Steady recirculating flow near static contact lines

Gaskell, Philip; Thompson, H. M.; Savage, M.; Ikin, J.B.

doi:10.1016/s0009-2509(98)00286-3

Cited by 5 publications

(6 citation statements)

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“…In previous simulations of coating flows containing static wetting lines, two methods of accommodating them have been proposed; either (i) prescribing h s and determining the position of the static wetting line or (ii) specifying the position of the static wetting line and determining h s via the numerical solution. The former approach, used successfully in determining the influence of h s on the adjacent flow structure in industrial coating applications [37], is adopted here; the h s condition is imposed via the following equality…”

Section: Boundary Conditionsmentioning

confidence: 99%

Thin film flow on surfaces containing arbitrary occlusions

et al. 2009

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Section: Boundary Conditionsmentioning

confidence: 99%

Thin film flow on surfaces containing arbitrary occlusions

et al. 2009

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“…The factors leading to defects in the wet coating phase have recently been considered by Gaskell et al (1999), Noakes et al (2002a) and Ikin et al (2007). This paper focuses on the defects that arise in the drying phase of, for example, multilayer curtain or slide-bead coating systems, when the drying air emerges from an array of slot nozzles arranged perpendicular to the machine direction and disturbs the surface of the wet coating.…”

Section: Introductionmentioning

confidence: 99%

Drying air-induced disturbances in multi-layer coating systems

Ikin

Thompson

2007

Chemical Engineering Science

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A range of new experimental techniques is developed to quantify drying-air induced disturbances on low viscosity single and multi-layer coating systems. Experiments on prototype slide-bead coating systems show that the surface disturbances take the form of a wavelike pattern and quantify precisely how its amplitude increases rapidly with wet thickness and decreases with viscosity. Heat transfer measurements show that the redistribution of water to form an additional lower viscosity carrier layer while increasing the solids concentration of the upper layer or layers enables the maximum drying rate, for which drying-air induced surface disturbances are acceptably small, to be increased with significant commercial benefits.

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“…Generally, a recirculation zone is present in the 'film-split' region, as indicated in figure 1. Regions of recirculation are undesirable in coating flows (Gaskell et al 1999;Gutoff 1993), however, since fluid trapped inside them can degrade and form solid deposits whose later ejection is detrimental to the quality of the finished coating. In some cases it may be possible to redesign the geometry of the coater to reduce the occurrence of such features (Noakes et al 2002), but where this is not possible it is of interest to investigate possibilities for inducing fluid exchange between the recirculation region and the surrounding flow.…”

Section: Introductionmentioning

confidence: 99%

Stirring and transport enhancement in a continuously modulated free-surface flow

et al. 2006

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The transport of fluid from a recirculation region adjacent to a free surface is studied using a numerical method validated with experimental flow visualization. The flow is an example of a liquid film coating process, and consists of two counter-rotating rolls placed side-by-side and half-submerged in a bath of fluid. In the gap between the rolls a recirculation zone exists just below the free surface, around which the flow splits into two films. Fluid recirculating for long periods has been identified as a source of coating defects, so this paper considers a possible method of inducing stirring. The flow is modulated by driving one of the rolls through a Hooke's joint, which delivers a well-characterized periodic perturbation to the roll speed. In response to this speed modulation, the free surface undergoes a periodic change in position and shape which drives an exchange of fluid between the recirculation region and the surrounding flow. The amplitude of the free-surface motion is strongly dependent on modulation frequency.The dynamics of the free surface preclude a quasi-steady approach, even in the small-frequency limit, and so a fully time-dependent analysis based on the finite element method is employed. Trigonometric temporal interpolation of the finite element data is used to make passive tracer advection calculations more efficient, and excellent agreement is seen between simulation and experiment. Computations of the stable and unstable invariant manifolds associated with periodic points on the free surface reveal that the exchange of fluid is governed by a self-intersecting turnstile mechanism, by which most fluid entrained during a modulation cycle is ejected later in the same cycle.Transport over several cycles is explored by observation of the evacuation of passive tracers initially distributed uniformly in the recirculation zone. Results demonstrate the persistence of unmixed cores whose size is dependent on the modulation frequency. By considering the percentage of tracers remaining after a fixed number of cycles, contours in frequency-amplitude space show that for each modulation amplitude there is a frequency which produces the most effective transport, with up to 80 % of tracers removed by a modulation which produces only a 5 % change in film thickness. Finally it is shown how modulation of both rolls at slightly different phases can reduce the film thickness variation to about 1 % while maintaining the level of transport.

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Steady recirculating flow near static contact lines

Cited by 5 publications

References 0 publications

Thin film flow on surfaces containing arbitrary occlusions

Thin film flow on surfaces containing arbitrary occlusions

Drying air-induced disturbances in multi-layer coating systems

Stirring and transport enhancement in a continuously modulated free-surface flow

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