Uniform flux heat transfer in concentric laminar flow of two immiscible liquids

The energy equation was solved exactly for fully developed steady laminar flow in a circular pipe of two immiscible Newton liquids with a concentric cylindrical interface between them, assuming invariant physical properties of the liquids, uniform heat flux at the wall and fully developed temperature profiles. It is shown that even if the viscosity of the annular liquid is orders of magnitude smaller than that of the core liquid, the improvement in heat transfer to the core liquid by injection of the annular liquid cannot exceed a factor of 1.8. (author)