title: Microfluidic converging/diverging channels optimised for homogeneous extensional deformation.
abstract: In this work, we optimise microfluidic converging/diverging geometries in order to produce constant strain-rates along the centreline of the flow, for performing studies under homogeneous extension. The design is examined for both two-dimensional and three-dimensional flows where the effects of aspect ratio and dimensionless contraction length are investigated. Initially, pressure driven flows of Newtonian fluids under creeping flow conditions are considered, which is a reasonable approximation in microfluidics, and the limits of the applicability of the design in terms of Reynolds numbers are investigated. The optimised geometry is then used for studying the flow of viscoelastic fluids and the practical limitations in terms of Weissenberg number are reported. Furthermore, the optimisation strategy is also applied for electro-osmotic driven flows, where the development of a plug-like velocity profile allows for a wider region of homogeneous extensional deformation in the flow field.
authors.affiliation: James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde , Glasgow G1 1XJ, United Kingdom.
authors.forename: K
authors.initials: K
authors.lastname: Zografos
authors.affiliation: Centro de Estudos de Fenómenos de Transporte, Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto , 4200-465 Porto, Portugal.
authors.forename: F
authors.identifier: 0000-0003-3046-938X
authors.initials: F
authors.lastname: Pimenta
authors.affiliation: Centro de Estudos de Fenómenos de Transporte, Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto , 4200-465 Porto, Portugal.
authors.forename: M A
authors.identifier: 0000-0001-6585-6609
authors.initials: MA
authors.lastname: Alves
authors.affiliation: James Weir Fluids Laboratory, Department of Mechanical and Aerospace Engineering, University of Strathclyde , Glasgow G1 1XJ, United Kingdom.
authors.forename: M S N
authors.initials: MS
authors.lastname: Oliveira