1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Problem based on the Energy equation (thermodynamics)

  1. Jun 7, 2013 #1
    1. The problem statement, all variables and given/known data
    We have compressed air @ 6 bar and 298 K. This is input to a pneumatic motor (in which pressure energy is converted into kinetic energy) flow rate is 22 L/sec and we get shaft power (1.06 KW) from pneumatic motor as output. And air leaves pneumatic motor @1 bar. Density of air @ 6 bar is 7 Kg/m^3. And we need to find the efficiency of motor.


    2. Relevant equations

    I'm using the Steady Flow Energy Equation (SFEE).
    So h1 +KE1 +PE1 +Q=h2 +KE2+PE2+W (shaft work)

    and h= u +pv

    3. The attempt at a solution

    Consider the motor as the control volume
    Inlet is state 1 and outlet is state 2
    State 1-
    P1=6 bar =600 KPa
    T1= 298K
    density= 7 kg/m^3
    Q=0.022m^3/s
    (all above are given)
    From calculation, mass= Qxdensity=0.154kg

    State 2-
    P2=1 bar=100Kpa
    V2= 0.08 m^3 (for the 0.154kg at the outlet)- after using the adiabatic law i.e. P1(V1^γ)=P2(V2^γ)
    T2= 178.6 K (from ideal gas equation, after putting (P1xV1)/T1 = (P2xV2)/T2

    We neglect the change in KE and PE

    But in a pneumatic motor, Q=0 and W is given....so how do we find the efficiency???
     
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?



Similar Discussions: Problem based on the Energy equation (thermodynamics)
  1. Thermodynamics Problem (Replies: 0)

Loading...