Theoretical study on thermal radiative properties of semitransparent porous media

Thermal radiative properties are significant to radiative transfer processes in semitransparent media.In order to calculate thermal radiative properties,conventional Mie formulism and its various abbreviations are generally used,which are based upon electromagnetic scattering by a sphere submerged in a non absorbing medium.For some semitransparent porous media such as ceramics where the matrix is absorbing,the conventional Mie solution is no longer valid.In this study a rigid Mie solution of electromagnetic scattering by a sphere in an absorbing medium is introduced to analyze the radiative properties of such a medium,and reliability of conventional Mie formulism is also tested.Parametric studies show that scattering coefficient and phase function of porous media are influenced significantly by matrix refractive index and size parameter.The matrix absorbing index usually has little influence.But when the absorbing index is greater than 0.01,especially under the condition where the size parameter is greater than 30,the conventional Mie formulism is not appropriate.Such a porous media may exhibit scattering or absorbing dominated characters under different conditions and an optimal pore diameter exists for a specified wavelength,which decreases with the matrix refractive index.

On the Radiative Properties of Ice Clouds:Light Scattering, Remote Sensing,and Radiation Parameterization

Presented is a review of the radiative properties of ice clouds from three perspectives： light scattering simulations, remote sensing applications, and broadband radiation parameterizations appropriate for numerical models. On the subject of light scattering simulations, several classical computational approaches are reviewed, including the conventional geometric-optics method and its improved forms, the finite-difference time domain technique, the pseudo-spectral time domain technique, the discrete dipole approximation method, and the T-matrix method, with specific applications to the computation of the singlescattering properties of individual ice crystals. The strengths and weaknesses associated with each approach are discussed.With reference to remote sensing, operational retrieval algorithms are reviewed for retrieving cloud optical depth and effective particle size based on solar or thermal infrared（IR） bands. To illustrate the performance of the current solar- and IR-based retrievals, two case studies are presented based on spaceborne observations. The need for a more realistic ice cloud optical model to obtain spectrally consistent retrievals is demonstrated. Furthermore, to complement ice cloud property studies based on passive radiometric measurements, the advantage of incorporating lidar and/or polarimetric measurements is discussed.The performance of ice cloud models based on the use of different ice habits to represent ice particles is illustrated by comparing model results with satellite observations. A summary is provided of a number of parameterization schemes for ice cloud radiative properties that were developed for application to broadband radiative transfer submodels within general circulation models（GCMs）. The availability of the single-scattering properties of complex ice habits has led to more accurate radiation parameterizations. In conclusion, the importance of using nonspherical ice particle models in GCM simulations for climate studies is proven.

Radiative properties of alumina/aluminum particles and influence on radiative heat transfer in solid rocket motor

The thermal radiation of micron-sized condensed phase particles plays a dominant role during the heat transfer process in aluminized Solid Rocket Motors(SRMs).Open research mainly focuses on the radiative properties of alumina particles while the study considering the presence of aluminum is lacking.In addition,the thermal radiation inside the SRM with consideration of the participating particles is seldom studied.In this work,the multiscale method of predicting the thermal environment inside SRMs is established from the particle radiation at microscale to the twophase flow and heat transfer at macroscale.The effective gray radiative properties of individual particles(alumina,aluminum,and hybrid alumina/aluminum)and particles cloud are investigated with the Mie theory and approximate method.Then a numerical method for predicting the thermal environment inside SRMs with considering particle radiation is established and applied in a subscale motor.The convective and radiative heat flux distributions along inner wall of motor are obtained,and it is found that the heat transfer in the combustion chamber is dominated by thermal radiation and the radiative heat flux is essentially a constant of 5.6–6.8 MW/m^(2).The convective heat transfer plays a dominant role in the nozzle and the heat flux reaches the maximum value of 11.2 MW/m^(2) near the throat.As the combustion efficiency of aluminum drops,the radiative heat flux remains unchanged in most regions and increases slightly along the diverging section wall of the nozzle.

Effects of microlens array orientation errors on plenoptic imaging of flame radiative properties and uncertainty analysis

Plenoptic imaging(PI)systems can flexibly record both spatial and angular information on flame radiation,enabling volumetric reconstruction of complex flames.The accuracy and efficiency of the reconstruction are significantly affected by the orientation parameters of the microlens array(MLA)in the system.To investigate the influence of potential parameter errors on flame light fields,we establish a typical orientation error model and employ ray-splitting-based Monte Carlo method to simulate the entire and sectioned PI for the three-dimensional flame under four error conditions,in which different radiative properties of flame(extinction coefficient,scattering albedo,and scattering phase function)are considered.Through the proposed uncertainty evaluation scheme,the flame image characteristics,intensity,structure deviations,and their local distribution for four error types are analyzed.The results show that the extinction coefficient and the MLA error type determine the flame PI uncertainty features,while the scattering properties only change the deviation levels.The major impact of the extinction coefficient on the transfer and accumulation of uncertainty in flame-sectioned PI is also revealed.

Parametrization of Mean Radiative Properties of Optically Thin Steady-State Plasmas and Applications

Plasma radiative properties play a pivotal role both in nuclear fusion and astrophysics.They are essential to analyze and explain experiments or observations and also in radiative-hydrodynamics simulations.Their computation requires the generation of large atomic databases and the calculation,by solving a set of rate equations,of a huge number of atomic level populations in wide ranges of plasma conditions.These facts make that,for example,radiative-hydrodynamics in-line simulations be almost infeasible.This has lead to develop analytical expressions based on the parametrization of radiative properties.However,most of them are accurate only for coronal or local thermodynamic equilibrium.In this work we present a code for the parametrization of plasma radiative properties of mono-component plasmas,in terms of plasma density and temperature,such as radiative power loss,the Planck and Rosseland mean opacities and the average ionization,which is valid for steady-state optically thin plasmas in wide ranges of plasma densities and temperatures.Furthermore,we also present some applications of this parametrization such as the analysis of the optical depth and radiative character of plasmas,the use to perform diagnostics of the electron temperature,the determination of mean radiative properties for multicomponent plasmas and the analysis of radiative cooling instabilities in some kind of experiments on high-energy density laboratory astrophysics.Finally,to ease the use of the code for the parametrization,this one has been integrated in a user interface and brief comments about it are presented.

Optical Properties and Spectroscopic Parameters of Sm(DBM)_3 Doped Polymethyl Methacrylate

Optical absorption spectra of Sm(DBM) 3 doped PMMA (polymethyl methacrylate) in near infrared and visible region are presented. The energy levels were assigned and analyzed in terms of the free-ion Hamiltonian model. Energy levels and reduced matrix elements calculations were carried out using the complete 198 SLJ basis sets for the 4f5 configuration. Judd-Ofelt parameters were evaluated and used to predict the radiative properties of the sample. The theoretical and experimental values for radiative lifetimes and branching ratios were discussed.

Analysis of microscopic properties of radiative shock experiments performed at the Orion laser facility

In this work we have conducted a study on the radiative and spectroscopic properties of the radiative precursor and the post-shock region from experiments with radiative shocks in xenon performed at the Orion laser facility. The study is based on post-processing of radiation-hydrodynamics simulations of the experiment. In particular, we have analyzed the thermodynamic regime of the plasma, the charge state distributions, the monochromatic opacities and emissivities, and the specific intensities for plasma conditions of both regions. The study of the intensities is a useful tool to estimate ranges of electron temperatures present in the xenon plasma in these experiments and the analysis performed of the microscopic properties commented above helps to better understand the intensity spectra. Finally, a theoretical analysis of the possibility of the onset of isobaric thermal instabilities in the post-shock has been made, concluding that the instabilities obtained in the radiative-hydrodynamic simulations could be thermal ones due to strong radiative cooling.

A Review of Aerosol Optical Properties and Radiative Effects

Atmospheric aerosols influence the earth＇s radiative balance directly through scattering and absorbing solar radiation,and indirectly through affecting cloud properties.An understanding of aerosol optical properties is fundamental to studies of aerosol effects on climate.Although many such studies have been undertaken,large uncertainties in describing aerosol optical characteristics remain,especially regarding the absorption properties of different aerosols.Aerosol radiative effects are considered as either positive or negative perturbations to the radiation balance,and they include direct,indirect（albedo effect and cloud lifetime effect）,and semi-direct effects.The total direct effect of anthropogenic aerosols is negative（cooling）,although some components may contribute a positive effect（warming）.Both the albedo effect and cloud lifetime effect cool the atmosphere by increasing cloud optical depth and cloud cover,respectively.Absorbing aerosols,such as carbonaceous aerosols and dust,exert a positive forcing at the top of atmosphere and a negative forcing at the surface,and they can directly warm the atmosphere.Internally mixed black carbon aerosols produce a stronger warming effect than externally mixed black carbon particles do.The semidirect effect of absorbing aerosols could amplify this warming effect.Based on observational（ground- and satellite-based） and simulation studies,this paper reviews current progress in research regarding the optical properties and radiative effects of aerosols and also discusses several important issues to be addressed in future studies.

THE IMPACT OF RELATIVE HUMIDITY ON THE RADIATIVE PROPERTY AND RADIATIVE FORCING OF SULFATE AEROSOL

With the data of complex refractive index of sulfate aerosol,the radiative properties of the aerosol under 8 relative humidity conditions are calculated in this paper.By using the concentration distribution from two CTM models and LASG GOALS/AGCM,the radiative forcing due to hygroscopic sulfate aerosol is simulated.The results show that:(1)With the increase of relative humidity,the mass extinction coefficiency factor decreases in the shortwave spectrum;single scattering albedo keeps unchanged except for a little increase in longwave spectrum,and asymmetry factor increases in whole spectrum.(2)Larger differences occur in radiative forcing simulated by using two CTM data,and the global mean forcing is—0.268 and—0.816 W/m^2, respectively.(3)When the impact of relative humidity on radiative property is taken into account, the distribution pattern of radiative forcing due to the wet particles is very similar to that of dry sulfate,but the forcing value decreases by 60%.

Effects of Contact Resistance on Heat Transfer Behaviors of Fibrous Insulation

In this article, a numerical model combining conduction and radiation is developed based on two flux approximation to predict the heat transfer behavior of fibrous insulation used in thermal protection systems. Monte Carlo method is utilized to determine the modified radiative properties with experimentally measured transient external temperature as high as 1 000 K. It is found that the estimated radiative properties become time-independent after about t = 3 000 s. By comparing the predicted to the measured results in transient state, the contact resistance exerts significant influences upon the temperature distribution in the specimen. Results show that the averaged absolute deviation is 3.25% when contact resistance is neglected in heat transfer model, while 1.82% with no contact resistance.

Optical extinction characteristics of three biofuel producing microalgae determined by an improved transmission method

The optical extinction characteristics of the three kinds of microalgae Nannochloropsis maritirna, Ellip- soidion sp. （277.03）, and Dunaliella tertiolecta were determined using an improved transmission method, in the 300-1800 nm spectral range. These three microalgae are promising candidates for the production of biofuels such as bio-hydrogen and biodiesel. The improved transmission method determines the spec- tral extinction coefficient of the microalgae. This is based on the measured transmittance, and employs an optical model that takes into consideration multiple reflections and refractions at the air-glass and glass-liquid interfaces. Silicon dioxide microspheres of monodisperse size were used as a model to verify the proposed method. The optical constants of the culture medium, size distributions, and extinction cross-sections of the microalgae cells were measured and analyzed. The improved transmission method is demonstrated to yield more accurate results than the traditional method. The spectral extinction effi- ciencies of the three kinds of microalgae show significant differences in the near ultraviolet and visible spectral regions. The spectral extinction efficiencies also exhibit small differences in the longer wave- length range of 950-1800 rim, with values generally less than 1.0. The measured extinction characteristics data of the three microalgae and the presented measurement method will facilitate process modeling in ohotobioreactors for biofuel oroduction.