By applying the angular momentum equation assuming

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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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