1. Limited time only! Sign up for a free 30min personal 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!

Thermodynamics exercise.

  1. Jan 18, 2015 #1
    1. The problem statement, all variables and given/known data
    An engine works with an ideal diatomic gas (γ=1.40) according to a thermodynamic cycle consisting in four
    processes that take the gas successively through the states 1, 2, 3 and 4. The processes 1 -> 2 and 3 -> 4 take
    place at constant pressure and the two other processes are adiabatic. The cycle’s lowest pressure is 1 atm and
    corresponds to the state 1.
    a. Find an expression for the cycle’s efficiency exclusively in terms of the temperatures of the states 1,
    2, 3 and 4.
    b. If the efficiency is φ=0.40, what is the gas pressure in state 3?

    2. The attempt at a solution

    Ok, first part is easy (I guess) here's what I did http://imgur.com/hpBxIex if someone could give it a look I'd be very thankful. I'm sorry I cannot give you the P-V diagram because I don't know how to draw in this PC.
    The second part is where it gets tougher because I only have 2 pieces of information and I really cannot relate them. If someone could sketch the solution I'd be very thankful.
  2. jcsd
  3. Jan 18, 2015 #2


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    OK for part (a). For part (b), think of a way to relate T and P for the adiabatic processes.
    Last edited: Jan 18, 2015
  4. Jan 19, 2015 #3
    Hello TSny, thx for replying, thing is my professor didn't give us a way to relate P and T however I found this formula in wikipedia but I'm not sure if it's correct: (It's valid iff the process is reversible) P1-γ Tγ=const. What do you think?
    The statement doesn't specify if the process is reversible actually...
  5. Jan 19, 2015 #4


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    Yes, that's the correct formula. For these types of questions you can generally assume that the entire cycle is reversible.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Thermodynamics exercise.
  1. Thermodynamics ? (Replies: 8)