Polymer-induced turbulence modifications in an impinging jet

Abstract

This effort explores the impact of dilute polymer solutions on the turbulence characteristics in a submersed liquid impinging-jet configuration. Turbulent impinging jets are commonly used in technological applications such as drying, scouring, cooling or heating due to an enhancement in transport characteristics in the impingement region under certain nozzle-to-wall configurations.Previous efforts have identified significant turbulence modifications in the presence of dilute concentrations of polymer (i.e., the Toms effect) in both bounded (suppression) and unbounded (either suppression or enhancement) flows. To this end, particle-image velocimetry measurements were made for an axisymmetric turbulent impinging jet with a nozzle-to-wall distance H/D = 6.8 and Reynolds number Re D = 23000. Measurements were made for both plain water and dilute polymer solutions of polyethylene oxide at concentrations of 50 and 100 ppm. The mean and turbulence characteristics of these three flows are contrasted and it is observed that the 50 ppm case yields a slight enhancement of the turbulence while the 100 ppm case exhibits clear suppression of the turbulence.iii

Grid turbulence in dilute polymer solutions: PEO in water

“…A similar behaviour has been reported by Sylvester & Tyler (1970) who speculated that the sudden change is due to polymer entanglements which start to form around 100 wppm. This is also consistent with the clear break in the characteristics of an impinging turbulent jet between 50 and 100 wppm observed by Mejia-Alvarez & Christensen (2011). We adhere to the view that the change of properties between 50 and 100 wppm corresponds to the transition between truly dilute solutions where there is essentially no interaction between PEO molecules and a regime where polymer entanglement is significant even though the critical coil overlap concentration c * is 0.77/[µ] ≈ 500 wppm, according to standard wisdom (see, e.g., Graessley 1980).…”