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Analysis of Radiation Heat Transfer in Furnace

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Analysis of Radiation Heat Transfer in Furnace

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    1. Analysis of Radiation Heat Transfer in Furnace P M V Subbarao Professor Mechanical Engineering Department

    2. Complexity of Gas-Wall Radiation Process

    3. Governing equation in a gas radiation For gas radiation governing differential equation is known as Radiative Transfer Equation (RTE) The RTE for an absorbing, emitting, gray medium is Classification: Basic models and their determinants Based on quadrature set Complex geometry of the furnace

    4. Basic models for RTE in gas radiation

    5. Radiation inside furnace Types of radiation: Surface and volumetric radiation Characterization of participating media: usually, the radiant energy is scattered, absorbed and emitted by tiny suspended particles or gases like CO2 and water vapor, such media are called participating media. Gas radiation involved Absorption: attenuation of intensity ? absorption coefficient ? Emission: augmentation of intensity? emission coefficient Scattering ? scattering coefficient ? Radiant heat transfer occur from the source (Flame) to sink (water walls) in a furnace

    6. Gas radiation-Governing equation

    7. Direction cosine in 2D geometry

    8. Boundary condition

    9. DOM with heat generation

    10. Solution of RTE The exact (analytical or numerical) solution of integro- differential radiative transfer equation (RTE) is generally a formidable task. Although there have been a few attempts to formulate RTE for non-isothermal rectangular enclosures . Explicit solutions are only available for simplified situations such as black walls and constant properties etc. There is growing interest in approximate solutions for furnace design and analysis. The exact solutions even for these simplest systems are used to serve as benchmarks against which the accuracy of approximate solutions is tested.

    11. Radiation heat transferred to furnace wall Radiation heat transfer Where eeff is the emissivity of flame and water wall system. Emissivity of PC flame S : Effective thickness of radiant (flame) layer.

    12. K is the coefficient of radiant absorption Volume fraction of RO2 & H2O : rRO2 & rH2O c1 : 1.0 for coal and 0.5 for wood c2 : 0.1 for PC flame, 0.03 for Stoker flame. mh : Concentration of ash particles dh : diameter of ash particles : 13 mm for PC & 20 mm for stoker.

    13. Thermal Efficiency Factor, y If clean water wall is a perfect black body all radiation falling on it will be absorbed. Fouling (x)leads to drop in emissivity of the wall. Water walls consists of tubes which generate an angular coefficient, x. Angular coefficient varies with the location of water wall. Thermal efficiency factor is defined as the fraction of incident radiation absorbed by the tubes: The average thermal efficiency factor is calculated as

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