title: Stream spreading in multilayer microfluidic flows of suspensions.
abstract: The goal of this experimental study is to quantify the spreading of parallel streams with viscosity contrast in multilayer microfluidic flows. Three streams converge into one channel where a test fluid is sheathed between two layers of a Newtonian reference fluid. The test fluids are Newtonian fluids with viscosities ranging from 1.1 to 48.2 cP and suspensions of 10-mum-diameter PMMA particles with particle volume fractions phi = 0.16-0.30. The fluid interface locations are identified through fluorescence microscopy. The steady-state width of the center stream is strongly dependent on the viscosity ratio between the adjacent fluids and exhibits a near power-law relationship. This dependence occurs for both the Newtonian fluids and the suspensions, although the slopes differ. The high-concentration suspension (phi = 0.30) diverges from Newtonian behavior, while the low-concentration suspensions (phi = 0.16, 0.22) closely approximate that of the Newtonian fluids. The observed suspension behavior can be attributed to shear-induced particle migration.
authors.affiliation: Department of Chemical Engineering, Columbia University, 500 W. 120th Street, MC 4721, New York, New York 10027, USA.
authors.forename: Mona Utne
authors.initials: MU
authors.lastname: Larsen
authors.forename: Nina C
authors.initials: NC
authors.lastname: Shapley