An experimental investigation on the turbulent drag reduction effect of polyacrylamide solution in the loop pipe

Abstract

Flexible long-chain polymer molecules with linear structures are widely used in the field of turbulent drag reduction. However, there is no single mechanism that can fully explain all the experimental phenomena of polymer drag reduction. In this paper, we have investigated the relationship between polymer macro-microscopic factors and loop pipe(inner diameter 32mm, wall thickness 3mm, length 19.02m) flow parameters to explain the polymer turbulent drag reduction and degradation mechanisms. Our conclusions are as follows: drag reduction exists in saturated concentration, the higher the Reynolds number corresponds to the larger saturated concentration; there is a maximum drag reduction Reynolds number(Re_max), the higher the concentration corresponds to the larger Re_max; with concentration θ=100ppm (parts per million) and molecular weight increasing, the drag reduction efficiency increases; with θ=100ppm, the solution shows shear thinning behavior, so the polymer molecules are mechanically fractured; in the concentration range θ=2-20ppm, with concentration and polymer particle size in solution increasing, the distribution range becomes wider; the Weissenberg number(Wi) is related to the molecular weight, and the solution shows a better elasticity with the Wi increasing. This paper elucidates the impact of macro-microscopic factors on the elasticity of polymers, thereby enhancing the understanding of the relationship between polymer elasticity and drag reduction efficiency.