radation

1. BIRLA VISHVAKARMA MAHAVIDYALAYA,BIRLA VISHVAKARMA MAHAVIDYALAYA,
ENGINEERING COLLAGE.ENGINEERING COLLAGE.
SUBJECT :-ENGINEERING THERMODYNAMICS ANDSUBJECT :-ENGINEERING THERMODYNAMICS AND
HEAT TRANSFER(2132502)HEAT TRANSFER(2132502)
TOPIC :-PRESENTATION ON RADIATIONTOPIC :-PRESENTATION ON RADIATION
GROUP NO.16GROUP NO.16
PREPARED BY :-PREPARED BY :-
 SAHARSH TANDEL -140080125029SAHARSH TANDEL -140080125029
 RUSHABH ZALAWADIAYA -140080125031RUSHABH ZALAWADIAYA -140080125031
 PATELIA KRUNAL -15PES301PATELIA KRUNAL -15PES301
 DHARMIK DAVE -15PES302DHARMIK DAVE -15PES302

2. SHAPE FACTORSHAPE FACTOR
ALGEBRAALGEBRA
PREPARED BY :- SAHARSH TANDELPREPARED BY :- SAHARSH TANDEL

3. Shape FactorShape Factor
• The shape factor may be defind as the
fraction of radiative energy that is diffusd from our
surface element and strikes the other surfce
directly with no intervenctions.

4. •Equation 31is applicable to black surface only and mut
not be used for surfaces having emissivities other than
one.
•For calculation of shape factors/geometry factors for
specific geometries and for the analiys of radiant heat
exchange between surfaces, the following propertis and
factors may be useful :
1) The shape factor is purely funcion of geometry
perameters and it is also known as geometry factor.
2) A1F12=A2F12 (reciprocity theorm)
Above relectionship is useful when one of the shape
factor is unity.
3) For a convex or flat surface, the shape factor with
respect to it self is zero (i.e F1-1=0), because one

5. Cannot see any other part of same surface.
4) For a concave surface, the shape factor with respect to
itself is not equal to zero because energy coming out from
one part of the surface is intercepted by the another part of
the same surface.
5) For the two infinite parallel surfaces the shape factor
value is unity.
F12=F21=1[A1=A2]

7. ELECTRICALELECTRICAL
ANALOGYANALOGY
PREPARED BY :- RUSHABH ZALAVADIYAPREPARED BY :- RUSHABH ZALAVADIYA

8. Electrical networkElectrical network
analogy for thermalanalogy for thermal
radiation systemradiation system
An electrical network analogy is an alternative
approach for analysing radiation heat exchange
between any surface(black or non-black).

9. Electrical network analogy for two non-Electrical network analogy for two non-
black/gray bodies exchanging heatblack/gray bodies exchanging heat
with each otherwith each other
(Q1-2)Net =Eb1-Eb2/1-ɛ1/A1ɛ1 +1/A1F12+1-ɛ2/A2ɛ2
=σA1(T1
4
-T2
4
) / 1-ɛ1/ɛ1 + 1 / F12 + 1-ɛ2/ɛ2*A1/A2
Q12 = 1 / 1-ɛ1/ɛ1 + 1/F12 + 1-ɛ2/ɛ2
Q12 = (fg)1-2σ*A1*(T1
4
-T2
4
)
(fg)1-2 is known as gray body factor .

10. Electrical network for two non-Electrical network for two non-
black bodies which are parallel toblack bodies which are parallel to
each othereach other
1)A1=A2,
2)F12=1
So, the intercharge factor or gray body
factor is reduced to,
 f1-2=(F)12=1 / 1-ɛ1/ɛ1 + 1 + 1-ɛ2/ɛ2
 1 / 1/ɛ1 + 1/ɛ2 - 1

11. Electrical network for concentricElectrical network for concentric
cylinders or spheres:cylinders or spheres:
For concentric cylinders and spheres, F1-2=1
A1 /A2 = πd1L /πd2L = d1 / d2 = r1 /r2
A1 / A2 = 4πr1
2
/ 4πr2
2
= r1
2
/ r2
2
 So,
f1-2 = (Fg)1-2 = 1 / 1-ɛ1/ɛ1 + 1/1 + 1-ɛ2/ɛ2*A1/A2

12. Radiation shieldsRadiation shields
PREPARED BY :- krunal pateliaPREPARED BY :- krunal patelia

13. •Radiation heat transfer between two surfaces can be reduced greatly by
inserting a thin, high-reflectivity (low-emissivity) sheet of material between
the two surfaces.
•Such highly reflective thin plates or shells are called radiation shields.
•Multilayer radiation shields constructed of about 20 sheets per cm
thickness separated by evacuated space are commonly used in
cryogenic and space applications.
•Radiation shields are also used in temperature measurements of fluids
to reduce the error caused by the radiation effect when the temperature
sensor is exposed to surfaces that are much hotter or colder than the fluid
itself.
•The role of the radiation shield is to reduce the rate of radiation heat
transfer by placing additional resistances in the path of radiation heat
flow.
•The lower the emissivity of the shield, the higher the resistance.

14. •Radiation heat
transfer between two
large parallel plates
•Radiation heat transfer between two large parallel plates with one
shield
•The radiation
shield placed
between
•two parallel
plates and the
radiation
network
associated
with it.
•14

17. IntroductionIntroduction
toto
Gas RadiationGas Radiation
PREPARED BY :- DHARMIK DAVEPREPARED BY :- DHARMIK DAVE

18. Radiation in absorbing- emitting mediaRadiation in absorbing- emitting media
• When a medium is transparent to radiation,
radiation propagating through such a media
remains unchanged
• However gases such as CO, NO, CO2, SO2,
H2O and various hydrocarbons absorb and emit
radiation over certain wavelength regions called
absorption bands
• We will discuss a very simple analysis of
radiation exchange in an absorbing and emitting
medium, exchange between a body of hot gas
and its black enclosure

21. Beer’s LawBeer’s Law
• If Io is the intensity of radiation at the source and I is the
observed intensity after a given path, then optical depth τ
is defined by the following equation:
∀β
•s

22. Characterization of Participating MediaCharacterization of Participating Media :-:-
 Absorption: attenuation of intensity
 Emission: augmentation of intensity
 Scattering →
– In-scattering: augmentation of intensity
– Out-scattering: attenuation of intensity

23. Equation of Radiative TranferEquation of Radiative Tranfer
• Increase in Intensity of radiation per unit length
along the direction of propagation is

24. Transmissivity, Absorptivity andTransmissivity, Absorptivity and
EmissivityEmissivity
• Solution of Radaitive Transfer Equation with the
assumption that κ λ and Ibλ(T) are constant
everywhere in the medium, gives

25. Radiation Exchange between a GasRadiation Exchange between a Gas
Body and its Black EnclosureBody and its Black Enclosure
• Assumption:
– Entire gas body is isothermal
– Enclosure wall is black
• Consider a hemispherical body of gas at uniform
temperature Tg and walls are at temperature Tw
• The intensity of spectral radiation Iλ(L) striking the
surface element dA as a result of the emission of
radiation by the gas along the path L is determined
from

26. Spectral Emissivity of GasSpectral Emissivity of Gas

27. Emissivity ChartsEmissivity Charts
• Hottel measured gas emissivity εg and presented
emissivity charts for gases such as CO2, H20,
CO, ammonia, SO2, etc. as a function of
temperature and product term PiL, where Pi is the
partial pressure (in atmospheres) of gas i in the
gas mass and L is the beam length.

29. Calculation of Radiation exchangeCalculation of Radiation exchange
between a Gas Body and Itsbetween a Gas Body and Its
enclosureenclosure
• The net radiative heat exchange Q between
the gas mass at temperature Tg and its black
surroundings at temperature Tw is

30. THANK YOUTHANK YOU