(129a) Turbulent Flow of Dilute Aqueous Suspensions of Multi-Walled Carbon Nanotubes In a Smooth Pipe

Turbulent flow of dilute aqueous suspensions of multi-walled carbon nanotubes in a smooth pipe was explored experimentally.  Industrial grade multi-walled carbon nanotubes, abbr MWCNT, of average diameter and length (d, l) = (12 nm, 30000 nm), were suspended at concentrations c from 1 to 1000 wppm in a solution containing 900 wppm of polyvinylpyrolidone surfactant in deionized water.  A seamless stainless steel test pipe with electropolished bore, of internal diameter and bore roughness (D, k) = (4.58 mm, 0.18 microns), was used, comprizing 6 sections, each of L/D = 30 with a pressure tap near its downstream end.  The test pipe was part of a single-pass, progressing cavity pump-driven flow system that could traverse Reynolds numbers from 8300 to 67000 and pipe wall shear stresses from 10 to 500 Pa.  Friction factors obtained with deionized water showed that fully-developed turbulent flow was established at axial distances x/D > 60 from the pipe entrance at all but the lowest Re; also   pressure drops between taps 4&5, across pipe section 5 at 120 < x/D < 150, yielded the relation  1/√f = (3.85±0.14) log Re/√f + (0.48±0.47) that was close to the Prantdl-Karman equation for Newtonian turbulent pipe flow.  On account of their scarcity, nanotube suspensions were tested in brief “scanning” 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/√f (11.2±0.1, 12.3±0.1, 13.3±0.1, 14.5±0.1) at Re√f (790, 1440, 2670, 4890) respectively.  Thereafter, scans of MWCNT suspensions at each of  c = (1.0, 10, 100, 1000) wppm provided sets of 1/√f (11.2±0.2, 12.2±0.1, 13.2±0.1, 14.4±0.1) at Re√f (770, 1450, 2650, 4850) respectively that were virtually indistinguishable from the basis scans at c = 0 wppm.  The dilute aqueous solutions of c = 1 to 1000 wppm MWCNTs in 900 wppm PVP surfactant thus exhibited Newtonian turbulent flow behavior, to within the experimental error of 0.1 units of 1/√f over the Re√f range from 750 to 4900 at non-dimensional pipe lengths x/D from 120 to 150.