MECHANICAL ENGINEERING
Paper-11
(Time Allowed: Three Hours) Maximum Marks 200 J
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 only. If any data is considered insufficient, assume suitable value and indicate the same clearly. Newton may be converted to kgf using the equality Neat sketches may be drawn, wherever required. A psychrometric chart is attached to this question paper. Important Note All parts/sub-parts of a question must be attempted contiguously. That is, candidates must complete attempting all parts/sub-parts of a question being answered in the answer-book before moving on to the next question. Pages left blank, if any, in the answer-book(s) must be clearly struck out. Answers that follow pages left blank may not be given credit.
SECTION-A
1. 0·05 kg of carbon dioxide (molar mass 44 kg/kmol) is compressed from 1 bar, 15°C until the pressure is 8·3 bar, and the volume is then 0·004 m3 Calculate the change of entropy. Take CP for carbon dioxide as 0·88 kJ/kg and assume carbon dioxide to be a perfect gas. Represent the states on pressure-volume and on temperature-entropy diagrams. . I 0

Petrol used in SI engine is assumed to have a chemical formula c7H16 Determine
stoichiometric NF ratio.
If 50% excess air is supplied then find the volumetric composition of dry exhaust products. Air contains 23% of 0 2 77% of N 2 by Mass 10
A refrigerator has working temperatures in the evaporator and condenser as- 23°C and 37°C respectively. The environment temperature is 27"C. The required refrigeration temperature is -13°C. What is the maximum COP possible If the actual COP of the refrigerator is 0·65 of the maximum, calculate the required power input for a refrigerating effect of 5 kW. 10
List' the merits and demerits of pulverized coal firing system. Differentiate between pulverized dry-bottom furnace and wet-bottom furnace. I 0
2. A test on a single cylinder engine, four stroke having bore 180 mm and stroke 360 mm
yielded the following results
Speed 285 rev/min.
Brake Torque 393 Nm
IMEP 7.2bar
Fuel consumption 3·5 kg/hr
Cooling water flow 4·5: kg/min
Cooling water temp rise 36°C
NF ratio by mass 25
Exhaust gas temp. 415°C
Barometric pressure I·0 13 bM
Room temperature 21oc
Fuel has a calorific value 45200 kJ/kg and contains 15% by mass of hydrogen.Determine
indicated thermal efficiency.
The volumetric efficiency based on atmospheric conditions.
Draw up a heat balance in terms of kJ/min explaining cleMiy the content of such term.
Take R 0·287 kJ/kgK,
Cv for dry exhaust gases 1·005 kJ/kgK
CP for superheated steam 2·05 kJ/kgK. 15

Consider three fluids with Prandtl numbers of 0·01, 1 and 100 flowing in a circular tube. Calculate the ratio of the L1 h and L0 L1 h is the length.required to achieve a fully developed temperature profile and L is the length required to obtain a fully-developed e velocity profile. Assume that the flow is laminar and that the heat transfer takes place with a constant wall heat flux boundary condition. Comment on the Prandtl numbers given in· this problem. Give suitable example corresponding to these Prandtl numbers. Lth and Le at these Prandtl numbers and justify the same. I0
Why are down comers fewer in number and bigger in diameter, while risers are more in number and smaller in diameter in a water tube boiler Describe the working principle of a modern natural circulation boiler. What are the functions of pre heater, reheater, economizer and superheaters Where are these located I 5

3. Discuss the process of combustion in CI engine and also explain various stages of combustion. Discuss the factors- that affect the delay period. I 5
What is fouling What "is fouling factor ls fouling desirable
(B)Sea water below 50°C is. passed through the cooling coils of a large electromagnet The Heat transfer coefficient· with Clean coils is 2000 W Calculate the heat transfer coefficient including the effects of fouling. What is the percentage reduction in the value of the heat transfer coefficient Fouling factor for sea water is 0·0001 m 2 K/W.
In addition to thermal aspects of designing a heat exchanger, list other factors which need careful consideration. Which of these factors influence running cost What should the basis for optimising .design of a heat exchanger
What are the functions of a condenser in a steam power plant How does a cooling tower operate Define a dry cooling tower. When is it recommended
Explain the meaning of draught as applied to boilers. How is it produced by various methods Write down the specific advantages of balance draught system. 10+5

4. A 4 stroke single cylinder diesel engine develops a 36 kW when running at 800 rpm and consumes 240 gms/kWh. The pressure of the air in the cylinder at the beginning of injection and at the end of injection are 40 bar and 60 bar. The injection pressure at the beginning and end of injection are 200 bar and 600 bar respectively.Determine the diameter of the nozzle if the injection is carried out during 15° rotation of the crank. The ambient pressure and temp. are 1·013 bar and 27°C. C dr= 0·6 and pr 800 kg/m315
A vapour compression plant uses R134-a and has a suction temperature of and a condenser saturation temperature of 45°C. The vapour is dry saturated on entering the compressor and there is no under cooling of the condensate. The compression is carried out is entropically in two stages and a flash chamber is employed at an interstage saturation temperature of 15°C. Calculate
the amount of vapour bled off at the flash chamber;
the state of the vapour at the inlet to the second stage of compression;
the refrigerating effect per unit mass of refrigerant in the condenser;
the work done per unit mass of refrigerant in the condenser;
the coefficient of performance. Properties of R134-a are given below. Data for Rl34-a Saturation Values Superheat 15
t Sat. v h 20 K
g g t=Pressure- . s h s .

kJ/kg kJ/kg K
kJ/kg kJ/kg K kJ/kg kJ/kg K
2-4371 0·081 93-46 291·77 0·9760 1·7155 302·18 1·7536 312·05 1·7884
15 4·8734 0·042 120·06 303-38 1-0709 1·7071 314·86 1·7463 325·59 1·7817
45 11·5447 0·017 162·93 319·54 1·2105 1·7028 332·87 1·7440. 345·04 1·7804
With the help of a sketch, discuss the working principle of boiling water reactor and
explain in brief the function of main elements. I 0
SECTION-B
5. Given that
CP and Cv
obtain the expressions of
[acPJ . · 8p T and 8v T usmg Maxwell's and other relatiOns.
Using the above derived equations, show that C and C for an ideal gas are . p v
functions of temperature only. 1 0
(Contd.)

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6.
Discuss the three-way catalytic converter used in S.I. engines. Why isn't a normal
three-way catalytic converter, as used with S.I. engines as useful, when used with
C.I. engines
Discuss main methods used to limit Nox emissions on a modem automobile.
5+5=10
A mild steel tank of wall thickness 10 mm water at 90°C when the atlJ!ospheric
temperature is 1S°C. The thermal conductivity of mild steel is 50 W/ml.( and the heat
transfer coefficients for the inside and outside of the. tank are 2800 and 11 W/m2 K
respectively. Calculate
the rate of heat loss per unit area of tank surface.
the temperature of the outside surface of the tank. 10
Explain stalling and surging phenomenon in compressors with the help of head-discharge
curves. 10
An automobile has 3·2 liter five cylinder, four stroke cycle diesel engine operating at
2400 rpm. Fuel injection occurs from 20° bTDCto 5° aTDC. The engine has a volumetric
efficiency of 0·95 operates with fuel equivalence ratio of 0·80. Light diesel fuel is
used: The pressure is 101 kPa, Temp. 298 R.= 0·287 kJ!kg K. Calculate
time for one injection.
v-.. ·-
. Define effective temperature Does it" meet comfort cnteria Justify.
10
Define Bypass Factor Illustrate the influence of bypass factor on various
parameters. Is it desirable to have high bypass factor Discuss extreme possible
cases.
Discuss evaporative cooling with the help of a schematic diagram and psychrometric
chart. Discuss limitations of evaporative cooling.
In an industrial evaporative cooling application with summer outdoor design conditions
of 40°C DBT, 27"C WBT; the indoor is to be maintained at a maximum relative
humidity of 55%. The room sensible heat is 581·5 kW. All outdoor air must be
used. Find the room dry bulb temperature and supply air quantity as a function of
humidifying efficiencies of 80 and I 00%. Comment on the DBT in the room and
supply air quantity in both these cases.
The incremental fuel costs for two generating units a and b of a power plant are
given by the following relations
dFA =0·06PA +11·4
dPA
dF
0·07 P8 0
dPs
(Contd.)
• ..
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where P is the power in MW and F is the fuel cost in rupees per hour.
Find ihe economic loading of the two units when the total load to be supplied
by the power station is I 50 MW.
Find the net increase in fuel cost per hour if the load is equally shared by the
two units.
What are the• considerations to be made while selecting the suitable site for a
steam and a hydro power plant I 0+5
7. You are required to predict performance of a given heat exchanger. What method
would you use Why
A parallel.flow heat exchanger has a hot and a cold ·water stream running through
it. The flow rates are 10 and 25 kg/min and the inlet temperatures are 70°C
and 25°C on the hot and the cold side respectively. Calculate the area of the
heat exchanger if the individual heat transfer coefficients on both sides are
1600 W/m2 effects of fouling can be neglected; and the exit.temperature
01! the hot side. is required to be 50°C.
For the problem in above; calculate the exit temperature of the hot and cold
streams in this heat exchanger if the hot water'flow rate is doubl!!d to 20 kg/min
and it is known that the individual heat transfer coefficit;nts are proportional to the

0·8th power of the flow rates. . · ·- · •-··
Illustrate with the help .of of psychrometric chart, determination of:......
apparatus dew point using ESHF. Discuss extreme possible cases and measures
to be taken to overcome such cases.
A laboratory having an unusually large latent heat gain is required to be airconditioned.
The design conditions and the loads are as under
Summer outdoor design conditions 40° DBT, 27°C WBt
Indoor design conditions
Room Sensible Heat
DBT, RH
34·9 kW
Room Latent Heat 18,6 kW
The ventilation air requirement is 85 m3 /min. Determine the following
Ventiiation load
Room Sensible Heat Factor (RSHF) and Effective Sensible Heat Factor (ESHF)
Apparatus Dew Point and amount of reheat for economical design
Supply air quantity
Condition of air entering and leaving coil and .supply air temperature.
Grand Total Heat.
Assume a suitable bypass factor. Solve ·this problem using psychrometric
chart. I 0=15
(Contd.)
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Explain the influence ratio of blade speed to steam speed on blade efficiency of a
single stage impulse turbine. 15
8. Mention the cycles which have an efficiency equal to that of the Carnot cycle working
between given temperature limits T 1 and T
2
. these cycles on T-s diagram.
Prove for one of the cycles the expression for efficiency of the cycle is the same as that
of the Carnot cycle. Comment on the work ratio (net work out divided by gross work
output) of the cycle chosen and that of the Carnot cycle. 10
Define log mean temperature difference (LMTD.) Develop expression for LMTD
in a parallel-flow heat exchanger. How is this expression modified for counter-flow
heat exchanger? Under what situations, LMTD is independent of the flow arrangements
namely parallel-flow, counter-flow and cross-flow Give practical examples for
such situations.
Steam is condensed on the shell side of a shell-and-tube heat exchanger with the
help of cooling water flowing inside the tubes. The entering steam is saturated and at
a temperature of 1 00°C. It leaves as saturated water at the same temperature. The
cooling water enters the tubes at 30°C and leaves at 70°C. Calculate the log mean
. temperature difference (LMTD.) 0
. .. .. .... .. ·-· _....
A gas turbine power plant consists of a two stage compressor with 'intercooling and a
single stage turbine with a regenerator. Air enters the compressor at 1 bar, 20°C. The
maximum temperature of the cycle is limited to 900°C and the maximum pressure ratio
is 6. The effectiveness of the regenerator is 0·7. The rate of airflow through the plant
is 210 kg/sand the calorific value of fuel used is 40·8 MJ/kg. The isentropic efficiency
of both the compressors is 0·82, the isentropic efficiency of the turbine 0·92, the
combustion efficiency is 0·95.
Take for air Cp 1·005 kJ/kg K and y 1·4 and for gases, Cp 1·08 kJ/kg K and
y 1·33. Assuming perfect intercooling and neglecting pressure and heat losses, estimate
the air-fuel ratio
the cycle efficiency
the power supplied by the plant and
the specific fuel consumption of the plant and the fuel consumption per hour.
20
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Serial No. 2143 0-GT-M
Do not write your Roll No.
on this Sheet
MECHANICAL ENGINEERING
Paper-11
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PSYCHROMETRIC CHART
BAROMETRIC PRESSURE 1.01325 bar
SEA LEVEL
-10 15 20 25
DRY BULB TEMPERATURE, •c

BELOW 0 •c PROPERTIES AND ENTHALPY DEVIATION LINES ARE FOR ICE
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