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Formula/Syntax to specify non-negative concentration
Posted 2012/02/02 15:52 GMT-5 Chemical Reaction Engineering, Parameters, Variables, & Functions Version 4.2 1 Reply
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Hello.
While using chemical reaction engineering physics, I was wondering if there is a function or syntax to prevent the concentration of species to become negative.
I found that in 3.5, the syntax ("mod1.cs_C3H6>0") works to prevent the concentration from becoming negative.
I am not sure what function or constraint can be used in 4.2.
Any advise?
Thank you
Brian
While using chemical reaction engineering physics, I was wondering if there is a function or syntax to prevent the concentration of species to become negative.
I found that in 3.5, the syntax ("mod1.cs_C3H6>0") works to prevent the concentration from becoming negative.
I am not sure what function or constraint can be used in 4.2.
Any advise?
Thank you
Brian
1 Reply Last Post 2012/02/06 20:09 GMT-5
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Posted:
1 decade ago
Well, I was having the same problem when working with a pde with reaction diffusion equations.
My advise to you would be not to "tweak" the equations at that level, but rather to let the solver pick the actual true solution from the pde. I think the negative solution happens because your model might be a little too sensitive.
A way around that is to make a simple change of variable. For example let w= log(c) and then rewrite the equation from there.
Good luck
My advise to you would be not to "tweak" the equations at that level, but rather to let the solver pick the actual true solution from the pde. I think the negative solution happens because your model might be a little too sensitive.
A way around that is to make a simple change of variable. For example let w= log(c) and then rewrite the equation from there.
Good luck