98 Mar B5 December 2016 Page 7 Of 20 Question 5 Steam Turbine Blade Efficiency Refer To The Examination Paper Attachment 1 (77.95 KiB) Viewed 30 times
98-Mar-B5 December 2016 Page 7 of 20 QUESTION 5 STEAM TURBINE BLADE EFFICIENCY Refer to the Examination Paper Attachments Page 14 Steam Turbine Velocity Diagram The attached diagram clarifies the nomenclature used in the question below. Use this same nomenclature in your answer One stage of a steam turbine operating on the impulse principle has the following blade characteristics: Moving blade velocity Ve Inlet steam velocity Vsi Nozzle exit angle Steam mass flow rate M 100 m/s = 300 m/s = 25 24 kg/s The moving blades are assumed to be symmetrical and frictionless, that is: Blade outlet angle y = Blade inlet angle o Relative velocity VR2 = Relative velocity VR1 Draw a velocity (vector) diagram (see note below) to a scale of 1 cm = 20 m/s show the absolute and relative velocities within the turbine blades. By measuring from this diagram determine the following: (a) (b) (c) (d) (e) Absolute exhaust steam velocity Impulse force on the moving blades. Energy transferred to the moving blades kJ/kg Inlet and exhaust kinetic energies in kJ/kg. Blade efficiency Power developed by the turbine stage. weeeee (5) (1) (1) (1) (1) (1) e Note: While calculation of velocities by trigonometric ratios with reference to a sketch is acceptable it is longer and more time consuming. [10 marks)
98-Mar-B5 December 2016 Page 14 of 20 EXAMINATION PAPER ATTACHMENTS QUESTION 5 STEAM TURBINE VELOCITY DIAGRAM Nomenclature for velocity vectors and angles A Vs1 VR1 O 8 VR2 Vs2 Vs VS1 VR1 Absolute steam velocity entering moving blades Relative steam velocity entering moving blades VE Moving blade velocity VR2 Vsz Relative steam velocity leaving moving blades Absolute steam velocity leaving moving blades
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