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-   -   Multiphase Reaction (Mass Arrhenius) (http://www.cfd-online.com/Forums/cfx/79520-multiphase-reaction-mass-arrhenius.html)

schokoundkeks August 26, 2010 03:49

Multiphase Reaction (Mass Arrhenius)
 
hey everyone,

i am working actually with an euler/lagrange simulation in ansys cfx 12.1 and i want to establish a reaktion inside a lagrage liquid droplet. The reaktions works with multiphase reaktion (mass arrhenisu). The Problem is that i don't know how to convert the pre exponential faktor from molebase arrhenius to a massbased.

Can anyone help me?

a.m. August 26, 2010 16:05

I'm not sure, but try this:
1) for 2 reactants the rate is: w = k*c1*c2
where k - Arrhenius reaction rate, c1 [mole/m3], c2 [mole/m3] - reactants concentrations
2) use molar weight of reactants mw1, mw2 [kg/mole] from periodic table.
3) some transformations: w = k [mole^-2 m^6 s^-1] * c1 [mole m^-3]* c2 [mole m^-3] = k1 [mole^-2 m^6 s^-1] * w1 [kg mole^-1] * c1 [mole m^-3]* w2 [kg mole^-1] * c2 [mole m^-3] where k1 = k / (w1*w2) [kg^-2 m^6 s^-1 ]

and if the activation temperature and the temperature exponent is the same, the pre-exponential factor A1 = A / (w1*w2).

Good luck
a.m.

schokoundkeks August 30, 2010 03:48

thanks so far.

I have a equlibrium reaction. One reaction ist SO2 (liq) -> H Ion + HSO3 Ion

k = 3.265E16 [s^-1]

transformed -> k* = k / M_SO2

The second reaction is H Ion + HSO3 Ion -> SO2 (liq)

k2 = k / Keq [m^3 s^-1 mol^-1]

K eq is the equlibrium constant of the reactions

transformed -> k2* = k2 / (M_H * M_HSO3)

is this the right transformation? Ativation Engery is the same is both reactions and Temperature Exponent ist Zero.

for some reason the expected equilibrium does not work out in the simulation.

thanks for your help

a.m. August 30, 2010 16:21

1) if the reaction is SO2 = H + HSO3, then equilibrium is wf = wb --> k1*c(SO2)= k2*c(H)*c(HSO3), where k1 = 3.265E16 [s^-1].
2) therefore k2 = k1 * {c(SO2)/(c(H)*c(HSO3))} and keq = {c(SO2)/(c(H)*c(HSO3))} ----> k2 = k1 *keq
for this reaction, keq must have a dimension (like [kg/m3]).

There is another reaction (equilibrium): H2O(liq) + SO2(gas) =(1)= H2SO3 =(2)= H + HSO3 =(3)= 2H + SO3. In point of fact there are 3 equilibriums because H2SO3 is unstable. In this case k2eq = 0.02, k3eq = 6*10^-8.
k1eq = 16 [mole/m3] = [SO2]*[H2O]/[H2SO3]=0.225[kg/m3].
If this case is suitable, you should use k1eq in spite of keq in order to find k2 (see p 2).


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