Page 225 - Design and Operation of Heat Exchangers and their Networks

214 Design and operation of heat exchangers and their networks

Q _ 3:563 10 5
t s,out ¼ t s,in ¼ 66 ¼ 61:3°C
_ m s c p,s 36:3 2077

66 + 61:3 459:5 66 + 61:3 32 + 36:9
k s
t s,w ¼ t s,m ð t s,m t t,m Þ ¼
α s 2 581:6 2 2
¼ 40:6°C

(6) Calculation of tube-side pressure drop
The tube-side total pressure drop is given by

G 2 t 1 2 1 1 1 L 1 2
Δp t ¼ 1 σ + K c +2 + f D 1 σ K e
2 ρ ρ ρ ρ ρ
in out in m d i out
(5.90)
The ratio of free flow area to frontal area can be expressed as
2
σ ¼ N t d =d 2
i s (5.91)
2
2
¼ 104 0:0166 =0:336 ¼ 0:2538
The entrance and exit pressure loss coefficients for turbulent flow for a
multiple circular-tube heat exchanger core with abrupt-contraction
entrance and abrupt-expansion exit are correlated as follows by taking
the data from Fig. 5-2 of Kays and London (1984). Since the inlet and
outlet properties for seawater will not change appreciably, we use the
mean seawater temperature to calculate its viscosity and density, that is,
μ in ¼μ out ¼μ m , ρ in ¼ρ out ¼ρ m .
" #

0:02744 0:1418 9:1465
K c ¼ σ 0:4016 +0:4079 +
ln Re t ln Re t ð ln Re t Þ 2

0:02744 0:1418 9:1465
¼ 0:2538 0:4016 +0:4079 + 2
ln 32, 401Þ ln 32, 401Þ ½ ln 32, 401ފ
ð
ð
ð
¼ 0:3778
(5.92)
!
0:109 0:6314 19:65
2σ 1+ + 2 + 3 σ
ln Re t ð ln Re t Þ ð ln Re t Þ
2
1 σ K e ¼
235
ð
1 +0:01277 ð 1 σ 0:25 Þ 1 σÞ
Re t
!
0:109 0:6314 19:65
2 0:2538 1+ + + 0:2538
ð
ln 32, 401Þ ½ ln 32, 401ފ 2 ½ ln 32, 401ފ 3
ð
ð
¼
235
ð
1 +0:01277 ð 1 0:2538 0:25 Þ 1 0:2538Þ
32,401
¼ 0:3977
(5.93)