A TEXTBook OF. ELECTRICAL. TECHNOLOGY. IN. S.I. UNITS. Volume II. AC & DC MACHINES. bestthing.info ELECTR. Basic Fluid Mechanics bestthing.infolic Machines Zoeb Husain Principal Hi-Point College of Engineering and Technology Hyderabad. Mohd. Zulkifly Abdullah. scanned by Fahid PDF created by AAZSwapnil A TextBook of Fluid Mechanics and Hydraulic Machines -Dr. R. K. Bansal Scanned by Fahid Converted to PDF.
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Hydraulic machinery. • Turbine is a device that extracts energy from a fluid ( converts the energy held by the fluid to mechanical energy). • Pumps are devices that. PDF | On Nov 10, , Vikram Kumar and others published hydraulics & hydraulic machines. PDF | Fluid properties: Definition of fluid, classification of fluids, properties of fluid density, specific weight, specific gravity, viscosity, surface.
Of course the first consideration in designing a press is the total pressure to be exerted, and the second is what hydraulic pressure is to be used or is available. This is at times governed by the space available for the machine, and I have known of instances where in order not to have too cumbersome a machine, and the space being limited, it became necessai-y to use a factor of safety of three or four referring to the ultimate strength of the materials of construction.
Of course, in every construction the expense is to be. At times extreme high pressures indicate the desirability of using steel forgings for cylinders.
If the cylinder is to receive a plunger which can be packed externally, cast iron Falkenau: [J. With castings a copper lining is frequently resorted to in order to present a smooth surface to the leather. A most important consideration is the density of the material entirely aside from the tensile strength.
Water under or pounds pressure will ooze through cylinder walls made of ordinary gray iron 3" to 4 p' thick, that is, if it is open-grained iron..
For these high pressures it is usual to use air-furnace iron, which, besides giving a tensile strength of 30, to 32,ooo pounds, furnishes a very dense material, and now that steel castings are so much more reliable than formerly, steel castings are supplanting the air-furnace iron. In this connection I would say that in my experience, however, I have known air-furnace iron to fail where a good ordinary casting was successful.
This was largely due to the manner of the casting and local shrinkages from gates and risers. The failure of cylinders or valve body castings to be thoroughly impervious to the water is frequently the cause of great annoyance and expense in the construction of hydraulic machinery.
I have had cases where on account of the anxiety of the customer t o obtain the machine we have had to pass cylinder or valve bodies Which when first tested failed to hold the pressure, the water oozing through the walls quite rapidly. We remedied the defect by pumping starchy fluid prepared from potatoes into the cylinders, and after half an hour to an hours work, the cylinders were bottle tight.
These cylinders were put to work under water pressure of 15oo pounds, and they have remained permanently tight. I designedly use the word "water-tight," as a later experience proved to me that the starch caulking method is not oil tight.
In building some ton pressure with Ioinch cylinders we used cupola iron castings. As they proved defective we next ordered some of the air-furnace iron. W i t h i n a half hour the cylinders were perfectly tight, and after having a hydraulic pressure of pounds per square inch applied to them, and locking this pressure in the cylinder, a drop of only March, 19o6. We thought that our annoying problem was solved, and expedited the machine to the customer's work. The next morning we were informed that the cylinder was leaking badly, and on inspection found that our customer was using oil, and that the oil oozed through the cylinder at an apparently greater rate than the water had done originally.
I suppose that the oil must have had some dissolving effect upon the starch.
As we had had such unsatisfactory results with the air-furnace iron I concluded that the only rapid solution of our trouble would be some other way of sealing up the pores of the cylinder. As the leak indicated, the porisity was mostly at the bottom of the cylinder.
We therefore had the inside of the cylinder towards the bottom brazed by the ferrofix process. This proved entirely successful and the cylinder has remained sound ever since. I understand that in the case of steel cylinders the sealing by means of the thermit process has been successfully used. It may be interesting to note here that in the year the first cylinders used in the hydraulic presses constructed for raising the tubes of the Brittania bridge into position proved porous and leaky, and were made tight by pumping oat meal gruel and sal ammoniac into them.
These cast-iron cylinders were 2o inches in diameter and had walls 82 inches thick. When they failed, they were replaced by cylinders made of wroughtiron with 8 inch walls. When the wrought-iron cylinders were first put to work, the engineers were discouraged due to the fact that the cylinders expanded under the great pressure causing the pistons to leak.
New pistons were made but the expansion continued. The outer diameter, however, remained constant, and this encouraged the engineers to persist in making new pistons until the inner portion of the cylinders had taken a permanent set.
In valves and pumps where water under high pressure attsins a high velocity it has been a general experience that castiron and steel are frequently subjected to a peculiar cutting action. Mach number where compressibility is important in flows over aerofoils in aircraft. The dimensionless parameters are also useful in design of prototypes from the models and can save a lot of money and effort.
For example, a model can be prepared in a laboratory and tested, and predictions can be made of the prototype for large machines with the help of suitable dimensionless parameters. This is usually done in making models of large hydraulic machines used in power stations or in construction of big dams by making suitable models in the laboratory.
The pressure p is defined as force per unit area. The standard atmospheric pressure at sea level is The gauge pressure is the pressure recorded by the gauge or manometer. In engineering calculations absolute pressure is used and the conversion from gauge pressure to absolute pressure is carried out using the following equation.
Also, zero absolute pressure in ideal vacuum. Dimensions and Systems of Units 7 The gauge pressure is negative whenever the absolute pressure is less than atmospheric pressure; it may be called vacuum. In this section several of the more common fluid properties are presented. A fluid property directly related to density is specific weight or weight per unit volume.
It is defined as the ratio of the density of the liquid to that of water. A fluid at rest has no shearing forces. Usually we are concerned with the flow past a solid boundary. The fluid in contact with the boundary sticks to it, and therefore will have the same velocity as the boundary. Considering successive layers parallel to the boundary as shown in Fig. For such a flow the shear stress 't in given by A thick liquid like honey which has high viscosity will take long time to flow than water.
Thus it controls the amount offluid that can be transported in a pipe line during a specific period of time. It accounts for pressure and energy losses in pipes. Dimensions and Systems of Units 9 If the shear stress is directly proportional to velocity gradient as it was assumed in eq. Common fluids such as water, air and oil are Newtonian. The other fluids which do not obey Newtonian law of viscosity are called Non-newtonian fluids.
Milk, plastic, paints are non-Newtonian. The force due to surface tension is the surface tension multiplied by the length or the circumference in case of a bubble or droplet of water. A surface tension effect can be illustrated by analysing a free-body diagram of half a droplet as shown in Fig. The liquid makes a contact angle p with the glass tube. Such liquids have a capillary drop instead of rise. Ifh is capillary rise, 0 is the diameter of the tube, p the density ofliquid and Ci the surface tension then the capillary rise h can be determined from equating the vertical component of surface tension force and the weight of liquid column.
Liquid -: Now we discuss deformation offluids from pressure changes. This is a very large pressure to cause such a small change in density and therefore water is considered incompressible whereas for gases density change is appreciable for change in pressure.
Determine the absolute pressure in the tank. Solution The vacuum is negative pressure i. From Table A. Vacuum is always negative pressure.
Determine the height that the water will rise to capillary action in the tube. The constant angle for water can be taken as zero. Solution A free-body diagram of water is shown in Fig.
Fluid Mechanics and Hydraulic Machines - FMHM Study Materials
It shows that the upward surface tension force is equal and opposite to the weight of water. Determine the value of Reynold's number in SI Units. When the tank is filled with a gauge pressure of 3 bar, determine density of air and weight of air in the tank. If the bubbles are intended to have a diameter of 2 mm, calculate by how much the pressure of air at the nozzle must exceed that of surrounding water. For small bubbles in the liquid, if this pressure is greater than pressure of vap0ur, the bubbles wi II collapse.
In many engineering problems the magnitude of surface tension is small compared with other gravitational and viscous forces acting on the fluid and therefore it can be safely neglected. How far over the water rise due to capillary action away from the ends of the plates? S The velocity distribution in a 1. Estimate the pressure inside the bubble. Table A. Vosper Thorny Croft. The liquid is either at rest or in motion. Fluid at rest isjluid statics; examples such as water in a container or reservoir of water behind a dam.
Fluid at rest has weight and exerts pressure. Fluid in motion isjluid dynamics. Examples are rivers, flow in pipes, flow in pumps and turbines. The fluids that are commonly studied are air and water.
External flow is study of fluid flow over car, aeroplane, ships and rockets. Flow in pipes, impellers of pumps are referred to as internal flow. Compressible flow is when density does not remain constant with application of pressure. Incompressible flow is the density remains constant with application of pressure. Water is incompressible whereas air is compressible.
Compressibility criteria is Mach number. The chapter deals with the concept of momentum and Newton's second and third law of motion. With the knowledge of continuity equation and momentum equation, Bernoullis and Eulers equations are derived.
With the help of second law of Newton force acting by a jet on stationary and moving plate is obtained. The impact ofjet on vanes has direct application on hydraulic turbines. The properties offluids deal with measurement of mass, density, specific weight, specific gravity, compressibility offluids, surface tension, capillary action. The fluid statics deals with fluid pressure, fluid at rest, manometry, hydrostatic forces, buoyancy floation and stability.
The fluid kinematics deals with one, two and three-dimensional flows, steady and unsteady flows, Reynold's number, streamlines, streaklines and pathlines. The external flow deals with flow over immersed bodies, lift and drag concepts, boundary layer laminar and turbulent, friction drag, pressure drag and drag coefficients.
The flow in turbomachines deals with energy considerations, angular momentum considerations, centrifugal pump and their characteristics, similarity laws, turbines, axial and rapid flow, impulse and reaction. The flow in pipes is laminar or turbulent; Osborne Reynolds has done experiment in pipe flow. Laminar flow is one where the streamline moves in parallel lines and turbulent flow when streamlines cross each other and the flow is diffused.
Flow of highly viscous syrup onto a pan cake, flow of honey is laminar whereas splashing water is from a faucet into a sink below it or irregular gustiness of wind represents turbulent flow. Reynold's number is to distinguish the two types of flow. Ifthe flow is laminar Reynolds no.
The hydraulic losses depend on whether the flow is laminar or turbulent. Fluid Flow 25 2. According to Newton's second law of motion, rate of change of momeHtum is proportional to the applied force. In order to determine the rate of change of momentum, consider a control volume of the fluid ABCD as shown in Fig. Assuming the flow to be steady and also assuming there is no storage within the control volume, we may write the continuity equation for mass flow rate Here the velocities have been assumed to be in straight line.
One must remember that this is the force acting on the fluid and according to Newton's third law of motion, force exerted by the fluid will be opposite to this force. The forces Fx and Fy are the components of the force F acting the fluid and components of reaction force on a plate or vane are equal and opposite to Fx and Fy. Fluid Flow 27 2. This control volume being fixed relative to the plate and is therefore moving with it. The components of velocities perpendicular to the plate are considered.
In cases where the plate is moving, the most helpful technique is to reduce the plate and associated volume to rest by superimposing on the system equal and opposite plate velocity.
This reduces all cases illustrated in the Fig. The mov ing vanes have a velocity u in the x-direction. At inlet the absolute velocity Y, makes an angle with the u, horizontal and adding vectorially the velocity u gives relative velocity Y rl making an angle i3, with horizontal.
Fluid Flow 29 The fluid leaves the vane at relative velocity Vr2 making an angle [32 with the direction ot vane. The velocity is tangential to the curvature of vanes at exit. The direction of the jet leaves the vane at absolute velocity V2 at an angle u 2 with the horizontal.
The force in the direction of motion will be: At section AB, area is A, pressure p, velocity V and elevation z. The surrounding liquid will exert pressure P, from the sides of the clcment.
The pressure will be normal to the tube in absence of shear stresses. The weight ofthe element mg will act downward vertically at an angle 0 to the centre line. The unit of elevation z is in meters. All the terms of Bernoulli equation is measured in meters. Therefore the const is total head in meters denoted by H along a streamline, but the constant may be different for different streamlines, eq. A wind tunnel shown in Fig. The models are tested in the test section of the wind tunnel.
The venturimeter has three important portions: We assume the flow is horizontal i. It consists of a short converging conical tube leading to cylindrical portion called the throat, followed by diverging section in which diameter increases again to that of the main pipeline.
The pressure difference is measured between points 1 and 2 by a suitable U-tube manometer. In the coverging part pressure decreases and therefore according to Bernoulli eq. In the diverging portion pressure increases and velocity decreases and in constant area velocity is maximum and pressure minimum.
The venturi meters are commonly used in power plants and chemical industries to measure flow rate of fluids in pipes with fairly good accuracy. Determine the pressure at station point 2. Determine the pressure at point 2 if flow rate is 0. The head loss from point 1 to 2 is 1. Determine flow rate of oil from syphon and also the pressure at point 2. Applying Bernoullis eq. Under standard and atmospheric conditions what is the maximum pressure experienced by the person on the hand.
S Blood of specific gravity 1 flows through an artery in the neck of a giraffe from its heart to the head. If the pressure at the beginning of the artery outlet of the heart is equal to 0. Turbines are. One such installation is shown in Fig. A dam is constructed to store water and to produce required head. Water passes through the turbine and goes downstream.
Fluid Flow 45 Solution Substituing proper values, 5. If manometer connected to the instrument indicates a difference of head between tappings of 4 mm of water, calculate the air velocity assuming density of air 1.
Calculate the force acting on a I m x 2 m window which is facing the storm. The window is in a high-rise building. The wind speed is not affected by ground effects. Assume density of air as 1. Working with gauge pressures, the pressure upstream in the wind is zero. A pitot probe at the same location indicates 24 mm of water. Calculate the Mach number and comment on compressibility of air. The pump draws water from a sump at A through alSO mm diameter pipe.
The pump is located at B at a height 2 m above the level of the sump. The velocity at the nozzle is 8. Determine the flow rate from the nozzle and the power required to drive the pump. B 2m Fig. Determine the difference of pressure between inlet and throat of the venturimeter. Owing to friction the velocity of the fluid relative to the vanes at exit is equal to 0. Calculate a inlet angle and outlet angle of the vane for no shock entry and exit. Solution a With reference to the Fig.
Determine the force components needed to move the deflector. The jet velocity is 8 mls. The nozzle area is 2 cm x 40 cm. The outlet triangle of velocity is shown in Fig. If the manometer connected to the instrument indicates the difference in pressure head between the tappings of 4 mm of water, calculate the air velocity assuming the coefficients of pitot tube to be unity.
Density of air l. The inside diameter of the pipe is mm while the nozzle jet diameter is 50 mm. If the pressure at inlet is kPa, determine the jet velocity.
Assume that the blood has a viscosity of approximately 4 X and sp. If the flow were steady it is not in reality with velocity equal to 0. S Glycerine of viscosity 0. Is the device inside the building a pump or a turbine? Explain and determine the power of the device. Estimate the velocity assuming in viscid flow. S Air flows into the atmosphere from a nozzle and strikes a vertical plate as shown in Fig.
A horizontal force of 12N is required to hold the plate in place. Determine the reading on the pressure gauge. Assume the flow to be incompressible and frictionless. Plate Area 0. IO A wind tunnel shown in Fig. The fan is located downstream of the test section. What pressure is to be expected in the test section if the atmospheric pressure and temperature 92 kPa and 20 DC. II A vacuum cleaner is capable of creating a vacuum of2 kPa inside the hose.
What maximum velocity would be expected in the hose? Black - Durr, Germany. Energy is avai lable in various forms and can be converted from one form to another. Electrical energy is produced in large power houses and is transmitted to users by cables.
The more a country is developed the more the energy utilised by the people for good living. In fact the criteria for a developed nation is how Illuch energy is being used by each person and that is the gauge of development of the country. If the energy needs are satisfied one can enjoy a comfortable life.
In thermal power plants the fossil fuel generally used is coal, oil or gas. In hydro power plants the source is water. The countries which have large reserves of fossi I fuel are in a better way to solve energy-related problems than countries which lack these reserves.
But the oil can be transported by pipelines from one country to another travelling some thousands of kilometers, or through pipelins under the sea, or by huge shipliners. Oil production is generally rated in barrels and each barrel is about Iitres. Oil-producing countries produce several millions of barrel per day that is why oil is sometimes called 'Black Gold'.
Crude oil is obtained by boring oil wells underground or under the sea bed. Coal is another source of fuel used in power plants.
It is used in crushed or powder form pulverised. Coal is obtained from coal mines, located several hundred meters below the surface of the earth. It has to be chemically treated before it can be used in power plants. Coal contains some percentage of ash about i. Ash removal is a big problem. Moreover, oil is used in vapour form which mixes readily with the molecules of airgiving high rate of combustion than coal.
Gas is perhaps the ideal fuel to be used in thermal power plants. It is clean, efficient and available in gaseous state as air. So one can expect efficient combustion. The plants also have high thermal efficiency. The cheapest way to produce electrical energy is by hydropower plants. First, water does not require any treatment as applied to fuels. It is abundant and free. The only criteria is water must have a fall from a height or create head, as it is called, and be available in large quantities for power generation.
Dams are constructed across the river to store water. The water is conveyed to the turbines by penstock which convert hydraulic energy to mechanical energy. Electrical generators convert it to electrical energy. India has large number of hydropower stations which produce thousands of kilowatts. Nuclear power plants and solar power plants also produce electrical energy.
A solar power plant is shown in Fig 3. The solar energy focussed with an array of heliostats on a central receiver at the top of the tower is transferred by liquid sodium as medium of heat transfer to a heat storage unit at the foot of the tower which is connected to steam generator. The high pressure super heated steam thus generated passes through a multi cylinder engine unit to drive a generator and produce electricity.
Fig 3. Liquid sodium has better heat transfer qualities than water. The kw Almenia solar power plant has been supplying power to southern Spain grid system since Thermal and Hydropower Plants 63 Steam power plant and gas turbine power plants are the two conventional ways to produce electricity on a large scale.
The electricity can also be produced by diesel plants which work independently or in conjuction with steam and gas turbine power plants as peak units.
Diesel power plants also work in hydropower plants as emergency units. Fossil fuels that are used in these power plants are depleting in the world and at one point of time will not be available.
These are therefore non-renewable source of energy and cannot be depended upon the years to come. Mankind looks for other renewable sources such as solar energy. Technology as such is not economical and is still not available for solar energy to be utilised on large scale.
Again bright sunlight is not avai lable throughout the day at any place. Other renewable source of energy is wind mills. The energy produced by wind mills is intermittent and difficult to connect to main eletrical power grid. So, where water is avai lable for producing electric power it is perhaps the best renewable source of energy.
Hydropower plants are clean, highly efficient and environmental friendly. They do not cause any pollution problems. They are also the source oftourist attraction. The steam turbine has been tailored for large fossil, nuclear, combined-cycle, geothermal, and small power facilitates and mechanical-drive service. Piping will continue to anchor the next generation of power plants. At present technology with high pressure superheat a: Thus steam turbine has no match with other machines.
The basic thermo dynamic cycle of steam power plant is shown in Fig. The water tubes are connected to the main boiler drum where high pressure, saturated steam is produced. The steam is then raised to a temperature higher than saturation temperature in the super heater. High pressure and high temperature super heated steam then enters the steam turbine.
The steam expands in the turbine from a high pressure to low pressure area of the condensor. The heat energy is converted to mechanical energy to drive a generator to produce electricity. The exhaust steam from the turbine is condensed inside a condenser by circulating water of the condenser tubes.
The condensate is sent back to the boiler by condensate pumps. The steam power plant needs a large quantity of water for producing power and much more water to cool the exhaust steam from the turbine.
So it is imperative that steam plants are located near river, lake or sea. The steam explands in the turbine from a very high pressure to a low pressure of the condenser less than atmospheric with a large enthalpy drop. A very large quantity of water has to be circulated in the condenser and that heated up by condensation of steam so circulating water is cooled in cooling tower-a visible sight for the power plant from outside.
Power produced by the turbine is mass flow rate of steam multiplied by the enthalpy drop. Versatility of gas turbines is also demonstrated by its growing acceptance in a wide variety of stationery energy systems for processing, power generation and mechanical drives.
Recent developments include adaptation of standard jet engines to base load generation and peaking services. An open gas turbine cycle system employs a compressor, combustor, gas turbine and generator for producing electrical power.
The schematic diagram is shown in Fig. Rotating compressor takes in atmospheric air and compresses it to high pressure. The pressurised air goes into combustor or furnace in steady flow. Fuel is forced into the air burns, raising the temperature of air and combustion products. This high-energy mixture then flows through the gas turbine, where it expands.
The pressure and temperature drops continuously as it does work on the moving blades of the turbine converting heat energy into mechanical energy, and the electric generator coupled to it produces electrical energy. The turbine drives the compressor and the generator by a single shaft. In the energy diagram shown in Fig 3. The thermal efficiency of gas turbine power installation is less compared to steam power plant.
Air in Fuel Exhaust Combustor , Compressor Fig. Thus there is very large enthalpy drop in the turbine to produce the work.
The gas turbine works at lower pressure but at higher temperature than steam turbine. The exhaust of gas turbine is atmospheric. Therefore the enthalpy drop in gas turbine is less and high temperature gas is exhausted into atmosphere which is energy loss. The overall efficiency of gas turbine power plant is almost half of steam power plant.
Thermal and Hydropower Plants 67 The steam turbine power plant requires lot of water whereas for gas turbine power plant water is not a criteria. It can be installed even in a desert. Time period is a factor in steam power plant for planning, installing and commissioning and it takes some years before it is ready for generating power.
The gas turbine power unit can be installed in a few days as compact units are available only to be connected to chimney.
Steam power plant requires a lot of land for installing boi ler, steam turbine, generator, and various other un its such as condensing plant, heat recovery units. The gas turbine does not require so much land, and can easily be installed and can be connected to the grid in few minutes after the installation.
With the present-day technology steam turbine can produce about MW on a single shaft, whereas gas turbines can produce MW of power. A high-efficiency steam turbine is combined thermodynamically to a low-efficiency gas turbine.
The high temperature exhaust gas from the gas turbine is led into the heat recovery steam generator HRSG thus increasing the mass flow rate of gas circulation, decreasing the fuel of the steam unit, developing more power and thus increasing the 5 Fuel Heat recovery Combustion 1 steam generator chamber 2 3 4 Steam turbine Compressor Gas turbine Condenser Air Fig. The combined cycle power plants have become very common in present times for their efficiency and better heat utilisation.
The arrangement of gas turbine and steam turbine at Lumut Power Plant is shown in Fig 3. The three gas turbines produce electric power by three electric generators. The exhaust gas is connected to three HRSGs. The steam produced by three HRSGs goes to a single steam turbine and electricity is produced by the generator. By this way steam turbine produces additional electric power by using exhaust gases with no additional fuel.
Thus it raises the overall efficiency of the plant. The potential energy is created by constructing a dam Fig. It is a cement concrete wall storing water as reservoir at upstream side of the dam. The water at head water -level which passes through the turbine and leaves downstream of the dam as tail water.
The turbines work between. The forces acting on the dam are wind forces, pressure forces of water on the upstream side of the dam. The pressure is zero at top level and increases to a maximum at the bottom of the dam. The structure must withstand the pressure of water. Again the pressure ofthe silt deposits is zero at the top level and maximum at the bottom.
For stability reason the dam is made narrow at the top and broader at the bottom as shown in Fig3. The construction of hydropower plants is not easy. It requires combined efforts and expertise of civil, mechanical and electrical engineers. A study oftopography of the place is important which includes land survey, amount of rainfaIl per year, and estimation of catchment area. Also a thorough planning of evacuating and rehabilitating the people is required when water will be filled up in the reservoir of the dam.
A lot of construction work has to be done by civil engineers making approach roads, culverts, water tunnels etc. On the mechanical side, heavy machinery is required which includes bull dozers, earthmover, tractors, etc.
The most in: The work goes on for years so much so temporary housing colonies and temporary shelters have to be made for the people. For surface power stations, creating the head is important and hence dam is necessary, whereas for underground power stations water is conveyed to the station from an elevated level by water tunnels and pressure shafts to the turbine. The figures show the reservoir dam site, flood gates in operation and the inside of the power house with elevators, and escalators.
The arrows indicate suggested flow of traffic. The hydropower plants are clean, neat and environment friendly. The dam site gives marvellous view ofthe reservoir and one hears only the humming sound of the generators in the power house.
Cubicle oJ D. The water is conveyed from the two pressure shafts to four turbine generator sets which produce electricity. The entrance is through access tunnel of gradient of 1 in 6. There is a by-pass tunnel connected to tailrace tunnel.
There is an emergency diesel alternator when electricity goes off in power station. There is also transformer hall where high voltage electricity is produced and transmitted to the sub-station located outside at the ground level. There is also a control board panel and where electric power is controlled and there are meters indicating power output, frequency of supply, and other monitoring devices. The four nozzles seen in the picture. Also given are the details of Tooma-Tumut water tunnel.
The tunnel is about 14 km long with several intakes connected to tunnel Fig. The diameter of tunnel is 3. Sturcture Tooma Tumut Tunnel t.. If the silt is deposited in the tunnel the flow rate gets reduced which will affect power generated by the turbines.
The pressure shafts are twin vertical shafts conveying water from the tunnel to the power station. The pressure shafts are 3.
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There is also a lift shaft and ventilation tunnel. There are four electrical generators, a transformer hall and a cable tunnel. The tailwater tunnel carries the discharge from the turbines. The entrance to the machine hall is through access tunnel. Lift Shaft Pressure Shafts 'l , Thermal and Hydropower Plants 75 Fig. The water enters the turbine through main inlet valve. The turbine is vertical and electric generator is connected to the turbine by a vertical shaft with a coupling.
There are 4 units with a total capacity of , kw.
The discharge from the turbine is connected to the draft tube. Thermal and Hydropower Plants n Fig 3. The spillway is used when the water rises above the maximum level or when it is flooding. The construction of power plant took 27i years. The installed capacity of power plant is MW. There are 4 turbine units each of 90 MW capacity. Thermal and Hydropower Plants 79 Fig. The capital cost is high and it takes long years of planning and construction. The maintenance cost is low.
There is no pollution and the environment is clean.
The hydropower plants are also useful for agriculture taking water of the tailrace. The overall. Life of the dam and hydro power plant is taken as years whereas steam turbine plants have a life span ranging from 30 years to a maximum 50 years. The life of gas turbines is given in hours of working.
The source in hydro power plants is water which is renewable source of energy whereas steam and gas turbines work on fossil fuels which are non-renewable source of energy. The generating capacity of the hydro power plants depends on reservoir capacity which depends on rainfall, whereas thermal power plants have no such problem.
The plant produces thermal output,of 47 MW and electrical output of 19 MW. KWU and the Japanese company Mitsubishi have each installed six gas turbine generator units at the R as Abq Fontas gas turbine power plant in Doha in the capital city of Sheikdom of Qater on the persian gulf.
The exhaust from the gas turbines is used for desalination of sea water. The plant in capable of producing MW electrical output and capable of producing , m 3 of drinking water Fig. The overall view of Megalopolis coal-fired power plant with two MW units and one MW unit stands in the vicinity of a lignite field in Greece.
The power plant is in operation since The power plant is justified because lignite reserves will last at least 50 years Fig. Thermal and Hydropower Plants 81 Fig. In positive displacement machines fluid is drawn into a finite space bounded by mechanical parts, then sealed in it, and then forced out from space and the cycle is repeated.
Gear pumps, vane pumps are all positive displacement pumps. In rotodynamic machines there is free passage between inlet and outlet of the machine without intermittent sealing taking place. In these machines there is a rotor which is able to rotate continuously and freely in the Iluitt The transfer of energy is continuous which results in change of pressure or momentum of the fluid.
Centrifugal blower, centrifugal pumps and hydraulic turbines are some examples ofrotodynamic machines. The term pump is used when the working fluid is water or oil. Fluid machines do a variety o I' jobs and are applied in hydro and thermal power stations, in aircraft as propulsive devices, in ships as propellers, in automobiles, and earth moving machinery.
Fluid machines serve in enormous array of applications in our daily lives, and they play an important role in modern world. The machines have a high power density large power output per size of the machine relatively few moving parts and high etliciency. The two criteria, namely, the energy transfer and type of action, form the basis of classification of hydraulic machines, as shown in Fig.
From the chart it can be seen that pumps and compressors increase the energy of the fluid and may be positive displacement or rotodynamic. Fans are always rotodynamic. Turbine does work and is rotodynamic. Further classification is based on flow and energy transfer. Fluid used as means of energy transfer. In axial flow machines the flow path is nearly parallel to the machine centre line and the path does not change.
In mixed flow it is partly axial and partly radial. Fig 4. Hydraulic steam Electric gas turbine Generator Fig.
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A pump is a turbo machine wherein the fluid is liquid and power is given by an electric motor to raise pressure of the fluid. In power absorbing machines the driver is usually an electric motor but it can be also an I. The rotating element is called the impeller which is contained within the pump housing or casing. Seals are required against the leakage of the fluid. Impeller Inlet Casing Fig. Fluid enters the machine nearly in axial direction at inlet through the eye of the impeller and leaves the impeller radially out.
Flow leaving the impeller is collected in a scroll or volute, which gradually increases in area as fluid moves out through exit.
The impeller has vanes to convey the fluid. A multi-stage pump is shown in Fig 4. In this pump exit of first impeller is connected to inlet of second impeller and pressure builds up. An axial pump is shown in Fig. The shaft is vertical and propeller type blades are fixed to it to form the impeller. The guide blades increase the pressure of the fluid. Outlet Inlet Fig 4. Air enters the unit near axial through the eye of the impeller and flows radially outwards.
The air leaves the volute at higher pressure. The impeller is mOllnted on a shaft supported by bearings. A typical blower is shown in Fig. The impeller has vanes and air is discharged into volute which increases the pressure. An axial flow compressor is shown in Fig. Flow enters nearly parallel to rotor axis and maintains nearly the same radius through the stage. A typical stage consists of a row of stationary vanes S and a row of rotating vanes R and pressure increases from stage to stage.
Axial flow compressors are typically used in turbo- jet engines and are multi-stage compressors. Inlet - - -. They are classified as: More general classification of hydraulic turbines are: Each jet is accelerated in a nozzle external to the turbine wheel known as turbine rotor. It is shown in Fig. It is driven by a singlejet which lies in the plane of runner.
A high velocity jet prossesing kinetic energy strikes the bucket in succession. The water falls into the tail race. In reaction turbines part of the fluid pressure change takes place externally and part takes place within the runnet.
External acceleration occurs in the guide vanes and flow is turned to enter the runner in proper direction. Additional acceleration of fluid relative to rotor occurs within the moving blades. So both relative velocity and pressure change over the runner.
Reaction turbines run full offluid. Water enters circumferentially through turbine casing. It enters from the outer periphery of guide vanes and flows into runner. It flows down the rotor radially and leaves axially. Water leaving the runner flows through a diffuser known as draft tube before entering the tail race.
The water from the spiral casing enters guide blades similar to Francis. The Kaplan turbine consists of an axial flow runner with 4 to 6 blades of an airfoil section. In this turbine both guide vanes and moving beades are adjustable and therefore high efficiency can be obtained. Steam is produced in high pressure boiler and after expansion steam condensed in condenser.
Fluid Machinery 93 Guide. The exhaust gases after expansion go into the atmosphere. The fluid flow through an impellerofacentrifugal pump is shown in Fig. R, Fig 4. The following assumptions are made. The angular velocity co is connected to tangential velocities u l and u2.
The velocity V I is vector sum ofV rl and u l at inlet and velocity V2 is vector sum ofV r2 and u2 at exit of vane. Equating eqs. The head available is actually less than Euler's head. From the velocity triangles of Fig 4. The second term II represents energy used in setting fluid into circular motion about impeller axis.
The third term III is to regain static head due to reduction in relative velocity. From the mode of derivation it is clear that Euler's equation is applicable to a pump and also to a turbine. However, the equation would change its sign. The operating head is m.
Sulzer Ester Wyss, Zurich, Switzerland. The capital cost of hydraulic power plants, i. The tlow is axial, i. Water supplied is from a high head through a long conduit called penstock. The water is accelerated in the nozzle and the head is converted into velocity and discharges at high speed in the form of a jet at atmospheric pressure.
The jet strikes detlecting buckets attached to the rim of a rotating wheel runner as shown in Fig. The kinetic energy of the jet is lost to the buckets and water discharged at relatively low speed falls into lower reservoir or tail race.
The tail race is set to avoid submerging the wheel during tloded conditions. When large amount of water is available the power can be obtained by connecting two wheels to a single shaft or by arranging two or more jets to a single wheel.
The buckets are double hemispherical in shape. The water strikes the bucket in the centre and tlows, out at both sides making a U tum. The surface inside the buckets is polished and smooth to reduce hydraulic losses. A costly material like broonze or stainless steel is generally used for the buckets.
The buckets are detachable. When the load is removed the water is suddenly cut off from the nozzle but it is directed to deflector plate. The deflector plate that comes into operation cuts off water supply to the wheel.
The water from deflector plate goes to the tail race. The nozzle spear moving inside the nozzle controls water to the turbine. Its operation is explained in the regulation of turbine. The two jets are directed to'the runner.
All the peripherals, deflector plate, spear are there as in single jet. Branch pipe Fig. Pelton Turbine Fig. A, Courtesy Voith Hydro. The water supply is from a constant head reservoir at an elevation H I above the centre I ine of the jet.
A surge tank is installed to dump out any fluctuations of pressure in the penstock. At the end of the penstock is the nozzle which converts head into velocity asjet. LhJet velocity C 0 Nozzle Fig. The net head is taken to calculate hydraulic efficiency of turbine. The jet strikes the bucket at the centre and takes a tum of almost and leaves on both sides of bucket as shown in Fig, 5.
The total energy transferred to the wheel is given by Euler's Equation. U1V1W - u 2 V2w The relative velocity vr2 is tangential to exit tip of the buckets. Superimposing peripheral velocity u we obtain absolute velocity V 2.
The velocity Vr2 makes an angle 8 with the centrel ine of bucket.The speed ratio is the ratio of the velocity u of the wheel at pitch circle to theoretical velocity of the jet. Dilhara Pinnaduwage. It is used in crushed or powder form pulverised. The flow enters the runner through guide vanes which can be set to any desired angle within limit to accommodate changes in power output demand. Pelton Turbine Solved Examples E. The impeller consists of a number of blades usually curved also sometimes called vanes, arranged in a regular pattern around the shall.
The tip diameter is 4. Also more than MW can be developed from a single unit. Multiple control valves may be stacked in series. This is usually done in making models of large hydraulic machines used in power stations or in construction of big dams by making suitable models in the laboratory.
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