The effects of formation aids on flow properties of cellulosic fibrous suspensions
(English)Manuscript (preprint) (Other academic)
The effects of high molecular weight anionic polymers on the flow behaviour of fibrous suspensions were studied using phase flow encoded nuclear magnetic resonance imaging (MRI). We examined whether formation improvements by high molecular weight polymers correlate with turbulence damping. Flow imaging measurements and pressure drop analysis were performed for water and fibrous suspensions (0.5 % consistency) with and without polymer added, at different mean velocities (1.0, 1.2 and 1.4 m/s). Our results are consistent with drag reduction of turbulent flows by additives. The results further show how fibres and high molecular weight anionic polymers reduce the drag of turbulent flows, in terms of damping turbulence fluctuations (as determined by signal intensities) and flow profile characteristics. The turbulence damping effect was also manifested through a decrease of pressure drop. When fibres and polymers were used together, we found that the drag was reduced by amounts greater than the sum of the two independent effects. The reinforced effect on drag reduction can be explained by the fact that fibres and polymers act differently with the turbulent flow. The study also reveals the influence of the polymer structure (from linear to highly structured). The overall results indicate that turbulence damping and paper formation improvements by the addition of high molecular weight polymers (Class II formation aids) are strongly correlated. This work can lead to better specification of retention aid systems and design of modern head boxes used for papermaking.
Drag reduction, Fibrous suspension, Formation aids, Flow imaging, High molecular weight polymer, MRI, Nuclear magnetic resonance imaging, Paper formation, Pressure drop, Turbulence damping, Velocity profiles
Paper, Pulp and Fiber Technology
IdentifiersURN: urn:nbn:se:kth:diva-96258OAI: oai:DiVA.org:kth-96258DiVA: diva2:529911