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-   -   Density setting in Fluent for compressed and heated air (https://www.cfd-online.com/Forums/fluent/201716-density-setting-fluent-compressed-heated-air.html)

bolbol May 9, 2018 02:58
Density setting in Fluent for compressed and heated air
 
2 Attachment(s)
Hi,
I'm trying to model compressed air (up to 5 bar) and heated to 200 Celsius at the Inlet.
The flow goes through the porous material and the outlet pressure is atm.


1. what is the best option for density setting? ideal gas, real gas or using some data I found for air (attached), and how to use these data? it varies with pressure & temp., in piecewise-linear I can input the variation with only 1 parameter.


2. If I want to know the temp. at the outlet and I want to find the temp. at the inlet, should I left the temp. in boundary condition as 300 K as default and Fluent will correct the value?

bolbol May 9, 2018 05:09
Assign Pressure and mass flow rate at inlet in Fluent
 
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LuckyTran May 9, 2018 20:09
It's up to you choose to model your fluid. Ideal gas is probably within 1 or 2 percent of what you'll get with more realistic properties (if it even matters). You need to start somewhere and get a result before worrying about all these settings. "Something mediocre is better than nothing perfect."

The inlet temperature you must provide, isn't it 300K? There is a backflow temperature at outlets, which is needed if there is reversed flow at an outlet (i.e. your outlet is an inlet). If there is no reversed flow, that value does nothing.

bolbol May 10, 2018 03:34
Quote:
Originally Posted by LuckyTran (Post 691840)
It's up to you choose to model your fluid. Ideal gas is probably within 1 or 2 percent of what you'll get with more realistic properties (if it even matters). You need to start somewhere and get a result before worrying about all these settings. "Something mediocre is better than nothing perfect."

The inlet temperature you must provide, isn't it 300K? There is a backflow temperature at outlets, which is needed if there is reversed flow at an outlet (i.e. your outlet is an inlet). If there is no reversed flow, that value does nothing.
yes, it's 300K which is the default value.
for outlet temp., it's 443K.
But I still got reversed flow sometimes in the results until the mass flow rate became stable after 1000 iterations. I heard that reversed flow effect only the converge process and make it slower or should I worried about the results itself?

LuckyTran May 10, 2018 13:51
The only solution you care about is the current/latest one and if the reversed flow goes away then it doesn't matter anymore. Of course putting in a reasonable value helps to make sure you eventually arrive at this nice answer, but once you are there (with no reversed flow).


Then with this final solution, you are the judge of whether your results make sense or not. "The first principle is that you must not fool yourself and you are the easiest person to fool." ~Feynman


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