Abstract
Three different polysaccharides, aloe vera, Tamarind powder and pineapple fibers, are utilized as drag reducing agents in a turbulent flow. Using a Taylor–Couette setup, consisting of a rotating inner cylinder, for measuring the drag reduction, a range of Reynolds numbers from 4 × 104 to 3 × 105 has been explored in this study. The results are in good agreement with previous studies on polysaccharides conducted in a pipe/channel flow and a maximum drag reduction of 35% has been observed. Further, novel additives such as cellulose nanocrystals (CNC), surfactants and CNC grafted with surfactants are also examined in this study for drag reduction. CNC due to its rigid rod structure reduced the drag by 30%. Surfactant, due to its unique micelle formation showed maximum drag reduction of 80% at low Re. Further, surfactant was grafted on CNC and was examined for drag reduction. However, drag reduction property of surfactant was observed to be significantly reduced after grafting on CNC. The effect of Reynolds number on drag reduction is studied for all the additives investigated in this study.
Highlights
The pressure drop in closed conduits is significant in turbulent flow and a considerable amount of energy is depleted in pumping the fluids to overcome this pressure drop, in rough walled geometries
Virk [4,5] observed the onset of drag reduction and concluded that turbulence is required for drag reduction to occur
Additives such as aloe vera, pineapple fibers and Tamarind powder are explored as drag reducing agents using a Taylor–Couette flow setup
Summary
The pressure drop in closed conduits is significant in turbulent flow and a considerable amount of energy is depleted in pumping the fluids to overcome this pressure drop, in rough walled geometries. Instead of commonly used pipe/channel flow, a Taylor–Couette setup is used for measuring the Drag reduction in this work as it has several advantages It is a fluid motion between two coaxial cylinders with one or both the cylinders co-rotating/counter-rotating and possesses similar characteristics of a turbulent boundary layer [17]. The TC setup has been proven as a convenient and reliable testing platform for drag reduction using both additives and super hydrophobic coatings [18,19,20,21] It allows for good control of the fixed batch of fluid and detailed monitoring of DRA degradation as a function of time as well as energy dissipation. Drag reduction can be computed using Equation (2), where cf,w is the skin friction coefficient of water and cf,s is the skin friction coefficient solution with drag reducing additives
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