Experimental investigation for temperature and emissivity by flame emission spectrum in a cavity of rocket based combined cycle combustor chamber

Flame temperature and spectral emissivity were the important parameters characterizing the sufficient degree of fuel combustion and the particle radiative characteristics in the Rocket Based Combined Cycle(RBCC)combustor.To investigate the combustion characteristics of the complex supersonic flame in the RBCC combustor,a new radiation thermometry combined with Levenberg-Marquardt(LM)algorithm and the least squares method was proposed to measure the temperature,emissivity and spectral radiative properties based on the flame emission spectrum.In-situ measurements of the flame temperature,emissivity and spectral radiative properties were carried out in the RBCC direct-connected test bench with laser-induced plasma combustion enhancement(LIPCE)and without LIPCE.The flame average temperatures at fuel global equivalence ratio(a)of 1.0b and 0.6 with LIPCE were 4.51%and 2.08%higher than those without LIPCE.The flame combustion oscillation of kerosene tended to be stable in the recirculation zone of cavity with the thermal and chemical effects of laser induced plasma.The differences of flame temperature at a=1.0b and 0.6 were 503 K and 523 K with LIPCE,which were 20.07%and42.64%lower than those without LIPCE.The flame emissivity with methane assisted ignition was 80.46%lower than that without methane assisted ignition,due to the carbon-hydrogen ratio of kerosene was higher than that of methane.The spectral emissivities at 600 nm with LIPCE were 1.25%,22.2%,and 4.22%lower than those without LIPCE at a=1.0a(with methane assisted ignition),1.0b(without methane assisted ignition)and 0.6.The effect of concentration in the emissivity was removed by normalization to analyze the flame radiative properties in the RBCC combustor chamber.The maximum differences of flame normalized emissivity were 50.91%without LIPCE and 27.53%with LIPCE.The flame radiative properties were stabilized under the thermal and chemical effects of laser induced plasma at a=0.6.

Improved Microwave Ocean Emissivity and Reflectivity Models Derived from Two-Scale Roughness Theory

The Geometrical Optics(GO)approach and the FAST Emissivity Model(FASTEM)are widely used to estimate the surface radiative components in atmospheric radiative transfer simulations,but their applications are limited in specific conditions.In this study,a two-scale reflectivity model(TSRM)and a two-scale emissivity model(TSEM)are developed from the two-scale roughness theory.Unlike GO which only computes six non-zero elements in the reflectivity matrix,The TSRM includes 16 elements of Stokes reflectivity matrix which are important for improving radiative transfer simulation accuracy in a scattering atmosphere.It covers the frequency range from L-to W-bands.The dependences of all TSRM elements on zenith angle,wind speed,and frequency are derived and analyzed in details.For a set of downwelling radiances in microwave frequencies,the reflected upwelling brightness temperature(BTs)are calculated from both TSRM and GO and compared for analyzing their discrepancies.The TSRM not only includes the effects of GO but also accounts for the small-scale Bragg scattering effect in an order of several degrees in Kelvins in brightness temperature.Also,the third and fourth components of the Stokes vector can only be produced from the TSRM.For the emitted radiation,BT differences in vertical polarization between a TSEM and FASTEM are generally less than 5 K when the satellite zenith angle is less than 40°,whereas those for the horizontal component can be quite significant,greater than 20 K.

Effect of ZrO_(2)Addition on Lanthanum Aluminate-based High Emissivity Coating Materials

In order to enhance the sintering resistance of lanthanum aluminate based high emissivity coatings,Ca^(2+)-Fe^(3+)doped LaAlO_(3)/ZrO_(2)specimens were prepared by solid state sintering using La_(2)O_(3),Al_(2)O_(3),CaCO_(3) and Fe_(2)O_(3) as raw materials,extra-adding fused Y_(2)O_(3)-stabilized ZrO_(2)(0,5%,10%,and 15%,by mass),ball milling,pre-calcining,pressing into shapes and sintering at 1600℃for 2 h.The effect of the ZrO_(2)addition on the properties of lanthanum aluminate based high emissivity coatings was explored.It is concluded that ZrO_(2)does not react with LaAlO_(3),which can inhibit the sintering of the specimens.With the increase of the ZrO_(2),addition,the linear shrinkage rate and the thermal conductivity decrease significantly,while the emissivity decreases,but the emissivity of all the specimens is all higher than 0.9.The optimal addition of ZrO_(2),is 10%.

Preparation of high emissivity NiCr_2O_4 powders with a spinel structure by spray drying

Spray-drying was used to produce the high emissivity NiCr2O4 powders with a spinel structure. Preliminary investigations focused on fabricating the high emissivity powders for infrared radiation coatings and finding the relationship between microstructure and emissivity. The NiCr2O4 powders were characterized for composition, microstructure, and infrared emissivity by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, infrared radiant instrument, and Fourier transform infrared spectra （FT-IR）. Thermogravimetry and differential thermal analysis show that the appropriate baking temperature for NiCr2O4 powder preparation is about 1200？C. The emissivity measurement and FT-IR spectra show that, because of the special spinel structure, the NiCr2O4 powders have a high emissivity about 0.91. Spray-drying is a suitable method to produce the high emissivity ceramic powders.

Design and calculation of low infrared transmittance and low emissivity coatings for heat radiative applications

The infrared transmittance and emissivity of heat-insulating coatings pigmented with various structural particles were studied using Kubelka-Munk theory and Mie theory. The primary design purpose was to obtain the low transmittance and low emissivity coatings to reduce the heat transfer by thermal radiation for high-temperature applications. In the case of silica coating layers constituted with various structural titania particles （solid, hollow, and core-shell spherical）, the dependence of transmittance and emissivity of the coating layer on the particle structure and the layer thickness was investigated and optimized. The results indicate that the coating pigmented with core-shell titania particles exhibits a lower infrared transmittance and a lower emissivity value than that with other structural particles and is suitable to radiative heat-insulating applications.

The Theoretical Analysis of Multi-wavelength Pyrometer:Check and Autosearch for Emissivity General Expression

In general, the dependence of the logarithm of the emissivity upon wavelength is usually used in the treatment of data measured by multi-wavelength pyrometer. In this paper, the suitability of this expression for different materials has been examined. Further more, an effective method for automatically searching the mathematical model between emissivity and wavelength has been procsed. The calculated results show that the accuracy is improved by using this data treatment method.

Microstructure and properties of high emissivity coatings

A new coating on lining in industrial furnace for energy saving has been developed. Properties and microstructure of the coatings were revealed by emissivity instrument,X-ray diffraction （XRD）,transmission electron microscope （TEM） and scanning electron microscope （SEM）,respectively. The result indicates that the emissivity of coatings is higher than 0.90 and the thickness of coatings is about 200 μm. ZrO2,Cr2O3 and SiC in the coating benefit practical applications of coatings at high temperature with durable high emissivity and the continuous structure between the coatings and the substrate makes the coatings high cohesion and excellent adhesion for both specimens with and without sintering at high temperature. Result from laboratory experiment shows that the heating speed of specimen with coating is higher than that of controlled specimen and the temperature increases 30°C during the heating. The average temperature drop of specimen with coatings has a 13.5% improvement in the cooling speed. The application of coatings on the checker brick in a blast furnace of 1750m^3 indicates that the coating causes the blast temperature to an average increase of 28°C,reduces the fluctuation of blast temperature before the blowing-in and leads to a fuel saving of 10% approximately.

Estimation of the Land Surface Emissivity in the Hinterland of Taklimakan Desert

An accurate accounting of land surface emissivity(ε) is important both for the retrieval of surface temperatures and the calculation of the longwave surface energy budgets.Since ε is one of the important parameterizations in land surface models(LSMs),accurate accounting also improves the accuracy of surface temperatures and sensible heat fluxes simulated by LSMs.In order to obtain an accurate emissivity,this paper focuses on estimating ε from data collected in the hinterland of Taklimakan Desert by two different methods.In the first method,ε was derived from the surface broadband emissivity in the 8–14 μm thermal infrared atmospheric window,which was determined from spectral radiances observed by field measurements using a portable Fourier transform infrared spectrometer,the mean ε being 0.9051.The second method compared the observed and calculated heat fluxes under nearneutral atmospheric stability and estimated ε indirectly by minimizing the root-mean-square difference between them.The result of the second method found a mean value of 0.9042,which is consistent with the result by the first method.Although the two methods recover ε from different field experiments and data,the difference of meanvalues is 0.0009.The first method is superior to the indirect method,and is also more convenient.

Preparation and Characterization of High Infrared Emissivity Mn-doped NCO Spinel Composites

NiCr2O4（NCO）spinel composites with different Mn/Ni atomic ratios（Mn/Ni=0.05,0.10,0.15,and 0.20）were synthesized via solid state reaction method.Phase compositions and microstructure of samples were characterized by X-ray diffraction（XRD）and X-ray photoelectron spectroscopy（XPS）.The TG-DSC curves showed that the appropriate baking temperature for Mn-doped NCO spinel preparation was approximately 1 320℃.X-ray diffraction patterns exhibited the formation of NCO spinel with Fd-3m space group.Valence state of the Mn ions was determined from 2p and 3s X-ray photoelectron spectra.Manganese ions were mostly in divalent and trivalent states,and the ratio of Mn^2＋/Mn^3＋was 0.78-0.98.Fourier transform infrared spectroscopy（FTIR）was used to analyze the spectral emissivity of Mn doped NCO spinel.It was revealed that the infrared emissivity of Mn-doped NCO spinel in 1.8-5μm could be significantly enhanced with increasing content of Mn^2＋,reaching as high as 0.9398.Mn-doped NCO spinel showed excellent radiation performance and good prospect in high emissivity applications in the temperature range of 800-1 200℃.

Preparation of ZAO powder and investigation on its infrared emissivity

According to the basic infrared stealth mechanism of low infrared emissivity powders,the ZAO powder materials were prepared by liquid coprecipitation method,and the starting materials were Zn( NO3) 6H2O and Al( NO3) 39H2O. The process parameters were obtained,and the relationship between technology parameters and infrared emissivity was investigated. The temperature of thermal treatment,crystal structure and surface micrograph of ZAO powder was analyzed by the help of TG-DTA,XRD and SEM. The infrared stealth performance of ZAO powder was studied by IR-2 emissivity spectroscopy. Results showed that the infrared emissivity was the lowest when pH was 8. 0,calcination temperature was 1100 ℃,calcination time was 2 h,and the Al2O3doping content was 3% ( mass percentage) . The crystal structure of doped ZAO powder was lead-zinc, and there exists distortion of crystal lattice in nanocrystalline ZnO. The average particle size was 10 μm. The lowest infrared emissivity reached to 0. 61 at between 8 μm and 14 μm. It means that the ZAO powders will be excellent infrared stealthy materials.

Synthesis of NiCr_2O_4 spinel coatings with high emissivity by plasma spraying

Air plasma spraying （APS） was used to produce high emissivity coatings with a NiCr204 spinel structure. The relationship between the emissivity and the crystal structure was investigated. X-ray diffraction （XRD） analyses show that NiCr204 spinel has been fabri- cated with the space group Fd3m. Scanning electron microscope （SEM） photographs show that the coating consists of a laminated structure with homogeneous grains and high porosity because of the unique feature of plasma spraying. The emissivity measurement and Fourier transformation infrared radiation （FT-IR） spectra show that NiCr204 has a high emissivity of about 0.91 because of its special spinel structure APS is a suitable method to produce high emissivity coatings.

Apparent directional spectral emissivity determination of semitransparent materials

An inverse estimation method and corresponding measurement system are developed to measure the apparent spectral directional emissivities of semitransparent materials. The normal spectral emissivity and transmissivity serve as input for the inverse analysis. Consequently, the refractive index and absorption coefficient of the semitransparent material could be retrieved by using the pseudo source adding method as the forward method and the stochastic particle swarm optimization algorithm as the inverse method. Finally, the arbitrary apparent spectral directional emissivity of semitransparent material is estimated by using the pseudo source adding method given the retrieval refractive index and absorption coefficient. The present system has the advantage of a simple experimental structure, high accuracy, and excellent capability to measure the emissivity in an arbitrary direction. Furthermore, the apparent spectral directional emissivity of sapphire at 773 K is measured by using this system in a spectral range of 3 μm-12 μm and a viewing range of 0°-90°. The present method paves the way for a new directional spectral emissivity measurement strategy.

Spatiotemporal Variations of Microwave Land Surface Emissivity(MLSE)over China Derived from Four-Year Recalibrated Fengyun 3B MWRI Data

Microwave Land Surface Emissivity(MLSE)over China under both clear and cloudy sky conditions was retrieved using measurements of recalibrated microwave brightness temperatures(Tbs)from Fengyun-3B Microwave Radiation Imager(FY-3B MWRI),combined with cloud properties derived from Himawari-8 Advanced Himawari Imager(AHI)observations.The contributions from cloud particles and atmospheric gases to the upwelling Tbs at the top of atmosphere were calculated and removed in radiative transfer.The MLSEs at horizontal polarizations at 10.65,18.7,and 36.5 GHz during 7 July 2015 to 30 June 2019 over China showed high values in the southeast vegetated area and low values in the northwest barren,or sparsely vegetated,area.The maximum values were found in the belt area of the Qinling-Taihang Mountains and the eastern edge of the Qinghai-Tibet Plateau,which is highly consistent with MLSEs derived from AMSR-E.It demonstrates that the measurements of FY-3B MWRI Tbs,including its calibration and validation,are reliable,and the retrieval algorithm developed in this study works well.Seasonal variations of MLSE in China are mainly driven by the combined effects of vegetation,rainfall,and snow cover.In tropical and southern forest regions,the seasonal variation of MLSE is small due to the enhancement from vegetation and the suppression from rainfall.In the boreal area,snow causes a significant decrease of MLSE at 36.5 GHz in winter.Meanwhile,the MLSE at lower frequencies experiences less suppression.In the desert region in Xinjiang,increases of MLSEs at all frequencies are observed with increasing snow cover.

A New Method of Measurement of the True Temperature and Emissivity of Non-Black Body Using One Component of Wien’s Spectrum of Thermal Radiation

It is shown that the measurement of only one component of the Wein’s spectrum of thermal radiation in range λT ≤ 3000 (°C μm) is sufficient to estimate the true temperature and spectral emissivity of the selected component with sufficient accuracy, although more than one hundred years this statement was considered as incorrect. The proposed method is based on the formation of the linear dependence of the logarithm of the emissivity of not real wavelengths and artificially generated “virtual” spectral components.

Effects of Wall Emissivity on Aerodynamic Heating in Scramjets

The effects of the wall emissivity on aerodynamic heating in a scramjet are analyzed.The supersonic turbulent combustion flow including radiation is solved in the framework of a decoupled strategy where the flow field is determined first and the radiation field next.In particular,a finite difference method is used for solving the flow while a DOM(iscrete ordinates method)approach combined with a WSGGM(weighted sum of gray gases)model is implemented for radiative transfer.Supersonic nonreactive turbulent channel flows are examined for a DLR hydrogen fueled scramjet changing parametrically the wall emissivity.The results indicate that the wall radiative heating rises greatly with increasing the wall emissivity.As the wall emissivity rises,the radiative source and total absorption increase,while the incident radiation decreases apparently.Notably,although the radiative heating can reach a significant level,its contribution to the total aerodynamic heating is relatively limited.

Kubelka-Munk Revised Theory for High Solar Reflectance and High Long-wave Emissivity Coatings Designing

The Kubelka-Munk revised theory was adopted to derive the mix design theory of high solar reflectance and high emissivity coatings.When the concentration of each colorant is within 20%,and the width of the coating is more than 200 μm,each colorant has enough covering power in visible and near-infrared spectral range.It can be assumed that the addition of colorants in coatings can only change the solar spectral absorption ratio rather than solar spectral scattering coefficient.The spectral scattering coefficient of coatings tends to a constant.The spectral absorption-scattering property of each colorant can be characterized through one parameter.The spectral absorption-scattering coefficient of coatings can be calculated with the multivariate linear relationship of each pigment.Moreover,the results can be expanded for high solar reflectivity and high long-wave emissivity coating preparation.The accuracy of Kubelka-Munk revised theory has been tested and verified through comparison between the calculated value and tested value of coating reflectance.

Experimental investigation of the normal spectral emissivity and other thermophysical properties of pulse-heated Ni-Ti and Au-Ni alloys into the liquid phase

In a previous paper it was shown that the normal spectral emissivity at 684.5 nm of a binary alloy can be lower than that of the pure constituent components. For the actual probes it was found that the observed values of normal spectral emissivity of the alloys are in between or higher than those of the pure constituent components. Experiments were conducted on the alloy systems Ni-Ti and Au-Ni. Their emissivity as well as electrical resistivity and enthalpy as a function of temperature is presented.

A Theoretical Model for the Microwave Emissivity of Rough Sea Surfaces

When sea surface wavelengths are not larger than microwave wavelengths,the microwave emissivity of Gaussian rough sea surfaces can be investigated by applying effective media theory(EMT)of rough surfaces.For one-dimensional Gaussian sea surface,the microwave emissivity model is proposed by EMT,which regards the air-sea rough interface as a new effective medium of isotropic permittivity between the top layer of air and the bottom layer of seawater.The emissivity model is controlled by the root mean square deviation(RMSD)of the rough surface height and the correlation length of the rough surface.Results clearly show that the emissivity increases along with the RMSD increase if the latter is smaller than a critical value.Furthermore,excess emissivities and the brightness temperature increments for a wind-roughened sea surface can be estimated from those of flat surfaces by fitting the RMSD as a function of wind speed.Good agreements are obtained by comparing the results of our model with the satellite data at microwave frequencies of 1.4,6.8,18,21,and 37 GHz,respectively.Moreover,these findings imply that our method can be extended to retrieve the sea surface parameters,such as RMSD and the correlation length of the rough surface,from the satellite data.

Infrared emissivity of transition elements doped ZnO

Infrared emissivity was studied in Zno.99Mo.olO （M is Mn, Fe or Ni） and Znl_xCoxO （x=0.01, 0.02, 0.03 and 0.04） powders synthesized by solid-state reaction at various temperatures. XRD patterns confirm the wurtzite structure of the prepared samples. No peaks of other phases arising from impurities are detected in Mn- and Co-doped ZnO, hut the peaks of ZnFe204 and NiO are observed in Zno.99Feo.010 and Zno.99Nio.o10. The SEM observations indicate that with larger grain sizes than those of Zn0.99Feo.010 and Zno.99Ni0.010, Co-doped ZnO exhibits smooth grain surfaces. The infrared absorption spectra show that infrared absorptions related to oxygen in Zn0.99M0.010 are much stronger than those in Co-doped ZnO. Co ions are dissolved into the ZnO lattice with Co2＋ state from XPS spectra analysis. The infrared emissivity results imply that the emissivity of Zno.99Ni0.010 is the highest （0.829） and that of Zno.99C00.010 is the lowest （0.784） at 1 200 ℃. The emissivity of Zno.99Co0.010 decreases to the minimum （0.752） at 1 150 ℃ and then increases with growing calcination temperature. As the Co doping content grows, the emissivity of Co-doped ZnO calcined at 1 200 ℃ falls to 0.758 in the molar fraction of 3% and then ascends.

Research of Environment-friendly Low Emissivity Glass

The environment-friendly glasses which integrate function and structure were introduced, among these glasses can save energy very efficiently due to its low infrared emissivity. The fundamental principle of the low emissivity glass and the research progress of this kind glass were analyzed. Meanwhile, high performance and low applied development trend of emissivity glass were reviewed.