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Railways NTPC (Technical Ability) Refrigeration and Air-Conditioning Question Bank Refrigeration and Air-Conditioning

  • question_answer
    In a Bell Coleman cycle refrigeration plant compression and expansion of air are isentropic if the temperatures of air entering and leaving the expander are 300 K and 180 K respectively, what is the coefficient of performance of the plant?

    A) 1.5                               

    B) 2.0

    C) 2.5                               

    D) 3.0

    Correct Answer: A

    Solution :

    \[{{T}_{3}}=300K,\]\[{{T}_{4}}=180\,K\] \[{{r}_{p}}=\frac{{{p}_{2}}}{{{p}_{1}}}\,\left( \frac{{{T}_{3}}}{{{T}_{4}}} \right){{\,}^{\frac{\gamma }{\gamma \,-\,1}}}\,={{\left( \frac{300}{180} \right)}^{3.5}}=5.977\] \[COP=\frac{1}{{{r}_{p}}^{\gamma \,-\,1/\gamma }-1}=\frac{1}{(5.977){{\,}^{0.4\,\,/1.4}}-1}=1.5\] \[COP=\frac{1}{\frac{{{T}_{3}}}{{{T}_{4}}}-1}=\frac{1}{\frac{300}{180}-1}=1.5\]


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