Question Paper: Mechanical Utility Systems Question Paper - May 17 - Mechanical Engineering (Semester 7) - Mumbai University (MU)
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## Mechanical Utility Systems - May 17

### Mechanical Engineering (Semester 7)

Total marks: 80
Total time: 3 Hours
INSTRUCTIONS
(1) Question No. 1 is compulsory.
(2) Attempt any three from remaining five questions.
(3) Assume suitable data if required.

Q1) Solve any four

• a) Enumerate the various components of reciprocating air compressor.
• b) What is the function of air vessel in reciprocating pump?
• c) Distinguish clearly between NPSH available and NPSH required and discuss the factor that affect them.
• d) What are the methods of energy conservation in pumping system?
• e) Explain the working of centrifugal compressor.
(20 marks)

Q2(a) Why inter cooling is used in multistage compressor? Derive an expression for intermediate pressure in a two stage compressor when inter cooling is perfect. (10 marks)

Q2(b) A rotary air compressor receives air at a pressure of 1 bar and 17$^o$C and delivers it at a pressure of 6 bar. Determine, per kg of air delivered, work done by the compressor and heat exchanged with the jacket water when the compression is isothermal, isentropic and by the relation pv$^{1.6}=$ constant. (10 marks)

Q3(a) The piston diameter and the stroke length of a single acting reciprocating pump are 150 mm and 300 mm respectively. The center of the pump is 5.0 m above the water level in the pump and 33 m below the delivery water level. Both the section and delivery pipes have the same diameter of 75 mm and are 6.5 m and 39 m long respectively. If the pump is working at 30 rpm, determine.

• i) The pressure head on the piston at the beginning, middle and the end of both suction and delivery strokes, and
• ii) The power required to drive the pump.
Take atmospheric pressure head = 10.3 m of water and friction co-efficient, f = 0.01 for both the pipes. (12 marks)

Q3(b) Explain the methods to balanced axial and radial trust in centrifugal pump. (8 marks)

Q4(a) In a three-stage compressor, air is compressed from 98 kPa to 20 bar. Calculate for 1m$^3$ of air per second

• 1) Work under ideal condition for n=1.3
• 2) Isothermal work
• 3) Saving in work due to multi staging.
• 4) Isothermal efficiency.
(10 marks)

Q4(b) How does the acceleration head and pipe friction affect the indicator diagram and work done? (10 marks)

Q5(a) Draw a neat sketch of various components of the centrifugal compressor and show the variation of pressure and velocity of air being compressed. (10 marks)

Q5(b) 3 m$^3$ of water per second is lifted to a height of 30 m with an efficiency of 75% by single stage centrifugal pump. The impeller diameter is 300 mm and it is rotating at 2000 rpm. Find the number of stages and diameter of each impeller of a similar multi-stage pump to lift 5 m$^3$ of water per second to height of 200 m when rotating at 1500 rpm. (10 marks)

Q6) Solve any four

• a) What do you mean by priming? Why is it necessary?
• b) What is cavitation? How can we avoid it in reciprocating pump?
• c) What is closed loop network? And its advantages?
• d) What are the methods of energy conservation in compressed air system?
• e) Draw and comment on performance characteristics of pump.
(20 marks)