Optically Transparent Thermally Insulating Silica Aerogels for Solar Thermal Insulation

2018-04-01
Günay, Ahmet Alperen
Kim, Hannah
Nagarajan, Naveen
Lopez, Mateusz
Kantharaj, Rajath
Alsaati, Albraa
Marconnet, Amy
Lenert, Andrej
Miljkovic, Nenad
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This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
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Rooftop solar thermal collectors have the potential to meet residential heating demands if deployed efficiently at low solar irradiance (i.e., 1 sun). The efficiency of solar thermal collectors depends on their ability to absorb incoming solar energy and minimize thermal losses. Most techniques utilize a vacuum gap between the solar absorber and the surroundings to eliminate conduction and convection losses, in combination with surface coatings to minimize reradiation losses. Here, we present an alternative approach that operates at atmospheric pressure with simple, black, absorbing surfaces. Silica based aerogels coated on black surfaces have the potential to act as simple and inexpensive solar thermal collectors because of their high transmission to solar radiation and low transmission to thermal radiation. To demonstrate their heat-trapping properties, we fabricated tetramethyl orthosilicate-based silica aerogels. A hydrophilic aerogel with a thickness of 1 cm exhibited a solar-averaged transmission of 76% and thermally averaged transmission of approximate to 1% (at 100 degrees C). To minimize unwanted solar absorption by O-H groups, we functionalized the aerogel to be hydrophobic, resulting in a solar-averaged transmission of 88%. To provide a deeper understanding of the link between aerogel properties and overall efficiency, we developed a coupled radiative-conductive heat transfer model and used it to predict solar thermal performance. Instantaneous solar thermal efficiencies approaching 55% at 1 sun and 80 degrees C were predicted. This study sheds light on the applicability of silica aerogels on black coatings for solar thermal collectors and offers design priorities for next-generation solar thermal aerogels.
https://hdl.handle.net/11511/92746
ACS APPLIED MATERIALS & INTERFACES
Department of Mechanical Engineering, Article

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Citation Formats
A. A. Günay et al., “Optically Transparent Thermally Insulating Silica Aerogels for Solar Thermal Insulation,” ACS APPLIED MATERIALS & INTERFACES, vol. 10, no. 15, pp. 12603–12611, 2018, Accessed: 00, 2021. [Online]. Available: https://hdl.handle.net/11511/92746.
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