"PROBLEMS ON IMPULSE STEAM TURBINES"
PROBLEMS ON IMPULSE STEAM TURBINES Classroom problems (1) Steam with an absolute velocity of 360 m/s enters a stage of an impulse turbine provided with a single row wheel. The nozzles are inclined at 20 to the plane of the wheel. The blade rotor with 95.5 cm diameter rotates at 3000 RPM. Find (i) suitable inlet and outlet angle for the moving blade so that there is no axial thrust on the blade. It may be assumed that friction in blade passages is 19% of the kinetic energy corresponding to the relative velocity of the steam at inlet to the blades (ii) power developed in blading for a steam flow rate of 1 kg/s, and (iii) kinetic energy of steam finally leaving the stage. (2) The blade speed of a single ring of an impulse turbine is 300 m/s and the nozzle angle is 20. The isentropic heat drop is 473 kJ/kg and the nozzle efficiency is 0.85. Given that the blade velocity coefficient is 0.7 and the blades are symmetrical, draw the combined velocity triangle and calculate for a mass flow rate of 1 kg/s: (i) axial thrust on the bearing (ii) steam consumption per brake power per hour if the mechanical efficiency is 0.9 (iii) blade efficiency, stage efficiency and maximum blade efficiency, and (iv) heat equivalent of the friction of blading. Home Assignment problems: (1) In a certain stage of an impulse turbine, the nozzle angle is 20 with the plane of the wheel. Four nozzles each of 1 cm diameter expand steam isentropically from 15.2 bar, 250C to 0.5 bar. The mean diameter of the blade ring is 2.8 metres. It develops 55.2 kW at 2400 RPM. The axial thrust is 3.45 N. Calculate (i) blade angles at inlet and outlet, and (ii) power lost in blade friction. (2) A single stage steam turbine is supplied with steam at 5 bar, 200C at the rate of 50 kg/min. It expands into a condenser pressure of 0.2 bar. The blade speed is 400 m/s. The nozzles are inclined at an angle of 20 to the plane of the wheel and the outlet blade angle is 30. Neglecting friction losses, determine the power developed, blade efficiency and stage efficiency. (3) A simple impulse turbine has a mean blade speed of 200 m/s. The nozzles are inclined at 20 to the plane of rotation of the blades. The steam velocity from the nozzles is 600 m/s. The turbine uses 3500 kg/hr of steam. The absolute velocity at exit is along the axis of the turbine. Determine (i) the inlet and outlet blade angles (ii) power output of the turbine (iii) diagram efficiency, and (iv) the axial thrust per kg of steam per second. (4) The following data refers to a single stage impulse turbine: Steam velocity = 600 m/s Blade speed = 250 m/s Nozzle angle = 20 Blade outlet angle = 25 Neglecting the effect of friction, calculate the work developed by the turbine for a steam flow rate of 20 kg/s. Also calculate the axial thrust on bearings.