Graham M. Harrison

The effect of added polymers on the formation of drops ejected from a nozzle

The presence of small amounts of polymer in Newtonian solvents can have a significant impact on the flow behavior of these fluids in extension-dominated flows. This study investigates the effect of elasticity on the on-demand drop formation through the use of low viscosity elastic liquids. A high-speed camera is employed to observe drops ejected from a nozzle. The drops are created using a piezoelectric sleeve that contracts around a nozzle forcing fluid out. We observe that the satellite drops commonly produced with Newtonian fluids of identical shear viscosity in the same geometry can be suppressed when polymers with sufficient molecular weight are added. For our nozzle, the minimum required molecular weight is 300k PEO at a concentration of 25 ppm. However, the resultant increased elasticity in the solution requires a greater pulse strength to eject the drop. In addition, the fluids containing polymers have a longer thread, a longer time to separation, and a lower velocity than the Newtonian fluids wit...

A note on the effect of polymer rigidity and concentration on spray atomisation

The atomisation of flexible, semi-rigid, and rigid polymer solutions through a single swirl-type spray nozzle is experimentally examined. The cone angle for the spray is correlated with the type of polymer and the concentration. We observe an initial increase, compared to that of water, in the cone angle as the concentration increases for all solutions. As the concentration is increased further the measured cone angle decreases until the cone collapses and the spray nozzle produces a single jet. The flexible polyacrylamide solutions collapsed at the lowest polymer concentration followed by the rigid Xanthan gum and then the semi-rigid carboxymethyl cellulose. The behaviour of spray cone angle may be explained by differences in the qualitative behaviour of the extensional viscosity for the different types of polymer and different polymer concentrations.

THE MEASUREMENT OF THE FLOW AROUND A SPHERE SETTLING IN A RECTANGULAR BOX USING 3-DIMENSIONAL PARTICLE IMAGE VELOCIMETRY

Abstract A novel three-dimensional particle image velocimetry technique is used to measure the planar three-dimensional flow field about the centreline of a sphere sedimenting in a rectangular shaped box. Measurements are made in the center of the container and also one diameter from a plane wall. Results are presented for a sphere falling in both a constant viscosity elastic (Boger) fluid and a shear-thinning elastic liquid. In the center of the box, the flow field is essentially two-dimensional as expected. Near the wall, there is substantial out-of-plane motion in the shear-thinning solution due to the presence of the wall. Surprisingly, there is little out-of-plane motion for a sphere sedimenting near the wall in the Boger fluid. There are significant qualitative differences in the flow field for the sphere sedimenting in the shear-thinning and constant viscosity elastic liquids. The results are compared with previously published work for a sphere settling in a non-Newtonian fluid and also with results obtained in an identical geometry for a Newtonian fluid. Reasons for the differences in the velocity maps are discussed. The drag coefficient for each geometry and fluid is calculated.

Combined Stereoscopic Particle Image Velocimetry and Line Integral Convolution Methods: Application to a Sphere Sedimenting Near a Wall in a Non-Newtonian Fluid

The flow fields for a sphere sedimenting through a Newtonian and two non-Newtonian liquids near a wall in a square tank are investigated using 3-D stereoscopic particle image velocimetry (PIV) and line integral convolution (LIC) methods. The PIV data were taken using an angular stereoscopic configuration with tilt and shift arrangements for the Scheimpflug condition and a pair of liquid correction prisms. Data were recorded from planes perpendicular and parallel to the wall for each fluid case over a range of distances from the wall. The PIV and LIC results highlight significant differences in the wake structure for all three cases. Out of plane flow was also found to persist up to two sphere diameters downstream in the wake for all cases.

The Rheology and Processing of Renewable Resource Polymers

Bio‐based polymers offer an alternative to conventional fossil fuel‐based materials, in particular for commodity applications such as single‐use products. In this work, we report on the rheology and processing of two bio‐based polymers, namely poly‐hydroxyalkanoate (PHA) copolymers and poly‐lactic acid (PLA), and their blends. These materials are derived from renewable resources, and can degrade under the appropriate conditions. The rheology is investigated in shear, elongation, and transient modes. Of particular importance is the degradation of these materials at typical processing conditions, and the impact of polymer architecture on the extensional properties. Using results from these rheological investigations, appropriate thermal and flow conditions are employed in a DSM Xplore microcompounder, with the cast film attachment, to produce films of PHA copolymers blended with PLA. The resultant films are characterized, as a function of both material composition and processing history, using DSC, WAXD, tensile testing, and SEM, to investigate the effect of varying PHA content on the final properties.Bio‐based polymers offer an alternative to conventional fossil fuel‐based materials, in particular for commodity applications such as single‐use products. In this work, we report on the rheology and processing of two bio‐based polymers, namely poly‐hydroxyalkanoate (PHA) copolymers and poly‐lactic acid (PLA), and their blends. These materials are derived from renewable resources, and can degrade under the appropriate conditions. The rheology is investigated in shear, elongation, and transient modes. Of particular importance is the degradation of these materials at typical processing conditions, and the impact of polymer architecture on the extensional properties. Using results from these rheological investigations, appropriate thermal and flow conditions are employed in a DSM Xplore microcompounder, with the cast film attachment, to produce films of PHA copolymers blended with PLA. The resultant films are characterized, as a function of both material composition and processing history, using DSC, WAXD, te...

A Study of the Sedimentation of a Sphere Near a Vertical Wall Using Three-Dimensional PIV

The sedimentation of a sphere through a fluid is a standard testbed problem in non-Newtonian fluid mechanics. The experimentally determined velocity fields may be compared with numerical predictions obtained using finite element simulations. In this work, the influence of an adjacent wall, in addition to elastic and shear thinning effects, on the velocity field in the fluid surrounding the sphere is studied. Three different test fluids are employed: a Newtonian reference fluid, a constant shear viscosity (elastic) Boger fluid, and a shear thinning elastic fluid. All three fluids have similar zero shear viscosities. For all experiments, the terminal velocity is achieved before measurements begin. Significant differences in both the location and magnitude of the recirculation zones are observed for the different test fluids. In addition, the shape of the wake is qualitatively different for the various fluids.Copyright