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.
Heat pipes play a critical role in determining the operations, safety, and energy efficiency of electronics. The main focus to improve the heat pipe performance is on the evaporator design or wicking structures. However, the intrinsic limitation comes from the condenser, which is fundamentally constrained by inefficient filmwise condensation (FWC). In this study, we successfully achieved a peak effective thermal conductivity (k eff ) of ~140 kW/(m•K) on widely used groove heat pipes by implementing sustianble dropwise condensation (DWC) and integrating with enhanced evaporator. To better understand the working mechanisms of the ultraefficient heat pipe, both the evaporator and condenser of the heat pipes have been modified accordingly. Our results show that up to 296% enhancements on the k eff can be achieved under various inclination angles by only inducing DWC in the condenser section. The drawback of temperature fluctuations induced by DWC in smooth heat pipes appears to be effectively solved using the grooves-wicking structure. Furthermore, by integrating the nanostructured evaporator, the k eff of the heat pipe can be boosted up to 517% compared to conventional groove heat pipes.This study, for the first time, demonstrates the huge potential of engineering both the condenser and evaporator simultaneously in developing ultraefficient heat pipes.
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