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-   -   Pressure rising with temperature (http://www.cfd-online.com/Forums/fluent/67562-pressure-rising-temperature.html)

Koranten August 19, 2009 05:57

Pressure rising with temperature
 
Hi,

I would like to calculate the rising pressure in an air tank. The geometry is very simple, it is a 2D cube, with walls surrounding the air.

My volume is 1m3, and the heat source is 100W.

I am doing an unsteady calculation, starting from 100 000 Pa and 293.15K.

After 20 seconds, the temperature is 294.8K, which is correct, but the pressure is just 0.15 Pa, which is not correct. According to the perfect gas law, the air pressure should be around 345 times the temperature, and no matter what I tried, I can't obtain a correct value for the rising pressure.

What did I do wrong? I am looking at the static pressure, by the way. Is there something I missed?

I am using the ideal law for the air density, with the default molecular weight. Is there another way to define the density I should use?

May be the calculation is not converged? When I try to converge it, looking at the pressure, it is rising and it doesn't seem to stop...

Thanks.


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