TURBINES

flowing fluid by the dynamic action of one or more rotating elements . TURBINES ‘Turbo Machine’ is defined as a device that extracts energy from a continuously flowing fluid by the dynamic action of one or more rotating elements . The prefix ‘turbo’ is a Latin word meaning ‘spin’ or ‘whirl’ implying that turbo machines rotate in some way.

Srinivas School of Engineering, Mukka Types of Turbines Steam Turbines Gas Turbines (Combustion Turbines) Water (Hydraulic) Turbines Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Steam Turbines A steam turbine is mainly used as an ideal prime mover in which heat energy is transformed into mechanical energy in the form of rotary motion. A steam turbine is used in Electric power generation in thermal power plants. Steam power plants. To propel the ships, submarines. In steam turbines, the heat energy of the steam is first converted into kinetic (velocity) energy which in turn is transformed into mechanical energy of rotation and then drives the generator for the power generation. Srinivas School of Engineering, Mukka

Classification of Steam Turbines Based on action of steam or type of expansion: Impulse or velocity or De Laval turbine Reaction or pressure or Parson’s turbine Combination turbine Based on number of stages: Single stage turbine 2. Multi-stage turbine Based on type of steam flow: Axial flow turbine 2. Radial flow turbine Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Steam Turbines Srinivas School of Engineering, Mukka

Impulse turbine (De Laval Turbine) Srinivas School of Engineering, Mukka

Working Principle of Impulse Turbine . The steam is made to fall in its pressure by expanding in a nozzle. Due to this fall in pressure, a certain amount of heat energy is converted into kinetic energy, which sets the steam to flow with a greater velocity. The rapidly moving particles of the steam enter the rotating part of the turbine, where it undergoes a change in the direction of motion, which gives rise to a change of momentum and therefore a force. This constitutes the driving force of the turbine. Srinivas School of Engineering, Mukka

Impulse Turbines (De Laval Turbine) In this type of turbine, steam is initially expanded in a nozzle from high pressure to low pressure. High velocity jet of steam coming out of the nozzle is made to glide over a curved vane, called ‘Blade’.

Srinivas School of Engineering, Mukka The jet of steam gliding over the blade gets deflected very closely to surface. This causes the particles of steam to suffer a change in the direction of motion, which gives rise to a change of momentum and therefore a force, which will be centrifugal in nature. Resultant of all these centrifugal forces acting on the entire curved surface of the blade causes it to move. Srinivas School of Engineering, Mukka

Pressure-velocity changes over Impulse steam turbine NOZZLE EXHAUST STEAM TURBINE SHAFT MOVING BLADES HIGH PRESSURE STEAM Schematic of Impulse Turbine VL PH Q PL VH R C B Nozzle Rotor Blades Velocity Variation Pressure Variation Pressure-Velocity diagram in Impulse Turbine A P Srinivas School of Engineering, Mukka

Reaction steam Turbine Principle of working - In this type of turbine, the high pressure steam does not initially expand in the nozzle as in the case of impulse turbine, but instead directly passes onto the moving blades. Srinivas School of Engineering, Mukka

Blade shapes of reaction turbines are designed in such a way that the steam flowing between the blades will be subjected to the nozzle effect. Hence, the pressure of the steam drops continuously as it flows over the blades causing, simultaneous increase in the velocity of the steam.

Forces acting on a reaction blade Reaction force: is due to the change in momentum relative velocity of the steam while passing over the blade passage. Centrifugal force: is the force acting on the blade due to change in radius of steam entering and leaving the turbine. Resultant force: is the resultant of Reaction force and Centrifugal force. Srinivas School of Engineering, Mukka

Pressure-Velocity change in reaction turbine Fixed Blade Moving Blade Srinivas School of Engineering, Mukka

Impulse Turbine Reaction Turbine Difference between Impulse & Reaction Turbines Impulse Turbine Reaction Turbine The steam expands (pressure drops) completely in nozzles or in the fixed blades The steam expands both in the fixed and moving blades continuously as it flows over them The blades have symmetrical profile of uniform section The blades have converging (aerofoil) profile The steam pressure while passing over the blades remains constant The steam pressure while passing over the blades gradually drops Because of large initial pressure drop, the steam and turbine speeds are very high Because of gradual pressure drop, the steam and turbine speeds are low The nozzles are fitted to the diaphragm (the partition disc between the stages of the turbine) The fixed blades attached to the casing serve as nozzles Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Impulse Turbine Reaction Turbine Power is obtained only due to the impulsive force of the incoming steam Power is obtained due to impulsive force of incoming steam as well as reaction of exit steam Suitable for small capacity of power generation & occupies less space per unit power Suitable for medium & high capacity power generation and occupies more space per unit power Efficiency is lesser Efficiency is higher Compounding is necessary to reduce speed Compounding is not necessary Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Compounding of Impulse Turbines As the complete expansion of steam takes in one stage (i.e., the entire pressure drop from high pressure to low pressure takes place in only one set of nozzles), the turbine rotor rotates at very high speed of about 30,000 rpm (K.E. is fully absorbed). High speed poses number of technical difficulties like destruction of machine by the large centrifugal forces developed, increase in vibrations, quick overheating of blades, impossibility of direct coupling to other machines, etc. To overcome the above difficulties, the expansion of steam is performed in several stages. Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Utilization of the high pressure energy of the steam by expanding it in successive stages is called Compounding. Methods of Compounding: Velocity compounding (Curtis Impulse Turbine) Pressure compounding Pressure-velocity compounding Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Velocity compounding Comprise of nozzles and two or more rows of moving blades arranged in series. In between two rows of moving blades, one set of guide (fixed) blades are suitably arranged. Guide (fixed) blades are fixed to casing and are stationary. Srinivas School of Engineering, Mukka

Velocity Compounding (Curtis Impulse Turbine) N – Nozzle M – Moving Blade F – Fixed Blade Velocity Compounding (Curtis Impulse Turbine) Srinivas School of Engineering, Mukka

Pressure compounding Consists of two stage of nozzles followed by two rows of moving blades.

Srinivas School of Engineering, Mukka Pressure Compounding Srinivas School of Engineering, Mukka

Pressure-Velocity Compounding (Combined Impulse Turbine) A – Axial clearance, N – Nozzle, M – Moving Blade, F – Fixed Blade Pi and Pe – Pressure at inlet & exit, Vi and Ve - Velocity at inlet & exit Total pressure drop is divided into two stages & the total velocity obtained in each stage is also compounded Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka GAS TURBINES Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka GAS TURBINES A Gas turbine uses the hot gases of combustion directly to produce the mechanical power. Fuels used - Kerosene, coal, coal gas, bunker oil, gasoline, producer gas, etc., Classification: Open cycle gas turbine Closed cycle gas turbine Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Applications Gas turbines are used in: Electric power generation plants Steel, oil and chemical industries Aircrafts, Ship propulsion Turbo jet and turbo-propeller engines like rockets, missiles, space ships etc., Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Open cycle gas turbine: The entire flow of the working substance comes from atmosphere and is returned to the atmosphere back in each cycle. Closed cycle gas turbine: The flow of the working substance of specified mass is confined within the cyclic path. ( Air or Helium is the working substance) Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Open cycle gas turbine COMPRESSOR: draws in air and compress it before it is fed into combustion chamber COMBUSTOR: fuel is added to the compressed air and burnt to produce high velocity exhaust gas TURBINE: extracts energy from exhaust gas Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Closed Cycle Gas Turbine Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Difference between open & closed cycle turbine Open cycle Closed cycle Lesser thermal efficiency Higher Loss of working fluid No loss of working fluid Bigger in size Smaller Big compressor is needed Smaller one is sufficient Possibility of corrosion of blades and rotor Free from corrosion Economical Not economical Exhaust gases from turbine exit to atmosphere Fed back into the cycle

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka WATER TURBINES Srinivas School of Engineering, Mukka

WATER (HYDRAULIC) TURBINES It is a prime mover, which converts hydro power (energy of water) into mechanical energy and further into hydro-electric power. Srinivas School of Engineering, Mukka

Classification of Water Turbines Srinivas School of Engineering, Mukka Based on action of water: Impulse turbine – pelton wheel. Reaction turbine – francis and kaplan. Based on name of originator: Pelton turbine or Pelton wheel Francis turbine Kaplan turbine Based on head of water: Low head turbine Medium head turbine High head turbine Srinivas School of Engineering, Mukka

Pelton Turbine (Pelton Wheel or Free Jet Turbine) High head, tangential flow, horizontal shaft, impulse turbine Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka PELTON TURBINE Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Pelton Turbine Runner Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka REACTION TURBINE Only a part of the pressure energy of the water is converted into K.E. and the rest remains as pressure head. Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka First, the water passes to the guide vanes which guide or deflect the water to enter the blades, called moving blades, mounted on the turbine wheel, without shock. The water from the guide blades are deflected on to the moving blades, where its part of the pressure energy is converted into K.E., which will be absorbed by the turbine wheel. The water leaving the moving blades will be at a low pressure. Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka The difference in pressure between the entrance and the exit of the moving blades is called Reaction pressure, which acts on moving blades of the turbine wheel and sets up the turbine wheel into rotation in the opposite direction. Examples: Francis turbine, Kaplan turbine, Propeller turbine, Thompson turbine, Bulb turbine. Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Francis Turbine Mixed flow, medium head reaction turbine. Consists of a spiral casing enclosing a number of stationary guide blades fixed all round the circumference of an inner ring of moving blades (vanes) forming the runner, which is keyed to the turbine shaft. Radial entry of water along the periphery of the runner and discharge at the center of the runner at low pressure through the diverging conical tube called draft tube. Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka FRANCIS TURBINE Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Francis Inlet Scroll, Grand Coulee Dam Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Francis Runner, Grand Coulee Dam Srinivas School of Engineering, Mukka

FRANCIS TURBINE & GENERATOR Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka Kaplan Turbine Axial flow, low head. Similar to Francis turbine except the runner and draft tube. The runner (Boss or Hub) resembles with the propeller of the ship, hence some times it is called as Propeller turbine. Water flows parallel to the axis of the shaft. Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka (SCROLL CASING) (GUIDE VANE) (RUNNER VANE) KAPLAN TURBINE Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Srinivas School of Engineering, Mukka

Vertical Kaplan Turbine Srinivas School of Engineering, Mukka (Courtesy: VERBUND-Austrian Hydro Power) Srinivas School of Engineering, Mukka

Propeller Turbine Runner Srinivas School of Engineering, Mukka

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