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td qp UPTO nov 2012 18092012

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  • 7/22/2019 td qp UPTO nov 2012 18092012



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    B.E./B.Tech. DEGREE EXAMINATIONS, NOV./DEC. 2011Regulations 2008

    Third Semester Mechanical EngineeringME2202 Engineering Thermodynamics

    ( Common to PTME 2202 Engineering Thermodynamics for B.E.(Part

    -Time) Third Semester Mech - Regulations 2009; Use of approved

    thermodynamic tables, Mollier diagram, Psychometric chart and Refrigerant

    property tables are permitted in the examination.)

    Time: Three Hours Maximum: 100 marks

    Answer ALL Questions

    Part A - (10 x 2 = 20 marks)

    1. Distinguish between the terms 'state' and 'process' of thermodynamics.2. Show that energy of an isolated system is always constant.

    3. What is a cyclic heat engine?4. What do you mean by entropy generation?

    5. What is a pure substance? Give examples.

    6. Why is Carnot cycle not practicable for a steam power plant?

    7. What is equation of state? State the van der Waals equation for a real gas of m kg.

    8. What is the partial pressure of carbon dioxide in a container that holds 5 moles of carbon

    dioxide, 3 moles of nitrogen and 1 mole of hydrogen and has a total pressure of 1.05 atmospheres?

    9. What is a psychrometer?

    10. Sketch the Cooling and Humidifying process on a skeleton Psychrometric chart.Part B - (5 x 16 = 80 marks)

    11. (a) (i) Define the following terms:

    (1) Thermodynamics(2) Macroscopic approach

    (3) Continuum(6)

    (ii) 25 people attended a farewell party in a small room of size 10 x 8 m and have a 5 m ceiling.

    Each person gives up 350 kJ of heat per hour. Assuming that the room is completely sealed off

    and insulated, calculate the air temperature rise occurring in 10 minutes. Assume Cv of air

    0.718 kJ/kg K and R = 0.287 kJ/kg K and each person occupies a volume of 0.05 m3. Take p

    = 101.325 kPa and T = 20C. (10)OR

    11. (b) (i) Considering a system which changes its state, prove that the internal energy is a

    point function. (8)

    (ii) Air flows at the rate of 0.5 kg/s through an air compressor, entering at 7 m/s,, 100 kPa and 0.95m3/kg and leaving at 5 m/s, 700 kPa, and 0.19 m

    3/kg. The internal energy of air leaving is 90 kJ/kg

    greater than that of the air entering. Cooling water in the compressor jackets absorbs heat from the air

    at the rate of 58 kW. (1) Compute the rate of shaft work input to the air in kW (2) Find the ratio of the

    inlet pipe diameter to outer pipe diameter. (8)

    12. (a) (i) An engine is supplied with 1120 kJ/s of heat. The source and sink temperature aremaintained at 560K and 280K. Determine whether the following cases represent the reversible,

    irreversible or impossible heat engines.

    (1) 900 kW of heat rejected

    (2) 560 kW of heat rejected

    (3) 108 kW of heat rejected(8)

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    (ii) A heat pump working on the Carnot cycle takes in heat from a reservoir at 5C and delivers

    heat to a reservoir at 60C. A heat engine is driven by a source at 840C and rejects heat to a reservoirat 60C. The reversible heat engine, in addition to driving the heat pump, also drives a machine that

    absorbs 30 kW. If the heat pump extracts 17 kJ/s from the 5C reservoir, determine (1) the rate of heatsupply from the 840C source, and (2) the rate of heat rejection to the 60C sink. (8)


    12. (b) (i) Derive an expression for the change in entropy of a perfect gas during polytropicprocess in terms of T1 and T2. (8)

    (ii) 2 kg of water at 90C is mixed with 3 kg of water at 10C in an isolated system. Calculate the

    change of entropy due to the mixing process. (8)

    13. (a) Two streams of steam, one at 2 MPa, 300C and the other at 2 MPa, 400 C, mix in asteady flow adiabatic process. The rates of flow of the two streams are 3 kg/min and 2 kg/min

    respectively. Evaluate the final temperature of the emerging steam, if there is no pressure drop due to

    the mixing process. What would be the rate of increase in the entropy of the universe? This steam

    with negligible velocity now expands adiabatically in a nozzle to a pressure of 1 kPa. Determine the

    exit velocity of the stream and exit area of the nozzle.(16)

    OR13. (b) (i) Define specific steam consumption, specific heat rate and work ratio. (6)

    (ii) In a Rankine cycle, the steam at inlet to turbine is saturated at a pressure of 35 bar and the

    exhaust pressure is 0.2 bar. The flow rate of steam is 9.5 kg/s. Determine (1) the pump work (2) the

    turbine work (3) Rankine efficiency (4) condenser heat flow (5) work ratio and (6) specific steamconsumption. (10)

    14. (a)(i) A vessel of volume 0.3 m3

    contains 15 kg of air at 303 K. Determine the pressure exerted

    by the air using, (1) Perfect gas equation (2) van der Waals equation. Take critical temperature of air

    as 132.8 K. Critical pressure of air is 37.7 bar. (6)

    (ii) A perfect gas mixture consists of 4 kg of N2 and 6 kg of CO2 at a pressure of 4 bar and a

    temperature of 25C. For N2: Cv = 0.745 kJ/kgK and Cp = 1.041 kJ/kgK. For CO2: Cv = 0.653

    kJ/kgK and Cp = 0.842 kJ/kgK. Find Cp , Cv and R of the mixture. If the mixture is heated at constant

    volume to 50C, find the changes in internal energy, enthalpy and entropy of the mixture.(10)

    OR14. (b) (i) Derive and explain the Maxwell's relations. (8)

    (ii) Derive the T dS equation taking T and p as independent variables. (8)

    15. (a) Atmospheric air at 1.0132 bar has a DBT of 32C and a WBT of 26C. Find(i) the

    partial pressure of water vapour (ii) the specific humidity (iii) the dew point temperature (iv) the

    relative humidity (v) the degree of saturation (vi) the density of the air in the mixture (vii) the density

    of the vapour in the mixture (viii) the enthalpy of the mixture. (8x2 = 16)OR

    15. (b) (i) Explain the process of heating with humidification of air, with the help of sketches of

    schematic of air duct with the elements involved as well as the representation on psychrometric chart.(6)

    (ii) 1 kg of air at 40C DBT and 50% relative humidity is mixed with 2 kg of air at 20C DBT and

    20C dew point temperature. Calculate the specific humidity, enthalpy and the dry bulb temperature

    of the mixture. (10)

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    Third Semester

    Mechanical EngineeringME 2202 ENGINEERING THERMODYNAMICS (Regulation 2008)

    (Common to PTME 2202 Engineering Thermodynamics for B.E (Part-Time) Mechanical

    Engineering Third Semester - Regulation 2009)

    Time : Three hours Maximum : 100 marks

    Answer ALL questionsPART A (10 x 2 = 20 marks)

    1.Calculate the actual pressure of air in the tank if the pressure of compressed air

    measured by manometer is 30 cm of mercury and atmospheric pressure is 101 kPa. (Take g

    = 9.78 m/s2)

    2. What is meant by 'Hyperbolic Process'?

    3. List out the generic types of irreversibilities.4. State : Carnot Theorem and Its Corollaries.

    5. What do you understand from the word 'Dryness fraction'?

    6. What are the ways by which Rankine cycle efficiency may be improved?

    7. State : Dalton's law of partial pressures.8. What do you mean by Compressibility factor?

    9. Define : Relative humidity.

    10. What do you understand from the Dew point temperature?

    PART B (5 x 16 = 80 marks)

    11. (a) A gas contained in a cylinder is compressed from 1 MPa and 0.05 m3 to

    2 MPa. Compression is governed by pF" constant. Internal energy of gas is given by; U =7.5 PV

    -425, kJ. where P is pressure in kPa and V is volume in m3. Determine heat, work and change in

    internal energy assuming compression process to be quasistatic. Also find out work interaction, if the

    180 kJ of heat is transferred to system between same states.Also explain why it is different fromabove? (16)


    (b) In a gas turbine installation air is heated inside heat exchanger up to 750 C from ambient

    temperature of 27 C. Hot air then enters into gas turbine with the velocity of 50 m/s and leaves at 600

    C. Air leaving turbine enters a nozzle at 60 m/s velocity and leaves nozzle at temperature of 500 C

    For unit mass flow rate of air determine the following assuming adiabatic expansion in turbine and

    nozzle, (16)(i) Heat transfer to air in heat exchanger (ii) Power output from turbine (iii) Velocity

    at exit of nozzle. Take up for air as 1.005 kJ/kg K.

    12. (a) A reversible heat engine operates between two reservoirs at 827 C and 27C.

    Engine drives a Carnot refrigerator maintaining -13C and rejecting heat to reservoir at 27C. Heat

    input to the engine is 2000 kJ and the net work available is 300 kJ. How much heat is transferred to

    refrigerant and total heat rejected to reservoir at 27 C? (16)


    (b) (i) How do you differentiate the Exergy (Availability) and energy based upon their

    characteristics? (4)

    (ii) Determine the rate of power loss due to irreversibility in a he

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