theory of heat exchanging p m v subbarao professor mechanical engineering department i i t delhi...
TRANSCRIPT
![Page 1: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/1.jpg)
Theory of Heat Exchanging
P M V SubbaraoProfessor
Mechanical Engineering Department
I I T Delhi
Understanding of Qualities of An Ideal Heat Exchangers…..
![Page 2: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/2.jpg)
Theoretical Base for Working of Heat Exchangers
• A Simple adiabatic Heat Exchanger model.
phihhot cTm ,, ,
pciccold cTm ,, ,
phehhot cTm ,, ,
pceccold cTm ,, ,
Hot fluid Cold fluid
hT
cT
![Page 3: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/3.jpg)
Electrical Analogy of A Finite Heat Exchanger
Hot fluid Cold fluid
hT
cT
![Page 4: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/4.jpg)
Basic Information for Overall Resistance/Conductance
![Page 5: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/5.jpg)
Heat Transfer between two fluids separated by finite thick surface wall
![Page 6: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/6.jpg)
First Level Engineering Compromise: Area
chgainiceccpcold TTLUDQTTcm 11,,,
Energy Balance:
2211 DUDU
chlossehihhphot TTLUDQTTcm 22,,,
1
2
2
1
D
U
D
U
![Page 7: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/7.jpg)
Second Level Engineering Compromise: Teffective
Mean Temperature Difference
• A Simple adiabatic Heat Exchanger model.
phihhot cTm ,, ,
pciccold cTm ,, ,
phehhot cTm ,, ,
pceccold cTm ,, ,
![Page 8: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/8.jpg)
Second Level Engineering Compromise: T
![Page 9: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/9.jpg)
Simple Counter Flow Heat Exchangers
cpcold
hphot
cm
cmC
,
,
1C
![Page 10: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/10.jpg)
Simple Counter Flow Heat Exchangers: C < 1
![Page 11: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/11.jpg)
Simple Parallel Flow Heat Exchangers
![Page 12: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/12.jpg)
Theoretical Base for Working of Heat Exchangers
• For an Infinitesimal Heat communication between cold and hot.
• A Simple adiabatic Heat Exchanger model.
phihhot cTm ,, ,
pciccold cTm ,, ,
phehhot cTm ,, ,
pceccold cTm ,, ,
![Page 13: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/13.jpg)
Third Level Engineering Compromise: variation of U
U
![Page 14: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/14.jpg)
How many "zones" are involved in A HX?
![Page 15: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/15.jpg)
Various Simple Zones (HX)
![Page 16: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/16.jpg)
How many "zones" are involved in A HX?
• "Zones" can best be defined as regimes of phase changes where the overall heat transfer coefficient (U) will vary.
• Using T-Q (Temperature-Heat) diagrams are the best way to pinpoint zones.
• The system is defined as co-current or countercurrent and the diagram is constructed.
• The diagram on the left illustrates the use of T-Q diagrams. • These diagrams should accompany your basic (input-
output) diagram of the heat exchanger. • Defining zones is one of the most important aspects of heat
exchanger design.
![Page 17: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/17.jpg)
Role of SG in Rankine Cycle
![Page 18: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/18.jpg)
Gas to Phase Changing Fluid Heat Exchange
Liquid Heating
![Page 19: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/19.jpg)
DPNL
Platen SHT
R
RHTR
LTSH
Economiser
APH ESP ID Fan
drum
Furnace
BCWpump
Bottom ash
stack
screentubes
Thermal Structure of A Boiler Furnace
![Page 20: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/20.jpg)
dido Di
TubularFlow
Annular Flow
Overall heat transfer coefficient of a used HX, based on outside area:
ofowallfi
i
out
ii
outoutsideOverall
hRRR
AA
hAA
U11
1,
A Simple Heat Exchanger
![Page 21: Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…](https://reader036.vdocuments.net/reader036/viewer/2022062517/56649f2b5503460f94c46af7/html5/thumbnails/21.jpg)
owall
ii
outoutsideOverall
hR
hAA
U11
1,
i
owall d
d
kR ln
2
1
Overall heat transfer coefficient of a new/cleaned HX, based on outside area:
Thermal resistance of any annular solid structure:
MeanoutDPHX TUAQ