thermodynamics question HELP PLEASE

[260ZRED]

Guys... can you help me out with this one? I have air, to be treated as an ideal gas @ 8 bar and 600K. I need to find either the density or the specific volume (which is just the inverse of density...)

 

I do NOT know the actual mass or the actual volume, but I need to find the specific volume, to find mass flow rate @ steady state. I have the area and Velocity, just need the sp.volume...

 

Can I do this: Pv=mRT with (R=Rgiven/M)

 

So,

v/m=[R*T] / [P*MolarMass of air]

 

v/m=specific volume, right?

 

Is this the right way or not??? I'm really confused..

 

Thanks for any help about this.

 

Igor

[GabeRoc]

the short answer is yes. pv=RT will give you what you want.

p= absolute pressure

R= R-bar/M

R-bar=universal gas constant=8.314 KJ/Kmol*K

M= molecular wight of air=28.97 kg/kmol

T=absolute temp

 

the long answer is that you are going to have to make sure your units work out. as it is currently 1:23am, i'm not going to do that for you.

 

hope this helps,

 

--gabe

[Michael]

Gabe beat me to it, so just to elaborate… use the “engineering form†(as opposed to the chemistry form) of the ideal gas law, P = rho*R*T, where rho is density. In S.I. units, the UNIVERAL gas constant is R = 287 J/(kg*K). So, rho = P/(R*T) = 8*(101325 N/m^2)/(287J/(kg*K) * 600K). The 101325 N/M^2, or 101325 Pa, is atmospheric pressure at STP. Units cancel to give kg/m^3, and the numerical answer is 4.707 kg/m^3.