PASSIVE RADIATIVE COOLING USING OPICAL THIN FILM COATINGS

Muhammed Ali Keçebaş
Mechatronics Engineering, MSc. Thesis, 2016

Thesis Jury

Assoc. Prof. İbrahim Kürşat Şendur (Thesis Advisor), Assoc. Prof. Burç Mısırlıoğlu, Asst. Prof. Erdem Öğüt.

Date & Time: 28th July, 2016 –  10:00 AM

Place: FENS G029

Keywords : Thin Films, Nanophotonics, Optical Behaviors, Radiative Cooling

Abstract

Radiative cooling is a passive way of cooling by which a body loses heat by emitting energy. When a body is exposed to sky, heat transfer between the body and sky occurs depending on transparency of the atmosphere through radiation. During nighttime, due to extremely low incident solar irradiation, cooling can be achieved. However, to achieve radiative cooling during daylight, incident solar energy has to be reflected strongly which prevents heating of the object. Also, by maximizing emission in the atmospheric transparency window in 8-13 µm range, in which very low amount of solar energy is carried, radiative cooling can be achieved.

In this study, design studies about thin film filters are carried out. The main goal is to achieve high reflection in the visible and near-infrared spectrums in which high amount of solar energy is present and maximize absorption/emissivity in 8-13 µm spectrum where atmospheric transparency window is present. For these purposes, different design methods are examined, e.g. quarter wavelength stacks for high reflection and an impedance matching technique, Chebyshev transform, is used to increase emission in 8-13 µm spectrum. For the performance evaluations, radiative heat transfer dynamics are examined and cooling powers are compared with a design results given in the literature. It is observed that significant performance improvement can be observed by proposed design methods.