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how to convert the pre-exponential coefficient?

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Old   March 13, 2006, 23:29
Default how to convert the pre-exponential coefficient?
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lily
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about the unit of the A in arrhennius equation. as i understand, for the monomolicular reation, its unit is s-1, for biomolecular reation, its unit is m3/kmol s(as required by fluent), in the references, usually the measure unit for A is cm-mol-j(cal)-s, for example, there are reactions (1)A+B=C+D and (2)A1=B1+C1 the pre-exponential coefficient As in the literatures are both 1E+15 for both reactions, what will be the value for A i should give to fluent for these two reactions respectively? I am so confused right now. Please help me. Thank you very much in advance.

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Old   March 14, 2006, 03:19
Default Re: how to convert the pre-exponential coefficient
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RoM
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The unit of the raection rate for volumetric reactions is always kmol/m3/s. The prexponential factor must be set according to this. Here some examples

Consider the reaction A+B->C+D

Case 1: Reaction is determined only by the concentration of A (Conc_A), reaction oder is 1

R=Conc_A^1*Rkin

To get kmol/m3/s Rkin has to be 1/s which means preexp. factor is 1/s

Case 2: Reaction is determined by the concentration of A and B, reaction oder is 1

R=Conc_A^1*Conc_B^1*Rkin

preexp. factor is (kmol/m3)^-1 * 1/s

Case 3: Reaction is determined by the concentration of A and B, reaction oder is 0.5

R=Conc_A^0.5*Conc_B^0.5*Rkin

preexp. factor is 1/s

Hope it helps, RoM

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