Enhancing the critical heat flux (CHF), which is the capacity of heat dissipation, is important to secure high stability in two-phase cooling systems. Coolant supply to a dry hot spot is a major mechanism to prevent surface burn-out for enhancing the CHF. Here, we demonstrate a more ready supply of coolant using aligned silicon nanowires (A-SiNWs), with a high aspect ratio (>10) compared to that of conventional random silicon nanowires (R-SiNWs), which have a disordered arrangement, for additional CHF improvement. We propose the volumetric wicking rate, which represents the coolant supply properties by considering both the liquid supply velocity and the amount of coolant (i.e., wicking coefficient and wetted volume, respectively). Through experimental approaches, we confirm that the CHF is enhanced as the volumetric wicking rate is increased. In good agreement with the fabrication hypothesis, A-SiNWs demonstrate higher coolant supply abilities than those of R-SiNWs. The longest (7 μm) A-SiNWs have the highest volumetric wicking rate (25.11 × 10 mm/s) and increase the CHF to 245.6 W/cm, which is the highest value obtained using nanowires among reported data (178 and 26% enhanced vs unmodulated plain surface and R-SiNWs, respectively). These well-aligned SiNWs can increase the CHF significantly with efficient coolant supply, and it can ensure high stability in extremely high thermal load systems. Moreover, our study provides nanoscale interfacial design strategies for further improvement of heat dissipation.

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We present a new concept of a structured surface for enhanced boiling heat transfer that is capable of self-adapting to the local thermal conditions. An array of freestanding nanoscale bimorphs, a structure that consists of two adjoining materials with a large thermal expansion mismatch, is able to deform under local temperature change. Such a surface gradually deforms as the nucleate boiling progresses due to the increase in the wall superheat. The deformation caused by the heated surface is shown to be favorable for boiling heat transfer, leading to about 10% of increase in the critical heat flux compared to a regular nanowire surface. A recently developed theoretical model that accounts for the critical instability wavelength of the vapor film and the capillary wicking force successfully describes the critical heat flux enhancement for the nanobimorph surface with a good quantitative agreement.

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This study considered effects from thermoelectric property changes due to mesoporous thin film ZnO lattice deformation through doping with various group III elements. The distorted hexagonal wurtzite structure occurred in the ZnO thin film due to ion size differences between Zn and other doping elements. These strains cause distortion, resulting in reduced mobility because they inhibit grain growth and reduce crystallinity. Al doping induced the largest strain since it represented the largest ionic radius difference from Zn, whereas strain differences between Ga and In doped ZnO were almost negligible. In is larger than Zn, whereas Al and Ga dopants have a smaller atomic radius. Thus, carrier concentration for the smaller ion was 18%–26% higher than for the larger ion, and electroconductivity and carrier concentration increased 2–3.5- and 5–10-fold, respectively, with increasing dopant concentration, regardless of the doping element. Ga was the best candidate among the group III elements for doping a ZnO thin film, achieving the highest power factor of 8.01 at 323 K. We verified that thermoelectric properties could be improved by controlling dopant concentration, being influenced from inducing crystal lattice deformation through ion radius differences between the dopant and Zn.