MECHANICAL ENGINEERING
Paper-II
I Time Allowed Three Hours I I Maximum Marks 200 I
INSTRUCTIONS
Candidates should attempt Question Nos. 1 and 5
which are compulsory, and any THREE of the
remaining questions, selecting at least ONE question
from each Section.
All questions carry equal marks.
Marks allotted to parts of a question are
indicated against each.
Answers must be written in ENGLISH ouly.
If any data is considered insufficient, assume
suitable value and indicate the same clearly.
Newton may be converted to kgf using the equality
1 kilonewton kNl 100 kgf, if found necessary.
All answers should be in Sl units.
Take 1 kcal 4·187 kJ and 1 kg/cm2 0·98 bar
1 bar 105 pascals.
Universal gas constant 8314·6 J/kmol-K.
Neat sketches may be drawn, wherever required.
The attached psychrometric chart is to be used for
answering Question No. 6(bj. Then the psychrometric
chart may be detached from the· question paper and
attached firmly your answer book.
P.T.O.
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Section-A
1.Answer any four parts
imaginary engine receives heat and
does work on a slowly moving piston at
such rates that the cycle of operation of
1 kg of working fluid can be represented
as a circle 10cm in diameter on a
p-v diagram on which 1cm 300 kPa
and 1cm= 0·1m3/kg.
(i)Determine how much work is done
by each kg of working fluid for
each cycle of operation.
(ii)If the heat rejected by the engine
in a cycle is 1000 kJ per kg of
working fluid, find the thermal
efficiency of the engine. 10
(b)Explain the principle of carburetion.
Develop an expression for air-fuel
ratio for a simple carburetor taking
compressibility into account. 10
(c)Explain the various mechanisms of
lubrication bringing out their functions.
What are the various desirable properties
of lubricants? Explain how additives
help to achieve these. 10
If a fin is thin and long and tip
losses are negligible, show that the
heat transfer from the fin is given by
Q0 mkAtheta0 tan hml
where m (hP/kA)2.

For a balanced heat exchanger
show that for counterflow arrangement
epsilon=NTU/NTU+1

An ideal gas cycle consists of three
reversible processes in the following
sequence-(i) constant volume pressure
rise, isentropic expansion to r times
the initial volume and constant
pressure decrease in volume. Sketch
the cycle on the p-v and T-s diagrams.
Show that the efficiency of the cycle is
<img src='./qimages/1479-2a.jpg'>
Evaluate the cycle efficiency, when gaama=4/3 and r 8.
(b)The following expressions for the
equation of state and the specific heat
CP are obeyed by a certain gas
<img src='./qimages/1479-2b.jpg'>
where alpha, C are constants. Obtain
an expression for the Joule-Thomson
coefficient and the specific heat Cv. 15
(c)Show that the efficiency of a reversible
engine is independent of the nature or
amount of the working substance going
through the cycle. 10

A petrol engine with a compression
ratio of 7 uses a mixture of isooctane
and hexane as fuel. The pressure and
temperature at the beginning of the
compression process are 1 bar and
55·22deg C respectively. If the fuel-air
mixture is 19·05% rich and the
maximum pressure developed is
115·26 bar, evaluate the composition
of the mixture (in percentage
weight). Take, Cv 0·717
(CV)hexane 43 MJ/kg,(CV)isooctane
42 MJ/kg and PV 1.31 is constant for
the expansion and compression
processes.
(b)(i)Explain the stages of combustion
in SI and CI engines.
(ii)Discuss the phenomenon of knock
in SI and CI engines.
(iii)Discuss the important qualities of
SI and CI engine fuels. How are
these fuels rated?
4.(a)What do you mean by radiation shield?
Where is it used?
Two parallel discs of 1m diameter are
situated 2m apart in the surroundings
at a temperature of 20deg C. One side of
a disc has an emissivity of 0·5 and is
maintained at 500deg C by electrical
resistance heating and the other side is
insulated. The other disc is open to
radiation on both sides. Determine the
equilibrium temperature of the second
disc and the heat flow rate from the
first disc. Take, F12 0.06 (for discs).
Discuss the effect on the solution if both
sides of the second disc are perfect
m1rrors. 17=20
that for laminar flow of air
(Pr 0·714), the local and average
values of Nusselt number for
natural convection heat transfer
from or to a vertical plate are
given by Nux= 0.378 Gr1/4 or
NuL =0.504 GrL1/4

A 15cm outer diameter steel
pipe lies 2m vertically and 8m
horizontally in a large room with
an ambient temperature of 30degc.
if the pipe surface is at 250deg c and
the emissivity of the steel is 0.60,
calculate the total rate of heat loss
from the pipe to the atmosphere.
Properties of air at 140deg c are
row=0·854kg/m3 Cp=1·01kJ/kg-K,
k =0·035 Pr=0·684 and
v 27·8 x 10-6 m2/s. For vertical
part, use the formula
Nu 0·13(Gr Pr)1/3
and for horizontal part
Nu 0·53 (Grd Pr)1/4

Section-B
5. Answer any Jour parts
(a)With the help of a schematic diagram,
describe the working of a 'Benson
boiler'. What are its advantages? 10
(b)How can the solar energy be used to
obtain refrigeration effect? Explain with
a neat and clear sketch. 10
(c)Differentiate between air-conditioning
and air cooling. Whether household
air -conditioners are properly named?
Justify your answer. Show how air
washer can be used for year-round
air-conditioning.
(d)Prove that in a multistage turbine
nt ns xRF
where nt overall turbine efficiency,
ns small-stage efficiency and RF =reheat factor. 10
(e)What is the pressure coefficient of a
centrifugal compressor? Derive
sieP 1-pie2 cos beta2
where pie2 =flow coefficient.
Which of the two factors (increase
in the upper pressure limit and
decrease in the lower pressure
limit) has more adverse effect on
COP of a refrigeration cycle?

Show the variation of capacity
factor with varying evaporator
temperature in the vapour compression
system of refrigeration,
the condenser pressure
remaining the same.
(iii)Show the actual vapour compression
cycle on a p-h
diagram and explain the various
irreversibilities with the help of
T-s diagram.
(iv)What is the difference between
multistage refrigeration and
cascade refrigeration?
(b)(i)Define Effective Sensible Heat
Factor (ESHF). How can ADP be
determined with its help?
The following data refer to a public
hall:
Total sensible heat 10pow5 kJ/h
Total latent heat 60000kJ/h
The room design condition
Tdb= 27deg c and pie= 60%.
The temperature rise of air (i.e.,
difference between the room
design condition and supply air
to the room) is 8°C.
Find the SHF, show the process
on the psychrometric chart and
also calculate the volume of air
supplied to room using approximate
expression based on sensible
heat and enthalpy drop.
(ii)To cut cooling loads to minimize
the size of the air-conditioning
plant, the energy conservation
measures can help a lot. List such
measures and discuss each in
brief. Draw the schematic arrangement
of a year-round air conditioning
system and explain
its working with the help of
psychrometric chart. 10+ 10=20

7.(a)What is a Fanno line and a Rayleigh
line? Why do the end states of a normal
shock lie on the Fanno line and
Rayleigh line? Show these lines on a
h-s diagram for various conditions. Give
the physical meaning of this. 10
nozzle is designed assuming
isentropic flow with an exit Mach
number of 2·6. Air flows through it with
a stagnation pressure and temperature
of 2MPa and 150deg c respectively. The
mass flow rate is 5 kg/ sec.
(i)Determine the exit pressure,
temperature, area and throat area.
(ii)If back pressure at the nozzle
exit is raised to 1·35 MPa, and the
flow remains isentropic except for
a normal shock wave, determine
the exit Mach number and
temperature, and the mass flow
rate through the nozzle. Assume
for the value of P/P0 of 0.675,
M 0.85 and T/T0=0.845 for
isentropic flow.

centrifugal compressor with 20m3 of
air per second at 1 bar and 15deg c is to
be compressed through a pressure
ratio of 1.5. The compression follows
the law pv1·5 constant.The velocity
of flow at inlet and outlet remains
constant and is equal to 60 m/s. The
inlet and outlet impeller diameters are
0·6m and 1·2m respectively, and the
speed of rotation is 5000 r.p.m.
(i)Find the blade angles at inlet and
outlet of the impeller, and the
angle at which the air from the
impeller enters the casing.
(ii)Find the breadth of impeller blade
at inlet and outlet.
It may be assumed that diffuser is not
fitted and the whole pressure increase
occurs in the impeller and that the
blades have negligible thickness.
(iii)Sketch the velocity triangles at
inlet and outlet of the impeller. 15
8.(a)Draw a neat sketch of a Heavy Water-cooled
Reactor or CANDU-type
reactor power plant.Clearly show the
various components. What are the
advantages and disadvantages of this
type of nuclear reactor over others? 10

(b)The yearly duration curve of a certain
power plant can be considered a
straight line from 30MW to 10MW. To
meet this load, three turbine generator
units, two rated at 15 MW each and one
at 7·5 MW, are installed. Evaluate-
(i)installed capacity;
(ii)plant factor;
(iii)maximum demand;
(iv)load factor;
(v)utilization factor.
turbine model of 1:10 develops
1·84kW under a head of 5m of water at
480 r.p.m. Find the power developed by
the prototype under a head of 40m.
Also find the speed of the prototype.
Assume efficiency of both the turbines
to be same. Find and verifY the specific
speeds. 15