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!

How to calculate amount of vapor given q(t) and p(t)?

  1. Dec 15, 2015 #1
    Hi everybody,

    I am trying to build a small model which basically should be able output "mass flow of water vapor as a function of time" given following inputs:
    - initial mass liquid water m_l_0 [kg]
    - initial temperature of liquid water T_l_0 [°C]
    - initial pressure p_0 [Pa]
    - heat added as a function of time q(t) [J/s]
    - pressure as a function of time p(t) [Pa]

    So for example a vessel with m_l_0 = 100 kg and T_l_0 = 80 °C is given.
    The heat added function q(t) = q1 for time t>=0 & t<t1 and q(t) = q2 for t>=t1.
    The pressure p(t) is given as a linear function with p(t) = p_0 - C x T, with C being some constant [Pa/°C].

    Given this example, what will the mass flow of water vapor m_vap(t) be?

    I started by calculating the system given enthalpy H_sys = m x T x cp and comparing it to the maximum enthalpy of the system at boiling point H_max = m x T_boil(p) x cp (which is pressure dependent). Once H_sys >H_max vapor will be released...

    I would like to know how what you think will be the best approach for to do so?

    Thank you!

  2. jcsd
  3. Dec 15, 2015 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You haven't constrained your problem adequately. Please give it another try.
  4. Dec 16, 2015 #3
    You mean temperature and pressure constraints?

    Ranges of temperature I am looking into:

    Pressure range:
    60 000 - 140 000 Pa (0.06-0.14 MPa)
  5. Dec 16, 2015 #4
    Is this in an open container or a closed container? Is there air present, or is the entire pressure comprised of water vapor pressure? Is the system insulated, aside from the heat added? Does the container have thermal inertia?

  6. Jan 2, 2016 #5
    Hi Chet,

    Answers to your question:
    - Open container
    - Container is filled with air
    - No heat loses
    - Thermal inertia is not considered

    Thank you and a happy new year!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook