Fluid machinery ppt

05/01/2023 Mahesh Kumar(ME Deptt.) 1

Mechanical Engineering Department PPT on Fluid Machinery

Prepared by

Assistant Professor :Mahesh Kumar


Unit-1Impact of jet and turbine


INTRODCTION TO FLUID MECHINERY

A fluid machine is a device which converts the energy stored by a fluid into mechanical energy or vice versa . The energy stored by a fluid mass appears in the form of

• potential, • kinetic • intermolecular energy.

The mechanical energy, on the other hand, is usually transmitted by a rotating shaft.


IMPACT ON JET

• The liquid comes out in the form of a jet from the outlet of a nozzle .

• which is fitted to a pipe through which the liquid is flowing under pressure.

• The following cases of the impact of jet, i.e. the force exerted by the jet on a plate will be considered :‐

• 1. Force exerted by the jet on a stationary plate a) Plate is vertical to the jet b) Plate is inclined to the jet c) Plate is curved


2. Force exerted by the jet on a moving plate a) Plate is vertical to the jet b) Plate is inclined to the jet c) Plate is curved

Force exerted by the jet on a stationary vertical plate• Consider a jet of water coming out from the nozzle strikes the vertical plate.


V = velocity of jet, d = diameter of the jet, a = area of x – section of the jet The force exerted by the jet on the plate in the direction of jet.Fx = Rate of change of momentum in the direction of force= (initial momentum – final momentum / time)= (mass x initial velocity – mass x final velocity / time)= mass/time (initial velocity – final velocity)= ρaV (V -0) = ρaV2


Force exerted by the jet on the moving plate1st Case: Force on flat moving plate in the direction of jetConsider, a jet of water strikes the flat moving plate moving with a uniform velocity away from the jet.V = Velocity of jet

a = area of x-section of jet

U = velocity of flat plate

Relative velocity of jet w.r.t plate = V – uMass of water striking/ sec on the plate = ρa(V - u)


Force exerted by jet on the moving plate in the direction of jetFx = Mass of water striking/ sec x [Initial velocity – Final velocity]= ρa(V - u) [(V - u) – 0]

In this case, work is done by the jet on the plate as the plate is moving, for stationary plate the work done is zero.Work done by the jet on the flat moving plate =Force x Distance in the direction of force/ Time=


Force exerted by the jet on the moving plate1st Case: Force on flat moving plate in the direction of

jet• Consider, a jet of water strikes the flat moving plate

moving with a uniform velocity away from the jet. V = Velocity of jet a = area of x-section of jet U = velocity of flat plate Relative velocity of jet w.r.t plate = V – u Mass of water striking/ sec on the plate = ρa(V - u)


V u


This normal force can be resolved into two components one in the direction of jet and other perpendicular to the direction of jet.Component of Fn in the direction of jet=

Component of Fn in the direction perpendicular to the direction of jet

sin)( 2uvafn

work done= uuva .sin.)( 22


IMPULSE TURBINE

The impulse turbine, the pressure change occurred in the nozzle, where pressure head was converted into kinetic energy. There was no pressure change in the runner, which had the sole duty of turning momentum change into torque.The flow of water is tangential to the runner so it is a tangential flow impulse turbine.The speed jet of water hits the bucket on the wheel and cause of wheel rotate. A spear rod which has spear shaped end can be moved by hand wheel.


Euler's equation

The Euler's equation for steady flow of an ideal fluid along a streamline of a moving fluid is a relation between• the velocity• pressure• density It is based on the Newton's Second Law of Motion. The integration of the equation gives Bernoulli's equation in the form of energy per unit weight of the following fluid.• It is based on the following assumptions:• The fluid is non-viscous (i,e., the frictional losses are zero).

Turbines

• Hydro electric power is the most remarkable development pertaining to the exploitation of water resources throughout the world

• Hydroelectric power is developed by hydraulic turbines which are hydraulic machines.

• Turbines convert hydraulic energy or hydro-potential into mechanical energy.

• Mechanical energy developed by turbines is used to run electric generators coupled to the shaft of turbines

• Hydro electric power is the most cheapest source of power generation.


Based on head and quantity of waterAccording to head and quantity of water available, the turbines can be classified into:-a) High head turbinesb) Medium head turbinesc) Low head turbinesa) High head turbinesHigh head turbines are the turbines which work under heads more than 250m. The quantity of water needed in case of high head turbines is usually small. The Pelton turbines are the usual choice for high heads.

Classification of turbines


Based on head and quantity of waterb) Medium head turbines The turbines that work under a head of 45m to 250m are

called medium head turbines. It requires medium flow of water. Francis turbines are used for medium heads.

c) Low head turbines Turbines which work under a head of less than 45m are

called low head turbines. Owing to low head, large quantity of water is required. Kaplan turbines are used for low heads.



Based on hydraulic action of waterAccording to hydraulic action of water, turbines can be classified intoa) Impulse turbinesb) Reaction turbinesa) Impulse turbine: If the runner of a turbine rotates by the

impact or impulse action of water, it is an impulse turbine.

b) Reaction turbine: These turbines work due to reaction of the pressure difference between the inlet and the outlet of the runner.



Based on direction of flow of water in the runnerDepending upon the direction of flow through the runner, following types of turbines are therea) Tangential flow turbinesb) Radial flow turbinesc) Axial flow turbinesd) Mixed flow turbines



Based on direction of flow of water in the runnera) Tangential flow turbinesb) Radial flow turbinesc) Axial flow turbinesd) Mixed flow turbines



Impulse Turbine:

Impulse turbine works on the basic principle of impulse. When the jet of water strikes at the turbine blade with full of its speed. It generates a large force which used to rotate the turbine. The force is depends on the time interval and velocity of jet strikes the blades. This turbine used to rotate the generator, which produces electric power.


Construction:• Blades:- The number of blades is situated over the rotary. They

are concave in shape. The water jet strikes at the blades and change the direction of it. The force exerted on blades depends upon amount of change in direction of jet. So the blades are generally concave in shape.

• Rotor: Rotor which is also known as wheel is situated on the shaft. All blades are pined into the rotor. The force exerted on blades passes to the rotor which further rotates the shaft.


Nozzle:- A nozzle play main role of generating power from impulse turbine. It is a diverging nozzle which converts all pressure energy of water into kinetic energy and forms the water jet. This high speed water strikes the blades and rotates it.Casing:- Casing is the outside are which prevent the turbine form atmosphere. The main function of casing is to prevent discharge the water from vanes to tail race. There is no change in pressure of water from nozzle to tail race so this turbine works at atmospheric pressure.Braking nozzle:-A nozzle is provided in opposite direction of main nozzle. It is used to slow down or stop the wheel.


Heads, Losses and Efficiencies of Hydraulic Turbines

• Heads These are defined as below: (a) Gross Head: Gross or total head is the difference between

the headrace level and the tail race level when there is no flow. (b) Net Head: Net head or the effective head is the head

available at the turbine inlet. This is less than the gross head, by an amount, equal to the friction losses occurring in the flow passage, from the reservoir to the turbine inlet.


Losses Various types of losses that occur in a power plant are given

below: (a) Head loss in the penstock: This is the friction loss in the

pipe of a penstock. (b) Head loss in the nozzle: In case of impulse turbines, there

is head loss due to nozzle friction. (c) Hydraulic losses: In case of impulse turbines, these losses

occur due to blade friction, eddy formation and kinetic energy of the leaving water. In a reaction turbine, apart from above losses, losses due to friction in the draft tube and disc friction also occur.


(d) Leakage losses: In case of impulse turbines, whole of the water may not be striking the buckets and therefore some of the water power may go waste. In a reaction turbine, some of the water may be passing through the clearance between the casing and the runner without striking the blades and thus not doing any work. These losses are called leakage losses.

(e) Mechanical losses: The power produced by the runner is not available as useful work of the shaft because some power may be lost in bearing friction as mechanical losses.

f) Generator losses: Due to generator loss, power produced by the generator is still lesser than the power obtained at the shaft output.


• Efficiencies Various types of efficiencies are defined as under: (a) Hydraulic efficiency: It is the ratio of the power developed

by the runner to the actual power supplied by water to the runner. It takes into account the hydraulic losses occurring in the turbine

ηh = Runner output / Actual power supplied to runner = Runner output / (ρ.Q.g.H) Where, Q = Quantity of water actually striking the runner

blades H = Net head available at the turbine inlet


(b) Volumetric efficiency: It is the ratio of the actual quantity of water striking the runner blades to the quantity supplied to the turbine. It takes into account the volumetric losses.

Let ∆Q = Quantity of water leaking or not striking the runner blades

ηv = Q / (Q+ ∆Q) (c) Mechanical efficiency: The ratio of the shaft output to the

runner output is called the mechanical efficiency and it accounts for the mechanical losses.

ηm = Shaft output / Runner output


(d) Overall efficiency: Ratio of shaft output to the net power available at the turbine inlet gives overall efficiency of the turbine

ηm = Shaft output / Net power available

Thus all the three types of losses, mechanical, hydraulic and volumetric have been taken into account.

gHQQoutputShaft

o )(.

QQQ

QgHoutputRunner

outputRunneroutputShaft

o

.

..

vhmo


Impulse Turbine and velocity triangle ,power and efficiency


• The stream is delivered to the wheel at an angle ai and velocity Vai..

• An increase in ai, reduces the value of useful component (Absolute circumferential Component).

• This is also called Inlet Whirl Velocity, Vwi = Vai cos(ai).• An increase in ai, 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 Vfi = Vai sin(ai) = Vri sin(bi).


Newton’s Second Law for an Impulse 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 : Vri cos(bi).

Tangential relative velocity at blade exit : -Vre cos(be).

Change in velocity in tangential direction: -Vre cos(be) - Vri cos(bi).

-(Vre cos(be) + Vri cos(bi)).

U

VriVai

Vre

Vae

biaiae be


The reaction to this force provides the driving thrust on the wheel.

The driving force on wheel iriereR VVmF bb coscos

Power Output of the blade,

iriereb VVUmP bb coscos

Diagram Efficiency or Blade efficiency:

steaminlet ofPower KineticouputPower

d

2

coscos2

ai

riered

Vm

iVVUm

bb


2

coscos2

ai

rierid V

iVkVU bb

2

coscos2

ai

erid V

ikUV bb

U

VriVai

Vre

Vae

biaiae be

iriiai VUV ba coscos

i

iairi

UVVb

acoscos

2

1coscoscos2

ai

eiai

d Vi

kUVU

bba


1

coscoscos2

2

eaii

aid i

kVU

VU

bba

2

1coscoscos2

ai

eiai

d Vi

kUVU

bba

Define Blade Speed Ratio, f

1

coscoscos2

ik e

id bbfaf


For a given shape of the blade, the efficiency is a strong function of f.

For maximum efficiency: 0fdd d

01coscos2cos2

ik e

i bbfa

2

cos02cos ii

affa

1

coscos

2coscoscos2max, i

k eiiid b

baaa


Governing of hydraulic turbine

As turbine is directly coupled to the electric generator which is required to run at constant sped.

The load on turbine is not constant through out the day or hour, hence speed of turbine varies with respect to load at constant head and discharge .

Therefore in order to have constant speed of generator ,governing of turbine is required to maintain the constant speed of turbine with respect to load.


Main part for governing of pelton wheel

1 .Centrifugal governor2 .Oil pump-gear pump with oil sump3 .Relay or control valve4 .Servomotor with spear rod and spear

5 .Deflector mechanism.


control valve

Relay valve is a spool valve having 5 ports. It is also called as control valve or distributor valve. It receives the pressurised oil from the oil pump which is diverted towards the ports to pipe A or pipe B. Through these pipes the oil is transferred to corresponding sides of double` acting servomotor cylinder. Simultaneously, the oil will be returned from the servomotor from the opposite pipe to the sump.


Governor and linkages

A centrifugal governor is used as the measuring element of the closed loop control system. It is driven by the turbine shaft through bevel gears. The sleeve of the governor is connected through linkages to relay valve. The movement of is transferred through the lever to move the piston rod of relay valve.


Working

Consider the case when the load on the generator increases, the speed of the generator and turbine will decreases. Since the governor is driven by the turbine shaft, its speed will also As a consequence, the fly balls of the governor will move inwards due to reduced centrifugal force on the balls. As a result the sleeve of the governor will move downwards.


Unit-2 Impulse and reaction turbine



FRANCIS TURBINE

INTRODUCTION: The Francis turbine is an inward flow reaction turbine which was designed and developed by the American engineer James B. Francis. Francis turbine has a purely radial flow runner; the flow passing through the runner had velocity component only in a plane of the normal to the axis of the runner. Reaction hydraulic turbines of relatively medium speed with radial flow of water in the component of turbine are runner.


Working of Francis TurbineFrancis Turbines are generally installed with their axis vertical. Water with high head (pressure) enters the turbine through the spiral casing surrounding the guide vanes. The water looses a part of its pressure in the volute (spiral casing) to maintain its speed. Then water passes through guide vanes where it is directed to strike the blades on the runner at optimum angles. As the water flows through the runner its pressure and angular momentum reduces. This reduction imparts reaction on the runner and power is transferred to the turbine shaft.If the turbine is operating at the design conditions the water leaves the runner in axial direction. Water exits the turbine through the draft tube, which acts as a diffuser and reduces the exit velocity of the flow to recover maximum energy from the flowing water.


Kaplan turbine construction and working

Kaplan is also known as propeller turbine. Kaplan turbine is a propeller type water turbine along with the adjustable blades. Mainly it is designed for low head water applications. The Kaplan turbine consists of propeller type of blades which works reverse. By using shaft power displacing the water axially and creating axial thrust in the turbine. The water flows axially and it creates axial forces on the Kaplan turbine blades to produce generating shaft power.


Due to the low water heads it allows the water flow at larger in the Kaplan turbine. With help of the guide vane the water enters. So the guide vanes are aligned to give the flow a suitable degree of swirl. The swirl is determined according to the rotor of the turbine. The water flow from the guide vanes are passes through the curved structure which forces the radial flow to direction of axial. The swirl is imparted by the inlet guide vanes and they are not in the form of free vortex. With a component of the swirl in the form of axial flow are applies forces on the blades of the rotor. Due to the force it loses both angular and linear momentum.


Degree of reaction.

Degree of reaction can be defined as the ratio of pressure energy change in the blades to total energy change of the fluid. If the degree of reaction is zero it means that the energy changes due to the rotor blades is zero, leading to a different turbine design called PeltonTurbine.


The draft tube is an important component of a Francis turbine which influences the hydraulic performance. It is located just under the runner and allowed to decelerate the flow velocity exiting the runner, thereby converting the excess of kinetic energy into static pressure.

Draft tube


Conical diffuser or straight divergent tube-This type of draft tube consists of a conical diffuser with half angle generally less than equal to 10° to prevent flow separation. It is usually employed for low specific speed,vertical shaft Francis turbine. Efficiency of this type of draft tube is 90%

2. Simple elbow type draft Tube-It consists of an extended elbow type tube. Generally, used when turbine has to be placed close to the tail-race. It helps to cut down the cost of excavation and the exit diameter should be as large as possible to recover kinetic energy at the outlet of runner. Efficiency of this kind of draft tube is less almost 60%

3. Elbow with varying cross section-It is similar to the Bent Draft tube except the bent part is of varying cross section with rectangular outlet. The horizontal portion of draft tube is generally inclined upwards to prevent entry of air from the exit end.


cavitationThe liquid enters hydraulic turbines at high pressure; this pressure is a combination of static and dynamic components. ... Thus, Cavitation can occur near the fast moving blades of the turbine where local dynamic head increases due to action of blades which causes static pressure to fall.


Net Positive Suction Head (NPSH)

• Net Positive Suction Head Available (NPSHA): The absolute dynamic head at the pump inlet (suction) in excess of the vapor pressure

• NPSHA is the theoretical amount of head that could be lost between suction and point of minimum pressure without causing cavitation(but this always overestimates actual amount that can be lost, because some velocity head must remain, even at point of pmin).


Specific speed Specific speed is an index used to predict desired pump or turbine performance. i.e. it predicts the general shape of a pumps impeller. It is this impeller's "shape" that predicts its flow and head characteristics so that the designer can then select a pump or turbine most appropriate for a particular application


Selection of water turbine• Hydropower turbines use water pressure to rotate its blades

and generate energy. Selecting the appropriate type of turbine depends primarily on available head and less so on available flow rate. The three primary types of turbines are: the Pelton turbine, for high heads; the Francis turbine, for low to medium heads; and the Kaplan turbine for a wide range of heads (see Figure 2.3a below). Several other types of turbines exist on the market, described below.

• To understand the operating characteristics of the reaction and impulse turbines encompassed in their governing mechanical laws that predicts their work and performance.

• Demonstrate the mechanism of the turbine-speed control in relationship with the various forms of energy explained in the mechanical laws that predicts their behavior.


Introduction

• A water turbine is a rotary machine that converts kinetic and potential energy of water into mechanical work.

• Water turbines are mostly found in dams to generate electric power from water kinetic energy.

• Water turbines take energy from moving water. Flowing water is directed on to the blades of a turbine runner, creating a force on the blades. Since the runner is spinning, the force acts through a distance to produce work. In this way, energy is transferred from the water flow to the turbine.


Water turbines are divided in two groups :• Reaction turbines- are acted on by water, which changes

pressure as it moves through the turbine and gives up its energy. They must be encased to contain the water pressure or must be fully submerged in the water flow.

• Impulse turbines- changes the velocity of a water jet that strikes on the turbine’s curved blades, consequently the flow is reversed and the resulting change in momentum causes a force in the turbines. The turbine doesn’t require housing for operation.


In both types of turbines the fluid passes through a runner having blades. The momentum of the fluid in the tangential direction is changed and so a tangential force on the runner is produced. The important feature of the impulse machine is that there is no change in static pressure, across the runner, while for the reaction turbine there are considerable changes in pressure energy.


Applying the first law of thermodynamics (principle of energy conservation) to a “control volume”. Assuming a steady flow operation of the turbine per unit of mass (j/kg). lossWhere ws is the work performed by the fluid on the turbine.


Actual work (wa) is the total useful specific energy supply by the liquid.

The total dynamic head of the turbine is described as:

The hydraulic power (Ph) is the useful power supplied by the liquid to the turbine.


Unit-3 Centrifugal pumps


Pumps• Machine that provides energy to a fluid in a fluid system.

• Converts the mechanical energy supplied to it externally to hydraulic energy and transfers it to the liquid flowing through a pipe

• Flow is normally from high pressure to low pressure


Pumps

• On the basis of mode of action of conversion of mechanical energy to hydraulic energy, pumps are classified as

• Roto-dynamic pumps• Positive displacement pumps

• In roto-dynamic pumps, increase in energy level is due to combination of centrifugal energy, pressure energy and kinetic energy

• In displacement pumps, liquid is sucked and then displaced due to the thrust exerted on it by a moving member that results in the lifting of liquid to a desired height.


Centrifugal Pumps

Centrifugal pumps are the roto-dynamic machines that convert mechanical energy of shaft into kinetic and pressure energy of water which may be used to raise the level of water. The wheel in which this conversion is to realized is known as a impeller. A centrifugal pump is named so, because the energy added by the impeller to the fluid is largely due to centrifugal effects.


Classification of Centrifugal Pumps

Centrifugal pumps may be classified according to,1.Working head2.Specific speed3.Type of casing4.Direction of flow of water5.Number of entrances to the impeller6.Disposition of shaft7.Number of stage


Classification of Centrifugal Pumps Working Head Centrifugal pumps may be classified in to low, medium and high-

head pumps.• Low-Head Centrifugal Pumps These are usually single-stage-centrifugal pumps and work below

15m head. • Medium-Head Centrifugal Pumps When the head lies between 15 and 45 m, the pumps are called

medium-head-centrifugal pumps.High-Head Centrifugal Pumps When the head exceeds 45m, the pumps are known as high-head-

centrifugal pumps. Usually these are multistage pumps, and are provided with guide vanes. These pumps may have horizontal or vertical shafts. Vertical shafts are useful in deep wells.


Specified Speed Specific speed of a pump is defined as the speed of a

geometrically similar pump which delivers unit discharge under unit head.

Ns = N√ Q / H3/4 Types of Casing Pumps can be divided into following type according to their

casing: a) Volute-Chamber Pump b) Vortex-chamber Pump c) Diffuser Pump


Work done by the impeller of a centrifugal pump

Figure shows the velocity triangles at the inlet and outlet tips of a vane fixed to the impeller.Let N=speed of the impeller in RPMD= Diameter of the impeller at inletD=Diameter of the impeller at outletU1 = Tangential velocity of the impeller at inlet πD1N/60U2= tangential velocity of the impeller at outlet πD2N/60V1=absolute velocity of the liquid at inletV2= absolute velocity of the liquid at outletVf1 & Vf2 =are the velocities of flow at inlet and outlet.Vr1 & Vr2=Relative velocities at inlet and outletVw2=whirl velocity at outlet05/01/2023 Mahesh Kumar(ME Deptt.) 72

ἀ =angle made by V1 with respect to the motion of the vaneᵩ=blade angle at inlet ᵦ= blade angle at outletFor a series of curved vanes the force exerted can be determined using the impulse momentum equation Work=force x distance.similarly the work done/sec/unit weight of the liquid striking the vane=1/g(Vw2u2-Vw1u1).But for a centrifugal pumpVw2=0Work done/sec/unit weight=Vw2u2And the work done/sec=Q/g(Vw2u2)


Pump efficiency

)()('

eh HHeadEuler

HHeadTotalsPump


22UVgH

wh

)()('

e

mm HHeadEuler

HHeadManometricsPump

22UVgH

w

mm

QQQ

v

cavitation of a Pump• Increase pressure at the suction of the pump.

• Reduce the temperature of the liquid being pumped.

• Reduce head losses in the suction piping.

• Reduce the flow rate through the pump.

• Reduce the speed of the pump impeller


• Degraded pump performance.

• Metal gets corroded seen as small pitting.

• Audiable rattling or crackling sounds which can reach a pitch of dangerous vibrations.

• Damage to pump impeller, bearings, wear rings and seals.


Unit-4Reciprocating pump


Reciprocating pump

• Pumps are used to increase the energy level of water by virtue of which it can be raised to a higher level.

• Reciprocating pumps are positive displacement pump, i.e. initially, a small quantity of liquid is taken into a chamber and is physically displaced and forced out with pressure by a moving mechanical elements.

• The use of reciprocating pumps is being limited these days and being replaced by centrifugal pumps.


Reciprocating pump

• For industrial purposes, they have become obsolete due to their high initial and maintenance costs as compared to centrifugal pumps.

• Small hand operated pumps are still in use that include well pumps, etc.

• These are also useful where high heads are required with small discharge, as oil drilling operations.


Main components• A reciprocation pumps consists of a plunger or a piston that

moves forward and backward inside a cylinder with the help of a connecting rod and a crank. The crank is rotated by an external source of power.

• The cylinder is connected to the sump by a suction pipe and to the delivery tank by a delivery pipe.

• At the cylinder ends of these pipes, non-return valves are provided. A non-return valve allows the liquid to pass in only one direction.

• Through suction valve, liquid can only be admitted into the cylinder and through the delivery valve, liquid can only be discharged into the delivery pipe.


Main components


Working of Reciprocating Pump

• When the piston moves from the left to the right, a suction pressure is produced in the cylinder. If the pump is started for the first time or after a long period, air from the suction pipe is sucked during the suction stroke, while the delivery valve is closed. Liquid rises into the suction pipe by a small height due to atmospheric pressure on the sump liquid.

• During the delivery stroke, air in the cylinder is pushed out into the delivery pipe by the thrust of the piston, while the suction valve is closed. When all the air from the suction pipe has been exhausted, the liquid from the sump is able to rise and enter the cylinder.


Working of Reciprocating Pump

• During the delivery stroke it is displaced into the delivery pipe. Thus the liquid is delivered into the delivery tank intermittently, i.e. during the delivery stroke only.


Classification of Reciprocating pumps

Following are the main types of reciprocating pumps:• According to use of piston sides

– Single acting Reciprocating Pump: If there is only one suction and one delivery pipe and the

liquid is filled only on one side of the piston, it is called a single-acting reciprocating pump.

– Double acting Reciprocating Pump: A double-acting reciprocating pump has two suction and

two delivery pipes, Liquid is receiving on both sides of the piston in the cylinder and is delivered into the respective delivery pipes.



• According to number of cylinder Reciprocating pumps having more than one cylinder are called

multi-cylinder reciprocating pumps.– Single cylinder pump A single-cylinder pump can be either single or double

acting– Double cylinder pump (or two throw pump) A double cylinder or two throw pump consist of two

cylinders connected to the same shaft.



• According to number of cylinder– Triple cylinder pump (three throw pump) A triple-cylinder pump or three throw pump has three

cylinders, the cranks of which are set at 1200 to one another. Each cylinder is provided with its own suction pipe delivery pipe and piston.

– There can be four-cylinder and five cylinder pumps also, the cranks of which are arranged accordingly.


Discharge through a Reciprocating Pump

Let A = cross sectional area of cylinderr = crank radiusN = rpm of the crank L = stroke length (2r)

Discharge through pump per second= Area x stroke length x rpm/60

This will be the discharge when the pump is single acting. 60NLAQth



Discharge in case of double acting pump Discharge/Second =

Where, Ap = Area of cross-section of piston rod However, if area of the piston rod is neglected Discharge/Second =

60

)(60

LNAAALNQ Pth

60)2( LNAAQ P

th

602ALN



• Thus discharge of a double-acting reciprocating pump is twice than that of a single-acting pump.

• Owing to leakage losses and time delay in closing the valves, actual discharge Qa usually lesser than the theoretical discharge Qth.


Slip Slip of a reciprocating pump is defined as the difference

between the theoretical and the actual discharge. i.e. Slip = Theoretical discharge - Actual discharge = Qth. - Qa

Slip can also be expressed in terms of %age and given by

10011001

100%

dth

act

th

actth

CQQ

QQQslip


Slip Slip Where Cd is known as co-efficient of discharge and

is defined as the ratio of the actual discharge to the theoretical discharge.

Cd = Qa / Qth. Value of Cd when expressed in percentage is known as

volumetric efficiency of the pump. Its value ranges between 95---98 %. Percentage slip is of the order of 2% for pumps in good conditions.


Negative slip

• It is not always that the actual discharge is lesser than the theoretical discharge. In case of a reciprocating pump with long suction pipe, short delivery pipe and running at high speed, inertia force in the suction pipe becomes large as compared to the pressure force on the outside of delivery valve. This opens the delivery valve even before the piston has completed its suction stroke. Thus some of the water is pushed into the delivery pipe before the delivery stroke is actually commenced. This way the actual discharge becomes more than the theoretical discharge.

• Thus co-efficient of discharge increases from one and the slip becomes negative.


Power Input

Consider a single acting reciprocating pump. Let hs = Suction head or difference in level between centre line of

cylinder and the sump. hd = Delivery head or difference in between centre line of

cylinder and the outlet of delivery pipe. Hst = Total static head = hs + hd Theoretical work done by the pump = ρ Qth g Hst

ds hhgALN

60


Power Input

Power input to the pump

However, due to the leakage and frictional losses, actual power

input will be more than the theoretical power. Let η = Efficiency of the pump. Then actual power input to the pump

ds hhgALN

60

ds hhgALN

601


Comparison of Centrifugal and Reciprocating Pumps

Centrifugal Pumps Reciprocating Pumps1. Steady and even flow 1. Intermittent and pulsating flow2. For large discharge, small heads 2. For small discharge, high heads.3. Can be used for viscous fluids e.g. oils, muddy water.

3. Can handle pure water or less viscous liquids only otherwise valves give frequent trouble.

4. Low initial cost 4. High initial cost.5. Can run at high speed. Can be coupled directly to electric motor.

5. Low speed. Belt drive necessary.

6. Low maintenance cost. Periodic check up sufficient.

6. High maintenance cost. Frequent replacement of parts.

7. Compact less floors required. 7. Needs 6-7 times area than for centrifugal pumps.


Hydraulic Ram?The hydraulic ram pump may be defined as a self-acting device that uses the energy of a large volume of water falling from a higher location (relative to the ram) and passing through it, to lift a small volume to a location significantly higher than the ram and the source of water. It has only 2 moving parts.


Characteristics of a Hydraulic Ram Water-Lifting System

(1) there is no other external energy input(e.g.human,animal, fossil fuel, etc.) that makes the ram work other than the energy of water passing through the pump.

(2) water has to come from a location higher than the ram;


(3) only a small portion of this water (around 25 % or less) is pumped up, the remainder passing out of the ram and must be drained to a lower location.

(4) the vertical distance to which water can be pumped up from the ram is significantly higher than the vertical distance from its source to the ram – up to 30 meters delivery height per 1 meter of supply fall, although typically the most efficient is within a ratio of 10:1 or less, and;



•The indicator diagram for a reciprocating pump is defined as the graph between the pressure head in the cylinder and the distance travelled by piston from inner dead centre for one complete revolution of the crank. •As the maximum distance travelled by the piston is equal to the stroke length and hence the indicator diagram is a graph between pressure head and stroke length of the piston for one complete revolution. •The pressure head is taken as ordinate and stroke length as abscissa.

Indicator diagram


•The graph between pressure head in the cylinder and stroke length of the piston for one complete revolution of the crank under ideal conditions is known as ideal indicator diagram. •Figure shows the ideal indicator diagram, in which line ‘EF’ represents the atmospheric pressure head equal to 10.3 m of water.


Reciprocating pump is a positive displacement pump. Here we will study reciprocating pump with air vessel. It can be used for less discharge at higher heads. Priming is not required because it is a positive displacement pump. Reciprocating pump is used in pumping water in hilly areas. Reciprocating pumps has lower efficiency compared to centrifugal pumps.

Air vessel reciprocating pump


Following are the main parts of reciprocating pump.. 1.Piston and cylinder. 2.Suction pipe.3.Suction valve.4.Delivery pipe.5.Delivery valve.


Piston and cylinder: Piston reciprocates in the cylinder. Crank shaft which is connected to motor and connecting rod give motion to piston. Main function of piston and cylinder is to pull the water in cylinder and push it at required height. Suction pipe: The suction pipe’s one end is connected to the pump and other is depth in the sump. Water enters from sump in to pump through suction pipe. Suction valve: The suction valve is fitted on suction pipe close to the cylinder. It allows the entry of water in to cylinder.


Delivery pipe: Delivery pipe is connected between pump and reservoir. Through the delivery pipe water transferred from pump to reservoir.

Delivery valve: The delivery valve is fitted on the delivery pipe close to the cylinder. It allows water to flow in delivery pipe from cylinder.


Strainer: It is used to prevent impurities and solid particles from entering the pump. Crank: Crank is used to pass motor work to the piston. Connecting rod: It connects crank with the piston. Air vessel: Air vessel is used to reduce frictional head and give a steady flow of liquid.


Jet pumps, also known as ejector pumps, are devices capable of handling and transporting all forms of motive fluid including gas, steam, or liquid. They can be considered mixers or circulators, since the intake combines multiple fluid sources. Multiple inlets are used to draw in a constant stream of fluid, using pressure to create lift through suction. The combination of intake pressure and velocity of the liquid or gas jets the media up from a well, tank, or pit through the pump to the discharge point


Jet pumps are centrifugal pumps with an ejector (venturi nozzle) attached at the discharge outlet. They function based upon the Venturi effect of Bernoulli's principle - utilizing constriction to reduce pressure and provide suction. After the pump is primed, a motive fluid is pumped through a standard centrifugal pump and enters an ejector. At the throat of the converging section of the ejector, the pressurized fluid is ejected at high velocity. This creates a low pressure (vacuum) at the throat, drawing the target fluid (from a well or other source) up into the nozzle. This picture is a diagram of the ejector portion of a jet pump.


Jet pumps are typically inserted vertically into the process media, but can be mounted horizontally as well. They are often used in applications where the material that is pumped assists in creating the motive force needed to move through the pump. For example, in marine applications, jet pumps are used to transfer seawater. In home applications, they are used to move wastewater up to the sewer line. A float level sensor and switch are used to turn on the pump.

Fluid machinery ppt

Engineering

Transcript of Fluid machinery ppt