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Railways NTPC (Technical Ability) Turbomachinery Question Bank Turbomachinery

  • question_answer
    Gas turbine develops 120 kJ of work while the compressor absorbed 60 kJ of work and the heat supplied is 200 kJ. If regenerator which would recover  40% of the heat in the exhaust were used, then the increase in the overall thermal efficiency would be:

    A) 10.2%              

    B) 8.6%

    C) 6.9%                

    D) 5.7%

    Correct Answer: D

    Solution :

    \[{{y}_{th}}\frac{{{W}_{t}}-{{W}_{c}}}{{{Q}_{s}}}=\frac{120-60}{200}=\frac{60}{200}=0.3\,\,or\,\,30%\]Heat in exhaust gases \[={{Q}_{s}}-{{W}_{t}}=200-120=80\,kJ\] Heat recovered in regenerator \[=0.4\times 30=32\,kJ\]. Heat supplied \[=200-32-168\,\,kJ\] New efficiency \[=\frac{200-60}{168}=35.7%\] Increase in efficiency \[=-35.7-30.0=5.7\]


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