203
6.4 The Single Impulse Stage or Laval Stage
recall that it has been reasoned in Chap. 4 that the conventional loss underestimates
somewhat the real loss. As the real loss is practically undeterminable, because it
depends on the details of the expansion path, the conventional nozzle loss is applied
in the further analysis.
We define a velocity coefficient φ s with
so that
.
2
ss
s
h
f
=
In the rotor of an impulse turbine, dp = 0. So the work equation can be integrated.
It follows that
or
q
w
w
irr =
−
1
2
2
2
2
2
.
The decrease of the kinetic energy in the relative system thus is the loss. Rotor
work (Eq. 6.3) can be written as
(6.5)
,
1
s 1s
v
v
f
=
0 0
1
2
2
= +
+
d w dq irr ,
∆W
v
w
w
v
=
−
−
−
1
2
1
2
2
2
2
2
2
2
2
2
.
Fig. 6.7 h-s diagram of an
impulse turbine stage; I:
nozzle loss; II: rotor loss; III:
outlet kinetic energy
6.4 The Single Impulse Stage or Laval Stage
recall that it has been reasoned in Chap. 4 that the conventional loss underestimates
somewhat the real loss. As the real loss is practically undeterminable, because it
depends on the details of the expansion path, the conventional nozzle loss is applied
in the further analysis.
We define a velocity coefficient φ s with
so that
.
2
ss
s
h
f
=
In the rotor of an impulse turbine, dp = 0. So the work equation can be integrated.
It follows that
or
q
w
w
irr =
−
1
2
2
2
2
2
.
The decrease of the kinetic energy in the relative system thus is the loss. Rotor
work (Eq. 6.3) can be written as
(6.5)
,
1
s 1s
v
v
f
=
0 0
1
2
2
= +
+
d w dq irr ,
∆W
v
w
w
v
=
−
−
−
1
2
1
2
2
2
2
2
2
2
2
2
.
Fig. 6.7 h-s diagram of an
impulse turbine stage; I:
nozzle loss; II: rotor loss; III:
outlet kinetic energy