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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


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


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


[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


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


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


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


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


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


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



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



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]

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