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Title: Bidirectional reflection of semitransparent polytetrafluoroethylene (PTFE) sheets on a silver film

Abstract

In our recent work, record-high solar reflectance (exceeding 99%) has been demonstrated by placing a layer of highly scattering, semitransparent polytetrafluoroethylene (PTFE) sheet on top of a silver film. This can significantly improve the performance of daytime radiative cooling system. Although a PTFE slab of 10-mm thick acts as an excellent diffuse reflector, it is unclear how this dual-layer structure made of a thin PTFE on a mirror-like reflector will alter the bidirectional reflection. Here, we report measurements of the bidirectional reflectance distribution function (BRDF) of the dual-layer structure using a laser scatterometer at the wavelength of 635 nm. Measurements of the BRDF and the bidirectional transmittance distribution function (BTDF) of free-standing PTFE sheets are also performed. The measured BRDF for a PTFE sheet as thin as 236 μm on Ag is essentially diffuse except at large incidence angles. A Monte Carlo ray-tracing method incorporating both surface scattering and volumetric scattering is developed to theoretically model the BRDF in order to elucidate the underlying mechanisms. Finally, the numerical model captures the main features and can be used to study the bidirectional properties for PTFE sheets thinner than what is experimentally available.

Authors:
 [1];  [1]
  1. Georgia Inst. of Technology, Atlanta, GA (United States)
Publication Date:
Research Org.:
Georgia Inst. of Technology, Atlanta, GA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
OSTI Identifier:
1594790
Alternate Identifier(s):
OSTI ID: 1580181
Grant/Contract Number:  
SC0018369; CBET-1603761
Resource Type:
Accepted Manuscript
Journal Name:
International Journal of Heat and Mass Transfer
Additional Journal Information:
Journal Volume: 148; Journal Issue: C; Journal ID: ISSN 0017-9310
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; bidirectional reflectance distribution function; polytetrafluoroethylene; solar reflector; surface roughness; volume scattering

Citation Formats

Yang, Peiyan, and Zhang, Zhuomin M. Bidirectional reflection of semitransparent polytetrafluoroethylene (PTFE) sheets on a silver film. United States: N. p., 2019. Web. doi:10.1016/j.ijheatmasstransfer.2019.118992.
Yang, Peiyan, & Zhang, Zhuomin M. Bidirectional reflection of semitransparent polytetrafluoroethylene (PTFE) sheets on a silver film. United States. doi:10.1016/j.ijheatmasstransfer.2019.118992.
Yang, Peiyan, and Zhang, Zhuomin M. Thu . "Bidirectional reflection of semitransparent polytetrafluoroethylene (PTFE) sheets on a silver film". United States. doi:10.1016/j.ijheatmasstransfer.2019.118992.
@article{osti_1594790,
title = {Bidirectional reflection of semitransparent polytetrafluoroethylene (PTFE) sheets on a silver film},
author = {Yang, Peiyan and Zhang, Zhuomin M.},
abstractNote = {In our recent work, record-high solar reflectance (exceeding 99%) has been demonstrated by placing a layer of highly scattering, semitransparent polytetrafluoroethylene (PTFE) sheet on top of a silver film. This can significantly improve the performance of daytime radiative cooling system. Although a PTFE slab of 10-mm thick acts as an excellent diffuse reflector, it is unclear how this dual-layer structure made of a thin PTFE on a mirror-like reflector will alter the bidirectional reflection. Here, we report measurements of the bidirectional reflectance distribution function (BRDF) of the dual-layer structure using a laser scatterometer at the wavelength of 635 nm. Measurements of the BRDF and the bidirectional transmittance distribution function (BTDF) of free-standing PTFE sheets are also performed. The measured BRDF for a PTFE sheet as thin as 236 μm on Ag is essentially diffuse except at large incidence angles. A Monte Carlo ray-tracing method incorporating both surface scattering and volumetric scattering is developed to theoretically model the BRDF in order to elucidate the underlying mechanisms. Finally, the numerical model captures the main features and can be used to study the bidirectional properties for PTFE sheets thinner than what is experimentally available.},
doi = {10.1016/j.ijheatmasstransfer.2019.118992},
journal = {International Journal of Heat and Mass Transfer},
number = C,
volume = 148,
place = {United States},
year = {2019},
month = {11}
}

Journal Article:
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This content will become publicly available on November 14, 2020
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