title: Experimental investigation into non-Newtonian fluid flow through gradual contraction geometries
Creators: name: Keegan, Fiona
Publisher: name: University of Liverpool Repository
Year: 2010

description: This thesis presents the results of an investigation into the flow of several non- Newtonian fluids through two curved gradual planar contractions (contraction ratios 8:1 and 4:1). The objectives were to determine whether a newly discovered effect (velocity overshoots were observed in the flow of a 0.05% polyacrylamide solution close to the sidewalls of a gradual contraction followed by a sudden expansion by Poole et al., 2005) could be reproduced in the absence of the expansion, learn more about the phenomenon and to provide a comprehensive set of experimental results for numerical modellers to compare their results to. The fluids investigated were a Newtonian control fluid (a glycerine-water mixture), four concentrations of polyacrylamide (PAA), varying from the ‘dilute’ range to the ‘semi-dilute’ range and two concentrations of xanthan gum (XG), both in the ‘semi- dilute’ range. All fluids were characterised using shear rheology techniques and where possible extensional rheology measurements were also undertaken. The fluid properties determined from this characterisation were used to estimate various non- dimensional numbers such as the Reynolds and Deborah numbers, which can then be used to characterise the flow. The flow under investigation was the flow through a gradual contraction section. Two smooth curved planar gradual contractions were used with contraction ratios of 8:1 and 4:1. The upstream internal duct dimensions were 80mm by 80mm in both cases and the downstream internal duct dimensions were 80mm by 10mm for the 8:1 contraction and 80mm by 20mm for the 4:1 contraction. Polymer degradation within the test rig was assessed and the maximum time that the solutions could be reliably used was found to be six hours. The fluid velocity was measured at discrete locations within the flow using laser Doppler anemometry (LDA), which is a non-intrusive flow measurement technique. Measurements were taken across the XZ-centreplane (side to side) and in some cases across the XY-centreplane (top to bottom). The flow of the Newtonian control fluid was as expected with the flow flattening into the ‘top hat’ shape usually observed in Newtonian flow through a gradual contraction (as utilised in wind tunnel design for example). The flows of 0.01% PAA (‘dilute’) and 0.07% XG (‘semi-dilute’) also flattened as the flow progressed through the 8:1 contraction as the Deborah numbers in these flows were very low. Velocity overshoots close to the plane sidewalls were observed in both the 0.03% and 0.05% PAA solutions through the 8:1 and 4:1 contractions. The overshoots through both contractions seemed to be influenced most by the Deborah number (i.e. the extensional properties of the flow and fluid). Velocity overshoots were observed in the 0.3% PAA solution through both contractions but they were different in shape to those seen at the lower concentrations. The overshoots were closer to the centre of the flow growing into one large ‘overshoot’ at the end of the contraction. This investigation showed that the velocity overshoots can be reproduced in both the 8:1 and 4:1 gradual contraction in several concentrations of PAA providing the right parameters are met (i.e. fluid properties, flow rate etc.). Good quality sets of data have been produced, which can be used in the future by researchers interested in numerical modelling of non-Newtonian fluid flows through similar contractions.