nitf.HRef = subst(subst(nitf.CpInt,nitf.pA,1[atm]),T,298.15[K])*298.15[K]/subst(subst(nitf.gammaInt,nitf.pA,1[atm]),T,298.15[K])+1[atm]/subst(subst(nitf.rhoInt,nitf.pA,1[atm]),T,298.15[K])
nitf.DeltaH = integrate(subst(nitf.CpInt,nitf.pA,1[atm]),T,298.15[K],T)+integrate((1+T*d(nitf.rhoInt,T)/nitf.rhoInt)/nitf.rhoInt,nitf.pA,1[atm],nitf.pA)
nitf.HRef is the Reference Enthapy
nitf.DeltaH is the Sensible Enthalpy
I didn't understand the terms subst and integrate in the formula