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Arrhenius Equation Definition
Posted 20 nov. 2017, 06:04 UTC−5 Chemical, Chemical Reaction Engineering, Parameters, Variables, & Functions Version 5.3 1 Reply
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Hello
I am trying to implement different simplified reaction mechanisms for methane combustion. How should I ensure that the units are consistent when defining the reaction rate when the input data comes in the units kmol, m^3, K, s, KJ ? For instant, for example for CH4 +1.5O2 => CO+2H2O , CO+0.5O2<=>CO2 and H2+0.5O2 <=> H2O knowing that the parameters are given as C3,C6r1,C6r2 and C8r1 and C8r2 (table in anex) ? When defining the reaction rate should I indicate the concentration units in which way? Also when I define the reaction rate as "user defined" for those reaction orders, mostly posite exponents(inferior to 1) and negative exponents it gives me an error of "unit syntax error", what is the correct way of defining it in COMSOL?
Example C3 : A=5.03e11 Ea/R=2.4056e4 e order CH4^(0.7).O2^(0.8)
Thank you very much,
Hello Mariana Freire
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"No, sqrt(x) is the same as x^0.5.
The problem is that the unit syntax in COMSOL Multiphysics only accepts integer exponents, so there is no unit for "square root of meter," but if this is not what you want, you can de-dimensionalize x using COMSOL unit syntax:
2*(x[1/m])^0.5
does not produce an error.
Magnus Ringh, COMSOL"
Make your concentration dimensionless then add the exponent, amend the units at the end.