Temperature- and Angle-Dependent Emissivity and Thermal Shock Resistance of the W/WAlN/WAlON/Al₂O₃-Based Spectrally Selective Absorber

Abstract

Spectral emissivity is considered as one of the most critical thermophysical properties influencing photothermal conversion efficiency of solar selective absorbers. In addition, long-term stability at high temperature and thermal shock resistance are the performance-limiting properties of spectrally selective absorbers. In this context, this study reports the variation of emissivity with a change in emergence angles and operational temperatures for the newly developed W/WAlN/WAlON/ Al 2 O 3 absorber. An analysis of the experimental results demonstrates that hemispherical emissivity values at elevated temperature are comparable while calculated using both room temperature and high temperature reflectance data. Hence, the applicability of the room temperature measurement method is validated to evaluate high temperature emissivity. The analysis of angular measurements indicates an insignificant difference between hemispherical and near-normal emissivity values for W/WAlN/WAlON/Al 2 O 3 . The study suggests that hemispherical emissivity can be well approximated from near-normal emissivity values by avoiding complex angular measurement procedure. Importantly, one can achieve a combination of high solar absorptance (α = 0.90), low thermal emittance (ε = 0.15), and appreciable heliothermal efficiency (η = 87% at a concentration factor of 100) at 500 °C for the W/WAlN/WAlON/Al 2 O 3 absorber. Thermal stability of this absorber was established by observing an insignificant change in the reflectance spectra while annealed at 80, 200, 300, and 400 °C. In addition, thermal cycling test for 30 times between room temperature and 450 °C in a high flux (40−60 kW/m 2 ) solar simulator confirmed the efficacy of W/WAlN/WAlON/Al 2 O 3 as a promising multilayer solar absorber for high temperature applications.

Near-perfect spectrally-selective metasurface solar absorber based on tungsten octagonal prism array

“…44 According to eqn (8), perfect spectral absorptivity (a l ) can be achieved when the effective impedance z l is matched to the impedance of the free space (z 0 ), as shown in eqn (9). In addition, near-zero absorptivity will be achieved when eqn (10) is met.…”

Toward a Scalable and Cost-Conscious Structure in Spectrally Selective Absorbers: Using High-Entropy Nitride TiVCrAlZrN

“…Among these technologies, solar thermal power generation, particularly concentrated solar power (CSP), exhibits great application prospects in addressing the pressing energy crisis, enabling a continuous energy supply day and night. The spectrally selective absorber (SSA) plays a decisive role in the CSP system, which simultaneously requires a high solar absorptance (α > 90%) in the wavelength range of 0.3–2.5 μm and a low thermal emittance (ε < 10%) in the infrared region (2.5–25 μm) . It has been reported that the photothermal conversion efficiency of the SSA could be highly enhanced by advancing the spectral selectivity (α/ε) at a specific concentration ratio .…”

“…The spectrally selective absorber (SSA) plays a decisive role in the CSP system, which simultaneously requires a high solar absorptance (α > 90%) in the wavelength range of 0.3− 2.5 μm and a low thermal emittance (ε < 10%) in the infrared region (2.5−25 μm). 11 It has been reported that the photothermal conversion efficiency of the SSA could be highly enhanced by advancing the spectral selectivity (α/ε) at a specific concentration ratio. 12 Furthermore, to meet the practical photothermal conversion applications, thermal stability of the involved SSA is required to provide energy under operating conditions for a prolonged duration.…”

Refractory Ultrathin Nanocomposite Solar Absorber with Superior Spectral Selectivity and Thermal Stability

“…[ 5,6 ] In recent years, significant efforts have been made in developing selective solar absorber coatings for mid‐temperature (370 K < T < 650 K) [ 7 ] to high‐temperature ( T > 650 K) applications. [ 8 ] The popular designs include plasmonic metamaterials, [ 9 ] non‐resonant carbon‐based structures, [ 10,11 ] and metal‐dielectric composites such as, MoSi 2 ‐Si 3 N 4 , [ 12 ] W‐WAlN‐WAlON‐Al 2 O 3 , [ 13 ] and WNi‐Al 2 O 3 . [ 8 ] Nevertheless, the tedious lithographic techniques to fabricate metamaterials, high infrared emissivity of carbon materials, and limited thermal/oxidation tolerance of multilayer cermet impede their utilization in real applications.…”