Page 117 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

114 Chapter 4 Shell and tube heat exchanger

In order to calculate bundle cross flow area A e , we adopt B ¼ 0:5D s ¼ 0:5 0:489 ¼ 0:2445 m,
which is less than the maximum unsupported length as per Table 4.13 and is greater than 50 mm or
D s =5 (as discussed in Section 4.6.6). and obtain A e from Eq. (4.10) as
D s ðP T D 0 Þ B 0:489 ð0.03175 0:0254Þ 0:2445 2
¼ 0:0239 m
A e ¼ ¼
P T 0.03175
From Eq. (4.9), shell-side mass velocity is
m s 10:8472 2
¼ 453:858 kg=m s
G s ¼ ¼
A e 0:0239
and the linear velocity on the shell side u s is
G s 453:858
¼ 0:6392 m s, which is > 0.6 m/s and <1.5 m/s (Ok as per point 8 in
u s ¼ ¼
r s 710
Section 4.4).
In order to estimate h o , shell-side equivalent diameter De is calculated for triangular pitch from
Eq. 4.12(b) as

n o
2
2
2 2 4 0:03175 0:866 p ð0:0254Þ =4
4 P sin 60 pD =4

T o
De ¼ ¼ ¼ 0:01836 m
pD o p 0:0254
0:01836 453:858
DeG s
¼ 30862:3
m s 0:00027
This gives Re De ¼ ¼
6
3
Since 2 10 < Re De < 1 10 , we obtain Nu De from Eq. (4.11) as
1
0:55 0:55 0:333
Nu De ¼ 0:36Re 3 ¼ 172:052
De Pr s ¼ 0:36 ð30862:3Þ ð4:2715Þ
Nu De k s 172:052 0:148225 W
¼ 1389:02 .
And h o from Eq. (4.13) as h o ¼ ¼ 2
De 0:01836 m K
To obtain h i , we use correlation from Table 2.6 i.e., Nu ¼ 0:023 Re 0:8 ðPrÞ 0:33 where Re t ¼
D i u t r t 0:01859 1:985 992:22 ¼ 57031:24.
m t ¼ 0:000642
This gives Nu t ¼ 0:023 Re 0:8 Pr 0:333 0:8 0:33 ¼ 236:768.
t t ¼ 0:023 ð57031:24Þ ð4:26Þ
236:768 0:62976
Nu i k i W
¼ 8020:82 2 .
and h i ¼¼ ¼ m K
D i 0:01859
In order to calculate tube wall resistance R w , we adopt carbon steel (1.5%C) tubes from Table 4.9
and obtain its thermal conductivity k w from literature as 36 W/mK.
Considering unfinned tubes, R w from Eq. (4.15a) is
2
D o D o 0:0254 0:0254 4 m K
ln ln ¼ 1:1 10
R w ¼ ¼
2k w D o 2t 2 36 0:01859 W
Based on fouling factor Table E1A included in Appendix E, for treated cooling water with inhibitor
2 2
for velocity>1 m/s, typical fouling factor is 0.00018 m K/W and for kerosene it is 0.00018 m K/W.