Page 218 - Design and Operation of Heat Exchangers and their Networks

Optimal design of heat exchangers 207

4 3
X n X n 2 2 3
ρ ¼ a n t + S b n t + b 4 S t kg=m (5.78)
sw
n¼0 n¼0
5
3
with a 0 ¼999.9, a 1 ¼0.02034, a 2 ¼ 6.162 10 , a 3 ¼2.261 10 ,
8
a 4 ¼ 4.657 10 , b 0 ¼802.0, b 1 ¼ 2.001, b 2 ¼0.01677,
b 3 ¼ 3.060 10 ,and b 4 ¼ 1.613 10 ,for p¼1bar, 0°C<t<180°
5
5
C, 0<S<0.16kg/kg, where S (kg/kg) is the salinity of seawater.
3
X
n
ð
c p,sw ¼ a n t 68 + 273:15Þ kJ=kgKÞ (5.79)
ð
n¼0
for 0°C<t 68 <180°C and 0<S p <180g/kg, where
4 2
2
a 0 ¼ 5:328 9:76 10 S p +4:04 10 S
p
4
6 2
a 1 ¼ 6:913 10 3 +7:351 10 S p 3:15 10 S
p
6
9 2
a 2 ¼ 9:6 10 6 1:927 10 S p +8:23 10 S
p
9 9 12 2
a 3 ¼ 2:5 10 +1:666 10 S p 7:125 10 S
p
andT 68 isthetemperaturebasedontheinternationalpracticaltemperaturescales
7 2
of 1968. For 0°C<t 68 <180°C, t 68 ¼1.000293t 90 3.894 10 t 90 (°C).
! 0:333

343:5+ 0:037S p t 68 + 273:15
ð
lg λ sw Þ ¼ lg 240 + 0:0002S p +0:434 2:3 1
t 68 + 273:15 647 + 0:03S p
(5.80)
for 0°C<t 68 <180°C, 0<S p <160g/kg and λ sw in mW/mK.
μ =μ ¼ 1+ AS + BS 2 (5.81)
w
sw
where
5 2
2
A ¼ 1:541 + 1:998 10 t 9:52 10 t
4 2
2
B ¼ 7:974 7:561 10 t +4:724 10 t
and μ w is the dynamic viscosity of pure water based on the IAPWS 2008
data:
5 2 1
μ ¼ 4:2844 10 +0:157 t +64:993Þ 91:296 sPa
ð
w
Let the outlet temperature of the seawater be its inlet value, that is,
t t,m ¼t t,w ¼32°C. Using Eqs. (5.78)–(5.81), we have
3
ρ ¼ 1020:6kg=m ,c p,t ¼ 4008:2J=kgK,λ t ¼ 0:61814 W=mK,
t
μ ¼ 8:2398 10 4 sPa, Pr t ¼ 5:3429:
t
The thermophysical properties of polyalkyleneglycol-based (PAG)
high-performance lubricant 11 are correlated for 0°C t 100°Cas
follows: