Turbo Machines Pumps and Turbines ME 268

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1 Turbo Machines Pumps and Turbines ME 268

2 Turbo Machines Turbo machines are dynamic fluid machines that either extract energy from a fluid (turbine) or add energy to a fluid (pump) as a result of dynamic interactions between the device and the fluid. (Latin Turbo means to spin or whirl)

3 Classifications According to energy consideration Machines that supply energy to fluid (Pumps) An increase in pressure takes place in pumps, fans, compressors and propellers. Machines that extracts energy from fluid (Turbines) A decrease in pressure takes place in turbines, wind mills. Machines that are a combination of both (Energy transmitters and torque converters)

4 Classifications (contd ) Based on direction of flow Axial flow Radial flow Mixed flow Based on the manner of transmission of energy Kinetic displacement (Centrifugal pumps and turbines) Positive displacement (Reciprocating pumps)

5 Pumps

6 Pumps A pump pis a device used to move liquids or slurries. A pump moves liquids or gases from lower pressure to higher pressure, and overcomes this difference in pressure by adding energy to the system. Mechanical Energy Hydraulic energy

7 Pumps Fig: Tire pump Fig: Human heart Fig: Centrifugal pump

8 Pumps Classification (contd) Pumps are divided into two fundamental types based on the manner in which hthey transmit energy to the pumped media: kinetic or positive displacement. In kinetic displacement,, a centrifugal force of the rotating element, called an impeller, impels kinetic energy to the fluid, moving the fluid from pump suction to the discharge. Positive displacement uses thereciprocating actionofoneof one or several pistons, or a squeezing action of meshing gears, or other moving bodies, to displace the fluid from one area into another (i.e., moving the material lfrom suction to discharge). Sometimes the terms inlet (for suction) and exit or outlet (for discharge) g) are used.

9 Pumps Applications To deliver fluid at a higher elevation or at a long distance. To deliver fluid at a pressurized device For the control of hydraulic systems For drainage system, removing slurries, mud, water For irrigation systems

10 Centrifugal Pumps The hydraulic machines that converts the mechanical energy into pressure energy by means of centrifugal force acting on the fluid are called centrifugal pumps. Centrifugal pump is radial flow type. Used for high head and relatively low flow rate 3 important parts are Impeller Vl Volute casing Suction and delivery pipes.

11 Centrifugal Pumps

12 Centrifugal Pumps (Contd ) The rotating part of the centrifugal pump is called impeller. It is a rotating solid disk with curved blades. Impellers could be open, semi open or closed. Open Semi - Open Closed

13 Centrifugal Pumps (Contd ) Backward curved Radial curved Forward curved For Incompressible fluids (water) backward curved vanes are used (pumps) For compressible fluids (air) forward curved vanes are used (compressors)

14 Centrifugal Pumps (Contd ) Casing is an airtight passage surrounding the impeller which converts the kinetic energy of the fluid leaving the impeller into pressure energy. Suction pipe is connected to the inlet of the pump and other side is dipped d into the fluid in a sump. Delivery pipe is connected to the outlet of the pump and other end delivers the fluid at required height.

15 Centrifugal Pumps (Contd ) Working principle The impeller is keyed onto a shaft which is mounted on bearings and is coupled to a motor which rotates the impeller. The kinetic energy of the impeller is transmitted to the fluid and its velocity increases. The volute casing converts the kinetic energy of the fluid to pressure energy. The pressure at the center of the impeller (eye) decreases as the fluid flows outward. The decrease in pressure causes the fluid of the sump to continuously flow through the suction pipes. The high pressure fluid is delivered through the delivery pipe.

16 Centrifugal Pumps (Contd )

17 Centrifugal Pumps (Contd )

18 Centrifugal Pumps (Contd )

19 Centrifugal Pumps (Contd ) Priming The pump casing must be filled with liquid before the pump is started, or the pump will not be able to function. A pump is said to be primed when all the air in suction pipe, casing, and in dli delivery pipe up to the valve is driven out and its place is occupied by liquid to be pumped.

20 Centrifugal Pumps (Contd ) Cavitations If the suction pressure at the eye of the impeller falls below the vapor pressure of the fluid being pumped, the fluid will start to boil. Any vapor bubbles formed by the pressure drop at the eye of the impeller are swept along the impeller vanes by the flow of the fluid. When the bubbles enter a region where local pressure is greater than saturation pressure farther out the impeller vane, the vapor bubbles bbl abruptly collapse. This phenomenon is called cavitation.

21 Centrifugal Pumps (Contd ) NPSH (Net positive suction head) To avoid cavitation in centrifugal pumps, thepressureof the fluid at all points within the pump must remain above saturation pressure. The net positive suction head available (NPSHA) is the difference between the pressure at the suction of the pump and the saturation pressure for the liquid being pumped. The net positive suction head required (NPSHR) is the minimum net positive suction head necessary to avoid cavitation. NPSHA must be greater than NPSHR to avoid cavitation. NPSHA > NPSHR

22 Centrifugal Pumps (Contd ) Configuration of pumps Pumps in parallel For high flow rate requirement Head or pressure developed is same as the individual pump Flow rate is the summation of the individual pumps Pumps in series For high head or pressure requirement Flow rate remains same as the individual pump Head or pressure is the summation of two pumps.

23 Centrifugal Pumps (Contd )

24 Centrifugal Pumps (Contd ) High velocity vs. High pressure Water can be raised from one level to a higher level in two ways High pressure and High velocity High velocity method is very inefficient since the friction increases with proportional to the square of the velocity High pressure method is efficient because of low velocity andfriction friction.

25 Axial flow pump Turbine pump o Used where high flowrates at low heads are required o Axial flow pumps are often called propeller pumps. o For this type of pump the flow is primarily in the axial direction (parallel to the axis of rotation of the shaft)

26 Centrifugal Pumps (Contd ) Specific Speed (N S ) S It is the speed of a pump with a discharging capacity of 1 m 3 /sec and a head of 1 m. N S = n Q / H 3/4 n = speed of the pump Q = discharge of the pump H = head of the pump Pump selection is done based on the specific speed.

27 Positive Displacement Pumps A positive displacement pump causes a liquid or gas to move by trapping a fixed amount of fluid and then forcing (displacing) that trapped volume into the discharge pipe. Periodic energy addition Added energy forces displacement of fluid in an enclosed volume Fluid displacement results in direct increase in pressure Two types of PDPs Reciprocating PDP (Tube well, diaphragm pump) Rotary PDP (Gear pump, Vane pump)

28 Reciprocating PDP In a reciprocating pump, a volume of liquid is drawn into the cylinder through the suction valve on the intake stroke and is discharged under positive pressure through the outlet valves on the discharge stroke. The discharge from a reciprocating pump is pulsating. This is because the intake is always a constant volume. Often an air chamber is connected on the discharge side of the pump to provide a more even flow by evening out the pressure surges. Reciprocating pumps are often used for sludge and slurry.

29 Reciprocating PDP

30 Turbines

31 Turbines Turbines are devices that convert the energy of fluid into mechanical energy. The fluid can be water, steam, flue gas etc The energy of the water can be in the form of potential or kinetic energy. Steam turbine and gas turbine uses the thermal energy of steam and flue gas respectively.

32 Hydroelectric Power Plant

33 Classification of Hydroelectric Power Plant According to the International EnergyAssociation (IEA), based on the installed capacity, hydroelectric stations can be divided are as follows: o Micro hydro installed capacity < 100 kw o Mini hydro installed capacity 100kW to 1 MW o Small hydro installed capacity 1 MW to 30 MW o Large hydro installed capacity > 30 MW

34 Turbines Classification According to the energy used Impulse turbine Reaction turbine Direction of water flow Ailfl Axial flow Rdili Radial in axial ilout Inward flow Outward flow According to the head available to the inlet of turbine High Head Turbine ( m), Pelton Wheel Medium Head Turbine (50 250m), Francis Turbine Low Head Turbine ( <50m), Kaplan Turbine According to the fluid used Water Turbine (Pelton Wheel, Francis Turbine, Kaplan Turbine) Gas Turbine Steam Turbine

35 Turbines Classification (Contd ) Impulse Turbine All available head of water is converted into kinetic energy or velocity head in a nozzle. The water shoots out of the nozzle and hits a bucket which rotates a shaft. Water is in contact with atmosphere all the time and water discharged from bucket fall freely The flow is similar to open channel flow and works under atmospheric pressure. The kinetic energy of water is converted to mechanical energy. The water entering the turbine exerts a force in the direction of theflow. Pelton wheel is an example.

36 Turbines Classification (Contd ) Reaction Turbine The entire water flow takes place in closed conduit and under pressure. At the entrance to turbine/runner only part of the energy is converted to kinetic energy, remaining into pressure energy The flow is similar to the closed conduit flow. The water exerts a reaction opposite to the direction of its flow while leaving the turbine. Reaction turbines may be inward or outward or radial flow. Francis turbine, Kaplan Turbines are some example

37 Pelton Wheel Impulse Turbine It consists of a wheel mounted on a shaft. Buckets are mounted on the periphery of the wheel Water is impinged on the buckets and energy is transferred The water has only kinetic energy Each bucket is shaped like a double hemispherical cup with a sharp edge at the center. Pl Pelton wheel lis used for high h head of water ( m) The flow is tangential.

38 Pelton Wheel

39 Pelton Wheel

40 Reaction Turbine Francis Turbine o The Francis turbine is a reaction turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy. o The water enters into a casing with a relatively low velocity, passes through guide vanes located around the circumference andflows through the runner and finally discharges into a draft tube sealed below the tailwater level. Th f h h d il i l l o The water passage from the headrace to tail race is completely filled with water which acts upon the whole circumference of the runner.

41 Francis Turbine (Contd.) A large part of the power is obtained from the difference in pressure acting on the front and back of the runner buckets, and only a part of total power is derived from the dynamic action of the water. Th j it f th F i t bi i d di l The majority of the Francis turbines are inward radial flow type and most preferred for medium heads.

42 Francis Turbine (Contd.)

43 Kaplan Turbine The Kaplan turbine is a propeller type water turbine that has adjustable blades. It is an inward flow reaction turbine Because of the adjustable blades it is possible to run at maximum efficiency at any load Water flows through the guide vanes, and then flows axially through the runners. The runner blade angles can be changed by a lever. It can work on very low head but requires high flow rate.

44 Kaplan Turbine

45 Kaplan Turbine

46 Application of Turbines Almost all electrical power on Earth is produced with a turbine of some type. Very high efficiency turbines harness about 40% of the thermal energy, with the rest exhausted as waste heat. Most jet engines rely on turbines to supply mechanical work from their working fluid and fuel as do all nuclear ships and power plants.

47 Gas Turbine Gas turbine works due to the flow of flue gas through the stator and runner blades. Gas turbines have 3 major components Compressor Combustion chamber Turbine Compressor compresses air and supplies it to the combustion chamber. In the combustion chamber the fuel is burnt with the help of the compressed air and the product of combustion also called flue gas is flowed through the turbine The flue gas moves the turbine blades.

48 Gas Turbine Application Gas turbine has two major applications In power generation For propulsion (Jet Engine) In power generation the main target tis to rotate tt the generator shaft with the help of the turbine. In the propulsion engines, the main target of the turbine is only to run the compressor. The Flue gas while getting out of the turbine gives a reaction force which gives the propulsion. (Jet engine) In modern aircraft engine, the turbine also acts as a propeller. In this type of engine only 25% of the propulsion comes from the reaction of the flue gas and the remaining 75% propulsion comes from the propelling action. (Turboprop, Turbofan)

49 Gas Turbine Power Plant Cycle

50 Jet Engine Turbo Jet

51 Jet Engine

52 The End

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Download From: Fluid Mechanics 1. A single acting reciprocating pump, running at 60 r.p.m, delivers 0.01 m2/sec of water. The area of the piston is0.05m2 and stroke length is 40 cm. Then theoretical discharge of the