M.P. Mengüç

Comparison of radiative transfer approximations for a highly forward scattering planar medium

Abstract We examine critically the accuracy of the two-flux, spherical harmonics and discrete ordinates methods for predicting radiative transfer in a planar, highly-forward scattering and absorbing medium. Numerical results for the radiative fluxes show that the two-flux and P3-approximations yield accurate results compared to solutions based on the FN-method. Indeed, these approximate methods are relatively simple and have potential for generalization to predict radiative transfer in multidimensional systems, as long as an appropriate simplification of the phase function is utilized.

Internal absorption cross sections in a stratified sphere

Series expressions for the radially dependent absorption cross section and angle-averaged absorption heat source function within a stratified sphere are presented. A numerically stable and accurate algorithm for computation of the internal radiative properties, as well as the overall scattering and extinction of a stratified sphere having an arbitrary number of layers is developed. The results allow for direct estimation of the degree of penetration and intensity of radiative heating in radially inhomogeneous spherical particles, and also provide an estimate of the thermal emission coefficient of particles having a radial temperature distribution.

Scattering matrix elements of fractal-like soot agglomerates

The possibility of measuring scattering-matrix (Mueller matrix) elements of soot agglomerates with laser diagnostic techniques is explored. To show this, we calculated the scattering-matrix elements of arbitrary-shaped soot agglomerates. The sensitivity of scattering-matrix elements to optical and morphological characteristics of fractal-like soot agglomerates is discussed. Finally, possible measurement techniques are suggested to identify soot structures from scattering-matrix elements.

Characterization of size and structure of agglomerates and inhomogeneous particles via polarized light

Characterization of size and structure of small particles is required in many fields, including environmental and process control and monitoring, biological and pharmaceutical research, atmospheric remote sensing, as well as combustion systems. In this paper, the use of polarized light and the concept of Mueller matrix elements for possible particle characterization studies is discussed. A summary of the research carried out in our laboratory for application to agglomerates and inhomogeneous spherical and cylindrical particles is presented. Sensitivity of the technique on a number of diAerent physical parameters is outlined. Finally, an inverse solution methodology is discussed to identify particle/ agglomerate characteristics. # 1998 Elsevier Science Ltd. All rights reserved.

On the Radiative Properties of Polydispersions : A Simplified Approach

Abstract In this paper an analysis is presented to predict the spectral absorption, extinction and scattering coefficients of polydispersions of carbon, different coals, and fly-ash particles. The normalization of the efficiency factors are given. Relatively simple, closed form expressions are derived for the spectral absorption and extinction coefficient. These simplified relations are promising for accurately predicting the radiative properties for use in multidimensional, spectral, radiative heat transfer analyses.

A sensitivity analysis for radiative heat transfer in a pulverized coal-fired furnace

Abstract An analysis is presented for the radiative transfer in a pulverized coal-fired furnace. The third order spherical harmonics approximation is used to model the radiative transfer equation (RTE) in an axisymmetric, cylindrical furnace. To account for the highly forward scattering of radiation by the particles, such as pulverized coal, char, and fly-ash, the delta-Eddington phase function approximation is employed. The temperature distribution in the medium is assumed to be given in order to decouple the RTE from the flow field and energy equations. To gain understanding of the radiative transfer in pulverized coal-fired furnaces, extensive parametric studies have been performed by changing the temperature distribution as well as the spatial and spectral radiative properties of the medium, i.e., extinction coefficient, single scattering albedo, and phase function parameters. The results of calculations are presented in graphical form and are compared with some published experimental results.

Polarized radiative transfer in a particle-laden semi-transparent medium via a vector Monte Carlo method

Abstract A vector Monte Carlo method (VMCM) is developed to model the transfer of polarized radiation in optically thick, multiple scattering, particle-laden semi-transparent media. A comprehensive description of the theoretical background of the general VMC algorithm is introduced. The model is validated against reference results in the case of a plane–parallel geometry and applied to the simulation of a nephelometric experiment to derive the effective Mueller matrix of the complete system. Details and various features of the numerical model are discussed.

Characterization of Individual Cotton Fibers via Light-Scattering Experiments

A detailed experimental/theoretical study is conducted to explore the fundamental nature of individual cotton fibers via light-scattering experiments. For this purpose, a new precision nephelometer is built and calibrated with quartz fibers. In the experiments, iris opening (viewing angle) and scanning range and rate were determined to be the key parameters for precision measurements. The experimental results are compared against the theoretical predictions based on a finite element model. It is shown that the scattered intensity profiles as a function of scattering angle (0) can be related to the quality (fineness) of cotton. At small scattering angles of θ < 10 deg, these profiles can be used to infer the shape (cross section) of cotton fibers. On the other hand, within the range of 30 deg < θ < 50 deg they may be used to evaluate single-fiber cotton quality (fineness)

Modeling of radiative transfer using multiple spherical harmonics approximations

Abstract The radiative transfer equation (RTE) has been modeled by using hybrid double and octuple spherical harmonics approximations for one-dimensional plane-parallel and two-dimensional cylindrical geometrics, respectively. The governing equations for these approximations are systems of first-order partial differential equations. In the formulation for the one-dimensional case, a linearly anisotropic scattering phase function is used, whereas, for the two-dimensional case, a delta-Eddington phase function is employed. Emitting and diffusely-reflecting boundaries are considered. Numerical solutions of the equations for the plane-parallel geometry are obtained using a software package DISPL2 and the results are compared with those available in the literature.

Spatially selective melting and evaporation of nanosized gold particles

We have developed an atomic force microscope-tip-based concept to pattern metallic nanoparticles on substrates. This new process has the potential to control the assembly of nanometer sized particles by combining their unique optical and thermophysical properties and is a flexible and low energy method of patterning at the nanoscale. The proof of concept is detailed by preliminary experimental work showing selective melting and evaporation of groups of 50 and 100 nm gold spherical particles.