燃烧流体力学讲义 (6).ppt

Chapter 6 Radiation Heat Transfer
§1 The Equation of Radiation Transfer
1. Attenuation by Absorption and Scattering
1) Absorption
(6-1)
Where Kη- linear absorption coefficient
Over a geometric path s
(6-2)
Where
Is optical thickness
Absorbtivity:
(6-3)
2) Scattering
difference between absorption and scattering
(6-4)
3) Total attenuation
extinction coefficient
Optical distance based on extinction
(6-5)
(6-6)
2. Augmentation by Emission and Scattering
1) Emission
(6-7)
Combined eqs (6-1) and (6-7) for an absorbing - emitting medium
(6-8)
For an isothermal gas layer of thickness s is
(6-9)
If only emission is considered, the emissivity is defined as
(6-10)
2) Scattering
The total spectral radiative heat flux impinging on dA
from solid angle dΩi as
This flux travels through dV for a distance
The total amount of energy scattered away from si is
The fraction
is scatteried into the cone
dW around the direction s
Fη- scattering phase function
The amount of energy flux from dWi scattered into dW
The energy flux scattered into the direction s from all ing direction si
or
(6-10)
Which is valid anywhere inside an arbitrary volume.