UNIT IV ROTODYNAMIC MACHINES

Transcription

1 UNIT I ROTODYNAMIC MACINES 4.. INTRODUCTION TO YDRAULIC TURBINES ydralic machines are those machines which converts either hydralic energy (energy possessed by flid) into mechanical energy or vice versa. A machine which converts hydralic energy into mechanical energy is known as Trbine. A machine which converts mechanical energy into hydralic energy is known as pmp. A trbine is a rotary engine that extracts energy from a flid flow and converts it into sefl work. The simplest trbines have one moving part, a rotor assembly, which is a shaft or drm with blades attached. Moving flid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor. Early trbine examples are windmills and water wheels. Gas, steam, and water trbines sally have a casing arond the blades that contains and controls the working flid. Credit for invention of the steam trbine is given both to the British Engineer Sir Charles Parsons (854 93), for invention of the reaction trbine and to Swedish Engineer Gstaf de Laval (845 93), for invention of the implse trbine. Modern steam trbines freqently employ both reaction and implse in the same nit, typically varying the degree of reaction and implse from the blade root to its periphery. 4.. EULER TURBINE EQUATION The flid velocity at the trbine entry and exit can have three components in the tangential, axial and radial directions of the rotor. This means that the flid momentm can have three components at the entry and exit. This also means that the force exerted on the rnner can have three components. Ot of these the tangential force only can case the rotation of the rnner and prodce work. The axial component prodces a thrst in the axial direction, which is taken by sitable thrst bearings. The radial component prodces a bending of the shaft which is taken by the jornal bearings. Ths it is necessary to consider the tangential component for the determination of work done and power prodced. The work done or power prodced by the tangential force eqals the prodct of the mass flow, tangential force and the tangential velocity. As the tangential velocity varies with the radis, the work done also will be varying with the radis. It is not easy to sm p this work. The help of moment of momentm theorem is sed for this prpose. It states that the torqe on the rotor eqals the rate of change of moment of momentm of the flid as it passes throgh the rnner. Let be the tangential velocity at entry and be the tangential velocity at exit. Let be the tangential component of the absolte velocity of the flid at inlet and let be the tangential component of the absolte velocity of the flid at exit. Let r and r be the radii at inlet and exit.

2 The tangential momentm of the flid at inlet = m The tangential momentm of the flid at exit = m The moment of momentm at inlet = m r The moment of momentm at exit = m r.... Torqe (T) m ( r r ). Depending on the direction of with reference to, the ve sign will become + ve sign... NT N Power m ( r r ) N N Bt r and r Power m ( ) The above eqation is known as Eler trbine eqation. ydralic Efficiency ( ): h It is defined as ratio of power given by water to the rnner of a trbine to power spplied to the power spplied by water at the inlet of the trbine. h RP WP Power delivered power spplied to rnner at inlet W Water Power (WP) = 000 KW Where W Weight of water striking the vanes of trbine per second Net head on trbine WP gq 000 kw

3 Mechanical Efficiency ( ): m It is the ratio of power available at the shaft of the trbine to the power delivered to the rnner. m power available power delivered at the to the shaft rnner SP = RP olmetric Efficiency ( ): v It is defined as ratio of volme of water actally striking the rnner to the volme of water spplied to the trbine. v volme volme of water actally striking the rnner of water spplied to the trbine. Overall efficiency ( ): o It is defined as ratio power available at the shaft of trbine to the power spplied at the inlet of the trbine O power available power spplied at the shaft of trbine at the inlet of the trbine SP WP SP WP RP RP SP RP RP WP m h O m h SP O gq 000

4 4.3. ELOCITY COMPONENTS AT TE ENTRY AND EXIT OF TE ROTOR The constrction of velocity vector diagram is shown figre (4.), elocity triangle notations: elocity of jet at inlet elocity of plate (vane) at inlet Relative velocity of jet & plate at inlet r w Figre 4. constrction of velocity vector diagram Gide blade angle or angle between direction of jet & direction of motion of plate ane angle at inlet or angle made by relative velocity with the direction of motion at inlet Whirl velocity at inlet

5 Flow velocity at inlet f elocity of jet leaving the vane elocity of plate (vane) at otlet Relative velocity of jet & plate at otlet r Angle made by velocity with direction of motion of vane at otlet Angle made by velocity r with direction of motion of vane at otlet CONSTRUCTION OF ELOCITY ECTOR DIAGRAM:. First of all, the parameters involved in hydralic machines are listed separately for inlet and otlet.. The centre O is marked as reference point. 3. The arcs are drawn corresponding to inner and oter radis of the wheel. 4. The point A is taken arbitrary over the arc drawn for inner radis. 5. From the point A blade profile is drawn. At the same time the otlet of the blade shold toch the arc drawn for oter diameter. The point where the otlet of the blade toches the oter diameter arc is denoted by B. 6. Then the inlet velocity vector diagram is drawn from point A and otlet velocity vector diagram is drawn from point B 7. Same sitable scale shold be sed for both inlet and otlet velocity vector diagrams. Inlet velocity vector triangle. elocity of flow is indicated by perpendiclar line from point A as shown in figre. The end point is denoted by C.. From the same point A, absolte velocity line is drawn at an angle of with the horizontal. The end point is denoted by D. 3. The end points C and D are joined by a horizontal line. The length CD indicates the whirl components of velocity. 4. The blade velocity is marked on the same line CD by taking C as reference point. The end point of blade velocity is marked as E.

6 5. Now, the points E and A are joined. The length EA indicates the relative velocity and angle made by this line with horizontal is denoted by. It is nothing bt blade tip angle at inlet. 6. To identify the inlet velocity vector diagram easily, the arrow heads are drawn towards the blade profiles. Otlet velocity vector triangle. First relative velocity at otlet is calclated from relative velocity coefficient or friction factor( r r ). Corresponding to otlet blade tip angle, the relative velocity line is drawn from point B in sch a way that it shold make ( ) with horizontal. The end point of the line is marked as F. 3. The blade velocity at otlet is marked horizontally from F by denoting as G. 4. Now, the points B and G are joined. The length BG indicates the absolte velocity at otlet and angle made by this line with horizontal is denoted by. ( ) refers to the angle at which the water leaves the wheel at otlet. 5. From point B, a vertical line is drawn and the line FG is extended to meet the vertical line drawn from the point B. The intersection point is marked as. The lengths G and B indicate the whirl velocity and velocity of flow at otlet. 6. Finally, the actal vales are obtained by mltiplying corresponding length with selected scale factor. 7. To identify the otlet velocity vector diagram easily, the arrow heads are drawn away from the blade profiles. According to the velocity, flow angle and blade angle, the velocity vector diagram may slightly change. If the discharge at otlet is radial, the angle ( =0). It means, the whirl velocity at otlet is zero and the absolte velocity at otlet is eqal to the flow velocity at inlet. Degree of Reaction (R) It is defined as the ratio of pressre energy change inside a rnner to total energy change inside the rnner. R pressre energy change inside a rnner total energy change inside the rnner Eler eqation is also known as total energy change inside the rnner

7 Total energy change inside the rnner e ale of Degree of Reaction (R): For pelton wheel R = 0 g w w For reaction trbine R = cot cot cot 4.4.Classification of ydralic trbine:. According to the type of energy at inlet (a) Implse trbine (b) Reaction trbine.. According to the direction of flow throgh rnner (a) Tangential flow trbine (b) Radial flow trbine (c) Axial flow trbine (d) Mixed flow trbine. 3. According to the head at inlet of trbine (a) igh head trbine (b) Medim head trbine (c) Low head trbine. 4. According to the specific speed of trbine (a) Low specific speed trbine (b) Medim specific speed trbine (c) igh specific speed trbine.

8 5. According to the name of the inventor (a) Pelton trbine (b) Francis trbine (c) Kaplan trbine IMPULSE TURBINES: The arrangements of the implse trbine is shown in figre 4. Figre 4.. Arrangements of the implse trbine In the case of implse trbine all the potential energy is converted to kinetic energy in the nozzles. The implse provided by the jets is sed to trn the trbine wheel. The pressre inside the trbine is atmospheric. This type is fond sitable when the available potential energy is high and the flow available is comparatively low. Some people call this type as tangential flow nits. Later discssion will show nder what conditions this type is chosen for operation. In an implse trbine, a fast-moving flid is fired throgh a narrow nozzle at the trbine blades to make them spin arond. The blades of an implse trbine are sally bcket-shaped so they catch the flid and direct it off at an angle or sometimes even back the way it came (becase that gives the most efficient transfer of energy from the flid to the trbine). In an implse trbine, the flid is forced to hit the trbine at high speed. Imagine trying to make a wheel like this trn arond by kicking soccer balls into its paddles. Yo'd need the balls to hit hard and bonce back well to get the wheel spinning and those constant energy implses are the key to how it works. These trbines change the direction of flow of a high velocity flid or gas jet. The reslting implse spins the trbine and leaves the flid flow with diminished kinetic energy. There is no pressre change of the flid or gas in the trbine rotor blades (the moving blades), as in the case of a steam or gas trbine; the entire pressre drop takes place in the stationary blades (the

9 nozzles). Before reaching the trbine, the flid's pressre head is changed to velocity head by accelerating the flid with a nozzle. Pelton wheels and de Laval trbines se this process exclsively. Implse trbines do not reqire a pressre casement arond the rotor since the flid jet is created by the nozzle prior to reaching the blading on the rotor. Newton's second law describes the transfer of energy for implse trbines REACTION TURBINES The arrangements of the reaction trbine is shown in figre 4.3 Figre 4.3 Arrangements of the reaction trbine In a reaction trbine, the blades sit in a mch larger volme of flid and trn arond as the flid flows past them. A reaction trbine doesn't change the direction of the flid flow as drastically as an implse trbine: it simply spins as the flid pshes throgh and past its blades. In reaction trbines the available potential energy is progressively converted in the trbines rotors and the reaction of the accelerating water cases the trning of the wheel. These are again divided into radial flow, mixed flow and axial flow machines. Radial flow machines are fond sitable for moderate levels of potential energy and medim qantities of flow. The axial machines are sitable for low levels of potential energy and large flow rates. The potential energy available is generally denoted as head available. With this terminology plants are designated as high head, medim head and low head plants. Trbines present a part of trbo machines in which the energy transfer process occrs from the flid to the rotor, in other words, in trbines, the flid energy is converted to a mechanical energy. At the inlet of any hydralic trbine the

10 water speed is relatively small and its energy is essentially pressre energy. This energy is totally transferred to kinetic energy (in case of implse trbines) or partially transferred to kinetic energy (in case of reaction trbines). Reaction trbines are those kind of trbines which the degree of reaction does not eqal zero, and the major of pressre drop takes place in the rotating wheel (in implse trbine, the pressre drop takes place in the nozzle). The reaction trbines are classified into three types according to the flow direction, - Radial: (Francis), low specific speed, sally sed for medim and high head installations. - Mixed: (Francis), medim specific speed, sally sed for medim head installations. - Axial: high specific speed, sally sed for low head installations TANGENTIAL FLOW TURBINE, RADIAL AND AXIAL TURBINES. Tangential flow trbine In tangential flow trbine, water flows along the tangent to the path of the rnner. E.g. pelton wheel.. Radial flow trbine In radial flow trbine, water flows along the radial direction and mainly in the plane normal to the axis of rotation, as it passes throgh the rnner. It may be either inward radial flow type or otward radial flow type. Inward radial flow trbine, the water enters at the oter circmference and flows radially inwards the center of the rnner. E.g. old Francis trbine, Thomson trbine. In otward radial flow trbine, water enters at the center and flows radially otwards towards the oter periphery of the rnner. E.g. Forneyron trbine. 3. Axial flow trbine In an axial flow trbine, the water flows parallel to the axis of the trbine shaft. E.g. Kaplan trbine, propeller trbine. 4. Mixed flow trbine In mixed flow trbine, the water enters the blades radially and comes ot axially, parallel to the trbine shaft. E.g. Modern Francis trbine. In or sbject point of view, the following trbines are important and will be discssed one by one.. Pelton wheel.

11 . Francis trbine. 3. Kaplan trbine. The varios trbine and their performance parameters are shown in the table. Name Trbine Type Type of Energy ead Discharge Direction of flow Specific speed Pelton wheel Implse Kinetic igh ead >50m to 000m Low Tangential to rnner Low <35 single jet mlti jet Francis Reaction Kinetic + Medim Medim Radial flow Medim Trbine Kaplan Pressre Energy 60m to 50m Mixed flow 60 to 300 Trbine Low < 30m igh Axial flow igh 300 to ANALYSIS OF YDRAULIC TURBINE USING ELOCITY TRIANGLE PELTON WEEL OR PELTON TURBINE By definition, the implse trbine is a machine in which the total drop in pressre of the flid takes place in one or more stationary nozzles and there is no change in the pressre of flid as it flows throgh the rotating wheel. Many designs has existed bt only one has been crrently sed named by man who designed it first in California at 80 Mr. A. Pelton. Usally, Pelton Wheel is sed for high head abot more than 300 m. The pelton wheel is a tangential flow implse trbine and now in common se. Leston A Pelton, an American engineer dring 880, develops this trbine. Figre 4.4 shows the schematic arrangement of a pelton wheel. Pelton wheel consists of the following main parts.. Penstock. Spear and nozzle 3. Rnner with bckets 4. Brake nozzle 5. Oter casing 6. Governing mechanism

12 Figre 4.4 Schematic arrangement of a pelton wheel. Penstock: It is a large sized pipe which conveys water from the high level reservoir to the trbine. Depending pon low head or high head installation a penstock may be made of wood, concrete or steel. For the reglation of water flow, the penstock is provided with control valves.. Spear and nozzle At the downstream end of the penstock, it is fitted with an efficient nozzle which converts whole hydralic energy into kinetic energy. Ths the nozzle delivers high-speed jet. To reglate the water flow throgh the nozzle and to obtain a good jet of water, a spear is arranged as shown in figre 4.5. The spear can move forward or backward thereby decreasing or increasing the annlar area of the nozzle flow passage.

13 Figre 4.5. Spear and nozzle 3. Rnner with bckets The rnner consists of a circlar disc with a nmber of bckets evenly spaced rond its periphery. The rnner is monted on a horizontal shaft spported in small thrst bearings. The bckets have a shape of doble semi-elliptical ridge known as splitter. The bckets are either cast internally with the disc or fastened separately. The bckets are so shaped that the angle at the otlet tip varies from 0 to 0 so that the jet of water gets deflected throgh 60 to 70. The jet of water impinges on the splitter, which divides the jet into two eqal portions. After flowing rond the smooth inner srface of the bcket water leaves at its oter edge. The advantage of having hemispherical doble cp bcket is that the bearings spporting the wheel shaft are not sbjected to any axial or end thrst. 4. Oter casing A casing is made of cast iron or fabricated steel plates. It has no hydralic fnction to perform. It is sed to prevent the splacing of water and discharge water to tailrace. It also acts as a safegard against accidents. 5. Brake nozzle When the nozzle is closed by moving the spear in forward direction, the amont of water striking on the bckets is redced to zero. Bt the rnner will revolve for long time de to inertia. To stop the rnner in a short time, a small nozzle is provided which directs a jet of water on the back of the bckets. This jet of water is called braking jet. 6. Governing mechanism Governing mechanism is sed to reglate the water flow to the trbine at constant level so that the speed of the trbine kept constant. This atomatically reglates the qantity of water flowing throgh the rnner in accordance with any variation of load.

14 BLADE PROFILE WIT RESPECT TO WORK DONE AND EFFICIENCY OF A PELTON WEEL Figre 4.6 shows the shape of the bcket of the pelton wheel. Figre 4.7 shows the section of bcket at x-x. Let, Figre 4.6 elocity Triangles Let D Diameter of the wheel d Diameter of the jet N Speed of wheel rpm - Absolte velocity of jet at inlet = gh -velocity of jet leaving the vane or bcket r - elocity of jet relative to bcket at inlet r -velocity of jet relative to bcket at otlet w -velocity of whirl at inlet tip of the bcket w -velocity of whirl at otlet tip of the bcket f -velocity of flow at inlet

15 -velocity of flow at otlet f - Peripheral velocity of rnner. It will be same at inlet and otlet ( = =), = 60 DN - Angle made by velocity with the direction of motion of the vane at otlet. - Angle made by angle at otlet. At inlet: r with the direction of motion of the vane at otlet and also called ane Since, the velocity and are collinear, th velocity triangle at the inlet tip of the bcket is a straight line as shown figre 4.7. Ths, r = - ( =) w = At otlet: From velocity triangle at otlet, r = r and = r cos w w = r cos ( =) Depending pon the magnitde of the peripheral speed(), the nit may have a slow, medim or fast rnner. The otlet velocity triangle will vary as follows. For slow rnner, 90 ; w is negative. Medim rnner, 90 ; 0 w

16 Fast rnner, 90 ; w is positive Force exerted by the in the water in the direction of motion is given by F a ( w w ) Where, - Mass density. A Area of jet = 4 d Work done by the jet on the rnner per second Work done per second per nit weight of water striking F a ( ) w a w a ( ) w w g ( Weight of water striking a g ) ( ) w w g The energy spplied to the jet at inlet is in the form of K.E. and is eqal to m K.E. of jet per second = ( ) a ( m a ) ydralic efficiency h work done per second K.E.of jet per second a ( w ( a w ) ) ( ).() w w h From inlet and otlet velocity triangle, w r r r

17 w r cos ( ) cos Sbstitting the vales and in eqation () w w h [ ( ) cos ] [ ( ) cos ] h ( )[ cos ].. () The hydralic efficiency will be maximm for given vale of when d ( ) 0 h d d ( d )[ cos ] 0 ( cos ) d ( d ) 0 d d ( ) 0 ( cos ) Since 0 0 From the above eqation it is obviosly that the hydralic efficiency is maximm when the velocity of the wheel is half the velocity of the jet of water at inlet. The maximm efficiency can be obtained by sbstitting vale of in eqation (),

18 ( ) h ( ) h ( ) h max max max ( )[ cos ] [ cos ] 4 cos ead and Efficiencies of Pelton wheel:. Gross head (g): The gross head is the difference between the water level at the reservoir and the level at the tail race.. Effective or Net ead (): The head available at the inlet of the trbine is known as effective or Net ead. Figre 4.8 ead on pelton wheel g h f h Where hf head loss de to friction in penstock. 4 fl h f gd h eight of the nozzle above the tailrace 3. Water and bcket power:

19 The power spplied by the water jet is known as water power. wq gq Where, Q Discharge spplied by the water jet, Effective or net head. The power developed by the bcket wheel is known as bcket or actal power, B.P. Power developed by the bcket wheel m 3 a ( ) w w s BP Q ( ) w w 4. ydralic efficiency ( ) h It is defined as the ratio of power developed by the rnner to the power spplied by the water jet. h power developed by the rnner power spplied by the water jet Q ( ( w w gq g w w ) ) r The parameter r g ( represents the energy transfer per nit weight and is referred ) w w to the rnner head or Eler head. ydralic loss within the trbine, r 5. Mechanical efficiency ( ) m It is the ratio of power available at the trbine shaft to the power developed by the trbine rnner. m power available the trbine shaft power developed by the trbine rnner = Shaft Power WaternPower

20 WQ a ( P w ) g w WQ P a r vales lie between 97 to 99% m 6. olme efficiency ( ) v It is defined as the volme of water actally striking the bckets to the total water spplied by the jet. v Q a Q Q q Q lies between 0.97 to 0.99 v 7. Overall efficiency ( ) o It is defined as the ratio of power available at the trbine shaft to the power available from the water jet. o Shaft Water Power Power P wq It may be obtained by mltiplying, and v m h o v h m vale lies between 0.85 to 0.9 o DESING ASPECTS OF PELTON WEEL The following points need consideration while designing a pelton wheel.. elocity of jet The velocity of jet at inlet is given by C g v Where, C v co-efficient of velocity = 0.98 to 0.99

21 = Net head on trbine.. elocity of wheel It is given by K g K Where, speed ratio = 0.43 to Mean diameter of wheel The mean diameter is obtained by the relation as given below. It is also known as pitch diameter. DN 60 D 60 N 4. Jet ratio(m): It is defined as the ratio of mean diameter of pelton wheel to the diameter of the jet. m D d m varies between to Nmber of jets: Normally pelton wheel has one nozzle or one set. When more power is to be prodced, the nmber of nozzles or jets may be employed with the same wheel. Theoretically six nozzles can be sed with one pelton wheel. Nmber of jets is obtained by dividing the total rate of flow throgh the trbine by the rate of flow of water throgh a single jet. 6. Bcket dimension: Some of the main dimensions of the bcket of pelton wheel as shown in figre 4.9 are expressed in terms of the jet diameter. Axial width, B=4d to 5d Radial length, L= d to 3d Depth, T= 0.8d to.d Angle 0 to 0

22 Figre 4.9. Bcket dimension 7. Nmber of bckets(z) It is obtained by the following formla D Z 5 d Problems on Pelton wheel:. A pelton wheel trbine rns nder a head of 400m at a speed of 000rpm. it develops a power of 5000kW. find the least diameter of jet and the pitch circle diameter of wheel. assme overall efficiency of trbine is 85%; Cv =0.99 as speed ratio is Also find the nmber of bckets. Assme any data if reqired. Given data: Soltion: ead, = 400m Speed, N=000rpm Power = 5000kW 85 % Overall efficiency 0 Cv =0.99 Speed ratio K =0.45 elocity of jet C g m v s

23 elocity of wheel K g m s We know that DN elocity of wheel D 0.76 m o 0.85 P wq D Q 400 Q.5m 3 / s Discharge Q = area of jet velocity of jet Q d 4.5 d d d m Nmber of bckets(z) Z Z D d er a net head of 800m. A pelton wheel is to develop 350kW nder a net head of 800m while rnning at a speed of 600 rpm. if co efficient of jet = 0,97, speed ratio = 0.46 and the ratio of jet diameter is /5of wheel diameter. Calclate (a) nmber of jets (b) diameter of jets (c) diameter of pitch circle (d)qantity of water spplied to wheel. Assme Given data: ead, = 800m Speed, N=600rpm Power =350kW o 85 %

24 85 % Overall efficiency 0 C v 0.97 Speed ratio K =0.46 d D 5 Soltion: elocity of jet C g m v s elocity of wheel K g m s We know that DN elocity of wheel D.834 m d D d 5 d 0. m o D P wq Q 800 Q.986 m 3 / s Discharge Q d 4 q (0. ) 4 of one jet q = area of jet velocity.53.4 m 3 s of jet

25 3. A doble jet pelton wheel is reqired to generate 7500kW when available head at the base of the nozzle is 400m. the jet is deflected throgh 65 o and the relative velocity of the jet is redced by 5% in passing over the bckets. determine (i) the diameter of each jet (ii)total flow (iii) force exerted by the jet on bckets in tangential direction. Assme generator efficiency of 95%, overall efficiency 80%,, K =0.46. Given data: Nmber of jets = Shaft power, P =7500kW net head, = 400m Angle of deflection = 65 o C v 0.97 Redction of relative velocity de to friction = 5% Generator efficiency of 95%, Overall efficiency = 0 80%, C v 0.97 K =0.46. Soltion: elocity of jet C g m v s

26 o P wq Q 400 Generator efficiency 95%, Total flow, Q.54 m 3 s Total Discharge Q = No. of jets area of jet velocity of jet.548 d d m 36.5mm Peripheral speed of the wheel K g m s At inlet to the trbine w r r w m / s 45.m / s At otlet of the trbine Figre 4.0 Otlet velocity triangle

27 blade r w w 0.85 angle r cos 80 r 38.4 cos m / s m / s No. of jets F F Q w kn w FRANCIS TURBINES (RADIAL AND MIXED): The Francis trbine original design was inward radial flow with high flow to make a more compact rnner. The diameter was redced and the water was discharged with a velocity having an axial component as well as a radial one. This type of rnners is called a mixed flow rnner. The inward flow trbine permits a better mechanical constrction since the rotor and shaft form a compact nit in the center while the stationary gide vanes are on the otside.francis trbine is a radial inward flow trbine and is the most poplarly sed one in the medim head range of 60 to 300 m. Francis trbine was first developed as a prely radial flow trbine by James B. Francis, an American engineer in 849. Bt the design has gradally changed into a mixed flow trbine of today.

28 Figre 4. Francis trbine The main components are (i) The spiral casing (ii) Gide vanes (iii) Rnner (iv) Draft tbe and Most of the machines are of vertical shaft arrangement while some smaller nits are of horizontal shaft type.. Spiral Casing The spiral casing srronds the rnner completely. Its area of cross section decreases gradally arond the circmference. This leads to niform distribtion of water all along the circmference of the rnner. Water from the penstock pipes enters the spiral casing and is distribted niformly to the gide blades placed on the periphery of a circle. The casing shold be strong enogh to withstand the high pressre.. Gide Blades Water enters the rnner throgh the gide blades along the circmference. The nmber of gide blades is generally fewer than the nmber of blades in the rnner. These shold also be not simple mltiples of the rnner blades. The gide blades in addition to giding the water at the proper direction serve two important fnctions. The water entering the gide blades are imparted a tangential velocity by the drop in pressre in the passage of the water throgh the blades. The blade passages act as a nozzle in this aspect. The gide blades rest on pivoted on a ring and can be rotated by the rotation of the ring, whose movement is controlled by the governor. In this way the area of blade passage is changed to vary the flow rate of water according to the load so that the speed can be maintained constant. The variation of area between gide blades is illstrated in Figre. The control mechanism will be discssed in a later section. 3. The Rnner The rnner is circlar disc and has the blades fixed on one side. In high speed rnnersin which the blades are longer a circlar band may be sed arond the blades to keep them in position. The shape of the rnner depends on the specific speed of the nit. These are classified as (a) Slow rnner (b) medim speed rnner (c) high speed rnner and (d) very high speed rnner.

29 The shape of the rnner and the corresponding velocity triangles are shown in figre. The development of mixed flow rnners was necessitated by the limited power capacity of the prely radial flow rnner. A larger exit flow area is made possible by the change of shape from radial to axial flow shape. This redces the otlet velocity and ths increases efficiency. As seen in the figre the velocity triangles are of different shape for different rnners. It is seen from the velocity triangles that the blade inlet angle changes from acte to obtse as the speed increases. The gide vane otlet angle also increases from abot 5 to higher vales as speed increases. The rnner blades are of dobly crved and are complex in shape. These may be made separately sing sitable dies and then welded to the rotor. The height of the rnner along the axial direction (may be called width also) depends pon the flow rate which depends on the head and power which are related to specific speed. As specific speed increases the width also increase accordingly. Two sch shapes are shown in figre. The rnners change the direction and magnitde of the flid velocity and in this process absorbs the momentm from the flid. 4. Draft Tbe The trbines have to be installed a few meters above the flood water level to avoid inndation. In the case of implse trbines this does not lead to significant loss of head. In the case of reaction trbines, the loss de to the installation at a higher level from the tailrace will be significant. This loss is redced by connecting a flly flowing diverging tbe from the trbine otlet to be immersed in the tailrace at the tbe otlet. This redces the pressre loss as the pressre at the trbine otlet will be below atmospheric de to the arrangement. The loss ineffective head is redced by this arrangement. Also becase of the diverging section of thetbe the kinetic energy is converted to pressre energy which adds to the effective head. The draft tbe ths helps () To regain the lost static head de to higher level installation of the trbine and () elps to recover part of the kinetic energy that otherwise may be lost at the trbine otlet. WORK DONE AND EFFICIENCIES OF FRANCIS TURBINE Figre 4. illstrates the velocity diagrams for an inward flow reaction trbine i.e. Francis trbine.

30 Figre 4. elocity vector diagram of Francis trbine General expression for work done follows from the Eler momentm eqation with sal notation. Q w Work done w wq = w w g Where, Q = discharge throgh the rnner. w and w =velocity of whirl at inlet and otlet respectively. and = Tangential velocity of wheel at inlet and otlet. For maximm otpt, the rnner is so designed that w =0, therefore

31 wq Work done= Q w w g ydralic inpt to the trbine=w Q Where, - net head.. ydralic efficiency ( ) h h Power developed ydralic by the inpt rnner wq w g w Q h w g w if h 0, then w w g The vale of h ranges from 85 to 95%. Power available at the rnner shaft Mechanical efficiency ( ) m m Power available at the rnner shaft Power developed by the rnner wq g P w If w 0, then m wq g w P w. Overall efficiency ( ) o Shaft power Water Power o Shaft power Water Power P wq

32 Otherwise, o m h Its vale range from 80 to 90%. DESIGN ASPECTS OF FRANCIS TURBINE Ratio of width to diameter B D the ratio of width B to wheel diameter D is represented by n, i.e. n=. Flow ratio K f The ratio of the velocity of flow at inlet known as flow ratio. K f f gh the vale of Kf varies from 0.5 to 0.3. Speed ratio K B D to the theoretical velocity gh It is the ratio of the peripheral speed at inlet to the theoretical jet velocity. K g The vale of 3. Design procedre K ranges from 0.6 to 0.9. Given data: power to be developed, P Speed, N andead, Assme sitable vales for,,n and K f Reqired: Size of the rnner and its vane angle: Step : h o The design procedre involves the following steps. Determine the reqired discharge, Q from the relation f is

33 o P wq Step : Obtain the flow velocity from the discharge and flow area. Figre 4.3 Flow entry to rnner vane Let B, D and t respectively be the width, diameter and thickness of the rnner vane at inlet. Then, total area at the oter periphery. A= ( ( D Zt ) B K D B t Where, Z- Nmber of vanes. K f =ane thickness coefficient=0.95 Flow velocity, f f Q K D t Q K nd t B n B D Also K g f f Eqating the above two eqations for f

34 K D f g K f Q K n t Q K nd t g From B nd Step 3 Calclate the tangential velocity from the relation D N 60 Step 4 Calclate the whirl velocity from the relation h w g w g h Step 5 By sing velocity triangle, obtain the angle of gide blade angle( )and rnner blade angle ( ) at the inlet. f tan w f tan w Step 6 Assme rnner diameter D at the otlet to be approximately one half of the diameter at inlet. D D and, Step 7 By sing continity eqation, find ot the flow velocity of exit ( f )

35 Q K t D B f K t D B f f f K t D B D B f Step 8 Assme radial discharge at the rnner exit ( 90 ) and obtain the rnner blade angle from the otlet velocity triangle. tan f Step 9 The nmber of vanes varies from 6 to 4 PROBLEMS ON FRANCIS TURBINE. The following data is given for a Francis trbine: Net head: 50m, Speed=600rpm; =90%; h o 84 % ; SP = 400P; flow ratio=0.; breath ratio =0.; The oter diameter of rnner is two times the inner diameter of rnner. The thicknesses of the vanes occpy 5% of circmferential area of the rnner. The velocity of flow is constant at inlet and also otlet and discharge is radial at otlet. Determine i) Gide blade angle ii) Rnner vane angle at inlet and otlet iii) Diameter of rnner at inlet and otlet iv) width of the wheel at inlet Given Data: : Net head = 50m Speed N=600rpm; =90% h 84 % ; o SP = 400P=400C735.75=94.3kW

36 Flow ratio Kf=0. Breath ratio n=0. D= D Soltion: Figre 4.4 o P wq Q 50 Q 0.74 m 3 / s Flow ratio, K g m / s f f Since, the thickness of the vanes is eqal to 5% of circmferential area of the rnner Actal flow area A 0.95 D B Discharge Q = Area velocity

37 Q 0.95 D B D B 68 mm D f 0.D mm f B ( 0. ) D Diameter of wheel at otlet D D / 309 mm D N 9.5m / s 60 g w h m / s h w g 9.5 i) Gide blade angle tan f w ii) Rnner vane angle at inlet and otlet f tan 6 w iii) Diameter of rnner at inlet and otlet D N m / s Gide blade angle at otlet (since f = f ) tan f f

38 . A Francis trbine works nder a head of 0 m. The oter diameter and width are m and 0.6 m. The inner diameter and width are. m and 0.7 m. The flow velocity at inlet is 8. m/s. The whirl velocity at otlet is zero. The otlet blade angle is 6. Assme = 90%. h Determine, power, speed and blade angle at inlet and gide blade angle. Given Data: f = 8. m/s D=m B=0.6m D=.m B=0.7m 6 = 90% h Soltion: The otlet velocity diagram is a right angled triangle as shown in figre 4.4 f = f DB / D B = /. 0.7 = 8 m/s Figre 4.4 tan f = 8/tan 6 = 7.9 m/s D N 60 N N 444 rpm D N 46.5m / s 60

39 g w h m / s h w g 60 The shape of the inlet triangle is shown. tan f w w f tan Flow rate = Dbf = = 8.43 m 3 /s Power = / 03 = 867 kw N P N = s The following data refers to an inward flow reaction trbine; external and internal diameters =.m and 0.6m. elocity of flow is constant and eqal to.5m/s; ead = m; Gide blade angle=0 o. The vanes are radial at inlet. Assming the discharge at otlet is radial. Calclate i) Speed of trbine ii) Rnner vane angle at otlet iii) ydralic efficiency Given Data: D=.m D=0.6m elocity of flow f = f=.5m/s ead = m 0 Soltion:

40 Rnner vanes are radial at inlet 90 w Discharge at otlet is radial 0;.5m / s w f i) Speed of trbine tan tan 0 f w.5 f 4.m / s D N 60 (.) N N 5.65 rpm D N m / s ii) Rnner vane angle at otlet From otlet velocity triangle tan f iii) ydralic efficiency h h w g %

41 KAPLAN TURBINE: A Kaplan trbine is an axial flow reaction trbine which was developed by Astrian engineer Kaplan. It is sitable for relatively low heads. ence, it reqires a large qantity of water to develop large power. The poplar axial flow trbines are the Kaplan trbine and propeller trbine. In propeller trbine the blades are fixed. In the Kaplan trbines the blades are monted in the boss in bearings and the blades are rotated according to the flow conditions by a servo mechanism maintaining constant speed. In this way a constant efficiency is achieved in these trbines. The system is costly and where constant load conditions prevail, the simpler propeller trbines are installed. In the discssions on Francis trbines, it was pointed ot that as specific speed increases (more de to increased flow) the shape of the rnner changes so that the flow tends towards axial direction. This trend when contined, the rnner becomes prely axial flow type. There are many locations where large flows are available at low head. In sch a case the specific speed increases to a higher vale. In sch sitations axial flow trbines are gainflly employed. A sectional view of a kaplan trbines in shown in figre. These trbines are sited for head in the range 5 80 m and specific speeds in the range 350 to 900. The water from spply pipes enters the spiral casing as in the case of Francis trbine. Gide blades direct the water into the chamber above the blades at the proper direction. The speed governor in this case acts on the gide blades and rotates them as per load reqirements. The flow rate is changed withot any change in head. The water directed by the gide blades enters the rnner which has mch fewer blades (3 to 0) than the Francis trbine. The blades are also rotated by the governor to change the inlet blade angle as per the flow direction from the gide blades, so that entry is withot shock. As the head is low, many times the draft tbe may have to be elbow type. The important dimensions are the diameter and the boss diameter which will vary with the chosen speed. At lower specific speeds the boss diameter may be higher. Figre 4.5 Arrangement of a Kaplan trbine Figre 4.5 shows all the main components of a Kaplan trbine, they are. scroll casing. stay ring

42 3. Gide vanes 4. Rnner 5. Draft tbe Figre 4.6 Main components of a Kaplan trbine The arrangements of above components are similar to those of a Francis trbine. In a Kaplan trbine, the rnner blades are adjstable and can be rotated abot pivots fixed to the hb of the rnner. Usally it has to 6 blades having no otside rim. The shape of the rnner blade is different from that of Francis trbine. The blades are made of stainless steel. The blades attached to the hb are so shaped that water flows axially throgh the rnner.

43 Figre 4.7 shows the inlet and otlet velocity triangles for Kaplan trbine. It is drawn similar to Francis trbine. Figre 4.7elocity triangles for Kaplan trbine WORKING PROPERTIES FOR KAPLAN TURBINE The expressions for workdone, efficiency and power developed by Kaplan trbine are identical with Francis trbine. owever the following are main deviations. (i) In case of Kaplan trbine, the ratio n D D b o D =Diameter of the hb or boss b D =otside diameter of the rnner o The vale of n varies from 0.35 to 0.6

44 (ii) Discharge Q = Area velocity ( D D ) o b 4 f Q ( D D ) K g D o b f o f 4 4 n K g (iii)the peripheral velocity of the rnner is dependent on the radis of the point nder consideration and ths varies from section to section along the blade. In order to have shock free entry and exit of water, the blade angles vary from section to section. The blade angles are greater at the oter trip than of the hb and ths rnner blades of a Kaplan trbine are wrapped or twisted. (iv) The velocity of flow (f) remains constant throghot. DIFFERENCE BETWEEN FRANCIS AND KAPLAN TURBINE The table explains the different between the Francis and Kaplan trbines. S.No FRANCIS TURBINE KAPLAN TURBINE. Mixed flow reaction trbine Axial flow reaction trbine. Rnner vanes are not adjstable Rnner vanes are adjstable 3. Large nmber of vanes (6 to 4) Less nmber of vanes (3 to 8) 4. Medim head trbine (60m to 50m) Low head trbine (p to 30m) 5. Medim specific speed (50 to 50) igh specific speed (50 to 850). A Kaplan trbine develops 60,000P at an overall efficiency of 68% nder a head of 5m. The speed ratio is.6 whereas the flow ratio is 0.5. If the boss diameter is 0.35 times the rnner diameter, find diameter of rnner and speed of trbine. Given Data: Power P= 60000(735.75)=44.5MW = 5m Speed ratio K=.6 Flow ratio Kf= % ; o

45 Boss diameter = 0.35 times the rnner diameter Db=0.35 Do Soltion: Tangential velocity, K g m / s Flow ratio, K g m / s f f o P wq Q 5 6 Q 64.7m 3 / s Discharge Q = Area velocity ( D D ) o b 4 f Q ( D o (0.35 D 4 o ) ). D D o o m Speed of the trbine: D N 60 (5.88 ) N N 5 rpm. A Kaplan trbine develops 0,000P nder a head of 35m and at a rotational speed of 40rpm. The oter diameter of the blades is.5m and the hb diameter is 0.85m. If overall efficiency is 85% and hydralic efficiency of 88%. Calclate the discharge, the inlet flow angle and blade angle at the inlet. Given Data: Power P= 0000kW = 35m Speed N=40rpm

46 85 % ; o h 88 % Do=.5m Db = 0.85m Soltion: o P wq Q 35 Q m 3 / s Discharge Q = Area velocity ( D D ) o b 4 f (.5 4 f 5.78 m / s (0.85 ) ) f D N 60 (5.88 )( 40 ) m / s g w h m / s h w g From inlet velocity triangle, f tan( 80 ) w vane angle at inlet tan f w Blade angle at the inlet A Kaplan trbine develops 6,000P nder a head of 0m. The oter diameter of the blades is 3.5m and the hb diameter is.75m.the gide blade angle at extreme edge of the rnner is

47 30. The overall efficiency is 88% and hydralic efficiency of 84%. If the velocity of whirl is zero at otlet. Calclate (i) Rnner vane angles at inlet and otlet at the extreme edge of the rnner (ii) Speed of the trbine Given Data: Power P= 6000(735.75)=77kW = 0m 84 % ; o h 88 % Do= 3.5m Db =.75m elocity of whirl, 0 w Soltion: o P wq Q 0 Q 7.43 m 3 / s Discharge Q = Area velocity ( D D ) o b 4 f 7.43 (3.5 4 f 9.9m / s (.75 ) ) f From inlet velocity triangle, tan 9.9 tan 30 w f w w 7.4 m / s

48 g w h m / s h g 7.4 w f tan( ) w vane angle at inlet For Kaplan trbine, = and f From otlet velocity triangle, = f tan 44.5 f w Peripheral velocity D N 0 60 (3.5) N N rpm 4.6.PERFORMANCE OF TURBINES To predict the behavior of a trbine working nder varying conditions of head, speed, otpt and gate opening the reslts are expressed in terms of qantities which may be obtained when head on trbine is redced to nity. UNIT QUANTITIES: Unit Speed: It is defined as speed of trbine working nder the nit head. N Speed of actal trbine Tangential velocity of trbine ead where

49 DN 60 N (or) N N = K When =; N=N (At nit speed) N = K = K N N N N Unit discharge: It is defined as discharge throgh a trbine which is working nder nit head. Q = Area velocity Q = A Q Q = K If = ; then Q = Q Q K Q Q Q Q

50 Unit Power: P = O gq 000 P = O gq 000 P Q (where O & are constants) Q P 3 P P = 3 3 K When = then P = P P= 3 3 K K 3 P P = P = 3 P P 3 N N N Q Q Q P = P 3 P 3

51 4.6.. SPECIFIC SPEED The pmp or hydralic trbine designer is often faced with the basic problem of deciding what type of trbomachine will be the best choice for a given dty. Usally the designer will be provided with some preliminary design data sch as the head, the volme flow rate Q and the rotational speed N when a pmp design is nder consideration. When a trbine preliminary design is being considered the parameters normally specified are the shaft power P, the head at trbine entry and the rotational speed N. A non-dimensional parameter called the specific speed, Ns, referred to and conceptalized as the shape nmber, is often sed to facilitate the choice of the most appropriate machine Derivation of specific speed: power available at the shaft of trbine = O power spplied at the inlet of the trbine power delivered gq 000 P = gq head nder which trbine is working Q- Discharge throgh trbine P = O gq 000 P = O gq 000 P Q (where & are constants) O D diameter of actal trbine N speed of actal trbine tangential velocity of trbine Ns specific speed of trbine Absolte velocity of water Absolte velocity, tangential velocity and head of trbine are related as where

52 bt tangential velocity is given by DN 60 DN From eqation 3 & 4, DN or D N Discharge throgh trbine is given by Q = Area velocity Area B (B-breath) D elocity Q D N From eqation 5, D N N N 3 Q N Sb Q in eqation, we get 3 P N

53 5 N 5 P = K N K is proportionality constant If P = and = then N = Ns K N s P = N s N 5 N N = P s 5 N = s N 5 4 P Specific speed plays an important role in selection of the type of trbine. By knowing the specific speed of the trbine the performance of the trbine can be predicted. The trbine of trbine for different specific speed is given below in the table 3. SPECIFIC SPEED TYPE OF TURBINE 0 30 PELTON TURBINE WIT SINGLE JET 7 50 PELTON TURBINE WIT TWO JETS 4 70 PELTON TURBINE WIT FOUR JETS FRANSIS TURBINE KAPLAN TURBINE

54 Problems on specific speed:. A trbine develops 0000kW nder a head of 5m at 35rpm. What is the specific speed? What wold its normal speed and otpt nder a head of 0m? Given Data: Power P= 0000kW = 5m Speed N=40rpm ead, =0m Soltion: Specific speed= N s = N 5 4 P (5 ) 5 4 N s 4.5 If N is the speed nder a head of 0m, then from nit speed relationship N N N N N 0.74 rpm Similarly if P is the otpt power nder a head of 0m, then from nit power speed relationship P 3 P 3 P P P kW A trbine is works nder a head of 5m at 00rpm.The discharge is 0m 3 /s. If the efficiency is 95%. Calclate its otpt and specific speed. Given Data:

55 = 5m N=00rpm Q=0m 3 /s =95% o Soltion: P o wq P 0.95 P kw Specific speed= N s = N 5 4 P (5 ) 5 4 N s 7.7 Since the specific speed lies between 70 to 57, the trbine is a Francis trbine. 3. A Kaplan trbine develops 5000kW power nder a head of 30m. Calclate specific speed? Given Data: Power P= 5000kW Speed ratio K= Flow ratio Kf= % ; o Db=0.35 D Soltion: Specific speed= N s = N 5 4 P (30 ) N s 60.8

56 4. In a hydro development a Kaplan trbine nder a head of.m. It develops 600kW at 80rpm. Assme overall efficiency of 80%. Determine discharge and specific speed? Given Data: =.m N=80rpm =80% o P=600kW Soltion: P o wq Q. Q 36.4m 3 / s Specific speed= N s = N 5 4 P (.) 5 4 N s A trbine is to operate nder a head of 30m rnning at 50rpm delivering 0m 3 /s of water. If the efficiency is 90%. Find (i) specific speed (ii) power developed (iii) Type of trbine. Given Data: = 30m N=50rpm =90% o Q= 0m 3 /s Soltion: P o wq P 0.90 P kw

57 Specific speed= N s = N 5 P (30 ) 4 N s 83.5 Since the specific speed lies between 70 to 57, the trbine is a francis trbine PERFORMANCE CURES OF TURBINE: The crves which are plotted from the reslts of the tests performed on the trbine nder different working conditions are known as characteristic crves. These crves predict the behavior and performance of a trbine nder different working conditions. The following are the important characteristic crves.. Main characteristic crves or constant head crves. Operating characteristic crves or constant speed crves 3. Constant efficiency or Mschel crves. Main characteristic crves or constant head crves: These crves are obtained by maintaining constant head and a constant gate opening. The speed of the trbine is varied by allowing a variable qantity of water to flow throgh the inlet. For each speed, the brake power P is measred mechanically by dynamometer and discharge also measred. Then overall efficiency for each vale of the speed is calclated. From these vales, nit speed, nit power and nit discharge are calclated. Taking N as abscissa, the vales of Q, Pand O. The typical Main characteristic of pelton and Kaplan trbines have depicted in figre.

58 Figre 4.8. Main characteristic crves. Operating characteristic crves or constant speed crves These crves are obtained by maintaining constant speed and for each gate opening. The discharge and head may vary according to their availability. The brake power P is measred mechanically by dynamometer. Then overall efficiency is calclated from the measred vales of Q, and P. Reslts are graphically represented by plotting v/s % of fll load. O Figre 4.9.Operating characteristic crves

59 3. Constant efficiency or Mschel crves These crves are also called as Iso efficiency crves. These crves are obtained from speed v/s efficiency and speed v/s discharge crves for different gate openings. For particlar efficiency say 70%, a horizontal line is drawn which intersects the crves for different gate opening. From the point of intersection, the corresponding nit speed vales are obtained. This information then transferred to the main crve P v/s N for corresponding gate opening. Points of the same efficiency are smoothly joined to get a constant efficiency crves. A crve for the best performance is obtained. The peak points of varios Iso efficiency crves are joined. These crves are sed for determining the zone of constant efficiency and for predicting the performance of trbine of trbine at varios efficiencies. Figre 4.0.Constant efficiency or Mschel crves 4.7. ELEMENTARY CASCADE TEORY

60 The operation of any trbomachine is directly dependent pon changes in the working flid s anglar momentm as it crosses individal blade rows. A deeper insight of trbomachinery mechanics may be gained from consideration of the flow changes and forces exerted within these individal blade rows. In the development of the highly efficient modern axial flow compressor or trbine, the stdy of the two-dimensional flow throgh a cascade of aero foils has played an important part. An array of blades representing the blade ring of actal trbo machinery is called the cascade. As the air stream is passed throgh the cascade, the direction of air is trned. Trbine cascade performance Figre 4. shows reslts obtained by Ainley (948) from two sets of trbine cascade blades, implse and reaction. The term reaction is sed here to denote, in a qalitative sense, that the flid accelerates throgh the blade row and ths experiences a pressre drop dring its passage. There is no pressre change across an implse blade row. The performance is expressed in the form p /( p p ) and against incidence. o o From these reslts it is observed that: Figre 4. cascade of trbine reslt comparision

61 (a) The reaction blades have a mch wider range of low loss performance than the implse blades, a reslt to be expected as the blade bondary layers are sbjected to a favorable pressre gradient, (b) The flid otlet angle remains relatively constant over the whole range of incidence in contrast with the compressor cascade reslts. For trbine cascade blades, a method of correlation is given by Ainley and Mathieson (95 ) which enables the performance of a gas trbine to be predicted with an estimated tolerance of within % on peak efficiency 4.8. INTRODUCTION CENTRIFUGAL PUMP A machine which converts mechanical energy into hydralic energy is known as pmp. On the basis of operating principle pmps can be classified as Roto dynamic and positive displacement pmps. In Rotodynamic Pmp flid is moved by dynamic action of importing momentm to the flid. In positive displacement pmp, the working principle is based on the changes of the volme occpied by the flid within the pmp. Present a part of trbo machines in which the energy transfer process occrs from the rotor to the flid, in other words, in pmp the mechanical energy is converted to a flid energy (head). Pmps are classified according to their impeller type to radial, mixed, and axial. Centrifgal pmps are sed in a wide variety of applications. These machines operate at high speeds and sally direct connected to the driver so that the transmission losses are small. These types of pmps are sally sed when relatively high pressre and large capacity are desired. There are minimm of moving parts which redces the maintenance and increase the working time, other advantages of centrifgal pmps are:. Its smaller size,. Its low installation costs. As discssed before the total energy gained by the flid = P / ρ g + / g, a part of it comes from pressre energy P / ρ g and the other is a kinetic energy / g. To increase the total pressreenergy at the pmp exit, kinetic energy shold be converted to pressreenergy. olte casing and diffser ring are sally sed to convert kineticenergy to pressre energy. Classification of Centrifgal Pmps: i) By Pressre (a) Single Stage centrifgal pmps A pmp that is based on one impeller is called single stage centrifgal pmp. It is sed for relatively low pressre applications. (b) Mlti Stage Centrifgal Pmps.

62 A pmp that is based on two or more than two impellers is known as mlti stage pmp. It is sed for high pressre reqirements. ii) By flow (a) Single Sction A pmp in which its impeller has only one sction eye at one of its side is called single sction pmp. It is sed for relatively low flow applications. (b) Doble Sction A pmp in which its impeller has sction eyes on both of its sides. It is sed for relatively high flow reqirements. (iii) By Installation (a) Parallel arrangement Pmps are installed in parallel to obtain high flow and same pressre. (b) Series Arrangement. Pimps are installed in series to obtain high pressre and same capacity. (iv) By Casing (a) ertical Split A pmp in which casing split is vertical w.r.t. grond level. (b) orizontal Split A pmp in which casing split is horizontal w.r.t. grond level COMPONENTS OF CENTRIFUGAL PUMP: The schematic arrangement of centrifgal pmp is shown in figre 4.

63 Figre 4. Schematic arrangement of Centrifgal Pmp The main components of Centrifgal Pmps are,. Impeller. Casing 3. Sction pipe with foot valve and strainer 4. Delivery pipe 5. Prime mover. Impeller Impeller is the heart of the centrifgal pmp. It rotates the liqid mass with a peripheral speed of its vane tips. The whirling movement of impeller imparts centrifgal force to the liqid and increases its velocity head. Impeller does not increase liqid pressre. Bt high velocity head is converted in to pressre head in the volte. Increase in velocity is directly proportional to the impeller diameter and pmp speed. The impeller is monted on the shaft which is spported by bearings and driven throgh a flexible or rigged copling by an electric motor or some times by a trbine.