DEPARTMENT OF MECHANICAL ENGINEERING

Academic Year 2014-15

ME 6404 – Thermal engineering

Question Bank

Staff In-Charge Head-Mechanical

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UNIT 1: GAS or AIR POWER CYCLES

1. Define Thermodynamic cycle.Thermodynamic cycle is defined as the series of processes performed on the system, sothat energy transfer takes place (heat and work) and the system attains its initial state.

2. What is Air standard or Air power cycles?If air is used as working substance in the thermodynamic cycles, it is called air standard or air power cycles.

3. What is the difference between the Gas power and vapour power cycle ?In gas power cycle, working medium is undergone different processes without phase

change. Whereas in a vapour power cycle the working medium is undergone different processes and energy transfer takes place due to phase change.

4. What are the assumptions made for air standard cycle analysis? 4. List out any four assumptions that are made in the analysis of air standard cycles.

the working medium is prefect gas throughout i.e. it follows PV=mRT The working medium has constant specific heats The working medium does not undergo any chemical change throughout the cycle The compression and expansion processes are reversible adiabatic i.e. there is no loss

or gain in entropy. Kinetic and potential energies of the working fluid are neglected The operation of the engine is frictionless Heat is supplied and rejected in a reversible manner.

5. Name the various (gas) air power cyclesCarnot cycle, Otto cycle, Diesel cycle, Dual cycle and Brayton cycle

6. Write the four processes in sequence for an Air power cycle?i) Suction process: induction of fresh charge into cylinderii) Compression and Combustion process iii) Power output or Expansion processiv) Heat rejection and Exhaust process

7. What is called Reciprocating mechanism?Mechanism which is used to convert the reciprocating or linear motion of a piston into rotary motion of crank shaft and vice versa

8. What are the basic components of a Reciprocating mechanism?i) Cylinder ii) Piston iii) Connecting rod iv) Crank and crank shaft

9. What is the Stroke?It is the maximum displacement of piston during the movement between TDC and BDC or vice versa

10. What is the Stroke or Swept volume? It is the theoretical volume of charge will be inducted for the movement of piston from TDC to BDC during the suction stroke

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11. What is the Clearance volume? It is volume exist between engine head and TDC (Top Dead Centre).

12. Define Compression ratio.

It is ratio between volume of the cylinder before starting of compression and volume of the cylinder at the end of compression.

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Express the compression ratio in terms of clearance and stroke volumes .

V1 = Total volume of the cylinder = VS + VC = Stroke volume + Clearance volumeV2 = VC = Clearance volume

14. Plot the P-V and T-S diagram of Otto cycle.

15. What is the explosion ratio ?

= 16. Sketch the Diesel cycle in p-v and T-s diagram .

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17. Which cycle is more efficient for the same compression ratio and heat input, Otto cycle or

Diesel cycle?For the same compression ratio and heat input, Otto cycle is having more efficiency

than Diesel cycle

18. Write the expression for efficiency of the otto cycle?

; RC = Compression ratio

19. What is the compression ratio for Petrol engine?Compression ratio for petrol engine is 6 to 10

20. What is the cut-off ratio? and write its significance.Cut-off ratio is the ratio between volume of the cylinder at the end of fuel injection and

volume of the cylinder at the starting of fuel injection during constant pressure heat supplied.

When cut off ratio increases efficiency of Diesel cycle decreases

21. Express the cut-off ratio of a Diesel cycle in terms of temperatures. As cut off period takes place during constant pressure process, volume is directly proportional to temperature.

22. What is the range of compression ratio for SI and diesel engine?For petrol of SI engine (petrol engine) RC is 6 to 10For diesel engine 12 to 18

23. Write any four differences between Otto and Diesel cycle?

Sl,.No Otto Cycle Diesel Cycle1 Otto cycle consist of Two

isentropic and two constant volume processes

Diesel cycle consist of two adiabatic, one constant volume and one constant pressure processes

2 Heat addition takes place in constant volume process

Heat addition takes place in constant pressure process

3 Efficiency is more than diesel cycle for the same compression ratio

Efficiency is less than Otto cycle for the same compression ratio

4 Compression ratio is equal to expansion ratio

Compression ration is greater than expansion ratio

24. What is the similarity between Diesel and Dual cycle ?Both cycle used in CI (compression Ignition) engine

25. What are the other names of Dual cycle ?Limited pressure cycle

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26. What are the advantages of Dual cycle over Diesel cycle ?In Dual cycle cut off ratio is smaller than diesel cycle and compression ratio of dual

cycle is less than Diesel cycle hence size of the engine working with Dual cycle is

27. What is the range efficiency of a Diesel cycle ? Diesel cycle efficiency is about 30%

28. Compare the compression ratio of a Diesel with that of Dual cycle?Compression ratio of Diesel cycle in the range of 20 to 25 whereas compression ratio of the Dual cycle is in the range 12 to 16

29. What is the relation between compression ratio and expansion ratio for Otto cycle?

For Otto Cycle compression ratio is equal to expansion ratio30. Why is Dual cycle called as Limiting pressure cycle.

Pressure attained at the end of compression stroke of a Dual cycle is limited to a smaller value compare with that of Diesel cycle. Hence Dual cycle is called as Limited pressure cycle.

31. Draw the P-V and T- S diagram of Dual cycle.

32. Discuss the compression ratio of an Otto , Diesel and Dual cycles.RC for Otto cycle is between 6 to 10Rc for Diesel cycle is between 20 to 25RC for Dual cycle is between 12 to 16

33. For the same compression ratio and heat rejected , which of the following cycle is the most efficient : Otto , Diesel or Dual ? Explain with p-v and T – s diagrams.

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From P V diagram work output from Otto cycle is greater than Dual Cycle which work output is greater than Diesel cycle.

Hence

34. What is the efficiency of an Otto cycle which is having compression ratio is 10?

35. What is the effect of air standard efficiency of Diesel cycle with compression ratio and cut off ratio?

Efficiency increases with the increase in compression ratio and vice-versa. The efficiency decreases with the increase in cut off ratio and vice-versa.

36. Define Mean effective pressure of an I.C. engine.Mean effective pressure is defined as the constant pressure acting on the piston duringthe working stroke. It is also defined as the ratio of work done to the stroke volume or

pistondisplacement volume.

37. What is the other name given to otto cycle?Constant volume cycle.

38. Define the following terms in the Air Standard cycle- i. Air standard efficiency, ii. Specific work transfer, iii. Specific air consumption and iv. work ratio.

Air standard efficiency is defined as the ratio of network transfer during the cycle to the net heat transfer to the cycle

Specific work transfer is the work transfer per unit mass of working substance Specific air consumption is the quantity of working substance required for doing

work transfer or the flow ratio of working substance for unit power. Work ration= Net work transfer in a cycle/possible work transfer in cycle

39. What is the difference between the Gas Turbine power plant and I.C. Engines ?Gas turbine cycle is having rotary compressor whereas IC engine cycles are using reciprocating compressor

40. Draw schematic diagram for Brayton cycle.

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41. Draw PV and Ts diagram of Brayton cycle

42. What are the methods to improve the efficiency of a Brayton cycle ?To increase the efficiency of Brayton cycle the following modifications are to be

providedi) Intercooler ii) Reheater iii) Regenerator

43.What are the effects of introducing regenerator in the basic gas turbine cycle?

i. The fuel economy is improved. The quality of fuel required per unit mass of air is lessii. The work output from turbine, the work required to the compressor will not change.

iii. Pressure drop will occur during regeneration iv. It increased thermal efficiency when the turbine operates at low-pressure ratio.

44. Define isentropic efficiency of turbine and compressor in a Joule cycle.

turbine = Actual internal work / Work of isentropic expansioncompressor = Work of isentropic compression / Actual internal work

45. Compare the Diesel and Brayton cycles

Diesel cycle Brayton cycle1. It consist of two isentropic, one constant volume and one constant pressure processes

1. It consist of two isentropic, one constant pressure processes

2. Heat is rejected at constant volume 2. Heat is rejected at constant pressure3. Used in Diesel engines 3. Used in gas turbines 46. Why Brayton cycle is used in gas turbine?

Inside the turbine the gas is continuously flowing in the processes are flow processes. Since all the processes involved in Brayton cycle is flow process, it has been used as the cycle for gas turbine.

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PART – B

1. A Six-cylinder petrol engine has a compression ratio of 5:1. The clearance volume of each cylinder is 110CC. It operates on the four-stroke constant volume cycle and the indicated efficiency ratio referred to air standard efficiency is 0.56. At the speed of 2400rpm, it consumes 10kg if fuel per hour. The calorific value of fuel is 44000KJ/kg. Determine the average indicated mean effective pressure. [APR’95]

2. An air standard dual cycle has a compression ratio of 16 and compression begins at 1bar and 500C. The maximum pressure is 70bar. The heat transferred to air at constant pressure is equal to heat transferred at constant volume. Find the temperature at all cardinal points, cycle efficiency and mean effective pressure. Take Cp = 1.005kJ/kgK; Cv = 0.718kJ/kgK. [MAY’03]

3. In an oil engine working on dual cycle, the heat supplied at constant pressure is twice that of heat supplied at constant volume. The compression and expansion ratios are 8 and 5.3. The pressure and temperature at the beginning of cycle are 0.93 bar and 270C. Find the efficiency of the cycle and mean effective pressure. Take Cp = 1.005kJ/kgK; Cv = 0.718kJ/kgK. [Anna Univ. May/June 2013]

4. The pressure, temperature and volume of air at the beginning of dual cycle are 1.03bar, 350C and 150liters respectively. The volume after compression is 10liters 42kJ of heat is added to constant volume and 63kJ at constant pressure. Determine air standard efficiency, clearance and cut off percentages. [APR’98]

5. In a Brayton cycle, the air enters the compressor at 1 bar and 250C. The pressure of air leaving the compressor is 3 bar and temperature at turbine inlet is 6500C. Determine per kg of air [i] Cycle efficiency [ii] Heat supplied to air [iii] Work input [iv] Heat rejected in the cooler and [v] Temperature of air leaving the turbine. [MAY’03]

6. In an air standard diesel cycle, the pressure and volume at the beginning of compression are 100kPa and 0.03m3 respectively. Pressure after Isentropic compression is 4.2MPa and after isentropic expansion is 200kPa. Determine [i] Compression ratio [ii] Cut-off ratio [iii] Expansion ratio and [iv] Cycle efficiency. Assume = 1.4, Cv = 0.718kJ/kgK. [NOV’04]γ

7. Consider a stationary power plant operating on an ideal Brayton cycle. The pressure ratio of the cycle is 8 and the gas temperature at the compressor inlet and turbine inlet are 270C & 10270C 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 pressure. [APR’05]

8. Explain a Diesel cycle. [Anna Univ. Apr. 05]

9. Derive an expression for the thermal efficiency of an ideal diesel cycle. [Anna Univ. Apr. 05]10. Show the dual cycle on p-v and T-s diagrams and derive and expression for its efficiency.[May 2014]

11. What are the differences between Otto, diesel and dual cycles?

12. Show that the efficiency of the diesel cycle is always lower than the efficiency of the Otto cycle for same compression ratio.

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13. Derive an expression for air standard efficiency of Brayton cycle in terms of [i] compression ratio and [ii] the pressure ratio.

14. Why the Brayton cycle is most suitable for gas turbine power plant?

15. Derive an expression for air the air standard efficiency of diesel cycle. Explain why the efficiency of Otto cycle is more than that of the diesel cycle for the same compression ratio.[Anna Univ. May/June 2013]

16. The maximum and minimum temperature of an otto cycle are limited to 1200 K and 300K. Find the maximum work done by the cycle per kg of fluid if air is used as working fluid. Find also the air standard efficiency. [16][AU., Nov./Dec. 2010]

17. [a] The mean effective pressure of an ideal diesel cycle is 8 bar. The initial pressure is 1 bar and compression ratio is 12. Determine the cut off ratio and air standard efficiency of the cycle. [b] Discuss the effects of operating variables on cycle analysis. [8] [AU., Nov./Dec. 2010]

18. The minimum pressure and temperature in an Otto cycle are 100 Kpa and 27°C. The amount of heat added to the air per cycle is 1500 KJ/kg. [a] Determine the pressure and temperature at all points of the air standard Otto cycle. [b] Also calculate the specific work and thermal efficiency of the cycle for a compression ratio of 8:1. Take for air: Cv = 0.72 KJ/kg K and = 1.4. [AU., May/June 2011]γ

19. An IC engine operating on the dual cycle the temperature of the working fluid [air] at the beginning of compression is 27°C. The ratio of the maximum and minimum pressure of the cycle is 70 and compression ratio is 15. The amounts of heat added at constant volume and constant pressure are equal. Compute the air standard thermal efficiency of cycle. State three main reasons why the actual thermal efficiency is different from the theoretical value. [AU., May/June 2011]

20. an air standard diesel cycle has a compression ratio of 18. The pressure at the beginning of compression stroke is 1 bar and the temperature is 30°C. the heat supplied is 1800 KJ/kg. (1) The Efficiency (2) Pressure and temperature at all salient points (3) Heat rejected (4) mean effective pressure [AU., Nov/Dec 2013]

(b) an air standard otto cycle has a compression ratio of 7. The pressure at the beginning of compression stroke is 1 bar and the temperature is 40°C. the heat supplied is 2510 KJ/kg. (1) The Efficiency (2) Max Pressure and temperature (3) Work done per of air (4) Mean effective pressure [AU., Nov/Dec 2013]

21. An engine works on a otto cycle. The initial pressure and temperature of the air is 1 bar and 400C. 825KJ of heat is supplied per kg of air at the end of compression. Find the temp and pressure at all salient points if the compression ratio is 6. Also find the efficiency and mean effective pressure for the cycle. Assume air is used as working fluid and take all idle conditions

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(b)An gas turbine works on air standard brayton cycle. The pressure at the beginning of compression stroke is 1 bar and the temperature is 40°C. the amx temperature and pressure is limited to 3bar and 6500C. determine (1) The Efficiency (2) Exhaust temperature (3) Work output (4) Heat supplied and rejected per kg of air. [AU., Nov/Dec 2014]

22. An engine works on a otto cycle has an air standerd efficiency of 56% and rejects 544KJ/Kg of air. The pressure and temperature of the air is 0.1 Mpa and 600C. (1) Compression ratio of the engine (2) Pressure and temperature at the end of compression (3) Work done per of air (4) Max pressure in the cycle (b) Draw the actual and theortical PV diagrams of a four stroke diesel engine and compare them. [AU., Apr/May 2015]

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UNIT 2- I C ENGINES

1. What is engine?Which system converts heat into mechanical work is called as Engine.

2. What is machine?Which system converts any form mechanical and electrical energy into

mechanical work is called as Machine.

3. What is the working principle of Automotive I C Engines?Automotive I C engines are working in the reciprocating mechanism principle.

4. What are the main components of a Reciprocating mechanism?Cylinder, piston, connecting rod, crank and crank shaft are the main components

of a reciprocating system.

5. How IC engines are classified based on construction?Based on the construction, the IC engines are classified as 4 stroke and 2 stroke

engine. In 4 stroke engine valves and valve actuating components are provided whereas in the a stroke engine there is no valves, only ports are provided in the cylinder.

6. How IC engines are classified based on the ignition methods?

Based on the ignition of fuel, IC engine are classified as Spark ignition (SI) engine and Compression ignition (CI) engine. In SI engine carburettor and spark plug is provided where as in CI engine fuel pump and fuel injectors are provided.

7. How IC Engines are classified based on fuel?Based on the fuel, IC engines are classified as Petrol engine and Diesel engine.

8. How IC Engines are classified based on applications?Based on applications, IC engines are classified for automotive vehicles which

are moving whereas IC engines used for stationary applications like for (electricity) power production and run the pump in the agricultural forms.

9. Name the different components of a valve actuating system of a 4 stroke engine. Cam on the cam shaft, follower rod, rocker arm valve stem, valve spring are the

components of actuating the valves.

10.What are the main processes taking place in one cycle of operation of an I C Engine?

The processes taking during one cycle of operation of an IC engines are: 1) Suction of fresh charge inside the cylinder 2) compression of fuel charge to increase its pressure and temperature 3) combustion of fuel charge and expansion of high pressure and high temperature gas (power stroke) 4) exhausting of waste gas.

11.What is the purpose of different piston rings in the piston?Piston rings are used give the grip with cylinder to prevent the fresh fuel charge

should not leak from combustion chamber to crank case.

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12.What is the relation between stroke length and crank radius?Stroke length L = 2×crank radius r

13.Define stroke or swept volume of an IC Engine.Stroke or Swept volume is the theoretical volume of the fresh charge inducted

into the cylinder during suction stroke.

14.What is the type of fuel used in SI engine?In SI engine, fuel with low viscosity and low density fuels with low firing can be

used.

15.What type of fuel can be used in CI engine?In CI engine, fuel with high viscosity and high density fuel can be used.

16.What is meant by 4 stroke engine?In 4 stroke engine all the suction, compression and combustion, power and

exhaust processes are taking place one after another in 4 stroke movement ( 2 revolution of crank shaft) of piston.

17.What is the 2 stroke engine?

In 2 stroke engine all the suction, compression and combustion, power and exhaust processes are taking place in 1 revolution of crank shaft or 2 stroke movement of the piston takes place.

18.Why compression ratio of a SI engine should be kept low compared to CI engine?If compression ratio of a SI engines is high then fresh charge which contains air

and fuel mixture will gets ignited on its own called pre-ignition due to high temperature due to high compression ratio. Hence compression ratio fir SI engines are kept low 8 to 10.

19.What is the effect of high compression ratio of a CI Engine?High compression ratio in CI engine causes the rapid atomization of diesel and

rapid increase in temperature to start the ignition.

20.What are the components in the SI engine for the combustion of fuel?Components for the combustion of fuel in the SI engines are carburetor and

spark plug.

21.What are the components used for the combustion of fuel in the CI engine?In the CI engines, for the combustion fuel, fuel pump and fuel injector are used.

22.What is Detonation or knocking in SI engine?Multiple flame front started due to auto ignition of fuel adjacent to the cylinder

walls causes the collision of flame fronts and collide with cylinder walls create vibration 12

in the cylinder and causes the large sound. This is called Detonation or knocking. This uncontrolled and uneven combustion causes the engine gets damage.

23.What are the effects of detonation in SI engine?Detonation or knocking causes the vibration and collision over the cylinder with

bell sound causes the engine cylinder and other parts like valve seat gets damage.

24.What is auto ignition?Very hotness of the cylinder walls which is due to deposition of unburned

carbon particles causes the fuel adjacent to the cylinder walls gets firing without spark from the spark plug is called auto ignition.

25.What is pre ignition?Due to high compression ratio, the fuel and air charge inducted into the cylinder

during suction stroke gets fired or ignited before electric spark is introduced into cylinder is called pre ignition.

26.Explain Octane Number.Octane number indicates the ability of fuel resists the detonation or knocking.

27.Explain the Ignition delay in CI engine?Ignition delay is the duration starts from the time of fuel injection to time of fuel

gets ignited. Ignition delay consists of physical delay and chemical delay.

28.What are two types of delay period during combustion of fuel in the CI engine? physical delay and chemical delay are the two delay period during combustion

in CI engine.

29.What is the fuel injector?Fuel injector is used in diesel engine to inject and atomize the diesel at the end of

the compression stroke.

30.Write any four major differences between two stroke and four stroke IC engine.Two stroke cycle engine Four Stroke cycle engine

One cycle is completed in two stroke of the piston or one revolution of the crank shaft.

One cycle is completed in four stroke of the piston or two revolution of the crank shaft.

For the same speed, twice the number of power strokes are produced than 4 stroke engine.

For the same speed, half of the number of power strokes are produced than 2 stroke engine.

Turning moment is more uniform and hence lighter flywheel is used.

Turning moment is not uniform and hence bigger flywheel is used.

It contains ports which is operated by the piston movement.

It contains valves which is operated by valve mechanism.

31.What is meant by CI Engine? Why it is called so? CI engine means compression ignition engine. In CI engine the fuel is injected by

a fuel injector in atomized form because of high compressed air it gets ignited automatically. Hence it is called as compression ignition engine.

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32.What is a two stroke engine?A two stroke engine is an engine in which one cycle of operation is completed in

two stroke of the piston or one revolution of the crank shaft.

33.What is a four stroke engine?A four stroke engine is an engine in which one cycle of operation is completed in

four stroke of the piston or two revolution of the crank shaft.

34.Name the four strokes of an IC engine?Suction, compression, power and exhaust stroke.

35.Differentiate petrol and Diesel engines.Petrol or SI engines Diesel or CI engine

1. Combustion of air fuel mixture takes place by spark produced by sparkplug.

1. Combustion takes place by high compressed air.

2. Carburetor is used to mix the air fuel mixture.

2. Fuel injector is used to inject the fuel in atomized form.

3. Compression ratio varies from 6 to 8.

3. Compression ratio varies from 12 to 18.

4.It works on Otto cycle. 4. It works on Diesel or Dual cycle.36.Write the importance of load test conducted in the I C Engines?

Load or performance test to calculate and analysis different efficiencies (Brake thermal, Indicated thermal, mechanical and volumetric efficiency).

37.Write the difference between Brake power and Indicated power.Brake power is the actual power available at the brake shaft for any useful

output. Indicated power is the theoretical power developed at the piston.

38.Define volumetric efficiency of an I C engine.It is the ratio between the actual volume of fresh charge inducted into the

cylinder during suction stroke and theoretical volume or stroke or swept volume of fresh charge inducted.

39.Write the difference between TFC and SFC.TFC is the Total Fuel Consumption in kg/s and SFC is the Specific Fuel

Consumption is the consumption of fuel to develop unit power output in kg/ kWhr.

40.For the load test conducted on I C engine, the torque of 500 Nm and speed of 3000 rpm, Calculate the Brake power.

41.Explain the Mean Effective Pressure.It is the average pressure acting on the piston with same work output as in the

air standard cycle with same stroke volume. It is the ratio between work output and stroke volume.

42.Write the importance of Heat balance test on an IC Engine.Heat balance test to calculate the % of heat utilized in useful output, % of heat

taken by the cooling water, % heat carried by the exhaust gas and % heat loss due to conduction through engine body out of total heat input by burning fuel.

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43.What will the mass of exhaust gas from the IC engine.Mass flow rate of air and mass flow rate of fuel consumption is the input to the engine. As per the

Mass conservation mass of input equals to mass of output. Hence mass flow rate of exhaust gas is the sum Of Mass flow rate of air and mass flow rate of fuel consumption.

me = mf + ma

PART – B1. A simple jet carburetor is required to supply 5.5 kg of air per minute and 0.6 kg of fuel per minute. The density of fuel is 750kg/m3. The air is initially at 1 bar and 300C. Calculate the throat diameter of the choke for a flow velocity of 95m/s. The velocity coefficient is taken as 0.78. If the pressure drop across the fuel metering orifice is 0.76 of that at the choke, calculate orifice diameter assuming Cdf = 0.62.

2. The throat diameter of a carburetor is 80mm and nozzle diameter is 6mm. The Cda = 0.85 and Cdf = 0.7. The nozzle lip is 6mm. The pressure difference causing the flow is 0.1bar. Find [a] Air-fuel ratio supplied by the carburetor neglecting nozzle lip. [b] Air-fuel ratio considering nozzle lip and [c] The minimum velocity of air required to start the fuel flow. Neglect air-compressibility. Take a = 1.2kg/m3 and f = 750kg/m3ρ ρ

3. Air fuel ratio of a mixture supplied to an engine by a carburetor is 13. The fuel consumption of the engine is 7.5kg/hr. The diameter of the venture is 20mm. Find the diameter of fuel nozzle if the lip of the nozzle is 4mm. Take the following data: f = 750kg/m3, Cda = 0.80, Cdf =ρ 0.7 and atmospheric pressure = 1.013bar and temperature = 270C.

4. The venture of a simple carburetor has a throat diameter of 20mm and the coefficient of flow is 0.8. The fuel orifice has a diameter of 1.14mm and coefficient of fuel flow is 0.65. The gasoline surface is 5mm below the throat, calculate [i] The air-fuel ratio for a pressure drop of 0.08bar when the nozzle lip is neglected. [ii] The air fuel ratio when the nozzle lip is taken into account. [iii] The minimum velocity of air or critical air velocity required to start the fuel flow when the nozzle lip is provided. Assume the density of air and fuel to be 1.2kg/m3 and 750kg/m3 respectively. [Anna Univ. Nov.’03]

5. A single cylinder four stroke diesel engine, having a swept volume of 750cm3 is tested at 300rpm. When a braking torque of 65N-m is applied, the mean effective pressure is 1100 kN/m2. Calculate the brake power and mechanical efficiency of the engine.

6. In a laboratory experiment, the following observations were noted during the test of a four stroke S.I. engine.Area of Indicator diagram = 510mm2Length of indicator diagram = 55mmSpring index = 1.25bar/mmDiameter of the piston = 120mmLength of the stroke = 180mmEngine rpm = 480rpmEffective brake load =25kgEffective brake radius = 0.45mDetermine [i] Indicated m.e.p. [ii] Indicated power, [iii] Brake power and [iv] Mechanical efficiency.

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7. A rope brake has a brake wheel diameter of 750mm and the diameter of the rope is 8mm. The dead load on the brake is 275N and spring balance reads 35N. If the engine rpm is 480, find the brake power developed.

8. A six-cylinder petrol engine has a compression ratio of 5 to 1. The clearance volume for each cylinder is 110CC. It operates on the four-stroke constant volume cycle and the indicated thermal efficiency ratio referred to the air standard cycle is 0.56. At a speed 2400rev/min it consumed 10kg of fuel per hour, the energy of combustion being 44MJ/kg. Determine the average indicated mean effective pressure in the cylinder. [MU, April 95]

9. A four cylinder diesel engine works on four-stroke cycle has a cylinder bore of 90mm and a stroke of 150mm. The crank speed is 370rpm, and fuel consumption is 15kg/hr, having a calorific value of 39000kJ/kg. The indicated mean effective pressure is 5bar. If the compression ratio is 14 and cut off ratio is 2.3. Calculate the relative efficiency. Taking = 1.4.γ10. The following observations were taken during a test on a single cylinder four – stroke cycle engine having a bore of 300 mm and stroke of 450mm. Ambient air temperature = 220C Fuel Consumption = 11kg/hr, CV of fuel = 42000kJ/kg Engine speed = 300rpm Mean effective pressure = 6 bar Net brake load = 1.0 kN. Brake drum diameter = 2 m Quantity of Jacket cooling water = 590kg/hr Temperature of entering cooling water = 220C Temperature of leaving cooling water = 700C Quantity of air as measured = 225kg/hr Specific heat of exhaust gas = 1005kJ/kgK Exhaust gas temperature = 4050C Rope diameter = 2 cm Determine indicated power, brake power, mechanical efficiency and draw a heat balance sheet on hour basis. [Anna Univ. May/June 2013]

11. Draw the typical port-timing diagram of a two stroke SI engine and explain the salient points. [Anna Univ. Apr.’03]

12. [i] Explain the construction and working of a fuel injector with a neat sketch [8]. [May 2014] [ii] Draw and explain the Port Timing diagram of two stroke cycle diesel engine. [8] [Anna Univ. May/June 2013]

13. Explain how knocking takes place in diesel engines and discuss the various methods of controlling it. Compare the knocking in diesel engines with that of the petrol engines. [Anna Univ. Nov.’03]100. Discuss the significance of various factors affecting flame speed in SI engines. [Anna Univ. Nov.’03].

14. [a] Discuss in detail the various types of fuel supply systems of a IC engine. [8][b] Compare and contrast petrol and diesel engine. [8] [AU. Nov/Dec. 2010]

15. [a] Discuss with neat sketches the various types of lubricating systems employed for an IC engine. [8] [May 2014][b] The petrol used in a SI engine contains 85% C and 15% H2. The amount of air supplied per kg of fuel is 14 kg. Assume all H2 is burned, no carbon is deposited and exhaust does not contain free O2, find[i] mass of carbon burning to CO2,[ii] mass of each of the gases in the wet exhaust air contains 23% O2 and 77% N2 by mass. [8] [AU. Nov/Dec. 2010]

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16. Explain why cooling is necessary in I.C. engine. With neat sketches describe the working of water cooling system used for multi-cylinder engine. Why should a pump and thermostat be provided in the cooling system on an engine? [AU. May/June 2011]

17. A six cylinder 4 stroke S.I. engine having a piston displacement of 700cm3 per cylinder developed 78 kW at 3200 r.p.m. and consumed 27 kg of petrol per hour. The calorific value of petrol is 44 MJ/kg. Estimate [a] The volumetric efficiency of the engine if the air – fuel ratio is 12 and intake air is at 0.9 bar, 32°C [b] The brake thermal efficiency [c] The brake torque. For air, R = 0.287 kJ/kg K. [AU. May/June 2011]

18. Discuss the working principle of a four stroke engine with sketch. [AU., Nov/Dec 2013](b) Explain the construction and working principle of Battery coil ignition system

19. Explain the working principle of diesel injector with neat Sketch.(b) Calculate the diameter and length of the stroke of a diesel engine working on four stroke constant pressure cycle from the following data. Indicated power = 18.75KW,RPM=220,Compression ratio= 14, Fuel cutoff = 1/20th of the stroke, Index of expansion =1.3, Index of compression=1.35,length/diameter=1.5. assume the pressure and temperature of the air at the inlet are 1bar and 400C respectively. [AU., Nov/Dec 2014]

20. With a neat sketch explain the working principle of simple carburetor.(b) Explain the working of Battery ignition system. [AU., Apr/May 2015]

UNIT III -STEAM NOZZLES AND TURBINES

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1. What are the various types of nozzles and their functions?Nozzle is a duct of varying cross-sectional area in which the velocity increases

with the corresponding drop in pressure.2. What is steam nozzle? How are they classified?

A steam nozzle is a device having variable cross-sectional passage in which thepotential energy of steam is converted into kinetic energy at low pressure when a highpressure steam flows through it. They are classified as convergent type, divergent type,and convergent-divergent type.

3. What are the effects of friction on the flow through a steam nozzle? The final fraction of the steam is increased as the part of the kinetic energy

gets converted into heat due to friction and absorbed by steam with n increase in enthalpy.

The expansion is no more isentropic and enthalpy drop is reduced thereby resulting in lower exit velocity.

The specific volume of steam is increased as the steam becomes drier due to this frictional reheating.

4. Define nozzle efficiency and critical pressure ratio.Nozzle efficiency: It is defined as the ratio of actual enthalpy drop to the isentropic enthalpy drop Nozzle efficiency = Actual enthalpy drop / Isentropic enthalpy drop.Critical pressure ratio: There is only one value of the ratio (P2/P1) which Produces maximum discharge from the nozzle. The ratio is called critical pressure ratio. Critical pressure ratio P2 /P1 = (2/n+1) n/n+1Where, P 1= Initial pressure

P 2= Throat pressure. 5. What is the significance of critical pressure ratio?

The critical pressure gives the velocity of sound. The flow in the convergent portion of the nozzle is subsonic and divergent

portion is supersonic For expanding the steam below critical pressure, the divergent portion of the

nozzle is necessary. When p2 approaches the critical value the rate of discharge will be

maximum.

6. What is the effect of friction in nozzle? It reduces the value of enthalpy drop. The expansion will not be isentropic. It increases the entropy.

7. Explain the phenomenon of super saturated expansion in steam nozzle. Or What is Meta stable flow?

When the supersaturated steam is expanded in the nozzle, the condensation should occur in the nozzle. Since the steam has a great velocity, the condensation does not take place at the expected rate. So the equilibrium between the liquid and vapour phase is delayed and the steam continues to expand in a dry state. The steam in such set of condition is said to be supersaturated or meta stable flow.

8. What are the conditions that produce super saturation of steam in nozzles?

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When the superheated steam expands in the nozzle, the condensation wil occur in the nozzle. Since, the steam has more velocity, the condensation will not take place at the expected rate. So, the equilibrium between the liquid and vapour phase is delayed and the steam continues to expand in a dry state. The steam in such set of condition is said to be supersaturated or meta stable flow.

9. What are the effects of super saturation in a steam nozzle? The following effects in a nozzle on steam, in which super saturation occurs, may be

summarized as follows. The dryness fraction of the steam is increased. Entropy and specific volume of the steam are increased. Exit velocity of the steam is reduced. Mass of stream discharged is increased

10. What are the differences between supersaturated flow and isentropic flow through steam nozzles?

Supersaturated flow Isentropic flow1. Entropy is not constant Entropy is constant2. Reduce in enthalpy drop No reduce in enthalpy drop3. We canot use molier diagram tosolve problems

We can use Mollier diagram tosolve problems

11. The critical pressure ratio initially dry saturated steam is.P2 /P 1=0.57

12. Define stagnation enthalpyThe stagnation enthalpy represents the enthalpy of fluid when it is brought rest

adiabatically.

13.What are the reasons for the drop in velocity of the steam for a given pressure drop in steam nozzle?

Friction between the surface of the nozzle and steam Due to internal fluid friction in the steam

Due to shock losses14.What are the effects of super saturation in nozzles?

i. The dryness fraction of the steam is increased ii. Entropy and specific volume of the steam are increased iii. Exit velocity of the steam is reduced iv. Mass of the steam discharged is increased.

15.What are the main functions of steam nozzles? i. To supply high velocity jet of steam in steam turbine ii. To inject feed water in to the boiler in a steam injector.

16. The critical pressure ratio for initially super heated steam is ____ as compared to initially dry saturated steam.

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Less.

17. When the backpressure of a nozzle is below the designed value of pressure at exit of nozzle, the nozzle is said to be ____

Under damping.

18 .What are the factors those change the fluid properties while a fluid flows through a nozzle with no work or heat transfer?

Change in flow area Frictional forces.

19. What is a steam turbine?Steam turbine is a device which is used to convert kinetic energy of steam into

mechanical energy.

20. What is the fundamental difference between the operation of impulse and reaction steam turbines?

Impulse Turbine Reaction turbine1. It consists of nozzles and movingblades.

It consists of fixed blades and movingblades

2. Pressure drop occurs only in nozzlesnot in moving blades

Pressure drop occurs in fixed as well asmoving blades.

3. Steam strikes the blades with kineticenergy.

Steam passes over the moving bladeswith pressure and kinetic energy.

4. It has constant blade channels area. It has varying blade channels area5. Due to more pressure drop perblade, number of stages required is les.

Number of stages required is more due tomore pressure drop.

21. Explain the need of compounding in steam turbines. (Or) Explain the purpose of compounding in steam turbines.

In simple impulse turbine, the expansion of steam from the boiler pressure to condenser presure takes place in a single stage turbine. The velocity of steam at the exit of turbine is very high. Hence, there is a considerable los of kinetic energy (i.e. about 10to 12%). Also the sped of the rotor is very high (i.e. up to 300rpm). There are several methods of reducing this sped to lower value. Compounding is a method ofabsorbing the jet velocity in stages when the steam flows over moving blades.

22. What are the different methods of compounding?

Velocity compounding Pressure compounding Pressure-velocity compounding.

23. What is meant by carry over loss?

The velocity of steam at exit is sufficiently high thereby resulting in a kinetic energy los called "Cary over loss" or "Leading velocity loss"

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24. Define degree of reaction. It is defined as the ratio of isentropic heat drop in the moving blades to isentropic

heat drop in the entire stage of the reaction turbine.

25. What for a governor is used? The governor is used to regulate the supply of steam to the turbine in such a way

that the speed of the turbine is maintained as for as possible a constant under varying load conditions.

26. What are the different methods of governing steam turbines? Throttle governing Nozzle control governing By-pass governing Combination of throttle and nozzle governing or throttle and by-pass governing.

27. What are the different losses involved in steam turbines? Losses in regulating valves, Losses due to steam friction, Losses due to mechanical friction, Losses due to leakage, Residual velocity losses, Carry over losses, Losses due to wetness of steam, and

28. What are advantages of velocity compound impulse turbine. It’s initial cost is less because of few numbers of stages. Less space is required. The system is reliable and easy to start. There is need of strong casing due to low pressure.

29. What is Wilson line?The limiting condition of under cooling at which condensation commences and is

assumed to restore conditions of normal thermal equilibrium is called “Wilson line”.

30.Define degree of super saturation.The ratio of super saturation pressures corresponding to the temperature

between super saturated region is known as the degree of super saturation.31.Why re-heater is necessary in gas turbine? What are its effects?

The expansion process is very often performed in two sperate turbine stages. he re-heater is placed between the H.P. and L.P. turbines to increase the enthalpy of the exhaust gas coming from H.P. turbine.

Effects: Turbine output is increased for the same compression ratio Thermal efficiency is less.

PART – B

1. Steam at 10.5bar and 0.95dryness is expanded through a convergent divergent nozzle. The pressure of steam leaving the nozzle is 0.85bar. Find [i] Velocity of steam at throat for maximum discharge, [ii] The area at exit, [iii] Steam discharge if the throat area is 1.2cm2.

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Assume the flow is isentropic and there are no friction losses. Take n = 1.135. [Anna Univ. Apr.’03]

2. Dry saturated steam at 2.8bar is expanded through a convergent nozzle to 1.7bar. The exit area is 3cm2. Calculate the exit velocity and mass flow rate for [i] Isentropic expansion and [ii] Super saturated flow. [Anna Univ. Apr.’03]

3. Dry saturated steam at a pressure of 8bar enters a convergent divergent nozzle and leaves it at a pressure of 1.5bar. If the steam flow process is isentropic and if the corresponding expansion index is 1.135, find the ratio of cross sectional area at exit and throat for maximum discharge. [Anna Univ. Oct.’02]

4. Steam enters a group of convergent-divergent nozzles at 21bar and 2700C; the discharge pressure of nozzle is 0.07bar. The expansion is equilibrium throughout and the loss of friction in convergent portion of the nozzle is negligible, but the loss by friction in the divergent section of the nozzle is equivalent to 10% of enthalpy drop available in that section. Calculate the throat and exit area to discharge 14kg/s of steam. [Anna Univ. Oct.’02 & Nov.’03]

5. The following data refer to a single stage impulse turbine: Isentropic nozzle entropy drop = 200kJ/kg, Nozzle efficiency = 90%, Nozzle angle 250 Ratio of blade speed to whirl component of steam speed = 0.5. Blade coefficient = 0.9. The velocity of steam entering the nozzle 30m/s. Find [i] The blade angles at the inlet and outlet if the steam enters the blade without shock and leaves the blade in the axial direction [ii] Blade efficiency [iii] Power developed and [iv] Axial thrust if the steam flow rate is 10kg/s. [Anna Univ. Apr.’03]

6. Steam enters the blade row of an impulse turbine with a velocity of 600m/s at an angle of 250 to the plane of rotation of the blades. The mean blade speed is 250m/s. The blade angle at the exit side is 300. The blade friction loss is 10%. Determine [i] The blade angle at inlet [ii] The work done per kg of steam [iii] The diagram efficiency [iv] The axial thrust per kg of steam per sec. [Anna Univ. Nov.’03]

7. At a particular stage of a reaction turbine, the mean blade speed is 60m/s and the steam pressure is 3.5bar with a temperature of 1750C. The identical fixed and moving blades have inlet angles of 300 and outlet angle 200. Determine [i] the blade height if it is 1/10 of the blade ring diameter for a flow rate of 13.5kg/s. [ii] The power developed by a pair and [iii] The specific enthalpy drop if the stage efficiency is 85%. [Anna Univ. Apr.’04]

8. Steam at a 3bar with 100C superheat is passed through a convergent nozzle. The velocity of steam entering the nozzle is 91.5m/s. The backpressure is 1.5bar. Assuming nozzle efficiency of 90%, determine the area of the nozzle at exit. Discharge though the nozzle is limited to 0.45kg/sec. Take Cps [superheated steam] = 2.2kJ/kg 0C. [Anna Univ. Nov.’04]

9. A convergent-divergent adiabatic steam nozzle is supplied with steam at 10bar and 2500C. The discharge pressure is 1.2bar. Assuming that the nozzle efficiency is 100% and initial velocity of steam is 50m/s, find the discharge velocity. [Anna Univ. Nov.’04]

10. Dry saturated steam at 10bar is expanded in a nozzle to 0.4bar. The throat area is 7cm2 and the inlet velocity is negligible. Determine the mass flow and the exit area. Assume isentropic flow and take the index n = 1.135 for dry saturated steam.[Anna Univ. Apr.’05]

11. Define critical pressure and critical temperature ratios of a nozzle. [Anna Univ. Apr.’05]

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12. Explain the supersaturated expansion of steam in a nozzle with h-s diagram [Anna Univ. Apr.’04]

13. Describe the construction of the combined velocity triangle of an impulse turbine and derive an expression for the power developed by the turbine. [Anna Univ. Nov.’04]

14. Explain the pressure-velocity compounding with a neat sketch. [Anna Univ. Nov.’04]

15. Define the following terms: [i] Diagram efficiency. [ii] Stage efficiency. [Anna Univ. Nov.’04]

16. Obtain the relationship between area, velocity and pressure in nozzle flow. [Anna Univ. Apr’04]

17. [a] Explain various types of nozzles and their distinguishing features [8] [b] Steam expands from 40 bar and specific volume of 0.0749 m3/kg to a pressure of 20 bar in a nozzle. Steam remains superheated throughout. Determine the exit area of cross section. [8] [AU., Nov/Dec. 2010]

18. [a] Derive an expression for critical pressure ratio. [8][b] Compare the throttle and nozzle control governing in steam turbines. [8] [AU. Nov/Dec. 2010]

19. Dry saturated steam at a pressure of 8 bar enters a convergent-divergent nozzle and leaves it at a pressure of 1.5 bar. If the flow is isentropic, and the corresponding expansion index is 1.135; find the ratio of cross-sectional area at exit and throat for maximum discharge. [AU., May/June 2011]

20. A simple impulse turbine has a mean blade speed of 200 m/s. The nozzles are inclined at 20° to the plane of rotation of the blades. The steam velocity from nozzles is 600 m/s. The turbine uses 3500 kg/hr of steam. The absolute velocity at exit is along the axis of the turbine. Determine :a] The inlet and exit angles of the bladesb] The power output of then turbinec] The diagram efficiencyd] The axial thrust [per kg steam per second]Assume the inlet and outlet angles to be equal. [AU. May/June 2011]

21. [i] What are the effects of friction in a nozzle? Explain. [8][ii] A convergent – divergent nozzle is required to discharge 2kg of steam per second.The nozzle is supplied with steam at 7 bar and 1800C and discharge takes place against a back pressure of 1 bar. The expansion up to throat is isentropic and the frictional resistance between the throat and exit is equivalent to 63kJ/kg of steam. Taking approach velocity of 75m/s and throat pressure of 4 bar, estimate [1] Suitable areas for the throat and exit and [2] Overall efficiency of nozzle based on the enthalpy drop between the actual inlet pressure and temperature and the exit pressure. [8] [Anna. Univ. May/June 2013]

22. [i] The velocity of steam, leaving the nozzle of an impulse turbine is 1000 m/s and the nozzle angle is 200. The blade velocity is 350 m/s and the blade velocity of coefficient is 0.85. Assuming no losses due to shock at inlet, calculate for a mass flow of 1.5kg/s and symmetrical blading.

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[1] Blade inlet angle [3][2] Driving force on the wheel [3][3] Axial thrust on the wheel and [3][4] Power developed by the turbine [3][ii] Differentiate between impulse and reaction turbine? [4] [Anna Univ. May/June 2013]

23. steam expands isentropically in a nozzle from 1Mpa to,2500C to 10Kpa .the flow rate is 1kg/s find the following [1] Quality of steam [2] Velocity of steam [3] Exit area of the steam(b) Explain the pressure and velocity compounding diagram of an multi stage turbine with sketch. [Anna Univ. Nov/Dec 2013]

24. Steam at a pressure of 10.5 bar and 0.95 dry is expanded through a convergent divergent nozzle. The pressure of steam leaving the nozzle is 0.85 bar. Find the velocity of steam at throat for maximum discharge. Take n=1.135. also find the area at the exit and steam discharge if throat area is 1.3cm2 . assume the flow is isentropic and there is no friction losses.(b) Explain the pressure and velocity compounding of multi stage turbine with neat sketch. [Anna Univ. Nov/Dec 2014]

25. The inlet condition to a steam nozzle are 10 bar and 2500C. the exit pressure is 2 bar. Assuming isentropic expansion and negligible inlet velocity determine [1] The throat area [2] Velocity of steam [3] Exit area of the nozzle

(b) What is velocity compounding ? list the advantages and limitations. [AU., Apr/May 2015]

UNIT IV - AIR COMPRESOR

(1) Classify the various types of air compressors.1) According to the and principle of operation

a)Reciprocating compressors24

b) Rotary compressors.2) According to the action

a) Single acting compressorsb) Double acting compressors

3) According to the number of stagesa) Single stage compressorsb) Multistage compressors

4) According to the pressure limita)Low pressure compressorsb )Medium pressure compressorsc) High pressure compressors

5) According to the capacitya)Low capacity compressorsb) Medium capacity compressors.c) High capacity compressors

(2) What is meant by single acting compressors?In single acting reciprocating compressor, the suction, compression and delivery

of air takes place on both sides of the piston.

(3)What is meant by single stage compressor?In single stage compressor, the compression of air from the initial pressure to

the final. Pressure is carried out in one cylinder only.

(4)What is meant by double acting compressor?In double acting reciprocating compressor, the suction, compression and delivery of air

takes place on both sides of the piston.

(5) Indicate the application of reciprocating compressors in industry?The applications of compressed air as follows:

Pneumatic brakes Pneumatic jakes. Pneumatic drills. Pneumatic lifts. Spray painting. Shop cleaning. Injecting fuel in diesel engines. Supercharging internal combustion engines. Refrigeration, and air conditioning systems.

(6) What are the advantages of multi stage compression with internal cooling over single stage compression for the same pressure ratio?

It improves the volumetric efficiency for the given pressure ratio. It reduces the leakage los considerably. It gives more uniform torque and hence a smaller size flywheel is required. It reduces the cost of the compressor.

(7) Define the terms as applied to air compressors: Volumetric efficiency and isothermal compression efficiency.(or)Define the mechanical efficiency and isothermal efficiency of a reciprocating air compressor.

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Volumetric efficiency is defined as the ratio of volume of free air sucked into the compressor per cycle to the stroke volume of the cylinder.Volumetric efficiency: Volume of free air taken per cycle/Stroke volume of the cylinder.

Isothermal compression efficiency: Isothermal efficiency is defined as the ratio between isothermal work to the actual work of the compressor.Isothermal efficiency = brake power/ Indicated power

(8) Define clearance ratio?Clearance ratio is defined as the ratio of clearance volume to swept volume (or)

stroke volume.C= Vc/VsVc=Clearance volumeVs=Swept volume

(9) Discus the effect of clearance upon the performance of an air compressor.The volumetric efficiency of air compressor increases with decrease in clearance

of the compressor.(10) Give two merits of rotary compressor over reciprocating compressor.

Rotary compressor gives uniform delivery of air where compared to reciprocating compressor.

Rotary compressors are small in size for the same discharge as compared with reciprocating compressors.

Lubricating system is more complicated in reciprocating compressor where as it is very simple in rotary compressor.

(11) Why clearance is necessary and what is its effect on the performance of reciprocating compresor?

When the piston reaches top dead center in the cylinder, there is a dead spacebetween piston top and cylinder head. This space is known as clearance space and thevolume occupied by this space is known as clearance volume.

(12) What is meant by inter cooler?An inter cooler is a simple heat exchanger. It exchanges the heat of compressed air

from the low-pressure compressor to the circulating.

(13) What are the factors that afect the volumetric efficiency of a reciprocatingcompressor?

1. Clearance volume.2. Compression ratio.

(14) What is compression ratio?Compression ratio is defined as the ratio between total volume and clearance

volume.Compression ratio = Total volume /Clearance volume.

15. What is meant by free air delivered? The free air delivered is the actual volume delivered at the stated pressure

reduced to intake pressure and temperature and expressed in m3 /min.

16. Define mechanical efficiency and isothermal efficiency of a reciprocating compressor.

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Mechanical efficiency is defined as the ratio between brake power to the indicated power.

Mechanical Efficiency = Brake power/Indicated power.Isothermal Efficiency: Isothermal efficiency is defined as the ratio between

isothermal work to the actual work of the compressor. Isothermal Efficiency = Isothermal work/Actual work.

17. What is the difference between perfect inter cooling and imperfect inter cooling? Perfect cooling: When the temperature of air leaving the inter cooler is equal to

the original atmospheric air temperature, then inter cooling is known as perfect inter cooling.

Imperfect Inter cooling: When the temperature of air leaving the inter cooling is more than original atmospheric air temperature, then inter cooling is known as imperfect inter cooling.

18. What factors limit the delivery pressure in a reciprocating compressor? To obtain high delivery pressure, the size of the cylinder will be large. Temperature of air

19. Why clearance is necessary and what is its effect on the performance of reciprocation compressor?

When the piston reaches top dead center in the cylinder, there is a dead space between piston top and cylinder head. This space is known as clearance space and the volume occupied by this space is known as clearance volume.

20. List out the application of compressed air Compressed air is mostly used in pneumatic brakes, pneumatic drills, pneumatic jacks, pneumatic lifts, spray painting, shop cleaning, injecting fuel in diesel engines, supercharging, internal combustion engines, refrigeration and air conditioning systems

21. State the effect of clearance on work done in a reciprocating compressor. Actual suction volume decreases Mass of air is reduced Volumetric efficiency decreases

22. Compressor Capacity is Volume of air delivered ii. Volume of air sucked iii. Both a and b iv. Nine of the above

23.Explain the flow of air controlled in reciprocating compressorsThe flow of air is controlled by three methods such as

Centrifugal governor mechanisms Maintaining the speed of motor constant Providing air pocket advancement to the cylinder.

24.Define mean effective pressure. How is it related to indicated power?The mean effective pressure is defined as hypothetical pressure, which is

considered to be acting on the piston throughout the compression stroke.

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The indicated power IP = Mean effective pressure x L x A x N

25.What are the factors that influence the power input to the compressor? The mass flow of air ii. The pressure ration of the compressor iii. The inlet temperature iv. Temperature difference between the inlet and outlet v. The properties of the working medium

26.What are the internal and external loses in centrifugal compressor?

The internal losses are due to friction between air and wall of flow passage ii. Disc friction iii. leakage between impeller and casing iv. turbulence v. shock and the external losses are mainly due to the bearing friction

27.What are the difference between rotary air compressor and reciprocating aircompressor?

Reciprocating Air compressor Rotary Air compressorThe maximum delivery pressure may beas high as 1000 bar

The maximum delivery pressure is10 bar only.

They are suitable for low discharge ofair at very high pressure

They are suitable for large dischargeof air at low pressure.

The speed of air compressor is low The speed of air compressor is highThe air supply is intermittent The air supply is continuous.The size of the compressor is large forthe given discharge

The size of air compressor is smallfor the same discharge.

The balancing is a major problem There is no balancing problem

28.What are the advantages of multi stage compressor over single stage compressor?

Less work is done by the compressor to deliver the same quantity of air. ii. It improves the volumetric efficiency for the given pressure ratio. iii. The size of the two cylinder may be adjusted to suit the volume and pressure

of the air. iv. It reduces the leakage losses considerably and provides effective lubrication. v. It provides more uniform torque and thus smaller size of the flywheel is

required. vi. It reduces the cost by selecting a cheap material for construction.

29.What is the difference between centrifugal and axial flow compressors?

Centrifugal compressor Axial flow compressorThe flow of air is perpendicular to theaxis of compressor

The flow of air is parallel to the axis ofcompressor

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It has low manufacturing and runningcost

It has high manufacturing and runningcost

It requires low starting torque It requires high starting torquIt is not suitable for multi staging It is suitable for multi staging.It requires large frontal area for a givenrate of flow

It requires less frontal area for a givenrate of flow. It makes the compressorsuitable for aircrafts.

30.What are the advantages of rotary compressor over reciprocating compressor? Maximum free air delivery is as high as 3000 m3/min. ii. Air supply is continuous, more clean. iii. Small size is required for the same discharge. iv. No balancing problem

PART - B1. A single stage reciprocating air compressor takes 1m3 of air per minute at 1bar and 150C and delivers it at 7bar. The law of compression is pV1.3 = constant, calculate the indicated power. Neglect clearance. If the speed of compressor is 300rpm and stroke to bore ratio is 1.5, calculate the cylinder dimensions. Find the power required if the mechanical efficiency of compressor is 85% and motor transmission efficiency is 90%. [NOV’02]

2. A single acting single stage-reciprocating compressor takes 1m3 of air per minute at 1.013bar and 170C and delivers it at 7bar. The law of compression is pV1.35 = constant. Clearance is neglected. Compressor runs at 300rpm. Stroke to bore ratio is 1.5. Mechanically efficiency compressor is 85% and motor transmission efficiency is 90%. Calculate mass or air delivered per minute, indicated power, bore and stroke, and the motor power. [Anna Univ. may 2004]

3. The free air delivery of a single cylinder single stage reciprocating air compressor is 2.5m3/min. The ambient air is at STP conditions and delivery pressure is 7bar. The clearance volume is 5% of the stroke volume and law of compression and expansion is pV1.25 = C. If L = 1.2D and the compressor runs at 150rpm, determine the size of the cylinders. [DEC’03]4. A Single stage single –acting compressor delivers 15m3 of free air per minute from 1bar to 8bar. The speed of compressor is 300rpm. 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. [DEC’03]

5. A single stage double acting compressor has a free air delivery [F.A.D] of 14m3/min measured at 1.013bar and 150C. The pressure and temperature in the cylinder during induction are 0.95bar and 320C respectively. The delivery pressure is 7bar and index of compression and expansion, n= 1.3. The clearance volume is 5% of the swept volume. Calculate the indicated power required and the volumetric efficiency. [Anna Univ. Apr.’04]6. A three-stage air-compressor delivers 5.2m3 of free air per minute. The suction pressure and temperature are 1bar and 300C. The pressure and temperature are 1.03bar and 200C at the free air condition. The air is cooled at 300C after each stage of compression. The delivery pressure of the compressor is 150bar. The R.P.M. of the compressor is 300. The clearance of L.P., I.P., and H.P. cylinders are 5% of the respective strokes. The index of compression and re-

29

expansion in all stages is 1.35. Neglecting pressure losses, find the B.P. of the motor required to run the compressor if the mechanical efficiency is 80%. [Anna Univ. Nov.’04]

7. Consider a single-acting 2 stage reciprocating air compressor running at 300rpm. Air is compressed at a rate of 4.5kg/min from 1.013bar and 288K 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 is 1.3. Assume a complete inter cooling, find the indicated power and the cylinder swept volumes required. Assume that the clearance volumes of both stages are 5% of their respective swept volumes. [Anna Univ. Apr.’05]

8. Explain with the help of a neat sketch the principle of operation of a reciprocating air compressor. [Anna Univ. Apr.’04]

9. With the help of a neat sketch explain the principles of operation of a centrifugal compressor. [Anna Univ. Apr.’04 & Nov.’04]

10. Compare reciprocating and rotary air compressors. [Anna Univ. Apr.’04]

11. Discuss the merits and demerits of rotary and reciprocating compressors. [Anna Univ. Dec.’03 & Nov.’04]

12. With the help of schematic and p-V diagrams, explain the working of a vane type compressor. [Anna Univ. Apr.’05]

13. [a] Show that in a reciprocating air compressor, with perfect inter cooling, the work done for compressing air is rejected to cooling medium.

[b] With the aid of P-V diagrams discuss the reasons for the use of multi stage compressors. [AU. Nov/Dec.2010]

14. [a] Compare reciprocating and rotary compressors and discuss.[b] What are the advantages of multi stage compressors over single stage compressors? Derive the condition of minimum work with complete inter cooling in a two stage compressor. [AU. May/June 2011] [May 2014]

15. A two stage single acting compressor takes in air at the rate of 0.2 m3/s the intake pressure and temperature are 0.1 MPa and 16°C. The air is pressed to a final pressure of 0.7 MPa. The intermediate pressure is ideal and inter cooling is perfect. The compression index in both the stages is 1.25 and the compressor runs at 600 r.p.m. Neglecting clearance, determine:[a] The intermediate pressure[b] The total volume of each cylinder[c] The power required to drive the compressor and[d] The rate of heat rejection in the inter cooler.Take Cp = 1.005 KJ/kg K and R = 0.287 KJ/Kg K. [AU. May/June 2011]

16. [a] Explain the working of a single stage single acting reciprocating compressor with a neat sketch and p-v diagram.[b] A single stage double acting reciprocating air compressor is required to deliver 14 m3 of air minute measured at 1.013 bar and 15°C. The delivery pressure is 7 bar and the seed 300 r.p.m. Take the clearance volume as 5% of the swept volume with the compression and expansion index of n= 1.3. Calculate

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[i] Swept volume of the cylinder[ii] The delivery temperature[iii] Indicated power. [AU. May/June 2011]

17. A single acting reciprocating air compressor has a piston diameter of 200mm and a stroke of 300mm and runs at 350rpm. Air is drawn at 1.1 bar pressure and is delivered at 8 bar pressure. The law of compression is pV1.35 = constant and clearance volume is 6% of the stroke volume. Determine the mean effective pressure and the power required to drive the compressor. [Anna Univ. May/June 2013]

18. Derive the work done by a two stage reciprocating air compressor with inter cooler and derive the condition for minimum work input and the expression for minimum work required for two stage reciprocating compressor? [Anna Univ. May/June 2013]

19 In a two stage compressor in which intercooling is perfect prove that work done in the compressor is minimum when the pressure in the intercooler geometric mean between the initial and final pressure. Draw the PV&TS diagram for two stage compression(b) Explain the construction and working principle of multi stage compressor and discuss the perfect and imperfect intercooling with neat sketch. [Anna Univ. Nov/Dec 2013]

20. Derive an expression for volumetric efficiency of a air compressor. [May 2014]

21. Derive an expression for volumetric efficiency of a reciprocating air compressor.(b) (b) Explain the construction and working principle of multi stage compressor and discuss the perfect and imperfect intercooling with neat sketch. [Anna Univ. Nov/Dec 2014]

22. A single stage single acting reciprocating air compressor delivers 15m3 of free air per min from 1.1 to 8 bar pressure. Assuming that compression and expansion follow pV1.35 = constant and clearance volume is 1/6th of the 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 200C and 1 bar respectively.

[AU., Apr/May 2015]

UNIT V- REFRIGERATION AND AIR–CONDITIONING

1. What is the difference between a heat pump and a refrigerator?

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Heat pump is a device which operating in cyclic process, maintains the temperature of a hot body at a temperature higher than the temperature of surroundings.

A refrigerator is a device which operating in a cyclic process, maintains the temperature of a cold body at a temperature lower than the temperature of thesurroundings.

2. Define the term COP?Co-efficient of performance is defined as the ratio of heat extracted or rejected to

work input. COP=Heat extracted or Rejected/Work Input

3.Define refrigeration effect.The amount of heat extracted in a given time is known as refrigeration effect.

4. Write the expression for COP of a heat pump and a refrigerator?

COP Of heat pump (COP)HP= T2/T2-T1

COP of Refrigerator (COP)REF= T1/T2-T1

5. Explain the term source and sink.Source is a thermal reservoir, which supplies heat to the system and sink is a

thermal reservoir, which takes the heat from the system.

6. What do you understand by the entropy principle?The entropy of an isolated system can never decrease. It always increases and

remains constant only when the process is reversible. This is known as principle of increase in entropy or entropy principle.

7. Define tone of refrigeration.A tone of refrigeration is defined as the quantiy of heat required to be removed

from one tone of water (100kg) at 0 C to convert that into ice at 0 C in 24hours. In actual practice,

1 tone of refrigeration= 210kJ/min=3.5kW

8. Define tone of refrigeration. Heat is removed from a space at a rate of 42,00kJ/h. Express this heat removal rate in tons.

A tone of refrigeration is defined as the quantity of heat required to beremoved from one tone of water (100kg) to convert hat into ice at 0˚ C 24 hours.

9. The vapour compression refrigerator employs the -- cycle.Reversed Carnot.

10. The door of a running refrigerator inside a room was left open. What will happen?

The room will be gradually warmed up.

11. In a vapor compression refrigeration system, where the lowest temperature willoccur?

At inlet of evaporator

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12. How does the actual vapour compression cycle differ from that of the ideal cycle? In actual cycles, pressure loses occur in both condenser and evaporator. Friction loses occur in compressor.

13. Name four important properties of a god refrigerant. Low boiling point. High critical temperature and pressure. Low specific heat of liquid

14. What is the difference between air conditioning and refrigeration?Refrigeration is the process of providing and maintaining the temperature in

space below atmospheric temperature.Air conditioning is the process of supplying sufficient volume of clean air

containing a specific amount of water vapour and maintaining the predetermined atmospheric condition with in a selected enclosure.

15. What is the function of the throttling valve in vapour compression refrigerationsystem?

The function of throttling valve is to allow the liquid refrigerant under high pressure and temperature to pas to controlled rate after reducing its pressure and temperature.

16. In a vapour compression refrigeration system, where the highest temperaturewill occur?

After compresion.

17. The vapour absorption system can use low-grade heat energy in the generator.Is true or false?

True.18. Name any two commonly used refrigerants.

Ammonia (NH3) Carbon dioxide (CO2).

19. Explain unit of Refrigeration.Unit of refrigeration is expressed in terms of tone of refrigeration. A tone of

refrigeration is defined as the quantity of heat required to be removed from one tone of water (100kg) to convert hat into ice at 0˚ C in 24 hours.

20. Why throttle valve is used in place of expansion cylinder for vapour compression refrigerant machine.

In throttling process, enthalpy remains constant and pressure is reduced sothrottle valve is used.

21. What are the effect pf superheat and sub cooling on the vapour compressioncycle?

Superheating increases the refrigeration effect and COP may be increased ordecreased. But sub cooling always increase the COP of the refrigeration and alsodecrease the mass flow rate of refrigerant.

22. What are the properties of god refrigerant?

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An ideal refrigerant should poses the following desirable properties. The refrigerant should have low freezing point. It must have high critical pressure and temperature to avoid large power

requirements. It should have low-specific volume to reduce the size of the compressor. It should be nonflammable, non-explosive, non-toxic and non-corrosive.

23. What is net refrigerating effect of the refrigerant?Refrigerating effect is the total heat removed from the refrigerant in the

evaporator.COP= Refrigeration effect / Work doneRefrigeration effect= COP * Work done.

24. Name the various components used in simple vapour absorption system. Absorber Pump Generator Condenser. Throttle valve. Evaporator.

25. Define refrigerant.Any substance capable of absorbing heat from another required substance can

be used as refrigerant.

26.What are the merits and demerits of air refrigeration system?Merits:

The refrigerant air is cheap and easily available ii. There is no danger of fire of toxic effects due to leakages. iii. The equipment weight to tonne of refrigeration is low

Demerits: The quantity of refrigerant used per of refrigeration is high ii. The COP of the system is very low iii. The danger of frosting at the expander valves is more as air contains

moisture.

27.Name some important refrigeration applicationsIce making, food preservation, milk processing, industrial air-conditioning,

chemical related industries, medical and surgical aids, oil refining and treatment of metals.

28. How does humidity affect human comfort?If the humidity is above a certain level, water vapour from human body moisture

cannot be absorbed by the atmospheric air. It results in discomfort because of sweating.

29. What are the advantages and disadvantages of air refrigeration system?Advantages:

The refrigerant used namely air is cheap and easily available.

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There is no danger of fire or toxic effects due to leakages. The weight to tonne of refrigeration ratio is less as compared to other

systems.

Disadvantages: The quantity of refrigerant used per tonne of refrigeration is high as

compared to other systems. The COP of the system is very low. Therefore running cost is high. The danger of frosting at the expander valves is more as the air contains

30. State any two advantages of vapour absorption system over compression system. No need of electric power. Wear and Tear is less. Tonne capacity is high. There is no leakage of refrigerant. Space requirement is less.

31. What is GSHF? GSHF = TSH/GTH = TSH/[TLH+TSH]TSH = Total sensible heat load.GTH = Grand total heat load.TLH = Total latent heat load.GSHF = Grand sensible heat factor.

32. Mention the desirable properties of refrigerant.

The refrigerant should have low freezing point. It must have high critical pressure and temperature to avoid large power

requirements. It should have low-specific volume to reduce the size of the compressor. It should be non flammable, non-explosive, non-toxic and non-corrosive. It should give high C.O.P in the working temperature range. This is

necessary to reduce the running cost of the system. It must have low specific heat and high latent heat. It should be odorful for leak detection. It should be of low cost.

33. Define sensible heating and sensible cooling process.

Sensible heat process: In sensible heating process, air is heated at constant specific humidity. It means, heating is done without adding moisture. During this process, dry bulb temperature is increased.

Sensible cooling process: In sensible cooling process, air is cooled at constant specific humidity. During this process, the dry bulb temperature is reduced.

34. What is humidification and dehumidification?Humidification is defined as the process of adding moisture at constant dry bulb

temperature. Dehumidification is defined as the process of removing moisture at constant dry

bulb temperature.

35. Enumerate the components of cooling load estimate.

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Heat flow through the exterior walls,ceilings,floors, doors and windows. Heat by solar radiation Heat received from the occupants Heat received by infietrated air etc..

36. Differentiate vapour absorption system and vapour compression system.

Vapour absorption system Vapour compression systemDue to compressor and fan more wearand tear

Only moving part is liquid pump, lesswear and tear

Electrical power is essential to operate the system

Electrical power is not essential to operate the system (heat energy is used)

The compressor is used to compress therefrigerant

Compressor is replaced by absorber andgenerator

Freon 12, Freon 22, NH3, Propane,Isobutane – used as refrigerants

NH3 water vapour system, LithiumBromide water vapour system is used.

Occupies less space. Occupies more space.Performance is poor at partial loads Performance is not affected at partial

loads.

Part B

1. A 5tonne refrigeration plant uses R12 as refrigerant. It enters the compressor at -50C as saturated vapour. Condensation takes place at 320C and there is no under cooling of refrigerant liquid. Assuming isentropic compression, determine COP of the plant, Mass flow of refrigerant, power required to rum the compressor in kW. The properties of R-12 are given in table. [Anna Univ. Nov.’02]

T0C P[bar]Enthalpy kJ/kg Entropy

kJ/kgK sghf hg32 7.85 130.5 264.5 1.542-5 2.61 ---- 249.3 1.557

2.A refrigerator works between -70C and 270C. The vapour is dry at the end of adiabatic compression. Assuming there is no under cooling determine [i] The C.O.P [ii] Power of the compressor to remove a heat load of 12140kJ/hr. the properties of refrigerant are given table. [Anna Univ. May 03]

T0C Sensible heat,[hf]

[kJ/kgK

Latent heat[hfg] kJ/kg

Entropy ofLiquid [sf]

kJ/kgK

Entropy ofVapour [sg]

kJ/kgK-7 -29.3 1297.9 -0.109 4.74827 117.23 1172.3 0.427 4.333

3.A vapour compression refrigeration system using R12 has a condensing temperature of 500C and evaporating temperature of 00C. The refrigeration capacity is 7tons. The liquid leaving the condenser is saturated liquid and compression is isentropic. The vapour leaving the

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evaporator is dry saturated. Assume that enthalpy at the end of isentropic compression = 210kJ/kg. Determine: [i] The refrigeration flow rate. [ii] The power required to run the compressor. [iii] The heat rejected in the plant. [iv] COP of the system. The properties of R12 are listed below: [Anna Univ. Nov.’03 & Dec.’04]

Temp[0C]

Pressure[bar]

hf [kJ/kg] hg[kJ/kg]

[sf]kJ/kgK

sg[kJ/kgK]

50 12.199 84.868 206.298 0.3034 0.6792

0 0.086 36.022 187.397 0.1418 0.6960

4. 28 tonnes of ice from and 00C is produced per day in an ammonia refrigerator. The temperature range in the compressor is from 250C to -150C. The vapour is dry and saturated at the end of compression performance of 62% of theoretical, Calculate the power required to drive the compressor. The properties of ammonia are given in the following table: [Anna Univ. Apr.’04]

TemperatureEnthalpy [kJ/kg] Entropy [kJ/kgK]

Liquid Vapour Liquid Vapour25 100.4 1319.22 0.3473 4.4852-15 -54.56 1304.99 -2.1338 5.0585

5. Air enters the compressor of an aircraft system at 100kPa, 277K and is compressed to 300kPa with an isentropic efficiency of 72%. After being cooled to 328K at constant pressure in a heat exchanger the air then expands in a turbine to 100kPa with an isentropic efficiency of 78%. The low temperature air absorbs a cooling load of 3tons of refrigeration at constant pressure before re-entering the compressor. Which is driven by the turbine. Assuming air as ideal gas, find the COP, the driving power required and the air mass flow rate. [Anna Univ. May.’05]

6. [i] An office is to be air-conditioned for 50 staff when the outdoor conditions are 300C DBT and 75%RH if the quantity of air supplied is 0.4m3/min/person, find the following: [1] Capacity of the cooling coil in tones of refrigeration. [4][2] Capacity of the heating coil in kW. [4][3] Amount of water vapour removed per hour. [4]Assume that required air inlet conditions are 200C DBT and 60% RH air is conditioned first by cooling and dehumidifying and then by heating. [ii] Describe the factors that affect human comfort. [4] [Anna Univ. Apr.’04 & May/June 2013][May 2014]

7. An air-vapour mixture at 0.1 MPa, 300C, 80% RH has a volume of 50m3, Calculate the specific humidity, dew point temperature, wet bulb temperature, mass of dry air and mass of water vapour. [Anna Univ. Apr.’05]

8. With a neat flow diagram, explain the working of a vapour compression refrigeration system. [MU, Apr’96, Apr.’98 & Anna Univ. Apr.’04 & Apr.’05] [May 2014]261. What are the desirable properties of good refrigerants? [Anna Univ. Apr.’05]

9. With a neat sketch, discuss briefly the ammonia absorption refrigeration cycle. [Anna Univ. pr.’05]

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10. Discuss the advantages and disadvantages of vapour absorption refrigeration system over vapour compression system. [Anna Univ. Dec.’03]

11. Define RSHF and ASHF. [Anna Univ. Dec.’03]

12. Draw a neat diagram of air conditioning system required in winter season. Explain the working of different components in the circuit. Is it possible to use steam for such air conditioning system. [Anna Univ. Dec.’03 & apr.’03]

13. Describe the working of summer air conditioning system suitable for hot and wet weather and for hot and dry weather with simple component diagrams. [Anna Univ. Apr.’03 & Apr.’04]

14. [a] Explain with a neat sketch the working principle of lithium bromide refrigeration system.[b] An R – 12 system is operating at conditions such that the vaporizing temperature is - 15° C and the condensing temperature is 40°C. If it is assumed that no sub cooling of the liquid occurs so that the temperature of liquid at the refrigerant control is also 40°C, find the following[i] the refrigerating effect per kilogram[ii] the mass of refrigerant circulated in kilograms per second per kilowatt[iii] the mass of refrigerant circulated per second for a ton system. [AU., Nov/Dec.2010]15. Write short notes on the following. [i] GSHF [ii] RSHF. [AU., Nov/Dec.2010]16. Explain vapour absorption refrigeration system with a neat sketch. Also bring out the difference between vapour compression and absorption refrigeration systems. [AU., May/June 2011]

17. An air-conditioning is to be designed for a small office for winter conditions. Out-door conditions 10°C DBT and 8°C WBT Required indoor conditions 20°C DBT and 60% R.H. Amount of air circulation 0.3 m3/min/person Seating capacity of the office 50 The required condition is achieved first by heating and then by adiabatic humidifying. Find the following:[a] Heating capacity of the coil in kW and the surface temperature required if the bypass factor of the coil is 0.32. [b] The capacity of the humidifier. [AU. May/June 2011]

18. [i] What are the properties of a good refrigerant? [4] [Anna Univ. May/June 2013][ii] An ammonia refrigerator produces 30 tons of ice at 00C in a day of 24 hours. The temperature range in the compressor is from 250C to -150C. The vapour is dry saturated at the end of compression. Assume a COP of 60% Theoretical value. Calculate the power required to drive the compressor. Assume latent heat of ice is 335kJ/kg. For properties of NH3, refer the table below. [12]Temperature [0C] hf hg Sf Sg

kJ/kgk kJ/kgk kJ/kgk kJ/kgk25 298.9 1465.8 1.124 5.039-15 112.34 1426.5 0.4572 5.549

19. The temperature limits of Ammonia refrigeration system are 250C and -100C. if the gas is dry at the end of the compression calculate the COP of the cycle assuming no undercooling of the liquid Ammonia the properties of ammonia are Temperature [0C] liquid heat latent heat liquid entropy

25 298.9 1166.8 1.2420 -10 135.34 1297.5 0.5443

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(b) Explain the construction and working of vapour compression refrigrigeration system with neat sketch. [Anna Univ. Nov/Dec 2013] 20. Explain the construction and working of vapour absorption refrigeration system.(b) explain the desirable thermodynamic properties and environmental safety aspects of alternative refrigents. [Anna Univ. Nov/Dec 2014]

21.

[AU., Apr/May 2015]

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