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Mumbai University Mechanical (Semester -VII)

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Solution for Mechanical Utility Systems

December 2015

Index

Q.1)

a) …………………………………………………………………………. 2

b) ………………………………………………………………………….2-3

c) …………………………………………………………………………. 3-5

d) ………………………………………………………………………….N.A

e) ……………………………………………………………………….. 6

f) ………………………………………………………………………. 7

Q.2)

a) ………………………………………………………………………….7-10

b) ………………………………………………………………………… 10-12.

c) ………………………………………………………………………… 12-14

Q.3)

a) ………………………………………………………………………….14-16

b) ………………………………………………………………………….16-17

Q.4)

a) …………………………………………………………………………. 18-20

b) ………………………………………………………………………….20-21

Q.5)

a) …………………………………………………………………………. 21-23

b) ………………………………………………………………………….N.A

Q.6)

a) ………………………………………………………………………….24

b) ………………………………………………………………………….24-25

c) ………………………………………………………………………….26

d) ………………………………………………………………………….27

e) ………………………………………………………………………… 27-28



Q1)

(a)Differentiate between reciprocator compressor and rotatory

compressor.

Ans:

(b) Advantages of multistaging of reciprocatory compressor .

Ans:



(c) Define the following terms in centrifugal pumps.

i) Suction head ii) Delivery head iii) Static head iv) Monometric head

Ans:



Various heads in a pumping installation

(1) Suction lift ,hs:

It represents the vertical distance between the top surface level of sump an the

centre of impeller.

(2) Delivery lift ,hd :

It represents the vertical distance between the centre of impeller and the

discharge level in delivery tank.

(3) Static head ,Hs :

(4) It is the sum of suction lift i.e . it represents the vertical distance between

the top surface level of sump to discharge level in delivery tank. Hence

static head .

Hs = suction lift ,hs + Delivery lift , hd



(d) A single –acting reciprocating pump ,running at 50 rpm ,dilevers 0.01

m3/s of water.The diameter of piston is 200mm and stroke length is 400mm.

Determine the i) Theoritical discharge of the pump ii) Co-efficient of discharge

and iii) Slip and the percentage slip of the pump.

Ans: N.A



(e) Discuss the performance characteristics of reciprocating pump.

Ans:



(f) What are the application of compressed air in industries?

Ans:

Q2)

(a) What are the axial thrust in centrifugal pumps ? Discuss the method of

balancing the axial thrust.

Ans Axial thrust in Centrifugal Pumps :

Methods of Balancing the axial thrust :

In order to balance the applied thrust ,following methods are adopted.

1) For small pumps :



3)Radial thrust:



(b) In a trial on two -stage,single acting ,reciprocating air compressor

following data were recorded.

i) Free air delivery per minute 6m3

ii) Free air conditions 1 bar 27 degree C



iii) Delivery pressure 30 bar

iv) Compressor speed 300rpm

v) Intermediate pressure 6 bar

vi) Temperature at the inlet of HP cylinder 270 C

vii) Law of compression PV1.3

viii) Mechanical efficiency 85 %

ix) Stroke to bore ratio for LP cylinder 1.2

Calculate i) cylinder diameter ii) Power input ,neglecting clearance

volume

Ans: note: Similar sum



Q3)

(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

the speed is 15,000rpm.The axit angle of the blade 27 degree

.Calculate the blade angle at inlet and work done per kg of air.



Ans: note: similar sum



(b) Explain working and construction of centrifugal pump with neat

sketch .

Ans: Working of Pump

Centrifugal pump works on the principle that when a certain mass of liquid is

made to rotate along the impeller from the central axis of rotation ,it impresses a

centrifugal head. It causes the water to move radially outwards at higher

velocity and causes the water to rise to a higher level .The motion of water is

restricted by casing of pump ,it results into pressure build up.In addition, the

change in angular momentum of liquid during its flow results into increase in

pressure head



(c) A single stage centrifugal pump with impeller diameter of 30 cm

rotates at 2000rpm and lift 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 5 m3 of wtare per

second to height of 200 m when rotating at 1500 rpm.




Q4)

(a) Explain construction and working of multistage ,reciprocating air

compressor with intercooler with the help of neat labelled schematic

diagram and P-V diagram.

Ans:

(p-v) diagram since without intercooling the curve of compression would have

followed the path .

Advanatges of Multistage Compression



Work Done:

(p-v ) Diagram representation for Reciprocating Compressor



(b) A centrifugal pump having outer diameter equal to two times the inner

diameter and running at 1000 rpm works against the total head of 40

m.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 degree 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) Monomeric efficiency.

Ans: note : similar sum



Q5)

(a) A centrifugal compressor running at 12000 rpm delivers 600 m3/min

of free air. The air is compressed from 1 bar to 27 degree C to a

pressure ratio of 4 with an isentropic efficiency of 85% .The blades

are radial at the impeller outlook 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 of compressor iii) Impeller diameter at inlet and

outlet and iv) Width of impeller at inlet .




(b) Write down energy conservation opportunities in pumping system.

Ans: N.A



Q6)

Write short note on the following (any four)

(a) Features of gear pump .

Ans:

(b) Air vessels



(c) Net positive suction head (NPSH)

Ans: Net positive suction head (NPSH)

NPHS Required

NPHS available



(d) Diffuser system

Ans:

Vaneless and Vaned Diffusers:



(e) Leak detection in compressor air net work

Ans:

(f) Choking and surging in case of centrifugal compressor .

Ans: Surging



Choking:

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