[cwl]

Hi everyone

I'm trying to think of modeling sulphuric acid dilution in water: the more water is added to the acid the more heat is generated.

Omitting the chemical mechanism - amount of heat released can be found using the enthalpy of mixing diagram as a function of concentration of water:

3-s2.0-B9780081010938000070-f07-11-9780081010938.jpg

So i suppose the easiest way would be - if enthalpy of the fluid mixture (acid + water) could be defined as a function of mass fraction of components(s), but .. from what i've found - enthalpy can only depend of temeprature and pressure.

Any ideas on how to implement that or advices in general? - Or maybe my idea is incorrect in general.

[fluid23]

Would an energy source linked by field function to your mixing diagram be appropriate?

I don't do a lot of reacting flows, just trying to be helpful. What about the 'user defined reaction-rate source term'?

Let me know if I am underthinking this.

[cwl]

Originally Posted by fluid23

Would an energy source linked by field function to your mixing diagram be appropriate?

Yes, fluid23, that was the first idea I had - and I also tried to implement approach described on Steve Portal ("An example of implementing the Enthalpy of Mixing"), but that article contains several mistakes (starting from incorrect units) and results in the article look ok only as a result of coincidence and the fact that gas mixture is considered, not fluid mixture.

I've corrected it, but honestly speaking I'm still facing heat imbalance problems with that approach.

I don't do a lot of reacting flows, just trying to be helpful.
What about the 'user defined reaction-rate source term'?

I'm grateful for the reply anyway
Reacting flow was right next idea after the one described above, but ...

Briefly - chemical heat release rate can be described as rᵢ·hᵢ, where hᵢ - is some heat or enthalpy difference (no problem with that), while rᵢ - is a rate of change of species.

In case of "usual" reaction A + B → C + D (like 2·H₂ + O₂ → 2·H₂O) - A and B disappear and chemical terms are ok since rᵢ of reactants is non-zero.

But in case of "dilution" reaction (unless we go deep down to H⁺, H₃O and HSO4⁻ etc) in case of sulphuric acid we have ... H₂SO₄ + H₂O → H₂SO₄ + H₂O.
And thus rᵢ is .. zero, and so is the heat release %)