such as material selection (photocurable or thermoplastic polymers) due to the double molding requirement, the need for the high vertical alignment of transferred nanofibers to achieve structural uniformity, and the possibility of post-treatment-induced damage due to the mechanical weakness of nanofibers.…”

Early-Stage Liquid Infiltration in Nanoconfinements

“…The most compelling and extensive application of infiltration is in evaporation or boiling, which is one of the most efficient mechanisms for heat transfer in small-scale systems due to the use of the latent heat of the fluid. The integrated two-phase liquid-cooling technology is envisioned to be a promising alternative for heat transfer in micrometer- and nanometer-scale devices. − Because of the structured wicks on the heated surface, coolant always flows toward the hot spots and resists dry patch formation.…”