Two-phase axial laminar flow in a pipe with naturally curved interface

Abstract The author considers the possibility of reducing the skin friction in pipes transmitting viscous liquid by the addition of less viscous liquid. This analysis provides the mathematical tools required to estimate the reduction in the pressure drop and power consumption which are necessary to maintain a given volumetric flow rate of the more viscous liquid. First a procedure which determines the geometry of the interface between the two, assumed immiscible, liquids is devised. It takes into account the interface tension, capillary forces and gravity. Then the two-phase Poiseuille flow problem is solved by obtaining an equivalent variational principle and applying the Rayleigh—Ritz method. The results show that when the viscosity ratio is about 1/20 one can get close to 50% reduction in the applied pressure gradient though somewhat smaller savings in the power consumption.