Paper Number
CS5 

Session
Colloids and Suspensions

Title
The role of viscoplasticity on the flow dynamics and low-flow limit in slot coating applications

Presentation Date and Time
October 14, 2024 (Monday) 11:10

Track / Room
Track 2 / Waterloo 4

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)
  4. de Souza Mendes, Paulo R. (Pontificia Universidade Catolica do Rio de Janeiro, Department of Mechanical Engineering)

Author and Affiliation Lines (in printed abstract book)
Ivan R. Siqueira1, Roney L. Thompson2, Márcio S. Carvalho1 and Paulo R. de Souza Mendes1
1Department of Mechanical Engineering, Pontificia Universidade Catolica do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro 22451-900, Brazil; 2UFRJ, Rio de Janeiro, Brazil

Speaker / Presenter 
de Souza Mendes, Paulo R.

Keywords
computational methods; advanced manufacturing; colloids; gels; non-Newtonian fluids; suspensions

Text of Abstract
Yield-stress materials, such as the structurally complex formulations found in paints, slurries, and waxes, have long been ubiquitous in the coating industry. However, coating engineering remains largely empirical, as the fundamental role of viscoplasticity, arising from the yield stress of these materials, is not yet fully understood in most coating applications. In this study, we couple a recent harmonic mean viscosity regularization for the Bingham model with a well-established finite element/elliptic mesh generation method for free surface flows. This allows us to present a detailed computational analysis of slot coating applications involving viscoplastic materials. By neglecting inertia and focusing on the downstream section of a slot coater, we introduce suitable dimensionless parameters and provide a comprehensive set of results. These results reveal the significant impact of viscoplasticity on flow dynamics and the low-flow limit. Our findings show that viscoplastic effects greatly influence the velocity field and recirculation pattern in the coating bead, as well as the development length and free surface in the film region. Most importantly, we discover that viscoplastic effects substantially widen the operating window of the low-flow limit. This suggests that structurally complex yield-stress materials can be used to coat thinner films and/or at higher speeds than the standards established for simple Newtonian liquids.