MECHANICAL ENGINEERING
Paper-II
ITime Allowed Three Hours I IMaximum Marks: 200I
INSTRUCTIONS
Candidates should attempt Question Nos. 1 and 5
which are compulsory, and THREE of the
remaining questions, selecting at least
ONE question from each Section.
The number of marks carried by each question is
indicated at the end of the question.
Answers must be written in ENGLISH only.
If any data is considered insufficient, assume
suitable value and indicate the same clearly.
Newton may be converted to kg! using the equality

1 kilonewton kN) 100 if found necessary.
All answers should be in 81 units.
Take: 1 kcal 4'187 kJ and 1 kg/cm2 0-98 bar

1 bar lOS pascals
Universal gas constant 8314-6 J/kmol-K

Section-A
1. Answer any four parts
With the help of Maxwell's relations, prove that Joule-Thomson coefficient of a gas is given by



What does this equation signify?
10 /21 P.T.G.
Discuss the functions of intake and
exhaust systems of an 81 engine with
their design objectives and sketches. 10
Discuss the parameters affecting engine
heat transfer. 10
Defme thermal boundary layer and
show its distribution over a flat
plate. 5
Prove Reynolds' analogy with
reference to turbulent flow as given
below: 5
CfxSt 2
Bring out the various psychrometric
processes that are shown on a
psychrometric chart and give a simple
sketch of each to achieve it. 10
2. 100 kg/s of steam enters a steam
turbine at an enthalpy of 3250 kJ/kg
and a velocity of 160 m/s. The steam
comes out at an enthalpy of 2640 kJ/kg
with a velocity of 100 m/s. At steady­
state condition, the turbine develops
work equal to 55 MW. Heat transfer
between the turbine and surroundings
occurs at an average Quter temperature
of 350 K. The entropy of steam at
inlet and exit of the turbine
are 6·93 kJ/kg-K and 7'35 kJ/kg-K
respectively. Neglect the changes in

2


potential aild kinetic energy between inlet and outlet. Work Qut the following:

Draw the system with control volume and show the processes on p and T-s diagrams


The rate at which entropy is produced within the turbine per kg of steam flowing


Suggest methods to improve the performance of the steam turbine 20
A satellite incorporates a reversible heat engine which operates between a hot reservoir at 7i and a radiating panel at T2 . The radiation from the panel is given by Q2 kAT24 where k is Stefan-
Boltzmann constant and A is the area of the panel. Work out the following:

Draw the system under gIven conditions


Prove that the area of the panel for a given work output and a value of 11 will be minimum when T2 /1i 3/4


Further, prove that the minimum area of the panel will be given by
A 256W
rom 27kT,4
1
where W IS the output of the engIne 20
B-JGT-J-NFB/21 3 P.T.G.
3. fa) In a simple carburettor, the petrol in the float chamber stands 6 mm below the jet opening. The engine consumes kg fuel/h. The fuel jet diameter is 1'25 rom and the discharge coefficient of the fuel orifice is 0·64. If the air-fuel ratio is 16: estimate­

the air velocity at the throat;


the throat diameter;


the pressure drop in em of water. The coefficient of discharge for air is 0'85 and the ambient conditions are pressure 1 bar and temperature 288 K. Take the density of fuel and air as 770 kg/m3 and 1'1122 kg/m3
respectively. Neglect compressibility effect. 20
A four-cylinder petrol-fueled car is to be converted to run on eNG and
hydrogen. Draw schematic diagrams indicating the changes required for conversion in each case. Justify your answer on the basis of the properties of the fuels. 20
4. For some high degree of research work
in the field of medicine, liquid nitrogen
is stored in a spherical thin-walled
metallic container at 100 K. The con­
tainer has a diameter of 0·8 m .and is
covered with an evacuated reflective
insulation composed of silica powder
0'0017 The insulation is
35 mm thick and the outer surface is

B-JGT-J-NFB/21 4
exposed to ambient air at 30°C. The
convective heat transfer coefficient
between ambient air and insulation
is 20 W1m 2_K. The latent heat of
vaporization and the density of liquid
nitrogen are 200 kJ/kg and 805 kg/rn3
respectively. Work but the following:

Sketch the system and thermal circuit, and write the assumptions made


The rate of heat transfer to the liquid nitrogen


The rate of liquid boil-off and the loss per day
With the help of a suitable diagram, explain the purpose of cascading vapour compression refrigeration systems.
In an ammonia vapour refrigeration plant, the pressure range is from 3'15 bar in the evaporator to 10·5 bar in the condenser, the compression is isentropic and before entering the throttle valve the refrigerant ammonia is subcooled. The temperatures of the refrigerant at entry and exit from the condenser are 50 °C and 20 DC respectively, and the water being circulated in the condenser at the rate of 10·5 kg/min has a temperature rise of 10°C. The compressor unit is single­cylinder, single-acting with bore 10 em, stroke 15 em while running at 200 rev/min having an indicated meap effective pressure equal to 3-5 bar.
5 P.T.C.
If the plant produces 50 kg/h of ice at o°C from water at 15°C, determine
COP, flow rate of refrigerant and
condition of vapour at entry to the compressor. Take latent heat of ice as 335 kJjkg. The relevant properties of ammonia are as follows
Pressure Saturation temperature Enthalpy Specific heat
Liquid Vapour Liquid Vapour
3-15 264 1264
10'5 304 134 1294 4·6

20
Section-B
5. Answer any four parts:
Discuss the stalling phenomena.in an axial flow compressor and write its effects on the performance. 10
Defme Fanno and Rayleigh lines with reference to normal shock wave. Show these lines on h-s diagram for subsonic, sonic and supersonic conditions. Give the physical meaning of these lines. 10
With the help of a sketch, discuss the working principle of a pulverized coal direct-firing system of a steam power plant. 10
With the help of a sketch, discuss the working principle of bubbling fluidized-bed boiler. 10
B-JGT-J-NFB/21 6

Discuss the need of governing of steam
turbines. With the help of a sketch,
discuss the working principle of a
hydromechanical speed-governing loop. 10
6.. In a solar water-heating system, a flat­
plate solar collector with no cover plate
is used to collect the solar radiation
to heat water. The surface emissivity of
the absorber is 0'15 while the solar
absorptivity is 0·96. At a time
of the day, the absorber temperature
is 120°C when the solar irradia­
tion is 800 ill2, the effective sky
temperature is -6°C. The ambient
temperature is 27 °C. Assume that the
heat transfer convection coefficient for
the calm dry condition is given by
h O· 23(Ts W1m 2_K
Assume steady-state condition, bottom
surface is well-insulated and the
absorber surface is diffused. Work out
the following
Sketch the system and its control
volume
The useful heat removal rate in
m 2 from the collector
The efficiency of the collector
State effect on collector efficiency
with reasoning, if the cover plate is
installed 20

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For an office of 6mx3mx4m SIze, the inside and outside conditions are dbt 22°C, 550/0 =45 kJI kg) and dbt 40°C, wbt 26°C 80-5 kJ/kg and v 0·94 m 3jkg of dry air) respectively. Further, it may be presumed that the office has structural load of 6000 kJIh, 5 tube lights each of 40 W ratings, 13'5 air changes per 24 hour for the infiltration load, x 10-3 m 3 Is per person of ventilatiop, 10 persons' occupancy and each occupant releases 500 kJIh.
Work out the capacity of a window
air-conditioner that will' suffice to
achieve the desired objective.
A steam power plant employs a wet­type cooling tower which receives warm water at 30°C at the rate of kg per kg of air. Air enters, the tower at the dbt of 20°C and relative humidity of 60% and leaves it at a dbt of 28°C and 900/0 relative humidity. Make-up water is added at 2a°C. Calculate­

the temperature of water leaving the tower;


the approach and range of the cooling tower;


the fraction of water evaporated.


B-JGT-J-NFB/21 8
For inlet and outlet air twq 15·2 °C =26·7 °C hI 43 kJ/kg dry air h2 83.5 kJ/kg dry air WI 0·00881 kg water vapour/ kg dry air w2 0 .02132 kgwatervapour/ kg dry air hv =84 kJjkg
7. fa) An industrial centrifugal compressor running at 9000 r.p.m. delivers 650 m 3 min of free air. The air is compressed from 1 bar and 30°C to a pressure ratio of with an isentropic efficiency of 0'86. Blades are radial at outlet and the flow velocity of 70 mls may be assumed throughout constant. The outer radius of impeller is twice the inner and the slip factor may be assumed as 0'92. At inlet, the blade area coefficient may be taken as 0·95. Work out the following:

Draw the system and show the compression process on h-s diagram. Also, draw velocity diagrams


The final temperature of air


The power input to compressor, if mechanical efficiency is 0·95
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I
L


The impeller diameter at inlet and outlet


The breadth of impeller at inlet


The impeller blade angle at inlet 20


A I5-stage 50% reaction turbine develops a diagram power of 10 MW. The inlet condition of stearn is at 15 bar, 350 while the condenser pressure is 0·14 bar. The stage efficiency is 750/0 for each stage and the reheat factor is 1·04. At a certain stage, the steam is at 1 bar, . dry saturated. The exit angle of the blades is 20° and the blade velocity ratio is 0·7. The blade height may be taken as 1/12 of the mean blade diameter. Work out the following:

The flow rate of steam required, assuming that all the stages develop equal work


The mean blade diameter


The speed of the rotor
Sketch the system and velocity diagrams, and show the process on h-s diagram
Given that enthalpy drop (from Mollier chart) 855 kJjkg. At 1 bar, v9= 1.694 m kg.
20
10
J

8. fa) Draw a labelled schematic diagram of
a modern radiant power boiler with
natural circulation. Clearly show
boiler drum, various accessories,
primary air and secondary air supply
systems, and feedwater system.
How is the balance draft created?
. Explain. 20
Differentiate between a base load and
a peak load power plant. Explain with
suitable examples.
A power plant caters to a peak load of
160 MW. It has an annual load factor of
capacity factor of 0·8 and use
factor of 0·82. Calculate­
the annual energy produced;
reserve c?-pacity over and above the
peak load;
hours during which the plant is not
. . m servlce per year;
annual revenue earned, if the
energy is sold at Rs 3 per kW. 20


lhTGT-J-NFB/21. 11 J8-3100