By applying the angular momentum equation (assuming negligible angular momentum
for the exiting jet) to the same control volume about the axis of the turbine shaft the absolute
value of the power developed by the turbine can be written as
NT
T
P
p
w
2
=
=
(2)
where
w
is the angular velocity of the runner,
T
is the torque acting on the turbine shaft, and
N
is
the rotational speed of the runner.
The efficiency of the turbine is defined as the ratio between the power developed by the
turbine to the available water power
available
P
P
=
h
(3)
In general the efficiency of the turbine is provided as isoefficiency curves.
They show
the interrelationship among
Q
,
w
, and
h
.
A typical isoefficiency plot is provided in Figure 2.
Figure 2.
Isoefficiency curve for a laboratory-scale Pelton turbine
Under ideal conditions the maximum power generated is about 85%, but experimental
data shows that Pelton turbine are somewhat less efficient (approximately 80%) due to windage,
mechanical friction, backsplashing, and nonuniform bucket flow.
The purpose of the present
experiment is to determine the efficiency of a laboratory-scale Pelton turbine.
240
210
180
150
120
90
60
30
0
Q (L/m)
0
500
1000
1500
2000
2500
3000
Speed (rpm)
Nozzle
full open
3/4 open
5/8 open
1/2 open
1/4 open
1/8 open
10%
20%
30%
40%
50%
60%
η
T

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