Learning Forum

[s.sethuraman]

Hi everyone,

I’m trying to understand how Energy Due to Reaction (also known as Heat of Reaction) is calculated in ANSYS Fluent.

According to the Fluent Theory Guide (Eq. 5-11), the energy source term due to reaction is given as:

S_h,rxn = ∑ h⁰_j * R_j / M_j 

where h⁰_j is the enthalpy of formation, M_j is the molecular weight and R_j is the creation rate of species. 

My main question is about R_j: Is R_j the net reaction rate (in [kg/m³·s]) as used in source terms, or is it R̂_{i,r}, the molar rate of creation/destruction of species i in reaction r, as defined in Eq. 7-11 of the Theory Guide? Intuitively, I believe it should be the net reaction rate (mass basis), especially since the units line up, and this is also suggested in the ANSYS Forum article here: Here

However, when I follow the method in that article, the calculated Sh_rxn values differ significantly from those shown in Fluent’s Heat of Reaction contour plot.

If anyone can help explain this discrepancy or clarify how Fluent computes the heat of reaction internally, I’d greatly appreciate it. 

Thanks in advance!