Page 215 - Design and Operation of Heat Exchangers and their Networks
P. 215
204 Design and operation of heat exchangers and their networks
J b is the correction factor for the effects of bundle and pass partition
bypasses (C and F streams):
1=3
½
ð
e C bh r b 1 2r ss Þ , r ss < 0:5
J b ¼ (5.61)
1, r ss 0:5
where
1:35, Re sd 100
C bh ¼ (5.62)
1:25, Re sd > 100
_ md o
Re sd ¼ (5.63)
A sc μ
r b ¼ A bp =A sc (5.64)
r ss ¼ N ss =N rc (5.65)
The correction factor for the effect of the bypass flow (C and F streams)
on the pressure drop, ζ b , is given by
1=3
½
ð
e C bp r b 1 2r ss Þ , r ss < 0:5
ζ ¼ (5.66)
b
1, r ss 0:5
where
4:5, Re sd 100
C bp ¼ (5.67)
3:7, Re sd > 100
J s is the correction factor for larger baffle spacing at the inlet and outlet
sections compared with the central baffle spacing:
1 n 1 n
N b 1+ l bi =l bc Þ + l bo =l bc Þ
ð
ð
J s ¼ (5.68)
ð
ð
N b 1+ l bi =l bc Þ + l bo =l bc Þ
The corresponding correction factor for pressure drop, ζ s , is given as
2 n 0 2 n 0
ð
ζ ¼ l bc =l bo Þ + l bc =l bi Þ (5.69)
ð
s
0
in which n¼1/3 and n ¼1.0 for laminar flow (Re sd 100), and n¼0.6 and
0
n ¼0.2 for turbulent flow (Re sd >100).
J r is the correction factor for adverse temperature gradient buildup in
laminar flows:
8
J r,l , Re sd 20
<
J r ¼ J r,l +1 J r,l Þ Re sd 20ð Þ=80, 20 < Re sd < 100 (5.70)
ð
:
1, Re sd 100
