hy2Foam: Adaptation of Keq from cgs to mks units for reversible reaction types

[Alex070720]

As I have seen in the chemical mechanisms in the hy2Foam tutorials, you calculate the forward reaction rate constant (k_f) in m^3/(kmole * s). Then you calculate the equilibrium constant K_eq by using the curve-fit coefficients in order to calculate k_b. But the unit of k_b can vary depending on the reaction. For example, the backward constant remains in m^3/(kmole * s) for such reactions as NO + O = O2 + N (exchange reaction). This means that K_eq is in this case dimensionless. For reactions of type AB -> A + B (dissociation reaction), such as N2 + M = 2N + M, k_b is in m^6/(kmole^2 * s). In this case K_eq is no longer dimensionless and gets the following dimensions: m^3/(kmole * s). Since the Arrhenius coefficients are mostly (Gupta, Dunn and Kang Park ...) given in cm^3/(mole * s) or cm^6/(mole^2 * s), you have to multiply K_eq by 1000 for the reactions of the type AB -> A + B in order to convert K_eq from CGS units to MKS units.

I changed the following:

1. Introduced an additional scalar to the ReversibleReaction class for converting the units from CGS to MKS
2. Added two kinetic mechanisms to the bluntedCone tutorial as an example

[vincentcasseau]

Hi Alex,

I have been away from GitHub for a while, I am starting with your post.
This issue has already been addressed in 2019. Please feel free to comment on my solution to this problem which does not require a new dictionary entry. Here's what I wrote:

In July 2019, in order not to modify the source code to solve this issue, I committed this fix: 79086c1

hyFoam/hy2Foam/hy2MhdFoam: reversible reactions in hTCReactionsEarth93 fixed. There was an issue with the units of the equilibrium constant for: dissociation reactions, impact dissociation reactions and impact ionisation reactions. The A1 array elements in hTCReactionsEarth93 and the deprecated hTCReactionsDPLR chemDicts were added ln(1000) for those reactions. PLEASE UPDATE YOUR CHEMISTRY DICTS.

[vincentcasseau]

Based on what was said in #59, I will let you decide whether you want to leave this pull request open or not.

[Alex070720]

I decided to close this pull request and keep working in mks units.