(358e) Turbulent Flow of Diutan Biopolymer Solutions and Carbon Nanotube Suspensions in a 4.6 mm ID x 200 L/D Smooth Pipe
AIChE Annual Meeting
Tuesday, October 31, 2017 - 1:50pm to 2:06pm
The Diutan biopolymer, MW ~ 5.0E6, had end-to-end length Le ~ 6.0 um, formal contour length Lc ~ 11.7 um and chain diameter Dch ~ 1.5 nm. Aqueous Diutan solutions of concentrations C from 1 to 100 wppm exhibited Type B drag reduction, characteristic of extended macromolecules, yielding turbulent flow segments roughly parallel to, but displaced upwards from, the Prandtl-Karman law, the more so with increasing concentration. At fixed Reâf = 5000, flow enhancements relative to solvent S' = [(1/âf)p - (1/âf)n]Reâf increased almost linearly with increasing concentration, with intrinsic flow enhancements [Sâ] = Limcâ0[Sâ/c] = 0.10Â±0.02.
Industrial grade multi-walled carbon nanotubes, abbr MWCNT, of average diameter and length (Dch, Le) = (12 nm, 30 um), were used. Suspensions of concentration C from 1 to 1000 wppm were made in deionized water containing 900 wppm of polyvinylpyrolidone surfactant. On account of their scarcity, nanotube suspensions were tested in brief âscanningâ runs of 30 s duration at each of four Re = (8300, 16700, 33000, 67000). First, two scans at C = 0, that is, of the 900 wppm PVP surfactant solution alone, served to establish a basis, yielding P-K results of 1/âf (11.2Â±0.1, 12.3Â±0.1, 13.3Â±0.1, 14.5Â±0.1) at Reâf (790, 1440, 2670, 4890) respectively. Thereafter, scans of MWCNT suspensions at each of c = (1.0, 10, 100, 1000) wppm provided sets of 1/âf (11.2Â±0.2, 12.2Â±0.1, 13.2Â±0.1, 14.4Â±0.1) at Reâf (770, 1450, 2650, 4850) respectively that were virtually indistinguishable from the basis scans at c = 0 wppm. Suspensions of C = 1 to 1000 wppm MWCNTs in 900 wppm PVP surfactant thus exhibited Newtonian turbulent flow behavior.
Under similar flow conditions, solutions of Diutan biopolymer, with Le ~ 6 um and aspect ratio Le/Dch ~ 4000, exhibit Type B turbulent drag reduction with intrinsic slip [Sâ] = 0.10, whereas suspensions of multi-walled carbon nanotubes, with Le ~ 30 um and aspect ratio Le/Dch ~ 2500, both the same order of magnitude as Diutan, exhibit Newtonian turbulent flow, without any hint of drag reduction. It would be most interesting to divine what skeletal attribute(s) allow(s) drag reduction by Diutan biopolymer but forbid(s) drag reduction by carbon nanotubes.