Liquid film dynamics with immobile contact line during meniscus oscillation

Zhang, Xiaolong; Nikolayev, Vadim

doi:10.1017/jfm.2021.540

Cited by 16 publications

(23 citation statements)

References 32 publications

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“…In all these applications, the phase change occurs simultaneously with dewetting; the liquid film is surrounded by the pure vapour of the same fluid. In this work, we continue the line of thought put forward in our previous paper (Zhang & Nikolayev 2021), where the lubrication approximation was used to describe the thin film flow. The objectives of this work are threefold.…”

Section: Introductionmentioning

confidence: 68%

“…In the frame of reference of the CL that recedes with the speed U cl , the governing equation reads (Zhang & Nikolayev 2021)…”

Section: Conventional Lubrication Equationsmentioning

confidence: 99%

“…is more convenient (Zhang & Nikolayev 2021) to provide a better numerical stability. Another equation is needed to determine the CL speed (which is a part of the problem); (2.49) can be used for this purpose.…”

Section: Boundary Conditions and Contact Line Receding Speedmentioning

confidence: 99%

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Dewetting acceleration by evaporation

Zhang

Nikolayev

2022

J. Fluid Mech.

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Dewetting of a substrate, i.e. the liquid film retraction under partial wetting conditions, has been studied extensively over the past decades. This theoretical work deals with the dewetting phenomenon in the presence of liquid evaporation into the pure vapour atmosphere driven by substrate superheating with respect to the saturation temperature corresponding to the vapour pressure. The dynamic profile of the vapour–liquid interface is analysed numerically by using the generalised lubrication approximation that can be applied to an interface slope larger than its conventional counterpart. This approximation uses a phenomenological argument to increase the precision of calculations. For small slopes, it reduces to the conventional lubrication approach. Several nanoscale effects are included in the theory to obtain more precise results: the Kelvin effect, the hydrodynamic slip, the Marangoni effect, the vapour recoil and the interfacial thermal resistance. Their relative importance is discussed. The results include the film shape evolution, the apparent contact angle and the contact line speed, all defined by the substrate superheating and its wetting properties. These dependencies agree with existing experimental results. It is found that the dewetting is accelerated by evaporation. The numerical results are compared to those of the multiscale theory that uses two main parameters, the Voinov angle (the apparent angle obtained within the microregion problem) and the Voinov length. The latter is studied for several fluids as a function of superheating, and an approximate expression for it is proposed. A good agreement between the numerics and the multiscale theory shows the validity of the latter. This means that the dewetting speed in the presence of evaporation can be calculated with an analytical expression that requires only the Voinov angle as a numerical input. Such results are important for many applications, for instance, bubble growth in boiling or film dynamics in heat pipes.

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Section: Introductionmentioning

confidence: 68%

“…In the frame of reference of the CL that recedes with the speed U cl , the governing equation reads (Zhang & Nikolayev 2021)…”

Section: Conventional Lubrication Equationsmentioning

confidence: 99%

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Dewetting acceleration by evaporation

Zhang

Nikolayev

2022

J. Fluid Mech.

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“…1, the moving meshed box which has the priority for computations to be done on, slides over a background mesh and follows the meniscus to enhance the accuracy near the high gradient of volume fraction regions. In this regard, the gradient of volume fraction far enough from the meniscus is normal to the wall [8] so that there is no need to have high resolution mesh parallel to the wall. The data transfer between the component and the background meshes is performed through the overset interfaces where both fine and coarse meshes of the component and background meshes exist at the same time.…”

Section: Domain Discretization and Boundary Conditionsmentioning

confidence: 99%

“…This liquid film plays a major role in the operation of those devices as it provides the available liquid 211-2 with low thermal resistance for evaporation [4]- [7]. With the assumption of a flat surface over the liquid film on the wall, the lubrication approximation of the hydrodynamics equation yields acceptable results in terms of film thickness [8]. However, this assumption fails to be valid for the meniscus and the de-wetting ridge due to curvature of the film, and its validity is also questionable for the evaporating liquid film.…”

Section: Introductionmentioning

confidence: 99%

CFD Modelling Of Film Deposition from a Receding Meniscus in a Capillary Tube Using the Approach of Overset Grid Technique

Nikkhah¹,

Karami²,

Tessier-Poirier³

et al. 2022

International Conference on Fluid Flow, Heat and Mass Transfer

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Meniscus motion in a capillary tube is a very common type of flow in thermal management devices such oscillating and pulsating heat pipes. It is well known, that the thin film deposited on the wall, which is due to liquid shear force, plays a major role in heat and mass transfer of those devices. This study focuses on the hydrodynamics of this flow using a CFD axisymmetric model of a 1mm diameter capillary, with the approach of volume of fluid (VoF). The CFD-VOF approach is tuned to capture the liquid film deposition from a receding meniscus at different constant velocities. Due to high required grid resolution, the moving overset mesh technique is used. In doing so, a fine meshed domain consists of meniscus slides over the background domain with a coarse mesh. By using this technique, the number of cells and computational time reduced considerably in comparison with regular meshing approach. With water as a working fluid, the numerical results for the liquid film thickness, at different velocities, compare well with experimental data from the literature. The simulations also show that at higher capillary number, the axial location where the film thickness becomes constant moves away from the meniscus nose. The shear stress distribution indicates higher values near the meniscus compared to uniform film and liquid plug zones which is due to the interface curvature in this zone. Also, a recirculating flow was observed within the liquid film left behind the receding meniscus which could have favourable effects in terms of heat and mass transfer. The present work on hydrodynamics is the first step toward complete modelling of an oscillating meniscus with mass and heat transfer inside the capillaries.

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Physical principles and state-of-the-art of modeling of the pulsating heat pipe: A review

Nikolayev

2021

Applied Thermal Engineering

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The Pulsating (called also oscillating) Heat Pipe (PHP) is a high performance passive heat transfer device. It consists in a closed capillary channel folded into several meanders, evacuated, and partially filled with a liquid and its vapor. One side is in thermal contact with a hot spot, the other with a cold spot. The oscillation of the liquid plugs and vapor bubbles spontaneously occurs after the heating beginning. The heat exchange takes place not only by latent heat transfer, but also by liquid convection. Both this advantage and the PHP structural simplicity make it competitive with respect to other kinds of heat pipes. However, the PHP operation is non-stationary and depends on many physical and material parameters. As a result, application of empirical correlations is quite unsuccessful. More sophisticated direct modeling is thus required. In this review, we present the past, present, and future perspectives of the theoretical PHP studies. The physical phenomena on the level of a single bubble and single liquid plug is addressed first. In this context, the modeling of the simplest, single branch PHP is described as a necessary first step toward the PHP understanding and model validation. The modeling of interaction between the bubbles and plugs (bubble generation and disappearance, plug evaporation) is discussed next. Finally, the state of the art of the physical modeling and simulation of the multi-turn PHP is reviewed and the difference between existing approaches is explained.

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Liquid film dynamics with immobile contact line during meniscus oscillation

Abstract: Abstract

Cited by 16 publications

References 32 publications

Dewetting acceleration by evaporation

Dewetting acceleration by evaporation

CFD Modelling Of Film Deposition from a Receding Meniscus in a Capillary Tube Using the Approach of Overset Grid Technique

Physical principles and state-of-the-art of modeling of the pulsating heat pipe: A review

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