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Contact line dissipation in short-time dynamic wetting
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0003-3336-1462
2012 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 97, no 4Article in journal (Refereed) Published
Abstract [en]

Dynamic wetting of a solid surface is a process that is ubiquitous in Nature, and also of increasing technological importance. The underlying dissipative mechanisms are, however, still unclear. We present here short-time dynamic wetting experiments and numerical simulations, based on a phase field approach, of a droplet on a dry solid surface, where direct comparison of the two allows us to evaluate the different contributions from the numerics. We find that an important part of the dissipation may arise from a friction related to the motion of the contact line itself, and that this may be dominating both inertia and viscous friction in the flow adjacent to the contact line. A contact line friction factor appears in the theoretical formulation that can be distinguished and quantified, also in room temperature where other sources of dissipation are present. Water and glycerin-water mixtures on various surfaces have been investigated where we show the dependency of the friction factor on the nature of the surface, and the viscosity of the liquid.

Place, publisher, year, edition, pages
2012. Vol. 97, no 4
National Category
Mechanical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-91343DOI: 10.1209/0295-5075/97/44004ISI: 000300844100016Scopus ID: 2-s2.0-84857572550OAI: oai:DiVA.org:kth-91343DiVA: diva2:509640
Funder
Swedish e‐Science Research Center
Note

QC 20120313

Available from: 2012-03-13 Created: 2012-03-13 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Capillarity and dynamic wetting
Open this publication in new window or tab >>Capillarity and dynamic wetting
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis capillary dominated two–phase flow is studied by means of nu- merical simulations and experiments. The theoretical basis for the simulations consists of a phase field model, which is derived from the system’s thermody- namics, and coupled with the Navier Stokes equations. Two types of interfacial flow are investigated, droplet dynamics in a bifurcating channel and sponta- neous capillary driven spreading of drops.

Microfluidic and biomedical applications often rely on a precise control of droplets as they traverse through complicated networks of bifurcating channels. Three–dimensional simulations of droplet dynamics in a bifurcating channel are performed for a set of parameters, to describe their influence on the resulting droplet dynamics. Two distinct flow regimes are identified as the droplet in- teracts with the tip of the channel junction, namely, droplet splitting and non- splitting. A flow map based on droplet size and Capillary number is proposed to predict whether the droplet splits or not in such a geometry.

A commonly occurring flow is the dynamic wetting of a dry solid substrate. Both experiments and numerical simulations of the spreading of a drop are presented here. A direct comparison of the two identifies a new parameter in the phase field model that is required to accurately predict the experimental spreading behavior. This parameter μf [P a · s], is interpreted as a friction factor at the moving contact line. Comparison of simulations and experiments for different liquids and surface wetting properties enabled a measurement of the contact line friction factor for a wide parameter space. Values for the contact line friction factor from phase field theory are reported here for the first time.

To identify the physical mechanism that governs the droplet spreading, the different contributions to the flow are measured from the simulations. An im- portant part of the dissipation may arise from a friction related to the motion of the contact line itself, and this is found to be dominating both inertia and viscous friction adjacent to the contact line. A scaling law based on the con- tact line friction factor collapses the experimental data, whereas a conventional inertial or viscous scaling fails to rationalize the experimental observation, supporting the numerical finding.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xi, 50 p.
Series
Trita-MEK, ISSN 0348-467X ; 2012:01
National Category
Fluid Mechanics and Acoustics Computational Mathematics
Identifiers
urn:nbn:se:kth:diva-91329 (URN)978-91-7501-282-7 (ISBN)
Public defence
2012-03-23, Salongen KTHB, Osquars Backe 25, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note

QC 20120313

Available from: 2012-03-13 Created: 2012-03-13 Last updated: 2013-04-09Bibliographically approved

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Amberg, Gustav

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