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Homework Help: Thermodynamics: Air compressor

  1. Sep 2, 2015 #1
    1. The problem statement, all variables and given/known data

    Air enters a compressor at 100 kPa and 290 K, where it is compressed adiabatically, where the flow rate is 0.1 kg/s. If the volume compression ratio is (V1/V2=8). Determine the following (Assuming the air is ideal with constant specific heat):

    1- The temperature and the pressure at the exit

    2- The compressor’s power in kW

    3- The transferred heat amount and the change in entropy

    2. Relevant equations
    W` - Q` = m`(h + KE + PE)
    ∆h = m CP (T2 – T1)
    P1 V1k= P2 V2k=C

    3. The attempt at a solution

    P1 V1k= P2 V2k=C --> (k=1.4 for air)

    P2= P1(V1/V2)1.4= 100(8)1.4

    P2=1837.9 kPa --> Pressure at exit

    Q1-2 = 0 (The process is adiabatic) --> The transferred heat amount

    ∆s1-2≈ 0 (The process is adiabatic) --> The change in entropy

    And we may compute ∆s1-2 using of the these two equations:

    ∆s1-2= CV ln(T2/T1) + R ln(V2/V1)

    ∆s1-2= CP ln(T2/T1) - R ln(P2/P1)

    W`1-2 = - m` ∆h = m CP (T1 – T2) = (0.1) (1.0035) (290 – 666.23)

    W`1-2 = -37.75 kW à The compressor’s power in kw

    (k, R, CP and Cv are constants we get it from the tables)
  2. jcsd
  3. Sep 7, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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