ME2301 THERMAL ENGINEERING Questions Bank 2015

Anna University, Chennai

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ME2301 THERMAL ENGINEERING L T P C

3 1 0 4

OBJECTIVE:

 To integrate the concepts, laws and methodologies from the first course in

thermo dynamics into analysis of cyclic processes

 To apply the thermodynamic concepts into various thermal application like IC engines, Steam Turbines, Compressors and Refrigeration and Air conditioning systems

UNIT I GAS POWER CYCLES 12

Otto, Diesel, Dual, Brayton cycles, Calculation of mean effective pressure, and air

standardefficiency - Actual and theoretical PV diagram of four stroke and two stroke engines

UNIT II INTERNAL COMBUSTION ENGINES 12

Classification - Components and their function - Valve timing diagram and port

timing diagram - Comparison of two stroke and four stroke engines - Carburettor system, Diesel pump and injector system. Performance calculation - Comparison of petrol and diesel engine - Lubrication system and Cooling system - Battery and Magneto Ignition System – Formation of exhaust emission in SI and CI engines

UNIT III STEAM NOZZLES AND TURBINES 12

Flow of steam through nozzles, shapes of nozzles, effect of friction, critical pressure

ratio, supersaturated flow, Impulse and Reaction principles, compounding,

velocity diagram for simple and multi-stage turbines, speed regulations –Governors.

UNIT IV AIR COMPRESSOR 12

Classification and working principle of various types of compressors, work of

compression with and without clearance, Volumetric efficiency, Isothermal efficiency and Isentropic efficiency of reciprocating compressors, Multistage air compressor and inter cooling –work of multistage air compressor

UNIT V REFRIGERATION AND AIR CONDITIONING 12

Vapour compression refrigeration cycle- super heat, sub cooling – Performance

calculations - working principle of vapour absorption system, Ammonia –Water, Lithium bromide –water systems (Description only) - Alternate refrigerants – Comparison between vapour compression and absorption systems - Air conditioning system: Types, Working Principles - Psychrometry, Psychrometric chart - Cooling Load calculations - Concept of RSHF, GSHF, ESHF -(Use of standard thermodynamic tables, Mollier diagram, Psychrometric chart and refrigerant property tables are permitted in the examination) TOTAL: 60 PERIODS

TEXT BOOKS:

1. Sarkar, B.K,”Thermal Engineering” Tata McGraw-Hill Publishers, 2007.

2. Kothandaraman.C.P., Domkundwar.S, Domkundwar. A.V., “A course in thermal engineering,”Dhanpat Rai &sons ,Fifth edition, 2002

REFERENCES:

1. Rajput. R. K., “Thermal Engineering” S.Chand Publishers, 2000

2. Arora.C.P,”Refrigeration and Air Conditioning,” Tata McGraw-Hill Publishers

1994

3. Ganesan V.” Internal Combustion Engines”, Third Edition, Tata Mcgraw-Hill 2007

4. Rudramoorthy, R, “Thermal Engineering “, Tata McGraw-Hill, New Delhi, 2003

ME 2301 THERMAL ENGINEERING

Part-B (16Marks questions)

1. Drive and expression for the air standard efficiency of Otto cycle in terms of volume ratio. (16)

2. Drive an expression for the air standard efficiency of Diesel cycle. . (16)

3. Drive an expression for the air standard efficiency of Dual cycle. . (16)

4. Explain the working of 4 stroke cycle Diesel engine. Draw the theoretical and actual PV diagram.

5. Drive the expression for air standard efficiency of Brayton cycle in terms of pressure ratio (16)

6. A Dual combustion air standard cycle has a compression ratio of 10. The constant pressure part of combustion takes place at 40 bar. The highest and the lowest temperature of the cycle are 1725 degree C and 27 0 C respectively. The pressure at the beginning of compression is 1 bar.

Calculate (i) the pressure and temperature at key points of the cycle. (ii) The heat supplied at constant volume, (iii) the heat supplied at constant pressure. (Iv) The heat rejected. (v) The work output. (vi) the efficiency and (vii) mep. (16)

7. An Engine-working on Otto cycle has a volume of 0.45 m3, pressure 1 bar and temperature 30˚C at the beginning of compression stroke. At the end of compression stroke, the pressure is 11 bar and 210 KJ of heat is added at constant volume. Determine (i) Pressure, temperature and volumes at salient points in the cycle.' (ii) Efficiency. (16)

8. Explain the working of 4-stroke cycle Diesel engine. Draw the theoretical and actual valve- timing diagram for the engine. Explain the reasons for the difference.

9. Air enters the compressor of a gas turbine at 100 KPa and 25˚ C. For a pressure ratio of 5 and a maximum temperature of 850°C. Determine the thermal efficiency using the Brayton cycle (16)

.

10. The following data in referred for an air standard diesel cycle compression ratio =

15, heat added= 200 KJ/Kg, minimum temperature in the cycle = 25°C, Suction pressure = 1 bar,

Calculate,

1. Pressure and temperature at the Salient point.

2. Thermal efficiency

3. Mean effective pressure,

4. Power output of the cycle, if flow rate of air is 2 Kg/s


UNIT II –INTERNAL COMBUSTION ENGINES

1. Explain full pressure lubrication system I.C Engine. (16)

2. Explain the water cooling system in I.C Engine. (16)

3. Explain the 2 types of Ignition system In 5.1 Engine. (16)

4. Draw and explain the valve timing diagram of 4 stroke Diesel Engine.(16)

5. Draw and explain the port timing diagram of 2stroke Petrol Engine. (16)

6. Explain with neat sketch the exhaust gas analysis. (16)

7. The following results refer to a test on a petrol engine: Indicated power = 30 Kw, Brake power = 26 Kw

Engine speed = 1000 rpm

Fuel brake power/ hour = 0.35 kg Calorific value of fuel = 43900kJ/kg Calculate the indicated Thermal efficiency The brake Thermal efficiency

The Mechanical efficiency (16)

8. A four cylinder 2 stroke cycle petrol engine develops 23.5 kW brake power at 2500 rpm. The mean effective pressure on each piston in 8.5 bar and mechanical efficiency is 85%. Calculate the diameter and stroke of each cylinder assuming the length of stroke equal to 1.5 times the diameter of cylinder. (16)

9. The following data to a particular twin cylinder two stroke diesel engine. Bore 15 cm, stroke 20 cm, speed 400 rpm. Indicated mean effective pressure 4 bar, dead weight on the brake drum 650 N. spring balance reading 25 N Diameter of the brake drum 1 m . Fuel consumption 0.075 kg/min and calorific value of the fuel is 44500 kJ/ kg.

Determine,

1. Indicated Power

2. Brake Power

3. Mechanical efficiency

4. Indicated thermal efficiency

5. Brake thermal efficiency (16)

.


UNIT III -STEAM NOZZLES AND TURBINES

1. An impulse turbine having a set of 16 nozzles receives steam at 20 bar, 400° C. The pressure of steam at exit is 12 bar. If the total discharge is 260 Kg/min and nozzle efficiency is 90%, find the cross sectional area of each nozzle, if the steam has velocity of 80 m/s at entry to the nozzle, finds the percentage increase in discharge. (16)

2. Dry saturated steam at a pressure of 8 bar enters the convergent divergent nozzle and leaves it at a pressure 1.5 bar. If the flow isentropic and if the corresponding index of expansion is 1.133, find the ratio of 0.3 are at exit and throat for max. discharge (16)

3. Steam enters a group of nozzles of a steam turbine at 12 bar and 2200 C and leaves at 1.2 bar. The steam turbine develops 220 Kw with a specific steam consumption of

13.5 Kg/ Kw. Hr. If the diameter of nozzle at throat Is 7mm . Calculate the number of nozzle (16)

4. Drive an expression for critical pressure ratio in terms of the index of expansion

(16)

5. Explain the method of governing in steam turbine. (16)

6. Explain various type of compounding in Turbine (16)

7. A 50% reaction turbine running at 400 rpm has the exit angle of blades as 20° and the velocity of steam relative to the blade at the exit is 1.35 times mean speed of the blade. The steam flow rate is8.33 kg/s and at a particular stage the specific volume is

1.38m3/kg .Calculate, suitable blade height, assuming the rotor mean diameter 12 times the blade height, and diagram work. (16)

8. The blade angle of a single ring of an impulse turbine is 300m/s and the nozzle angle is 200.The isentropic heat drop is 473kJ/kg and nozzle efficiency is 85%.Given the blade velocity coefficient is 0.7 and the blades are symmetrical, Draw the velocity diagram and calculate for a mass flow of 1 kg/s i) axial thrust on balding ii) steam consumption per BP hour if the mechanical efficiency is 90% iii) blade efficiency and stage efficiency. (16)


UNIT IV - AIR COMPRESSOR

1. Drive an expression for the work done by single stage single acting reciprocating air compressor. (16)

2. Drive an expression for the volumetric efficiency of reciprocating air compressors

(16)

3. Explain the construction and working of a root blower (16)

.

4. Explain the construction and working of a centrifugal compressor (16)

5. Explain the construction and working of a sliding vane compressor and axial flow compressor (16)

6. A single stage single acting air compressor is used to compress air from 1 bar and

22° C to 6 bar according to the law PV1.25 = C. The compressor runs at 125 rpm and the ratio of stroke length to bore of a cylinder is 1.5. If the power required by the compressor is 20 kW, determine the size of the cylinder (16)

7. A single stage single acting air compressor is used to compress air from 1.013 bar and 25° C to 7 bar according to law PV1.3 = C. The bore and stroke of a cylinder are

120mm and 150mm respectively. The compressor runs at 250 rpm .If clearance volume of the cylinder is 5% of stroke volume and the mechanical efficiency of the compressor is 85%, determine volumetric efficiency, power, and mass of air delivered per minute. (16)

8. A two stage singe acting air compressor compresses 2m3 airs from 1 bar and 20° C to 15 bar. The air from the low pressure compressor is cooled to 25° C in the intercooler. Calculate the minimum power required to run the compressor if the compression follows PV1.25 =C and the compressor runs at 400 rpm. (16)

UNIT V- REFRIGERATION AND AIR–CONDITIONING

1. Draw neat sketch of simple vapor compression refrigeration system and explain. (16)

2. Explain with sketch the working principle of aqua Ammonia refrigeration system. (16)

3. Explain with sketch the working principle of water-Lithium bromide refrigeration system. (16)

4. Briefly explain the cooling load calculation in air conditioning system. (16)

5. Explain winter, summer, and year round A/C system. (16)

6. Explain unitary A/C and central A/C system. (16)

7. Explain any four psychometric processes with sketch. (16)

8. A refrigeration system of 10.5 tonnes capacity at an evaporator temperature of -

12°C and a condenser temperature of 27°C is needed in a food storage locker. The refrigerant Ammonia is sub cooled by6°C before entering the expansion valve. The compression in the compressor is of adiabatic type.

Find 1. Condition of vapor at outlet of the compressor.2. Condition of vapor at the

Entrance of the Evaporator 3.COP & Power required. (16)

9. A sling psychrometer in a lab test recorded the following readings, DBT=35°C, WBT=25°C,

Calculate the following

1. Specific humidity

2. Relative humidity

3. Vapor density in air

4. Dew point temperature

5. Enthalpy of mixing per kg of air .take atmospheric pressure=1.0132 bar. (16)