3.4 Internal Losses with Radial Fans
121
The volume flow rate is Q sw
= 2
2
cos β and s is the spacing of the cascade element.
The momentum conservation equation thus results in
The total pressure drop −∆p def
0,
due to tangential deflection is
In energy measure, the loss equals the kinetic energy associated to the deflection velocity. This result is similar to that of dump diffusion. With a real
cascade, the incidence loss is overestimated with the formula found, as the
deflection is not sudden, but is spread over a finite length. Incidence loss follows from
(3.32)
ρ
δ
β
Q w w
s p p
(
c os ) (
) cos .
2
1
1
2
2
−
=
−
p p
w w w
1
2
2
2
1
−
=
−
ρ
δ
(
c os ).
−
=
−
+
−
=
−
+
−
(
)
∆p
p p
w
w
w w
w
ww
def
0
1
2
1
2
2
2
1
2
2
2
2
2
1 2
2
2
1
2
2
2
,
cos ,
ρ
ρ
δ
−
=
+
−
(
) =
∆p
w w
w w
w
def
def
0
1
2
2
2
1 2
2
1
2
2
1
2
,
cos
.
ρ
δ
−
=
∆p
w
def
d ef
def
0
2
2
,
,
µ ρ
2
β
1
β
2
β
s
1
w
1
β
2
w
u
m
1
w
2
w
def
w
Fig. 3.15 Incidence at rotor entrance