Modeling silica aerogel optical performance by determining its radiative properties

Zhao, Lin; Yang, Sungwoo; Bhatia, Bikram; Strobach, Elise; Wang, Evelyn N.

doi:10.1063/1.4943215

Cited by 47 publications

(24 citation statements)

References 35 publications

(40 reference statements)

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“…By describing this behavior via the 1 -D Radiative Transfer Equation, an intrinsic property known as the scattering coefficient, cs, can be defined as the likelihood that an incident photon is scattered. 24 Similarly, during the same calculation the absorption coefficient, 0 a, can be found.…”

Section: Optical Absorption and Scatteringmentioning

confidence: 99%

“…The spectral transmission and reflection data can be related to the intrinsic optical properties, particularly the scattering and absorption coefficients, as described by Zhao et a1 24 to further understand the different effects of annealing. Light scattering is the mechanism by which a path of light is affected by a change in refractive index.…”

Section: Optical Absorption and Scatteringmentioning

confidence: 99%

“…24 Because high transparency aerogel requires small features (relative to the wavelength of interest), often times the pore and particles sizes overlap and this effective scattering radius will represent a weighted light interaction with both features. …”

Section: Optical Scattering Radiusmentioning

confidence: 99%

See 2 more Smart Citations

High temperature annealing for structural optimization of silica aerogels in solar thermal applications

Strobach

Bhatia

Yang

et al. 2017

Journal of Non-Crystalline Solids

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Optically transparent, thermally insulating monolithic silica aerogel, with its high solar transmittance and low thermal conductivity, is well-suited for solar thermal applications, particularly concentrated solar power systems. The properties of silica aerogel are directly determined by the structure of the highly porous, interconnected silica network. By using high temperature annealing to control this structure post-synthesis, we were able to optimize the material to increase solar transmittance using an easy and scalable method.The changes caused by annealing were investigated with respect to both temperature and time to relate the structural change to the optical and thermal performance change. The temperaturedependent study samples were annealed for 1 hour at various temperatures ranging from 400-1000 'C. The time-dependent studies used samples made from two silica aerogel chemistries and were annealed at two temperatures (400 'C and 600 C). In general, lower temperatures and times have less overall change (slower change rates) than higher temperature or longer time annealing. Both annealing studies indicate optical performance has an optimum with respect to annealing time, and additional temperature or time negatively affects optical properties due to appreciable structural change.After the temperature annealing studies were used to understand general trends, the timedependent studies were used to maximize the properties of aerogel for CSP applications. The samples showed an increase in solar spectral transmittance of over 3% while the effective thermal 3 conductivity was shown to increase by as much as 40%, indicating a need to optimize the annealing time for maximum performance. The properties of the characterized aerogels were used to demonstrate aerogel annealing optimization in a concentrated solar power receiver model operating at 400 *C. The model predicted a 1% receiver efficiency increase for an operating temperature of 400 *C by annealing for 24 hours, representing a significant gain in overall system efficiency.

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Section: Optical Absorption and Scatteringmentioning

confidence: 99%

Section: Optical Absorption and Scatteringmentioning

confidence: 99%

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High temperature annealing for structural optimization of silica aerogels in solar thermal applications

Strobach

Bhatia

Yang

et al. 2017

Journal of Non-Crystalline Solids

Self Cite

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“…Also, a transparent buffer layer like Silica aerogel can be filled in the gap to maintain mechanical support. Silica aerogel is made of highly porous Silica with a refractive index close to unity, which also exhibit high melting point [58].…”

Section: Practical Design Considerationsmentioning

confidence: 99%

Thermophotovoltaics with spectral and angular selective doped-oxide thermal emitters

Sakr

Bermel

2017

Opt. Express

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Deliberate control of thermal emission properties using nanophotonics has improved a number of applications including thermophotovoltaics (TPV), radiative cooling and infrared spectroscopy. In this work, we study the effect of simultaneous control of angular and spectral properties of thermal emitters on the efficiencies of TPV systems. While spectral selectivity reduces sub-bandgap losses, angular selectivity is expected to enhance view factors at larger separation distances and hence to provide flexibilities in cooling the photovoltaic converter. We propose a design of an angular and spectral selective thermal emitter based on waveguide perfect absorption phenomena in epsilon-near-zero thin-films. Aluminum-doped Zinc-Oxide is used as an epsilon-near-zero material with a cross-over frequency in the near-infrared. A high contrast grating is designed to restrict the emission in a range of angles around the normal direction, while an integrated filter ensures spectral selectivity to reduce sub-bandgap losses. Theoretical analysis shows an expected relative enhancement of the TPV system efficiency of at least 32% using selective emitters with ideal angular and spectral selectivity at large separation distances compared to a blackbody. This enhancement factor, however, reduces to 3.9% with non-ideal selective emitters. This big reduction of the efficiency is attributed to sub-bandgap losses, off-angular losses and high-temperature dependence of optical constants.

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“…The optical transparency of silica aerogel is tied closely to scattering centres within its microstructure [18]. This transparency, particularly in the solar spectrum, is crucial for many solar related applications [19][20][21][22].…”

Section: Introductionmentioning

confidence: 99%

Tuned optical transmittance in single-step-derived silica aerogels through pH-controlled microstructure

et al. 2017

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We have systematically studied the relationship between synthesis pH and morphological and optical properties of silica aerogels. We have determined through SEM and BET that there is a systematic correlation between the pH of the initial silica solution and the surface area, porosity, and pore size of the resulting aerogel. We find that optical transmittance, particularly its wavelength dependence (dispersion), is strongly governed by the microstructure and, therefore, synthesis pH. We have determined that the microstructure of the aerogels fall into three broad categories: monostructural, which is characterized by repeating elongated microstructural features; fractal, which shows a distinctive structure that is emulated on multiple length scales; and isotropic, which is characterized by having no distinct features in its microstructure. Simply by controlling the pH of the synthesis environment, we can tune the optical properties of silica aerogels through pH controlled the microstructural modification. We have found that pH = 1-5 gives high dispersion, pH = 6-7 results in low transmittance and low dispersion, pH = 8 shows the highest transmittance with the lowest dispersion, and pH = 9-10 transitions back to lower transmittance and higher dispersion.

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Modeling silica aerogel optical performance by determining its radiative properties

Cited by 47 publications

References 35 publications

High temperature annealing for structural optimization of silica aerogels in solar thermal applications

High temperature annealing for structural optimization of silica aerogels in solar thermal applications

Thermophotovoltaics with spectral and angular selective doped-oxide thermal emitters

Tuned optical transmittance in single-step-derived silica aerogels through pH-controlled microstructure

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