Page 220 - Design and Operation of Heat Exchangers and their Networks

Optimal design of heat exchangers 209

N t,p ¼ roundup N t =N p ¼ roundup 104=2ð Þ ¼ 52
To determine the number of baffles, we set the initial values of the tube
length as L¼4.3m, which yields
ð
N b ¼ int L=l bc Þ 1 ¼ int 4:3=0:279ð Þ 1 ¼ 14
In the crossflow section, the number of effective tube rows is calculated
with Eq. (5.13):

d s 2l c 0:336 2 0:0867
N rc ¼ int ¼ int ¼ 9
s l 0:01768
As is shown in Fig. 5.1, the central angle of baffle cut can be calculated
with Eq. (5.17):
θ ds ¼ 2cos 1 ð 1 2l c =d s Þ ¼ 2cos 1 ð 1 2 0:0867=0:336Þ ¼ 2:131,
and the upper central angle of baffle cut is calculated with Eq. (5.18):
1 1
θ ctl ¼ 2cos ð ½ d s 2l c Þ=d ctl Š ¼ 2cos ð ½ 0:336 2 0:0867Þ=0:3058Š
¼ 2:020
The fraction of the number of tubes in one window section F w and the
fraction of the total number of tubes in the crossflow section F c are given by
Eq. (5.21), (5.23), respectively:

F w ¼ θ ctl sinθ ctl Þ= 2πð Þ ¼ 0:1782
ð
F c ¼ 1 2F w ¼ 0:6437
The shell-to-tube bundle clearance is defined by Eq. (5.5):

δ st ¼ d s d otl ¼ 0:336 0:3248 ¼ 0:0112 m
The shell-to-baffle clearance can be determined with Eq. (5.15):

δ sb ¼ 0:0031 + 0:004d s ¼ 0:0031 + 0:004 0:336 ¼ 0:0044 m
Because the baffle spacing l bc <0.914m, according to the TEMA
standards (TEMA, 2007), the baffle hole-to-tube clearance is taken as

δ bt ¼ 0:0008 m
The effective width of pass divider lane for rating is given by Eq. (5.31):
∗
δ tp ¼ δ tp =2 ¼ 0:019=2 ¼ 0:0095 m
Using Eq. (5.27), we obtain the shell-side crossflow area of main stream as
h p ffiffiffi i
A sc ¼ l bc δ st + 2d ctl 1 d o =sð Þ
h p ffiffiffi i
¼ 0:279 0:0112 + 2 0:3058 1 0:019=0:025Þ ¼ 0:03209m 2
ð
The shell-to-baffle leakage area is evaluated with Eq. (5.28):