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This study delves into the thermal performance of a furnace, analyzing its cooling capacity, radiation heat transfer, and combustion processes. It covers the determination of furnace size based on geometry and heat transfer efficiency, focusing on factors like emitted radiation heat flux and the absorption of heat by walls. The text explores different types of coal-fired furnaces, burner arrangements, and flame shapes, providing insights into the transfer of chemical energy and heat within the furnace. Additionally, it discusses radiation classification, participating media, and the role of gas radiation in heat transfer processes. The governing equations and models for radiation transfer in furnaces are also examined, including RTE, optical properties, and numerical methods for analysis.
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Thermal Performance Analysis of A Furnace P M V Subbarao Professor Mechanical Engineering Department Test for Cooling Capacity of Furnace Surface….
Determination of Furnace Size • = 30 to 50O • > 30O • = 50 to 55O • E = 0.8 to 1.6 m • d = 0.25 b to 0.33 b
Heat Transfer in A Furnace • The flame transfers its heat energy to the water walls in the furnace by Radiation. • Convective Heat Transfer < 5%. • Only Radiation Heat Transfer is Considered for Performance Analysis!
Simplified Approach • Emitted Radiation heat flux of flame: • Emitted Radiation = Available Heat • Heat flux absorbed by walls : Thermal efficiency factor, y. • The rate of heat absorption
Coal fired furnace • Two functions of coal fired furnace: • Release of chemical energy by combustion of fuel • Transfer of heat from flame to water walls • Combustion space surrounded by water walls Furnace Exit Structure of water walls* Hot Exhaust gases Heat Radiation & Convection Flame Burner
Tangential fired furnace* Down fired furnace Burner arrangement & flame shapes • An array of burner installed on walls or at corners of furnace • Fuel and combustion air projected from the each burner create a complex shape of flame. • Intense mixing of fuel and air stream at the centre Opposed wall fired furnace
Types of Radiation from Flames • Tri-atomic gases - CO2, H2O and SO2 • Soot particles • Coke particles • Ash particles
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
Face 1 Face 5 n North Face 3 H y η w Face 4 μ East x West e z ξ s South W Face 6 Face 2 L Gas radiation-Governing equation • Assumptions: • All six boundaries are diffuse and gray • Absorbing, emitting, non scattering gray medium • Same absorption coefficient at all points • Thermophysical properties e.g. density, specific heat, thermal conductivity and optical property like extinction coefficient are constant. • Absorption coefficient = emission coefficient Co-ordinate system for cubic enclosure Governing equation for participating media (RTE): Where; S is line of sight distance in the direction of propagation of the radiant intensity I
RTE Optically Thin Self-absorbing Optically Thick Directional Averaging Differential Approximation Energy Hybrid DTM Ray Tracing Radiation Element Basic models for RTE in gas radiation 2-Flux 4-Flux Multiflux DOM Zone MCM Numerical (FD, FV) Moment Modified- Moment PN - Approx.
