Thermodynamics Miscellaneous

Thermodynamics Miscellaneous

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Thermodynamics

Thermodynamics Miscellaneous

Direction: In a simple Brayton cycle, the pressure ratio is 8 and temperature at the entrance of compressor and turbine are 300 K and 1400 K, respectively. Both compressor and gas turbine have isentropic efficiencies equal to 80%. For the gas, assume a constant value of cp (specific heat at constant pressure) equal to 1 kJ/kgK and ratio of specific heats as 1.4. Neglect changes in kinetic and potential energies.

  1. The power required by the compressor in kW/ kg of gas flow are is








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    T2 = 543.43 K

    ηc =
    T2 - T1
    T2' - T1

    ηc = ηT = 0.8
    rp = 8
    T1 = 300 K
    T3 = 1400 K
    ηc =
    543.43 - 300
    T2' - 300

    0.8 =
    543.43 - 300
    T2' - 300

    T2' = 604.3K
    ρc = mCp(T2' - T1) = Cp(T2' - T1)
    KW
    kg

    = 1 (604.3 - 300)
    = 304.3
    KW
    kg

    Correct Option: C



    T2 = 543.43 K

    ηc =
    T2 - T1
    T2' - T1

    ηc = ηT = 0.8
    rp = 8
    T1 = 300 K
    T3 = 1400 K
    ηc =
    543.43 - 300
    T2' - 300

    0.8 =
    543.43 - 300
    T2' - 300

    T2' = 604.3K
    ρc = mCp(T2' - T1) = Cp(T2' - T1)
    KW
    kg

    = 1 (604.3 - 300)
    = 304.3
    KW
    kg

  1. A p-V diagram has been obtained from a test on a reciprocating compressor. Which of the following represents that diagram?








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    At the time of intake, intake valve operates only when the pressure inside the cylinder is lower than the atmospheric pressure. And appreciable large pressure difference at the time of suction starting, causing fluttering at initial. At the time of compression, process followed is Polytropic and continues till pressure exceeds the delivery line pressure for opening the delivery valve.

    Correct Option: D

    At the time of intake, intake valve operates only when the pressure inside the cylinder is lower than the atmospheric pressure. And appreciable large pressure difference at the time of suction starting, causing fluttering at initial. At the time of compression, process followed is Polytropic and continues till pressure exceeds the delivery line pressure for opening the delivery valve.

  1. A single acting two stage compressor with complete inter cooling delivers air at 16 bar. Assuming an intake state of 1 bar at 15°C, the pressure ratio per stage is








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    For perfect inter cooling, pressure ratio are same in each stage

    r² =
    16
    1

    r = 4

    Correct Option: C

    For perfect inter cooling, pressure ratio are same in each stage

    r² =
    16
    1

    r = 4

  1. A steam power cycle with regeneration as shown below on the T-s diagram employs a single open feedwater heater for efficiency improvement. The fluids mix with each other in an open feedwater heater. The turbine is isentropic and the input (bleed) to the feedwater heater from the turbine is at state 2 as shown in the figure. Process 3-4 occurs in the condenser. The pump work is negligible. The input to the boilder is at state 5. The following information is available from the steam tables:

    The mass flow rate of steam bled from the turbine as a percentage of the total mass flow rate at the inlet to the turbine at state 1 is _____.








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    From energy balance equation,
    mh2 + (1 - m) h4 = h5
    m(h2 + h4) = h2 - h4

    = 0.2 or 20%
    ∴ 20% of mass flow rate of steam bled from the turbine of total mass flow rate.

    Correct Option: A

    From energy balance equation,
    mh2 + (1 - m) h4 = h5
    m(h2 + h4) = h2 - h4

    = 0.2 or 20%
    ∴ 20% of mass flow rate of steam bled from the turbine of total mass flow rate.

  1. Select the correct statement for 50% reaction stage in a steam turbine.








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    NA

    Correct Option: D

    NA