## 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 m^{2}/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)