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EME(21EME15) MODULE 1: Extra Notes, More VTU exam problems on Steam Formation, Problem 1 Find the enthalpy of 1kg of steam at 12 bar when, (a) steam is dry saturated, (b), steam is 22% Wet and (c) superheated to 250⁰C Use the steam table. Assume the specific heat of, the superheated steam as 2.25 kJ/kgK., Solution :, , From the steam tables @ 12 bar,, Ts = 188⁰C, , hf = 798.43 kJ/kg, , Enthalpy of Dry saturated steam :, , hfg = 1984.3 kJ/kg, , hf = hf + hfg, = 798.43+ 1984.3, , kJ/kg, , = 2782.73 kJ/kg, (a) Enthalpy of wet steam :, When the steam is 22% wet, it will be 78% dry. Therefore the dryness faction x = 0.78, h = hf + hfg = 798.43 +0.78, , 1984.3 kJ/kg, , (c) Enthalpy of Superheated steam : hsup = hf +x hfg + cps (Tsup – Tsat), = 798. 43 + 1984.3 + 2.25(250 - 188), , = 2922.23 kJ/kg, , Problem 2 A steam at 10 bar and dryness 0.98 receives 140 kJ/kg at the same pressure. What is, the final state of the steam?, Solution : From the steam tables, @ 10 bar,, Ts = 179.9⁰C, , hf =762. 61 kJ/kg, , hfg = 2013.6 kJ/kg, , Enthalpy of wet steam at dryness fraction 0.98 is found out., Enthalpy of Wet steam :, = 2735.9 kJ/kg, , h = hf, , + xhfg, , = 762.61 + 0.98, , 2013.6 kJ/kg, , When 140 kJ of heat is added at the constant pressure its enthalpy its enthalpy will increase,, Enthalpy of heat addition = 2735.9 + 140, At 10 bar the enthalpy of dry saturated steam,, , = 2875.9 kJ/kg, , hg = hf + hfg, =762.61 +20136.6 kJ/kg, =2776.2kJ/kg, , Since the enthalpy of steam after heat addition is greater than the enthalpy of dry saturated steam at the, same pressure, the steam is superheated. The superheated of the steam is found as follows., hsup = hf + Cps (Tsup- Tsat ), 2875.9 = 2776.2 + 2.25 (Tsup – 179.9, , ) kJkg, , TSUP = 224.2⁰ C, DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 1

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EME(21EME15) MODULE 1: Extra Notes, Problem 3 Find the specific volume and enthalpy of 1kg of steam at 0.8 MPa : (a) when the, dryness fraction is o.9 and (b) when the steam is superheated to a temperature of 300⁰ C. The, specific heat of superheated steam is 2.25 kJ/kgK., Solution :, From the steam tables at 0.8 MPa = 8 bar, the following values are noted., Ts = 170.4⁰C, , hf = 720.94 kJ/kg, , Vs = 0.2403 m3/kg, , hfg= 2046.5 kJ/kg, , Vf = 0.001115 m3/kg, , hg = 2767.5 kJ/kg, , (a) Specific Volume of Wet steam : V = x vg m3/kg, =0.9, , 0.2403, , = 2. 627 m3/kg, (b), , Specific Volume of the superheated steam :, Vsup = Vg, , =0.3105 m3/kg, , =0.2403, , (c) Enthalpy of Wet Steam; H = hf + xhfg ; = 720.94 + 0.9, , 2046.5 =2562.8 kJ/kg, , d) Enthalpy of Superheated steam :, hsup = hf +hfg + cps (Tsup – Tsat), , = 720.94 + 2046.5 + 2.25(300 - 170.4) =3059.1 kJ/ kg, , problem 4, 5kg of wet steam of dryness 0.8, passes from a boiler to a superheated at a constant, pressure of 1MPa abs. In the superheated its temperature increases to 350⁰C. Determine the amount, of heat supplied in the superheater. The specific heat of superheated steam Cps = 2.25kJ/kg, From the steam tables, at 10 bar, the following values are noted., Ts = 179.9⁰C, , hf =762. 61 kJ/kg, , hfg = 2013.6 kJ/kg, , Enthalpy of wet steam at dryness fraction 0.8 is found out., Enthalpy of Wet steam :, , h = hf + xhfg, = 762.61 + 0.8, , 2013.6= 2373.5 kJ/kg, , Enthalpy of Superheated steam :, hsup = hf +hfg + cps (Tsup – Tsat), , = 762. 61+ 2013.6 + 2.25(350 - 179.9) =3159kJ/ kg, , Amount of heat supplied in the superheated; Hsup – h = (3159 – 2373.5) kJ/kg 785.5 kJ/kg, Total amount supplied in the Superheater =5 785.5 kJ/kg = 3927.5 kJ, , DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 2

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EME(21EME15) MODULE 1: Extra Notes, , HYDRO ELECTRIC POWER PLANT:, Reservoir: Water is collected during rainy season is stored in the reservoir. A dam is built across the, river adequate water head. Penstock: It is a passage through which water flows from reservoir to, turbine. Surge Tank: It is installed along the penstock between turbine and reservoir to control or, regulate the sudden water over flow and to protect the penstock from bursting. It reduces the pressure, and avoids damage to the penstock due to the water hammer effect. This occurs when the load on, the turbine is decreased there will be a back flow. Power House: It houses water turbine, generator,, transformer & control room Water Turbine: Water turbines such as Pelton, Kaplan and Francis are, used to convert pressure and kinetic energy of flowing water into mechanical energy. Draft Tube: It, is connected to the outlet of the turbine. Tailrace: It refers to the downstream level of water, discharged from turbine. Generator: It is a machine used to convert mechanical energy into, electrical energy. Step up transformer: It converts the AC into high voltage current suitable for, transmission., , WORKING PRINCIPLE: It uses the potential energy of water of water stored in a reservoir. The water, from the reservoir through a penstock and then forced through nozzle or nozzles before reaching the, turbine. The hydraulic turbine converts the kinetic energy of water under pressure into mechanical, energy. The shaft of the turbine is coupled to a generator that generates electricity. The electricity generated, is fed to the step-up transformer to increase its voltage. Power is fed to the transmission lines for, distribution. The output power of Hydel power plant depends on the head of water stored in the reservoir, and the quantity of water discharged., , Nuclear Power Plant:, , A nuclear reactor is used to generate steam to run turbine & generating, electricity. Fuel in the form of pellets is enclosed in several tubular claddings of steel or aluminium., Enriched U-235 or Pu-239 is the fuel material. Rods made of boron or cadmium which are neutron, absorbers are used as control rods. The neutrons available for fission are controlled by moving the control, rods in and out of the nuclear core. The rods can be used to shut down the reactor., A coolant is circulated through the reactor to remove the heat generated. Ordinary water is most commonly, used coolant. Heat produced during fission process is absorbed by the coolant and is used to convert water, in to steam in the heat exchanger. The steam is used to rotate the steam turbine. The steam turbine is, connected to a generator which generates electricity. The entire reactor is enclosed in a concrete building, with lead sheets covered inside to prevent radioactive radiations being released in to the environment., Nuclear Fuels: Nuclear fission is the process, where a heavy nucleus splits into two fragments of more or, DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 3

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EME(21EME15) MODULE 1: Extra Notes, less of equal mass., energy, , i.e. Neutron + Heavy nucleus → Fission fragments + Neutrons ( 2 to 3 ) +, , A common nuclear fission reaction, where a Uranium-235 nucleus is bombarded with a neutron particle., This causes the U-235 nucleus to split, producing, on average, Barium-141, Krypton-92, and three neutrons., , The energy released by fission of I gram of U-235 is equal to that due to combustion of 50 million tons of, coal ; it is about 8.5 x 1010 J., Nuclear fusion: Fusion energy is a form of nuclear energy released by the fusion (combustion) of two light, nuclei( i.e. nuclei of low mass ) to produce heavier mass. Deuterium &tritium are some of the fusible, elements, , Advantages, , DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Disadvantages, , Dr. Rajashekar Matpathi, , 4

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EME(21EME15) MODULE 1: Extra Notes, THERMAL POWER PLANT: In a thermal power plant, the steam is produced at high pressure in the, steam boiler due to the burning of fuel (pulverized coal) in boiler furnaces. This steam is further supper, heated in a superheater. This superheated steam then enters into the turbine and rotates the turbine blades., The turbine is mechanically so coupled with an alternator that its rotor will rotate with the rotation of, turbine blades. After entering in turbine the steam pressure suddenly falls and the corresponding volume of, the steam increases. After imparting energy to the turbine rotor, the steam passes out of the turbine blades, into the condenser., In the condenser, the cold water is circulated with the help of a pump which condenses the low-pressure wet, steam. This condensed water is further supplied to a low-pressure water heater where the low-pressure, steam increases the temperature of this feed water; it is again heated at high pressure., , First, the pulverized coal is burnt into the furnace of steam boiler. High-pressure steam is produced in the, boiler. This steam is then passed through the superheater, where it further heated up. This super heated, steam is then entered into a turbine at high speed. In turbine, this steam force rotates the turbine blades that, means here in the turbine the stored potential energy of the high pressured steam is converted into, mechanical energy. After rotating the turbine blades, the steam has lost its high pressure, passes out of, turbine blades, and enters into a condenser. In the condenser, the cold water is circulated with help of a, pump which condenses the low-pressure wet steam. This condensed water is then further supplied to a lowpressure water heater where the low-pressure steam increases the temperature of this feed water, it is then, again heated in a high-pressure heater where the high pressure of steam is used for heating. The turbine in, the thermal power station acts as a prime mover of the alternator., In a steam boiler, the water is heated up by burning the fuel in the air in the furnace, and the function of the, boiler is to give dry superheated steam at the required temperature. The steam so produced is used in driving, the steam Turbines. This turbine is coupled to the synchronous generator (usually a three-phase synchronous, alternator), which generates electrical energy., The exhaust steam from the turbine is allowed to condense into the water in the steam condenser of turbine,, which creates suction at very low pressure and allows the expansion of the steam in the turbine to very low, DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 5

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EME(21EME15) MODULE 1: Extra Notes, pressure.The principal advantages of the condensing operation are the increased amount of energy extracted, per kg of steam and thereby increasing efficiency, and the condensate which is fed into the boiler again, reduces the amount of fresh feed water.The condensate along with some fresh makeup feed water is again, fed into the boiler by a pump (called the boiler feed pump).In the condenser, the steam is condensed by, cooling water. Cooling water recycles through the cooling tower. This constitutes a cooling water circuit., The ambient air is allowed to enter the boiler after dust filtration. Also, the flue gas comes out of the boiler, and gets exhausted into the atmosphere through stacks. These constitute air and flue gas circuits, Advantages of a thermal power station, 1. Economical for low initial cost other than any generating plant., 2. Land required less than hydropower plant., 3. Since coal is the main fuel and its cost is quite cheap than petrol/diesel so generation cost is economical., 4. Maintenance is easier., 5. Thermal power plants can be installed in any location where transportation and bulk of water are available., Disadvantages of Thermal Power Station, 1., 2., 3., , The running cost for a thermal power station is comparatively high due to fuel, maintenance, etc., A large amount of smoke causes air pollution. The thermal power station is responsible for Global warming., The heated water that comes from the thermal power plants has an adverse effect on the aquatic lives in, the water and disturbs the ecology., 4. The overall efficiency of the thermal power plant is low like less than 30%., Wind Power Plant (Wind Mill): The major parts are 1.The tower: most often metallic and, cone shaped, it is usually white and meets aeronautical requirements. It is 40 to 110 meters tall, with a base, diameter of 4 to 7 meters. It contains an opening on the ground to allow access to variety of equipment. The, rotor is located upwards where the wind is strongest, and which allows for a lengthy blade., 2. The rotor: It is made up of three blades of composite material from 25 to 60 meters in length, connected, by a hub. The rotor pivots 360° to face the wind and to allow a maximum production of electricity. The, height at the tip of the blade varies between 90 and 150 meters for the largest wind turbines. The blades of a, wind turbine turn at an average speed of 10 to 20 rotations per minute., 3. Gearbox: Inside the nacelle (the main body of the turbine sitting on top of the tower and behind the, blades), the gearbox converts the low-speed rotation of the drive shaft (perhaps, 16 revolutions per minute,, rpm) into high-speed (perhaps, 1600 rpm) rotation fast enough to drive the generator efficiently., 4. The pivoting nacelle: located at the peak of the tower, it houses the generator that transforms the, mechanical wind energy into electric energy. The nacelle pivots automatically depending on the direction of, the wind. Access to the nacelle is made by a ladder and/or a lift located inside the tower. The primary, characteristic of a wind turbine is its power or capacity. It is measured in kilowatts (kW) or in megawatts, (MW). Wind turbines installed today range from 850 kW to 3,000 kW (or 3 MW). The energy produced by, a wind turbine during its operation is measured in kilowatt hours (kWh) and mainly depends on the wind, speed., 5. Anemometers: is an automatic speed measuring devices and wind vanes on the back of the nacelle, provide measurements of the wind speed and direction. The Brakes are also applied during routine, maintenance., , DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 6

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EME(21EME15) MODULE 1: Extra Notes, Working Principle: To start, a wind mill needs wind of at least 12 to 15 km/hr. The strength of the wind, makes the blades turn and initiates the rotor that transmits the energy received to a generator that produces, electric energy. The electricity is channeled by an underground electric cable to the public grid. The, difference in pressure between the two sides of the blade creates an aerodynamic force that puts the rotor in, motion. This motion is generally accelerated by a gear-box and the mechanical energy transmitted by the, gear-box is transformed into electrical energy by the generator. The generator’s rotor turns at a high speed, and produces an electric charge of around 690 volts. This electricity cannot be used directly. It is handled, thanks to a converter, and then its charge is increased to 20,000 volts by a Step up transformer. The wind, turbines are set in the ground thanks to reinforced concrete foundations, often circular, covered over with, seeded soil. They are interconnected among themselves by underground electric cables. Each wind turbine, is connected to the transformer located at the foot and inside the tower. The electric energy produced is sent, towards the public distribution grid through a delivery station., , Advantages, , Disadvantages, , Very low carbon dioxide emissions (effectively zero once High up-front cost (just as for large nuclear or fossilconstructed)., fueled plants)., No air or water pollution., No environmental impacts from mining or drilling., No fuel to pay forever!, , Economic subsidies needed to make wind energy viable, (though other power forms are subsidised too, either, economically or because they don't pay the economic and, social cost of the pollution they make)., , Completely sustainable—unlike fossil fuels, wind will Extra cost and complexity of balancing variable wind, power with other forms of power., never run out., Turbines work almost anywhere in the world where it's Extra cost of upgrading the power grid and transmission, reliably windy, unlike fossil-fuel deposits that are lines, though the whole system often benefits., concentrated only in certain regions., Variable output—though that problem is reduced by, Unlike fossil-fueled power, wind energy operating costs are operating wind farms in different areas and using, interconnectors between neighboring countries., predictable years in advance., Large overall land take—though at least 95 percent of, DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 7

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EME(21EME15) MODULE 1: Extra Notes, Freedom from energy prices and political volatility of oil wind farm land can still be used for farming, and offshore, and gas supplies from other countries., turbines can be built at sea., Wind energy prices will become increasingly competitive, as fossil fuel prices rise and wind technology matures., , Can't supply 100 percent of a country's power all year, round, the way fossil fuels, nuclear, hydroe, and biomass, power can.Loss of jobs for people working in mining ., , New jobs in construction, operation, & manufacture of, turbines, , Solar Power Plant, Types of Solar Power Plant: There are 2 types of solar power plant, 1. Solar Photovoltaic Power Plant, 2. Solar Thermal Power Plant, The photovoltaic technology will directly convert the sunlight into electricity, while the solar thermal technology, will capture the heat of the sun., , Solar Photovoltaic Power Plant, , Solar Cell (Photovoltaic Cell) :The solar cell is a device which is made of p-n junction diode which, effect photo voltaic effect to convert light energy into electrical energy. The capacity of solar cells is 0.5 V, and 6 Amp generating 3W power. The number of cells is connected in series or parallel and makes a, module. The number of modules forms a solar panel., Solar panels are wired in series when you connect the positive terminal of one panel to the negative, terminal of another. When solar panels are wired in series, the voltage of the panels adds together, but the, amperage remains the same. And in parallel connection voltage remains same, the current gets added., Construction of Solar Cell: The junction diode is made of SI OR GaAs. A thin layer of p-type is grown on, the n-type semiconductor. Top of the p-layer is provided with a few finer electrodes which leaves open, space for the light to reach the thin p-layer and it under lays p-n junction. Bottom of the n-layer is provided, with a current collecting electrode, Inverter; The output of the solar panel is in the form of DC. The most of load connected to the power, system network is in the form of AC. Therefore, we need to convert DC output power into AC power. For, that, an inverter is used in solar power plants., Battery storage The storage components are the most important component in a power plant to meet the, demand and variation of the load. This component is used especially when the sunshine is not available for, few days.The capacity of a battery is that how much amount of electrical power it can store. The capacity of, batteries is measured in Ampere-hours (AH) rating. Example: Lead-Acid battery, Nickel-Cadmium battery, Charge Controller; The charge controller is used to avoid the overcharging of the battery. The, overcharging of a battery may lead to corrosion and reduce plate growth. And it may damage the electrolyte, DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 8

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EME(21EME15) MODULE 1: Extra Notes, of the battery. Example: MPPT (“Maximum Power Point Tracking”) charge controller., System balancing component; It is a set of components used to control, protect and distribute power in the, system. These devices ensure that the system working in proper condition and utilize energy in the proper, direction. Blocking diode is a diode that is connected between the battery and panel to avoid reversal, current from battery to panel. Voltage regulator; The output of solar panels depends on sunlight. And the, sunlight is not constantly available. It is continuously varying. Similarly, the output of the solar panel is also, varying with respect to sunlight. This results in fluctuation in load current. The voltage regulators are used, to maintain fluctuation within an acceptable range., . Solar constant: the total radiation energy received from the Sun per unit of time per unit of area on a, theoretical surface perpendicular to the Sun’s rays and at Earth’s mean distance from the Sun. It is most, accurately measured from satellites where atmospheric effects are absent. Its value for earth is 1366w/m2, , Fig. Construction of Solar Cell, Fig. Solar Constant, Working Principle of Solar Cell:, When light reaches the p-n junction, electron is excited to the valance band under the condition that light, energy is higher than the band gap energy, it generates the electron and holes which are equal in number in, the valance and conduction band respectively. These electron hole pairs move in opposite directions to the, barrier field. Electrons move towards the n-side and the hole is moved towards the p-side. So a voltage is set, up which is known as photo voltage and when a load is connected, the current flows., Materials Used in Solar Cell, The materials which are used for this purpose must have band gap close to 1.5ev. Commonly used materials, are- 1.Silicon. 2. GaAs. 3. CdTe. 4.CuInSe2, Criteria for Materials to be Used in Solar Cell, 1., Must have band gap from 1ev to 1.8ev., 2., It must have high optical absorption., 3., It must have high electrical conductivity., 4., The raw material must be available in abundance and the cost of the material must be low., Advantages of Solar Cell, 1. No pollution associated with it., 2. It must last for a long time., 3. No maintenance cost., , Disadvantages of Solar Cell, 1. It has high cost of installation., 2. It has low efficiency., 3. During cloudy day, the energy cannot be produced and also at, night we will not get solar energy., , Uses of Solar Generation Systems, 1., It may be used to charge batteries., 2., Used in light meters., 3., It is used to power calculators and wrist watches., 4., It can be used in spacecraft to provide electrical energy., DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 9

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EME(21EME15) MODULE 1: Extra Notes, Solar thermal power plants: Solar thermal power plants are electricity generation plants that utilize, energy from the Sun to heat a fluid to a high temperature. This fluid then transfers its heat to water, which, then becomes superheated steam. This steam is then used to turn turbines in a power plant, and this mechanical energy is converted into electricity by a generator., , It's like coal fired thermal power plants work except the steam is produced by the collected heat from sun., The solar thermal power plants, generally install in desert which use parabolic trough solar collectors covered with more mirrors that are north-south aligned and able to pivot to follow the sun as it moves east to, west during the day to generate maximum 80MW of electricity The hot fluid with 400C got from parabolic, collectors is 30 to 100 times their normal is used to produce steam, and the steam then spins a turbine that, powers a generator to make electricity., A proven form of storage system operates with two tanks. The storage medium for high-temperature heat, storage is molten salt. The excess heat of the solar collector field heats up the molten salt, which is pumped, from the cold to the hot tank. If the solar collector field cannot produce enough heat to drive the turbine, the, molten salt is pumped back from the hot to the cold tank and heats up the heat transfer fluid. Figure 3 shows, the principle of the parabolic trough power plant with thermal storage., Advantages of Solar Thermal Power Plants, , Disadvantages of Solar Thermal Power Plants, , Renewable Source of Energy, , High Initial Investment, , Round the Clock Operation, , Issue of Thermodynamic Fluid (Water), , Space Efficient Technology, , Ecological Issues, , Cost-Efficient Technology, , Larger Space Requirement, , Tidal Power Plant:, Tide or wave is periodic rise and fall of water level of the sea. Tides occur due to the attraction of sea water by, the moon. Tides contain large amount of potential energy which is used for power generation. When the water, is above the mean sea level, it is called flood tide. When the water level is below the mean level it is called, ebb tide. Working: The arrangement of this system is shown in figure. The ocean tides rise and fall and water, can be stored during the rise period and it can be discharged during fall. A dam is constructed separating the, tidal basin from the sea and a difference in water level is obtained between the basin and sea., , DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 10

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EME(21EME15) MODULE 1: Extra Notes, , During high tide period, water flows from the sea into the tidal basin through the water turbine. The height of, tide is above that of tidal basin. Hence the turbine unit operates and generates power, as it is directly coupled to, a generator., During low tide period, water flows from tidal basin to sea, as the water level in the basin is more than that of, the tide in the sea. During this period also, the flowing water rotates the turbine and generator power., The generation of power stops only when the sea level and the tidal basin level are equal. For the generation, of power economically using this source of energy requires some minimum tide height and suitable site., Kislaya power plant of 250 MW capacity in Russia and Rance power plant in France are the only examples, of this type of power plant., The main components of tidal power plants are:, 1., , Dam, , 2., , Sluice ways from basin to sea and vice versa, , 3., , Power house, , 1.Dam:The function of dam is to form a barrier between the sea and the basin or between one basin to the, other basin in case of multiple basins.. Barrages ;have to resist waves whose shock can be serve and were, pressure changes sides continuously., 2. Sluice ways from basin to sea and vice versa: The sluice ways are gate-controlled devices. Sluice gates are, employed to fill the basin during the high tide or empty the basin during low tide. Flap gates are also used, for this purpose. Flap gates allow only in the direction of sea to basin., 3.Power house:, Auxiliary equipment’s ,turbines and generators are the main components of the power house.Large sized, turbines are used because of low head available, Advantages of Tidal Power, 1. Free source of energy, 2. Everlasting source of energy, 3. No extra submerging of land is involved., 4. Pollution free source, 5. It is inexhaustible., Limitations of Tidal power, 1. It has uneven operation., 2. It has heavy initial capital and long construction period., 3. Sea water is corrosive., 4. The plant efficiency is affected because of variable tidal range., 5. Sedimentation and siltation of basins are the serious problems of tidal power plant., DEPT.OF MECHANICAL ENGG. BKIT, BHALKI, , Dr. Rajashekar Matpathi, , 11