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Viscoelastic droplet dynamics in a y-shaped capillary channel
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.ORCID iD: 0000-0002-5915-0789
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.ORCID iD: 0000-0003-2830-0454
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.ORCID iD: 0000-0003-3336-1462
2016 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 28, no 3, 033103- p.Article in journal (Refereed) Published
Abstract [en]

Non-Newtonian droplet dynamics commonly exist in microfluidic systems. We report simulations of viscoelastic (VE) droplets traveling in a two dimensional capillary bifurcation channel. A numerical system combining phase field method, VE rheology, and Stokes flow equations is built. As a generic microfluidic two-phase problem, we study how a non-Newtonian droplet that approaches a channel bifurcation will behave. We identify conditions for when a droplet will either split into two or be directed into one of the branches. In particular, we study the importance of the non-Newtonian properties. Our results reveal two different non-Newtonian mechanisms that can enhance splitting and non-splitting of droplets with respect to Newtonian droplets, depending on the size of droplet and capillary number.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2016. Vol. 28, no 3, 033103- p.
National Category
Natural Sciences
Research subject
Engineering Mechanics
Identifiers
URN: urn:nbn:se:kth:diva-184141DOI: 10.1063/1.4943110ScopusID: 2-s2.0-84960904107OAI: oai:DiVA.org:kth-184141DiVA: diva2:914969
Note

QC 20160329

Available from: 2016-03-28 Created: 2016-03-28 Last updated: 2016-03-29Bibliographically approved
In thesis
1. Capillarity and wetting of non-Newtonian droplets
Open this publication in new window or tab >>Capillarity and wetting of non-Newtonian droplets
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Capillarity and dynamic wetting of non-Newtonian fluids are important in many natural and industrial processes, examples cover from a daily phenomenon as splashing of a cup of yogurt to advanced technologies such as additive manufacturing. The applicable non-Newtonian fluids are usually viscoelastic compounds of polymers and solvents. Previous experiments observed diverse interesting behaviors of a polymeric droplet on a wetted substrate or in a microfluidic device. However, our understanding of how viscoelasticity affects droplet dynamics remains very limited. This work intends to shed light on viscoelastic effect on two small scale processes, i.e., the motion of a wetting contact line and droplet splitting at a bifurcation tip.

 

Numerical simulation is employed to reveal detailed information such as elastic stresses and interfacial flow field. A numerical model is built, combining the phase field method, computational rheology techniques and computational fluid dynamics. The system is capable for calculation of realistic circumstances such as a droplet made of aqueous solution of polymers with moderate relaxation time, impacting a partially wetting surface in ambient air.

 

The work is divided into three flow cases. For the flow case of bifurcation tube, the evolution of the interface and droplet dynamics are compared between viscoelastic fluids and Newtonian fluids. The splitting or non-splitting behavior influenced by elastic stresses is analyzed. For the flow case of dynamic wetting, the flow field and rheological details such as effective viscosity and normal stress difference near a moving contact line are presented. The effects of shear-thinning and elasticity on droplet spreading and receding are analyzed, under inertial and inertialess circumstances. In the last part, droplet impact of both Newtonian and viscoelastic fluids are demonstrated. For Newtonian droplets, a phase diagram is drawn to visualize different impact regions for spreading, splashing and gas entrapment. For viscoelastic droplets, the viscoelastic effects on droplet deformation, spreading radius and contact line motion are revealed and discussed.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. 50 p.
Keyword
Dynamic wetting, contact line, diffusive interface, viscoelasticity, non-Newtonian, microfluidics, droplet impact, droplet spreading
National Category
Physical Sciences
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-184146 (URN)978-91-7595-921-4 (ISBN)
Public defence
2016-04-22, Kollegiesalen, Brinellvägen 8, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

QC 20160329

Available from: 2016-03-29 Created: 2016-03-28 Last updated: 2016-04-02Bibliographically approved

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