Institute for Manufacturing

Inkjet Research Centre

Inkjet Research Centre: Next Generation Inkjet Technology Project

Projects

Oliver Harlen, Leeds | Tom McLeish, Leeds | DAMTP |
Oliver Harlen, School of Mathematics, University of Leeds
"Droplet Formation in Inkjet Printing"

The aim of this project is to determine how fluid properties, flow conditions and surface tension affect drop formation in both continuous mode and drop-on-demand inkjet printing by developing a numerical simulation of droplet formation in both types of printing process. In particular, we intend to examine how viscoelasticity affects the formation of ligaments and satellite drops during drop break-up.

The action of surface tension causes a jet of fluid to evolve into spherical drops connected by thin fluid filaments. When these filaments break they may evolve into smaller satellite droplets that are detrimental to image quality. The addition of even very small amounts of high molecular weight polymers to a fluid can dramatically lengthen the break-up time of these fluid filaments and is also expected to affect their subsequent evolution.

mpeg movie

The mpeg movie shows a numerical simulation of the thinning of a filament of a polymeric fluid by surface tension. The colours indicate the value of the polymer stress. Notice that filament remains quite stable as the elastic stress builds. Also note that the highest stress is not located in the centre of the filament, but at the ends next to the spherical drops, indicating that the filament will eventually break at these points.

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Tom McLeish, Physics and Astronomy, University of Leeds (Now at the University of Durham)
"Molecular Rheology"
pom1a (10K)

Tom McLeish is bringing an interest in molecular rheology to the project. He and his group have successfully considered different structures of polymers (like the branched case of figure 1) in coarse-grained physical models to predict the non-Newtonian properties they give to the fluid.

Pom1bb (3K)

In the entangled case, this gives rise to a strong separation of time scales (flow rates) in which different parts of the molecules matter (figure 2).

FLOW (3K)

In the case of ink-jet rheology, both bulk and surface molecularly-controlled rheology are being explored. The mathematical form of the models are constructed so that they can be solved numerically in complex flows (an example is in figure 3) in collaboration with Dr. Oliver Harlen (Applied Mathematics, Leeds).

Tom McLeish has since moved to Durham since the beginning of this project:

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Jocelyn Etienne and John Hinch, DAMTP, and Jie Li, CUED
University of Cambridge
Numerical simulations of inkjet printing

We investigate the mechanisms of jet break-up in both the drop-on-demand and
continuous inkjet printing processes. A key issue is to track the interface
movements with a sufficient accuracy to be able to predict the formation of
satellite droplets, and hence to determine the range of satellite-free
conditions. In particular, the study aims at providing practical information,
such as the influence of the nozzle shape and pressure impulse or disturbance
on the drop formation.

The fluids considered are either Newtonian or viscoelastic, using the
differential constitutive equation FENE-CR.

In order to provide the desired accuracy, the arbitray Lagrange-Euler
method is employed together with a finite-element discretisation. The
method of characteristics is used to provide an efficient discretisation
of the material derivative, both for inertia and for the objective
derivative in the constitutive equation.

Images: Drop formation in drop-on-demand configuration with,

(a) a nozzle ended by a straight tube

a nozzle ended by a straight tube

link to an animation

(b) a tapered nozzle

a tapered nozzle

link to an animation

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