Microdevices for extensional rheometry of low viscosity elastic liquids : a review

Extensional flows and the underlying stability/instability mechanisms are of extreme relevance to the efficient operation of inkjet printing, coating processes and drug delivery systems, as well as for the generation of micro droplets. The development of an extensional rheometer to characterize the extensional properties of low viscosity fluids has therefore stimulated great interest of researchers, particularly in the last decade. Microfluidics has proven to be an extraordinary working platform and different configurations of potential extensional microrheometers have been proposed. In this review, we present an overview of several successful designs, together with a critical assessment of their capabilities and limitations

The Inertio-Elastic Planar Entry Flow of Low-Viscosity Elastic Fluids in Micro-fabricated Geometries

The non-Newtonian flow of dilute aqueous polyethylene oxide (PEO) solutions through microfabricated planar abrupt contraction-expansions is investigated. The contraction geometries are fabricated from a high-resolution chrome mask and cross-linked PDMS gels using the tools of soft-lithography. The small length scales and high deformation rates in the contraction throat lead to significant extensional flow effects even with dilute polymer solutions having time constants on the order of milliseconds. The dimensionless extra pressure drop across the contraction increases by more than 200% and is accompanied by significant upstream vortex growth. Streak photography and videomicroscopy using epifluorescent particles shows that the flow ultimately becomes unstable and three-dimensional. The moderate Reynolds numbers (0.03 ⤠Re ⤠44) associated with these high Deborah number (0 ⤠De ⤠600) microfluidic flows results in the exploration of new regions of the Re-De parameter space in which the effects of both elasticity and inertia can be observed. Understanding such interactions will be increasingly important in microfluidic applications involving complex fluids and can best be interpreted in terms of the elasticity number, El = De/Re, which is independent of the flow kinematics and depends only on the fluid rheology and the characteristic size of the device.NS

Formulation, characterisation and flexographic printing of novel Boger fluids to assess the effects of ink elasticity on print uniformity

Model elastic inks were formulated, rheologically characterised in shear and extension, and printed via flexography to assess the impact of ink elasticity on print uniformity. Flexography is a roll-to-roll printing process with great potential in the mass production of printed electronics for which understanding layer uniformity and the influence of rheology is of critical importance. A new set of flexo-printable Boger fluids was formulated by blending polyvinyl alcohol and high molecular weight polyacrylamide to provide inks of varying elasticity. During print trials, the phenomenon of viscous fingering was observed in all prints, with those of the Newtonian ink exhibiting a continuous striping in the printing direction. Increasing elasticity significantly influenced this continuity, disrupting it and leading to a quantifiable decrease in the overall relative size of the printed finger features. As such, ink elasticity was seen to have a profound effect on flexographic printing uniformity, showing the rheological tuning of inks may be a route to obtaining specific printed features

Investigation of the layering mechanism of agglomerate growth during drum pelletization

Conventional drum pelletization circuits exhibit undesirable surging behavior that is known to result from uncontrolled occurrence of the mechanisms of nucleation, coalescence and layering. This study was undertaken to investigate the mechanism of pellet growth by layering. Several laboratory experiments were carried out to delineate the effect of feed moisture content and feed quantity. This paper presents an analysis of the experimental results and a simple model to describe the layering process. (C) 2002 Published by Elsevier Science B.V

Virtual Teams: Report 1

Executive Summary Business globalization, rapid technology advancements and the current economic situation have many companies reviewing and expanding their electronic communication channels. One of the ways companies capitalize on the new business environment is through virtual teams – people working towards a common purpose, who can be located across the world or working at any time of the day. The purpose of this paper is to review the literature on virtual teams and accentuate areas that require in-depth attention of the virtual team and its management. The specific subjects explored here are considered some of the basic elements of virtual teams. These subjects - leadership, communication, and technology - show that the basic elements of teamwork stay intact, however specific measures can be taken to reinforce operational team excellence and relieve many of the uncertainties perceived to surround virtual teams. Trust is paramount; establishing trust via electronic communication and through transparent, consistent and pro-active leadership assists in creating a strong team bond. Training and coaching to further develop the team members’ knowledge of technology, communication protocols and team progress measurements will facilitate success for virtual teams

Report 2: Team Self-Diagnosis

Executive Summary This team self-diagnosis examines the team’s strengths, weaknesses, and overall performance via an examination of team development and dynamics. The team formed primarily on the basis of existing relationships. These relationships helped to quickly build trust and enabled the team to progress rapidly through the forming and storming phases. Team members established their roles and responsibilities at the first meeting along with a common vision and a common working approach. The use of a shared leadership model worked for this team because members kept their commitments right from the start. Knowing that one’s teammates would honor their commitments quickly established mutual accountability. Trust was developed so rapidly that the team was not compelled to establish explicit ground rules. Though several national cultures were represented on the team, culture proved to be an insignificant factor in team development or function. Team interactions were primarily task oriented rather than social. Team members easily came to consensus and demonstrated they would yield their personal viewpoints for the betterment of the team. Weaknesses identified by the team were occasionally rushing too quickly to consensus; on some topics, more time might have been needed to thoroughly understand another’s viewpoints. Also, the team might have benefited from formal ground rules, occasional checks to ensure there was explicit agreement on decisions, and evaluating individual personalities earlier in the life of the team. Overall, the team functioned very well. The team felt it had the potential to be a highperformance team had members been able to spend more time together to focus more on social interaction