## Mechanical Utility Systems - December 2016

### 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 Q1 (a,b,c,d,e)

**1(a)**Difference between centrifugal compressor and axial compressor. 5 marks

**1(b)** Explain Screw pump with neat diagram
5 marks

**1(c)** Define following terms for reciprocating compressors.

1) Mechanical efficiency

2) Indicated power

3) Volumetric efficiency

4) Free Air Deliverry
5 marks

**1(d)** A single-acting. Single-cylinder reciprocating air compressor is compressing 20 kg/min of air from 110kPa, 30°C to 600 kPa and delivers. It to a receiver. Law of comparision is pV^{125}=constant Mechanical efficiency is 80%. Find the power input to compressor, neglecting losses due to clearance, leakages and cooling.
5 marks

**1(e)** Write a note on leak detection in compressed air network
5 marks

**2(a)** Explain construction and working of single-stage, double-acting reciprocating air compressor with neat labelled diagram.
5 marks

**2(b)** A double-acting reciprocating pump. Running at 40 rpm, is discharging 1m ^{3} of water per minute The pump has a stoke of 400 mm. The diameter of piston is 200 mm. The delivery and suction head are 20 m and 5 m respectively. Find the slip of the pump and power required to drive the pump.
5 marks

**3(a)** Explain consruction and working of axial compressor with neat diagram.
5 marks

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

**4(a)** What is cavitation? State the effects of cavitation and what precautions should be taken against cavitation.
5 marks

**4(b)** A two-stage, single-acting reciprocating air compressor takes in air 1 bar and 300 K. Air is discharged at 10 bar. The intermediate pressure is ideal for minimum work and perfect inter-cooling. The law of compression is pV ^{-3} = constant The rate of discharge is 0.1 kg/s

Calculate

1) Power required to drive the compressor.

2) Saving in work in compression with single stage compression.

3) Isothermal efficiency

4) Heat transferred in intercooler Take R = 0.287 kJ/kg K and C_{p} = 1kJ/kg K.
5 marks

**5(a)** Write down the energy conservation opportunities in pumping system.
5 marks

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

**5(c)** The internal and external diameters of a centrifugal pump are 200 mm and 400 mm resp. The pump is running at 1200 rpm. The vane angles of the impeller at inlet and outlet are 20° and 30° resp. The water enters the impeller radially and velocity of flow is constant Determine the work done by he impeller per unit weight of water.
5 marks

### Write short note on following any four Q6.(a,b,c,d,e)

**6(a)**Trouble shooting in centrifugal pump 5 marks

**6(b)** Model testing of centrifugal pump.
5 marks

**6(c)** Diffuser system in centrifugal compressor
5 marks

**6(d)** Losses in axial compressor
5 marks

**6(e)** Applications of compressed air in industry
5 marks