Fiwl Det 18 Enam

Sessin Jl'i8 Dec 8

JALPAIGURI GOVERNMENT ENGINEERING COLLEGE
A GOVERNMENT AUTONOMOUS cOLLEGE
B.TECH./ ME/ SEM-3/ME-301/2018-2019
2018

THERMODYNAMICS

Full Marks: 70 Time Allotted: 3 Hours

The figures in the margin indicate full marks.

Candidates are requested to write their answers in their own words as far as practicable.
Only Steam Table and Mollier diagram are allowed.

GROUP-A
OBJECTIVE TYPE QUESTIONS]
Answer All the questions 5x2-10
1. Steam at initial enthalpy of 100 kJ/kg and inlet
an
velocity of 100 m/s, enters an adiabatic
horizontal nozzle. It leaves the nozzle at 200 m/s. Determine the exit
enthalpy of steanm.
2. What is the purpose of
keeping evaporator outlet refrigerant temperature at some degree
superheated condition in vapour compression refrigeration systems?
3. Write short
a
'Supercritical boiler'.
note on

4. What is the 'Principle of increase of

entropy?
5. For two cycles coupled in
series, the topping cycle has an efficiency of 30% and
bottoming cycle has an efliciency of 20%. Determine the overall combined the
cycle efficiency.

GROUP-BB
LONG ANSWER TYPE QUESTIONS]
Answer any Four of the following
4x15-60
6. a) What are the problems in implementing Carnot engine in practice?
(4)
b) Prove that the COP of all reversible
refrigerators are same when the reservoir
are the same. What inference
can you draw from this
result?
temperatures
(6)
c) A Carnot heat engine receives heat at 750 K and
The entire work rejects heat to the environment at 300 K.
ouput of the heat engine is used to
heat from a cooled space at 258 K at a rate drive a Carnot refrigerator that removes
of 400
which is at 300 K. Determine : kJ/min and rejects it to the environment
1) the rate of heat suppiied to the heat
engine and
ii) the total rate of heat rejection to the environment.
(5)
7.(a) State Clausius Inequality. (2)
D) An inventor claims to have designed a device which gives equal amount of hot air at 0.10
MPa, 400 K and cold air at 0.10 MPa, 200 K when the device is fed with air at 0.50 MPa and
300 K. It is also claimed that the device does not require any energy from outside eitner n

the form of heat or, work. Judge whether the claim is justified or, not. Treat air as an ideal
gas
With Cp3.5 R, where "R' for air is 287 J/(kg-K). 6)

(C) Define Joule-Thompson coefficient (). Prove that: = (1/Cp). I T.(ov/OT)p- V J

Notations have their usual meanings.
(7)
Detemine for an idealgas
8.(a) Define 2nd law or, exergetic efficiency. (2)
it with saturated steam.
(6) Liquid water at 15'C is heated in an adiabatic chamber by mixing
rate of 4.6 kg/s and the saturated
Liquid water enters the chamber at the steam pressure at a
chamber as a liquid at
steam enters at a rate of 0.23 kg/s. The mixture leaves the mixing
45c. Ifthe surroundings are at 15 C, determine:
i) the temperature of the saturated steam entering the chamber
ii) the exergy destruction during this mixing process and
i) the related 2nd law efficiency.
Consider steady state process. Neglect any change in kinetic and potential energies. (8)
(c) Derive Clapeyron-Clausius equation. (5)

9.(a) Derive efficiency of Otto cycle in terms of its compression ratio. (5)
(b) Make a comparison among Otto, Diesel and Dual cycle. (4)
(c) Consider an engine operating on a simple ideal Brayton cycle with a pressure ratio of 10.
Heat is added to the cycle at a rate of 500 kW. Air flow rate through the cycle is 1 kg/s.
Pressure and temperature of air at the beginning of the compression are 70 kPa and 273 K
Tespectively. Determine the power produced by the engine anditsthermaleficiency.
Consider for air, Cp 1.005 kJ/kg-K. (6)
=

10.(a) Why exit pressure of steam from the turbine at the inlet of condenser is kept below
atmospherie pressure in steam power plants? Does this exit pressure depend on condenser
cooling water temperature?
4)
(b) What are the purposes of "Reheating' in a steam power plant?
(2)
(c) A steam power plant operates on ideal reheat Rankine cycle. Steam enters the
an
pressure turbine at 8 MPa and 500°C and leaves at 3 MPa.
high
Steam is then reheated at constant
ressure to 500 Cbefore it expands to 20 kPa in the low pressure turbine.
Determine the turbine work output, in
Show the cycle on T-S and h-S
kJ/kg, and the thermal efficiency of the cycle.
diagrams with respect to saturation lines. (9)
11.(a) What major advantages of Vapour Absorption Refrigeration(VAR) system over
are the
a Vapour Compression Refrigeration(VCR) system? (3)
(6) What types of refrigerants in Vapour Compression refrigerators are being used now-a
days and why? (3)
(c) Draw T-S and P-V diagrams of a simple ideal Gas Refrigeration cycle and name the
processes. Mention one application of Gas Refrigeration system. 4)
1 MPa and
(d) An ideal Vapour Compression Refrigeration system maintains its condenser at
the evaporator at 4"C. Determine the COP and the amount of power required by compressor
to serve a 400 kW cooling load.
exit from
Consider the enthalpy values of the refrigerant at the inlet to compressor, at
the condenser as 253 kJ/kg, 276 kJ/kg and 107 kJ/kg
compressor, and at exit from
respectively. (5)

-- END
 nds on f a ' 2A
NLINE XAn) exam hld m
1 feb/22
3 O MAMy
40
JGEC/ BTech/ MEI
MAM (CnA) Mea Aw
PC-ME301/ 2021-2022
(Exam. on February 2022)
THERMODYNAMICS Felb 2022 Exam.
GROUP- B (Answer any Three questions) Full marks = 3 x10 30

1. a) Draw Carnot Cyele in PV and TS diagrams and name the processes involved. Determine
the efficiency of a Carnot engine.
b) Explain why Carnot engine is not practicable to implement. (6+4 10)

2. An inventor claims to have designed a flow device which gives cqual amounts ot hot air at
0.10 MPa, 400 K and cold air at 0.10 MPa, 200 K when the device is fed with air at O.50 MPa
and 300 K. It is also claimed that the device does not require any energy from outside either
in the form of heat or, work. Judge whether the claim is justified or, not. Treat air as an ideal
gas w i t h Cp = 3.5 R, w h e r e R * for air is 287 J/(kg-K).
(10)

3.a) Makea comparison between Energy and Exergy. (4)

b) I kg of ice at 0'c is mixed with 12 kg of water at 27c. Assuming the surrounding
temperature as 1S°C, caleulate the net increase in entropy and unavailable energy when the
system reaches common i.c., cquilibrum temperature.
Consider specific heat of water = 4.18 kJ/kg-"C . Specific heat of ice
2.1 k/kg-"C and
enthalpy of fusion of ice (latent heat) 333.5 kJ/kg. (6)

4. a) Why exit pressure of steam from the turbine at the inlet of condenser is
kept bclow
atmospheric pressure in steam power plants?
(2)
b) A steam power plant
operates on a simple Rankine cycle. The steam enters the turbine at
3 MPa and 350°C and exists at 5 kPa in two
phase condition.
Determine: (i) thermal efficiency of thecycle and (ii) the work ratio
(8)
5. In a
sinmple air-standard Brayton cycle pressure ratio is 6. The air enters the
bar and 27°C. The
maximum temperature of compressor al i
the cycle 850°C. Consider Cp of air1.005
is
kJ/kg-K
Calculate: i) the thermal
i) work
efficiency of the eycle
input to the compressor
111) net work done
by the cycle. Compare this with maximum
possible work done. (10
 Fiwl Det 18 Enam
Sessin Jl'i8 Dec 8
JALPAIGURI GOVERNMENT ENGINEERING COLLEGE
A GOVERNMENT AUTONOMOUS cOLLEGE
B.TECH./ ME/ SEM-3/ME-301/2018-2019
2018

THERMODYNAMICS

Full Marks: 70 Time Allotted: 3 Hours

The figures in the margin indicate full marks.

Candidates are requested to write their answers in their own words as far as practicable.
Only Steam Table and Mollier diagram are allowed.

GROUP-A
OBJECTIVE TYPE QUESTIONS]
Answer All the questions 5x2-10
1. Steam at initial enthalpy of 100 kJ/kg and inlet
an
velocity of 100 m/s, enters an adiabatic
horizontal nozzle. It leaves the nozzle at 200 m/s. Determine the exit
enthalpy of steanm.
2. What is the purpose of
keeping evaporator outlet refrigerant temperature at some degree
superheated condition in vapour compression refrigeration systems?
3. Write short
a
'Supercritical boiler'.
note on

4. What is the 'Principle of increase of

entropy?
5. For two cycles coupled in
series, the topping cycle has an efficiency of 30% and
bottoming cycle has an efliciency of 20%. Determine the overall combined the
cycle efficiency.

GROUP-BB
LONG ANSWER TYPE QUESTIONS]
Answer any Four of the following
4x15-60
6. a) What are the problems in implementing Carnot engine in practice?
(4)
b) Prove that the COP of all reversible
refrigerators are same when the reservoir
are the same. What inference
can you draw from this
result?
temperatures
(6)
c) A Carnot heat engine receives heat at 750 K and
The entire work rejects heat to the environment at 300 K.
ouput of the heat engine is used to
heat from a cooled space at 258 K at a rate drive a Carnot refrigerator that removes
of 400
which is at 300 K. Determine : kJ/min and rejects it to the environment
1) the rate of heat suppiied to the heat
engine and
ii) the total rate of heat rejection to the environment.
(5)
7.(a) State Clausius Inequality. (2)
D) An inventor claims to have designed a device which gives equal amount of hot air at 0.10
MPa, 400 K and cold air at 0.10 MPa, 200 K when the device is fed with air at 0.50 MPa and
300 K. It is also claimed that the device does not require any energy from outside eitner n

the form of heat or, work. Judge whether the claim is justified or, not. Treat air as an ideal
gas
With Cp3.5 R, where "R' for air is 287 J/(kg-K). 6)

(C) Define Joule-Thompson coefficient (). Prove that: = (1/Cp). I T.(ov/OT)p- V J

Notations have their usual meanings.
(7)
Detemine for an idealgas
8.(a) Define 2nd law or, exergetic efficiency. (2)
it with saturated steam.
(6) Liquid water at 15'C is heated in an adiabatic chamber by mixing
rate of 4.6 kg/s and the saturated
Liquid water enters the chamber at the steam pressure at a
chamber as a liquid at
steam enters at a rate of 0.23 kg/s. The mixture leaves the mixing
45c. Ifthe surroundings are at 15 C, determine:
i) the temperature of the saturated steam entering the chamber
ii) the exergy destruction during this mixing process and
i) the related 2nd law efficiency.
Consider steady state process. Neglect any change in kinetic and potential energies. (8)
(c) Derive Clapeyron-Clausius equation. (5)

9.(a) Derive efficiency of Otto cycle in terms of its compression ratio. (5)
(b) Make a comparison among Otto, Diesel and Dual cycle. (4)
(c) Consider an engine operating on a simple ideal Brayton cycle with a pressure ratio of 10.
Heat is added to the cycle at a rate of 500 kW. Air flow rate through the cycle is 1 kg/s.
Pressure and temperature of air at the beginning of the compression are 70 kPa and 273 K
Tespectively. Determine the power produced by the engine anditsthermaleficiency.
Consider for air, Cp 1.005 kJ/kg-K. (6)
=

10.(a) Why exit pressure of steam from the turbine at the inlet of condenser is kept below
atmospherie pressure in steam power plants? Does this exit pressure depend on condenser
cooling water temperature?
4)
(b) What are the purposes of "Reheating' in a steam power plant?
(2)
(c) A steam power plant operates on ideal reheat Rankine cycle. Steam enters the
an
pressure turbine at 8 MPa and 500°C and leaves at 3 MPa.
high
Steam is then reheated at constant
ressure to 500 Cbefore it expands to 20 kPa in the low pressure turbine.
Determine the turbine work output, in
Show the cycle on T-S and h-S
kJ/kg, and the thermal efficiency of the cycle.
diagrams with respect to saturation lines. (9)
11.(a) What major advantages of Vapour Absorption Refrigeration(VAR) system over
are the
a Vapour Compression Refrigeration(VCR) system? (3)
(6) What types of refrigerants in Vapour Compression refrigerators are being used now-a
days and why? (3)
(c) Draw T-S and P-V diagrams of a simple ideal Gas Refrigeration cycle and name the
processes. Mention one application of Gas Refrigeration system. 4)
1 MPa and
(d) An ideal Vapour Compression Refrigeration system maintains its condenser at
the evaporator at 4"C. Determine the COP and the amount of power required by compressor
to serve a 400 kW cooling load.
exit from
Consider the enthalpy values of the refrigerant at the inlet to compressor, at
the condenser as 253 kJ/kg, 276 kJ/kg and 107 kJ/kg
compressor, and at exit from
respectively. (5)

-- END
 Exam. in Deunbei'o|9
JALPAIGURI GOVERNMENT ENGINEERING COLLEGE
A GOVERNMENT AUTONOMOUS COLLEGE|
JGEC/ B.TECH./ ME/ SEM-3/PC-ME 301 / 2019-20
2019

THERMODYNAMICS
Full Marks: 70 Time Allotted: 3 Hours

The figures in the margin indicate full marks.

Canaidates are instructed to write their answers in their own words as far as practicable.

Only Steam Table and Mollier diagram are allowed.

GROUP-A
OBJECTTVE TYPE QUESTIONS]
Answer All the questions 5x2=10

1. Can a reversible heat engine have an efficiency of 100 %? State with reason.

2. Define Tonne of Refrigeration.

3. Will an isentropic process be necessarily reversible and adiabatic? Explain with an

example.
4. State Kelvin-Planck statement of the second law of thermodynamics.
5. Write the reference values that are considered for tabulation of themodynamic properties
of water in the Steam Table.

GROUP-B
LONG ANSWER TYPE QUESTIONS|

Answer any Four of the following 4x15-60

6.a)Draw the P-V and T-S diagrams for the Carmot cycle and name the processes involved.(4)

b) Prove that the COP of all reversible refrigerators operating between the same temperature
levels is the same. What inference can you draw from this result? (6)

c) Two reversible engines Ej and E; are kept in series between a hot reservoir at temperature
T of600 K and a cold reservoir at a temperature T of 300 K. Engine Ej receives 500 kJof
heat from the reservoir at Ti. Both the engines have equal thermal efficiency.
Determine:
i) the temperature at which heat is rejected by engine Ej and is received by engine E2.
ii) the thermal efficiency of each engine
i) the work done by each of the engines.
 Dec L619. &yam

7.(a) State Clausius theorem. (2)

D) Atmospheric air at 101 kPa and 30c is allowed to get in slowly into an evacuaated
yinder from a supply pipe through a valve. If no heat is transferred to or, from the air in
tnc
cyunder, what will be the final temperature in the cylinder when the cylinder pressure reaches
101 RPa? Consider for air, Cp= 1.005 kJ/kg-°c and C, =0.718. kJ/kg-"C. (5)

(c) Air at 20'C and 1.05 bar occupies 0.025 m., The air is heated at constant volume unti
the pressure is 4.5 bar, and then cooled at constant pressure back to original temperature:
Determine: (i) The net heat flow from the air and (ii) The net entropy change
Sketch the processes on T-S and P-V plots.
Consider air as an ideal gas and for air, Cp = 1.005 kJ/kg-"C and C, = 0.718 kJ/kg-"C. (8)

8.(a) Develop entropy balance for a closed system. (5)

b) 3 kg of air at 150 kPa pressure and 360 K temperature is compressed polytropically to

pressure 750 kPa according to the law PV =

constant. Subsequently the air is cooled to

initial temperature at constant pressure. This is followed by expansion at constant

temperature till the original pressure of 150 kPa is reached.

Sketch the cycle on P-V and T-S plots and determine the work done, heat transfer and

entropy change for each process.

Consider air as an ideal gas and for air, Cp = 1.005 kJ/kg-"C and Cy = 0.718 kJ/kg-°C. (10)

9.(a) Define Exergy. (2)

(b) Elaborate the concept of 2" law efficiency. (3)
(c) Make a comparison between Energy and Exergy. (4)
(d) A piston-cylinder device, initially contains 0.002 m of air at 100 kPa and 25 C. Air is
now compressed to a final state of 600 kPa and 150'c. The actual work input is 1.20 kJ.
Assuming surroundings are at 100 kPa and 25°C, determine
i) the exergy of air at the initial and final states
ii) the minimum work that must be supplied to accomplish the compression process and
ii) the second law efficiency of this process.

Air may be treated as an ideal gas.

Consider for air, Cp 1.005 kJ/kg-"C and Cy 0.718 kJ/kg-"c 6)
10.(a) Write the assumptions for air-standard cycle analysis. (5)
(b) Derive the efficiency of Braylon cycle in terms of its pressure ratio. (5)
(c) In an air-standard Otto cycle based engine, the temperature at the end of compression
stroke is 650 K and the maximum cycle temperature is 2400 K. If the engine delivers 700
kJ/kg of net work, find the thermal efficiency and compression ratio of the engine.
Consider for air Cp = 1.005 kJ/(kg-K) and C,= 0.718 kJ/(kg-K). (5)
 Dec' 20 19 Exam

11.(a) Elaborate the purpose of Condenser in a steam power plant. (2)

(6) A steam power plant operates on a simple Rankine
cycle. The steam enters the turbine at
3 MPa and 350°C and exists at 5 kPa in a two
phase condition..
Determine : (i) thermal efficiency of the cycle. (ii) the work ralio and
(iii) the steam rate. (7)
(c) Write briefly about the refrigerants being used at present in domestic refrigerators (2)

(d) A cold storage is to be maintained at (-) 5'C while the

surroundings are at 35 C. The heat
leakage from the surroundings into the cold storage is estimated to be 29 kW and
the actual
Coefficient of Performance (COP) of the refrigeration plant is one-third of a reversible
working between the same temperature limits.
plant
Find the power required to drive the plant.
(4)

END