Radiative Heat Pumping from the Earth Using Surface Phonon Resonant Nanoparticles

Abstract

Nanoparticles that have narrow absorption bands that lie entirely within the atmosphere's transparent window from 7.9 to 13 mum can be used to radiatively cool to temperatures that are well below ambient. Heating from incoming atmospheric radiation in the remainder of the Planck radiation spectrum, where the atmosphere is nearly "black", is reduced if the particles are dopants in infrared transmitting polymers, or in transmitting coatings on low emittance substrates. Crystalline SiC nanoparticles stand out with a surface phonon resonance from 10.5 to 13 mum clear of the atmospheric ozone band. Resonant SiO(2) nanoparticles are complementary, absorbing from 8 to 10 mum, which includes atmospheric ozone emissions. Their spectral location has made SiC nanoparticles in space dust a feature in ground-based IR astronomy. Optical properties are presented and subambient cooling performance analyzed for doped polyethylene on aluminum. A mixture of SiC and SiO(2) nanoparticles yields high performance cooling at low cost within a practical cooling rig.

Radiative cooling of solar absorbers using a visibly transparent photonic crystal thermal blackbody

“…Whereas historically radiative cooling was largely developed for night-time applications (1)(2)(3)(4)(5)(6)(9)(10)(11)(12)(13), recent works have achieved daytime radiative cooling (7,14). In particular, it was shown that the radiative cooling to below ambient air temperature can be achieved (7), with a photonic structure that reflects almost all incident sunlight and simultaneously emits significant thermal radiation in the midinfrared.…”

Nanophotonics-enabled smart windows, buildings and wearables

“…What such cameras see outdoors for the best cool surfaces is thus almost entirely thermal emission and little reflectance of IR. Sharp absorption peaks in the sky window zone are thus desirable and can be achieved by wellknown dielectric materials in nanoparticle form on metal as we demonstrated in 2010 ( Figure 6) [8]. Polymers that absorb selectively in the sky window band are also useful.…”

“…Only then is reduction of P A,DW the best way to maintain net cooling to even lower temperatures. The crossover temperature at which a selective emitter is preferred depends upon heatload, relative surface temperature and environmental conditions [8,39]. Reduction of P A,DW is done using a high IR reflectance outside the sky window and can be angularly enhanced if incoming rays from the lower sections of the sky are reflected or replaced with those from a low E surface.…”

“…It is not until a subambient temperature of more than~6°C is attained that a crossover to an IR selective coating is preferred as only then is the high E radiative output not enough to overcome the extra gain due to its greater absorption of atmospheric radiation. This is explained in detail in [8] and [39]. An example is enhanced cooling of solar cells utilizing an etched photonic crystal pattern, which needs as high an emittance as possible plus high solar transmittance [42].…”

“…Another optical goal is stunning appearance from new visual effects. Novel color, including spectral sharpness and striking changes with viewing angle, are a feature of visual responses enabled by nanostructures [7,8]. In buildings, smart blinds and curtains can add to energy conservation, daylighting and viewing performance of windows and skylights [9].…”