Simulation of the Coalescence and Subsequent Mixing of Inkjet Printed Droplets

M.H.A. van Dongen[1], H.J. van Halewijn[2]
[1]Fontys University of Applied Sciences, Expertise Centre Thin Films & Functional Materials, Eindhoven, The Netherlands
[2]Fontys University of Applied Sciences, Eindhoven, The Netherlands

Coalescence of droplets is a widely investigated phenomenon. In inkjet printing micrometer sized droplets are deposited on a substrate which when positioned close enough to each other will coalesce and mix. Little is known about the flows and mixing behaviour within these small droplets. In this investigation we follow the time evolved coalescence of two droplets with volume ratios ranging from 20 to 80 pl. with differently coloured dyes both experimentally and in simulation.

A 3D simulation of two coalescing droplets was created in COMSOL Multiphysics® based on the combination of the Laminar Two-Phase flow (phase field) and the Transport of Diluted Species Interfaces. The results of the COMSOL Multiphysics® simulation are compared to the experimental results. It was found that the COMSOL Multiphysics® simulation predicts the coalescence reasonably well compared to the experimental observations.