CHAPTER 2 - FIRST LAW OF THERMODYNAMICS CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 1
1. At the inlet to a certain nozzle the enthalpy of fluid passing is 2800 kJ/kg, and the
velocity is 50 m/s. At the discharge end the enthalpy is 2600 kJ/kg. The nozzle is
horizontal and there is negligible heat loss from it.
a. Find the velocity at exit of the nozzle.
b. If the inlet area is 900 cm2 and the specific volume at inlet is 0.187 m3/kg,
find the mass flow rate.
c. If the specific volume at the nozzle exit is 0.498 m3/kg, find the exit area of
nozzle.
[Ans: 634.4 m/s, 24.06 kg/s, 188.87 cm2] [3.42, R. K. Rajput]
2. In a gas turbine unit, the gases flow through the turbine is 15 kg/s and the power
developed by the turbine is 12000 kW. The enthalpies of gases at the inlet and outlet
are 1260 kJ/kg and 400 kJ/kg respectively, and the velocity of gases at the inlet and
outlet are50 m/s and 110 m/s respectively. Calculate:
a. The rate at which heat is rejected to the turbine, and
b. The area of the inlet pipe given that the specific volume of the gases at the
inlet is 0.45 m3/kg.
[Ans: 828 kW, 0.135 m2] [3.33, R. K. Rajput]
3. The mass flow rate of steam into a steam turbine is 1.5 Kg/s and heat loss from the
turbine is 8.5 KW. The steam is entering the turbine at the pressure of 2MPa,
temperature 350°C, Velocity 50 m/s, elevation 6 m/s and is leaving the turbine at a
pressure of 0.1 MPa, quality of 100%, velocity of 200 m/s, elevation of 3 m/s.
Determine power output of turbine. [GTU, JUN-2015][Ans:
4. In an air compressor air flows steadily at the rate of 0.5 kg/s through an air
compressor. It enters the compressor at 6 m/s with a pressure of 1 bar and a specific
volume of 0.85 m3/kg and leaves at 5 m/s with a pressure of 7 bar and a specific
volume of 0.16 m3/kg. The internal energy of the air leaving is 90 kJ/kg greater than
that of the air entering. Cooling water in a jacket surrounding the cylinder absorbs
heat from the air at the rate of 60 kJ/s. Calculate:
a. The power required to drive the compressor;
b. The inlet and output pipe cross-sectional area.
[Ans: 118.5 kW, 0.016 m2] [3.34, R. K. Rajput]
CHAPTER 2 - FIRST LAW OF THERMODYNAMICS CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 2
5. A centrifugal pump delivers 50 kg of water per second. The inlet and outlet
pressures are 1 bar and 4.2 bar respectively. The suction is 2.2 m below the centre of
the pump and delivery is 8.5 m above the centre of the pump. The suction and
delivery pipe diameters are 20 cm and 10 cm respectively. Determine the capacity of
the electric motor to run the pump. [Ans: 22.2 kW] [3.45, R. K. Rajput]
6. Air at a temperature of 20°C passes through a heat exchanger at a velocity of 40
m/s where its temperature is raised to 820°C. It then enters a turbine with same
velocity of 40 m/s and expands till the temperature falls to 620°C. On leaving the
turbine, the air is taken at a velocity of 55 m/s to a nozzle where it expands until the
temperature has fallen to 510°C. If the air flow rate is 2.5 kg/s, calculate:
a. Rate of heat transfer to the air in the heat exchanger;
b. The power output from the turbine, assuming no heat loss;
c. The velocity at exit from the nozzle, assuming no heat loss.
(Take the enthalpy of air as h = cpt, where cp is the specific heat equal to 1.005 kJ/kg-
°C and t is the temperature.)
[Ans: 2010 kJ/s, 504.3 kW, 473.4 m/s] [3.47, R. K. Rajput]
7. The air speed of a turbojet engine in flight is 270 m/s. Ambient air temperature is -
15 °C. Gas temperature at outlet of nozzle is 600 °C. Corresponding enthalpy values
for air and gas are respectively 260 and 912 KJ/kg. Fuel-air ratio is 0.0190. Chemical
energy of the fuel is 44.5 MJ/kg. Owing to incomplete combustion 5% of the
chemical energy is not released in the reaction. Heat loss from the engine is 21 KJ/kg
of air. Calculate the velocity of the exhaust jet.
[Ans: 560m/s] [5.7, P. K. Nag]
CHAPTER 3 – 2nd LAW OF THERMODYNAMICS CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 1
1. A reversed Carnot cycle operates at either a refrigerator or heat pump. In either
case, the power input is 20.8 kW. Calculate the quantity of heat extracted from the
cold body for either type of machine. In both case 3500 kJ/min heat is delivered by
the machine. In case of the refrigerator the heat is transferred to the surroundings
while in case of heat pump, the space is to be heated. What is their respective
coefficient of performances? If the temperature of cold body is 0°C for the
refrigerator and 5°C for heat pump what will be respective temperatures of
surrounding for refrigerator and heated space for heat pump? What reduction in
heat rejection temperatures would be achieved by doubling the COP for same cold
body temperature? GTU Jun 2010
2. A Carnot engine receives 4000 KJ as heat addition at 3370C and rejects energy at
triple point of water. Calculate (1) thermal efficiency (2) The net work output in KJ,
if the efficiency of an irreversible engine is 70 % of Carnot engine. Find the % change
in heat rejected for the same input and fluid temperature. GTU Nov 2011
3. An engine manufacturer claims to have developed a heat engine with following
specifications:
Power developed = 75 kW
Fuel burnt = 5 kg/hr
Heating value of fuel = 75000 kJ/kg
Temperature limits = 1000 K and 400 K
Is the claim of an engine manufacturer true or false? Provide your explanation.
[Answer: Claim is false] D.S Kumar 211/7.20
4. A heat engine is supplied with 2512 kJ/min of heat at 650⁰C. Heat rejection takes
place at 100⁰C. Specify which of the following heat rejections represents reversible,
irreversible and impossible results: D.S Kumar 217/7.21
(i) 867 kJ/min, (ii) 1015 kJ/min, (iii) 1494 kJ/min]
[Answer: (1) Impossible cycle; (2) Reversible cycle; (3) Irreversible cycle]
5. A reversible engine receives heat from two thermal reservoirs maintained at
constant temperature of 750 K and 500 K. The engine develops 100 kW and rejects
3600 kJ/min of heat to a heat sink at 250 K. Determine thermal efficiency of the
engine and heat supplied by each thermal reservoir. D.S Kumar 219/7.25
CHAPTER 3 – 2nd LAW OF THERMODYNAMICS CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 2
[Answer: (1) ηth = 62.5%; (2) Heat supplied by source at 750 K = 7200 kJ/min, heat
supplied at 500 K = 2400 kJ/min]
6. Two reversible engines A and B are arranged in series. Engine ‘A’ rejects heat
directly to engine ‘B’. Engine ‘A’ receives 200 kJ at temperature of 421⁰C from the
hot source while engine ‘B’ is in communication with a cold sink at a temperature of
5⁰C. If the work output of ‘A’ is twice that of ‘B’. Find (1) intermediate temperature
between A and B; (2) efficiency of each engine and (3) heat rejected to the sink.
[Answer: (1) T2 = 416.67 K; (2) ηA = 39.96%, ηB = 33.28%; (3) Q2 = 120.08 kJ, Q3 =
80.12 kJ] D.S Kumar 225/7.32
7. A reversible heat engine operates between 875 K and 310 K and drives a reversible
refrigerator operating between 310 K and 255 K. The engine receives 2000 kJ of
heat and the net work output from the arrangement equals 350 kJ. Make calculations
for the cooling effect. D.S Kumar 230/7.38
[Answer: (1) Cooling effect, Q3 = 4364.3 kJ]
8. A reversible heat engine operates within the higher and lower temperature limits of
1400K and 400K respectively. The entire output from this engine is utilized to
operate a heat pump. The pump works on reversed Carnot cycle, extracts heat from
a reservoir at 300K and delivers it to the reservoir at 400K. If 100 KJ/s of net heat is
supplied to the reservoir at 400K, calculate the heat supplied by the reservoir at
1400K. GTU Oct 2012
CHAPTER 4 – ENTROPY CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 1
1. A lump of steel of mass 8 kg at 1000 K is dropped in 80 kg of oil at 300 K. Find out
entropy change of steel, oil and the universe. Take specific heats of steel and oil as
0.5 kJ/kg K and 3.5 kJ/kg K respectively. D.S Kumar 248/8.6
[Answer: (dS)st = -4.686 kJ/K, (dS)oil = + 9.0547 kJ/K, (dS)uni = + 4.369 kJ/K]
2. An inventor claims that he has developed a heat engine which absorbs 1200 kJ and
800 kJ of heat from reservoirs at 800 K and 600 K respectively and rejects 600 kJ
and 200 kJ of heat to reservoirs at 400 K and 300 K. The engine is further stated to
give an output equivalent to 1200 kJ. Determine whether the engine suggested by
the inventor is theoretically possible. D.S Kumar 256/8.18
[Answer: Suggested claim is theoretically not possible]
3. The connections of a reversible engine to three sources at 400 K, 300 K and 200 K.
The engine draws 1200 kJ of work. Determine: (1) The amount and directions of
heat reservoirs with the other heat sources, (2) Make calculations for the entropy
changes due to each of the heat interactions with the engine, (3) How much entropy
change occurs for the cycle?
[Answer: (1) Q2 = -1200 kJ, Q3 = -200 kJ; (2) dS1 = -3 kJ/K, dS2 = +4 kJ/K, dS3 = -1
kJ/K; (3) dScycle = 0 kJ/K] D.S Kumar 257/8.19
Entropy Change during Non Flow Thermodynamic Processes
4. A volume of 0.14 m3 of air at 1 bar and 90:C is compressed to 0.014 m3 according to
the law of pv1.3 = C. Heat is then added at constant volume until the pressure is 66
bar. Determine: (1) Heat exchange with cylinder walls during compression and, (2)
Entropy change during each portion of process. Take γ = 1.4, R = 0.286 kJ/kg K.
[Answer: (1) Q1-2 = -429. 47 kJ; (2) dS1-2 = -0.0222 kJ/K, dS2-3 = +0.1154 kJ/K]
5. 1 m3 of air is heated reversibly at constant pressure from 290 K to 580 K and is then
cooled reversibly at constant volume back to initial temperature. If the initial
pressure is 1 bar. Workout the net heat flow and overall (net) change in entropy.
Represent the processes on T-s diagram. Take Cp = 1.005 kJ/kg K and R = 0.287
kJ/kg K.
[Answer: (1) Qnet = +100.224 kJ/K; (2) dSnet = + 0.2387 kJ/K] D.S Kumar 271/8.31
6. 3 kg of air at 150 kPa pressure and 360 K temperature is compressed polytropically
to pressure 750 kPa according to the pv1.2 = C. 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 plot. Determine work done, heat transfer, and change in entropy during each
process. D.S Kumar 272/8.33
[Answer: Process 1-2: W1-2 = -477.85 kJ, Q1-2 = -238.76 kJ, dS1-2 = -0.5762 kJ/K;
Process 2-3: W2-3 = -95.57 kJ, Q2-3 = -334.66 kJ, dS2-3 = -0.8104 kJ/K; Process 3-1: W3-
1 = +498.86 kJ, Q3-1 = +498.86 kJ, dS3-1 = +1.3857 kJ/K]
CHAPTER 5 – ENERGY CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 1
Available Energy and Unavailable Energy
1. Calculate availability (available energy) and unavailability (unavailable energy) of a
system that absorbs 15000 kJ of heat from a heat source at 500 K temperature while
the environment at 290 K temperature. D.S Kumar 287/9.1
[Answer: Availability = 6300 kJ, Unavailability = 8700 kJ]
2. A source at 1000 K is available for transfer of heat at the rate of 100 kW to a system
at 500 K. If these temperatures remain constant. Determine (1) entropy production
during heat transfer, (2) the increase in unavailable energy. Take ambient
temperature as 300 K.
[Answer: (1) dSnet = 6 kJ/K min, (2) ↑in UAE = 1800 kJ/min] D.S Kumar 289/9.6
Decrease in Available Energy due to Heat Transfer at Finite Temperature
Difference
3. A system at 450 K receives 225 kJ/s of heat energy from a source at 1500 K, and the
temperatures of both the system and source remains constant during heat transfer
process. Represent process on T-s diagram. Determine, (1) the net change in
entropy, (2) available energy of heat source and system, and (3) decrease in
available energy.
[Answer: (1) dSnet = +0.35 kJ/s K, (2) AE1 = 180 kJ/s, AE2 = 75 kJ/s, (3) ↓in AE = 105
kJ (or ↑in UAE)] D.S Kumar 292/9.10
4. 20 kg of water at 90:C is mixed with 30 kg of water at 30:C and the pressure
remains constant during the mixing operation. Calculate the decrease in available
energy. It may be presumed that the surroundings are at 10:C temperature and for
water Cpw = 4.187 kJ/kg K.
[Answer: ↓in AE = 233.7 kJ] D.S Kumar 291/9.9
5. 10 Kg of water undergoes transformation from initial saturated vapour at 150°C,
velocity of 25 m/s and elevation of 10 m to saturated liquid at 20°C, velocity of
10m/s and elevation of 3m. determine the availability of for initial state, final state
and change if availability considering environment to be taken at 0.1 MPa and 25°C
and g=9.8 m/s2 GTU Jun 2010
Availability for Closed System
6. One kg of air is contained in a piston cylinder assembly at 10 bar pressure and 500 K
temperature. The piston moves outwards and the air expands to 2 bar pressure and
CHAPTER 5 – ENERGY CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 2
350 K temperature. Calculate: (1) the availability in the initial and final states, (2)
the maximum useful work, and (3) the irreversibility for the system. Assume that
system is insulated and the environment conditions are 1 bar and 290 K. Further for
air, R = 0.287 kJ/kg K, Cv = 0.718 kJ/kg K.
[Answer: (1) A1 = 114.77 kJ, A2 = 12.97 kJ, (2) Wmax = 101.81 kJ, (3) irreversibility (I)
= 30.16 kJ] D.S Kumar 296/9.14
7. A closed system contains 2 kg of air and during an adiabatic expansion process;
there occurs a change in its pressure from 500 kPa to 100 kPa and its temperature
from 350 K to 320 K. If the volume doubles during the process. Calculate: (1)
maximum work, (2) change in availability and (3) irreversibility. Take T0 = 300 K
and P0 = 10 kPa. D.S Kumar 297/9.15
[Answer: (1) Wmax = 123.87 kJ, (2) A1 – A2 = 83.69 kJ, (3) Irreversibility = 80.79 kJ]
8. Two Kg of air at 500 KPa, 80°C expands adiabatically in a closed system until its
volume is doubled and its temperature becomes equal to that of surrounding which
is at 100 kPa, 5 °C . For this process, determine (a) maximum work, (b) Change in
availability and irreversibility , for air take Cv =0.718 kJ/Kg K, R=0.287 kJ/Kg K
GTU Jun 2010
Availability for Open (steady flow) System
9. The air in a steady flow enters the system at pressure 12 bar and temperature 180:C
with a velocity of 100 m/s. The corresponding values at exit from the system are 1.5
bar, 20:C and 50 m/s. if the surrounding are at 1 bar and 20:C. Determine: (1) the
reversible work and actual work assuming process to be adiabatic, (2) irreversibility
& effectiveness of the system. D.S Kumar 300/9.17
[Answer: (1) Wrev = 177.04 kJ/kg, Wact = 164.55 kJ/kg (2) Irreversibility = 12.49
kJ/kg, effectiveness (Є) = 92.94%]
10. A single stage air turbine is to be operated with an inlet pressure and temperature of
6 bar and 800 K. The outlet pressure and temperature are 1.0 bar and 500 K. During
expansion, the turbine losses 25 kJ/kg to the surroundings which are at 1 bar and
300 K. For unit mass flow rate, determine, (1) decrease in availability, (2) the
maximum work, and, (3) irreversibility. For air take R = 0.287 kJ/kg K, Cp = 1.005
kJ/kg K. D.S Kumar 300/9.16
[Answer: (1) ↓in AE = 414.57 kJ/kg, (2) Wmax = 414.57 kJ/kg, (3) irreversibility (I) =
32.57 kJ/kg]
CHAPTER 6 – VAPOR POWER CYCLES CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 1
1. A steam power plant operates on the Carnot cycle using dry steam at 17.5 bar. The
exhaust takes place at 0.075 bar into condenser. The steam consumption is 20
kg/min. Calculate:
a. Power developed in the cycle
b. The efficiency of the cycle
[Ans: 220.95 KW, 34.56%][12.1; Mahesh Rathore]
2. A power generating plant uses steam as working fluid and operates on an ideal
Carnot cycle. Dry saturated steam at 17.5 bar pressure is supplied to the engine and
it expands isentropically to a condenser pressure of 0.07 bar. Assuming the liquid to
be saturated at entry to the boiler, make calculations for the work ratio, thermal
efficiency and specific steam consumption.
[Ans: 0.823, 34.87 %, 5.39 kg/kWh] [15.2, D. S. Kumar]
3. A steam turbine working on Rankine cycle is supplied with dry saturated steam at
25 bar and the exhaust takes place at 0.2 bar. For a steam flow rate of 10 kg/s,
determine:
a. Quality of steam at the end of expansion.
b. Turbine shaft work.
c. Power required to drive the pump.
d. Work ratio and Rankine efficiency.
e. Heat flow in the condenser.
[Ans: 0.776, 739.3 kJ/kg, 25.52 kW, 0.996, 28.9 %, 18100 kW] [15.4, D. S.
Kumar]
4. In a thermal power plant operating on an ideal Rankine cycle, superheated steam
produced at 5 MPa and 500°C is fed to a turbine where it expands to the condenser
pressure of 10 kPa. If the net power output of the plant is to be 20 MW, determine:
a. Heat added in the boiler per kg of water.
b. Thermal efficiency of the cycle.
c. Mass flow rate of steam in kg/s.
d. Mass flow rate of cooling water in the condenser if the cooling water enters
the condenser at 25°C and leaves at 35°C.
[Ans: 3236.96 kJ/kg, 37.68 %, 16.39 kg/s, 789.79 kg/s] [15.7, D. S. Kumar]
CHAPTER 6 – VAPOR POWER CYCLES CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 2
5. Steam at 20 bar, 360°C is expanded in a steam turbineto 0.08 bar. It then enters a
condenser, where it is condensed to saturated liquid water. The pump feeds back the
water into the boiler. (a) Assuming ideal processes, find per kg of steam the net
work and the cycle efficiency. (b) If the turbine and the pump have each 80%
efficiency, find the percentage reduction in the net work and cycle efficiency.
[Ans: 969.61 kJ/kg, 32.5%, 20.1%, 20.1%] [12.2, P. K. Nag]
6. A steam power plant uses the following cycle:
Steam at boiler outlet – 150 bar& 550°C
Reheat at 40 bar to 550°C
Condenser at 0.1 bar.
Using the Mollier chart and assuming ideal processes, find the (a) Quality of steam at
turbine exhaust, (b) Cycle efficiency and (c) Steam rate.
[Ans: 0.88, 43.9%, 2.18 kg/kWh] [12.4, P. K. Nag]
7. In a single heater regenerative cycle the steam enters the turbine at 30 bar, 400°C
and the exhaust pressure is 0.1 bar. The feed water heater is a direct contact type
which operates at 5 bar. Find:
a. The efficiency and the steam rate of the cycle.
b. The increase in mean temperature of heat addition, efficiency and steam rate
as compared to the Rankine cycle (without regeneration).
Pump work may be neglected.
[Ans: 36.08%, 3.85 kg/kWh, 27.4°C, 1.9%, 0.39 kg/kWh] [12.13, R. K. Rajput]
8. An ideal steam power cycle combines the reheat and regenerative cycles. Steam is
supplied to the turbine at 17.5 bar and 300°C. the steam expands isentropically to a
pressure of 8.5 bar, is reheated at constant pressure to 290°C and isentropic
expansion follows to a condenser pressure of 0.04 bar. Steam is extracted at 1 bar
for the purpose of feed water heating. The bled steam raises the temperature of feed
water to 70°C. Assuming the temperature of hot well 26°C, determine the thermal
efficiency of the steam plant.
[Ans: 34.1%] [15.12, D. S. Kumar]
CHAPTER 7 – GAS POWER CYCLES CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 1
1. A Carnot cycle has lowest pressure and temperature equal to 1bar & 20°C. Pressure
after Isothermal compression is 4 bar. Pressure after isentropic compression is 12
bar and after Isothermal heat addition process is 6 bar. Calculate:
a. The highest temperature in the cycle.
b. The change in entropy during Isothermal expansion.
c. Heat added to the cycle.
d. Heat rejected by the cycle [Dec – 2010]
2. An engine uses 6.5 Kg of oil per hour of calorific value of 30,000 kJ/Kg. If the Brake
power of engine is 22 kW and mechanical efficiency is 85% calculate (a) indicate
thermal efficiency (b) Brake thermal efficiency (c) Specific fuel consumption in
Kg/B.P/hr. [June-2010]
3. An engine working on Otto cycle has a volume of 0.45 m3, pressure 1 bar and
temperature 30°C at the beginning of compression stroke. At the end of compression
stroke, the pressure is 11 bar. 210 kJ of heat is added at constant volume. Determine:
a. Pressures, temperatures and volumes at salient points in the cycle.
b. Percentage clearance.
c. Efficiency.
d. Mean effective pressure.
e. Ideal power developed by the engine if the number of working cycles per
minute is 210.
Assume the cycle is reversible.
[Ans: 600 K, 0.081 m3, 1172 K, 21.48 bar, 0.081 m3, 1.97 bar, 591.8 K, 0.45 m3, 21.95
%, 49.5 %, 2.818 bar, 364 kW] [21.13, R. K. Rajput]
4. In an Otto cycle air at start of isentropic compression is at 20˚C and 110kPa. If
clearance volume is 20% of the swept volume and temperature at end of constant
volume heat addition is 1400˚C, find the air standard efficiency and mean effective
pressure in kPa. Take
. [June-2011]
5. The following data pertains to a C.I. engine working on air standard Diesel cycle:
Cylinder bore = 15 cm; Stroke length = 25 cm, Clearance volume = 400 cm3
Calculate the air standard efficiency of the engine if fuel injection takes place at
constant pressure for 5 % of the stroke. How this efficiency value will be affected if
the fuel supply continues up to 8 % of the stroke?
[Ans: 59.35 %, 2 %] [12.18, D. S. Kumar]
6. A four stroke engine working on Diesel cycle has a piston diameter of 25 cm, a
stroke of 40 cm and a clearance volume of 1200 cc. The fuel injection takes place for
5 % of stroke. If the induction pressure corresponds to 1 bar and engine turns 5
CHAPTER 7 – GAS POWER CYCLES CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 2
rev/sec, find the air standard efficiency, mean effective pressure and power
developed.
[Ans: 63.5 %, 6.03 bar, 29.58 kW] [12.24, D. S. Kumar]
7. An engine with 200 mm cylinder diameter and 300 mm stroke works on theoretical
Diesel cycle. The initial pressure and temperature of air used are 1 bar and 27°C.
The cut-off is 8% of the stroke. Determine:
a. Pressures, temperatures and volumes at all salient points.
b. Theoretical air standard efficiency.
c. Mean effective pressure.
d. Power of the engine if the working cycles per minute are 380.
Assume that compression ratio is 15 and working fluid is air. Consider all
conditions to be ideal.
[Ans: 0.0101 m3, 44.31 bar, 886.2 K, 0.0006728 m3, 0.001426 m3, 1878.3 K, 2.866
bar, 858.38 K, 59.8 %, 7.424 bar, 44.27 kW] [21.21, R. K. Rajput]
8. The compression ratio for a single cylinder engine operating on Dual cycle is 9. The
maximum pressure in the cylinder is limited to 60 bar. The pressure and
temperature of the air at the beginning of the cycle are 1 bar and 30°C. Heat is added
during constant pressure process up to 4 percent of the stroke. Assuming the
cylinder diameter and stroke length as 250 mm and 300 mm respectively,
determine:
a. The air standard efficiency of the cycle.
b. The power developed if the number of working cycles are 3 per second.
Take for air Cv = 0.71 kJ/kg-K and Cp = 1.0 kJ/kg-K.
[Ans: 57.56 %, 51 kW] [21.25, R. K. Rajput]
9. In a gas turbine plant working on Brayton cycle, the air at inlet is 27°C, 0.1 MPa. The
pressure ratio is 6.25 and the maximum temperature is 800°C. The turbine and
compressor efficiencies are each 80 %. Find compressor work, turbine work, heat
supplied, cycle efficiency and turbine exhaust temperature. Mass of air may be
considered as 1 kg. Draw T-s diagram.
[Ans: 259.29 kJ/kg, 351.6 kJ/kg, 517.57 kJ/kg, 17.83 %, 723.13 K] [21.38, R. K.
Rajput]
10. In an air standard Brayton cycle, the minimum temperature T1 is governed by the
ambient atmosphere and the maximum temperature T3 is dictated by the material of
construction of the turbine blades. For fixed values of T1 and T3, determine the
pressure ratio rp for obtaining maximum net work per unit mass of air undergoing
the cyclic change.
Consider a gas turbine plant operating on Brayton cycle with minimum and
maximum temperature limits being 300 K and 1000 K. What would be the optimum
CHAPTER 7 – GAS POWER CYCLES CLASS TUTORIAL
Engineering Thermodynamics (2131905) Department of Mechanical Engineering Darshan Institute of Engineering and Technology, Rajkot 3
value of pressure ratio if the turbine is to be operated for maximum power output?
For the pressure ratio thus calculated, determine the plant efficiency, work ratio and
specific power output. Assume working substance to be air and expansion and
compression to be truly isentropic. Comment on the results obtained.
[Ans: 8.22, 45.13 %, 0.4513, 205.02 kW] [12.40, D. S. Kumar]
11. A simple open cycle gas turbine takes in air at atmospheric pressure and 15°C and
compresses air in the compressor up to 12bar. Then air enters the combustion
chamber and is heated to maximum temp of 1350°C, then it enter the turbine and
expands to atmospheric pressure. If the isentropic efficiency of compressor and
turbine is 0.86, combustion efficiency is 0.97, fall of pressure through the
combustion system is 0.3bar, Cp for both air and gas 1.005, γ=1.4. Determine the
flow of air and gas for net power of 200MW developed. Calculate also the heat
supplied per kg of air, work ratio, thermal efficiency and specific fuel consumption if
C.V. of fuel is 42000 kJ/kg.
[Ans: 560kg/s & 13.64kg/s, 1021.92kJ/kg of air, 51.05%, 34.9%, 0.245kg/kWh]
[17.5; R Yadav]
12. In a gas turbine plant, the air is at 100C and 1bar is compressed to 12bar with
compression efficiency of 80%. The air is heated in the regenerator and the
combustion chamber till its temp raised is to 14000C, and during the process the
pressure falls by 0.2 bar. The air then expanded in the turbine and passes to
regenerator which has 75% effectiveness, and causes a pressure drop of 0.2bar. If
the isentropic efficiency of the turbine is 85%, determine the thermal efficiency of
the plant.
[Ans: 42.69%] [17.7; R Yadav]