LiquidEvaporationBoil spalding number defined on molar basis
In OpenFOAM-2.4.0 at src/lagrangian/intermediate/submodels/Reacting/PhaseChangeModel/LiquidEvaporationBoil/LiquidEvaporationBoil.C line 318:
dMassPC[lid] += pi d Sh Dab rhos log(1.0 + Xr) dt;
where d is the droplet diameter, Sh is the Sherwood number (Sh(Re,Sc)), Dab the vapor diffusivity assuming properties at the film, rhos the density at the film and Xr (line313):
// molar ratio
const scalar Xr = (Xs - Xc)/max(SMALL, 1.0 - Xs);
The units of dMassPC are in kg. However, the dimensionless group Xr is expressed in terms of molar fractions. In literature, Xr is better known as the Spalding mass number (BM) where the ratio is expressed in terms of mass fractions rather than molar fractions [1,2] I wonder if there is an implementation reason, which I do not see immediately, or if this is an implementation issue that should be fixed in order to correctly predict the evaporation rate.
Thank you in advance for your support and reply. Alessandro
 Sergei S. Sazhin, Advanced models of fuel droplet heating and evaporation, Progress in Energy and Combustion Science, Volume 32, Issue 2, 2006.
 Patrick Jenny, Dirk Roekaerts, Nijso Beishuizen, Modeling of turbulent dilute spray combustion, Progress in Energy and Combustion Science, Volume 38, Issue 6, 2012.