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willy May 25, 2004 02:35

Two phase chemical reaction
 
CFX-4.4 provides gaseous chemical reaction model. Now I am making effort to simulate solid-gas two phase chemical reation.For example,solid carbon and gaseous oxygen react. How do I set about the research. I really appreciate your help!

Willy

test May 25, 2004 08:33

Re: Two phase chemical reaction
 
You can use the coal combustion model. The process will be broken down into three steps. Devolatilization of volatiles form solid, combustion of volatiles in gas phase and combustion of char.

Refer to the example problem in CFX-4.4 help manuals.

It would be easier to set up the problem in CFX-5.7

willy May 25, 2004 23:28

Re: Two phase chemical reaction
 
Thank you for your reply. To proceed would you please guide me how to set a 8-steps chemical reaction like this: C+O2->CO2 ; 2C+O2->2CO ; C+CO2->2CO ; C+H2O->CO+H2 ; CH4+H2O->CO+3H2 ; CH4+(1/2)O2->CO+2H2 ; CO+H2O->CO2+H2 ; CO+(1/2)O2->CO2. And C is solid phase,other species are gaseous phase. Thank you a lot. Regards, Willy

test May 26, 2004 00:11

Re: Two phase chemical reaction
 
Hi, can you tell me if u r using CFX-4.4 /CFX-5.7?. It would be easier to set up the reactions and materials properties in CFX-5.7. Decide first as to which version of the software u will be using.


willy May 26, 2004 00:58

Re: Two phase chemical reaction
 
I am a CFX-4.4 user. And is CFX-5.7 a better choice for this case? Thank you. Willy

matej May 26, 2004 03:47

Re: Two phase chemical reaction
 
man! read the answers to your question carefully!!! Test told you twice, that CFX 5.7 is easier. Why do you ask again??

and try to go through the manual. your problem is tutorised in the manuals of cfx4. oh. those wednesdays!

matej

willy May 26, 2004 08:35

Re: Two phase chemical reaction
 
I am very sorry for my mistake. I am a CFX-4.4 user and please guide me how to start the multi-step and two phase chemical reaction. The manual just provides gaseous reactions.Thank you both.Willy.

matej May 27, 2004 03:29

Re: Two phase chemical reaction
 
sorry, I was bit nervous with my own code :o)).

I cannot find the documentation for CFX4.4. not even the installation disks any more, but there is a whole documentation availible on cfx community web site: http://www-waterloo.ansys.com/cfxcommunity . You need a user account to get there, but its free to get it, so ask the man who's holding the licenses. The documentation availible there is also comming in pdf with the installation.

In there, the multistep chemistry is described in Application Example 2.4. You get there, if you click on EXAMPLES on the first page in the pdf manual.

Application Example 2.3 is giving coal combustion example.

I've never done any solid combustion in cfx yet, so I cannot give you my command file, but if you use the command file editor, or what is the name of it, it will give you allways the physics boxes you need to fill in.

With few days or weeks of trying you may get it.

Small hint No.1: it's allways more likely to have a nice and valuable answer from such a forum, if you spend some time first digging into the problem yourself and asking more detailed question, then just 'please help me how to do it' from which is evident, that you haven't spent much time going through the documentation to find the answers yourself. something like "is this the thing to use?"

small hint No.2: if you have difficulties setting up the case, start with simple physics and add the bits one at a time to the whole multistep solid-gas combustion.

what a great thursday!

good luck

matej

Jeff May 30, 2004 02:07

Re: Two phase chemical reaction
 
Willy,

The issue with gas solid reactions like coal combustion is that it is pretty well turbulence dominated. The Coal combustion model allows for the relative amounts of Carbon and other components of the solid to be specified on a compositional basis. This is, however, only done for the heat release calculation. It is assumed that after volatilization, the gases react at the turbulent mixing rate (chemical rate is usually much faster, but limited by the mixing). Therefore, you don't need any of the finite rate information for this case. Of course your carbon particles are treated as a lagrangian particle. Look in the tutorials for a coal combution example and then study the manual section on Coal Combustion to see how to set your particular composition.

Jeff


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