CFD Online Discussion Forums - Unburnt absolute enthalpy equation

Hello,

I am looking into the unburnt absolute enthalpy equation file of OpenFOAM (EauEqn.H) from the solver XiFoam and I have a question about its implementation.
I still can not understand why the terms of the transport equation were no enthalpy is present are multiplied by rho/thermo.rhou() and would appreciate if someone could explain me this and maybe we can discuss it in detail.

Code:

fvScalarMatrix heauEqn

    (

        fvm::ddt(rho, heau) + mvConvection->fvmDiv(phi, heau)

      + (fvc::ddt(rho, K) + fvc::div(phi, K))*rho/thermo.rhou()

      + (

            heau.name() == "eau"

          ? fvc::div

            (

                fvc::absolute(phi/fvc::interpolate(rho), U),

                p,

                "div(phiv,p)"

            )*rho/thermo.rhou()

          : -dpdt*rho/thermo.rhou()

        )

      - fvm::laplacian(turbulence->alphaEff(), heau)



        // These terms cannot be used in partially-premixed combustion due to

        // the resultant inconsistency between ft and heau transport.

        // A possible solution would be to solve for ftu as well as ft.

        //- fvm::div(muEff*fvc::grad(b)/(b + 0.001), heau)

        //+ fvm::Sp(fvc::div(muEff*fvc::grad(b)/(b + 0.001)), heau)



     ==

        fvOptions(rho, heau)

    );

Thanks in advance,
Mateus Dias Ribeiro