Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thermodynamic cycle and entropy

  1. Mar 30, 2010 #1
    Alright, I'm confused about why thermodynamic cycles can never have 100% efficiency. There reversible processes right? And a reversible process has zero change in entropy, so then why can't they achieve 100% efficiency. I thought entropy was the measure of energy that cannot be used. How would you measure efficiency if the system increases in entropy?
     
  2. jcsd
  3. Mar 30, 2010 #2

    rock.freak667

    User Avatar
    Homework Helper

    In a thermodynamic cycle, not all of the energy inputted is converted into work. Some heat is always rejected. Not all processes are 100% reversible.
     
  4. Mar 30, 2010 #3

    russ_watters

    User Avatar

    Staff: Mentor

    .....so why no try buiding a cycle with all reversible processes, so no heat is rejected? You'll find you can't. Real processes that can be combined into real thermodynamic cycles will always result in a cycle with some entropy.

    Try drawing a cycle with no heat rejection on a t-s diagram and see if you can find real processes (devices) that do what the t-s diagram suggests.
     
    Last edited: Mar 30, 2010
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Thermodynamic cycle and entropy
Loading...