Epidermal biopolysaccharides from plant seeds enable biodegradable turbulent drag reduction

Abstract

The high cost of synthetic polymers has been a key impediment limiting the widespread adoption of polymer drag reduction techniques in large-scale engineering applications, such as marine drag reduction. To address consumable cost constraints, we investigate the use of high molar mass biopolysaccharides, present in the mucilaginous epidermis of plant seeds, as inexpensive drag reducers in large Reynolds number turbulent flows. Specifically, we study the aqueous mucilage extracted from flax seeds (Linum usitatissimum) and compare its drag reduction efficacy to that of poly(ethylene oxide) or PEO, a common synthetic polymer widely used as a drag reducing agent in aqueous flows. Macromolecular and rheological characterisation confirm the presence of high molar mass (≥2 MDa) polysaccharides in the extracted mucilage, with an acidic fraction comprising negatively charged chains. Frictional drag measurements, performed inside a bespoke Taylor-Couette apparatus, show that the as-extracted mucilage has comparable drag reduction performance under turbulent flow conditions as aqueous PEO solutions, while concurrently offering advantages in terms of raw material cost, availability, and bio-compatibility. Our results indicate that plant-sourced mucilage can potentially serve as a cost-effective and eco-friendly substitute for synthetic drag reducing polymers in large scale turbulent flow applications.

Cooperative drag reduction in turbulent flows using polymer additives and superhydrophobic walls

“…The rotor is designed to have a hollow interior recess which remains air-filled during experiments, thereby providing a shear-free interface at the bottom that eliminates extraneous torque which would otherwise arise from fluid friction acting on the lower face. The bespoke TC apparatus has previously been extensively tested in the course of our prior experimental work on drag-reducing superhydrophobic textures [23] and biopolymer solutions [25], and further details of its construction and flow characteristics may be found in these earlier reports.…”

“…Prior to tests employing a superhydrophobic rotor wall, the working fluid was allowed to aerate freely inside a ventilated container for several hours to reach air saturation at ambient temperature, so as to prevent undue depletion of the plastron layer by diffusion of gas into the liquid phase. Furthermore, the experimental procedure was carefully designed to mitigate effects of flow-induced polymer degradation: freshly prepared solutions were used in each experiment and then discarded after the test, the total duration of each test (about 6 min) was kept well below the typical time scale for chain scission [which was determined by regression of degradation data to the well-known Brostow expression to be characterized by a rate constant of r ≈ (12 min) −1 [25]], and the rotor speeds were traversed from low to high so as to minimize undue effects of degradation at the later steps. For each flow curve, multiple replicate experiments were performed and the data sets were averaged before subsequent analysis; the number of replicates used in each test is indicated in the respective figure legends.…”

Spectral Universality of Elastoinertial Turbulence

“…III and Table S1 provided in the Supplemental Material and includes Refs. [26][27][28][29][30][31]. All of the solutions are dilute with c=c à < 1, where c à is the coil overlap concentration.…”

Spatio-temporal Signatures of Elasto-inertial Turbulence in Viscoelastic Planar Jets

“…The rheological properties of the solutions are summarized in Table I. The zero shear viscosity η 0 is measured using an Ubbelöhde-type suspended-level capillary viscometer (size 0B, Cannon Instrument) immersed in an isothermal water bath at 25 ○ C. We calculate the reduced viscosity η red as [70,71]…”