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

Conceptual thermodynamics/physics question.

  1. Mar 10, 2010 #1
    Hey Guys,

    Say you have an air compressor with a constant volume. And were given the temperature and pressure at the inlet. And also, the temperature and pressure at the outlet. Would the mass of the air at the inlet equal the mass at the outlet? When applying the ideal gas law to the inlet and outlet (assuming air behaves as an ideal gas), is it possible get two different masses? It seems as though that would conflict with the conservation of mass principle.
  2. jcsd
  3. Mar 11, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Yes, mass in = mass out. Note that air compressors may 'leak' so if you're actually measuring a compressor and finding a discrepency, you may want to look for leaks.
  4. Mar 11, 2010 #3
    Actually, I was told to find the change in entropy for the compressor. Ie., S(out) - S(in). So I would have to multiply the specific entropy by the mass of the air. That's why I asked if mass is conserved. That way I could just find the mass of the air at the inlet and multiply that by the specific entropy. Unfortunantly, by using the IG law, both masses were not equal so that is why I asked the question. So maybe I am thinking that the volume of the air at the inlet was not the volume at the outlet? Because it is being compressed, it would have a smaller volume at the outlet.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook