Introduction

Abstract

When Toms (1949) discovered that minute amounts of added long-chain polymer molecules could reduce the pressure losses in a turbulent pipe flow, this was not the first time that such an effect by additives was observed. It was already known that fibre suspensions, mainly fibres used in the paper making process, showed the same effect in concentrations, however, that were two orders of magnitude higher than in Toms’ experiment (for a review of these earlier papers see Radin et al. 1975). Toms however, showed for the first time that minute amounts, 5–10 ppm per weight, of polymers could have a really dramatic effect. In other words, the drag reducing effect became a promising candidate for partial solutions of the problem of energy saving.