THESIS
2018
xii, 81, that is, xiv, 81 pages : color illustrations ; 30 cm
Abstract
Passive radiative cooling dissipates heat from sky-exposed surfaces to the cold universe by
strongly emitting thermal radiation within the 8-13 μm wavelength range of the electromagnetic
spectrum and reflecting radiations elsewhere, resulting in the surface temperature being
perpetually lower than ambient. It is a potential scheme for dramatically conserving energy for
refrigeration and space cooling in buildings. After the discovery of daytime radiative cooling, a
wide range of materials have been found promising for an 8-13 μm wavelength range emissive
solar reflective cooling device. Here, we consider the thermal selective emitter inspired by the thermoregulatory effect of triangular hairs on Sahara silver ants. FDTD simulations were utilized
to optimize the biomimetic surface...[
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Passive radiative cooling dissipates heat from sky-exposed surfaces to the cold universe by
strongly emitting thermal radiation within the 8-13 μm wavelength range of the electromagnetic
spectrum and reflecting radiations elsewhere, resulting in the surface temperature being
perpetually lower than ambient. It is a potential scheme for dramatically conserving energy for
refrigeration and space cooling in buildings. After the discovery of daytime radiative cooling, a
wide range of materials have been found promising for an 8-13 μm wavelength range emissive
solar reflective cooling device. Here, we consider the thermal selective emitter inspired by the thermoregulatory effect of triangular hairs on Sahara silver ants. FDTD simulations were utilized
to optimize the biomimetic surface made of 8-13 μm wavelength range emissive materials such as
SiO
2 and polydimethylsiloxane (PDMS), and bottom solar mirror, revealing improved emissivity
in the 8-13 μm wavelength range by patterning triangular arrays on the surface. With the optimized
model, we have successfully fabricated bio-inspired daytime passive radiative cooler and this
cooler has a potential to provide 172 W/m
2 net cooling power, more than 40 % increase compared
to that reported previously, and 11 °C temperature reduction below the ambient air temperature
under the direct sunlight. Furthermore, we developed an energy balance mathematical model to
study the potential application of passive radiative coolers in HVAC systems of buildings. Fluid
flows in an isolated loop such that the coolant can be chilled by the radiative cooler and transported
to the demand side for spacing cooling. This leads to the partial replacement of conventional vapor
compression refrigeration by the radiative cooling panel. The cooling performance and indoor air
temperature are evaluated by numerical analysis. The simulation results show that the proposed
passive radiative cooling system with 100 m
2 can retain an indoor temperature maximum to 10 °C
below ambient and produce nearly 1600 W cooling power.
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