Mechanical Utility Systems - December 2015

MU Mechanical Engineering (Semester 7)

Total marks: --
Total time: -- INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

Solve any four:

1 (b) Advantages of multistaging of reciprocating compressors. 5 marks

1 (c) Define following terms in centrifugal pump.
i) Suction head
ii) Delivery head
iii) Static head
iv) Manometric head 5 marks

1 (d) A single-acting reciprocating pump, running at 50 rpm, delivers 0.01 m³/s of water. The diameter of the piston is 200 mm and stroke 400 mm.
Determine:
i) The theoretical discharge of the pump,
ii) Co-efficient of discharge and
iii) Slip and the percentage slip of the pump. 5 marks

1 (e) Discuss the performance characteristics of reciprocating pumps. 5 marks

1 (f) What are the applications of compressed air in industry? 5 marks

2 (a) What are the axial thrust in centrifugal pumps? Discuss the methods of balancing the axial thrust. 5 marks

2 (b) In a trial on a two-stage, single acting, reciprocating air compressor, following data were recorded.

3 (a) An axial-flow compressor has a constant axial velocity of 150 m/s and 50% reaction. The mean diameter of the blade ring is 35 cm and speed is 15,000 rpm. The exit angle of the blade is 27°. Calculate blade angle at inlet and work done per kg of air. 5 marks

3 (b) Explain construction and working of centrifugal pump with neat sketch. 5 marks

3 (c) A single-stage centrifugal pump with impeller diameter of 30 cm rotates at 2000 rpm and lifts 3 m³ of water per second to a height of 30 m with an efficiency of 75%. Find the number of stages and diameter of each impeller of a similar multistage pump to lift 5m³ of water per second to a height of 200m when rotating at 1500 rpm. 5 marks

4 (a) Explain construction and working of multi-stage, reciprocating air compressor with intercooler with help of neat labelled schematic diagram and P-V diagram. 5 marks

4 (b) A centrifugal pump having outer diameter equal to two times the inner diameter and running at 1000 rpm works against a total head of 40m. The velocity of flow through the impeller is constant and equal to 2.5 m/s. The vanes are set back at an angle of 40° at outlet. If the outer diameter of the impeller is 500 mm and width at outlet is 50 mm, determine:
i) Vane angle at inlet
ii) Work done by impeller on water per second and iii) Manometric efficiency. 5 marks

5 (a) A centrifugal compressor running at 12000 rpm delivers 600 m³/min of free air. The air is compressed from 1 bar and 27°C to a pressure ratio of 4 with an isentropic efficiency of 85%. The blades are radial at the impeller outlet and flow velocity of 60 m/s may be assumed throughout constant. The outer radius of the impeller is twice the inner one and slip factor is 0.9 Calculate: i) Final temperature of air, ii) Power input to compressor, iii) Impeller diameter at inlet and outlet and iv) Width of impeller at inlet. 5 marks

Write short note on following (any four):

6 (b) Air vessels 5 marks

6 (c) Net Positive suction head (NPSH) 5 marks

6 (d) Diffuser system 5 marks

6 (e) Leak detection in compressed air net work. 5 marks

6 (f) Choking and surging in case centrifugal compressor. 5 marks