Drag Reduction

Abstract

Turbulent drag reduction in fluid flow by additives has been an exotic field of research ever since its reported discovery in 1949. Various technical applications have been envisaged both for polymeric and surfactant drag reduction. Some successful applications include increased flow of oil and other fluids through pipelines, improved fire fighting and irrigation, improved flow in storm sewers, and flow augmentation by drag reducers in pipeline transport of sediments and slurries. Other possible applications include district heating circuits, industrial and agricultural sprays, and slow‐release fertilizers and pesticides. However, the mechanism of drag reduction still eludes exact explanation mainly because of the inability to characterize polymers, surfactants, and their interactions at molecular or micellar levels in turbulent flows. The main features of polymeric and surfactant homogeneous and heterogeneous drag reduction have been investigated by two‐component laser‐Doppler velocity meter in fully developed, well‐mixed, low concentration (1–2 ppm) drag‐reducing channel flows. Advances in computer technology have led to improved accuracies and reliability of experimental techniques and made possible direct numerical simulation of drag‐reducing turbulent flows. The role of extensional viscosity and elasticity of drag reducers is being keenly debated for the origin of drag reduction in theoretical and experimental investigations. A better understanding is emerging. Some synergistic effects have been observed in combining passive drag‐reducing devices such as riblets with polymers surfactants. Similar observations have been made in combination with microbubbles. This article provides an overview of the latest salient developments in materials, mechanisms, and applications in the field of polymeric drag reduction of various forms and geometries.

Analysis of Unsteady Flow and Heat Transfer of Nanofluid Using Blasius–Rayleigh–Stokes Variable

“…It is noted that the magnitude of thermophoretic and Brownian diffusion parameters for nanoparticles is very small [1,9], therefore we consider N b and N t of O(ε), ε → 0 . We expand θ and φ in small parameter ε and write…”

“…The mechanism of drag and heat loss reduction [1] has been the focus of intensive analysis due to its application in the prevention of loss of mechanical energy. Drag and heat loss reduction may create energy savings, processing time reduction, enhancement in thermal rating, and make equipment more durable.…”

Modification and Applications of Guar Gum in the Field of Green Chemistry

“…These materials even at concentration of a few parts per million by weight, reduce turbulent intensity in flow and, therefore, allow liquids to flow at lesser resistance [5,70].…”

“…Synthetic polymers of high molecular weight (>10 5 ) are very effective drag reducers but get degraded in turbulent flows and lose their effectiveness after a short interval of time or flow. Recently, three approaches have been put forward to enhance the drag reduction effectiveness (DRE) and shear stability of polymers [5,70]: a. The drag reduction effectiveness of guar gum can be enhanced by grafting synthetic polyacrylamide branches onto its main chain; resulting graft copolymers combine efficiency of synthetic polymer and robustness of guar gum main chain.…”

High-technology materials based on modified polysaccharides

“…Even at a concentration of a few parts per million by weight, these materials reduce turbulent intensity in flow and therefore allow liquids to flow at lesser resistance [2,18,74]. The soluble polymers are the most potential drag-reducing agents of all the additives mainly because DR up to 80 % can be obtained with the addition of a few tens of ppm by weight in a particular solvent.…”