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Unit 1 GAS POWER CYCLES

SYLLABUS

GAS POWER CYCLES 9

Otto, Diesel, Dual, Brayton cycles, Calculation of mean effective pressure and air standard efficiency,Actual and theoretical PV diagram of Four stroke engines, Actual and theoretical PV diagram of two stroke

engines.

PART A

1. What are the assumptions made for air-standard cycle analysis? [APRIL/MAY 2003/5] [NOV/DEC2003/6] [APRIL/MAY 2005/4]

2. What is the name of the process of heat rejection in diesel cycle? [NOV/DEC 2006/5]3. Define air standard efficiency of Dual cycle.[NOVEMBER/DECEMBER 2006R/1]4. For a given compression ratio and heat addition explain why Otto cycle is more efficient than Diesel

cycle? [MAY/JUNE 2006R/1]

5. With the help of p-v and T-s diagrams, show that for the same maximum pressure and temperature ofthe cycle and the same heat rejection, OttoDualDiesel >> .[APR/MAY 03/6]

6. Name the gas power cycle for a gas turbine.[NOVEMBER/DECEMBER 2006/6]7. Explain the effect of pressure ratio on the net output and efficiency of a Brayton cycle.[MAY/JUNE

2006R/2]

8. Sketch the diesel cycle on P-v and T-s diagrams.[NOVEMBER/DECEMBER 2004/6]9. Prove that for the same quantity of heat added, increase of compression ratio increases the thermal

efficiency of Otto-cycle.[NOVEMBER/DECEMBER 2003/5]

10.Define compression ratio of an IC engine. What are its typical values for SI and CI engines?[APRIL/MAY 2005/6]

11.Define the terms as applied to reciprocating I.C. engines. "Mean effective pressure" and "Compressionratio".[NOVEMBER/DECEMBER 2004/5]

12.Define mean effective pressure of an I.C engine.[NOVEMBER/DECEMBER 2006R/2] [APR/MAY05/5]

PART B

13.Derive an expression for efficiency for Otto cycle in terms of compression ratio. (6)[NOVEMBER/DECEMBER 2006/13a(i)]
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14.Sketch the Otto cycle on PV and TS diagrams and derive the expression for the mean effective pressureof Otto cycle. [MAY/JUNE 2006R/12a]

15.Explain a Diesel cycle. (4) [APRIL/MAY 2005/13a(i)]

16.Derive an expression for the thermal efficiency of an ideal diesel cycle. (12)[APRIL/MAY2005/13a(ii)]

17.An engine working on Otto cycle has a volume of 0.45 m3, pressure 1 bar and temperature 30C at thebeginning of compression stroke. At the end of compression stroke, the pressure is 11 bar and 210 kJ ofheat is added at constant volume. Determine

(i) pressures, temperatures and volumes at salient points in the cycle(ii) efficiency. [MAY/JUNE 2007R/11a]

18.The compression ratio in an air-standard Otto cycle is 8. At the beginning of compression process thepressure is 1 bar and the temperature is 300 K. The heat transfer to the air per cycle is 1900 kJ/kg of air.Calculate:

(i) The pressure and temperature at the end of each process of the cycle(ii) Thermal efficiency(iii) The mean effective pressure.[NOVEMBER/DECEMBER 2003/13a]

19.1 kg of air is taken through a diesel cycle. Initially the air is at 25C and 1 bar. The compression ratio is14 and the heat added is 1850 kJ. Calculate the ideal cycle efficiency and mean effective pressure.

(16)[MAY/JUNE 2006R/12b]

20.An air standard diesel cycle has a compression ratio of 18 and the heat transferred to the working fluidper cycle is 1800 kJ/kg. At the beginning of the compression process the pressure is 0.1 MPa and thetemperature is 15C. Determine

a. The pressure and temperature at each point in the cycle.b. The thermal efficiency.c. The mean effective pressure. (10)[NOVEMBER/DECEMBER 2006/13a(ii)]

21.In an air standard diesel cycle, the pressure and volume at the beginning of compression are 100 kPa and0.03 m

3 respectively. Pressure after Isentropic compression is 4.2 MPa, and after isentropic

expansion is 200 kPa. Determine (i) compression ratio (ii) cut-off ratio (iii) expansion ratio and (iv)cycle efficiency. Assume = 1.4, Cv= 0.718 kJ/kgK. [NOVEMBER/DECEMBER 2004/11]

22.An air-standard diesel cycle has a compression ratio of 18, and the heat transferred to the working fluidper cycle is 1800 kJ/kg. At the beginning of the compression stroke, the pressure is 1 bar and thetemperature is 300 K. Calculate:

(i) The pressure and temperature at each point in the cycle(ii) The thermal efficiency(iii) The mean effective pressure.[NOVEMBER/DECEMBER 2003/13b]

23.An air standard dual cycle has a compression ratio of 16, and compression begins at 1 bar, 50C. Themaximum pressure is 70 bar. The heat transferred to air at constant pressure is equal to that at constantvolume. Estimate (i) the pressures and temperatures at cardinal points of the cycle (ii) the cycle
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efficiency (iii) the m.e.p. of the cycle. (For air 005.1=pC kJ/kg K and 718.0=vC kJ/kgK). (8

+ 3 + 5)[APRIL/MAY 2003/14a]

24.An air standard dual cycle has compression ratio of 16 and begins at 1 bar, 50C. The heat transferred atconstant pressure is 312 kJ/kg and it is equal to that at constant volume. Determine the temperature at all

the cardinal points of the cycle and thermal efficiency. Take Cpand Cv for air as 1.005 and 0.718 kJ/kgK respectively. [NOVEMBER/DECEMBER 2006/13b]

25.A dual combustion air standard cycle has a compression ratio of 10. The constant pressure part ofcombustion takes place at 40 bar. The highest and the lowest temperatures of the cycle are 1727 C and27 C respectively. The pressure at the beginning of compression is 1 bar. Calculate (i) the pressures andtemperatures at key points of the cycle, (ii) the heat supplied at constant volume, (iii) the heat suppliedat constant pressure, (iv) the heat rejected, (v) the work output, (vi) the efficiency and (vii) mep.

[NOVEMBER/DECEMBER 2006R/11a]

Brayton cycles

26.A gas turbine works on an air standard Brayton cycle. The initial condition of the air is25C and 1 bar. The maximum pressure and temperature are limited to 3 bar and 650C.

Determine the following :

(i) Cycle efficiency

(ii) Heat supplied and heat rejected/kg of air

(iii) Work output/kg of air

(iv) Exhaust temperature.[NOVEMBER/DECEMBER 2007R/11b

27.Derive an expression for the air-standard efficiency of a Brayton cycle in terms of pressure ratio. (8) (ii)Prove that the pressure ratio for maximum work is a function of the limiting temperature ratio.(8)

[APRIL/MAY 2007/11b]

3.Air enters the compressor of a gas turbine at 100 kPa and 25 C. For a pressure ratio of 5 and amaximum temperature of 850 C determine the thermal efficiency using the Brayton cycle.(6)

[NOVEMBER/DECEMBER 2006R/11b(ii)]

4.Consider a stationery power plant operating on an ideal Brayton cycle. The pressure ratio of the cycleis 8 and the gas temperature at the compressor inlet and turbine inlet are 27C & 1027C respectively.

Determine the following:(i) Gas temperature at the compressor and turbine exit,

(ii) back work ratio, and(iii) thermal efficiency

Assume Pr1= 1.386 and Pr3= 330.9 Where Pr is the relative press. (16)[APRIL/MAY 2005/13b]

5.In a Brayton cycle the air enters the compressor at 1 bar and 25C. The pressure of air leaving thecompressor is 3 bar and temperature at turbine inlet is 650C. Determine per kg of air (i) cycle

efficiency (ii) heat supplied to air (iii) work output (iv) heat rejected in the cooler and (v) temperatureof air leaving the turbine. (3+4+6+3)[APRIL/MAY 2003/14b]


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Unit 2 INTERNAL COMBUSTION ENGINES

SYLLABUS

INTERNAL COMBUSTION ENGINES 9Classification of IC engine, IC engine components and functions. Valve timing diagram and port timingdiagram. Comparison of two stroke and four stroke engines. Fuel supply systems, Ignition Systems,Performance calculation. Comparison of petrol & diesel engine. Fuels, Air-fuel ratio calculation, Knocking

and Detonation. Lubrication system and cooling system. Exhaust gas analysis, pollution control norms.

PART A

1. What is the function of push rod and rocker arm?[NOV/DEC06R/3]2. What are the importance of valve timing diagram?[MODEL PAPER/5]3. What do you mean by scavenging in I.C. Engines?[APRIL/MAY 2003/5]4. What are the basic requirements of a fuel injection system of a diesel engine? [NOV/DEC06R/4]

[MAY/JUNE06R/4]

5. What is the purpose of a Thermostat in an engine cooling system?[APRIL/MAY 2003/6]6. What are the antifreeze solutions used in the water cooling system of an

IC Engine?[MODEL PAPER/6]

7. Define Cetane number.[APRIL/MAY 2003/7]8. Define delay period and delay period angle in CI Engine.[MODEL PAPER/7]9. What are the major losses in an IC Engine?[MODEL PAPER/8]10.What are the various methods to determine the FHP of the engine?[MAY/JUNE 06R/3]11.Differentiate between brake power and indicated power of an I.C. Engine.[APRIL/MAY 2003/8]

PART B

12.Explain with neat sketches the method of lubrication of the following parts of the I.C. Engines.(i) Piston and cylinder(ii) Crank-pin and Gudgeon pin(iii) Cam-shaft.[NOV/DEC06R/12b]

13.Explain with suitable sketch the Magneto-ignition system used in petrol engine and state its advantagesand disadvantages over battery ignition system. (12)[MAY/JUNE 06R/13a(ii)]


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14.What are the important requirement of the spark ignition system? Name two ignition systems which are incommon use and what is the basic difference between them. (8)[MODEL PAPER/14a(i)]

15.What are the advantages and disadvantages of water cooling system in I.C. Engine?(8) [MODELPAPER/14a(ii)]

16.Explain why cooling is necessary in I.C. engine. With neat sketches describe the working of water coolingsystem used for multi-cylinder engine. Why should a pump and thermostat be provided in the cooling

system of an engine?[NOV/DEC06R/12a]

17.Explain with neat diagram the pressure lubrication used in I.C. Engine. (8)[MODEL PAPER/14b(i)]18.What are the various factors affecting the Ignition Lag. (8)[MODEL PAPER/14b(ii)]19.

Discuss the phenomenon of knocking and the various engine factors which affect it in a SI engine.(10)[APRIL/MAY 2003/14a(i)]

20.What are the causes of knock in C.I. engines? (4)[MAY/JUNE 06R/13a(i)]21.Discuss the need, effects and the methodology of supercharging. (6)[APRIL/MAY 2003/14a(ii)]22.Explain the various methods of finding the frictional power of an IC engine and discuss the relative merits.

(8)[APRIL/MAY 2003/14b(i)]

23.Explain the significance and the methodology of heat balance test conducted on an IC engine.(8)[APRIL/MAY 2003/14b(ii)]

24.During the trial (60 minutes) on a single cylinder oil engine having cylinder diameter 300 mm, stroke 450mm and working on the four stroke cycle, the following observations were made :

Total fuel used : 9.6 litersCV. of the fuel : 45000 kJ/kgTotal No. of Revolutions : 12624Gross IMEP : 7.24 barPumping IMEP : 0.34 bar

Net load on the brake : 3150NDiameter of the brake wheel drum : 1.78m

Diameter of the rope : 40 mmCooling water circulated : 515 litersCooling water temperature rise : 25CSpecific gravity of oil : 0.8.

Determine the indicated power, brake power and mechanical efficiency. (6 + 6 + 4)[APR/MAY 10/12b]

25.Air consumption for a four stroke petrol engine is measured by means of a circular orifice diameter 3.2cm. The co-efficient of discharge for the orifice is 0.62 and the pressure across the orifice is 150 mm ofwater. The barometer reads 760 mm of Hg. The temperature of air in the room is 20C. The piston

displacement volume is 0.00178 m3. The compression ratio is 6.5. The fuel consumption is 0.135 kg/min

and the calorific value is 43,900 kJ/kg. The brake power developed at 2500 rpm is 28 kW. Determine,
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(i) The volumetric efficiency on the basis of air alone.(ii) The air fuel ratio.

(iii) The brake mean effective pressure.

(iv) The relative efficiency on the brake thermal efficiency basis. [NOV09/12b]

26.An eight-cylinder, 4 stroke engine of 0.09 m bore and 0.08 m stroke with a compression ratio of 7 is testedat 4500 rpm on a dynamometer which has 0.54 m arm. During a 10 min test the dynamometer scale beamreading was 42 kgf and the engine consumed 4.4 kg of gasoline having a calorific value of 44,000 kJ/kg.

Air 300 K and 1 bar was supplied to the carburettor at the rate of 6 kg/min. Find the brake powerdelivered, brake mean effective pressure, brake specific fuel consumption, brake specific air consumption,

brake thermal efficiency, volumetric efficiency and the air fuel ratio. [APR/MAY 09/12b]

27. The following details were noted in a test on a four-cylinder, four stroke engine, diameter = 100mm ;stroke = 120 mm ; speed of the engine = 1600 rpm ; fuel consumption = 0.2 kg/min ; fuel calorific value =

44,000 kJ/kg ; difference in tension on either side of the brake pulley = 40 kg ; brake circumference is 300cm. If the mechanical efficiency is 80 %, calculate:(i) brake thermal efficiency(ii) indicated thermal efficiency(iii) indicated mean effective pressure and(iv) brake specific fuel consumption.[NOV08/12b]

28.Following data are available for a four stroke petrol engine :Air fuel ratio (by weight) 15.5:1Calorific value of the fuel 45,000 kJ/kgMechanical efficiency 80%

Air standard efficiency 53%Relative efficiency based onindicated thermal efficiency 70%

Volumetric efficiency 80%Stroke/Bore ratio 1.25

Suction conditions 1 bar, 27CSpeed 2400 RPM

Power at brakes 75 kW.Calculate

(i) Compression ratio (3)(ii) Indicated thermal efficiency (3)

(iii) Brake specific fuel consumption (5)(iv) Bore and stroke. (5)[APR/MAY 08/12b]

29.The following data refer to a single cylinder four stroke petrol engine :Compression ratio = 5.6Mechanical efficiency = 80%Brake specific fuel consumption = 0.37 kg/kW hCalorific value of fuel = 44000 kJlkgAdiabatic index for air = 1.4

Find (i) brake thermal efficiency (ii) indicated thermal efficiency (iii) air standard efficiency (iv)relative efficiency with respect to indicated thermal efficiency and (v) relative efficiency withrespect to brake thermal efficiency. [NOV 2007/12b]
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30.Following data relates to 4 cylinder, A stroke petrol engine. Air/Fuel ratio by weight 16:1. Calorific valueof the fuel = 45200 Kj/kg, mechanical efficiency = 82%. Air standard efficiency = 52%, relative efficiency

= 70% volumetric efficiency = 78%, stroke/bone ratio = 1.25 suction conditions = 1 bar, 25C. Speed =2400 rpm power at brakes = 72 kW. Calculate(i) Compression ratio(ii) Indicated thermal efficiency(iii) Brake specific fuel consumption and(iv) Bore and stroke. [MAY 2007/12b]

31.A four cylinder, four stroke cycle petrol engine 79 mm bore, 132 mm stroke develops 28.35 kw brakepower while running at 1450 r.p.m. and using a 20% rich mixture. If the volume of the air into the cylinderwhen measured at 15.5C and 760 mm of mercury is 70% of the swept volume, the theoretical air fuel

ratio is. 14.8, the heating value of petrol used is 44000 kJ/kg and the mechanical efficiency of the engine is

90%, find the indicated thermal efficiency. Take R = 0.287 kJ/kg K. (16)[MAY/JUNE 06R/13b]
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Unit 3 STEAM NOZZLES AND TURBINES

SYLLABUS

STEAM NOZZLES AND TURBINES 9

Flow of steam through nozzles, shapes of nozzles, effect of friction, criticalpressure ratio, supersaturated flow. Impulse and reaction principles, compounding,velocity diagrams for simple and multistage turbines, speed regulations-governorsand nozzle governors.

STEAM NOZZLES

PART A

1. Explain the phenomenon of supersaturated expansion in steam nozzle.[APRIL/MAY 2003/1]2. What are the effects of friction on the flow through a steam nozzle?[APRIL/MAY 2003/2]3. What is metastable flow?[NOV/DEC 2003/1]4. Explain the term 'critical pressure' as applied to steam nozzles.[NOV/DEC 2003/1]

5. What are the effects of friction on the flow through a steam nozzle?[NOV/DEC 2004/1]6. What are the conditions that produce super saturation of steam in nozzles?

[NOVEMBER/DECEMBER 2004/2]

7. Draw the T-s and h-s plot of supersaturated expansion of steam in a nozzle.[APRIL/MAY 2005/1]8. What are the various types of nozzle arid their functions?[APRIL/MAY 2005/2]9. Define the term 'Steam nozzle'. What are the types of nozzle? [NOVEMBER/DECEMBER

2006/1]

10.State the relationship between the velocity of steam and heat drop during any part of a steam nozzle.[NOVEMBER/DECEMBER 2006/2]11.What is the effect of friction on the flow through a steam nozzle?[MAY/JUNE 2006R/5]12.What is super saturated flow in a nozzle? [NOVEMBER/DECEMBER 2006R/5]

PART B

13.Steam at 10.5 bar and 0.95 dryness is expanded through a convergent divergent nozzle. The pressureof steam leaving the nozzle is 0.85 bar. Find (i) the velocity of steam at throat for maximum
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discharge (ii) the area at the exit (iii) the steam discharge if the throat area is 1.2 cm2. Assume the

flow is isentropic and there are no friction losses. Take 135.1=n . (5 + 8 + 3) [APRIL/MAY2003/12a]

14.Dry saturated steam at 2.8 bar is expanded through a convergent nozzle to 1.7 bar. The exit area is 3cm2. Calculate the exit velocity and the mass flow rate, assuming (i) isentropic expansion and (ii)

supersaturated flow. (8 + 8)[APRIL/MAY 2003/12b]

15.The inlet condition of steam to a convergent-divergent nozzle is 2.2 MN/m 2 and 260C. The exitpressure is 0.4 MN/m2. Assuming frictionless flow up to the throat and a nozzle efficiency of 85percent, determine (i) the flow rate for a throat area of 32.2 cm2; (ii) the exit area. [NOV/DEC

2003/11]

16.Steam at 3 bar with l00C superheat is passed through a convergent nozzle. The velocity of steamentering the nozzle is 91.5 m/s. The back pressure is 1.5 bar. Assuming nozzle efficiency of 90%,determine the area of the nozzle at exit. Discharge through the nozzle is limited to 0.45 kg/sec. Take

Cps (superheated steam) = 2.2 kJ/kg0C.[NOVEMBER/DECEMBER 2004/12a]

17.A convergent-divergent adiabatic steam nozzle is supplied with steam at 10 bar and 250C. Thedischarge pressure is 1.2 bar. Assuming that the nozzle efficiency is 100% and initial velocity of

steam is 50 m/s, find the discharge velocity.[NOVEMBER/DECEMBER 2004/12b]

18.Define critical pressure and critical temperature ratios of a nozzle. (4)[APRIL/MAY 2005/11(i)]19.Dry saturated steam, at 10 bar is expanded in a nozzle to 0.4 bar. The throat area is 7 cm2and the

inlet velocity is negligible. Determine the mass flow and the exit area. Assume isentropic flow andtake the index n - 1.135 for dry saturated steam.(12)[APRIL/MAY 2005/11(ii)]

20.Steam is expanded in a set of nozzles from 10 bar and 200 C to 5 bar. What type of nozzle is it?Neglecting the initial velocity find minimum area of the nozzle required to allow a flow of 3 kg/sunder the given conditions. Assume that expansion of steam to be isentropic. (8)

[NOVEMBER/DECEMBER 2006/11a(i)]

21.Discuss why attainment of sonic velocity determines the maximum mass rate of flow through steamnozzle. (8)[NOVEMBER/DECEMBER 2006/11a(ii)]

22.Steam enters a group of convergent-divergent nozzles at a pressure of 2.2 Mpa and with atemperature of 260 C. Equilibrium expansion takes place through nozzles to an exit pressure of 0.4MPa. Up to the throat of the nozzles the flow can be considered as frictionless. From the throat toexit the isentropic efficiency of expansion is 85%. The rate of stem flow through the nozzles is 11kg/so Using mollier chart determine the velocities and areas of throat and exit.

[NOVEMBER/DECEMBER 2006/11b]

23.Dry saturated steam enters a steam nozzle at pressure of 12 bar and is discharged to a pressure of1.5 bar. If the dryness fraction of a discharged steam is 0.95 what will be the final velocity of steam?

Neglect initial velocity of steam. (8)[MAY/JUNE 2006R/14b(ii)]


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24.Steam at a pressure of 15 bar with 50 C of superheat is allowed to expand through a convergent-divergent nozzle. The exit pressure is 1 bar. If the nozzle is required to supply 2 kg/sec. of steam to

the turbine, then calculate(i) The velocities at throat and exit(ii) Areas at throat and exit

Assume 10% frictional loss in divergent part only and percentage taken as % of total heat drop.[NOVEMBER/DECEMBER 2006R/13a]

STEAM TURBINES

PART A

1. What is compounding of a turbine? [MODEL PAPER/3][MAY 2010/6]2. Define stage efficiency of a multistage turbine.[MODEL PAPER/4]3. Explain the need of compounding in steam turbines.[MAY 2003/3]4. Define degree of reaction for a reaction turbine.[APRIL/MAY 2003/4]5. Define 'degree of reaction' in a steam. turbine.[MAY/JUNE 2006R/6]6. Explain the diagram efficiency of steam turbine.[NOV006R/6]

PART B7. Explain with sketches the working principle of a single stage reaction turbine.(8)[MAY/JUNE

2006R/14b(i)]

8. The blade speed of a single ring of an impulse turbine is 300 m/s and the nozzle angle is 20. Theisentropic heat drop is 473 kJ/kg and the nozzle efficiency is 0.85. Given that the blade velocitycoefficient is 0.7 and the blades are symmetrical, draw the velocity diagrams and calculate for a

mass flow of 1 kg/s :(i) Axial thrust on the blading

(ii) Steam consumption per B.P. hour if the mechanical efficiency is 90 per cent

(iii) Blade efficiency, stage efficiency and maximum blade efficiency.[MODEL PAPER/13a][NOVEMBER/DECEMBER 2006R/13b]9. At a particular stage of a reaction turbine, the mean blade speed is

60 m/s and the steam pressure is 3.5 bar with a temperature of 175C. The identical fixed and

moving blades have inlet angles of 30and outlet angles of 20. Determine

(i) the blade height if it is 1/10 of the blade ring diameter, for a flow rate of 13.5 kg/s(ii) the power developed by a pair and

(iii) the specific enthalpy drop if the stage efficiency is 85%. [MODEL PAPER/13b]

10.The following data refer to a single stage impulse turbine :
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Isentropic nozzle enthalpy drop 200 kJ/kgNozzle efficiency 90%

Nozzle angle 25

Ratio of blade speed to whirl component of steam speed 0.5Blade velocity coefficient 0.9The velocity of steam entering the nozzle 30 m/sec

Find (i) the blade angles at the inlet and outlet if the steam enters the blade without shock and leavesthe blade in the axial direction (ii) blade efficiency (iii) power developed (iv) axial thrust if the

steam flow rate is 10 kg/sec. (16)[APRIL/MAY 2003/11]

11.One stage of an impulse turbine consists of a converging nozzle ring and one ring of moving blades.The nozzles are inclined at 22

0to the blades whose tip angles are both 35. If the velocity of steam at

exit from the nozzle is 660 m/s, find the blade speed so that the steam passes without shock. Find the

diagram efficiency neglecting losses if the blades are run at this speed. (16)[MAY 2010/13b]

12.A single row impulse turbine develops 132.4 kW at a blade speed of 175 m/s, using 2 kg of steamper sec. Steam leaves the nozzle at 400 m/s. Velocity coefficient of the blades is 0.9. Steam leaves

the turbine blades axially. Determine nozzle angle, blade angles at entry and exit, assuming noshock.[NOV09/13b]

13.Steam enter the blade row of an impulse turbine with a velocity of 500 m/s at an angle of 30 to theplane of rotation of the blades. The mean blade speed is 285 m/s. The blade angle on the exit side is35. The blade friction coefficient is 12%. Determine.

(i) The angle of the blade on the entry side(ii) The work done per kg of steam

(iii) The diagram efficiency and(iv) The axial thrust per kg of steam/second. (16) [MAY/JUNE 2006R/14a]


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14.Sketch and explain a centrifugal compressor.[NOV/DEC 2004/13b(i)]15.A two-stage co with the help of schematic and p-V diagrams explains the working of a vane type

compressor.[APRIL/MAY 2005/12b]

16.Discuss the merits and demerits of Rotary compressor over reciprocating compressors.[NOV/DEC 2004/13b(ii)] [NOV/DEC 2003/12b]

17.A single acting single stage compressor is belt driven from an electric motor at 400rpm. Thecylinder diameter is 15 cm and the stroke 17.5 cm. The air is compressed from 1 bar to 7 bar and thelaw of compression PV

1. 3= constant. Find the power of the motor, if transmission efficiency is

97% and the mechanical efficiency of the compressor is 90%. Neglect clearance effects.(10)[MAY/JUNE 2006R/11(ii)]

18.A single-stage single-acting compressor delivers 15 m

3

of free air per minute from 1 bar to 8 bar.The speed of compressor is 300 rpm.Assuming that compression and expansion follow the law pV1.3

= constant and clearance is 1/16th of swept volume, find the diameter and stroke of the compressor.Take L/D = 1.5.The temperature and pressure of air at the suction are same as atmospheric air.

[NOV/DEC 2003/12a]

19.A single stage, single acting compressor running at 1000 rpm delivers air at 25 bar. The suctionconditions are 1.013 bar and 15C, and the volume delivered measured at this suction conditions is0.25 m

3/min. The clearance volume is 3% of the swept volume and the stroke/bore ratio is 1.2 : 1.

The index of compression is 1.3. Calculate :(1) The volumetric efficiency,

(2) The bore and stroke,(3) The indicated power,(4) The isothermal efficiency. (10)[NOVEMBER/DECEMBER 2006/12a(ii)]

20.Compressor delivers 2 m3free air per minute. The temperature and pressure of air at the suction are27C and 1 bar. The pressure at the delivery is 50 bar. The clearance is 5% of the stroke in L.P.

cylinder as well as in H.P. cylinder. Assume perfect inter-cooling between the two stages, find (i)

the minimum power required to run the compressor. (ii) If the compressor is to run at 200 rpm find

the diameters and strokes assuming the strokes of both the cylinders are equal to the diameter of L.P.

cylinder. (4 + 12)[APRIL/MAY 2003/13a]21.A single-acting two-stage compressor with complete inter-cooling delivers 5 kg/min of air at a

pressure of 15 bar. The intake state of air is 1 bar and 15C. The clearance volumes of L.P. and H.P.cylinders are 5% and 6% of the respective cylinder swept volumes. The speed of the compressor is

420 rpm. Assuming the compression and expansion processes are polytropic with 3.1=n . Calculate(i) the power required (ii) the isothermal efficiency (iii) swept and clearance volumes of the L.P.and H.P. cylinders. (4 + 2 + 10)[APRIL/MAY 2003/13b]

22.A three-stage air-compressor delivers 5.2 m3of free air per minute. The suction pressure andtemperature are 1 bar and 30C. The pressure and temperature and 1.03 bar and 20C at the free air
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condition. The air is cooled to 30C after each stage of compression. The delivery pressure of thecompressor is 150 bar. The R.P.M. of the compressor is. 300. The clearances of L.P., I.P., and H.P.

cylinders are 5% of the respective strokes. The index of compression and re-expansion in all stages

is 1.35. Neglecting pressure losses, find the B.P. of the motor required to run the compressor if themechanical efficiency is 80%.[NOV/DEC 2004/13a]

23.Consider a single-acting 2-stage reciprocating air compressor running at , 300 rpm. Air iscompressed at a rate of 4.5 kg/min from 1.013 bar and 288 K through a pressure ratio of 9 to 1. Both

the stages have the same pressure ratio and the index of compression and expansion in both stages is1.3. Assume a complete inter cooling, find the indicated power and the cylinder swept volumesrequired. Assume that the clearance volumes of both stages are 5% of their respective sweptvolumes. [APRIL/MAY 2005/12a]

24.A two stage compressor with complete inter-cooling delivers 10 kg/min of air at 16 bar. The suctionoccurs at 1 bar and 15C. The expansion and compression processes are reversible polytropic withindex n = 1.25. Calculate the power required and isothermal efficiency. (8)

[NOVEMBER/DECEMBER 2006/12b(ii)]

25.Determine the size of the cylinder of a double acting air-compressor of 32 KW LP. in which air isdrawn in at 1 bar and compressed to 16 bar according to the lawpv1.25=constant. R.P.M. = 300,Piston speed = 180 m/min, Volumetric efficiency = 0.8.[NOVEMBER/DECEMBER

2006R/14a(ii)]

26.A two-stage double acting air compressor, operating at 200 r.p.m, takes in air at 1.013 bar and 27C. The size of the L.P. cylinder is 350 x 380 mm, the stroke of H.P. cylinder is the same as that ofthe L.P. cylinder and the clearance of both the cylinders is 4%. The L.P. cylinder discharges the airat a pressure of 4.052 bar. The air passes through the inter-cooler so that it enters the H.P. cylinder at

27 C and 3.850 bar, finally it is discharged from the compressor at 15.4 bar. The value of n is bothcylinders is 1.3. Cp= 1.0035 kJ/kg-K and R = 0.287 kJ/kg-K.Calculate :

(i) The heat rejected in the inter-cooler.(ii) The diameter of H.P. cylinder and

(iii) The power required to drive H.P. cylinder.[NOVEMBER/DECEMBER 2006R/14b]


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Unit 5 REFRIGERATION AND AIR-CONDITIONING

SYLLABUS

REFRIGERATION AND AIR CONDITIONING 9

Vapour compression refrigeration cycle- super heat, sub cooling Performance calculations - workingprinciple of vapour absorption system, Ammonia Water, Lithium bromide water systems (Descriptiononly) - Alternate refrigerants Comparison between vapour compression and absorption systems - Airconditioning system: Types, Working Principles - Psychrometry, Psychrometric chart - Cooling Loadcalculations - Concept of RSHF, GSHF, ESHF.(Use of standard thermodynamic tables, Mollier diagram,Psychrometric chart and refrigerant property tables are permitted in the examination)

REFRIGERATION

PART A

1. Define COP of refrigeration.[NOV/DEC 2007/9]2. A carnot refrigerator requires 1.3 kW per tonne of refrigeration to maintain a region at low

temperature of - 38C. Determine the COP of the refrigerator and the higher temperature of thecycle.

[MAY/JUNE 2007/9]

3. What is the unit of refrigeration and explain.[NOVEMBER/DECEMBER 2006/9]4. What is a ton of refrigeration?[MAY/JUNE 2006/9]5. What should be the properties of an ideal refrigerant?[MAY/JUNE 2006/10]

PART B

6. Draw a neat sketch of a simple vapour compression refrigeration system and explain its principle ofoperation. (5)[NOV/DEC 2007/15a(i)]

7. An ammonia refrigerator produces 30 tonnes of ice from and at OC in a day of 24 hours. Thetemperature range in the compressor is from 25C to 15C. The vapour is dry saturated at the end of

compression and an expansion valve is used. Calculate the coefficient of performance. Theproperties of the refrigerant are given in the following table : (11)[NOV/DEC 2007/15a(ii)]

Temperature C Enthalpy KJ/kg Entropy of Liquid Entropy of VapourKJ/kg-K KJ/kg-K

Liquid Vapour25 100.04 1319.22 0.3473 4.4852-15 -54.56 1304.99 -2.1338 5.0585


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8. A refrigeration system of 10.5 tonnes capacity at an evaporator temperature of 12C anda condenser temperature of 27C is needed in a food storage locker. The refrigerant ammonia is sub

cooled by 6C before entering the expansion valve. The vapour is 0.95 dry as it leaves theevaporator coil. The compression in the compressor is of adiabatic type. Find(i) Condition of vapour at the outlet of the compressor

(ii) Condition of vapour at the entrance of the evaporator(iii) COP and

(iv) The power required.Neglect valve throttling and clearance effect. [MAY/JUNE 2007R/15 (a)]

9. Freon 12 is compressed from 200 kPa to 1.0 MPa in an 80 percent efficient compressor. Thecondenser exiting temperature is 40 C. Calculate the COP and the refrigerant mass flux for 100 tons

(352 kW) of refrigeration.[NOVEMBER/DECEMBER 2006R/15a]

10.A simple R-12 plant is to develop 5 tonnes of refrigeration. The condenser A and evaporatortemperatures are to be 40

0C and l0C respectively. Determine

(i) the refrigerant flow rate in kg/s(ii) the volume flow rate handled by the compressor in m

3/s

(iii) the compressor discharge temperature(iv) the heat rejected to the condenser in kW(v) the COP and(vi) the power required to drive the compressor.How does this COP compare with that of a Carnot refrigerator operating between 40C and

l0C. (16) [MAY/JUNE 2006R/15a]

AIR-CONDITIONING

PART A11.Define wet bulb temperature and degree of saturation.[NOV/DEC 2007/10]12.Define dew point temperature.[MAY/JUNE 2007/10]13.Define degree of saturation and specific humidity.[NOVEMBER/DECEMBER 2006R/10]

PART B

14.An office is to be air-conditioned for 50 staff when the outdoor conditions are 30C DBT and 75 RHif the quantity of air supplied is 0.4 m

3/min/person, find the following :

(i) Capacity of the cooling coil in tonnes of refrigeration(ii) Capacity of the heating coil in kW

(iii) Amount of water vapour removed per hourAssume that required air inlet conditions are 20C DBT and 60% RH, Air is conditioned first by

cooling and dehumidifying and then by heating.(iv) If the heating coil surface temperature is 25C, find the by-pass factor of the heating coil?

[NOV/DEC 2007/15b]
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15.A sling psychrometer in a laboratory test recorded the following readings.Dry bulb temperature = 35C

Wet bulb temperature = 25CCalculate the following :(i) specific humidity

(ii) relative humidity(iii) vapour density in air

(iv) dew point temperature and(v) enthalpy of mixture per kg of dry air

Take atmospheric pressure = 1.0132 bar. [MAY/JUNE 2007/15b]

16.100 m3of air per minute at 15 C DBT and 80% R.H. is heated until its temperature becomes 22 C.Find the following

(i) Heat added to the air per min.(ii) R.H. of the heated air. Assume air pressure is at 1.033 bar.[NOVEMBER/DECEMBER

2006R/15b]

17.An office is to be air-conditioned for 50 staff when the outdoor conditions are 30C DBT and 75RH if the quantity of air supplied is 0.4 m

3/min/person, find the following :

(i) Capacity of the cooling coil in tonnes of refrigeration(ii) Capacity of the heating coil in kW(iii) Amount of water vapour removed per hour.

Assume that required air inlet conditions are 25C DBT and 65% RH. Air is conditioned first bycooling and dehumidifying and then by heating. If the heating coil surface temperature is 28C, find

the by-pass factor of the heating coil. (16)[MAY/JUNE 2006R/15b]

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