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!

Deriving an equation for the density of air

  1. Jan 20, 2004 #1
    First of all, I'm new to this forum, so please excuse any newbie etiquette errors I have made =)

    My problem is this: I'm doing a lab report on an experiment where we attempted at measuring the density of air. I won't go to the details, but basically we just measured air on different pressures.

    The task is to, given the following equations, derive an equation for the density of dry air as a function of the density of moist air, relative humidity, pressure of saturated 'steam' (can't figure a better translation..Oh yeah, I'm a Finn :) ) and the total pressure.

    The first equation:
    [tex]
    \frac{M_i^'}{M_i}=\frac{\rho_i^'}{\rho_i}=1-\frac{M_i-M_v}{M_i}*\frac{e}{p}\approx 1-0,378\frac{e}{p}
    [/tex]

    ...and the second:
    [tex]
    f=\frac{F}{F_m}*100\%=\frac{e}{e_m}*100\%
    [/tex]

    Notations:
    [tex] M_i [/tex] = molemass for completely dry air
    [tex] M_i^'[/tex] = molemass for moist air (air with some water vapour in it)
    rhos are densities of dry & moist air, respectively
    [tex] M_v [/tex] = molemass for water
    e = partitial pressure of water vapour
    p = total pressure
    f = relative humidity
    [tex] e_m [/tex] = the pressure required for the condensation of water ( again, not so sure of the translation)
    F = absolute humidity (measured in, for example, g/m^3)


    I hope I didn't forget anything. I have been trying to solve this with my mates for days and days now, and I'd really appreciate any help...

    Oh yeah, and I'm sorry, but I can't provide you with any of my sketches, as all I have are red-rimmed eyes and a heap of trash paper =)
     
  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?
Draft saved Draft deleted