Fluid Machinery Lab MCE 4362 Experiment no 2: Study and Performance Test of a Hydraulic Reaction 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: Kaplan Turbine Unit. Kaplan Turbine Unit Runner. THEORY: In a hydraulic turbine, water is used as the source of energy. Water or hydraulic turbines convert kinetic and potential energies of the water into mechanical power. The main types of hydraulic turbines are: • Impulse Turbine • Reaction turbine The predominant type of impulse turbine is the Pelton wheel, which is suitable for a range of heads of about 150–2,000 m. The reaction turbine is further subdivided into the Francis type, which is characterized by a radial flow impeller, and the Kaplan or propeller type, which is an axial-flow machine. Francis Turbines are the most preferred hydraulic turbines for commercial production of electricity mainly because they work efficiently under a wide range of operating conditions (Head: 45400m, Flowrate: 10-700 m3 / s ). Kaplan turbines are suitable for power extraction when water energy is available at Low Head (2-25m) and High Flowrate (70800 m3/ s). “IMPULSE” VS “REACTION TURBINE”: The basic and main difference between impulse and reaction turbine is that there is pressure change in the fluid as it passes through runner of reaction turbine while in impulse turbine there is no pressure change in the runner. In the impulse turbine, first, all pressure energy of water is converted into the kinetic energy through a nozzle and a highspeed jet of water is generated. This water jet strikes the blade of turbine and rotates it. In the reaction turbine there is pressure change of water when it passes through the rotor of turbine. So, it uses kinetic energy as well as pressure energy to rotate the turbine. Due to this, it is known as reaction turbine. KAPLAN TURBINE The Kaplan Turbine is an inward flow reaction turbine which means that the working fluid changes pressure as it moves through the turbine and gives up its energy. Water enters into and leaves the turbine runner in axial direction (that’s why it is called axial flow turbine). Water enters into the turbine through a scroll-shaped casing that wraps around the turbine’s inlet guide vanes. Water is directed tangentially through the guide vanes and spirals on to a propeller shaped runner, causing it to rotate. • SPIRAL/VOLUTE/SCROLL CASING: It constitutes a closed passage whose cross-sectional area gradually decreases along the flow direction, area is maximum at the inlet and negligible at the exit. GUIDE VANES/WICKET GATES: Guide Vanes are present between scroll casing and runner. This is the gate that guides water from scroll casing to runner. The motion to these vanes is given either manually by mean directing the water on to the runner at an angle appropriate to the designs of a hand wheel or automatically by a governor. The outlet is a specially shaped Draft Tube that helps to decelerate the water. Reduction of exiting water velocity facilitates pressure increment and thus minimizes the possibility of Cavitation. CORROSION • When the pressure of the water at the exit of the runner is lower than the atmosphere pressure then the cavitation phenomenon occurs. • Cavitation: Cavitation is the formation and collapsing of cavities or bubbles in a liquid mostly developed in the areas which have relatively low pressure around the pump impeller. The draft tube is channel that connects runner exit to tail race from which water is discharged from the turbine. Its main function is to reduce the velocity of water discharged to minimize the loss of kinetic energy at the outlet. Cavitation is the formation and collapsing of cavities or bubbles in a liquid mostly developed in the areas which have relatively low pressure around the pump impeller. • DRAFT TUBE: It is a gradually expanding tube which discharges water, passing through the runner, to the tailrace. Kaplan Turbines are widely used throughout the world for electrical power production. They cover the lowest head hydro sites and are especially suited for high flow conditions. Large Kaplan Turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90%. They are very expensive to design, manufacture and install but operate efficiently for decades. General layout of hydro power plant using a reaction turbine HYDRAULIC POWER ( Ph ) In the experimental setup, the “Flow Rate Q” of water can be estimated from the “differential height reading of the manometric fluid (mercury), Δh ” by using the following empirical formula, 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: 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 ) (i) Draw a simple 2D figure of Kaplan Turbine Identifying its salient parts. (ii) What will happen if we use Kaplan Turbine for high water head applications? (iii) What is most likely to happen to a Kaplan Turbine without having any Draft Tube if we use it in commercial Hydropower sites? (iv) Consider two Kaplan Turbines: one has GV (guide vanes) at its inlet and the other hasn’t. Do you think there will be any difference between their performances? Explain your points. (v) How the geometrical features of the runner blade of Kaplan Turbine make it possible to convert Hydropower/Waterpower into rotational shaft power? (vi) Why is it necessary to twist the runner blade along its length? (vii) What would be the consequences of using a casing designed with a constant cross-sectional area, in the direction of the flow rather than spiral casing? (viii) Write short note on Cavitation. (ix) What is the basic difference between Kaplan Turbine and Propeller Turbine? (x) Define specific speed of a turbine. What is the significance of it? How do you categorize Kaplan Turbine based on its specific speed? (xi) Consider 5 Hydro-electric power stations ‘A’; ‘B’; ‘C’; ‘D’ and ‘E’. ‘A’ has been designed to operate with a head of 390m and a discharge rate of 503/ whereas ‘B’ has an operational head and discharge rate of 10m and 793/ respectively. Plant ‘C’ is a Tidal power plant in a lake in South Korea. Plant ‘D’ is operating at the estuary of a river in France and plant ‘E’ is located at the base of one of the tallest mountains in Switzerland. List the plants which will be most suitable for installing a Kaplan turbine? (xii) What is Reaction Pressure?
