Film splitting model with entrainment

The ribbing instability, an extremely common cause of non-uniform liquid films in coating operations, is investigated both theoretically and experimentally. The Navier–Stokes system for the two-dimensional flow in symmetric film-splitting in forward roll coating is solved by finite-element analysis. Stability of the flow with respect to three-dimensional disturbances is examined by applying linear stability theory in a consistent finite-element approach, taking Fourier components in the transverse direction. The resulting generalized asymmetric eigenproblem is solved for the growth rates of disturbances as functions of wavenumber. The theory accurately predicts the critical capillary number and wavenumber at the transition to large-amplitude ribs. A sensitive experimental technique for detecting the ribs was developed that relies on low-angle reflection of a focused strip of white light off the meniscus between the rolls. This allowed detection of much smaller amplitude ribs, and much smaller critical capillary numbers were measured. The results indicate that the transition to ribbing is an imperfect bifurcation due to end effects, and clarify earlier discordances in the literature.

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A Driving Method for Reducing Oil Film Splitting in Electrowetting Displays

Membranes ◽

10.3390/membranes11120920 ◽

2021 ◽

Vol 11 (12) ◽

pp. 920

Author(s):

Wenjun Zeng ◽

Zichuan Yi ◽

Yiming Zhao ◽

Li Wang ◽

Jitao Zhang ◽

...

Keyword(s):

Exponential Function ◽

Characteristic Curve ◽

Quadratic Function ◽

Voltage Characteristic ◽

Experimental Results ◽

Oil Film ◽

Initial Voltage ◽

Aperture Ratio ◽

Driving Waveform ◽

Film Splitting

Electrowetting displays (EWDs) are one of the most potential electronic papers. However, they have the problem of oil film splitting, which could lead to a low aperture ratio of EWDs. In this paper, a driving waveform was proposed to reduce oil film splitting. The driving waveform was composed of a rising stage and a driving stage. First, the rupture voltage of oil film was analyzed by testing the voltage characteristic curve of EWDs. Then, a quadratic function waveform with an initial voltage was applied at the rising stage to suppress oil film splitting. Finally, a square wave was applied at the driving stage to maintain the aperture ratio of EWDs. The experimental results show that the luminance was increased by 8.78% and the aperture ratio was increased by 4.47% compared with an exponential function driving waveform.

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Acoustic characterisation of film splitting in a HSWO printing nip

Nordic Pulp & Paper Research Journal ◽

10.3183/npprj-2007-22-04-p424-431 ◽

2007 ◽

Vol 22 (4) ◽

pp. 424-431

Author(s):

Joakim Voltaire ◽

Ulla Mattila ◽

Andrew Fogden ◽

Susanna Nieminen ◽

Heidi Reinius

Keyword(s):

Film Splitting

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Cavitational Film-Splitting of Lubricants

10.4271/2003-01-3118 ◽

2003 ◽

Author(s):

M. S. Barrow ◽

A. Al-Hussany ◽

R. L. Williams ◽

P. R. Williams

Keyword(s):

Film Splitting

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Capillary and Viscoelastic Effects on Elastohydrodynamic Lubrication in Roller Nips

Journal of Tribology ◽

10.1115/1.2831621 ◽

1996 ◽

Vol 118 (4) ◽

pp. 872-879 ◽

Cited By ~ 3

Author(s):

M. S. Carvalho ◽

L. E. Scriven

Keyword(s):

Reynolds Equation ◽

Film Flow ◽

Viscoelastic Behavior ◽

Elastohydrodynamic Lubrication ◽

Deborah Number ◽

Capillary Effects ◽

Simple Set ◽

Viscoelastic Effects ◽

Liquid Movement ◽

Film Splitting

A viscocapillary model of liquid movement and film-splitting in deformable nips between an elatomer-covered roll and a hard roll is presented here. This “soft” elastohydrodynamic regime is described by Reynolds’ equation of lubrication flow and a simple set of spring-and-dashpot elements for the viscoelastic behavior of elastomeric roll covers. Capillary effects around the film-split are accounted for with an augmented Young-Laplace equation from film-flow theory. Effects of the liquid’s surface tension (via capillary number) and the elastomeric cover’s relaxation time (via Deborah number) are predicted and compared with available experiments. Application to the flows through the multiple roller nips of printing press systems is discussed.

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