# BC´s natural convection??

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 March 14, 2005, 12:06 BC´s natural convection?? #1 Thomas Guest   Posts: n/a Hello, I want to simulate natural convection in a simple chimney. I don´t want to use the boussinesq modell, as delta T is about 40 K. I have a pressure inlet at the bottom and a pressure outlet at the top. The sourrunding walls have a temperature condition. How do I have to specify to density when I use the incompressible ideal gas law? How do I specify the operating density? I´ve read in a tutorial that I should set the operating density to 0.?? Thank you for your help! Thomas

 March 14, 2005, 13:11 Re: BC´s natural convection?? #2 Evan Rosenbaum Guest   Posts: n/a I've had good results setting the operating density to the density at approximately the mean gas temperature.

 March 15, 2005, 03:33 Re: BC´s natural convection?? #3 Thomas Guest   Posts: n/a Did you use the the incompressible-gas-law or the boussinesq modell? So for example: Incompressible gas-law: Operating pressure: 102325 Operating Temperature: 288.16 Operating: Density: 1.225 As the opertation temperature is coupled withe the operating density, I think I have to adapt the density and temperature to my problem. Right??

 March 15, 2005, 13:08 Re: BC´s natural convection?? #4 Evan Rosenbaum Guest   Posts: n/a We have typically used a piecewise linear density for fluids and ideal gas for gases. You only need the operating density as a reference point for computing local buoyancy force, so the exact value isn't overly critical as long as it falls in your actual range of local densities.

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