Steam-Turbine-Design - Steam Turbine Design Impulse Turbine...

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Steam Turbine Design
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Impulse Turbine Impulse steam turbine stage consists as usual from stator which known as the nozzle and rotor or moving blades Impulse turbine are characterized by the that most or all enthalpy and hence pressure drop occurs in the nozzle. The rotor blades can be recognized by their shape, which is symmetrical and have entrance and exit angles around 20 o . They are short and have constant cross sections.
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Single Stage Impulse Turbine Nozzles Blades IMPLUSE STAGE It is usually called De-Laval turbine The steam is fed through one or several convergent-divergent nozzles The nozzles do not extend completely around the circumference of the rotor, so that only part of the blades are impinged upon by the steam. Pressure drop occurs in the nozzle and not in the blades. Maximum velocity and hence kinetic energy of the steam occurs at the nozzle exit Velocity change occurs in the rotor blades where the steam gives up its energy to the rotor blades. Pressure Velocity
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Compounded Steam Turbines Compounded steam turbine means multistage turbine. Compounding is needed when large enthalpy drop is available. Since optimum blade speed is related to the exit nozzle speed. It will be higher as the enthalpy drop is higher. The blade speed is limited by the centrifugal force as well as needs of bulky reduction gear Compounding can be achieved either by velocity compounded turbine or pressure compounded turbine.
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Velocity Compounded Impulse Turbine The velocity compounded turbine was first proposed by C.G Curtis. It is composed of one stage of nozzles, as the single stage turbine, followed by two rows of moving blades instead of one. These two rows are separated by one row of fixed blades which has the function of redirecting the steam leaving the first row of the moving blades to the second row of moving blades.
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Velocity Compounded Impulse ).Turbine )Contd
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Velocity Compounded Impulse ).Turbine )Contd In Curtis turbine steam leaving the nozzle is utilized in both rows of moving blades instead of single raw as in the de-Laval turbine. The velocity remain almost constant across the fixed blades. Using an analysis similar to that used for the single stage , The work of the Curtis turbine is as follows: } { 2 2 3 2 4 2 4 2 3 2 1 2 2 2 2 2 1 r r s s r r s s o o V V V V V V V V m w First Row Second Row
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Due to friction effect inlet and exist velocities for different rows are related as follows: 3 3 4 3 4 2 2 3 2 3 1 1 2 1 2 v r r r r v s s s s v r r r r k V V V V k V V V V k V V V V
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