P.T.Lee. CHENGALVARAYA NAICKER COLLEGE OF ENGG.

& TECH,
OOVERY, KANCHIPURAM

Third Semester – MECH

ME 3391Engineering Thermodynamics
(Regulation 2021)

PART-A

1. State the Kelvin- Plank statement of second law of thermodynamics.

Kelvin-Plank states that it is impossible to construct a heat engine working on cyclic process,
whose only purpose is to convert all the heat energy given to it in an equal amount of work.
2. What do you mean by the term ‘entropy’?
Entropy is an index of unavailability or degradation of energy. Heat always flows from hot body to
cold body and thus becomes lesser value available. It is an important thermodynamics property of the
working substance. It is denoted as “S”. The S.I unit for entropy is KJ/K.
3. State Carnot Theorem.
No heat engine operating in a cyclic process between two fixed temperatures can be more
efficient that a reversible engine operating between the same temperature limits.
4. Define – PMM of second kind.
Perpetual motion machine of second kind draws heat continuously from single reservoir and
converts it into equivalent amount of work. Thus it gives 100% efficiency.
5. What are the Corollaries of Carnot theorems?
(i) All the reversible engines operating between the two given thermal reservoirs with fixed
temperature have the same efficiency.
(ii) The efficiency of any reversible heat engine operating between two reservoirs is independent of the
nature of the working fluid and depends only on the temperature of the reservoirs.
6. Define the term COP?
Coefficient of performance is defined as the ratio of heat extracted or rejected or rejected to work
input.

COP =

COP HP = =
 COP for refrigerator,

COP ref =
8.Why Carnot cycle cannot be realized in practice?
(i) In a Carnot cycle, all the four processes are reversible but in actual practice there is no process is
reversible.
(ii) It is not possible to avoid friction between moving parts completely.
9.What do you mean by “Clausius Inequality”?
It is impossible for a self acting machine working in a cyclic process unaided by any external
agency to convey heat from a body at a lower temperature to a body at a higher temperature.
10. In an isothermal process 1000 KJ of work is done by the system at a temperature of
100 °C .What is the entropy change of this process?

Given data:
W=1000 KJ, T=100+273=373 K
To find:
∆S=?
Solution:
For isothermal
Q=W=1000 KJ
∆S=Q/T
= 1000/373 =2.68 KJ/kg K
11. A heat engine receives heat at the rate of 1500 kJ/min and gives an output of 8.2 kW. Determine :
(i) The thermal efficiency ; (ii) The rate of heat rejection.

12. Find the co-efficient of performance and heat transfer rate in the condenser of
a refrigerator in kJ/h which has a refrigeration capacity of 12000 kJ/h when power
input is 0.75 kW.

13. A Carnot cycle operates between source and sink temperatures of 250°C and – 15°C. If the system
receives 90 kJ from the source, find : (i) Efficiency of the system ; (ii) The net work transfer ; (iii)
Heat rejected to sink.

PART-B

1. A reversible heat engine operates between two reservoirs at 820°c and 27°c. Engine drives a
reversible refrigerator which operates between reservoirs at temperature of 27°c and - 15°c. The
heat transfer to the engine is 2000KJ and network available for the combined cycle is 300KJ. (1)
How much heat is transferred to the refrigerant and also determine the total heat rejected to the °
reservoir at 27°c. (2) If the efficiency of the heat engine and COP of the refrigerator are each 40%
of their maximum values, determine heat transfer to the refrigerator and also heat rejected to the
reservoir at 27°c.
2. Two heat engines operating in series are giving out equal amount of work. The total work is 50
KJ/cycle.If the reservoirs are at 1000 K and 250 K,find the indermediate temperature and the
efficiency of the each engine.Also,find the heat extracted from the source.
3. An engine is supplied with 1120 KJ/S of heat. The source and sink temperature are maintained at
560°K and 280°K. Determine whether the following cases represent the reversible, irreversible or
impossible heat engines.
(i) 900 KW of heat rejected
(ii) 560 KW of heat rejected
 (iii) 108 KW of heat rejected.
4. An ideal gas of molecular weight 30 and specific heat ratio 1.4 is compressed according to the law
PV1.25=C from 1 bar absolute and 27°C to a pressure of 16 bar calculated the temperature at the end
of compression the heat received or rejected work done on the gas during the process and changes in
enthalpy. Assume mass of the gas as 1kg.
5. 5 m3 of air at 2 bar, 27 °C is compressed up to 6 bar pressure following PV 1.3 = constant. It is
subsequently expanded adiabatically to 2 bar. Considering the two processes to be reversible, determine
the network, net heat transfer, and change in entropy. Also plot the processes on T-s and P-V diagrams.

6. 300 kJ/s of heat is supplied at a constant fixed temperature of 290C to a heat engine. The heat rejection
takes place at 8.5C. The following results were obtained : (i) 215 kJ/s are rejected. (ii) 150 kJ/s are
rejected. (iii) 75 kJ/s are rejected. Classify which of the result report a reversible cycle or irreversible
cycle or impossible results.

A reversible heat engine operates between two reservoirs at temperatures of 600°C and 40°C. The
engine drives a reversible refrigerator which operates between reservoirs at temperatures of 40°C and –
20°C. The heat transfer to the heat engine is 2000 kJ and the net work output of the combined engine
refrigerator plant is 360 kJ. (a) Evaluate the heat transfer to the refrigerant and the net heat transfer to
the reservoir at 40°C. (b) Reconsider (a) given that the efficiency of the heat engine and the COP of the
refrigerator are each 40% of their maximum possible values.
 PART-A

1. Mention the expression for COP of heat pump. APR/May 2023

2. Specify the two major conclusions deduced from the Carnot principles. APR/May 2023

3. Define Kelvin-Planck statement of second law of thermodynamics. Nov/Dec 2022

4. Prove COPHp = COPR +1. Nov/Dec 2022

5. Prove COP of the heat pump is greater than the COP of the refrigerator. Nov/ Dec 2023

6. Calculate the entropy change of the universe as a result of placing a copper block 600 g mass with Cp
of 150 J/K at 100°C in a lake at 8°C. Nov/ Dec 2023

7. Differentiate Heat Engine and Refrigerator. APRILMAY 2024

8. How COP of a heat pump is estimated? APRILMAY 2024

9. Define a heat engine and list its two essential components. APRILMAY 2025

10. Write the Clausius inequality and state its physical meaning. APRILMAY 2025
11. Draw the simple layout of Heat Pump and write its COP equation. Nov/ Dec 2024

PART-B

1. Deduce the expression for in-equality of Clausius and interpret the results. Apr/ May
2023

2. A heat exchanger circulates 5000 kg/hr of water to cool oil from 150°C to 50°C. The
rate of flow of oil is 2500 kg/hr. The average specific heat of oil is 2.5 kJ/kg K. The water
enters the heat exchanger at 21°C. Determine the net change in the entropy due to the
heat exchange process and the amount of work obtained if cooling of oil is done by using
the heat to run a Carnot engine with sink temperature of 2 1°C.
Apr/ May 2023

3. A heat engine receives heat at the rate of 1500 kJ/min and gives an output of 8.2 kW.
Determine: (6+7) Apr/ May 2024

(i) The thermal efficiency: (i) The rate of heat rejection.

4. Brief on the following (4+4+5)

(i) Clausius Statement

(ii) Kelvin-Planck Statement

(iii) Equivalence of Clausius Statement to the Kelvin-Planck Statement. Apr/ May

2024

5. A reversible heat engine operates between two thermal reservoirs at temperature 1000
K and 300 K. The engine drives a reversible refrigerator which operates between
reservoirs at temperatures 250 K and 300 K. The heat transfer to the heat engine is 2000
kJ and the net work output of combined engine-refrigerator plant 360 kJ. Evaluate the heat
transfer to the refrigerant, (COP) of the refrigerator and heat transfer to the 300 K
reservoir. Nov/Dec 2022

6. A power cycle operating between two thermal reservoirs receives energy Q H by heat
transfer from a hot reservoir at T H = 2000 K and rejects energy Q C by heat transfer to a
cold reservoir at TC = 400 K. For each of the following cases determine whether the cycle
operates reversibly. operates irreversibly, or is impossible.

(1) QH = 1000 kJ, η =60%

(ii) QH = 1000 kJ, Wcycle = 850 kJ

(ii) QH= 1000 kJ, QC= 200 kJ. Nov/Dec 2022

7. Two Carnot heat engines A and B are connected in series between two thermal
reservoirs at Tı = 1000K and T2 = 100 K, respectively. Engine A receives 1700 KJ of heat
from the high temperature reservoir and rejects heat to the Carnot engine B. Engine B
takes in heat rejected by engine A and rejects heat to the low temperature reservoir. If
engines A and B have equal thermal efficiencies, determine (i) the heat rejected by engine
B, (ii) The temperature at which heat is rejected by engine A, and (ii) The work done
during the process by engines A and B, respectively. If engines A and B, deliver equal
work, determine (iv) The amount of heat taken in by engine B, and (v) the efficiencies of
engines A and B. Nov/Dec 2023

8. An aluminium block (Cp = 400 Jkg K) with a mass of 5 kg is initially at 40°C in room air
at 20°C. It is cooled reversibly by transferring heat to a completely reversible cyclic heat
engine until the block reaches 20°C. The 20°C room air serves as a constant temperature
sink for the engine. Compute (i) the change in entropy for the block, (i) the change in
entropy for the room air, (iii) the work done by the engine.

9. If the aluminium block is allowed to cool by natural convection to room air, compute (1)
the change in entropy for the block, (2) the change in entropy for the room air (3) the net
change in entropy for the universe. Nov/Dec 2023

10. Compare the performance of a Carnot cycle and a Reversed Carnot cycle. Highlight
their key differences. Apr/ May 2025

11. A reversible heat engine operates between two reservoirs at temperatures 700 0 C and
50 0 C. The engine drives a reversible refrigerator which operates between reservoirs at
temperatures of 50 0 C and – 25 0 C The heat transfer to the engine is 2500 kJ and the
network output of the combined engine refrigerator plant is 400 kJ.

(i) Determine the heat transfer to the refrigerant and the net heat transfer to the reservoir
at 500 C (6)

(ii) Reconsider (i) given that the efficiency of the heat engine and the C.O.P. of the
refrigerator are each 45 per cent of their maximum possible values.
(7) Apr/ May 2025

12. A reversible heat engine operates between reservoirs at temperature of 873 K and 313
K. The engine drives a reversible refrigerator which operates between reservoirs at
temperature of 313 K and 253 K. The heat transfer to the heat engine is 2 MJ and the net-
work output from the combined engine-refrigerator plant is 360 kJ. Evaluate the heat
transfer to the refrigerant and the net heat transfer to the reservoir at 313 K. Nov/Dec
2024

13. Consider 1 kg of ice at - 120 C as a system. It is exposed to surroundings at 20 deg 0C

The ice melts to water ultimately coming to equilibrium with the surroundings. Calculate
the entropy change of the system, the surroundings and the universe. Specific heat of ice
and water are 2.2 kJ/kgK and 4.2 kJ/kgK respectively and the latent heat of fusion of ice is
334 kJ/kg. Nov/Dec 2024

PART C (1x 15 = 15 marks)

1. A household refrigerator is maintained at a temperature of 2°C. Every time the door is

opened, warm material placed inside, introducing an average of 420 kJ, but making only
small changes in the temperature of the refrigerator. The door is opened 20 times a day,
and the refrigerator operates at 15% of the ideal COP. The cost of work is 550 paise per
kW-hr. What is the monthly bill for this refrigerator? The atmosphere is at 30° C.
Apr/ May 2023

2. A reversible heat Engine operates between two reservoirs at temperature of 600 °C

and 40 °C. The engine drives a reversible refrigerator which operates between reservoirs
at temperatures of 40 °C and 20 °C, The heat transfer to the heat engine is 2000 kJ and
the network output of the combined engine refrigerator plant is 360 kJ.

(i) Evaluate the heat transfer to the refrigerant and net heat transfer to the reservoir at
40 °C. (10)

(ii) Reconsider given that the 'n' of the heat engine and COP of the refrigerator are each
40% of their maximum possible values. (5) April/ May 2024

3. (i) Explain: Carnot cycle, its assumptions and reasons for rating it as a theoretical
cycle. (5)

(ii) A domestic food refrigerator maintains a temperature of -12 °C. The ambient air
temperature is 35 °C. If heat leaks into the freezer at the continuous rate of 2 kJ/s,
determine the least power necessary to pump this heat out continuously. April/
May 2024

7. A heat engine operating between two reservoirs at 1000 and 300k is used to
drive a heat pump which extracts heat from the reservoir at 300 k at a rate
twice that at which the engine rejects heat to it. If the efficiency of the engine is
40% of the maximum possible and the cop of the heat pump is 50% of the
maximum possible, what is the temperature of the reservoir to which the heat
pump rejects heat ? What is the rate of heat rejection from the heat pump if the
rate of heat supply to the engine is 50 kW ?
8. An ice plant working on a reversed Carnot cycle heat pump produces 15 Tonnes
of ice per day. The ice is formed from water at 0C and the formed ice is
maintained at 0C. The heat is rejected to the atmosphere at 25C. The heat
pump used to run the ice plant is coupled to a Carnot engine which absorbs
heat from a source which is maintained at 220C by burning liquid fuel of
44500 kJ/kg calorific value and rejects the heat to the atmosphere.
Determine : (i) Power developed by the engine ; (ii) Fuel consumed per hour.
Take enthalpy of fusion of ice = 334.5 kJ/kg.