Session: 08-04-02: Sustainable Energy Systems for Heating and Cooling

Paper Number: 120260

120260 - Efficient Radiative Cooling of Low-Cost Baso4 Nanoparticle-Paper Dual-Layer Thin Films 

In 2019, the World Economic Forum reported that greenhouse gas emissions from air conditioning technologies will account for as much as a 0.5 degree Celsius increase in global temperatures by the end of the century. These traditional air conditioning technologies not only contribute to global warming – they are inaccessible to as much as 92% of the world’s population, and extreme heat conditions are predicted to kill 255,000 people annually by 2050 according to the World Health Organization. As sustainable air conditioning has clearly acquired a crucial role in fighting climate change and its effects, radiative cooling, a highly promising passive cooling phenomenon, has been chosen to develop several state-of-the-art air conditioning alternative technologies in the past few decades for its versatility, environmental friendliness, and accessibility. By utilizing the large temperature differential between the few degrees of deep space and 300 K of a surface on earth, radiative cooling allows for an energy transfer to occur. This effectively allows for the treatment of deep space as a blackbody, and by utilizing the atmospherically transparent “sky window” of 8-13 microns,  up to 150 W/m² of thermal energy may be emitted into deep space and another 1000 W/m² of solar irradiation reaching the earth’s surface can be reflected. This creates an effect of cooling the surface on earth.

Many materials have been explored for the purpose of creating structures with high radiative cooling potential, such as nanocellulose based structures which are environmentally friendly, and nanoparticle-based coatings which have shown the highest reported solar reflectance in current literature. However, they each have their own advantages and disadvantages. In nanocellulose based structures, it is known that the material has an absorption peak in the UV wavelengths, giving it a lower total solar reflectance and reducing its radiative cooling potential. However, the interwoven-fiber structure of cellulose gives high mechanical strength. In nanoplatelet based coatings, the applications are limited due to the high volume concentration of nanoparticle need to reach their signature high solar reflectance, therefore weakening the polymer matrix and creating more brittle structures. This work will study several cellulose-based structures and combine these with radiative cooling paints in dual layer thin films, composed of of cellulose based cotton paper or cellulose acetate and a thin top layer of nanoparticle-based coating. This allows for maximizing both radiative cooling potential and mechanical strength. Total solar reflectance was improved from 80% for the cotton paper to 93% with only 125 microns of paint top layer. Experimental and theoretical thickness vs. reflectance studies are conducted for the top coating layer while maintaining a consistent control of the thickness of the bottom layer. This allows for identifying the point of saturation in this relationship and ideal thickness for the top-layer to maximize material use efficiency, which in this dual-layer system was demonstrated with increased cooling performance of an estimated 149.6 W/m² through the improved total solar reflectance.

 

Presenting Author: Andrea Felicelli Purdue University

Presenting Author Biography: Andrea Felicelli is a PhD student in Mechanical Engineering at Purdue University, working in the laboratories of Professor Xiulin Ruan and Professor George Chiu. Her work focuses on development, manufacturing, and bio-inspiration of nanocomposites and multifunctional materials with applications in cooling technologies.

Authors:

Andrea Felicelli Purdue University
Xiulin Ruan Purdue University
George Chiu Purdue University
Jie Wang Purdue University
Endrina Forti Purdue University
Sami El Awad Azrak Purdue University
Joseph Peoples Purdue University
Jeffrey Youngblood Purdue University