CFD Online Discussion Forums

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-   -   surface reaction (https://www.cfd-online.com/Forums/fluent/31998-surface-reaction.html)

pepa August 19, 2003 10:06

surface reaction
 
Does anybody do the simulation with the equilibrium raction on the surface? Please could you help me?

andrew_garrard August 19, 2003 10:23

Re: surface reaction
 
Yes, I was doing this sort of simulation about six months ago. I was using fluent5 and there was the option to turn on the backward reaction in a surface reaction. However in fluent 6 the option seems to be removed, leading me to think that the option was probably not avaliable or very good in the earlier version. The easiest way aroud it is to create your own reaction sheme via a UDF. It isn't that difficult. it is improtant to know that the *rr varibale specifies the molar rate of production of your species rather than the equlibrium constant. If you need anymore help with this I can help you as much as I can.

pepa August 19, 2003 11:57

Re: surface reaction
 
Okey, before I start with the UDF I would like to try something. Meybe I have stupid question, but which units of pre-exponencial factor does FLUENT use by the reaction type - wall surface. Or the reaction is in [kmol/m2-s]??? Is it right?

andrew_garrard August 20, 2003 05:04

Re: surface reaction
 
The manual says that the units of pre-exponencial factor are consistent, but I do not know what this means. from equation 13.1-9 I can only assume the units are s-1 k-1. If you are specifying the surface reaction rate, as in define -> user -> function hooks surface reaction, then yes, kmol/m2-s looks like the right unit for that.

Greg Perkins August 20, 2003 22:05

Re: surface reaction
 
Actually they should be determined by you depending upon for example the exponent of the temperature term and concentration term, such that the overall rate will come out to be in kmol/m3-s.

I foudn this all a little confusing to begin with too, but it all makes sense. Consider some reactions with say 2nd order reactant dependencies and then figure out what the k term will be. You'll find it does depend on the exponents.

Greg

Greg Perkins August 21, 2003 00:14

Re: surface reaction
 
sorry in the above I was thinking about volume reactions, for surface reactions the rate should be in kmol/m2-s


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