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The plenoptic imaging technique provides a promising approach to the non-invasive three-dimensional measurement, especially for the high-temperature combustion diagnosis. We establish a light-field convolution imaging model for diffusion flame in this work, considering the radiation transfer process inside the diffusion flame and the light transfer process inside the focused plenoptic camera together. The radiation transfer process is described by the radiation transfer equation and solved by the generalized source multi-flux method. Wave optics theory is adopted to describe the light transfer process, combining Fresnel diffraction and the phase conversion of the lens. The flame light-field image is obtained by the light-field convolution imaging model and adopted as the measurement signal to reconstruct three-dimensional temperature field. The inverse problem of temperature reconstruction is solved by the least square QR decomposition method. The simulative temperature reconstruction work is conducted, including the inverse analysis, the uncertainty analysis, and the measurement noise influence. All the results show that the proposed measurement method is available to reconstruct three-dimensional temperature with satisfactory accuracy and acceptable uncertainty. Both symmetric and asymmetric distributed temperature fields are investigated, and the reconstructed results prove the validity and universality of the measurement method.

Solar photocatalysis splitting water for hydrogen production is a very hot issue nowadays, and great expectations are laid on g-C3N4 due to its low-cost, thermal stability, low toxicity. However, pure g-C3N4 is not perfect and it still has some shortcomings. By using first-principles calculations, Br and Na are considered being co-doped into the g-C3N4 to get whose photocatalytic performance further enhanced. By studying the electronic structure, optical properties, we find that doping Br Na atom can obviously narrow the band gap, and promote the optical absorption characteristics of g-C3N4, which means a better performance in photocatalysis. Furthermore, the optical absorption cross section and optical scattering cross section of two typical morphologies nano particle and nano rode are calculated by optical simulations to analyze the effects of doping on the optical absorption and scattering characteristics, which could provide another view in analyzing photocatalysis mechanisms and can make great difference on future photocatalyst designing.

Converting solar energy efficiently into hydrogen is a promising way for renewable fuels technology. However, high-temperature heat transfer enhancement of solar thermochemical process is still a pertinent challenge for solar energy conversion into fuels. In this paper, high-temperature heat transfer enhancement accounting for radiation, conduction, and convection heat transfer in porous-medium reactor filled with application in hydrogen generation has been investigated. NiFe-Aluminate porous media is synthesized and used as solar radiant absorber and redox material. Experiments combined with numerical models are performed for analyzing thermal characteristics and chemical changes in solar receiver. The reacting medium is most heated by radiation heat transfer and higher temperature distribution is observed in the region exposed to high radiation heat flux. Heat distribution, O2 and H2 yield in the reacting medium are facilitated by convective reactive gas moving through the medium's pores. The temperature gradient caused by thermal transition at fluid-solid interface could be more decreased as much as the reaction chamber can store the transferred high-temperature heat flux. However, thermal losses due to radiation flux lost at the quartz glass are obviously inevitable.

Unlike silicon carbide ceramic, the alumina ceramic and zirconia ceramic are by its very nature weakly absorbing in visible and near infrared wavebands. Therefore, open-cell foams made of such ceramics are rarely used in applications requiring strong absorption of radiation energy, such as solar absorbers. In order to improve the potential of such foams, open-cell foams with dual-scale pores were digitally designed in the limit of geometric optics. The first-order pores are obtained by Voronoi tessellation technique and then the second-order pores are realized by the design of 'porous strut'. A Monte Carlo Ray-tracing method is applied in the dual-scale foam structure for radiative transfer calculation. The parameterized study is conducted on the radiation absorption of alumina foam sheets and zirconia foam sheets. The results show that for the present cases, the designed dual-scale alumina foams with strut porosity p s = 0.3 can increase the normal absorptance within the wavebands from 0.4 μm to 7.0 μm by 62.7% than the foams with single-scale pores. For the zirconia foams, this increase is 115.9% within the wavebands from 1.2 μm to 7.6 μm. The findings can provide strong confidence on dual-scale foams to enhance the absorption of radiation energy in potential applications.

In this work, a two-dimensional droplet confined between two parallel electrodes under the combined effects of a nonuniform electric field and unipolar charge injection is numerically investigated using the lattice Boltzmann method (LBM). Under the non-Ohmic regime, the interfacial tension and electric forces at the droplet surface cooperate with the volumetric Coulomb force, leading to complex deformation and motion of the droplet while at the same time inducing a bulk electroconvective flow. After we validate the model by comparing with analytical solutions at the hydrostatic state, we perform a quantitative analysis on the droplet deformation factor D and bulk flow stability criteria T_{c} under different parameters, including the electric capillary number Ca, the electric Rayleigh number T, the permittivity ratio ɛ_{r}, and the mobility ratio K_{r}. It is found that the bulk flow significantly modifies the magnitude of D, which in turn decreases T_{c} of the electroconvective flow. For a droplet repelled by the anode, ɛ_{r}1, an interesting linear relationship can be observed in the D-Ca curves. However, for a droplet attracted to the anode, ɛ_{r}1, the system is potentially unstable. After first evolving into a quasisteady state, the droplet successively experiences steady flow, periodic flow, second steady flow, and oscillatory flow with increasing T. Moreover, discontinuities can be observed in the D-T curves due to the transitions of bulk flow.

The use of packed beds containing encapsulated capsules can markedly improve the efficiency of latent heat thermal energy storage systems. The capsule effective thermal conductivity is a crucial parameter for modelling the melting process within the capsule and to investigate the thermal performance of the packed bed. This study simulated the effect of radiation on the melting process of encapsulated high-temperature molten salt using a numerical model. Results showed that radiative processes inside the molten salt could accelerate the melting process. When comparing simulations that incorporated radiation compared to those that did not, melting time differed by as much as 18% because the radiation changed the temperature distribution of the liquid molten salt and enhanced heat transfer. The effect of radiation on the molten salt melting process was then qualitatively analyzed using dimensionless numbers. When the ratios of conductive and radiative heat transfer N were 0.91, 1.62, and 2.24, the effect of radiation became less significant and the time required to complete the melting process was reduced by 25%, 19%, and 7%, respectively. An equation for effective thermal conductivity considering radiative heat transfer in encapsulated capsules was derived, which was valid within a limited range.

The continuous consumption of fossil fuels causes two important impediments including emission of large concentrations of CO2 resulting in global warming and alarming utilization of energy assets. The conversion of greenhouse gas CO2 into solar fuels can be an expedient accomplishment for the solution of both problems, all together. CO2 reutilization into valuable fuels and chemicals is a great challenge of the current century. Owing to limitations in traditional approaches, there have been developed many novel technologies such as photochemical, biochemical, electrochemical, plasma-chemical and solar thermochemical. They are currently being used for CO2 capture, sequestration, and utilization to transform CO2 into valuable products such as syngas, methane, methanol, formic acid, as well as fossil fuel consumption reduction. This review summarizes different traditional and novel thermal technologies used in CO2 conversion with detailed information about their working principle, types, currently adopted methods, developments, conversion rates, products formed, catalysts and operating conditions. Moreover, a comparison of these novel technologies in terms of distinctive key features such as conversion rate, yield, use of earth metals, renewable energy, investment, and operating cost has been provided in order to have a useful review for future research direction.

As the world’s largest energy consumer (i.e., 24% of the world) and one of the largest biomass resource reserve countries (i.e., total reserves of 73.42 × 108 t a–1), for China, using biomass to pr...

Taking centrifuge system for space utilization as the research object, an active air-cooling thermal control system is put forward. Physical models of the centrifuge thermal control system are built on the basis of simplifying assumptions under actual conditions. A numerical calculation model of centrifuge system is established by using the sliding mesh technique and flow resistance model of heat exchanger is introduced based on the porous medium theory. A numerical analysis of the dynamic heat exchange performance of the centrifuge is carried out and the results show the flow and heat exchange characteristics of each part of the system in the dynamic equilibrium state. Also, the centrifuge system and its heat exchange performance test platform are designed and built, and the monitoring probes are placed at the key position. The curves of the whole equilibrium process of key points are obtained and the test condition is consistent with numerical simulation condition. The equilibrium temperatures of the test are in agreement with that of the numerical analysis, which proves that the numerical model and calculation method are accurate. Meanwhile, the test and numerical analysis results can also improve each other to provide data and supporting techniques for in-orbit engineering utilization of manned space station in future.

A good understanding of the catalytic mechanism of alkali and alkaline earth metal species during pyrolysis is required for the development of biomass utilization, to take advantage of its special thermochemical properties. The mechanism of the volatile–biochar interaction, especially between H radical/CO2/H2O and K/Ca in biochar, was systematically investigated by combining experimental analyses and density functional theory calculation. The results indicate that, at 500–900 °C, the yield of biochar from rice husk pyrolysis is basically constant, which mainly shows the mutual conversion between gas and liquid products. With the increase of loading alkali and alkaline earth metal species (AAEMs), the tar yield gradually decreased, and with it reaching a certain content, a significant catalytic effect of AAEMs can be observed. K is more beneficial to maintain the stability of the biochar structure than Ca. The intensities of CO and C–O–C functional groups would appear with a certain increase with the increasing concentration of bond-linking AAEMs. At 700–900 °C, the precipitation ratio of K is almost twice that of Ca and even more. The presence of AAEMs can largely inhibit the formation of three-ring tar components, and more converted to one-ring tar components. The H radicals in the volatile can be bonded to C in the C–O–K structure, thereby causing the K element to decouple with the functional group, and tend to be adsorbed on the carbon matrix. For the Ca-loaded structure, it is manifested in strong adsorption of H radicals by Ca, resulting in the weakening of C–O bonds and the looseness of the biochar structure. The interaction between K/Ca in biochar and H2O/CO2 is reflected in the mutual attraction of AAEMs and the O atom in the H2O/CO2 molecule.

In this paper, the heat flow diagram of steam turbine model K-6-35 has been analyzed for innovative approaches towards improving the techno-economic and ecological indices of the small-scale power generation system. The numerical analysis is performed using IPSEpro process simulation software based on heat balance method under four different cases. It was found that the study of Solar Assisted Power Generation (SAPG) system has important practical significance in power generation with minimum pollutants and maximum efficiency. Both fuel-saving (FS) and power-boosting (PB) operation modes of the SAPG system are considered. Various types of stand-alone solar thermal power plants exhibited very low overall efficiency with many ecological advantages compared to the conventional thermal power plant based on fossil fuels. Besides, SAPG system with FS mode presented higher techno-economic indices and operation performance. An important reduction in fuel consumption and pollutant emissions could be obtained with SAPG system. Considering the hourly, daily, monthly, and yearly amount of saved fuel and reduced pollutants in the whole power plant, the SAPG system with FS mode can largely contribute to high ecological indices power generation. A thermal efficiency increased by 1.31% with specific equivalent fuel consumption decreased by 22.54 g/kWh was obtained with SAPG system. The coal consumption was reduced by 4.75% when SAPG system operates in FS mode.

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.

The harmonious condition between nature and humans experiences severe challenges due to the continuous consumption of fossil fuels and the consequent rapid release of large CO2 levels into the atmosphere. It is urgent to explore sustainable resources of green energy and develop efficient techniques for CO2 conversion into value-added products. Being an indispensable component for CO2 re-utilization, the conversion of CO2 into valuable chemicals and fuels can provide a win–win situation to accomplish the effective exploitation of carbon resources and reduce the large volumes of CO2. Among the presently adopted CO2 conversion techniques, the electrochemical approach is a promising route to produce low carbon chemicals required for heavy-duty applications. Although significant progress has been accomplished in the electrochemical reduction of CO2 (ERC), there is a lack of basic research to understand the different factors that strongly influence the performance of ERC. In particular, very few studies have incorporated the effect of an electrolytic cell on ERC. This review summarizes the role of metal electrodes in the production of different products, the effect of the electrolyte, pressure and temperature, membrane, and CO2 mass transfer coefficient on the performance of ERC. Moreover, we have also comprehensively discussed the different types of an electrolytic cell in terms of their structure, working principle and capabilities of producing selective products to understand the impact of different cell configurations on the reduction process, and have presented a useful review of the future research prospects.

The outbreak of 2019 novel coronavirus (COVID-19) has hugely impacted the world and becomes a global public threat. To prevent the spread of COVID-19, human activities are largely restricted in China in early February, 2020. The influence of strict COVID-19 control policies on air quality and the potential influence of particulate matter concentration on COVID-19 infection in China are of great interest. This study analyzes the concentrations of six major air pollutants in 366 urban areas across mainland China during January 1 to April 30 in 2017–2020. Results show that strict COVID-19 control policies have significantly improved the air quality in many provinces. Compared to 2019, national mean concentrations of PM2.5, PM10, SO2, NO2 and CO in 2020 decrease by 14%, 15%, 12%, 16% and 12%, respectively, while the concentration of O3 increases by 9%. Generally, the diurnal variation of PM2.5 and PM10 concentrations remains unchanged during COVID-19 and their concentrations are high in the morning and evening while low in the afternoon. Correlation analysis shows that daily COVID-19 infections are positively correlated with PM2.5 concentration in many provinces, indicating a potential risk of aerosol transmission in high PM2.5 environment. Thus it is suggested to stay at home in highly polluted days and go out in the afternoon to reduce the risk of infection due to aerosol transmission.

Pipe height in cylindrical neutron moderator is an important factor to flow pattern, temperature distribution and even the neutron characters. In this paper, the steady-state thermal analysis of cold neutron moderator is carrying out with different heights, conjugated heat transfer method and one-way coupled with a neutron transfer software. The different pipe heights, which is the jet-to-surface distances (H/D = 0.5~6), were compared using a 2D moderator model. The results show that vortex size and velocity gradient from container wall to vortex center vary with H/D, the center of recirculation zone nearly remain constant, and heat transfer effect is weakened on the target bottom surface. With H/D increasing, the velocity at bottom target surface is progressively decreased, and cooling effect is poor, leading to the rise in temperature. The optimal range cooling performance is (H/D) = 0.5~1 at Re = 1.7 × 105, and the enhancement of beam power further strengthens the thermal deposition difference between container and liquid hydrogen. The results can be applied to moderator component design and optimization in the future spallation neutron source.

Oxygen-fuel combustion is a promising technology for CO2 emission reduction. The high-temperature entrained flow reactor and high-temperature drop tube furnace were used to analyses the formation and O2/CO2 combustion characteristics of real-environment coal char in high-temperature oxy-fuel conditions. It proposed “inflection point standard” of high-temperature flame method for the preparation of real-environmental oxy-fuel coal char according to the flame method. The results show that the ratios of C=O/C-O and C=O/Car increase in the coal char compared with the raw coals. The trend of C=O/Car in oxy-fuel condition is opposite to that in the inert atmosphere, due to the effect of high-concentration CO2. To achieve the burnout rate similar to air combustion for coal char, with the increase of coal rank, the O2 concentration should be enhanced. The optimal O2 concentration for the oxy-fuel combustion of JC anthracite is 30%, while that of other low-rank coals could be lower than 30%. The combustion characteristic of JC anthracite is with the highest sensitivity to temperature and O2 concentration.

In this study, the influence of aerosol type classification on estimating surface PM2.5 concentrations was assessed by using ground-based aerosol optical depth (AOD) at 22 ground-based observation points in the United States. To clarify the influence, a two-stage model consisting of a multiple regression model (MRM) and an aerosol classification model (ACM) was proposed to estimate surface PM2.5 concentrations, and results from a traditional MRM and the new ACM-MRM were compared. Results show that the average determination coefficient (R2) of the ACM-MRM (0.52) was greater than that of the MRM (0.44), while the root mean square error (RMSE) and mean absolute percent error (MAPE) of the ACM-MRM (3.74 μg/m3 and 34.91%, respectively) were lower than the values obtained with the MRM (4.09 μg/m3 and 37.64%, respectively). The use of ACM improved the estimation of daily PM2.5 concentrations in different regions and different seasons by reducing the deviations caused by aerosol type changes. Further analysis demonstrated that aerosol type changes had adverse influences on the estimation of short-term PM2.5 concentrations and the introduction of ACM can effectively restrain the adverse influences when aerosols change frequently.

With the application of oxyfuel combustion technology, the status of radiative heat transfer in oxyfuel flames is prominent, and accurate description of it is essential. This study simulates the turbulence radiation interaction (TRI) in a swirling gas-fired furnace to understand the thermal radiation behavior under oxycombustion conditions. Employing the non-gray weighted sum of gray gases model calculates the radiative properties of the participating media and the TRI is modeled. The effects of TRI on the radiative heat transfer in the furnace under different oxycombustion conditions and swirl numbers are analyzed. The results show that the effects of thermal radiation on temperature fields are critical in the gas-fired furnace, especially for oxycombustion condition with high oxygen concentration, and the same is true for TRI effect. With the increase of O2 concentration in O2/CO2 oxidizer, the radiative heat flux on the chamber wall, the radiative heat flux contribution to total heat flux, and the net radiative heat loss are increased. Increasing swirl number can weaken the TRI effect. It is observed that with 35% O2 in oxidizer, the radiation contribution to heat flux along the entire wall and local increase of radiative heat flux due to TRI effect are almost than 45% and 18%, respectively.

As is reported, the photocatalytic activity will increase significantly when TiO2 nanoparticles are agglomerated into TiO2 nanofibers (NFs), but the photocatalytic activity enhancement mechanisms are still not fully understood. As is widely accepted, the optical absorption process plays a key role in photocatalysis, and it can even be said that the optical absorption capability of the photocatalyst directly determines its photocatalytic activity, while the influence of the structure on the optical absorption characteristics of TiO2 has largely been ignored in the existing explanations. In this paper, optical simulations are introduced into analyzing optical characteristics of TiO2 Nanofibers with which, the photocatalytic activity enhancement mechanism is further discussed, and a photocatalytic activity enhancement mechanism of TiO2 Nanofibers is proposed.

The real-time measurement and reconstruction of three-dimensional temperature are essential when studying the combustion process inside a flame. In the proposed sectioned flame light field imaging model, flame sections are reconstructed based on the characteristics identified using the Lucy-Richardson or nearest neighbor filtering methods, or a joint method involving a combination of both, to improve on the accuracy of two-dimensional temperature reconstruction. Compared to the results of a previous work, the proposed method increases the resolution in the depth of field direction and the extraction of the flame temperature of all sections from the same height ensures the accuracy of the reconstructed temperature distribution across the cross-section of the flame. The relative error when compared to the actual flame is less than 10%. Thus, this approach allows the accurate estimation of the three-dimensional temperature distribution inside a flame, and enables the rapid and effective reconstruction of the three-dimensional temperature field.

In this paper, a fast estimating method of thermal infrared radiation signatures for low-altitude exhaust plumes was proposed. In engineering application, it is essential to predict the thermal radiation effect of the plume as soon as possible. A simple numerical model was established considering thermal, species formation, entrainment and radiating effects. In this methodology, the mixing region was treated as a hot, under-expanded, reacting and isotonic flow. The reacting flows were simulated by solving the governing equations with finite rate kinetics and conservation matching relations. A single-line-group (SLG) model with Curtis-Godson approximation was utilized to evaluate radiative properties of radiating species. A line-of-sight (LOS) method was used to compute the spectral radiation intensity. This computational model was verified against the Atlas-II’s reference data within the wavelengths of 2–6 μm. The simulation analyzed combustion flows and infrared thermal effects of a typical exhaust plume along flight trajectory points. Results show that the current model can dramatically improve the computational efficiency by 100–1000 times by comparing with the commonly used method. According to this model, the plume’s range and an appropriable cutoff temperature for thermal radiation calculations are easy to obtain. Infrared radiation phenomena accord with the experimental observations. As a main outcome, this simple model can provide a time-saving and range-unlimited method for the infrared radiation signature prediction of a low-altitude plume in engineering application.

Considering the existence of edge effect caused by the cut surface of struts or sintering points will affect the actual radiative transfer process in metallic foams, a three-layer structure model is constructed to obtain their spectral radiative properties. Using the double-thickness model for reference, the real spectral radiative properties of metallic foams are calculated based on transmittance spectra. To verify the feasibility of this method, transmittance spectra of nickel foams with different cell sizes and thicknesses are measured by FTIR spectrometer system in the near infrared band. Through comparing extinction coefficients obtained by traditional single-layer structure model and the three-layer structure model proposed in this paper, it is found that extinction coefficient will be underestimated by the latter method, while the deviation can reach 13% for 20ppi nickel foam and 8% for 40ppi nickel foam. Then absorption coefficient and scattering coefficient are calculated by a prediction model with parameters corrected. Based on this method, temperature influence on extinction coefficient of nickel foam is studied from 293 K to 773 K and it is found that extinction coefficient decreases with temperature in the researched band while the maximum changing rate is 2.1% in the researched band.

The proportion of radiative heat transfer in the total heat transfer increases with the increase in temperature. However, the effect of radiative heat transfer has often been omitted in the heat transfer simulation of molten salt used in complex geometrical systems such as the thermal energy storage (TES) system. In this paper, a 3D helical-coil tube heat exchanger, simplified from a TES system, is established. The temperature difference obtained with and without considering radiative heat transfer is compared. The results show that the effect of radiative heat transfer at high temperatures should be considered. The wall heat transfer coefficient is analyzed, and a heat transfer correlation considering radiative heat transfer is derived. The heat transfer between the molten salt and water is found to enhance when considering the radiative heat transfer. Finally, the effects of different scattering albedo and refractive indices are studied.

Temperature detection is important in flame structure analysis. However, there are few studies focusing on the effect of the distribution of radiative properties on the accuracy of flame temperature reconstruction. Based on an established temperature reconstruction system using sectioned flame imaging, this study adjusts the microlens parameters of a light field camera, combining the nearest neighbor filtering method with the light field refocusing technique, and then accurately reconstructed flame images are obtained. In addition, predicted attenuation coefficient is used to reconstruct flame sections in uniform and nonuniform participating media, to investigate comparatively the effect of nonuniform radiative properties on flame temperature reconstruction. The results show that, the temperature reconstruction results for more than 94% of pixels of the flame imaging are accurate (within 10%), and only few parts at the boundary of the flame have a relative error larger than 10%, and less than 20%. Though the difference of the attenuation coefficient between that estimated for temperature reconstruction and that of the actual flame medium is an important factor influencing the temperature reconstruction accuracy, the effect is investigated in a range using the presented method. Thus, it provides a practical method to reconstruct the flame temperature accurately in unknown radiative properties.

Radiative heat transfer plays an important role in combustion systems. Good compromise between the accuracy and computational requirements of the weighted sum of gray gases (WSGG) model makes it widely used in CFD simulations. In this paper, the accuracy of various WSGG models is assessed by the comparison with the results of radiative heat source and heat flux calculated by line by line (LBL) approach in a realistic non-isothermal and non-homogeneous flame using decoupled calculations. Then these models are implemented to CFD code to investigate the radiative heat transfer for a 600 kW furnace using coupled calculations. The experimental data from the furnace has been used to evaluate the computational applicability and reliability of WSGG models. Results show that the non-gray formulation of WSGG model is more accurate than gray modelling approach, compared with LBL results. The non-gray WSGG models of Krishnamoorthy et al. (2013), Bordbar et al. (2014) and Shan et al. (2018) provide the minimal overall errors compared with the measured temperature fields. The results demonstrate that using the non-gray approach instead of gray approach for global CFD simulation improves the simulation accuracy of thermal radiation transfer. The computing time of non-gray models is larger, approximately 3–4 times that of gray WSGG models.

Highly efficient conversions and utilizations are long-standing topics of interest in energy field. Owing to the unique potentials of metamaterial in regulating thermal and electrical behaviors, classical research on efficient energy utilization has been further motivated. However, current investigations are mostly implemented with single basic transformation, which lead to the simple functions on single field. Hence, hybrid functions are of particular importance in achieving highly efficient devices for multiple energies. In this paper, the above concerns are addressed with hybrid maps to design a class of novel discrete source array, which significantly re-configures each field generated by an excited source into arrayed distributions. The expected energy collection and allocation are first exhibited only with one single source, and intense convergences/divergences are observed in tailored directions. Contrasts reveal that such designs robustly act as circular source arrays with multiple sources. The findings provide a novel function of efficiently manipulating and allocating energy generated by excited sources, which see potentials in conventional applications, such as extensive harvesting strategies with local energy focus, light routing on the sun-facing side of solar cells, and thermal-electric devices.

The effects of major flue gases (CO/CO2/SO2/H2O/O2) on the NO–char interaction at realistic high temperatures in the reburning zone of boiler are investigated, through the HEFR and HDTF at 1200–1500 °C. The results indicates that CO could significantly promote the NO–char interaction, with its temperature-sensitive region at 3%–5% CO. CO2 (

The radiative characterization of open-cell foams made from semitransparent solids is more complex than that made from opaque media. This study aims to understand how the component radiative properties and structural parameters of such open-cell foams affect their radiative characteristics. A radiative transfer model was established in the limit of geometric optics for the radiative characterization of a family of numerically generated Voronoi foams with open cells. It considers the reflection and refraction at the solid surface and the transmission, absorption and scattering process inside the solid phase. It is found that when the solid phase is in reality partially transparent, the opaque solid assumption will lead to inaccurate outcomes. Strongly scattering solid phase may cause much radiative energy to be rejected via reflection behavior, which will weaken the absorptive capability of the foam sheets as radiation absorbers. In addition, the radiative transfer model established was applied in three popular ceramic foams (alumina, silicon carbide and zirconia). The model shows advances in the field of analyzing and explaining the spectral radiative characteristics of ceramic foams. The present work can provide useful guidance when open-cell foams made from semitransparent media become potential candidates for thermal applications.

A novel scale-coupled approach was proposed to model the radiative transfer inside open-cell foams made of semitransparent absorbing-scattering media such as oxide ceramics. This new approach was established by integrating the equivalent continuous zone with the exact distribution of solid and void zones into a single computational domain. As a key treatment, a scale-coupled zone with variable local optical and radiative properties was proposed to allow gradual transition between different subzones. After a validation by experiments on a normal transmittance measurement, the scale-coupled approach was applied in predicting the radiative behaviors and local absorbed radiative fluxes of a real alumina ceramic foam. The results were confronted with the classical continuous-scale approach which assimilates the foam material to an equivalent continuous medium with homogeneous radiative properties and discrete-scale approach which considers the exact distribution of foam geometry in the medium. This new approach was found reliable in calculating the radiative behaviors of open-cell foams made of relatively opaque to transparent or relatively absorbing to scattering media. It can offer information on the fluctuant local radiative quantities and at the same time equivalent continuous quantities through a single simulation. Besides, this new approach leads to a reduction in computational time by approximately one order of magnitude compared to the discrete-scale approach which relies on full-size foam geometry. The scale-coupled approach is promising to simulate engineering problems where geometry-dependent radiative quantities are required.

A silica-based embedded aluminum grating polarizer suitable for a near- and mid-infrared light field camera is investigated to fully utilize the direction information recorded by the detector in the light field camera. A grating with good polarizer performance was obtained by using the finite-difference time-domain (FDTD) method to simulate and optimize the structural parameters affecting the performance. The optimized structure reaches TM transmission efficiency exceeding 84% and extinction ratios greater than 27.9 dB in the 1.5–5.5 μm band. The optimized grating is suitable for a wide incident angle range of 0°−70° and for infrared polarization light field imaging. Keywords: The embedded grating, Light field imaging, Finite-difference time-domain method, Extinction ratios, TM wave transmission efficiency

In this study, a novel elliptical jet-stabilized combustor is developed; the combustion and emission characteristics are numerically investigated and compared with those of a circular jet-stabilized combustor. Five elliptical combustors with different semi-major/semi-minor axis ratios (1.00, 1.27, 1.56, 1.89, and 2.25) are considered, and an optimization method for adjustable stabilizer jet air supply is proposed. An Eulerian-Lagrangian approach is used for solving the liquid fuel spray. Employing the realizable k-e turbulence model and the finite-rate/eddy-dissipation model simulates the turbulent combustion. The discrete ordinate method is used to model thermal radiation, and the thermal and prompt NO formations are to be predictive of NO emissions. The numerical models are validated against available experimental data. The results show that the semi-major/semi-minor axis ratio significantly affects the performance of elliptical jet-stabilized combustors. To improve the temperature uniformity and to reduce NO emissions, the proposed optimization method is successfully applied. Compared with the circular combustor, the optimized elliptical combustor achieves strong mixing performance, resulting in improved combustion and emission performance. By adjusting the major/minor axis jet mass flow rate ratio (ma/mb = 0.6) in the elliptical combustor with semi-major/semi-minor axis ratio of 1.56, NO emissions are reduced by 50% compared with the circular combustor.

Molten salt is widely used in many fields as an important working fluid at high temperature as the increase in the use of new energy sources. In addition to studies on the thermal properties, research on the radiative properties of molten salts is mainly in the wavelength range of 0.3–2.5 μm, but most of emission energy falls in range of 2.5–25 μm at 600 °C. In this study, an emissivity measurement system for a liquid molten salt was developed on the basis of the black body emission method. The spectral emissivities of Hitec and Solar Salts were measured in the wavelength range of 5–25 μm. Moreover, the effects of the radiation of the inner wall of the large crucible and the emission and reflection at the upper surface of the bottom of the small crucible were eliminated. The results showed that the spectral emissivity of a molten salt increases with the temperature. In the wavelength range of 6–8.5 μm, two continuous depressions were observed in the emissivity of the Hitec, whereas there was only one depression in the emissivity of the Solar Salt in the range of 6.5–7.5 μm. The uncertainty of the experiment is less than 5.9% in experimental temperature and wavelength range. The results are supposed to be useful in designing and optimizing the equipment and operating conditions in the concentration solar power (CSP), as well to be helpful in accurately measuring the thermal properties of the molten salt.

Classifying aerosol types using spectral aerosol optical properties plays a key role in promoting the accuracy of remote sensing observations and expanding our knowledge of the internal relations between aerosol and climate. However, studies on verifying the correctness for aerosol type classification methods are particularly scarce. In this study, data from three month optical and chemical measurements of atmospheric aerosols in Harbin, Northeast China, were used to verify the optical classification methods by comparing their results with the actual aerosol types. Aerosol optical properties like aerosol optical depth (AOD), Angstrom Exponent (AE), and single scattering albedo (SSA) were obtained through a CE318 sun-photometer, and aerosol type was then identified based on four previously published aerosol classification schemes. To acquire the actual aerosol states, satellite observations from MODIS and CALIPSO was combined and then the morphology, chemical composition, and molecular structure of sample particles were examined by energy-dispersive X-ray spectroscopy (SEM-DES), X-Ray fluorescence spectrophotometer (XRF), and Fourier transform infrared spectroscopy (FTIR) measurements. Results show that aerosol types over urban Harbin varied a lot during the studying period and mixed aerosol was the dominant type. The optical classification methods mentioned in this study could identify aerosol types correctly in most cases, but sometimes made improper estimations. Besides, they are able to descript the distinct variation of aerosol type on seasonal and daily scale, but at present the result is still too rough to discriminate the detailed changes of actual aerosol state accurately. The combination of different classification methods or chemical measurements would help reducing the misjudgment of aerosol types. Our findings demonstrate that a more comprehensive way to identify changes in aerosol state is urgently needed to enhance our understanding of the impacts of aerosols on climate and remote sensing.

This study aims to fully investigate the volumetric radiative properties of irregular open-cell foams made from semitransparent absorbing-scattering media such as ceramics. A Monte Carlo ray-tracing model was established in the limit of geometric optics to extract volumetric radiative properties of foams generated by a Voronoi tessellation technique. Three shape parameters for struts were proposed to mimic real struts. It was found that for extinction coefficient, the most influent parameters are porosity, mean cell diameter, and cross-sectional shape. For scattering albedo, it no longer depends on the surface reflectivity of solid struts but on the component radiative properties and strut shape parameters. Similarly, the scattering phase function no longer depends on the local reflection type but on an integrated contribution of the surface reflection, interface refraction, and volumetric radiation propagation inside the struts. The asymmetry factor is found closely related to the transparency of struts. Using the component radiative properties and structural parameters as input parameters, three analytical relations were established to respectively predict the extinction coefficients, scattering albedos, and asymmetry factors, which can be useful for the design and application of open-cell foams made from semitransparent media.

As the core component of the micro thermophotovoltaic (MTPV) system, the micro combustor with a high and uniform wall temperature distribution is beneficial to improve the energy conversion efficiency. In this paper, a micro tube combustor with converging-diverging channel is proposed and the thermal performance is numerically investigated, compared with that of the micro combustor with cylindrical channel. The effects of inlet velocity of H2/air mixture, dimensionless position and diameter of throat, and solid material on the thermal performance are widely analyzed. Results show that the outer wall temperature and emitter efficiency of the micro combustor with converging-diverging channel are higher than that of the micro combustor with cylindrical channel, and the converging-diverging channel has more uniform temperature distribution. The converging-diverging micro combustor with dimensionless throat position l = 0.375 and dimensionless throat diameter β = 0.4 is more suitable for the application of MTPV system. When H2/air inlet velocity is 11 m/s and H2/air equivalence ratio is 1.0, the mean wall temperature is increased by 82.39 K and the emitter efficiency is increased by 6.59%, while the normalized temperature standard deviation is reduced by 65.85%. Additionally, the use of SiC as wall material can improve the thermal performance of the micro combustor. It is worth noting that this work will offer us significant guidelines for the optimized work of micro tube combustor.

In this paper, by using a microcomblike metamaterial, noncontact control of near-field evanescent photon tunneling is achieved. With the control of spoof surface modes inside the comb, resonant fre...

All-dielectric metasurfaces have attracted extensive attention because of their ability to control electromagnetic waves with low loss. However, compared with the research on the physical basis of a single nanoparticle controlling electromagnetic waves, foundational research on the influence of the periodicity of all-dielectric metasurfaces on their control of electromagnetic waves is still insufficient. Thus, the aim of this article is to further explore and emphasize the effect of the periodicity of metasurfaces on their optical performance and their electromagnetic response and coupling, and to describe how the above theoretical exploration can be employed for designing devices. We first explore some optical performance caused by the periodicity of cube silicon metasurfaces in the near-infrared band and reveal that these phenomena cannot be explained by the Mie resonances of the single nanoparticles composing the metasurfaces but by the lattice resonance theory and guided-mode resonance filter theory. Then, the influence of the periodicity on the electromagnetic response and coupling in the metasurfaces are analyzed via the multipole expansion method. We emphasize that the electromagnetic coupling between array nanoparticles enhances dipole and octupole radiation in the metasurfaces and analyze how the radiation is enhanced. We also study some phenomena and applications caused by the guided-mode resonances for future design. The results of this study may have potential applications in lasers, reflectors, absorbers, detectors, and other fields, and provide theoretical basis for the design of specific performance devices by adjusting the size of metasurfaces related to periodicity.