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Old   October 1, 2003, 10:18
Default surface reaction rate
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zhou
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I use ˇ°DEFINE_SR_RATEˇ± to define a custom surface reaction rate. It is one UDF of my source file. I have hooked this UDF in FLUENT panel successfully. What I try to do is to assign a certain consumption or production of a specified species. Question: Do I still need to define the ˇ°finite rateˇ± and ˇ°mechanismˇ± under the panel of ˇ°Define-Materials-Reaction-finite rate and Mechanismˇ±? If not, how this UDF is used in FLUENT because this surface reaction rate is only a general rate and does not mean how much the consumption or production of a specified species is. How to get the consumption or production of a specified species by this UDF? If it is need to define the ˇ°finite rateˇ± and ˇ°mechanismˇ±, what is relation between this UDF and ˇ°finite rateˇ±?
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Old   October 1, 2003, 10:26
Default Re: surface reaction rate
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Andrew Garrard
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I had this same problem. When you specify the *rr value in DEFINE_SR_RATE you are specify the molar rate of production or consumption of the species.Once hooked, this takes precedance over the values in the the materials panel. Hope this helps.
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Old   October 1, 2003, 11:31
Default Re: surface reaction rate
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zhou
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Hi,andrew Could you explain in detail? I understand the *rr is the total surface reaction rate that have precedence, but how to define that it is one species reaction rate like H+ or OH-. I think i need to supply the stoichmetric coefficient somewhere. I don't know how to do that. By the way, if i want to define two different surface reaction rate on anode and cathode wall by this UDF, how to do that?
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Old   October 2, 2003, 04:36
Default Re: surface reaction rate
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Andrew Garrard
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I am assuming that you have access to the manuals. If so the defining a reaction is explained in 4.3.16 of the UDF manual. As for defining reaction rate for several reactions, this can be done with a conditional if statement that is shown on this page. e.g.

if (STREQ(r->name, "reaction-1"))

*rr = [molar rate of production/comsumption]

eles *rr = [molar rate of production/comsumption]

As for speditying stoichmetric coefficients, I am unsure, but I believe that you will have to specify this in the UDF that you create. I believe that when you set *rr you are setting the value of Ri in equation 13.1-5.

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Old   October 2, 2003, 16:16
Default Re: surface reaction rate
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zhou
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Hi,Andrew I still have some confused. Let me make an example. Could you explain it? Thanks. I have a reaction H2+2(OH-) = 2(H2O)+2e- Now i define a surface reaction rate *rr . I want to let R(H2O)=K*Y(OH-) R(OH-)=-K*Y(OH-) Right now, i want to know how to set the relation between *rr and R(H2O), R(OH-). The "*rr" is the consumption rate of OH- ? or The "*rr" is the production rate of H2O.
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