MPPSC AE 2017: State Engineering Service Examination, Mechanical Engineering Paper-II
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We
RoU No.
700095
Candidate should write his/her Roll No. here.
Total No. of Questions : 7 No. of Printed Pages : 7
SEM-2017(03HI
MECHANICAL ENGINEERING
Paper—II
Time ; 3 Hours ] [ Total Marks : 300
Instructions to the candidates:
i c=3
i^
Please read each of thefollowing instructions carefully before 1 IB
attempting questions. i
Candidates should attempt FIVE questions in all.
Question No. 1 is compulsory. The remaining FOUR questions are to be
attempted by selecting anyfour out ofthese six questions Q2 to Q7.
All questions carry equal marks. The number of marks carried by a part
ofa question is indicated against it.
Answers must be written in ENGLISH only. Unless otherwise mentioned, symbols
and notations have their usual standard meanings. Assume suitable data,
if necessary and indicate the same clearly.
Neat sketches may be drawn, wherever required.
All parts and sub-parts ofa question are to be attempted together in the answer book.
\
Any pages left blank in the answer book must be clearly struck out.
SEM-2017/ME-2 [ P.T.O.
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1. (a) In new temperature scale say °p, the boiling and freezing points of water at
1 atmosphere pressure are 100° and 300° respectively. Correlate this scale
with centigrade scale. Find the value of 0 °p on the centigrade scale at
1 atmospheric pressure.
(b) A reversible heat engine receives 6 kJ of heat from the thermal reservoir at
800 K and 8 kJ of heat from another thermal reservoir at temperature of
600 K. If it rejects heat to a third thermal reservoir at a temperature of
100 K, find the thermal efficiency of the engine.
(c) For the maximum transmission of power through a pipeline -with total head
H, find the value of total head loss due to friction in terms of H. 6
(d) The sling psychrometer that is used to measure the condition of moist air
gives the following readings :
Dry-bulb temperature (DBT) = 35 °C, P^s/DBT—saturation pressure
at dry-bulb temperature is 0563 bar, wet-bulb temperature
(WBT) = 25 °C, Pys/WBT—saturation pressure at wet-bulb
temperature is -0317 bar.
Calculate specific humidity and vapor density of the air.
(e) A counterflow shell and tube heat exchanger are used to heat water with
hot exhaust gases.The water(Cp = 4180 J/kg-°C)flows at the rate of 2 kg/s
while the exhaust gas(Cp = 1030 J/kg-°C) flows at the rate of 5-25 kg/s. If
the heat transfer surface area is 32-2 m^ and the overall heat transfer
coefficient is 200 W/m^-°C, find NTU of heat exchanger.
(f) A solid copper ball of mass 500 grams when quenched in a very large size
water bath at 30 °C, cools from 530 °C to 430 °C in 10 seconds. Find the
temperature of the ball in next 10 seconds.
SEM-2017/ME-2
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( 3)
(g) The working temperatures in the evaporator and condenser coils of the
refrigerator are -30 °C and 32 °C respectively. If the actual refrigerator has
a COP of 0-75 of the maximum, find the required power input for a
refrigerating effect of 5 kW.
(h) A 40 kW engine has a mechanical efficiency of 80%. If the frictional power
is assumed to be constant with load, what is the approximate value of the
mechanical efficiency at 50% of the rated load?
(i) In a gas turbine, hot combustion products with the specific heats
Cp =0-98 kJ/kgK and C„ =0-7538 kJ/kgK, enter the turbine at 20 bar
and 1500 K and exit at 1 bar. The isentropic efficiency of the turbine is
0-94. Find the work developed by the turbine per kg of gas.
(j) Compare NC and CNC machines on the basis of different parameters.
2. (a) Two identical bodies of constant heat capacity are at the same initial
temperature 7). A refrigerator operates between these two bodies until one
body is cooled to temperature T2. If the bodies remain at constant pressure
and undergo no change of phase, show that the minimum amount of work
needed to do this work is
^r-2 ^
^(min) -
h J 30
(b) The internal energy of air is given by
u = UQ+0-718t
where u is in kJ/kg, Uq is any arbitrary value of u at 0 °C in kJ/kg and t is
the temperature in °C. Also for air P„ =0• 287(t +273), where p is in kPa and
V is in m^/kg.
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(4)
A mass of air stirred by a paddle wheel in an insulated constant volume
tank. The velocities due to stirring make a negligible contribution to the
internal energy of the air. Air flows out through a small valve in the tank at
a rate controlled to keep the temperature in the tank constant. At a certain
instance, the conditions are as follows :
Tank volume 0-12 m®, pressure 1 MPa, temperature 150 °C, and
power to paddle wheel 0-1 kW.
Find the rate of flow of air out of the tank at this instant. 30
(a) Two parallel plates kept 0-1 m apart have laminar flow of oil between them
with a maximum velocity of 1-5 m/s. Calculate the discharge per metre
width, the shear stress at the plates, the difference in pressure in pascals
between two points 20 m apart, the velocity gradient at the plates and
velocity at 0-02 m from the plate. Take viscosity of oil to be 2-453 N.s/m^. 30
(b) Air flows over a flat plate 1 m long at a velocity of 6 m/s.
Determine—
(i) the boundary layer thickness at the end of the plate;
(ii) shear stress at the middle of the plate;
(Hi) total drag per unit length on the sides of the plate.
Take p = 1-226 kg/m^ and u =0-15x10"'^ m^/s for air. 30
4. (a) An inward flow reaction turbine discharges radially and the velocity of flow
is constant and equal to the velocity of discharge from the turbine. Show
that the hydraulic efficiency can be expressed by
h=— ^
tan^ a
.4
1+-
tana ]
1-
tan0 J
where a and 0 Eire respectively the guide vane angle and wheel vane angle
at inlet. 30
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(b) The temperature limits of an NH3 refrigeration system are 25 °C and
-10 °C. If the refrigerator is dry saturated at the end of compression and
the refrigerant leaves as saturated liquid at the end of condenser, calculate
COP. Use the following table ;
1
t(°C)
0
hf (kJ/kg) LH (kJ/kg) Sf (kJ/kg-K)
0
0
25 °C 298-9 1166-94 1-1242
135-37 1297-68 0-5443
where,
hf—enthalpy of saturated liquid (kJ/kg)
LH—latent heat of vaporization (kJ/kg)
Sf—entropy of saturated liquid (kJ/kg-K) 30
5. (a) A gas turbine plant's turbine and compressor isentropic efficiencies are
85% and 86%. The maximum cycle temperature is 875 °C. The working
fuel can be taken as air (Cp = 1 kJ/kgK and y = 1 • 4), which enters the
compressor at 1 atm pressure and 27 °C. The pressure ratio is 4. The fuel
used has a calorific value of 42000 kJ/kg. There is a loss of 10% calorific
value in the combustion chamber. Calculate the thermal efficiency and air
fuel ratio of the gas turbine plant. 30
(b) An adiabatic steam turbine receives diy-saturated steam at 1 MN/m^ and
discharges it at 0-1 MN/m^. The steam flow rate is 3 kg/s and the
moisture at exit is negligible at the ambient temperature. Calculate the
power output of the turbine and its isentropic efficiency. 30
Properties of steam are given below :
(MN/m2) ^^sat (°C) hf (kJ/kg) hg (kJ/kg) Sf (kJ/kg-K) Sg (kJ/kg-K)
1-0 179-9 762-8 2778-7 2-139 6-586
0-1 99-6 417-5 2675-5 1-303 7-359
where f—saturated liquid, g—saturated vapor.
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6. (a) Two concentric cylinders having diameters of 10 cm and 20 cm have a
length of 20 cm. Calculate the shape factors between the open ends of
cylinders.. Given that
F21 =0-4126
F22 =0• 3286
where 1 stands for inner cylinder and 2 stands for outer cylinder. 30
(b) Hot water at 98 °C flows through a 2-in schedule 40 horizontal steel pipe
[k = 54 W/m °C] and is exposed to atmospheric air at 20 °C. The water
velocity is 25 cm/s. Calculate the overall heat-transfer coefficient for this
situation, based on the outer area of pipe.
Given that, the dimensions of 2-in schedule 40 pipe are
ID = 2-067 in = 0-0525 m
CD = 2-375 in = 0-06033 m
Properties of water at 98 °C : p .= 960 kg/m^, p = 2-82 x 10""* kg/m-s,
k = 0-68 W/m °C, Pr = 1-76. 30
7. faj Explain in detail about the thermodjmamic, chemical and physical
requirements of a refrigerant. Also vsrrite the chemical formula of following
refrigerants : 20
fij R-12
(n) R-114
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(Hi) R-134
(iv) R-718
(b) Explain different lypes of industrial robots in detail with neat sketches. 20
(c) What do you understand by automated material handling system? Explain
in detail about different lypes of material heindling devices used in
manufacturing industries. 20
★★★
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Source: Madhya Pradesh Public Service Commission. Question paper published by Madhya Pradesh Public Service Commission.