FLUID MACHINERY LAB MCE 4512 EXPERIMENT NO 1: STUDY AND PERFORMANCE TEST OF A HYDRAULIC IMPULSE TURBINE LECTURER: MUHAMMAD AWAIS OBJECTIVES: i) To draw overall efficiency (η0 ) vs Flowrate (Q) curve as well as overall efficiency (η0 ) vs Head (H) curve. ii) To draw mechanical efficiency (η𝑚 ) vs Flowrate (Q) curve as well as mechanical efficiency (η𝑚 ) vs Head (H) curve. APPARATUS: Compact Pelton Turbine Unit. CIRCUIT UNIT PELTON WHEEL PUMP NOZZLE Bucket design: Spoon shaped/hemispherical bucket embedded with the periphery of disc. SPLITTER TIP THE BUCKET Function: Splits the jet into two parts. Jet after being splitted into two parts takes a U-turn in both sides of the wheel. FRONT SIDE OF THE BUCKET Nozzle Water Jet A fluid jet is a stream of fluid issuing from a nozzle with a high velocity and hence a high kinetic energy. When jet impinges on a plate or a vane, it exerts a force on it due to change in momentum. This force can be evaluated by using impulse momentum principle. THEORY: PELTON WHEEL/TURBINE: An American Engineer Lester A. Pelton discovered this turbine in 1880. It operates under very high heads (up to 1800 m or more) and requires comparatively less quantity of water. The Pelton wheel is a classical example of an impulse turbine. In these machines the total head of the incoming fluid (the sum of the pressure head, velocity head, and elevation head) is converted into a large velocity head at the exit of the supply nozzle (or nozzles if a multiple nozzle configuration is used). General layout of hydro power plant using a reaction turbine PELTON WHEEL/TURBINE: Both the pressure drop across the bucket (blade) and the change in relative speed (i.e., fluid speed relative to the moving bucket) of the fluid across the bucket are negligible. The space surrounding the rotor is not completely filled with fluid. It is the impulse of the individual jets of fluid striking the buckets that generates the torque. PELTON WHEEL PELTON WHEEL/TURBINE: The buckets are fixed on the periphery of a circular wheel (also known as runner), which is generally mounted on a horizontal shaft, vertical shaft configuration is also possible. Vertical Shaft Circular wheel Buckets The primary feature of the impulse turbine with respect to fluid mechanics is the power production as the water jet is deflected by the moving buckets. The impact of water on the buckets causes the runner to rotate and thus develops mechanical energy PELTON WHEEL The buckets deflect the jet through an angle of about 160 and 165 degrees in the same plane as the jet. The buckets are so shaped that water enters tangentially in the middle and discharges backward and flows again tangentially in both the directions to avoid thrust on the wheel. A1 >A2 A1 A2 • A force exerted by the Jet on the Stationary Curved Plate Q= AV • Jet strike the plate at the center After doing work on the buckets water is discharged in the tailrace, and the whole energy transfer from nozzle outlet to tailrace takes place at constant pressure. • Pelton wheel as a hydraulic turbine is used to generate electricity with the help of mechanical energy. • In this way, at first the hydraulic power/water power ( Ph ) is converted into mechanical power/shaft power ( Pm ) by Pelton wheel. • The shaft of the Pelton wheel is coupled to the rotor of the generator hence the mechanical power is transferred to the generator. • The generator then converts this mechanical power into electrical power ( Pe ). MATHEMATICAL FORMULATION: HYDRAULIC POWER ( Ph ) This is the power of water which is developed due to height (head) of water. But here in this experiment the huge water head (H) required for Pelton wheel is not practical to achieve due to limitation of height in the laboratory. So, a pump is used to create this head artificially. HYDRAULIC POWER ( Ph ) In the experimental setup, the “Flow Rate Q” of water can be estimated directly from the Rotameter in the unit of cubicmeter/hour. The water head H, developed artificially by the pump at the turbine inlet can be calculated with the help of a differential pressure gage. The pressure gage measures the pressure difference which is developed across the pump. The gage reading ΔP and water head H are related by the following expression: MECHANICAL POWER (𝑷𝒎 ) This power is the result at the turbine shaft that means the rotational power of the shaft. This output power of the turbine is the mechanical power. Mechanical power is measured by measuring the torque (T) created in the shaft as well as its rotational speed ( n ) simultaneously. The torque developed (T) at the turbine shaft can be measured by applying an external torque equivalent to this torque. To apply this external torque a weight (W) is loaded at a perpendicular distance (r) from the shaft center. ELECTRICAL POWER (𝑷𝒆 ) DATA TABLE Assignment Questions: Draw a simple figure of Pelton Wheel Turbine Identifying its distinct features. A Pelton Wheel operates in High head, Low flow condition. What will happen if you use Pelton Wheel for low water head applications? How was the required head for Pelton Wheel generated during the experiment? Write down the Advantages and Disadvantages of Pelton Wheel over other types of impulse turbine. What is the function of a casing in a Pelton Wheel? The rotational speed of a Pelton Wheel’s Runner is 500 rpm, diameter of the runner is 2.5 m. The speed of water jet impinging on the buckets is 40 m/s. How much power has been extracted from water? What would be your answer if you increase the water jet speed around 3.27 times? Calculate the efficiency of the generator in this particular experiment for all the observations you have taken. In order to get the maximum generator efficiency, at what flowrate water should be supplied to the turbine? Suppose you are the “Chief Engineer, Turbine Operation and Maintenance” of a Hydro-electric powerplant which supplies electricity demand on Peak Hours (i.e. 8 pm to 12 am) only. Your Powerplant uses a Pelton Wheel as the prime mover of the generators. The Average load expectancy on the plant is around 50 MW. On a cold winter night, the load on the plant suddenly reduced to 25 MW. What would you do as an on-duty engineer to synchronize the generators to the new reduced demand? Describe the flow control and stopping (or braking) mechanism of Pelton Wheel. Appropriate figures are preferred. Write short notes on the main elements (or components) of a Hydroelectric Power Plant run by Pelton Wheel. According to researcher M. Nechleba, for a Pelton Turbine which has diameter ratio (Water jet dia. to Runner dia.) of 1/6, 17 to 21 buckets to be installed on the runner for optimum performance. What is most likely to happen if the number of buckets is inadequate? REFERENCES a) Turbomachinery Design and Theory by Rama S.R. Gorla and Aijaz A. Khan. b) Fundamentals of Fluid Mechanics by Munson and Young. c) https://www.youtube.com/watch?v=rf9meqw2SQA, “Pelton Turbine/Wheel Working & Design” from YouTube Channel “Learn Engineering”. d) https://www.youtube.com/watch?v=qbyL--6q7_4, “Pelton Turbine” from YouTube Channel “mekanizmalar”.
