Page 235 - Design and Operation of Heat Exchangers and their Networks

224 Design and operation of heat exchangers and their networks

G 2 1 2 1 1 4fL 1 2
Δp ¼ 1 σ + K c +2 + 1 σ K e
2 ρ in ρ out ρ in ρ d h ρ out
m
(5.106)

The entrance and exit pressure loss coefficients K c and K e for turbulent
flow for a multiple square-tube heat exchanger core with abrupt-
contraction entrance and abrupt-expansion exit are correlated by taking
the data from Fig. 5-4 of Kays and London (1984) as follows:

0:008106 9:5455
2
K c ¼ 0:05972σ 0:4287σ +0:3737 + 2 (5.107)
ln Re 1ðÞ
ln Re 1ðÞ
!
0:1813 0:6714 19:68
2σ 1+ + + σ
2
3
ln Re 1ðÞ
2 ln Re 1ðÞ ln Re 1ðÞ
K e ¼ 1 σ
204:9
ð
1 +0:1216 ð 1 σ 0:208 Þ 1 σÞ
Re 1ðÞ
(5.108)
At the entrances, Re (1),h,in ¼Gd h(1),h /μ h,in ¼14.6 0.002912/2.672
10 5 ¼1591, Re (1),c,in ¼1793. Similarly, we have Re (1),h,out ¼1591 and
Re (1),c,out ¼1793. Substituting the data into Eqs. (5.107), (5.108),we obtain
the coefficients as K c,h ¼0.5057, K c,c ¼0.4855, K e,h ¼0.2867, and
K e,c ¼0.2269.
The entrance pressure drop of flue gas flow can be expressed as
G 2 14:6 2
1 ðÞ,h 2 2
Δp in,h ¼ 1 σ + K c,h ¼ 1 0:3923 +0:5057
h
2ρ h,in 2 0:6988
¼ 206:2Pa
(5.109)
The exit pressure drop is calculated as
G 2 2
1 ðÞ,h 2 14:6 2
Δp out,h ¼ K e,h 1+ σ ¼ 0:2867 1+ 0:3923
2ρ h 2 0:6988
h,out
¼ 85:31 Pa
(5.110)
The frictional pressure drop is obtained by
L
2f 2ðÞ,h G 2 2 ðÞ,h h 2 0:03709 15:95 0:994
2
Δp f,h ¼ ¼ ¼ 10,270 Pa
ρ d h2ðÞ,h 0:6988 0:002614
h
(5.111)