Fluid Machine: Fluid Machines Fluid Machinery
Fluid machine:Fluid machine is a device exchanging energy (work) between a fluid and a mechanical systemIn particular : a turbo machine is a device using a rotating mechanical systemFluid machines are those devices that are used to either move fluid or extract energy from it.Broadly speeaking, fluid machines are divided into two groups:1-Positive-displacement machines2-TurbomachinesFluid Machinery Fluid machinery is used to convert hydraulic energy to mechanical energy or vice versa.Introduction to Turbo Machinery A turbo machine is basically a rotating MachineThe rotating wheel is called a rotor / runner /impellerThe rotor will be immersed in a fluid ContinuumThe fluid medium can be gas / steam /water / airEnergy transfer takes place either Turbine rotorfrom rotor to fluid, orfrom fluid to rotor Using working fluids to Boost output, either increase ordecrease pressure by using Machinery
Turbo machine – DefinitionA turbo machine is a device where mechanical energy in the form of shaft work, is transferredeither to or from a continuously flowing fluid by the dynamic action of rotating blade rows.The interaction between the fluid and the turbo machine blades also results in fluid dynamic lift.A turbo machine produces of the fluid passing change in enthalpy through it.A turbo machine is a device in which energy transfer occurs between a flowing fluid and rotating elementdue to dynamic action. This results in change of pressure and momentum of the fluid.The word turbo or turbinis is of Latin origin and implies that which spins or whirlsaround.Essentially, a rotating blade row, a rotor or an impeller changes the stagnation enthalpy ofthe fluid moving through it by doing either positive or negative work, depending upon theeffect required of the machine.These enthalpy changes are intimately linked with the pressure changes occurringsimultaneously in the fluid.PARTS OF A TURBO MACHINEThe principle components of a turbo machine are:1. Rotating element (vane, impeller or blades)2. Stationary elements – which usually guide the fluid in proper direction for efficient energyconversion process.3. Shaft – which either gives input power or takes output power from fluid under dynmicconditions and runs at required speed.4. Housing – to keep various rotating, stationery and other passages safely under dynamicconditions of the flowing fluid.
Turbo machine – ClassificationTurbo machines may also be classified as : Turbines, compressors, pumps, fans , blowers Incompressible or compressible Axial-flow, mixed-flow or radial-flow geometry Single stage or multi-stage Turbo-pump, turbo-compressor or torque-converter Impulse, reaction or impulse-reaction
Power Absorbing Turbo machinesFans - air is the working mediumaxial flowradial flow (centrifugal)Blowers - air is the working mediumaxial flowradial flow (centrifugal)Propellers and Ducted Fans- air is the workingmediumCompressors - air is the working mediumreciprocatingrotaryaxial flowradial flow (centrifugal)mixed flowPumps - water is the working mediumreciprocatingrotaryaxial flowradial flow (centrifugal)mixed flowPower Producing Turbo machinesGas turbines – air and combustion gas is theworking mediumaxial flowradial flowSteam turbine – steam is the working mediumimpulse turbinereaction turbineHydraulic turbines – water is the workingmediumimpulse turbinereaction turbinemixed flowaxial flowWind turbines – air / wind is the workingmediumvertical axishorizontal axisClassification of Turbo Machines:1. According to the nature of energy transfer: Power generating turbo machines: In this, energy is transferred from the flowing fluid to therotor. Hence, enthalpy of the flowing fluid decreases as it flows across. There is a need for anoutput shaft. Ex: Hydraulic turbines such as Francis turbine, Pelton wheel turbine, Kaplan turbine, steamturbine such as De-Laval turbine, Parsons Turbine etc, Gas turbines etc,
Power absorbing Turbo machines: In this, energy is transferred from the rotor to the flowingfluid. The enthalpy of the fluid increases as it flows there is a need for an input shaft. Ex: Centrifugal pump, Compressor, blower, fan etc, Power transmitting turbo machines: In this energy is transferred from one rotor to another bymeans of a flowing fluid. There is a need for an input / output shafts. The transfer of energyoccurs due to fluid action. Ex: Hydraulic coupling, torque converter etc,Schematic representation of different types of turbo machine based on fluid flow: Axial flow fan. Radial outward flow fan. Mixed flow hydraulic turbine.2. Based on the type of fluid flow:o Tangential flow in which fluid flows tangential to the rotor Ex: Pelton wheel etc,o Axial flow in which the fluid flows more or less parallel to the axes of the shafts /rotors.Ex: Kaplan turbine, Axial flow compressor.o Radial flow in which fluid flows along the radius of the rotor this is again classified as: Radially inward flow. Ex: Old fancies turbine. Radially outward flow. Ex: Centrifugal Pumpo Mixed flow which involves radius entry & axial exit or vise-versa. Ex: Modern francisesturbine & Centrifugal Pump3. Based on the type of Head: High head &low discharge .Ex: Pelton wheel. Medium head &medium discharge. Ex: Francis turbine. Low head & high discharge. Ex: Kaplan turbine.CLASSIFICATION OF TURBO MACHINES1. Based on energy transfera) Energy is given by fluid to the rotor - Power generating turbo machine E.g. Turbinesb) Energy given by the rotor to the fluid – Power absorbing turbo machinec) E.g. Pumps, blowers and compressors2. Based on fluid flowing in turbo machinea) Waterb) Airc) Steamd) Hot gasese) Liquids like petrol etc.3. Based on direction of flow through the impeller or vanes or blades, with reference to the axis ofshaft rotationa) Axial flow – Axial pump, compressor or turbine
b) Mixed flow – Mixed flow pump, Francis turbinec) Radial flow – Centrifugal pump or compressord) Tangential flow – Pelton water turbine4. Based on condition of fluid in turbo machinea) Impulse type (constant pressure) E.g Pelton water turbineb) Reaction type (variable pressure) E.g. Francis reaction turbine5. Based on position of rotating shafta) Horizontal shaft – Steam turbinesb) Vertical shaft – Kaplan water turbinesc) Inclined shaft – Modern bulb micr
Losses associated with turbo-machineryInternal Losses:Losses which take place in the inner passages of the machine and directly connected with rotor orflow of the medium and which are adding heat to the flow mediumExternal losses:Losses which appear outside of the inner passages of the casing and which do not transfer thegenerated heat directly into the flow mediumInternal Losses Due to the inner losses, the total energy exchange between the rotor and the flow medium isaltered. In the case of the working machine more energy has to be exchanged In the case of the power machine less energy is exchanged than by a machine under the samecondition but without losses.The losses can be :Specific Energy LossesVolume/mass‐flow lossesHydraulic Loss ZhHydraulic Loss is a specific Energy Loss due to friction, separation, contraction,diffusion, eddy formation etc. while the flow passes through the main flow passages from entrance todischarge flange of the machineIn case of turbines the needed energy to overcome the hydraulic loss Zh is taken from the availablespec. energy Y.
In case of working machines, the impeller has to transfer in addition to the spec. energy Y a spec.energy ZhDisc Friction Loss ZrThe surface of the rotor which does not form the main flow passage is surrounded by a fluidmediumWhile the rotor rotates, a friction is generated between this rotor surface and its surrounding fluidmedium. The needed power to overcome this friction can be written as:Where: Zr disc friction spec. energy loss and is involved with ρVReturn‐Flow Loss ZaA return flow of already energy loaded medium may be noted in pumps. Especially bythose of the axial‐flow type.Na is very small for the design point and, thus it is normally neglected. But it may increase greatly whendischarge Vx is less that the design point discharge V.Leakage Loss ΔV (Loss of Volume or mass‐flow)Due to possible leakage, the volume V passing through the pressure flange of the machine differsfrom the volume V’ passing through the rotor vane channels.External Losses All external losses due to friction in the bearings, sealing and due to fluid friction f f at the outsiderotating surfaces of the machine can be counted together as a power loss: External losses also include losses from auxiliary equipments (oil pump, bearing lubrication speedregulators) since they are mostly driven directly by the shaft of the turbo machine The coupling power N which considers all internal and external losses is
Internal losses of the machine occurring in the casing and impeller are referred to as hydraulic lossesP Pm gHhQh gHQPower in Mech loss Hydr loss Useful powerHydraulic losses can involve : Impeller power loss { ine ciencies in the impeller design Leakage power loss { some ow evades the impeller Casing power loss { friction with casing Leakage losses: In case of impulse turbines, whole of the water may not be striking thebuckets and therefore some of the water power may go waste. In a reaction turbine, someof the water may be passing through the clearance between the casing and the runnerwithout striking the blades and thus not doing any work. These losses are called leakagelosses.Mechanical losses: The power produced by the runner is not available as useful work of the shaftbecause 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 thepower obtained at the shaft output.Comparison with positive displacement machinesFluid machines may also be broadly classified as either positive-displacement machines or dynamicmachines, based on the manner in which energy transfer occurs.In positive-displacement machines: Fluid is force fluid into confined volumesEnergy transfer to the fluid is accomplished by movement of the boundary of the closed volume, causingthe volume to expand or contract, thereby sucking fluid in or squeezing fluid out, respectively.
(a) The human heart is an example of a positive displacement pump; blood is pumped byexpansion and contraction of heart chambers called ventricles.(b) The common water meter in your house is an example of a positive displacementturbine; water fills and exits a chamber of known volume for each revolution of the outputshaftA dynamic fluid machine which is called turbo machine uses a moving (rotating) rotor,carrying assetof blades or vanes, to transfer work to or from a moving stream of fluid. If the work done on the fluidby the rotor, the machine is called a pump or compressor. If the fluid delivers work to the rotor, themachine is called turbine.Turbo machines classified as all those devices in which energy is transferred either to, or from, acontinuously flowing fluid by the dynamic action of one or more moving blade rows. Example, ceilingfans.Essentially, a rotating blade row, a rotor or an impeller changes the stagnation enthalpy of the fluidmoving through it by either doing positive or negative work, depending upon the effect required of themachine. These enthalpy changes are intimately linked with the pressure changes occurringsimultaneously in the fluid.Dynamic machines: There is no closed volume; instead, rotating blades supply or extract energy to orfrom the fluid. For pumps, these rotating blades are called impeller blades, while for turbines, the rotatingblades are called runner blades or buckets.A wind turbine is a good example of a dynamic machine of the open type; air turns the blades, and theoutput shaft drives an electric generator.Examples of dynamic pumps include enclosed pumps and ducted pumps and open pumps.
Examples of dynamic turbines include enclosed turbines, such as the hydro turbine that extracts energyfrom water in a hydroelectric dam, and open turbines such as the wind turbine that extracts energy fromthe windCOMPARISON BETWEEN POSITIVE DISPLACEMENT MACHINES AND TURBO MACHINESAction:A positive displacement machine creates thermodynamic and mechanical action between near static fluidand relatively slow moving surface and involves in volume change and displacement of fluid as in ICengines.A turbo machine creates thermodynamic and dynamic action between flowing fluid and rotating elementinvolving energy transfer with pressure and momentum changes as shown in gas turbines.Operation:The positive displacement machine commonly involves reciprocating motion and unsteady flow of fluidslike in reciprocating IC engines or slow rotating fluids like in gear pumps.A turbo machine involves steady flow of fluid with pure rotary motion of mechanical elements. Onlyunsteadiness will be there during starting, stopping and changes in loads on the machine.Mechanical features:A positive displacement machine commonly work at low speeds and involves complex mechanicaldesign. It may have valves and normally will have heavy foundation.A turbo machine works at high speeds, simpler in design, light in weight, have less vibration problemsand require light foundationEfficiency of energy conversion:A positive displacement machine gives higher efficiency due to energy transfer near static conditionseither in compression or expansion processes.
A turbo machine gives less efficiency in energy transfer. The energy transfer due to dynamic action willbe less during compression process of fluid like pumps and compressors and will be slightly more duringexpansion processes like in turbines but still lower than reciprocating machinesVolumetric efficiency:The volumetric efficiency of a positive displacement machine is low due to closing and opening of thevalves during continuous.In turbo machines, since there are no valves under steady flow conditions, the volumetric efficiency willbe close to 100 per cent. A turbo machine has high fluid handling capacityWeight to mass flow rate:A reciprocating air craft IC engine power engine developing 300 KW handles 2 kgs/sec of air weighsaround 9500 N. Whereas, a rotary gas turbine of an air craft for same 300 KW power can handle 22kgs/sec of air and weighs only 8000N handling more mass of air/sec. In stationary power plants, thespecific weight of reciprocating power plants will be 10-15 times higher than the turbo power plants.Fluid phase:Turbo machines have the phase changes occurring in fluid like cavitation in hydraulic pumps andturbines and surge and stall in compressors, blowers and fans if the machines are operated at off designcondition leading to associated vibrations and stoppage of flow and damage to blades.Positive displacement machines have no such problemsApplicationsPower GenerationHydro electric- Hydro-electric turbo machinery uses potential energy stored in water to flow over anopen impeller to turn a generator which creates electricitySteam turbines- Steam turbines used in power generation come in many different variations. The overallprinciple is high pressure steam is forced over blades attached to a shaft, which turns a generator. As thesteam travels through the turbine, it passes through smaller blades causing the shaft to spin faster,creating more electricity.Gas turbines- Gas turbines work much like steam turbines. Air is forced in through a series of bladesthat turn a shaft. Then fuel is mixed with the air and causes a combustion reaction, increasing the power.This then causes the shaft to spin faster, creating more electricity.Wind mills- Also known as a wind turbine, windmills are increasing in popularity for their ability toefficiently use the wind to generate electricity. Although they come in many shapes and sizes, the mostcommon one is the large three-blade. The blades work on the same principle as an airplane wing. Aswind passes over the blades, it creates an area of low and high pressure, causing the blade to move,spinning a shaft and creating electricity. It is most like a steam turbine, but work with an infinite supplyof wind.MarineSteam turbine- Steam turbines in marine applications are very similar to those in power generation. Thefew differences between them are size and power output. Steam turbines on ships are much smallerbecause they don’t need to power a whole town. They aren’t very common because of their high initialcost, high specific fuel consumption, and expensive machinery that goes with it.Gas turbines- Gas turbines in marine applications are becoming more popular due to their smaller size,increased efficiency, and ability to burn cleaner fuels. They run just like gas turbines for powergeneration, but are also much smaller and do require more machinery for propulsion. They are mostpopular in naval ships as they can be at a dead stop to full power in minutes (Kayadelen, 2013), and aremuch smaller for a given amount of power. Flow of air through a turbocharger and engineTurbochargers- Turbochargers are one of the most popular turbomachines. They are used mainly foradding power to engines by adding more air. It combines both forms of turbomachines. Exhaust gasesfrom the engine spin a bladed wheel, much like a turbine. That wheel then spins another bladed wheel,sucking and compressing outside air into the engine.
Superchargers- Superchargers are used for engine-power enhancement as well, but only work off theprinciple of compression. They use the mechanical power from the engine to spin a screw or vein, someway to suck in and compress the air into the engine.GeneralPumps- Pumps are another very popular turbo machine. Although there are very many different types ofpumps, they all do the same thing. Pumps are used to move fluids around using some sort of mechanicalpower, from electric motors to full size diesel engines. Pumps have thousands of uses, and are the truebasis to turbo machinery (Škorpík, 2017).Air compressors- Air compressors are another very popular turbo machine. They work on the principleof compression by sucking in and compressing air into a holding tank. Air compressors are one of themost basic turbo machines.Fans- Fans are the most general type of turbo machines. They work opposite of wind turbines.Mechanical power spins the blades, forcing air through them and forcing out. Basic desk-top fans to largeturbofan airplane engines work this way.Fundamental equation governing turbo machinesBasic Physical laws of Fluid Mechanics and Thermodynamics used in Turbomachines are:the continuity of flow equationthe first law of thermodynamics and the steady flow energy equationthe momentum equationthe second law of thermodynamicsNewton’s Second Law of MotionThe Equation of ContinuityFor steady flow through a turbo machine, m remains constant. If A1 and A2 are the flow areas at Secs.1 and 2 along a passage respectively, thenorThis Law States that, in absence of sources and sinks, there is no accumulation of fluid within theControl volume. Hence.m 1cn1 A1 2 cn 2 A2 cn AIn Turbo machines There are three components of velocityFirst Along the Direction of Main Flow DirectionSecond Perpendicular to that DirectionThird Along a direction Perpendicular to These Directions.Usually a two dimensional approach is used for analysis. Here One Dimensional analysis isused mostly
The First Law of Thermodynamics [Internal Energy]The first law of thermodynamics states that if a system is taken through a complete cycle duringwhich heat is supplied and work is done, then Q W 0whererepresents the heat supplied to the system during the cycle andthe work doneby the system during the cycle. The units of heat and work are taken to be the same.During a change of state from 1 to 2, there is a change in the property internal energy and the law iswritten asFor an infinitesimal change of statedE δQ – δWSteady Flow Energy EquationFirst law of thermodynamics is applied to the steady flow of fluidthrough a control volume so that the steady flow energy equation is obtained. Energy is transferred fromthe fluid to the blades of the turbo machine, positive work being done (via the shaft) at the rate W. In thegeneral case positive heat transfer takes place from the surroundings to the control volume.Thus, with this sign convention the steady flow energy equation becomeswhere h is the specific enthalpy, 1/2c2 the kinetic energy per unit mass and gz the potential energy perunit mass.Except for hydraulic machines, the contribution of the last term is small and usually ignored.Defining stagnation enthalpy by h0 given byAssuming gz to be negligible, steady flow energy equation becomes
OrMost turbomachinery flow processes are adiabatic (or very nearly so) and it is permissibleto writeFor work producing machines (turbines) W 0 the equation becomesFor the machines which absorb work and increase enthalpy the work needed is given asMomentum EquationNewton’s Second Law of MotionOne of the most fundamental and valuable principles in mechanics is Newton’ssecond law of motion. The momentum equation relates the sum of the external forcesacting on a fluid element to its acceleration, or to the rate of change of momentum in thedirection of the resultant external force.In the study of turbomachines many applications of the momentum equation can befound, e.g. the force exerted upon a blade in a compressor or turbine cascade caused bythe deflection or acceleration of fluid passing the blades.Considering a system of mass m, the sum of all the body and surface forces acting on malong some arbitrary direction x is equal to the time rate of change of the total xmomentum of the system,For a control volume where fluid enters steadily at a uniform velocity cx1 and leavessteadily with a uniform velocity cx2, thenThe one-dimensional form of the steady flow momentum equation isEuler’s Equation of MotionIt can be shown for the steady flow of fluid through an elementary control volume that, inthe absence of all shear forces, the relation1 p cdc gdz 0is Euler’s equation of motion for one-dimensional flow and is derived from Newton’ssecond law.
By shear forces being absent we mean there is neither friction nor shaft work. However, itis not necessary that heat transfer should also be absent.Bernoulli’s EquationThe one-dimensional form of Euler’s equation applies to acontrol volume whose thickness is infinitesimal in the stream direction Integrating thisequation in the stream direction we obtainwhich is Bernoulli’s equation.For an incompressible fluid, is constant and Bernouli's equation BecomesThis can be written asWhere stagnation pressure p02 and p01 are the stagnation pressures at 2 and 1 stationrespectively. Stagnation pressures are given asIn hydraulic turbomachines, the term head H is used frequently. Head describes thesummation given as underThus equation becomesH2 - H1 0
If the fluid is a gas or vapour, the change in gravitational potential is generally negligibleand equation becomesIf the gas or vapour is subject to only a small pressure change the fluid density is sensiblyconstant and equation becomesThat is(1)The stagnation pressure is constant in gas or vapour flows for all incompressible andcompressible isentropic process.(2) Head remains constant in hydraulic machines.Moment of MomentumUseful information is obtained by employing Newton’s second law in the form where itapplies to the moments of forces.This form is of central importance in the analysis of the energy transfer process in turbomachines.For a system of mass m, the vector sum of the moments of all external forces acting on thesystem about some arbitrary axis A fixed in space is equal to the time rate of change ofangular momentum of the system about that axis, i.e.
Where r is distance of the mass centre from the axis of rotation measured along the normalto the axis and c is the velocity component mutually perpendicular to both the axis andradius vector r.For a control volume the law of moment of momentum can be obtained. Swirling fluidenters the control volume at radius r1 with tangential velocity cθ1 and leaves at radius r2with tangential velocity cθ2. For one-dimensional steady flowWhich states that, the sum of the moments of the external forces acting on fluidtemporarily occupying the control volume is equal to the net time rate of efflux of angularmomentum from the control volume.RothalpyThis relationship is true for steady, adiabatic and irreversible flow in compressor or inpump impellers. The Function has same value at Inlet and Exit of the Pump.The function I is rothalpy, a contraction of rotational stagnation enthalpy, and is a fluidmechanical property of some importance in the study of relative flows in rotating systems.Rothalpy I can be written asWhereh is Static Enthalpy of Fluid, c is the absolute velocity, U is the Blade velocity andis the tangential velocitySecond Law of ThermodynamicsThe second law of thermodynamics introduces the concept of Entropy and define idealthermodynamic processes.The Inequality of Clausius states that for a system passing through a cycle involving heatexchanges.where dQ is an element of heat transferred to the system at an absolute temperature T.If all the processes in the cycle are reversible thenThe equality hold true for reversible flows.The property called entropy, for a finite changeof state, is then defined asFor an incremental
where m is the mass of the system.With steady one-dimensional flow through a control volume in which the fluidexperiences a change of state from condition 1 at entry to 2 at exit.If the process is adiabatic, 0 ThenIf the process is reversible as well, thenFirst law and Second law can be Combined using Entropy definition. This yields,
Turbo machine – Definition A turbo machine is a device where mechanical energy in the form of shaft work, is transferred either to or from a continuously flowing fluid by the dynamic action of rotating blade rows. The interaction between the fluid and the turbo ma
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the fluid path through them. 1. Radial / centrifugal flow Part one : Introduction of Pump 3. FLUID MACHINES 2. Axial flow 3. Mixed-flow type In general usage, the word ‘PUMP’ is applied to a machine dealing with a liquid. A machine in which the working fluid is a gas is more usually termed as fan, blower or compressor. Part one : Introduction of Pump 4. FLUID MACHINES HEAD OF PUMP Part one .
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Contents Chapter 1 Welcome to the AutoCAD Civil 3D Tutorials . . . . . . . . . . . . 1 Getting More Information . . . . . . . . . . . . . . . . . . . . . . . . . 2
