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!

Air Density: How to calculate Relative Humidity

  1. Mar 12, 2010 #1
    Hi there,

    I'm trying to calculate air density; I noticed on http://en.wikipedia.org/wiki/Density#Density_of_air" that there is a table that makes it seem that air density is a function of temperature... I suppose I could safely say that temperature has a significant effect on air density? What error could one expect if they had to use measurements from this table?

    Anyway, I know that humidity plays an important role in air density and there's a nice formula on http://en.wikipedia.org/wiki/Density_of_air#Water_vapor": ρhumid air = pd/Rd.T + pv/Rv.T.

    This seems like it's the only way to calculate the density of humid air. I have temperature, absolute humidity and ambient pressure of the system (all in the appropriate SI unit). This is insufficient information to calculate the relative humidity as specified on http://en.wikipedia.org/wiki/Relative_humidity" [Broken].

    I understand that vapour pressure readings can be taken from steam tables to calculate the saturated vapour pressure. But then everything gets really blurry. But before I get into that... I saw this example from http://www.cheresources.com/questions/thermodynamics-41.html" that suggests that I can calculate the relative humidity from the absolute humidity... I haven't come across anything else that explicitly linked the two so I'd like to know if the answer is sound. The equation given was:

    Humidityabsolute=Humiditysaturation * RelativeHumidity/100

    Can anyone please advise if this would be a valid?

    Kind regards
    Pooven
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted