MegaMan64 Posted February 24, 2012 Share Posted February 24, 2012 Hi, I am working on building a simple simulator in C# that find both the temperature and the pressure in pascals for a given air mass at different altitudes. I am also trying to find the density of the air mass as well. The equation for the density I am using is D = (P / R * T) where D = Density P = Presser in Pascals R = the gas constant i.e 287.05 (this is dry air) T = Temperature I need an equation that I can use to find the pressure and the temperature much like the one above simple and easy to understand. Thank you for any help with this Link to comment Share on other sites More sharing options...
am19psu Posted February 24, 2012 Share Posted February 24, 2012 Assuming this a homework question, use the hypsometric equation. If it's not, you have too many unknowns and not enough equations. Link to comment Share on other sites More sharing options...
LocoAko Posted February 24, 2012 Share Posted February 24, 2012 How accurate does this need to be? P=ρRdTv uses the Virtual Temperature, since you are using the gas constant for dry air. It won't make too much of a difference but if you want it to technically be correct.. Link to comment Share on other sites More sharing options...
MegaMan64 Posted February 24, 2012 Author Share Posted February 24, 2012 No this is not homework its for a skydiving simulation that I am playing around with; I need more equation? I think I can use the lapse rate of a dry air parcel to estimate the temperature. i.e. a drop of 6.5 C every 1000 meters But the pressure is still not there yet. I found an equation like this p = 100 * ( 44331 * 514 - z / 11880 * 516 )^ (1 / 0.1902632) which is I think atmospheric density and not pressure am I right? Link to comment Share on other sites More sharing options...
MegaMan64 Posted February 24, 2012 Author Share Posted February 24, 2012 How accurate does this need to be? I would like for it to resemble real pressures to a degree Kinda like this page http://www.respirome...re-vs-altitude- I found this and I dont know if this would work but It seams right to me p = 101325 (1 - 2.25577 10-5 h)5.25588 where p is the pressure in pa and h is the hight in meters Link to comment Share on other sites More sharing options...
LocoAko Posted February 24, 2012 Share Posted February 24, 2012 No this is not homework its for a skydiving simulation that I am playing around with; I need more equation? I think I can use the lapse rate of a dry air parcel to estimate the temperature. i.e. a drop of 6.5 C every 1000 meters But the pressure is still not there yet. I found an equation like this p = 100 * ( 44331 * 514 - z / 11880 * 516 )^ (1 / 0.1902632) which is I think atmospheric density and not pressure am I right? That's an (estimate of) the moist adiabatic lapse rate, not the dry. A dry parcel's lapse rate is 9.76C/km. The hypsometric equation is So if you set your bottom pressure to the surface pressure you could calculate the height of another given pressure level, if you know the mean [virtual] temperature of the layer in question, which I'm not sure you do. You could also assume constant density, an isothermal atmosphere, or a constant lapse rate atmosphere, but none of these is truly representative of the real atmosphere. Your best bet is definitely to use the hypsometric equation, but you'll need the mean temperature of the layer in question. That equation you gave is the "barometer equation" (according to my thermo book, anyway). I suppose that would work for you since it is just a simulation, but it assumes a surface temperature of 288.15K and a lapse rate of 0.0065K/m, which may or may not be representative of the real atmosphere. Should be fine for a simulation, though? Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.