In traditional phase field models of solidification, the dynamics of the fields ϕ α are assumed to follow dissipative dynamics that relax a free energy while coupled to the evolution of conserved solute fields c i . Here, we will employ a different approach where we couple the evolution of the order parameters ϕ α to the the intensive variables μ i that enter Ω and whose evolution is derived from the conservation law of c i . This will prove to have several practical features.