Page 191 - Design and Operation of Heat Exchangers and their Networks

Thermal design of evaporators and condensers 179

single-phase water-to-water test results is given by Eq. (4.101) or (4.113).
The condensation heat transfer coefficients are correlated as
αd h,b 0:4 1=3
Nu ¼ ¼ 4:118Re Pr (4.189)
eq l
λ l
where the equivalent Reynolds number is defined as (from Eqs. 4.104, 4.106)
" #
0:5
Gd h,b ρ l
Re eq ¼ 1 _x + _x (4.190)
μ l ρ v
The Fanning friction factor is provided as
Δp f ρ d h,b 0:0467 0:4 0:5 0:8
m
f ¼ ¼ 94:75Re eq Re lo Bo p r (4.191)
2
2G L
where ρ m is determined with the homogenous model (from Eq. 4.109)
1
ρ ¼ _x=ρ +1 _xð½ v Þ=ρ Š (4.192)
m
l
Gd h,b
Re lo ¼ (4.193)
μ l
q
Bo ¼ (4.194)
GΔh v
With the same plate heat exchanger, Kuo et al. (2005) further investi-
gated the condensation heat transfer and pressure drop of R-410A and gave
the following correlation equations
0:45 0:25 0:75
Nu=Nu lo ¼ 0:25Co Fr + 75Bo (4.195)
Δp f ρ d h,b 1:14 0:085
m
f ¼ ¼ 21,500Re eq Bo (4.196)
2
2G L
The convection number Co is defined as
ρ v 1 _x 0:8
Co ¼ (4.197)
ρ l _ x
The Froude number Fr is defined as
G 2
Fr ¼ (4.198)
2
ρ gd
l h,b
The boiling number Bo is defined by Eq. (4.194), and the equivalent Reyn-
olds number is defined by Eq. (4.190). The vapor mass fraction changes over
the exchanger were not given.