1 Teaching Innovation - Entrepreneurial - Global The Centre for Technology enabled Teaching & Learning D M I E T R, Wardha DTEL DTEL (Department for Technology Enhanced Learning)

DEPARTMENT OF MECHANICAL ENGINEERING IV -SEMESTER HYDRAULIC MACHINES 2 UNIT NO.2 TURBOMACHINE AND THEIR CLASSIFICATION

CHAPTER 2:- SYLLABUSDTEL. Theory of turbo machines and their classification 1 Elements of hydro-electric power plant 2 ImpulseTurbine:- principle, constructional features 3 Installation of Pelton Turbine, Velocity Diagram and Analysis, 4 3 Working proportions, Design parameters, Performance characteristics, Governing 5

CHAPTER-2 SPECIFIC OBJECTIVE / COURSE OUTCOMEDTEL Understand turbo machines and their classification The student will be able to: Working proportions, Design parameters, Performance characteristics

LECTURE 1:- Turbo MachineDTEL Definition of A Turbo Machine 5 Turbines are energy developing machines. Turbines convert fluid energy into mechanical energy. The mechanical energy developed by the turbines is used in running an electric generator, which is directly connected, to the shaft of the electrical generator. Earlier days method – wooden wheel Overshot Wheel  Had very good efficiency  Could not handle large quantity of water Undershot Wheel  Low Efficiency

LECTURE 1:- NUMBER SYSTEMDTEL General layout of Hydro-Power Plant 6 a) Reservoir Reservoirs ensure supply of water through out the year, by storing water during rainy season and supplying the same during dry season. b) Dam The function of the dam is to increase the reservoir capacity and to increase the working head of the turbine. c) Penstock A pipe between dam and turbine is known as penstock. It will carry the water from dam to turbine. Penstock is commonly made of steel pipes covered with RCC. LECTURE 1:- Turbo Machine

LECTURE 1:- NUMBER SYSTEMDTEL 7 d) Surge tank/Forebay When the rate of water flow through the penstock is suddenly decreased, the pressure inside the penstock will increase suddenly due to water hammer and thereby damage the penstock. Surge tank/Forebay is constructed between the dam and turbine. It will act as a pressure regulator during variable loads. e) Turbine Turbines convert the kinetic and potential energy of water into mechanical energy to produce electric power. f) Generator and Transformer Electric generator converts mechanical energy into electrical energy. A step up transformer will increase the voltage for loss free transmission. LECTURE 1:- Turbo Machine General layout of Hydro-Power Plant

LECTURE 1:- Turbo MachineDTEL General layout of Hydro-Power Plant 8

LECTURE 1:- Turbo MachineDTEL Advantages & Disadvantages 9 Advantages of hydraulic power plants  Operating cost is very low  Less Maintenance cost and less manpower required  Pollution free  Quick to start and easy to synchronize  Can be used for irrigation and flood control  Long plant life. Disadvantages of Hydraulic Power Plants  Initial cost of total plant is comparatively high  Power generation depends on availability of water  Cost of transmission is high since most of the plants are in remote areas  Project duration is long.

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LECTURE 2:- Hydraulic TurbinesDTEL Head of Hydraulic Turbines 11 1) Gross Head  Difference Between the Head race level and Tail race level  Static (No water flow) / Total Head – H 1 2) Net or Effective Head Head available at the entrance of the turbine: H = H 1 - h f a) Net Head for a Reaction Turbine H = {(P 1 /w) + (V 1 2 /2g) + Z 1 } – {Z 2 + V 2 2 /2g)} b) Net Head for Impulse Turbine H = {(P 1 /w) + (V 1 2 /2g) + Z 1 } – Z 2

LECTURE 2:- Hydraulic TurbinesDTEL Efficiencies of Hydraulic Turbines 12 1)Hydraulic Efficiency – due to hydraulic losses Power developed by the runner Net power supplied at the turbine entrance SI Unit: kW Metric Unit : Horse Power/Water Horse Power (W.H.P) 2) Mechanical Efficiency – Due to mechanical losses ( bearing friction) Power available at the turbine shaft (P) Power developed by the runner

LECTURE 2:- Hydraulic TurbinesDTEL Efficiencies of Hydraulic Turbines 13 3) Volumetric Efficiency – due to amt of water slips directly to the tail race Amount of water striking the runner Amount of water supplied to the turbine 4) Overall Efficiency Power available at the turbine shaft (P) Net power supplied at the turbine entrance

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LECTURE 3:- TurbinesDTEL Classification of Turbines 15 Turbines are classified according to several considerations as indicated below. i) Based on working principle a) Impulse turbine b) Reaction turbine

LECTURE 3:- TurbinesDTEL Classification of Turbines 16 Impulse Turbine: The pressure of liquid does not change while flowing through the rotor of the machine. In Impulse Turbines pressure change occur only in the nozzles of the machine. One such example of impulse turbine is Pelton Wheel. Reaction Turbine: The pressure of liquid changes while it flows through the rotor of the machine. The change in fluid velocity and reduction in its pressure causes a reaction on the turbine blades; this is where from the name Reaction Turbine may have been derived. Francis and Kaplan Turbines fall in the category of Reaction Turbines.

LECTURE 3:- TurbinesDTEL Definition of A Turbo Machine 17 ii) Based on working media a) Hydraulic turbine b) Steam turbine c) Gas turbine d) Wind Turbine iii) Based on head Head is the elevation difference of reservoir water level and D/S water level. a) High head turbine (Above 250 m)Pelton Turbine b) Medium head turbine (60 – 250 m)Francis Turbine c) Low head turbine (Below 60 m)Kaplan Turbine

LECTURE 3:- TurbinesDTEL Definition of A Turbo Machine 18 iv) Based on specific speed Turbines can be classified based on Specific Speed. Specific speed is defined as the speed in rpm of a geometrically similar turbine, which is identical in shape, dimensions, blade angles and gate openings with the actual turbine working under unit head and developing unit power. Specific speed is used to compare the turbines and is denoted by Ns. Specific speed Ns = N √P / H 5/4 a) Low specific speed (8.5 – 30)- Pelton Turbine b) Medium specific speed (50 – 340) - Francis Turbine c) High specific speed (255 – 860)- Kaplan Turbine

LECTURE 3:- TurbinesDTEL Definition of A Turbo Machine 19 v) Based on disposition of turbine main shaft a) Horizontal shaft b) Vertical shaft vi) Based on flow through the runner a) Radial flow 1. Inward 2. Outward b) Axial flow- Kaplan Turbine c) Mixed flow- Francis Turbine d) Tangential flow- Pelton Turbine

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LECTURE 4:- Turbo MachineDTEL Definition of A Turbo Machine 21 Design of Pelton Wheel Turbine  It has a circular disk with cup shaped blades/buckets,  Water jet emerging from a nozzle is tangential to the circumference of the wheel.

LECTURE 4:- Turbo MachineDTEL Working Principle of Pelton Turbine 22 Working Principle of Pelton Turbine  Water jets emerging strike the buckets at splitter.  Stream flow along the inner curve of the bucket and leave it in the direction opposite to that of incoming jet.  The high pressure water can be obtained from any water body situated at some height or streams of water flowing down the hills.  The change in momentum (direction as well as speed) of water stream produces an impulse on the blades of the wheel of Pelton Turbine. This impulse generates the torque and rotation in the shaft of Pelton Turbine.  Horizontal shaft - Not more than 2 jets are used and Vertical shaft - Larger no. of jets (upto 6) are used.  Iron/Steel casing to prevent splashing of water and to lead water to the tail race.

LECTURE 4:- Turbo MachineDTEL Impulse Turbine 23 Uses the velocity of the water to move the runner and discharges to atmospheric pressure. The water stream hits each bucket on the runner. No suction downside, water flows out through turbine housing after hitting. High head, low flow applications. Types : Pelton wheel, Cross Flow

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LECTURE 5:- Turbo MachineDTEL Definition of A Turbo Machine 25 Nozzles direct forceful streams of water against a series of spoon-shaped buckets mounted around the edge of a wheel. Each bucket reverses the flow of water and this impulse spins the turbine.

LECTURE 5:- Turbo MachineDTEL Definition of A Turbo Machine 26 Suited for high head, low flow sites. The largest units can be up to 200 MW. Can operate with heads as small as 15 meters and as high as 1,800 meters.

LECTURE 5:- Turbo MachineDTEL Definition of A Turbo Machine 27 – Purely multistage impulse turbines are mainly preferred in medium capacities of power generations.(30 – 60 MW units). The main advantages are simplicity of construction, low costs, reliability and convenience of operation. The height of blades in last stages of multistage turbine rapidly increase. It is difficult to obtain tall, smooth and streamlined shape for the turbine. Turbines of compound impulse stages are considered obsolete at present. It is current practice for multistage turbines to allow for some amount enthalpy drop to take place in the moving blades as well.

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U V ri V ai V re V ae ii ii ee ee p vava vrvr The reaction effect is an addition to impulse effect. The degree of reaction LECTURE 6:- Turbo Machine

First law for fixed blades: First law for moving blades: LECTURE 6:- Turbo Machine

The steam is delivered to the wheel at an angle  1 and velocity V a1. The selection of angle  i is a compromise. An increase in  1, reduces the value of useful component (Absolute circumferential Component). This is also called Inlet Whirl Velocity, V w1 = V a1 cos(  1 ). An increase in  1, increases the value of axial component, also called as flow component. This is responsible for definite mass flow rate between to successive blade. Flow component V f1 = V a1 sin(  1 ) = V ri sin(  1 ). The absolute inlet velocity can be considered as a resultant of blade velocity and inlet relative velocity. The two points of interest are those at the inlet and exit of the blade. U V r1 V a1 V r2 V a2 11 11 22 22 LECTURE 6:- Turbo Machine

If the steam is to enter and leave the blades without shock or much losses, then relative velocity should be tangential to the blade inlet tip. V r1 should enter at an angle  1, the inlet blade angle. Similarly, V r2 should leave at  2, the exit blade angle. In an impulse reaction blade, V r2 > V r1 U V r1 V a1 V r2 V a2 11 11 22 22 The flow velocities between two successive blade at inlet and exit are V f1 & V f2. The axial (basic useful) components or whirl velocities at inlet and exit are V w1 & V w2. LECTURE 6:- Turbo Machine

Newton’s Second Law for an Impulse-reaction Blade: The tangential force acting of the jet is: F = mass flow rate X Change of velocity in the tangential direction Tangential relative velocity at blade Inlet : V r1 cos(  1 ). Tangential relative velocity at blade exit : -V r2 cos(  2 ). Change in velocity in tangential direction: -V r2 cos(  2 ) – V r1 cos(  1 ). -(V r2 cos(  2 ) + V r1 cos(  1 )). Tangential Force, U V r1 V a1 V r2 V a2 11 11 22 22 LECTURE 6:- Turbo Machine

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The reaction to this force provides the driving thrust on the wheel. The driving force on wheel Power Output of the blade : Diagram Efficiency or Blade efficiency: LECTURE 7:- TURBO MACHINE

0 1 2

Nozzle blade factor,  LECTURE 7:- TURBO MACHINE

For a given shape of the blade, the efficiency is a strong function of U/V fitc  For maximum efficiency: LECTURE 7:- TURBO MACHINE

Stage Sizing Steam Path LECTURE 7:- TURBO MACHINE

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DTEL References Books: 1. Fluid Mechanics with Engineering Applications, E. Finnemore & Franzini, Tata Mc-Graw Hill 2. Hydraulic Machines-Theory and Design, V. P. Vasandani, Khanna Publishers 3. Fluid Mechanics, A. K. Jain, Khanna Publishers 4. Hydraulic & Compressible Flow Turbo-machines, A. T. Sayers, Mc-Graw Hill 5. Mechanics of Fluids, Merle C. Potter, CL-Engineering 6. Fluid Mechanics, John F. Douglas, Pearson 42