Turbo Machines - Jun 2014
Mechanical Engg. (Semester 5)
TOTAL MARKS: 100
TOTAL TIME: 3 HOURS (1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks. 1 (a) Define turbo machine. Classify them on basis of work transfer.(4 marks) 1 (b) Define the.following efficiencies of power absorbing turbo machines:
i) Total-to-total efficiency.
ii) Static-to-static efficiency(6 marks) 1 (c) Explain specific speed and specific power.(4 marks) 1 (d) A model turbine 1 m in diameter acting under a head of 2 m runs at 150 RPM. Estimate the scale ratio if the prototype develops 20 MW under a head of 225 m with a specific speed Of 100.(6 marks) 2 (a) Define polytropic efficiency of a compressor(4 marks) 2 (b) What is reheat factor in a multi stage turbine? Prove that R.F is greater than unity(8 marks) 2 (c) In a three stage turbine the pressure ratio of each stage is 2 and the stage efficiency is75%. Calculate the overall efficiency and reheat factor(8 marks) 3 (a) Derive an alternate form of Euler's turbine equation and explain the significance of each energy components.(10 marks) 3 (b) Al a 50% reaction stage axial flow turbine, the mean blade diameter is 0.60 meter. The maximum utilization factor is 0.85 and steam flow rate is 12 kg/s. Calculate the inlet and outlet absolute velocities and power developed if the speed is 2500 RPM(10 marks) 4 (a) Derive an expression of theoretical head capacity relationship of radial outward flow devices(centrifugal machines).(10 marks) 4 (b) An inward flow reaction turbine has outer and inner diameter wheel as 1 m and 0.5 m respectively. The vanes are radial at inlet and discharge is radial at outlet and fluid enters the vanes at an angle of 10°. Assuming the velocity of flow to be constant and equal to 3 m/sec. Find: i) Speed of wheel, ii) Vane angle at outlet, iii) Degree of reaction(10 marks) 5 (a) What is compounding or staging? Name the different compounding method(4 marks) 5 (b) The data pertaining to an impulse turbine is as follows:
Steam velocity : 500 m/sec, blade speed : 200 m/sec, exit angle at moving blade : 25° measured from tangential direction, nozzle angle : 20° Neglecting the effect of friction when passing through blade passages. Calculate:
1)Inlet angle of moving blade
ii) Exit velocity and direction
iii) Work done per kg of steam
iv) Power developed
v) Diagram deficiency.(16 marks) 6 (a) Obtain an expression for the work done per second by water on the runner a pelton Wheel and Hydraulic efficiency.(10 marks) 6 (b) A kapaln turbine has an outer diameter of 8 m and inner diameter as 3m and developing 30,000 KW at 80 RPM under a head of 12m. The discharged through the runner is 300 m2/sec. If the hydraulic efficiency is 95 % , determine:
i) Inlet and out let blade angles
ii) Mechanical efficiency
iii) Overall efficiency.(10 marks) 7 (a) Derive the expression for the minimum speed for starting a centrifugal pump(12 marks) 7 (b) A centrifugal pump having outer diameter equal to two times inner diameter and running at 1200 RPM, words against a total head of 75m. The velocity of flow through the impeller is constant and equal to 3m/sec. The vanes are setback at an angle of 30° at outlet. If the outlet diameter of the impeller is 60cm and width at outlet is 5 cm. Determine:
i) Vane angle at inlet.
ii) work done per second by impeller.
iii) Manometric efficiency.(8 marks) 8 (a) Explain the phenomena of surging, stalling and chocking in centrifugal compressor stage(6 marks) 8 (b) Draw velocity triangles at the entry and exit for the axial compressor stage.(6 marks) 8 (c) An axial compressor/blower supplies air to furnace at the rate of 3 kg/sec. The atmospheric conditions being 100 kPa and 310 K. The blower efficiency is 80% and mechanical efficiency is 85%. The power supplied to 30 kW. Estimate the overall efficiency and pressure developed in mm WG(8 marks)