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!

Phase equilibrium with unsteady flow

  1. Jul 24, 2008 #1
    Hi All - I tried this question in Introductory Physics, but thought I'd plonk it here too. Hope that's acceptable.

    1. The problem statement, all variables and given/known data

    I have an initially closed, pressurised vessel at ambient temperature, with a single species in it at dynamic equilibrium with some volume fraction of vapour and liquid. I am in the "wet vapour" region of the P-v-T surface, described by the Clausius-Clapeyron equation.

    I then draw some mass of liquid out. I view the problem in discreet terms, but could possibly model with a mass flow rate out.

    In the real world, the vessel will cool - energy will be drawn into the vapour - partially from the effect of vapour expansion (thinking of the liquid rather like a piston in a cylinder) and partially from the effect of vapourisation of some of the remaining liquid. I presume if the mass flow rate is low, the expansion effect will be negligible. I want to quantify the energy flux due to vapourisation.

    2. Relevant equations

    Clausius-Clapeyron equation, describing vapour pressure at some temperature - the vapour-liquid equilibrium line in the P-T plane. ln(p2/p1) = (dHvap/R)(1/T2 - 1/T1)

    Ideal gas law; pV = mRT

    (heat flux at constant volume; Q = m.cv.dT; not used)

    Possibly use the relative volatility theory described here (http://tinyurl.com/676gsb) for a binary, 2-species problem.

    3. The attempt at a solution

    I have approached this by first presuming the temperature recovers to ambient at every liquid mass increment drawn from the vessel. I have no model for heat flux across the vessel wall.

    I draw mass m of liquid from the tank, then the volume change of vapour is easily calculated from mass/liquid density. I presume if the temperature remains constant that we equilibrate back along the clausius-clapeyron line, and that the vapour pressure remains constant also (not sure if that's valid). Then the new mass of vapour can be found from pV = mRT. The energy flux drawn in to vapourise the mass difference is calculated from Q = dHvap.m.

    I'd like to know the volume fractions of vapour and liquid, but I'm not sure if that's useful/misleading.
     
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you help with the solution or looking for help too?



Similar Discussions: Phase equilibrium with unsteady flow
  1. SHO in phase space (Replies: 0)

  2. Phase Space Graph (Replies: 0)

Loading...