1. Thermal Performance Analysis of A Furnace
P M V Subbarao
Professor
Mechanical Engineering Department
Test for Cooling Capacity of Furnace Surface….

2. Further Geometrical Details of A Furnace

3. 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

4. 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!

5. Simplified Approach Thermal efficiency factor, y.
Emitted Radiation heat flux of flame:
Emitted Radiation = Available Heat
Heat flux absorbed by walls :
Thermal efficiency factor, y.
The rate of heat absorption

6. Coal fired furnace Furnace Exit 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
Burner
Flame
Heat Radiation & Convection

7. 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
Tangential fired furnace*
Down fired furnace
Opposed wall fired furnace

9. Classification of Radiation
Surface radiation
Gas radiation
Surface phenomena
Volumetric phenomena
Constant radiation intensity
Variable intensity
Basic radiation quantity-
emissive power
intensity
Simple analysis
Complex analysis

10. Types of Radiation from Flames
Tri-atomic gases - CO2, H2O and SO2
Soot particles
Coke particles
Ash particles

11. 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

12. 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
Face 5
Face 4
Face 1
Face 2 x y z L W
Face 6
Face 3
South
North
East
West H w n e s μ η ξ
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

13. Basic models for RTE in gas radiation
Optically Thin
Self-absorbing
Optically Thick
Directional Averaging
Differential Approximation
Energy
Hybrid
DTM
Ray Tracing
Radiation Element
2-Flux
4-Flux
Multiflux
DOM
Moment
Modified- Moment
PN - Approx.
Zone
MCM
Numerical
(FD, FV)