The traditional telecommunications band performs poorly in harsh weather conditions due to atmospheric absorption. In recent years, researchers have begun to study optical communication through ...atmospheric windows, and optical switches are an essential component of optical communication. A broadband atmospheric window optical switch was proposed based on Vanadium dioxide and magnetic polaritons (MP). It is formed by the stacking of two metal-dielectric-metal structures. The simulation results show that the modulation depth can reach 98.38%, and the extinction ratio is 17.93 dB. By calculating the magnetic field, we confirmed that the reason for the “off” mode is the coupling between the different MP modes, while the “on” mode is the excitation of MP. The optical switch we proposed may be applied to radiation cooling and optical satellite communication.
Abstract
The burning of fossil fuels in industry results in significant carbon emissions, and the heat generated is often not fully utilized. For high-temperature industries, thermophotovoltaics ...(TPVs) is an effective method for waste heat recovery. This review covers two aspects of high-efficiency TPV systems and industrial waste heat applications. At the system level, representative results of TPV complete the systems, while selective emitters and photovoltaic cells in the last decade are compiled. The key points of components to improve the energy conversion efficiency are further analyzed, and the related micro/nano-fabrication methods are introduced. At the application level, the feasibility of TPV applications in high-temperature industries is shown from the world waste heat utilization situation. The potential of TPV in waste heat recovery and carbon neutrality is illustrated with the steel industry as an example.
Highlights
The state of the art of the thermophotovoltaic (TPV) generation on heat recovery is highlighted.
At the system level, representative results of TPV systems and components are compiled.
At the application level, feasibility of TPV in high-temperature industrial applications is exhibited.
Key points of TPV systems to improve energy conversion efficiency are further analyzed.
Monolayer graphene has poor absorption in the near-infrared region. Its layer is only as thick as a single atom so it cannot have a high absorptivity. In this paper, in order to form a hybrid system, ...the absorption characteristics of monolayer graphene covering a metal/dielectric/metal substrate has been theoretically analyzed. The magnetic polaritons in the metal/dielectric couple with the plasmonic resonance in the graphene to dramatically enhance the graphene absorptivity. This study analyzes the factors that enhance the absorptivity, including the geometric parameters and the relative positions of the graphene. The local electromagnetic field and the power dissipation density are illustrated to explain the underlying mechanisms further. These numerical results can provide potential application in the field of optical detection and optoelectronic devices.
The splitting of carbon dioxide through the two-step solar thermochemical cycle presents enormous potential, for it holds the dual functionalities of solar fuel production and carbon-based energy ...recovery. However, the industrialization of this technology is impeded by two critical factors: The absence of fully developed oxygen carriers and advanced reaction devices that deliver exceptional performance. In order to identify a potentially effective oxygen carrier, 50 wt% NiO-modified CoFe
2
O
4
is selected as the active component and characterized by means of thermogravimetry, scanning electron microscopy, and energy dispersive spectroscopy, so as to clarify its oxygen exchange capacity, micromorphology and elemental composition in high-temperature thermochemical cycles. Further, nanoparticle-coated foam-structured materials are prepared in combination with SiC ceramic foam for experimental testing in a high-flux solar reactor. The results indicate that a peak CO yield of 1.96 mL min
−1
g
−1
can be gained in a 1500–1250 K preliminary test, demonstrating the application potential of the material. In contrast to conventional redox materials, the CO
2
activity of the materials synthesized in this study exhibits an enhancement with rising oxidation temperature. It means that isothermal cycles can potentially achieve higher conversion and fuel yield than non-isothermal cycles, while simultaneously reducing the amount of irreversible heat loss during high-temperature cycling. Although the estimated steady-state thermal efficiency of the solar reactor can reach up to 42%, further optimization of the reactor design is necessary to enhance energy conversion efficiency, as it is partially limited by the dimensions of the reaction chamber.
A graphene covered on square-ring structure is designed and fabricated to achieve narrow band absorption of three peaks in the infrared band. The absorption rates of graphene/square-ring structures ...calculated by simulation are 90.49%, 65.67% and 20.38%, respectively, and the experimentally measured absorption rates are 82.12 %, 53.13 %, and 16.58 %, respectively. Comparing the absorption rate of simulation calculation with experimental measurement, as well as the reasons for the differences are presented. The dynamic control characteristics of the graphene device are not observed with this structure in the experiment, which is different from the simulation. We analyzed the reason for this distinction and proposed three solutions based on the experimental design. The research results of this paper provide an important reference to the design and preparation of graphene devices.
This study investigated the catalytic pyrolysis of waste polyethylene (PE) using a ZSM-5/Al2O3 porous media catalyst in a continuous feeding mode. The findings revealed that the porous media catalyst ...with 100 mm height and 40 PPI (pore per inch) pore size had the supreme catalytic performance, which could obtain the highest pyrolysis oil yield and the light fraction (<C12) and aromatics in the oil, and improve the catalytic stability of the porous media catalyst. The optimal operating conditions were the pyrolysis temperature of 460 °C, the carrier gas velocity of 65 mL/min, and the plastic feeding rate of 25 g/h, of which the light fraction and aromatics in the oil were up to 95.25 % and 97.33 %. Moreover, the catalytic cycling performance of the porous media catalyst was thoroughly investigated. The catalytic activity declined and the catalyst deactivation rate decreased after multiple regeneration cycles. This study presents a comprehensive investigation of waste PE catalytic cracking using the porous media catalyst in continuous feeding mode, which can provide insightful guidance on the industrialization of plastic waste valorization.
•Plastic waste was continuously pyrolyzed in the structured ZSM-5/Al2O3 catalyst.•Operating conditions and catalyst cycling performance were thoroughly studied.•The synthesized porous media catalyst with 40 PPI has the optimal performance.•The light fraction and aromatics in oil were up to 95.25 % and 97.33 %.
•A novel medium-high temperature PBLHS system is designed and constructed.•The thermal efficiency of the initial stage of the heat storage and release process is higher.•The overall efficiency of the ...PBLHS system based on binary nitrate is 79.3%.•The temperature and flow rate of the air has a significant effect on the pressure loss of the PBLHS system.
The packed-bed latent heat storage (PBLHS) system has received extensive attention due to its low investment cost and good application prospects. In the past, the research on this system mainly focused on the establishment of mathematical models and the structural optimization of the thermal energy storage (TES) tank. There are few experimental studies on the thermal performance of PBLHS systems under medium-high temperature conditions. In this work, a novel medium-high temperature PBLHS experimental system is designed and constructed. Based on binary nitrate NaNO3–KNO3 (55-45 wt%) as the phase change materials (PCM), a spherical encapsulated PCM suitable for the packed bed TES is prepared. The heat transfer characteristics of the charging process, the static heat preservation process, and the discharging process are experimentally studied, respectively. In addition, the influence of the temperature and flow rate of the heat transfer fluid on the pressure drop of the PBLHS system is also investigated. The results indicate that with the continuous increase of the average air temperature inside the TES tank, the temperature difference inside the tank shows a trend of first increasing and then decreasing. When the average air temperature is around 225–272 ℃, the temperature difference is almost at a stable stage, and the temperature difference is about 84 ℃ (±1 ℃). The temperature difference decreases slowly in the initial stage of the discharging process. The overall efficiency of the current PBLHS system based on binary nitrate is 79.3%. The results also indicate that the air temperature and flow rate have a significant effect on the pressure loss of the packed-bed system. The experimental results of this work can provide experimental data support for the structural optimization design and industrial application of the packed-bed TES system.
The two-step solar thermochemical cycle is a prospective clean energy technology that enables the direct splitting of water and carbon dioxide for solar fuel production. However, immature oxygen ...carriers fundamentally restrict the solar-to-fuel conversion efficiency and thus prevent this technology from immediate industrial uptake. Focusing on the conventional iron-based oxygen carriers, this study intends to find a modified oxygen carrier with low reaction temperature requirements and excellent reaction performance, so as to attain dual optimization in terms of thermal efficiency and chemical efficiency. The thermochemical reaction characteristics of six common ferrites and four metal dopants are compared via thermogravimetric analysis under the same programmed temperature control. For further practical applications of the selected oxygen carrier, a foam-structured material with SiC as support is prepared and subsequently experimented in a self-designed 18-kW thermochemical system. The results indicate that the modified oxygen carriers obtained by direct doping of CoFe2O4 with 50wt% NiO exhibit optimal reaction performance, giving the highest CO yield of 439μmol/g. Additionally, the foam-structured material enable a peak CO yield of 7.0 mL min−1 g−1 and CO2 conversion of 45.5% at a reduction temperature of only 1100°C, which might be attributed to the micron-scale pore structure as well as the generation of aluminosilicate crystal structures.
•Six iron-based oxygen carriers with four metal dopants were investigated via TGA.•Three preparation methods were examined in combination with SEM and XRD.•Foam-structured materials were prepared and tested in a self-designed 18-kW system.•A peak CO yield of 7.0 mL/(min⋅g) with CO2 conversion of 45.5% was gained at 1373 K.•Experimental phenomena were clarified by numerical analysis of thermodynamics.
•MD and first-principles calculations derived parameters for thermal radiation.•Simulations revealed temperature variations due to microthermal sources.•Interface structures improved the continuity ...and stability of heat diffusion.•Phonon-polaritons stabilized thermal transport in micro- and nanoscale gaps.•Nonlinear effects emerged due to high-energy-level heat source values.
The thermal transmission properties of polymer-based composites, commonly used in satellites, are crucial for high-precision thermal management applications. The study constructed the structures of polyimide polymers and polyimide/graphene interfaces based on molecular dynamics and fluctuation dissipation theorem. Optical parameters were determined through first-principles calculations, and the thermal transport from a microthermal source was simulated using Reverse Non-Equilibrium Molecular Dynamics (RNEMD) and the modified four-dimensional transfer matrix method (M4D-TMM). Simulations of polymers, interface structures, and interfacial thermal radiation models investigated the transmission dynamics of microthermal sources during heat transport. Findings showed that the differences in the temperature fields formed within the polymer from microthermal heat sources were less than 20 K for heat source inputs ranging from 0.002 W/m² to 20 GW/m². With a microthermal source, the heat diffusion was extensive, the heat transport was continuous, and the temperature field remained stable. At the level of the heat source up to the intermolecular energy level, the temperature field distribution showed significant instability, leading to nonlinear effects. Within the interface structure, the continuity of heat diffusion increased as the heat source intensified. The interface structure demonstrated enhanced temperature sensitivity and improved stability, with minimal fluctuations of only 0.59 %. The increase in heat flux perpendicular to the interface structure was ascribed to near-field radiative heat transfer. As the temperature difference decreased to less than 0.1 K, the influence of evanescent waves on radiative heat flux nearly disappeared. Phonon polaritons maintained temperature stability during thermal transport through micro- and nanoscale gaps. Integrating thermal conduction principles in polyimide polymers and interface structures with near-field thermal radiation provides a theoretical framework for high-precision thermal management in gravitational wave detection.
This study proposes a deep learning architecture for automatic modeling and optimization of multilayer thin film structures to address the need for specific spectral emitters and achieve rapid design ...of geometric parameters for an ideal spectral response. Multilayer film structures are ideal thermal emitter structures for thermophotovoltaic application systems because they combine the advantages of large area preparation and controllable costs. However, achieving good spectral response performance requires stacking more layers, which makes it more difficult to achieve fine spectral inverse design using forward calculation of the dimensional parameters of each layer of the structure. Deep learning is the main method for solving complex data-driven problems in artificial intelligence and provides an efficient solution for the inverse design of structural parameters for a target waveband. In this study, an eight-layer thin film structure composed of SiO
/Ti and SiO
/W is rapidly reverse engineered using a deep learning method to achieve a structural design with an emissivity better than 0.8 in the near-infrared band. Additionally, an eight-layer thin film structure composed of 3 × 3 cm SiO
/Ti is experimentally measured using magnetron sputtering, and the emissivity in the 1-4 µm band was better than 0.68. This research provides implications for the design and application of micro-nano structures, can be widely used in the fields of thermal imaging and thermal regulation, and will contribute to developing a new paradigm for optical nanophotonic structures with a fast target-oriented inverse design of structural parameters, such as required spectral emissivity, phase, and polarization.
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