Multilayer Selective Passive Daytime Radiative Cooler Optimization Utilizing Memetic Algorithm

Abstract

수동복사냉각(Passive Daytime Radiative Cooling; PDRC)은대기의창(Trans-parent Atmospheric Windows; TAWs)를통해우주로열을방출하는시스템이다.많은구조들이수동복사냉각을 이루기위해제안되었지만, 8-13μm (first TAW, i.e., TAW1)과16-26μm (second TAW, i.e., TAW 2)대역에서높은방사율을달성하는것은어려운일이다.이논문에서는TAW 1에서각각최대99 %와98 %의방사율을가진Design 1과Design 2라는총2가지의PDRC (Passive Daytime Radiative Cooler)후보군을제시한다. Design 1은TAW 1만을고려하여계산된반면Design 2는TAW 1과TAW 2를모두고려하여계산되었다.두디자인모두3층의 유전체(SiN, SiC, SiO2)과금속(Ag)으로구성된다. “Memetic Algorithm”(MA)이라는유전알고리즘을사용하여유전체의최적의두께를계산하였다.유전체들의종류는MA에의해TAW 1의흡수파장대가서로겹치지않고서로간섭이없는형태로선택되어최소두께로대기의창영역에서높은선택적방출을얻게끔한다.이러한최적화기술은용도에PDRC를설계에있어서새로운패러다임이될수있다.또한Design 1과2라는선택적방출기는비복사열교환계수hc가0 Wm`2K`1일때각각열적평형상태에서100.72 Wm−2및112.27 Wm−2의냉각전력을가지기때문에49.8 K및44 K의냉각온도를보인다.이연구에서제시하는에미터는1D평면구조이다.따라서쉽게접할수있는물질들로제작할수있기때문에대규모샘플제작에더적합하다는장점이존재한다.|Passive Daytime Radiative Cooling (PDRC) process radiates excess heat by dumping heat into space through Transparent Atmospheric Windows (TAWs). Many structures are proposed for the PDRC but their main constraint is achieving near unity selective emission over 8-13 µm (first TAW, i.e., TAW 1) and 16-26 µm (second TAW, i.e., TAW 2) wavelength regions. In this paper, we have presented two Passive Daytime Radiative Coolers (PDRCs) referred as Design 1 and Design 2 which have respectively maximum 99% and 98% emissivity in TAW 1. While Design 1 is simulated considering only TAW 1, Design 2 is found acknowledging both TAW 1 and TAW 2. Both the models consist of three dielectric layers (i.e., SiN, SiC and SiO2) and a metal (i.e., Ag) back reflector. A genetic algorithm named” Memetic Algorithm” (MA) is utilized to identify the dielectric materials and determine their optimum thickness. The dielectric materials are selected by MA in such a way that their absorption peaks in the TAW 1 do not overlap and destructively interfere with each other, which in turn helps to obtain a high selective emission in that particular window with minimum thickness. This technique can be a new paradigm in designing PDRCs via tailoring material configuration. Additionally, the selective emitters are capable of providing a cooling temperature of 49.8 K and 44 K with a cooling power of 100.72 Wm−2 and 112.27 Wm−2 at equilibrium respectively for Design 1 and 2 when non-radiative heat exchange coefficient hc is 0 Wm−2K−1 and the studied wavelength range is in between 0.3 to 30 µm. The proposed emitters have only 1D planar layers. Therefore, they can be fabricated with promptly accessible materials which make them a better candidate for large scale fabrication.