Subject: Re: Nitrogen...
From: drela@athena.mit.edu (Mark Drela)
Date: 18 Jan 1997 23:30:27 GMT
In article <853440793.357328@smd.fast.co.za>, gckerr@fast.co.za (Grant Kerr) writes:
|> Raphael London wrote:
|>
|> >Hello there!
|>
|> >Could someone give me some help?
|> >I would like to know what the bulkmodulus of
|> >Nitrogen at STP is as well as how to extrapolate it
|> >for any other temperature less 100 degC.
|>
|> >Thanks.
|> >Ralph
|>
|> Ralph
|>
|> The term 'bulk modulus' as I know it applies to the elasticity of
|> solids and not gases. Nitrogen is a gas at STP and therefore does not
|> have a bulk modulus.
The bulk modulus is defined as the change in pressure
per fractional change in volume, i.e.
-dp
Ev = --------
dVol/Vol
Whether the stuff in question is a solid, liquid, or gas is immaterial.
The bulk modulus can take on different values depending on whether
the changes are taken at constant temperature or constant entropy.
For ideal gases, the bulk moduli follow from the state equation,
the identity d(Vol)/Vol = -d(rho)/rho), and the isentropic relations:
Ev = RT (isenthalpic)
Ev = gamma * RT (isentropic)
The isentropic Ev is also the speed of sound squared for any medium.
- Mark Drela
- MIT Aero & Astro
