MODELING OF RADIATIVE HEAT TRANSFER IN MULTIDIMENSIONAL ENCLOSURES USING SPHERICAL HARMONICS APPROXIMATION (COMBUSTION, SCATTERING)
Abstract
The radiative heat transfer in multidimensional enclosures containing inhomogeneous, absorbing, emitting, and anisotropically scattering media is studied. The first and the third order spherical harmonics approximations (i.e., P(,1) and P(,3), respectively) are employed to solve the radiative transfer equation (RTE) in three-dimensional rectangular as well as two-dimensional, axisymmetric cylindrical enclosures. For the P(,3)-approximation, the RTE is analytically reduced to six elliptic partial differential equations for three-dimensional enclosures, and to four equations for axisymmetric, cylindrical enclosures. For the P(,1)-approximation, only one elliptic partial differential equation is obtained for both two- and three-dimensional enclosures. These equations are solved using accurate finite difference and finite element algorithms. The model equations are evaluated by comparing the predictions with experimental data as well as with results obtained from rigorous models. In solving the radiative transfer equation, the radiative properties of the medium are required. For the radiative properties of polydispersions, such as pulverized coal, char, and fly-ash, simple, closed form expressions are obtained. For the radiative properties of combustion gases, the models available in the literature are discussed and the appropriate and compatible models are identified. The models developed are used to study the radiative transfer in a pulverized coal-fired furnace, and the results are compared with the available experimental data. For the particular system studied here it has been found that the concentration distribution of pulverized coal and fly-ash particles, and soot volume fraction have the largest impact on the predictions of the radiative fluxes and radiative flux divergences in the medium as well as on the cylindrical wall. Scattering of radiation by coal and fly-ash particles, the scattering phase function for the particles, the wall emissivity, and the radial temperature distribution have been identified as the important model parameters in calculating the radiative heat transfer in pulverized coal-fired furnaces.
Degree
Ph.D.
Subject Area
Mechanical engineering
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