Exam Details
| Subject | mechanical engineering | |
| Paper | paper 2 | |
| Exam / Course | indian forest service | |
| Department | ||
| Organization | union public service commission | |
| Position | ||
| Exam Date | 2015 | |
| City, State | central government, |
Question Paper
I.F.S. EXAM-2015
MECHANICAL· ENGINEERING
Paper-II
Time Allowed Three Hours Maximum Marks 200
QUESTION PAPER SPECIFIC INSTRUCTIONS
Please read each of the following instructions carefully before attempting questions There are EIGHT questions in all, out of which FIVE are to be attempted. Question Nos. 1 and 5 are compulsory. Out of the remaining SIX questions, THREE are to be attempted selecting at least ONE question from each of the two Sections A and B. Attempts of questions shall be counted in sequential order. Unless struck off. attempt of a question shall be counted even if attempted partly. Any page or portion of the page left blank in the Questioncum- Answer Booklet must be clearly struck off All questions carry equal marks. The number of marks carried by a question/part is indicated against 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 c(ear/y.
Neat sketches may be drawn, wherever required. I Newton. may be converted to kg[ using the equality 1 kilonewton kN) 100 kg/. if found necessary. All answers should be in SJ units. Take 1 kcal 4.187 kJ and 1 kg/cm1 0.98 bar 1 bar I 05 pascals Universal gas constant 8314.6 Jlkmol-K Psychrometric chart is enclosed
SECTION-A
Q.l(a) Mention what are the requirements oflgnition System for J.C. Engine. 5
Q.1(b) What do you mean by Scavenging Discuss Ideal Scavenging and its limitations. 5
Q.l(c) Explain Air Cooling System for LC. Engine.
Q.l(d) Why is excess air always required to be supplied for combustion What is excess air factor 5
Q.l(e) Explain what is meant by critical thickness of insulation. 5
Q.l(f) A refrigeration system exhibits a COP one half of the Carnot cycle operating between the same temperature limits. It removes 600 kJ/min from a reservoir at -100 °C while upper temperature
is maintained at 200 °C. How much energy is rejected to the high temperature reservoir? If the refrigerator was reversed to operate as an engine what is the power developed 5
Q.l(g)Explain Joule Thomson coefficient. What is inversion temperature Show the inversion curve and explain the features. 5
Q. Two equal parallel black discs 0.5 m diameter are located at 0.25 m apart and directly opposite to each other. If the temperatures of the discs are 200 °C and 50 calculate the net heat exchange between them per square meter area. Assume the view factor for this configuration between the plates 0.38. 5
Q.2(a) The roof of a hemispherical furnace 0.8) of radius 1 m is maintained at 800 while the temperature of the flat circular floor 0.5) is at 600 K. Calculate the heat loss. What will be the heat loss if both the floor and the roof would have been black?l0
Q.2(b) A full load test on a two-stroke engine yielded the following results:
Speed 440 rpm
Brake load 490.5 N
IMEP 3 bar
Fuel Conswnption 5 .4 kg/hour
Rise in jacket water temperature 36 °C
Jacket water flow 450 kg/hour
Air fuel ratio by mass 30 l
Temperature of exhaust gas 360 °C
Temperature of the test room 19 °C
Barometric pressure 76 cm of Hg
Cylinder diameter 22 cm
Stroke 25 cm
Brake diameter 1.20 m
Calorific value of fuel 43000 kJ/kg
Proportion of hydrogen by mass in the fuel 15%
Given,
Rair 0.287 kJ/kgK, CP of water 4.18 kJ/kgK
Specific heat of dry exhaust gases 1 kJ/kgK
Specific heat of dry steam 2 kJ/kgK
Assume enthalpy of superheated steam to be 3180 kJ/kg. Calculate,
the indicated thennal efficiency
the specific fuel consumption in kg/kWh
volumetric efficiency based on atmospheric conditions.
Draw up a heat balance for the test on the percentage basis indicating the content of each item in the balance. 20
Q.2(c) Calculate the available energy in 40 kg of water at 75°C with respect to the surroundings at the pressure being 1 bar. l0
Q.3(a) Helium contained in a cylinder with piston expands according to the ]aw py l .2 C from 20 ml, 5 bar, 220 K to a pressure of 2 bar. Calculate the work done and heat transfer during the process. For helium molecular weight 4.0, CP 5.2 kJ/kg K and 1.66. IO
Q.3(b) Air flows at the rate of 0.5 kg/s through an air compressor, entering at 7 mis velocity, 100 kPa pressure and 0.95 m3/kg specific volume and leaving at a velocity of 5 mis, pressure 700 kPa and specific volume 0.19 ml/kg. The internal energy of the air leaving is 90 kJ/kg less than that at entry. Cooling water in the compressor jackets absorbs 58 kW of heat. Compute the rate of shaft work input to the air and also calculate the ratio of inlet pipe to outlet pipe diameter. 10
Q.3(c) The vqlumetric analysis of a fuel gas used in a boiler is given as: C2H6 22.6%, CH4 73.6%, CO2 and N2 1.4%. Assuming combustion air to be dry and in 25% excess, find the
The molecular weight of the combustion products
the total gas volume for complete combustion at 260°C, 1.013 bar and
the dry flue gas analysis based on CO2, .02 and N2• 20
Q.4(a) Explain the characteristic features of a Pressurized Water Reactor with the help of a neat sketch. 10
Q.4(b) Explain what do you mean by Rayleigh Flow. What are the assumptions made Write down the governing .equations for Rayleigh Flow. With the help of h-s diagram, show the occurrence of Normal Shock in Rayleigh Flow. 10
Q.4(c) Derive an expression for the temperature distribution for the case of a homogeneous cylinder With uniformly distributed heat source of strength q W/m3 and hence show that T-Tw/Te-Tw=1 where T w is the surface temperature and Tc is the centre temperature for a one dimensional steady state conduction. 15
Q.4(d) Compare between water tube boiler and fire tube boiler. 5
SECTION-B
Q.S(a) In vapour compression refrigeration for an ideal refrigerant, it is desirable that the evaporator pressure should be positive and neat atmospheric. Explain why. 5
Q.5(b) Show that in an ideal gas turbine cycle, the optimum pressure ratio corresponding to which the network output is maximum is given by, r0ptimum (Tmax/Tmin )t/2where T max and T min are the maximum and minimum temperatures in the cycle. 5
Q.S(c) Show in the form of a table, how do the following properties change in a sensible cooling process and, a cooq and dehumidifying process. Show the processes on a skeleton psychrometric chart Dry bulb temperature, Wet bulb temperature, Dew point temperature, specific humidity and relative hwnidity. 5
Q. 5 Show in the form of a table, how the following flow parameters change in the rotor and stator blades of a 50% reaction axial flow compressor stage Absolute velocity Static temperature Static pressure Stagnation temperature and Stagnation pressure. Draw the corresponding T-s diagram. 5
Q.5(e) What is a Surge tank Explain its importance in a hydroelectric power plant. 5
Q.5(f) Explain what do you mean by Kinetic Energy Correction factor. While considering flow through a round pipe, does its value remain constant both for Laminar and Turbulent flows If not, explain why.
Q.5(g) Write down the steady flow energy equation and reduce it to apply for the following systems Centrifugal water pump Steam turbine Steam Nozzle. 5
Q.5(h) A stationary mass of gas is compressed without friction from an initial state of 0.3 m3 0.105 MPa to a final state of0.15 m3 and 0.105 MPa, the pressure remaining constant. During the process, an amount of 37.6 kJ of heat is rejected by the gas. What is the change in internal energy of the gas during the process 5
Q. An ammonia ice plant operates between a condenser temperature of 35°C and an evaporator temperature of It produces 10 tons of ice per day from water at 30°C to ice at The refrigerant is dry and saturated at the end of compression. Determine
the capacity of the refrigeration plants in TR
the mass flow rate of the refrigerant in kg/h
C.O.P.
Properties of Ammonia
Sat. Temp. °C Sat. liquid Sat. vapour Sat. liquid Sat. vapour
enthalpy
enthalpy entropy. entropy
kJ/kg kJ/kg kJ/kg-K kJ/kg-K
112.3 1426.0 0.457 5.549
I
35 347.5 1471.0 1.282 4.930
Take C 4..1868 kJ/kg..K 1.94 kJ/kg-K
P
CP
water
.
Ice
Latent heat of fusion of ice 335 kJ/kg
15
.
Q.6(b)
Explain the functions of a steam superheater and reheater in a steam power plant. With the help
of T-s diagram, explain howdo they affect the performance of the steam power plant. 10
.
Q.6( Water enters a counterflow do·ublc pipe heat exchanger at l 5 C flowing at a rate of
1300 kg/hr. It is heated by an oil 2.000 flowing at the rate of 550 kg/hr with
p
an inlet temperature of 94 C. For an area of 1 m2 and an overall heat transfer coefficient of
1075 W/m2K, determine the total heat transfer and outlet temperatures of water and oil.
Assume for counterflow exchanger·:
-NTu(t
CnlRX
l e
15
Q.7(a)
Using Buckingham's 1t-Theorcm method, derive suitable parameters to present the thrust developed
by a propeller. Assume that the thrust P depends on the
angular velocity co
speed of advance v
diameter D
dynamic viscosity µ
Mass density p
Elasticity of the fluid medium which can be denoted by the speed of sound in the
medium C. 15
Q.7(b) Explain Reynold's model law and its applications. 5
r.
I I
O-NFF8
Q.7(c) 1 A centrifugal compressor running at 16000 rpm takes in air at 17 °C and 1 bar, and compresses
it through a pressure ratio of 4 1 with an isentropic efficiency of 82 percent. The blades are
radially inclined and the slip factor is 0.85. Guide vanes at inlet give the air an angle of prewhirl
of 20° to the axial direction. The mean diameter of the impeller eye is 200 mm and the
absolute air velocity at inlet is 120 mis. Calculate the impeller tip diameter.
Take CP 1.005 kJ/kg-K and y 1.4
Draw the T-s diagram and the velocity triangles at the impeller inlet and impeller tip. 20
Q.8(a) Show that for equimolal counter diffusion of a two component system as shown in figure, the
no. of moles diffused, NA is given by the following relation
NA DA(pA1 CD
. RJ(X2-X1)
I I
NA..-.
where:o is the diffusion coefficient. -.. NB
X
10
Figure
Q.8(b)
An air-conditioned room is maintained at 25 °C DBT and 50 percent RH. The ambient
conditions are 40 °C DBT and 27 °C WBT. The air-handling unit supplies a total of 4500 cnun
ofury air which comprises, by weight, 20 percent fresh air and 80 percent recirculated air at
the room conditions. The air leaves the cooling coil at 13 °C saturated state. Calculate
Fresh air load
t
Room heat gain
Total cooling load.
Draw the configuration and show the process on psychrometric diagram. 15
..
t
Qo not wHte your Roll No.
on Ulis Sheet
MECHANICAL ENGINEERING Paptr-11 120 1 4_5 130 140145
. .,.0;35 I
..
.. PS-YCHROMETRIC CHART
BAROMETRIC PRESSURE 1.01 325 bar
SEA t.EVEL ,..,.....
b.40
0.45
Ii"N
..
·..
.. 12
ro
·a: o·.so g
o..., ..
0.60 ..
0.65 ffi
0.70
0.75
0.80
?II
0.90
111 0.95
1.00
119
118
.007 ....
1.006 ffi
...
,.aos z c
WQ
0.003
,.1J02
a
1.001 0 ..
51OJIGO
15 20 25
PRY BULB TEMPERATURE,
C
... m3.. ..m.. ....m.. O..m.
SPECIAC VOLUME, m3/kg DRY AIR
BELOW O "C PROPERTIES ANO ENTHALPY DEVIATION LINES ARE FOR ICE
Q.8(c) The original value of an equipment is Rs. 5,00,000/-and its salvage value at the end of its useful
life of 20 years is Rs. 50,000/-. Find the value of the equipment at the end of IO years of its
use by the following methods
Straight line depreciation and
Sinking fund depreciation
when it is compounded annually at the rate of 8%. 10
Q...(d) What is the function of the draught system in a steam power plant Derive an expression to
show that for a given chimney height and ambient air temperature, the draught is a function of
the flue gas temperature. 5
MECHANICAL· ENGINEERING
Paper-II
Time Allowed Three Hours Maximum Marks 200
QUESTION PAPER SPECIFIC INSTRUCTIONS
Please read each of the following instructions carefully before attempting questions There are EIGHT questions in all, out of which FIVE are to be attempted. Question Nos. 1 and 5 are compulsory. Out of the remaining SIX questions, THREE are to be attempted selecting at least ONE question from each of the two Sections A and B. Attempts of questions shall be counted in sequential order. Unless struck off. attempt of a question shall be counted even if attempted partly. Any page or portion of the page left blank in the Questioncum- Answer Booklet must be clearly struck off All questions carry equal marks. The number of marks carried by a question/part is indicated against 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 c(ear/y.
Neat sketches may be drawn, wherever required. I Newton. may be converted to kg[ using the equality 1 kilonewton kN) 100 kg/. if found necessary. All answers should be in SJ units. Take 1 kcal 4.187 kJ and 1 kg/cm1 0.98 bar 1 bar I 05 pascals Universal gas constant 8314.6 Jlkmol-K Psychrometric chart is enclosed
SECTION-A
Q.l(a) Mention what are the requirements oflgnition System for J.C. Engine. 5
Q.1(b) What do you mean by Scavenging Discuss Ideal Scavenging and its limitations. 5
Q.l(c) Explain Air Cooling System for LC. Engine.
Q.l(d) Why is excess air always required to be supplied for combustion What is excess air factor 5
Q.l(e) Explain what is meant by critical thickness of insulation. 5
Q.l(f) A refrigeration system exhibits a COP one half of the Carnot cycle operating between the same temperature limits. It removes 600 kJ/min from a reservoir at -100 °C while upper temperature
is maintained at 200 °C. How much energy is rejected to the high temperature reservoir? If the refrigerator was reversed to operate as an engine what is the power developed 5
Q.l(g)Explain Joule Thomson coefficient. What is inversion temperature Show the inversion curve and explain the features. 5
Q. Two equal parallel black discs 0.5 m diameter are located at 0.25 m apart and directly opposite to each other. If the temperatures of the discs are 200 °C and 50 calculate the net heat exchange between them per square meter area. Assume the view factor for this configuration between the plates 0.38. 5
Q.2(a) The roof of a hemispherical furnace 0.8) of radius 1 m is maintained at 800 while the temperature of the flat circular floor 0.5) is at 600 K. Calculate the heat loss. What will be the heat loss if both the floor and the roof would have been black?l0
Q.2(b) A full load test on a two-stroke engine yielded the following results:
Speed 440 rpm
Brake load 490.5 N
IMEP 3 bar
Fuel Conswnption 5 .4 kg/hour
Rise in jacket water temperature 36 °C
Jacket water flow 450 kg/hour
Air fuel ratio by mass 30 l
Temperature of exhaust gas 360 °C
Temperature of the test room 19 °C
Barometric pressure 76 cm of Hg
Cylinder diameter 22 cm
Stroke 25 cm
Brake diameter 1.20 m
Calorific value of fuel 43000 kJ/kg
Proportion of hydrogen by mass in the fuel 15%
Given,
Rair 0.287 kJ/kgK, CP of water 4.18 kJ/kgK
Specific heat of dry exhaust gases 1 kJ/kgK
Specific heat of dry steam 2 kJ/kgK
Assume enthalpy of superheated steam to be 3180 kJ/kg. Calculate,
the indicated thennal efficiency
the specific fuel consumption in kg/kWh
volumetric efficiency based on atmospheric conditions.
Draw up a heat balance for the test on the percentage basis indicating the content of each item in the balance. 20
Q.2(c) Calculate the available energy in 40 kg of water at 75°C with respect to the surroundings at the pressure being 1 bar. l0
Q.3(a) Helium contained in a cylinder with piston expands according to the ]aw py l .2 C from 20 ml, 5 bar, 220 K to a pressure of 2 bar. Calculate the work done and heat transfer during the process. For helium molecular weight 4.0, CP 5.2 kJ/kg K and 1.66. IO
Q.3(b) Air flows at the rate of 0.5 kg/s through an air compressor, entering at 7 mis velocity, 100 kPa pressure and 0.95 m3/kg specific volume and leaving at a velocity of 5 mis, pressure 700 kPa and specific volume 0.19 ml/kg. The internal energy of the air leaving is 90 kJ/kg less than that at entry. Cooling water in the compressor jackets absorbs 58 kW of heat. Compute the rate of shaft work input to the air and also calculate the ratio of inlet pipe to outlet pipe diameter. 10
Q.3(c) The vqlumetric analysis of a fuel gas used in a boiler is given as: C2H6 22.6%, CH4 73.6%, CO2 and N2 1.4%. Assuming combustion air to be dry and in 25% excess, find the
The molecular weight of the combustion products
the total gas volume for complete combustion at 260°C, 1.013 bar and
the dry flue gas analysis based on CO2, .02 and N2• 20
Q.4(a) Explain the characteristic features of a Pressurized Water Reactor with the help of a neat sketch. 10
Q.4(b) Explain what do you mean by Rayleigh Flow. What are the assumptions made Write down the governing .equations for Rayleigh Flow. With the help of h-s diagram, show the occurrence of Normal Shock in Rayleigh Flow. 10
Q.4(c) Derive an expression for the temperature distribution for the case of a homogeneous cylinder With uniformly distributed heat source of strength q W/m3 and hence show that T-Tw/Te-Tw=1 where T w is the surface temperature and Tc is the centre temperature for a one dimensional steady state conduction. 15
Q.4(d) Compare between water tube boiler and fire tube boiler. 5
SECTION-B
Q.S(a) In vapour compression refrigeration for an ideal refrigerant, it is desirable that the evaporator pressure should be positive and neat atmospheric. Explain why. 5
Q.5(b) Show that in an ideal gas turbine cycle, the optimum pressure ratio corresponding to which the network output is maximum is given by, r0ptimum (Tmax/Tmin )t/2where T max and T min are the maximum and minimum temperatures in the cycle. 5
Q.S(c) Show in the form of a table, how do the following properties change in a sensible cooling process and, a cooq and dehumidifying process. Show the processes on a skeleton psychrometric chart Dry bulb temperature, Wet bulb temperature, Dew point temperature, specific humidity and relative hwnidity. 5
Q. 5 Show in the form of a table, how the following flow parameters change in the rotor and stator blades of a 50% reaction axial flow compressor stage Absolute velocity Static temperature Static pressure Stagnation temperature and Stagnation pressure. Draw the corresponding T-s diagram. 5
Q.5(e) What is a Surge tank Explain its importance in a hydroelectric power plant. 5
Q.5(f) Explain what do you mean by Kinetic Energy Correction factor. While considering flow through a round pipe, does its value remain constant both for Laminar and Turbulent flows If not, explain why.
Q.5(g) Write down the steady flow energy equation and reduce it to apply for the following systems Centrifugal water pump Steam turbine Steam Nozzle. 5
Q.5(h) A stationary mass of gas is compressed without friction from an initial state of 0.3 m3 0.105 MPa to a final state of0.15 m3 and 0.105 MPa, the pressure remaining constant. During the process, an amount of 37.6 kJ of heat is rejected by the gas. What is the change in internal energy of the gas during the process 5
Q. An ammonia ice plant operates between a condenser temperature of 35°C and an evaporator temperature of It produces 10 tons of ice per day from water at 30°C to ice at The refrigerant is dry and saturated at the end of compression. Determine
the capacity of the refrigeration plants in TR
the mass flow rate of the refrigerant in kg/h
C.O.P.
Properties of Ammonia
Sat. Temp. °C Sat. liquid Sat. vapour Sat. liquid Sat. vapour
enthalpy
enthalpy entropy. entropy
kJ/kg kJ/kg kJ/kg-K kJ/kg-K
112.3 1426.0 0.457 5.549
I
35 347.5 1471.0 1.282 4.930
Take C 4..1868 kJ/kg..K 1.94 kJ/kg-K
P
CP
water
.
Ice
Latent heat of fusion of ice 335 kJ/kg
15
.
Q.6(b)
Explain the functions of a steam superheater and reheater in a steam power plant. With the help
of T-s diagram, explain howdo they affect the performance of the steam power plant. 10
.
Q.6( Water enters a counterflow do·ublc pipe heat exchanger at l 5 C flowing at a rate of
1300 kg/hr. It is heated by an oil 2.000 flowing at the rate of 550 kg/hr with
p
an inlet temperature of 94 C. For an area of 1 m2 and an overall heat transfer coefficient of
1075 W/m2K, determine the total heat transfer and outlet temperatures of water and oil.
Assume for counterflow exchanger·:
-NTu(t
CnlRX
l e
15
Q.7(a)
Using Buckingham's 1t-Theorcm method, derive suitable parameters to present the thrust developed
by a propeller. Assume that the thrust P depends on the
angular velocity co
speed of advance v
diameter D
dynamic viscosity µ
Mass density p
Elasticity of the fluid medium which can be denoted by the speed of sound in the
medium C. 15
Q.7(b) Explain Reynold's model law and its applications. 5
r.
I I
O-NFF8
Q.7(c) 1 A centrifugal compressor running at 16000 rpm takes in air at 17 °C and 1 bar, and compresses
it through a pressure ratio of 4 1 with an isentropic efficiency of 82 percent. The blades are
radially inclined and the slip factor is 0.85. Guide vanes at inlet give the air an angle of prewhirl
of 20° to the axial direction. The mean diameter of the impeller eye is 200 mm and the
absolute air velocity at inlet is 120 mis. Calculate the impeller tip diameter.
Take CP 1.005 kJ/kg-K and y 1.4
Draw the T-s diagram and the velocity triangles at the impeller inlet and impeller tip. 20
Q.8(a) Show that for equimolal counter diffusion of a two component system as shown in figure, the
no. of moles diffused, NA is given by the following relation
NA DA(pA1 CD
. RJ(X2-X1)
I I
NA..-.
where:o is the diffusion coefficient. -.. NB
X
10
Figure
Q.8(b)
An air-conditioned room is maintained at 25 °C DBT and 50 percent RH. The ambient
conditions are 40 °C DBT and 27 °C WBT. The air-handling unit supplies a total of 4500 cnun
ofury air which comprises, by weight, 20 percent fresh air and 80 percent recirculated air at
the room conditions. The air leaves the cooling coil at 13 °C saturated state. Calculate
Fresh air load
t
Room heat gain
Total cooling load.
Draw the configuration and show the process on psychrometric diagram. 15
..
t
Qo not wHte your Roll No.
on Ulis Sheet
MECHANICAL ENGINEERING Paptr-11 120 1 4_5 130 140145
. .,.0;35 I
..
.. PS-YCHROMETRIC CHART
BAROMETRIC PRESSURE 1.01 325 bar
SEA t.EVEL ,..,.....
b.40
0.45
Ii"N
..
·..
.. 12
ro
·a: o·.so g
o..., ..
0.60 ..
0.65 ffi
0.70
0.75
0.80
?II
0.90
111 0.95
1.00
119
118
.007 ....
1.006 ffi
...
,.aos z c
WQ
0.003
,.1J02
a
1.001 0 ..
51OJIGO
15 20 25
PRY BULB TEMPERATURE,
C
... m3.. ..m.. ....m.. O..m.
SPECIAC VOLUME, m3/kg DRY AIR
BELOW O "C PROPERTIES ANO ENTHALPY DEVIATION LINES ARE FOR ICE
Q.8(c) The original value of an equipment is Rs. 5,00,000/-and its salvage value at the end of its useful
life of 20 years is Rs. 50,000/-. Find the value of the equipment at the end of IO years of its
use by the following methods
Straight line depreciation and
Sinking fund depreciation
when it is compounded annually at the rate of 8%. 10
Q...(d) What is the function of the draught system in a steam power plant Derive an expression to
show that for a given chimney height and ambient air temperature, the draught is a function of
the flue gas temperature. 5