Experimental study on the kinetics of water vapor sorption on the inner surface of silica nano-porous materials

Hu, Zhang; Gu, Wei; Li, M.J.; Li, Z.Y.; Hu, Zhiqiang; Tao, Wen‐Quan

doi:10.1016/j.ijheatmasstransfer.2014.07.047

Cited by 37 publications

(20 citation statements)

References 46 publications

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“…Silica aerogels are intrinsically hydrophilic and can adsorb 5-15 wt% water in ambient conditions. 29 Annealing the aerogel samples for a sufficiently long time and at high temperatures drives out adsorbed water and decreases water absorption and overall density, resulting in higher transmission. When the sample is left to rest in ambient conditions, it readsorbs water from the atmosphere which reduces the overall transmittance.…”

Section: Optical Property Change With Annealing Timementioning

confidence: 99%

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 Property Change With Annealing Timementioning

confidence: 99%

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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“…Since the thermal conductivity of water is much higher than that of the nano-porous material of aerogel, the adsorbed water film will enhance heat transfer in the material, and the thermal insulation performance of the nano-porous material deteriorates. By experimental study, Zhang et al [49] demonstrated that the data of kinetic water vapor adsorption process in the silica nano-porous materials can be well fitted by an exponential-decay-2 model. Temperature and relative humidity of the moist air at ambient pressure are the two dominant factors that affect the adsorption extent and rate.…”

Section: Effect Of Water Vapor Adsorptionmentioning

confidence: 99%

“…Consequently, the specific extinction coefficient can be obtained by Beer's law E s ðTÞ ¼ ÀlnðR d ðwi/wjÞÞ=Lr ae (49) where L is the thickness and r ae is the density of bulk aerogel. The major restriction of the Monte Carlo method for porous media is that it requires the characteristic scale to be large enough compared to the wavelength of the incoming radiation, so that the rules of geometric optics can be applied [100].…”

Section: Numerical Simulationmentioning

confidence: 99%

“…Firstly, according to the environment temperature and humidity, one can calculate the water content in nano-porous material by adsorption equations [67,68], such as Langmuir equation, BET equation, Pseudo model, exponential-decay-2 model, and details of water adsorption in silica nano-porous material can be found in Ref. [49]. Secondly, it is simply assumed that the adsorbed liquid water forms a liquid film attached to the surface of solid backbone [48,51], as schematic in Fig.…”

Section: Numerical Modelmentioning

confidence: 99%

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Thermal transport in nano-porous insulation of aerogel: Factors, models and outlook

Tang

Zhao

et al. 2015

Energy

Self Cite

177

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“…Water and silica are two molecular systems, whose interactions manifest on geological timescales in rock and clay in the Earth crust geosphere, chemical formulations of tablets for drug delivery, concrete, lubricants, and in thermal heat transfer systems, amongst many others. 1 Silica water interactions can lead to the formation of astrochemical grains, 2 where it is postulated, that the first organic compounds were processed. Silica can take many forms and its interaction with water can change dramatically.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Microporous Silica Nanoparticles to Study Water Phase Transitions by Vibrational Spectroscopy

Rosenberg¹,

Alayoǧlu²,

Kostecki³

et al. 2019

Preprint

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Microporous silica nanoparticles have been developed by a reverse microemulsion method utilizing zinc nanoclusters encapsulated hydroxyl-terminated polyamidoamine (PAMAM-OH) dendrimers as a soft template and made tunable within the outer diameter range of 20-50 nm with a core mesopore of 2-15 nm. Synthesized nanoparticles were used to study the effects of surface area and microporous volumes on the vibrational spectroscopy of water. These spectra reveal contributions from bulk interfacial/interparticle water, ice-like surface water, liquid-like water, and hydrated silica surfaces suggesting that microporous silica nanoparticles allow a way to probe silica water interactions at the molecular scale.

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Experimental study on the kinetics of water vapor sorption on the inner surface of silica nano-porous materials

Cited by 37 publications

References 46 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

Thermal transport in nano-porous insulation of aerogel: Factors, models and outlook

Synthesis of Microporous Silica Nanoparticles to Study Water Phase Transitions by Vibrational Spectroscopy

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