Page 184 - Design and Operation of Heat Exchangers and their Networks

172 Design and operation of heat exchangers and their networks

plate spacing. The Fanning friction factor for the single-phase flow is
given by
f sp ¼ 6:431Re 0:25 (4.140)

By means of the dimensional analysis, they proposed the evaporation
heat transfer and pressure drop correlations as

αd h,b
Nu ¼
λ l
! 0:1 0:5 1:1 2
2
G 2 ρ Δh v ρ σ ρ l
l
0:1 2
0:5
l
¼ 0:603Re lo Pr l _ x
2
ρ c p,l ΔT G 2 η G ρ ρ v
l
l
l
(4.141)
The evaporation friction factor is correlated as
Δp f ρ d h,b 4 0:35 1
m
f ¼ ¼ 3:521 10 Re lo Re eq 440 Re eq 3200 (4.142)
2
2G L
where Re lo and Re eq are calculated with Eqs. (4.105), (4.106), respectively.
Huang et al. (2007) compared their field measurement data of plate heat
exchangers with some available correlations and found that these correlations
are likely to become inaccurate outside their original ranges. For large-scale
PHE thermosiphon evaporators (flooded operation model), Cooper’s pool
boiling correlation (Cooper, 1984) appears to predict the heat transfer coef-
ficient quite accurately. The comparison among three well-known correla-
tions was studied by Garcı ´a-Cascales et al. (2007) and compared with the
Cooper correlation. Large deviation among them can be observed.
4.2 Condensation

4.2.1 Condensation on vertical plate
The laminar film condensation on a vertical plate with constant wall tem-
perature was first analyzed by Nusselt (1916), which results in the local Nus-
selt number as

1=3
α x l 1 ρ =ρ l
v
Nu x,lam ¼ ¼ (4.143)
λ f 3Re x
where the characteristic length
2 1=3
μ
l ¼ l (4.144)
gρ 2
l