me421 heat exchanger and steam generator designweb.iitd.ac.in/~pmvs/courses/mel709/mel7… · ppt...
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Results of Kern Method
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Basic Kinematic DetailsGroup
No.Tube Side
Velocity (m/s)
Number of Tubes
Shell Diameter
length STHX
(m)
Ds/L
1
2
3
4
5
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Performance Details
Group No.
Number of Tubes
Tube side Re
Shell side Re
Tube side h
(W/m2.K)
Shell side h
(W/m2.K)
1
2
3
4
5
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Performance Details
Group No.
Tube side p, Pa
Shell side p, kPa
Uclean Ufouled
1
2
3
4
5
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Actual Shell Side Heat Transfer Coefficient :Bell-Delaware Method
P M V SubbaraoProfessor
Mechanical Engineering DepartmentI I T Delhi
Five corrections to Cross Flow Heat Transfer…..
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Shell-side heat transfer coefficient
Where hi is heat transfer coefficient for ideal cross flow past a tube bank.
Jc : Segmental baffle window correction factor Jl : Correction factors for baffle leakage effects for heat transferJb : Correction factors for bundle bypass effects for heat transfer Js : Heat transfer correction for unequal baffle spacing at inlet and/or outlet.Jr : correction factor for adverse temperature gradient in laminar flow
rsblcis JJJJJhh
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Heat transfer coefficient for Ideal Cross Flow
14.0
,
32
ws
s
sps
s
m
spsii C
kSmCjh
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Area for Ideal Cross Flow
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Selection of Shell Diameter
A simple but reasonably accurate correlation was developed by Bell’s Group for single pass.
2
278.0
T
ctltubes PCL
DN
CL is tube layout constant , CL =0.87 for 30º and 60º layouts or CL=1.0 for 45º and 90º layouts.
For multipass arrangement, a correction factor ψn must be used to account for the decrease of tube count due to tube pass
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2Re33.11
as
a
o
Ti
dPaj
Where 43
Re14.01 as
aa
2Re33.11
bs
b
o
Ti
dPbf
Where 43
Re14.01 bs
bb
s
outertube
s
ss
dAm
Re
Shell-Side Reynolds Number
14.0
,
32
ws
s
sps
s
m
spsii C
kSmCjh
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Coefficients of Correlations
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Baffle Geometry
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Segmental baffle window correction factor, Jc
cc FJ 72.055.0
2sin
3602121 ctlctl
twC FF
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Segmental Baffle Cut Geometry
Segmental baffle cut height :Lbch
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Recommended segmental baffle cut values
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Jl : Correction factors for baffle leakage effects for heat transfer
Ssb is the shell-to-baffle leakage area.
Stb is the tube-to-baffle hole leakage area.
Sm is the cross flow area at the bundle centerline
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Shell-to-baffle leakage area• The shell-to-baffle leakage area within the circle
segment occupied by the baffle is calculated as:
Lsb is the diametral leakage clearance between the shell diameter and the baffle diameter, Db .
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Tube-to-baffle hole leakage area for one baffle
The total tube-to-baffle leakage area within one baffle is Stb.
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Correction factors for bundle bypass effects for heat transfer Jb, and pressure drop Rb
ptlotlsb LDDBS m
bsbp S
SF
Lptl =0 for single pass
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Unequal Baffle Spacing
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Heat transfer correction for unequal baffle spacing at inlet and/or outlet, Js
n is approximately a constant, found to be 0.6 for laminar flow and 0.333 for turbulent flow. If L* is larger than 2, it would be considered poor design, especially if combined with low Nb .
In such cases an annular distributor or other measures should be used.
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Heat transfer correction factor for adverse temperature gradient in laminar flow
where Nc is the total number of tube rows crossed in the entire heat exchanger:
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Shell side Fluid Flow in STHE