Paper Number
IR6 

Session
Interfacial Rheology, Surfactants, Foams, and Emulsions

Title
Free surface flows with Boussinesq-Scriven viscous interfaces: Planar extrudate swell and slot coating

Presentation Date and Time
October 14, 2024 (Monday) 11:30

Track / Room
Track 6 / Room 501

Authors (Click on name to view author profile)

  1. Siqueira, Ivan R. (Pontifícia Universidade Católica do Rio de Janeiro, Department of Mechanical Engineering)
  2. Thompson, Roney L. (UFRJ)
  3. Carvalho, Márcio S. (Pontifícia Universidade Católica do Rio de Janeiro, Department of Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Ivan R. Siqueira1, Roney L. Thompson2 and Márcio S. Carvalho1
1Department of Mechanical Engineering, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro 22451-900, Brazil; 2UFRJ, Rio de Janeiro, Brazil

Speaker / Presenter 
Siqueira, Ivan R.

Keywords
computational methods; interfacial rheology

Text of Abstract
Fluid–fluid interfaces are ubiquitous both in natural phenomena and industrial applications. In practice, the interface between two immiscible fluid phases is often doped with surface-active components such as functionalized nanoparticles and surfactant molecules. As a result, fluid interfaces may display complex rheological signatures characterized by viscous, elastic, plastic, and/or time-dependent responses under external loads and deformations. Phenomenologically, the interfacial stress tensor that describes the dynamic behavior of complex interfaces is not as simple as isotropic, thereby requiring the introduction of other interfacial material properties in addition to the traditional interfacial tension coefficient. Of course, complex interfaces play a major role in small-scale free surface flows where interfacial stresses are relevant to the flow dynamics. Here, we present a computational study of free surface flows with rheologically complex interfaces. Specifically, we use finite element simulations to study planar extrudate swell flows and slot coating flows with viscous interfaces; in both cases, we model the bulk fluid as an incompressible Newtonian liquid and describe the liquid–gas interface with the Boussinesq–Scriven model. We show that the shear and dilatational surface viscosities make viscous interfaces essentially stiffer than their simple counterparts, which slows down the flow and leads to dramatic changes in the shape of the free surface. In planar extrusion, for example, we find that the interfacial viscosities induce a substantial enlargement of the extrudate size; in slot coating, we find that they affect not only the recirculation pattern in the coating bead but also the curvature of the downstream meniscus and the operating limits of the low flow-limit of the process.