Particles radiative property

Tegen, I., and A. A. Lacis, Modeling of Particle Size Distribution and Its Influence on the Radiative Properties of Mineral Dust Aerosol, J. Geophys. Res., 101, 19237-19244 (1996). 

Radiative influences of aerosols on climate are generally distinguished as direct, referring to scattering and absorption of radiation by the aerosol particles themselves, and indirect, referring to the influence of aerosols on the radiative properties... 

CCN). Changes in the concentrations of CCN may alter the cloud droplet concentration, the droplet surface reflectivity, the radiative properties of clouds (cloud albedo) (2), and hence, the earth s climate (8-101. This mechanism has been proposed for the remote atmosphere, where the radiative properties of clouds are theoretically predicted to be extremely sensitive to the number of CCN present (ID). Additionally, these sulfate particles enhance the acidity of precipitation due to the formation of sulfuric acid after cloud water dissolution (11). The importance of sulfate aerosol particles to both radiative climate and rainwater acidity illustrates the need to document the sources of sulfur to the remote atmosphere. 

The atmosphere is a complex medium in which several phases coexist gas, aerosol particles, condensed water, liquid, and ice particles. All of the interactions that may occur between these various phases are included in the term multiphase or heterogeneous chemistry. Clouds favor the development of atmospheric multiphase chemistry, as they are composed of all three atmospheric phases (i.e., gas, liquid, and solid phases that stimulate a full set of reactions). Moreover, clouds modify radiative properties by diffusion of short-wavelength radiation coming from... 

The effect of aerosol on cloudiness consists in the following (i) a certain part of aerosols acts as condensation nuclei, causing an increase in the amount of suspended small droplets, and (ii) aerosol particles, caught by clouds, change the radiative properties of clouds and, consequently, the vertical temperature profile. In its turn, this affects the conditions of the formation of cloudiness and of its subsequent transformation. 

For all categories the exact determination of the elemental carbon content is a difficult physico-chemical problem. This may seem surprising as soot is so easily observable with the eye. The role of soot in atmospheric optics and climate is now attracting substantial attention (Novakov, 1979 Wolff and Klimish, 1982). Because of its radiative properties, deliberate weather modification with soot particles has been proposed and discussed (Gray et al., 1976 Chen and Orville, 1977). 

Skocypec and Buckius [180,181] presented an analytical formulation to obtain the radiation heat transfer from a mixture of combustion gases and scattering particles. They considered band models for the gases and accounted for the absorption and scattering by particles. They developed charts similar to Hottel charts for combustion gases. The results presented can be used to obtain the average radiative properties if the particle loading information is not known accurately. (See also Refs. 182-184 for a discussion on the limits of this formulation.)... 

If the agglomeration is not considered, calculation of required radiative properties of soot particles will be straightforward. Since the size of an individual soot sphere is much smaller than the wavelength of radiation, the Rayleigh limit (for small x = kD/X) to the Lorenz-Mie theory can be used. Then, the soot absorption and scattering efficiency factors are given as... 

Fly Ash Particles. When coal particles burn in a combustion system, the ash present in coal coalesces into small micron- and submicron-sized particles and are carried throughout the system [240]. It has been shown that the shape of the fly ash particles in combustion chambers is primarily spherical. This suggests that, if the complex index of refraction of fly ash particles is known, the Lorenz-Mie theory can be used to determine the required radiative properties. 

The temperature has an insignificant effect on the radiative properties of fly ash particles [247]. Yet, if the medium temperature varies, the spectral variation of fly ash particles be-... 

In this chapter, we presented a general overview of radiative heat transfer. A number of practical models were included for the solution of the radiative transfer equation and to calculate the required radiative properties of particles, combustion gases, and surfaces. Even though the material presented can allow the reader to tackle a radiative transfer problem, it is not possible to claim that our coverage of the subject was comprehensive. We tried to list most significant references, and the reader is encouraged to consult the literature for more detailed and the most up-to-date analyses and data. 

C. Kim and N. Lior, Easily Computable Approximations for the Spectral Radiative Properties of Particle Gas Components and Mixtures in Pulverized Coal Combustors, Fuel, 74(12), pp. 1891-1902,1995. 

J. C. Ku and K-H Shim, The Effects of Refractive Indices, Size Distribution, and Agglomeration on the Diagnostics and Radiative Properties of Flame Soot Particles, in W. L. Grosshandler and H. G. Semerjian (eds.), Heat and Mass Transfer in Fires and Combustion Systems, ASME HTD-vol. 148, ASME, New York, 1990. 

T. L. Farias, U. O. Koylil, and M. G. Carvalho, Effects of Polydispersity of Aggregates and Primary Particles on Radiative Properties of Simulated Soot, Journal of Quant. Spectrosc. Radiative Transfer, 55, p. 357,1995. 

S. Manickavasagam and M. P. Mengii , Effective Optical and Radiative Properties of Coal Particles as Determined from FT-IR Spectroscopy Experiments, Energy and Fuel, 7(6), pp. 860-869,1993. 

It is assumed that the particle size is much smaller than the linear size of the system. Then, the radiative properties are FIGURE 9.7 A schematic of the coordinate system. averaged over a representative elementary volume with a... 

The scattering-absorption of incident beams by a long circular cylinder has also been studied by van de Hulst [50], He also considers other particle shapes. Wang and Tien [62], Tong and Tien [63], and Tong et al. [64] consider fibers used in insulations. They use the efficiencies derived by van de Hulst [50] and examine the effects of ks and d on the overall performance of the insulations. The effect of fiber orientation on the scattering-phase function of the medium is discussed by Lee [65]. The effective radiative properties of a fiber-sphere composite is predicted by Lee et al. [66]. 

The effective radiative properties, that is, effective transmissitivity (Tr), effective reflectivity (p,), and effective emissivity (assumed equal to absorptivity) (e,) are determined for various two-dimensional arrangements of spherical particles. Emerging correlations, relating these effective properties to the particle surface emissivity e, and medium porosity e, do not appear to depend significantly on the arrangement. These correlations obtained by Mazza et al. [76] are... 

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