Construction and Experimental Study of a Pelton Turbine
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Pelton turbine
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Introduction Pelton Wheel Turbine is an impulse or a constant pressure water turbine. In this case water head is very high. Pelton wheel consists of a wheel called rotor. The rotor of the turbine consists of a circular disc with a number of double spoon shaped buckets evenly distributed over the periphery. The water is the supplied from the reservoir. In such type of Turbine available hydraulic energy of the water is converted into the kinetic energy at atmospheric pressure by means of the nozzle. Each nozzle directs the jet along a tangent to the circle through the centers of the buckets. Each bucket consists of a splitter which divides the incoming jet in to two equal portions and after flowing round the smooth inner surface of the bucket the water leaves with a relative velocity almost opposite in direction to the original jet. The change in momentum of the water jet in passing over the buckets exerts tangential force on the wheel causing it to rotate. Thus converts the hydraulic energy into the mechanical energy by means of the shaft rotation.
Objective To study the operation of Pelton Wheel and also to determine the efficiency and power output of Pelton Turbine.
1
Procedures
1. First of all, perform the general start-up procedures. 2. Fully open the throttle valve and allow the water to circulate until all air bubbles have dispersed. 3. Open and adjust the spear valve for a particular nozzle opening. 4. Tighten up the tensioning screw on the pulley wheel until the turbine is almost stalled ( rotor just turning). 5. Decide on suitable increments in force to give adequate sample points and note the value of the pulley brake. 6. Slacken off the tensioning screw so no force is being applied to the turbine. 7. Tighten the screw to give the first increment in force for the brake. When readings are steady enough, record all the readings again. 8. Repeats step 7 above for a gradually increasing set of fb values. The final sample point will correspond to the turbine stalling. 9. The data may now be used for analysis and to plot the pelton turbine characteristics curve. 10. Now decrease the volume flow rate to a new setting by changing the throttle valve position and at the same time also change the spear valve position to maintain the pressure at 1.0 kgf/cm.
2
RESULT ANALYSIS
Formula Used : 1. Hi = 2. Ph =ρ 3. T = Fb r 4. Pb = 2 × π × N × T 5. Et =
×100%
Experiment 1 : Turbine Characteristic g = 9.81 m/s2 π = 3.142 r = 0.04 m ρ = 1000 kg/m3
= 9.99 m Hydraulic Power at Input, Ph Ph = p×g×Hi×Q = 1000 kg/
× 9.81 m/
×9.99 m ×9.0E - 04
= 88.20 W
Torque, T T = Fb × r = 0.0981 × 0.04 m = 0.00392 Nm
7
/s
Brake Power, Pb Pb = 2 × π × N × T = 2 × 3.142 × 29.46 × 0.00392 Nm = 7.249 W Turbine Efficiency, Et Et =
× 100%
=
× 100%
= 8.218 %
Discussion
The working principle of Pelton wheel turbine is water flows along the tangent to the path of the runner. Nozzles direct forceful streams of water against a series of spoon-shaped buckets mounted around the edge of a wheel. As water flows into the bucket, the direction of the water velocity changes to follow the contour of the bucket. When the water-jet contacts the bucket, the water exerts pressure on the bucket and the water is decelerated as it does a "u-turn" and flows out the other side of the bucket at low velocity. In the process, the water's momentum is transferred to the turbine. This "impulse" does work on the turbine. For maximum power and efficiency, the turbine system is designed such that the water-jet velocity is twice the velocity of the bucket. A very small percentage of the water's original kinetic energy will still remain in the water; however, this allows the bucket to be emptied at the same rate it is filled, thus allowing the water flow to continue uninterrupted. From the results obtained, we can see how Pelton Wheel reacts to different kind of input. Different flow rates give different value of work input. The slower the flow rates, the larger the work being put into the wheel. The efficiency of the slower flow rates is also better than faster one. The speed of the wheel also dropped when much weight being dropped until it stopped suddenly when the weight is too much for it to go against. 8
Conclusion
As a conclusion from the experiment that had been performed, we can conclude that different range of flow rates and rotational speeds influences the performance of Pelton wheel turbine. The combination of flow rate and jet velocity manipulates the power or work input. The bigger the diameter nozzle the faster the flow rates but lower in velocity jet. Therefore we need the perfect combination of both. In general, impulse turbine is high-head, low flow rate device. So we can assume that our experiment is successful due to the result we obtained.
REFERENCE
Frank M. White. 2008. Fluid Mechanics. Sixth Edition. New York: Mc Graw Hill International Edition. pp341-446.
Brady, James E. Engineering Thermodynamic. New York: John Wiley & Sons, 1997.
