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Proceedings of the 24th National and 2nd International ISHMT-ASTFE Heat and Mass Transfer Conference (IHMTC-2017)


ISBN Онлайн: 978-1-56700-478-6

SCATTERING CROSS SECTION FOR ABSORBING AND NONABSORBING SPHERES OF Al2O3 PARTICLES WITH SPECTRAL EMISSIVITY ESTIMATION

DOI: 10.1615/IHMTC-2017.1320
pages 939-946

Rony C. Varghese
Aerothermal Design and Analysis Division Vikram Sarabhai Space Centre

Sundar B
Aerodynamic Characterization Division Vikram Sarabhai Space Centre Thiruvavanthapuram

M. J. Chacko
Aerothermal Design and Analysis Division Vikram Sarabhai Space Centre Thiruvananthapuram

Аннотация

Scattering cross sections for absorbing and non absorbing particles were derived with the spectral variation of emissivity using Mie model.
Scattering laws apply with equal validity for all wavelengths. These depend upon the size parameter which is the ratio of the circumference of the particle to the wavelength of incident radiation. Depending on the range of values of size parameter, different theories exist to define the scattering efficiencies. Scattering cross section and efficiencies of spherical particles of Al2O3 are estimated as a function of their size parameter and wavelength of the incident energy.
The Mie scattering is valid over a wide range of the size parameter. The theory of Mie scattering makes use of Ricatti Bessel function. The Ricatti Bessel functions and their derivatives appearing in the Mie coefficients are expressed uniquely in terms of polynomials of the size parameter. Validation has been carried out with approximate method suggested by Van de Hulst.
Spectral variation of emissivity for Al203 particle has been computed by Mie scattering and compared by approximate method. It is observed that trends of the curve generated by the two methods are the same and show good comparison in certain region. However the approximate formulas are not able to capture the behavior of scattering cross sections for higher particle sizes. The variation for scattering efficiency with wavelength and size parameter is nonlinear. It is seen that spectral emissivity shows an increasing trend and reaches maximum value of 0.95 at 10µm. The spectral variation of Al2O3 Particles obtained from the present study shall be used for studying the effect of Al203 particles in plume radiance intensity which can be attempted as a future work.