Page 419 - Design and Operation of Heat Exchangers and their Networks

402 Design and operation of heat exchangers and their networks

" #
N N
1 X 1 X 1
2 n + NC 2 ¼ 0 (8.41)
C 1 Re W ð kAÞ i
i¼1 1 i i¼1
which yields
N N N
X 1 X 1 X 1
N n n
1 i¼1 ð kAÞ Re W i i¼1 ð kAÞ i i¼1 Re W i
1
1
i
¼ " # 2 (8.42)
C 1 N N
X 1 X 1
N n
2
n
i¼1 Re W i i¼1 Re W i
1
1
N N N N
X 1 X 1 X 1 X 1
n n
2
ð kAÞ n ð kAÞ Re W Re W
i¼1 i i¼1 Re W i i¼1 i 1 i i¼1 1 i
1
C 2 ¼ " # (8.43)
N N 2
X 1 X 1
N n
2
n
i¼1 Re W i i¼1 Re W i
1
1
For calculating the dynamic viscosity at the wall temperature, μ w ,we
shall at first assume a wall temperature, and after we have got α 1 , the assumed
wall temperature can be modified with Eq. (8.30), and therefore, an iteration
is required.
The Wilson plot method was also applied to the determination of con-
densation heat transfer coefficient on horizontal tubes. Kumar et al. (2001)
used Eq. (8.33) as the tube-side correlation with n¼0.8 and m¼1/3 and the
Nusselt model for film condensation on horizontal plain tube:
" # 1=4
2 3
gρ λ Δh v,o
l,o l,o
α o ¼ C o (8.44)
μ ð t
l,o s,o t w,o Þd o
With the help of Eqs. (8.33), (8.44), Eq. (8.34) can be expressed as
Y 1
Z ¼ + (8.45)
C i C o
where
" # 1=4
2 3
gρ λ Δh v,o
l,o l,o
A o
μ ð t
l,o s,o t w,o Þd o
Y ¼ 1=3 0:14 (8.46)
Re 0:8 Pr λ i μ
i i i
A i
d i μ w,i