TY - JOUR
T1 - The impact of dispersed nanoparticles on long wavelength heat radiation through opaque and transparent passive cooling skylight glass
AU - Gangisetty, Gopalakrishna
AU - Smått, Jan-Henrik
AU - Zevenhoven, Ron
PY - 2024/6/13
Y1 - 2024/6/13
N2 - Selecting materials for passive radiative cooling (PRC) skylights is crucial, but finding affordable options for widespread use is challenging. Åbo Akademi University (ÅAU) introduced a passive skylight enhancing heat transfer through thermal convection and radiation, effective at night but challenging for daytime use. Dispersions of randomly distributed TiO
2-SiO
2 or ZnS-SiO
2 nanoparticles (NPs) were used on conventional window glasses (WG) and on long-wavelength (LW) translucent Cleartran® ZnS glasses (CG®) to control the surface temperature and absorptivity (α)/emissivity (ε) at different heat source temperatures. The tested NPs are known for their optical properties underwent testing via capturing IR imaging with a thermal camera (wavelength: 7.5-14 μm) and pyrgeometer (wavelength: 4.5-42 μm). LW heat flux measurements through the glass samples were taken on conventional WGs and CG®s, each with randomly dispersed NPs on one side, with the thermal camera or pyrgeometer positioned at different distances from the heat source. The data analysis compared heat fluxes from the different distances, forming the basis for determining glass sample LW emissivities via a mathematical model. Additionally, scanning electron microscope (SEM) analysis conducted on WG samples allowed for precise determination of NP quantity (in g/m²) and NP surface coverage (%). The results showed an average of 0.25 mg/m² for TiO
2-SiO
2 NPs and 0.3 mg/m² for ZnS-SiO
2 NPs, with surface coverages approximate . Although conventional WG glass exhibited a heat flux increase when using NPs of 2 to 4 times, CG® indicated only marginal change by the NPs. The findings indicate that a larger quantity, possibly five times the current amount of NPs, may be required. Further, Vis-NIR spectrophotometry measures reflectance and transmittance in the 0.25-2.5 m range for all WGs with NPs and without NPs for comparison. Maximum reflectance is 4.20% with TiO
2 SiO
2 NPs and 1.50 % with ZnS-SiO
2 NPs, while transmittance is 69.6% with TiO
2 -SiO
2 NPs and 85.5 % with ZnSSiO
2 ZnSSiO
2 NPs. Solar Reflective Index (SRI) quantifies solar radiation reflection, with maximum SRI being 70.5 with TiO
2 -SiO
2 NPs and 68.2 with ZnS-SiO
2 NPs.
AB - Selecting materials for passive radiative cooling (PRC) skylights is crucial, but finding affordable options for widespread use is challenging. Åbo Akademi University (ÅAU) introduced a passive skylight enhancing heat transfer through thermal convection and radiation, effective at night but challenging for daytime use. Dispersions of randomly distributed TiO
2-SiO
2 or ZnS-SiO
2 nanoparticles (NPs) were used on conventional window glasses (WG) and on long-wavelength (LW) translucent Cleartran® ZnS glasses (CG®) to control the surface temperature and absorptivity (α)/emissivity (ε) at different heat source temperatures. The tested NPs are known for their optical properties underwent testing via capturing IR imaging with a thermal camera (wavelength: 7.5-14 μm) and pyrgeometer (wavelength: 4.5-42 μm). LW heat flux measurements through the glass samples were taken on conventional WGs and CG®s, each with randomly dispersed NPs on one side, with the thermal camera or pyrgeometer positioned at different distances from the heat source. The data analysis compared heat fluxes from the different distances, forming the basis for determining glass sample LW emissivities via a mathematical model. Additionally, scanning electron microscope (SEM) analysis conducted on WG samples allowed for precise determination of NP quantity (in g/m²) and NP surface coverage (%). The results showed an average of 0.25 mg/m² for TiO
2-SiO
2 NPs and 0.3 mg/m² for ZnS-SiO
2 NPs, with surface coverages approximate . Although conventional WG glass exhibited a heat flux increase when using NPs of 2 to 4 times, CG® indicated only marginal change by the NPs. The findings indicate that a larger quantity, possibly five times the current amount of NPs, may be required. Further, Vis-NIR spectrophotometry measures reflectance and transmittance in the 0.25-2.5 m range for all WGs with NPs and without NPs for comparison. Maximum reflectance is 4.20% with TiO
2 SiO
2 NPs and 1.50 % with ZnS-SiO
2 NPs, while transmittance is 69.6% with TiO
2 -SiO
2 NPs and 85.5 % with ZnSSiO
2 ZnSSiO
2 NPs. Solar Reflective Index (SRI) quantifies solar radiation reflection, with maximum SRI being 70.5 with TiO
2 -SiO
2 NPs and 68.2 with ZnS-SiO
2 NPs.
KW - passive cooling
KW - skylight
KW - Nanoparticle
KW - heat radiation
U2 - 10.11159/jffhmt.2024.010
DO - 10.11159/jffhmt.2024.010
M3 - Article
SN - 2368-6111
VL - 11
SP - 91
EP - 105
JO - Journal of Fluid Flow, Heat and Mass Transfer
JF - Journal of Fluid Flow, Heat and Mass Transfer
ER -