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-   -   Inlet air preheating (https://www.cfd-online.com/Forums/siemens/55615-inlet-air-preheating.html)

usker September 14, 2006 21:51

Inlet air preheating
 
I am trying to simulate a gas burner (transient, unremixed/diffusion combustion). First I calculated temperature and NOx with inlet air temperature 293K. Now I want to calculate with inlet air preheating. I selected 3 different air temperatures 473,673 and 873K. I insert these temp values into "Define Boundary Regions" and I also insert the air density at that particular temperature (for example temp-473K, density-0.738404kg/m3). The solution method and analysis controls are the same for every case. But when I get the results of Temperature and NOx distribution, the values of flame temp and NOx appears to be the same for all conditions (temp 293,473,673 and 873). Could you please advise what I have to do to get correct results.

Regards

Mike H September 17, 2006 12:27

Re: Inlet air preheating
 
One possible reason for this is that you may be using the Presumed Probability Density Function model in version 3.26.

This model (in version 3.26) doesn't allow you to change the boundary temperature in the BC panel - you have to change it in the combustion model setup. The BC panel only determines the mass flow rate as the product of your velocity and density if you're using the 'Mass flux' option.

This has been fixed in Star-CCM+ and I think in Star-CD version 4.0 also but I'm not sure.

If you are using the eddy breakup model then something else is wrong with your model.

Good luck - Mike

usker September 20, 2006 05:27

Re: Inlet air preheating
 
I have used CEA with PPDF. I have assigned temperature 873K for the air inlet. If I assign higher temperature in CEA for air inlet then I get higher flame temperature. But shouldn't it be like if the temperature increases, at atmosheric pressure, then the air density decreases, which means the mass of air (or mass flow rate) also decreases. This can affect the reaction rate, the reaction rate becomes slower and adiabatic flame temperature decreases, and therefore, NOx also decreases. In Boundary Conditions I have assigned velocity, air density (with respect to temperature). But it seems to me that Pro-Star does not sense anyhow the changes in density and temperature in BC. It only senses the temperature changes in CEA (chemical equilibrium with applications), without considering the change in mass flow rate.

Could anybody advise please, how to calculate this kind of problem with inlet air preahiting and propane combustion.

Regards

Ralphie September 21, 2006 09:21

Re: Inlet air preheating
 
Try Switch 127.


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