Exam Details
| Subject | mechanical engineering | |
| Paper | paper 2 | |
| Exam / Course | indian forest service | |
| Department | ||
| Organization | union public service commission | |
| Position | ||
| Exam Date | 2010 | |
| City, State | central government, |
Question Paper
Indian' FcneslSe.'Yvi ce
0362
IB-JGT-K-NFBI
..
MECHANICAL ENGINEERING Paper II
ITime Allowed: Three.Hoursl IMaximum Marks: 200I
INSTRUCTIONS
. Candidates should .attempt 1 and 5 which are compulsory, and ofthe remaining questions, selecting at lea:st ONE question from each Section.
All questions carry equal marks. . Marks allotted to parts ofa question are indicated against each.
Answers must be written in ENGLISH only.
If any data is considered in;sufficient, assume suita;blevu.lue and indicate the same clearly. Newton may be converted to kgf using the equality 1 kilonewton kN) 100 kgf, iffound necessary.
All answers should be in 81 units.
Take: 1 kccil.=.4·187 kJ and 1 kglcm2 =0·98 bar
1 bar =105 pascals.
Universal gas constant =8314'6 Neat sketches may be drawn, wherever required. I· .-A psychrometric chart is attached to, and forms part ofthis question paper.
B-JGT-K-NFB 1 IContd.]
SECTION A
1. For a gas, the equation of state is as
below over a certain range of temperatures and
pressures: V a h were a IST constant.
Prove that the change in enthalpy is given by
4a .
3 T {PI for isothermal process. Also find
out the expression for change of entropy. 8
What"js the function of a catalyst in the catalytic
converter for smoke emission control? What are
" .
the oxidation and reduction processes that take
place? Why is unleaded petrol preferred in cars
fitted with catalytic converter? 8
What do you mean by compact heat exchanger?
What are their applications? 8 ..
Describe the malO sources of evaporative
emissions in a S.1. engine. 8
A metal plate size,500 mm x 800 mm x 20 mm
and thermal conductivity 30· WattJrn-C IS
maintained at 250o q. Air at 20°C is blowing over
the plate. If convection heat transfer coefficient is
25 W/m2C and 200 v..7 is lost" by the plate by .j
radiation, compute the inside temperature. 8
.2. Consequent upon first law of thermodynamics,
show .that the heat is a path function. 7
Using pressure time diagram, explain the
combustion process in diesel engine. 8
B-JGT-K-NFB 2
The following, data relates a four-stroke coal gas Bore and stroke of cylinder 380 mm and' 585 mm respectively At 240 rpm, torque developed =5·16 kNm Coal gas to air mixture ratio to 7by volume Estimated volumetric efficiency
Net calorific value of coal gas 16800 kJlkg Calculate the brake power, brake mean effective pressure, piston speed in meter per second and
brake thermal efficiency. 20
Draw the labelled schematic diagram of a
common rail injectio.n system in a C.I. engine.
3. The cylinder volume of an I.e. engIne' is 3000 cm3. It contains products of combustion in gaseous form, which can be assumed to be an ideal gas. The combustion products, just before the exhaust valve opens, are at pressure ,of
6. bar and temperature of 1123 K. Assuming specific heats at constant volume and constant pressure as 0·718 and 1·005. kJ/kg-K respectively, analyse and discuss the availability of specific energy of the gas. The initial pressure and temperature of gas can be taken as 1 bar and 15°C respectively. 10
What are the characteristics of liquid oil, coal-oil mixture, natural and gas fuels? What are their major constituents Where are they suitably used 15
B-JGT-K-NFB. 3
lContd.J
A'sample of coal contains 93% carbon, hydrogen and rest ash. A test was conducted in a Bomb calorimeter using 0·92 kg of coal burnt and following data obtained:
Weight of water taken' 550 Water of Bomb calorimeter 2200 gIn, Rise in temperature of water' Fuse wire correction 10 cal, Acid correction 50 cal. Taking latent heat of condensation of steam as 530 caVgm, calCulate .gross and net calorific value of coal. 15
4. The air-conditioning unit of a pressurised jet aircraft receives its air from the compressor driven by the at a pressure of 1·4 bar. The pressure and temperature of the surrounding air at the height of the aircraft are 0·2 bar and 225 respectively." The air-conditioning unit consists of a secondary compressor and a turbine mounted on the same shaft. The pressure and temperature of air leaving the turbine are 1 bar and K. Calculate the pressure after the secondary compressor and temperature of air at. the exit from the cooler. Assume that all
. are reversible adiabatic. 20
Cold air is to be supplied for a library at a rate of
" 100 m 3/min. The air is to enter the building at 20°C with 40% relative humidity. Suppose. the atmospheric air is at 35°C with 70% relative suggest a suitable and estimate the rates of cooling and "heating required. 20
B-JGT-K-NFB 4 {Contd.l
SECTION B
5. Describe in brief how the fly ash is disposed off by (dry and twet system'. What problems are caused by present systems of fly ash disposal? Give the applications of fly ash. 8
Name the essential parts of a centrifugal. . compressor along with their functioning. Sketch a simple figure of a 'diffuser' and write down the . names of important parts. 8
With the help of figure, describe the working of 'Velox boiler'. Enumerate its advantages. 8
Derive the for temperature distribution for a fin insulated the end. The base temperature of fin is constant. Write typical application for this type of fin. 8
Describe the desirable properties of refrigerants suitable for ice plant applications. Name a few of these. 8
• 6. Prove that the simple arithmetic mean temperature difference gives results within . cqmpared to LMTD when the. ratio of end temperature differences is not more than 2·2. 7
B-JGT-K-NFB
5 lContd.]
..
...
A vapour compression refrigerator uses R-12 as refrigerant and the liquid evaporates In the evaporator at -15°C. The temperature of this refrigerant at the delivery from the compressor is 15°G when the vapour is condensed at 10°C.. Find the coeffiCient of performance if there is
. no under cooling the liquid is cooled 5°C before expansIOn by throttling. Take specific
..
heat constant pressure for the superheated vapour as. 0·64 kJlkg-K and that for liquid as 0·94 kJ/kg-K. The properties of refrigerant are as given below:
Temp Enthalpy Entropy °C in kJ/kg in kJlkg-K Liquid Vapour Liquid Vapour -15 22·3 180·88 0-0904" 0·7051
+10 45·4 191·76 0-.1750 0·6921
What are' the methods used to reduce the 'heat radiation between two parallel plates? Write the process, material and specific .application of one such technique. .7
Define the second law efficiency of a vapour compression cycle. Derive its efficiency in terms of COP. 6
lContd.l
"B-JGT-K-NFB 6
..
.
..
7. A conical diffuser entry and exit of 15 cm and 30 em respectively. The pressure, temperature and velQcity of air at entry are 0·69 bar,. 340 K and 180 mls respectively. Determine
the exit pressure
the exit velocity
the force exerted on the diffuser waIls. For solution the following table may be used. Suffix is stagnation pressure values. The star values are critical values corresponding to M =1. M is Mach number and. .M* is corresponding. to critical velocity of sound 15
Isentropic flow of a perfect gas 1·4) M TlTo p/po NA* FIF* Ap/A*po
0·00 0-000 1·000 1·000
0000 00
0·05 0·0548 0·999 0·998 11·592 9·158 11·571
I
0·10 1094 0·998 0·993 5·822 4·624 5·781 0·15 0·1640 0·996 0·984 3·910 3·132 3·849 0·20 0·218 0·992 ,0,973 2-964 2·400 2·882 0·25 0·272 0·987 0·957 2·403 1·973 2·301 0·30 0·326 0·982 0·939 2,035, 1·698 1-912 0·35 0-378 0·976 0·918 1·778 1·509 1·634 0·40 ,0,431 0·969 0·895 1·590 ]..375 '1·424 0·45 0·483 0·961 0·870 ]..448 1·276 1·261 0·50 0·534 0·952 0·843 1·339 1·203 1·129 0·55 0·585 '0·943 0·814 1·255 1·147· 1·022 0-60 0·635 0·933 0·784 1·188 1·105 0·932 0·65 0·684 0·922 0,7.53 1·135 1·073 0·855 0·70 0·732 0·910 0·721 1·094 1·049 0·789 0·75 0·779 0·898 0·688 1·062 1·031 0·731 0·80 0·825 0'886 0·656 1·038 1·018 0·681
B-JGT-K-NFB 7 IContd.J
The rnmamum demand of a power station is 96,000 MW and daily load curve is described as follows:
Time
hours 0-6 6-8 8-12 12-14 14-18 18-22 22-24 Load
48 6072 60 84 96 48
MW
Determine the load factor of power station.
What is the load factor of standby equipment rated at 30 MW that takes up all load in excess of 72 MW Also calculate its use factor. 15
What do you mean by depreciation cost? Name the methods used to· calculate the depreciation cost. Explain these methods. 10
8. The following data refers to a stage of an impulse
reaction turbine
Steam velocity coming out of nozzle 245 mls;
nozzle angle blade mean speed 145
speed of 3000 rpm; blade height =10 em;
specific volume of steam at nozzle outlet and
blade outlet 3·45 m3/kg and 3·95 m3/kg
respectively. Power developed by turbine
390 hp; efficiency of nozzle and blades jointly is
carry over coe,fficient is 0·82. Determine
the heat drop in each stage
degree of reaction t stage
Construct velocity triangles. 20
B-JGT-K-NFB 8 [Contd .J
•
With the help of figure, explain the functioning of 'breeder reactor'. Also enumerate the advantages arid disadvantages of breeder reactors,
10
Discuss the site selection for the nuclear power plants based on
.poJ)ulation distribution
land use
.(iii) geology.
hydrology. 10
•
B-JGT-K-NFB 9
•
•
•
•
f
t
B-JGT-K-NFB
PSYCHROMETRIC CHART
BAROMETRIC PRESSURE 1.01325 bar SEA LEVEL
12.0 12.5 130 135 140 145 0.35
.. ""
0.40
...
0.45
""""
GO
9
.Dl
.01
r-..
1
t-..
t
.r
I"-r-..l
35 40 50
0.85 0"90
SPECIFIC VOLUME. DRY AIR
..
0362
IB-JGT-K-NFBI
..
MECHANICAL ENGINEERING Paper II
ITime Allowed: Three.Hoursl IMaximum Marks: 200I
INSTRUCTIONS
. Candidates should .attempt 1 and 5 which are compulsory, and ofthe remaining questions, selecting at lea:st ONE question from each Section.
All questions carry equal marks. . Marks allotted to parts ofa question are indicated against each.
Answers must be written in ENGLISH only.
If any data is considered in;sufficient, assume suita;blevu.lue and indicate the same clearly. Newton may be converted to kgf using the equality 1 kilonewton kN) 100 kgf, iffound necessary.
All answers should be in 81 units.
Take: 1 kccil.=.4·187 kJ and 1 kglcm2 =0·98 bar
1 bar =105 pascals.
Universal gas constant =8314'6 Neat sketches may be drawn, wherever required. I· .-A psychrometric chart is attached to, and forms part ofthis question paper.
B-JGT-K-NFB 1 IContd.]
SECTION A
1. For a gas, the equation of state is as
below over a certain range of temperatures and
pressures: V a h were a IST constant.
Prove that the change in enthalpy is given by
4a .
3 T {PI for isothermal process. Also find
out the expression for change of entropy. 8
What"js the function of a catalyst in the catalytic
converter for smoke emission control? What are
" .
the oxidation and reduction processes that take
place? Why is unleaded petrol preferred in cars
fitted with catalytic converter? 8
What do you mean by compact heat exchanger?
What are their applications? 8 ..
Describe the malO sources of evaporative
emissions in a S.1. engine. 8
A metal plate size,500 mm x 800 mm x 20 mm
and thermal conductivity 30· WattJrn-C IS
maintained at 250o q. Air at 20°C is blowing over
the plate. If convection heat transfer coefficient is
25 W/m2C and 200 v..7 is lost" by the plate by .j
radiation, compute the inside temperature. 8
.2. Consequent upon first law of thermodynamics,
show .that the heat is a path function. 7
Using pressure time diagram, explain the
combustion process in diesel engine. 8
B-JGT-K-NFB 2
The following, data relates a four-stroke coal gas Bore and stroke of cylinder 380 mm and' 585 mm respectively At 240 rpm, torque developed =5·16 kNm Coal gas to air mixture ratio to 7by volume Estimated volumetric efficiency
Net calorific value of coal gas 16800 kJlkg Calculate the brake power, brake mean effective pressure, piston speed in meter per second and
brake thermal efficiency. 20
Draw the labelled schematic diagram of a
common rail injectio.n system in a C.I. engine.
3. The cylinder volume of an I.e. engIne' is 3000 cm3. It contains products of combustion in gaseous form, which can be assumed to be an ideal gas. The combustion products, just before the exhaust valve opens, are at pressure ,of
6. bar and temperature of 1123 K. Assuming specific heats at constant volume and constant pressure as 0·718 and 1·005. kJ/kg-K respectively, analyse and discuss the availability of specific energy of the gas. The initial pressure and temperature of gas can be taken as 1 bar and 15°C respectively. 10
What are the characteristics of liquid oil, coal-oil mixture, natural and gas fuels? What are their major constituents Where are they suitably used 15
B-JGT-K-NFB. 3
lContd.J
A'sample of coal contains 93% carbon, hydrogen and rest ash. A test was conducted in a Bomb calorimeter using 0·92 kg of coal burnt and following data obtained:
Weight of water taken' 550 Water of Bomb calorimeter 2200 gIn, Rise in temperature of water' Fuse wire correction 10 cal, Acid correction 50 cal. Taking latent heat of condensation of steam as 530 caVgm, calCulate .gross and net calorific value of coal. 15
4. The air-conditioning unit of a pressurised jet aircraft receives its air from the compressor driven by the at a pressure of 1·4 bar. The pressure and temperature of the surrounding air at the height of the aircraft are 0·2 bar and 225 respectively." The air-conditioning unit consists of a secondary compressor and a turbine mounted on the same shaft. The pressure and temperature of air leaving the turbine are 1 bar and K. Calculate the pressure after the secondary compressor and temperature of air at. the exit from the cooler. Assume that all
. are reversible adiabatic. 20
Cold air is to be supplied for a library at a rate of
" 100 m 3/min. The air is to enter the building at 20°C with 40% relative humidity. Suppose. the atmospheric air is at 35°C with 70% relative suggest a suitable and estimate the rates of cooling and "heating required. 20
B-JGT-K-NFB 4 {Contd.l
SECTION B
5. Describe in brief how the fly ash is disposed off by (dry and twet system'. What problems are caused by present systems of fly ash disposal? Give the applications of fly ash. 8
Name the essential parts of a centrifugal. . compressor along with their functioning. Sketch a simple figure of a 'diffuser' and write down the . names of important parts. 8
With the help of figure, describe the working of 'Velox boiler'. Enumerate its advantages. 8
Derive the for temperature distribution for a fin insulated the end. The base temperature of fin is constant. Write typical application for this type of fin. 8
Describe the desirable properties of refrigerants suitable for ice plant applications. Name a few of these. 8
• 6. Prove that the simple arithmetic mean temperature difference gives results within . cqmpared to LMTD when the. ratio of end temperature differences is not more than 2·2. 7
B-JGT-K-NFB
5 lContd.]
..
...
A vapour compression refrigerator uses R-12 as refrigerant and the liquid evaporates In the evaporator at -15°C. The temperature of this refrigerant at the delivery from the compressor is 15°G when the vapour is condensed at 10°C.. Find the coeffiCient of performance if there is
. no under cooling the liquid is cooled 5°C before expansIOn by throttling. Take specific
..
heat constant pressure for the superheated vapour as. 0·64 kJlkg-K and that for liquid as 0·94 kJ/kg-K. The properties of refrigerant are as given below:
Temp Enthalpy Entropy °C in kJ/kg in kJlkg-K Liquid Vapour Liquid Vapour -15 22·3 180·88 0-0904" 0·7051
+10 45·4 191·76 0-.1750 0·6921
What are' the methods used to reduce the 'heat radiation between two parallel plates? Write the process, material and specific .application of one such technique. .7
Define the second law efficiency of a vapour compression cycle. Derive its efficiency in terms of COP. 6
lContd.l
"B-JGT-K-NFB 6
..
.
..
7. A conical diffuser entry and exit of 15 cm and 30 em respectively. The pressure, temperature and velQcity of air at entry are 0·69 bar,. 340 K and 180 mls respectively. Determine
the exit pressure
the exit velocity
the force exerted on the diffuser waIls. For solution the following table may be used. Suffix is stagnation pressure values. The star values are critical values corresponding to M =1. M is Mach number and. .M* is corresponding. to critical velocity of sound 15
Isentropic flow of a perfect gas 1·4) M TlTo p/po NA* FIF* Ap/A*po
0·00 0-000 1·000 1·000
0000 00
0·05 0·0548 0·999 0·998 11·592 9·158 11·571
I
0·10 1094 0·998 0·993 5·822 4·624 5·781 0·15 0·1640 0·996 0·984 3·910 3·132 3·849 0·20 0·218 0·992 ,0,973 2-964 2·400 2·882 0·25 0·272 0·987 0·957 2·403 1·973 2·301 0·30 0·326 0·982 0·939 2,035, 1·698 1-912 0·35 0-378 0·976 0·918 1·778 1·509 1·634 0·40 ,0,431 0·969 0·895 1·590 ]..375 '1·424 0·45 0·483 0·961 0·870 ]..448 1·276 1·261 0·50 0·534 0·952 0·843 1·339 1·203 1·129 0·55 0·585 '0·943 0·814 1·255 1·147· 1·022 0-60 0·635 0·933 0·784 1·188 1·105 0·932 0·65 0·684 0·922 0,7.53 1·135 1·073 0·855 0·70 0·732 0·910 0·721 1·094 1·049 0·789 0·75 0·779 0·898 0·688 1·062 1·031 0·731 0·80 0·825 0'886 0·656 1·038 1·018 0·681
B-JGT-K-NFB 7 IContd.J
The rnmamum demand of a power station is 96,000 MW and daily load curve is described as follows:
Time
hours 0-6 6-8 8-12 12-14 14-18 18-22 22-24 Load
48 6072 60 84 96 48
MW
Determine the load factor of power station.
What is the load factor of standby equipment rated at 30 MW that takes up all load in excess of 72 MW Also calculate its use factor. 15
What do you mean by depreciation cost? Name the methods used to· calculate the depreciation cost. Explain these methods. 10
8. The following data refers to a stage of an impulse
reaction turbine
Steam velocity coming out of nozzle 245 mls;
nozzle angle blade mean speed 145
speed of 3000 rpm; blade height =10 em;
specific volume of steam at nozzle outlet and
blade outlet 3·45 m3/kg and 3·95 m3/kg
respectively. Power developed by turbine
390 hp; efficiency of nozzle and blades jointly is
carry over coe,fficient is 0·82. Determine
the heat drop in each stage
degree of reaction t stage
Construct velocity triangles. 20
B-JGT-K-NFB 8 [Contd .J
•
With the help of figure, explain the functioning of 'breeder reactor'. Also enumerate the advantages arid disadvantages of breeder reactors,
10
Discuss the site selection for the nuclear power plants based on
.poJ)ulation distribution
land use
.(iii) geology.
hydrology. 10
•
B-JGT-K-NFB 9
•
•
•
•
f
t
B-JGT-K-NFB
PSYCHROMETRIC CHART
BAROMETRIC PRESSURE 1.01325 bar SEA LEVEL
12.0 12.5 130 135 140 145 0.35
.. ""
0.40
...
0.45
""""
GO
9
.Dl
.01
r-..
1
t-..
t
.r
I"-r-..l
35 40 50
0.85 0"90
SPECIFIC VOLUME. DRY AIR
..