DRAG REDUCTION IN LARGE TUBES AND BEHAVIOR OF ANNULAR FILMS OF DRAG REDUCING FLUIDS

Turbulent flow drag reduction is governed by elastic effects within the boundary layer of the flow. The effect of elasticity is to reduce the radial momentum transfer rates of large eddies that exist near the tube wall, and in so doing a reduction in the turbulent flow drag occurs. A recent theoretical analysis is used to formulate a general discussion of the significant features of drag reducing systems and is used to predict quantitatively the percentage reductions in drag for systems of practical significance. It is shown that little or no drag reduction can be expected in large tubes using polymeric materials that are presently available though micellar systems show effects of substantial magnitude which appear to be exploitable. An analysis is presented which indicates that laminar annular films of dilute polymeric fluids, used to enable the core fluid or a capsule to “slide” through a pipeline at reduced pressure drop, are of especial interest in that the normal stress field may generate forces which increase the concentricity of the core in the presence of major density differences. This exploitation of non‐Newtonian fluid properties, suggested some years ago by Lummus, does not appear to have been subjected to analysis before, nor do verifying experimental data appear to be available. Copyright © 1969 Canadian Society for Chemical Engineering