Turbulent Flow of Dilute Aqueous Suspensions of Single Wall Carbon Nanotubes in a Smooth Pipe

The object of the present work was to experimentally explore the turbulent flow of dilute aqueous suspensions of single-walled carbon nanotubes in a smooth pipe. The industrial grade single-walled carbon nanotubes, of average diameter and length (d, l) = (1.1 nm, 17500 nm), were suspended at concentrations c from 0.01 to 100 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/�ãf = (3.85±0.14) log Re�ãf + (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 gscanningh 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/�ãf (11.1±0.1, 12.2±0.1, 13.2±0.1, 14.5±0.1) at Re�ãf (750, 1370, 2520, 4580). Thereafter, scans of SWNT suspensions at each of c = (0.01, 0.10, 1.0, 10, 100) wppm provided sets of 1/�ãf (11.2±0.2, 12.2±0.1, 13.2±0.0, 14.5±0.0) at Re�ãf (740, 1375, 2520, 4590) that were virtually indistinguishable from the basis scans at c = 0 wppm. The dilute aqueous solutions of c = 0.01 to 100 wppm SWNTs in 900 wppm PVP surfactant thus exhibited Newtonian turbulent flow behavior to within the experimental error of 0.1 units of 1/�ãf over the Re�ãf range from 750 to 4600.