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Research Papers: Radiative Heat Transfer

Wavelength-Selective Solar Thermal Absorber With Two-Dimensional Nickel Gratings

[+] Author and Article Information
Bong Jae Lee

Department of Mechanical Engineering,
Korea Advanced Institute of Science and Technology,
Daejeon 305-701, South Korea
e-mail: bongjae.lee@kaist.ac.kr

Yu-Bin Chen

Department of Mechanical Engineering,
National Cheng Kung University,
Tainan City 701, Taiwan
e-mail: ybchen@mail.ncku.edu.tw

Sunwoo Han

Department of Mechanical Engineering,
Korea Advanced Institute of Science and Technology,
Daejeon 305-701, South Korea

Feng-Cheng Chiu

Department of Mechanical Engineering,
National Cheng Kung University,
Tainan City 701, Taiwan

Hyun Jin Lee

Department of Solar Energy,
Korea Institute of Energy Research,
Deajeon 305-343, South Korea

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 16, 2013; final manuscript received February 23, 2014; published online March 26, 2014. Assoc. Editor: He-Ping Tan.

J. Heat Transfer 136(7), 072702 (Mar 26, 2014) (7 pages) Paper No: HT-13-1206; doi: 10.1115/1.4026954 History: Received April 16, 2013; Revised February 23, 2014

The direct utilization of solar radiation has been considered a promising energy source because of its abundance, sustainability, and cleanness. The conversion of solar radiation into usable heat largely depends on the absorption characteristics of a solar thermal collector. In the present study, we conducted design analysis of a wavelength-selective absorber composed of a two-dimensional Nickel grating, a thin SiO2 film, and a Nickel substrate. Dimensions of the two-dimensional grating were determined with the Taguchi method, which optimized the spectral absorptance for both polarizations. The spectral absorptance demonstrated a broad-band plateau within the visible and the near-infrared spectral region, but it was significantly suppressed at longer wavelengths. Moreover, the absorptance plateau was nearly insensitive to the incident orientation of solar radiation. Physical mechanisms of the absorption enhancement were elucidated with the local magnetic field distribution.

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Figures

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Fig. 1

(a) Schematic of one period of a 2-D Ni grating with a SiO2 film on a Ni substrate; and (b) Convergence test of RCWA

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Fig. 2

(a) Direct solar irradiance at air mass 1.5 [27] (in the primary y-axis) and the polarization-averaged absorptance of the absorber 4441 and a plane Ni surface at θ = 20 deg and ϕ = 0 deg (in the secondary y-axis). Dimensions of the absorber 4441 are Λ = 600 nm, f = 0.85, dg = 400 nm, and df = 100 nm; and (b) comparison of absorptance of the absorber 4441 (dashed line) with that of the absorber 4441 without SiO2 film (solid line) for TE (upper panel) and TM wave (lower panel).

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Fig. 3

Directional absorptance of the absorber 4441 with respect to θ at 500 nm and 1000 nm. In both cases, ϕ = 0 deg.

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Fig. 4

Absorptance spectra of the absorber 4441 for unpolarized incidence with θ = 20 deg at ϕ = 0 deg (dashed line) and ϕ = 45 deg (solid line)

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Fig. 5

Square of the parallel component of magnetic field normalized to that of incident field at the interface between SiO2 and the substrate (refer to inset): (a) TM wave at 440 nm (αλ = 0.912); (b) TM wave at 970 nm (αλ = 0.999); (c) TE wave at 470 nm (αλ = 0.921); and (d) TE wave at 990 nm (αλ = 0.999). Gray line represents the location underneath the hollow region of concave grating.

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Fig. 6

Comparison of the absorptance spectra of three different concave-grating structures at: (a) TM-wave incidence; and (b) TE-wave incidence

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Fig. 7

Separate contribution of the grating region and substrate region to the absorptance of the optimized grating: (a) TM-wave incidence; and (b) TE-wave incidence at θ = 20 deg and ϕ = 0 deg. For comparison purpose, the absorptance of plane Ni surface is also plotted for both polarizations at θ = 20 deg.

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