Mixed convection and radiation from an isothermal bladed structure

Torres, Juan F.; Ghanadi, Farzin; Wang, Ye; Arjomandi, Maziar; Pye, John

doi:10.1016/j.ijheatmasstransfer.2019.118906

Cited by 25 publications

(8 citation statements)

References 26 publications

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“…48 Even if the macro-scale features are larger than the viscous sublayer, pockets of hot air can be generated between macro-scale protrusions, as in the bladed solar thermal receiver of ref. 49, yielding a reduction in convective heat transfer.…”

Section: Resultsmentioning

confidence: 99%

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Highly efficient and durable solar thermal energy harvesting via scalable hierarchical coatings inspired by stony corals

Torres

Tsuda

Murakami

et al. 2022

Energy Environ. Sci.

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Section: Resultsmentioning

confidence: 99%

“…2a.5) that slightly increases the absorption efficiency. The photo-thermal efficiency includes convection and radiation losses, 43,49 the latter considering measured emittance values (Fig. 3d).…”

Section: Scalability For Commercial Solar Thermal Receiversmentioning

confidence: 99%

Highly efficient and durable solar thermal energy harvesting via scalable hierarchical coatings inspired by stony corals

Torres

Tsuda

Murakami

et al. 2022

Energy Environ. Sci.

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“…2a.5) that slightly increases the absorption e ciency. The photo-thermal e ciency includes convection and radiation losses 33,34 , the latter considering measured emittance values (Fig. 3d).…”

Section: Scalability For Commercial Solar Thermal Receiversmentioning

confidence: 99%

Coral-inspired hierarchical structures for sunlight harvesting

Torres¹,

Tsuda²,

Murakami³

et al. 2021

Preprint

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Concentrating solar thermal (CST) is an efficient renewable energy technology with low-cost thermal energy storage. CST relies on wide-spectrum solar thermal absorbers that must withstand high temperatures (> 700°C) for many years, but state-of-the-art coatings have poor optical stability. Here, we show that the largely overlooked macro-scale morphology is key to enhancing both optical resilience and light trapping. Inspired by stony-coral morphology, we developed a hierarchical coating with three tuneable length-scale morphologies: nano- (~ 120 nm), micro- (~ 3 µm) and macro-scales (> 50 µm). Our coating exhibits outstanding, stable solar-weighted absorptance of > 97.75 ± 0.04% after ageing at 850°C for more than 2,000 hours. The scalability of our coating is demonstrated on a commercial solar thermal receiver, paving the way for more reliable high-performance solar thermal systems. Scleractinia, commonly known as stony corals (Fig. 1a), have evolved their morphology over millions of years to improve their chances of survival. A symbiotic relationship with algae, which need sunlight for photosynthesis, was an evolutionary milestone 240 million years ago that enabled corals to secure nutrients in otherwise infertile waters1 and thrive in all Earth’s oceans. Sunlight attenuation in seawater initially restricted coral colonies to shallow waters2,3. To thrive in deeper waters where light is more scarce, coral morphology4 has evolved to improve light trapping5 via multiple internal light reflections (Fig. 1b, c). We can then learn from stony-coral morphology in engineering and science where light trapping is needed, including sunlight harvesting using concentrating solar thermal (CST) systems6,7. Absorber coatings applied to solar receivers in CST plants have the function of converting concentrated sunlight in a wide-spectrum into thermal energy8 for many applications, including electric power generation (Fig. 1d) 9,10. Importantly, CST incorporates thermal energy storage, a more affordable, scalable, and durable alternative than other well-known storage technologies for long duration energy storage11. A key barrier to the wide adoption of CST, contributing to both increasing cost and reducing performance, is the poor durability of its light-absorbing coatings12. These coatings need to withstand high temperatures (> 700°C) and thousands of thermal cycles over many years of operation13. The best-known CST coatings are spinel-based coatings (Supplementary Note 1) such as Pyromark 2500® (henceforth referred to as Pyromark)14, which is widely considered the gold-standard in the CST industry. These coatings implement an organic binder15 that decomposes during a curing process to produce a nano-textured porous coating with spinel pigments, without macro-scale (> 50 µm) features. Solar-weighted absorptance, the key performance metric16, is typically reported after long-term isothermal exposure at high temperature, with the highest reported values being 94.6% after ageing for 2350 h at 850°C14, 97.2% after aging for 2,000 h at 800°C15, and 96.3% after aging for 3800 h at 770°C13. However, unstable optical performance is generally observed in CST coatings because the elevated temperatures re-arrange the material phases, alter the material composition13, and modify the nano-scale morphology via sintering and crystal grain growth17. Advanced light absorbers made of carbon nanotubes18 and graphene19 can absorb more than 99% of incoming light from every angle, but these coatings burn at the surface temperatures commonly found in conventional receivers20. Most coating research so far has focused on texturing the nano-scale morphology and improving the thermal stability of the materials13,15,21−23, while neglecting the micro- (~ 3 µm) and macro-scale (> 50 µm) geometries24 and the tuning of various length-scale morphologies in the coating to maximise light absorptance. Hierarchical structures have been shown to be a powerful tool to improve radiative cooling in clothing25, as well as mechanical rigidity and stability in sea sponges26. Here, we show that a hierarchical design with coral-inspired micro- and macro-scale features can produce high-temperature solar absorbers with enhanced light absorption and outstanding optical resilience, which we define as the capacity to retain stable optical properties despite material degradation.

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“…Atashafrooz et al (2020) investigated the impact of radiation on forced convection flow in the exhaust problem by comparing the differences between the spectral line WSGG and gray models. Torres et al (2020) used a CFD simulation to understand the characteristics of mixed convection and radiation and to predict thermal losses from an isothermal bladed structure.…”

Section: Introductionmentioning

confidence: 99%

Interaction of mixed convection with non-gray gas radiation in a partially heated horizontal pipe: entropy generation analysis

Mazgar

Jarray

Hajji

et al. 2021

HFF

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Purpose This paper aims to numerically analyze the effect of non-gray gas radiation on mixed convection in a horizontal circular duct with isothermal partial heating from the sidewall. The influence of heater location on heat transfer, fluid flow and entropy generation is given and discussed in this study. Design/methodology/approach The numerical computation of heat transfer and fluid flow has been developed by the commercial finite element software COMSOL Multiphysics. Radiation code is developed based on the T10 Ray-Tracing method, and the radiative properties of the medium are computed based on the statistical narrow band correlated-k model. Findings The obtained results depicted that the radiation considerably contributes to the temperature homogenization of the gas. The findings highlight the impact of the heater location on swirling flow. It is also shown that the laterally heating process provides better energy efficiency than heating from the top of the enclosure. Originality/value This study is performed to improve heat transfer and to minimize entropy generation. Therefore, it is conceivable to improve the model design of industrial applications.

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Mixed convection and radiation from an isothermal bladed structure

Cited by 25 publications

References 26 publications

Highly efficient and durable solar thermal energy harvesting via scalable hierarchical coatings inspired by stony corals

Highly efficient and durable solar thermal energy harvesting via scalable hierarchical coatings inspired by stony corals

Coral-inspired hierarchical structures for sunlight harvesting

Interaction of mixed convection with non-gray gas radiation in a partially heated horizontal pipe: entropy generation analysis

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