Fluid Machinery ME 306 Fluid Mechanics II • Fluid machinery is used to convert hydraulic energy to mechanical energy or vice versa. Part 3 Power absorbing Power producing Turbomachinery Work is done on the fluid Work is done by the fluid Mechanical Energy → Hydraulic Energy Hydraulic Energy → Mechanical Energy These presentations are prepared by Dr. Cüneyt Sert Department of Mechanical Engineering Middle East Technical University Ankara, Turkey [email protected] Please ask for permission before using them. You are NOT allowed to modify them. Pump Turbine 3-1 3-2 Classification of Fluid Machinery Classification of Fluid Machinery (cont’d) • Fluid machinery can be classified based on the motion of moving parts. 2 ) Turbomachines 1 ) Positive Displacement Machines • Turbo means ‘‘spin’’ or ‘‘whirl’’ in Latin. • Fluid is directed into a closed volume. • Turbomachines use rotating shafts with attached blades, vanes, buckets, etc. • Energy transfer is accomplished by movement of the boundary of the closed • In ME 306 we’ll study turbomachines, mostly pumps. volume. • Closed volume expands and contracts, sucking the fluid in or pushing it out. http://www.britannica.com http://www.noehill.com/ http://en.wikipedia.org nevada_county_california http://speakeasies.biz http://www.bicycleaccessories.us http://en.wikipedia.org /cal1012.asp Kaplan type Axial fan Centrifugal pump Pelton wheel Human heart Water well pump Tire pump Gear pump hydraulic turbine 3-3 3-4 Classification of Turbomachines Classification of Turbomachines (cont’d) Turbomachines Turbomachines Power absorbing Power producing Power absorbing Power producing Incompressible Compressible Incompressible Compressible Incompressible Compressible Incompressible Compressible Pump Pump Propeller • Propellers are used to generate thrust. • Pumps increase the pressure of a liquid without changing its velocity considerably. • Marine propellers work with incompressible water and aircraft propellers work with • Shown centrifugal (radial) pump is the most compressible air. common type. • Pressure difference between the front and back • Visit www.standartpompa.com to get more surfaces of the blades create the thrust. information on sizes and capacities. 3-5 3-6 Classification of Turbomachines (cont’d) Classification of Turbomachines (cont’d) Turbomachines Turbomachines Power absorbing Power producing Power absorbing Power producing Incompressible Compressible Incompressible Compressible Incompressible Compressible Incompressible Compressible Pump Propeller Fan Pump Propeller Fan Blower • The main difference between fans, blowers and compressors is the pressure difference they • create. Blowers work with medium amout of flow rates and pressure ratios. • Fans create small pressure difference. Their main • purpose is to put high amount of fluid into They are mostly centrifugal type. motion. • Shown is an industrial type blower. • Shown is axial fan of a wind tunnel. 3-7 3-8 Classification of Turbomachines (cont’d) Classification of Turbomachines (cont’d) Turbomachines Turbomachines Power absorbing Power producing Power absorbing Power producing Incompressible Compressible Incompressible Compressible Incompressible Compressible Incompressible Compressible Pump Propeller Fan Blower Compressor Pump Propeller Fan Blower Compressor Pelton wheel • Compressors work with smaller flow rates, but • Pelton wheels have buckets attached to a create very high pressure ratios. rotating disk (wheel). • Shown is a multi-stage axial compressor. • They convert kinetic energy of a high speed liquid jet into mechanical energy. • Compressors are used in gas and steam turbines, natural gas pumping stations, turbochargers, • Largest ones used at hydraulic power plants have refrigeration cycles, etc. capacities up to 200 MW. 3-9 3-10 Classification of Turbomachines (cont’d) Classification of Turbomachines (cont’d) Turbomachines Turbomachines Power absorbing Power producing Power absorbing Power producing Incompressible Compressible Incompressible Compressible Incompressible Compressible Incompressible Compressible Pump Propeller Fan Blower Compressor Pelton Hydraulic Pump Propeller Fan Blower Compressor Pelton Hydraulic Steam wheel turbine wheel turbine turbine • Hydraulic turbines are used at dams to generate • Steam turbines are used at power plants to electricity using high pressure water. generate electricity using high temperature and high pressure steam. • Common types are Francis and Kaplan. • 80 % of world’s electricity is produced by steam • Shown are the runner blades of the Francis turbines. turbines used at Three Gorges Dam / China. • Afşin-Elbistan thermal power plant has a • Atatürk Dam has a capacity of 8 x 300 MW. capacity of 4 x 344 MW. 3-11 3-12 Classification of Turbomachines (cont’d) Classification of Turbomachines (cont’d) Turbomachines Turbomachines Power absorbing Power producing Power absorbing Power producing Incompressible Compressible Incompressible Compressible Incompressible Compressible Incompressible Compressible Pump Propeller Fan Blower Compressor Pelton Hydraulic Steam Gas Pump Propeller Fan Blower Compressor Pelton Hydraulic Steam Gas Wind wheel turbine turbine turbine wheel turbine turbine turbine turbine • Gas turbines are similar to steam turbines, but • As of 2017 Turkey’s wind energy production is they use high temperature and high pressure 6 GW. Total available capacity is 48 GW. combustion gases. • World’s total wind energy production is 490 GW, • A Boeing 777 is powered by 2 turbofan engines, which is about 2.5 % of all electricity usage. each generting a thrust of ~500 kN. • There are wind turbines with more than 120 m • To learn how a turbofan engine operates visit rotor diameter, producing 6 MW of electricity http://www.youtube.com/watch?v=GpklBS3s7iU (enough for 4500 homes) (http://www.youtube.com/watch?v=LQxp6QTjgJg) 3-13 3-14 Another Classification of Turbomachines Another Classification of Turbomachines (cont’d) Turbomachines Turbomachines Power absorbing Power producing Power absorbing Power producing Uncased Cased Impulse Reaction Uncased Cased Impulse Reaction Axial Flow Axial Flow Axial Propeller Propeller Out • Fluid enters an axial flow turbomachine parallel • Uncased turbomachines do not have a solid to the axis of rotation. casing around them. • Fluid leaves the machine also in axial direction. In 3-15 3-16 Another Classification of Turbomachines (cont’d) Another Classification of Turbomachines (cont’d) Turbomachines Turbomachines Power absorbing Power producing Power absorbing Power producing Uncased Cased Impulse Reaction Uncased Cased Impulse Reaction Axial Flow Axial Radial Axial Flow Axial Radial Mixed Pelton Wind Axial Propeller Propeller wheel turbine (Kaplan) In • Kaplan turbines are axial flow machines. • In radial flow machines fluid intake is parallel to In In Out the axis of rotation. • They are preferred for low head and high flow • Rotating impeller blades push the fluid in radial rate configurations. direction. • Their capacities are less than Francis type, less • Fluid leaves the machine perpendicular to the than 200 MW. rotation axis. Out Out • They can provide efficiencies higher than 95 %. 3-17 3-18 Another Classification of Turbomachines (cont’d) Centrifugal Pump Turbomachines • Centrifugal pump is the most commonly used type of turbomachine. Power absorbing Power producing Discharge (outflow) Uncased Cased Impulse Reaction Impeller Hub Axial Flow Axial Radial Mixed Pelton Wind Axial Radial Mixed Propeller wheel turbine (Kaplan) (Banki) (Francis) Eye • Francis turbines are the most widely used Inflow turbomachines for hydropower. Blade Munson • They are of mixed flow type. Casing, housing • They can provide more than 800 MW power. or volute • For more information http://www.voithhydro.com 3-19 3-20 Centrifugal Pump (cont’d) Pump Head (ℎ푠) • For centrifugal pump details watch 푝표푢푡 http://www.youtube.com/watch?v=9nL1XhKm9q8 (Principles and parts) 푄 푉표푢푡 http://www.youtube.com/watch?v=Vq3hEe5jzSM (Pump Parts) 푝 퐴표푢푡 http://www.youtube.com/watch?v=UrChdDwHybY (Impeller animation) 푛 푉푛 푄 http://www.youtube.com/watch?v=RvOzKhUDmJM (Computer aided blade design) 푧 퐴푛 • Most important part is the impeller. It may have different designs such as Datum • Backward-curved, radial or forward-curved • Consider the BE between the inlet (suction) and outlet (discharge) of a pump. • Closed (shrouded) or open 2 2 Open, radial Closed (Shrouded) 푝푛 푉푛 푝표푢푡 푉표푢푡 + + 푧푛 = + + 푧표푢푡 − ℎ푠 Open 휌푔 2푔 휌푔 2푔 Pump head • Pump head is the difference between the total heads at the pump inlet and outlet. Called backward- Called forward- curved if rotates in curved if rotates • Pump head is a positive quantity with units of length. this direction in this direction 3-21 3-22 Pump Head (cont’d) Theoretical Analysis of a Centrifugal Pump • Elevation difference between inlet and outlet is generally negligibly small. Exercise: Consider the given schematic of a centrifugal pump. Perform a control volume analysis to derive a relation for the variation of the theoretical (ideal) pump • If suction and discharge pipe diameters are the same → 푉 = 푉 푛 표푢푡 head as a function of discharge (volumetric flow rate). • For this simplified case 푝 − 푝 ∆푝 Out ℎ = 표푢푡 푛 = 푠 휌푔 휌푔 훽2 i.e. pump head is the pressure rise across the pump expressed as a head. 푏 훽1 푟2 • Pump head is directly related to the power delivered to the fluid, known as water In 푟1 휔 1 Inlet horsepower 1 In 2 Outlet 풫푓 = 휌푔푄 ℎ푠 2 푓 for fluid Weight flow rate Blade • Pump head can be defined as the power delivered to the