2 research outputs found
Multiresonant Selective Emitter with Enhanced Thermal Management for Infrared Camouflage
Tailoring the optical properties of metamaterials is
crucial for
improving the performance of infrared (IR) applications. Generally,
IR camouflage materials are required to have low IR-emission properties
for the detected bands (3–5 and 8–12 μm), in which
IR detection is accomplished. However, the heat residue by suppressed
thermal radiation degrades the thermal dissipation capacity and thermal
stability of IR camouflage materials. Herein, a multilayer metal–dielectric–metal
(MDM) selective emitter with high IR-emission performance in the undetected
band for thermal management and low IR-emission performance in the
detected band for IR camouflage is introduced. Compared to a conventional
selective emitter and a low-emission material (Au film), the multiresonance
selective emitter exhibited 125 and 2910% increases in heat dissipation
within the undetected band, respectively. In addition, the proposed
camouflage material exhibited a substantial reduction in emissive
energy within the detected bands of 3–5 and 8–12 μm,
with reductions of 72 and 83%, respectively, compared to that of a
high-emission surface. The effectiveness of our IR camouflage was
demonstrated by IR camera measurements. When the surface temperature
was 360 K, the radiance temperatures of the multilayer multipeak selective
emitter were 314 and 309 K for the 3–5 and 8–12 μm
bands, respectively. Thermal management experiments demonstrated the
enhanced thermal stability of the multiresonance selective emitter,
especially in conditions of low pressure and high heat flux, when
compared to that of the low-emissivity film. This work provides a
practical strategy to enhance the thermal emission of a selective
emitter, expanding its potential beyond IR camouflage to various energy
applications
Enhancement of Pool Boiling Heat Transfer Using Aligned Silicon Nanowire Arrays
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<sup>–3</sup> mm<sup>3</sup>/s) and increase the CHF to 245.6 W/cm<sup>2</sup>, 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