Impact of droplets on inclined flowing liquid films

Che, Zhizhao; Deygas, Amandine; Matar, Omar

doi:10.1103/physreve.92.023032

Cited by 46 publications

(32 citation statements)

References 63 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This effect of film thickness on the crown direction is also shown clearly in Fig. 12a, and is consistent with previous finding for the impact of droplets on miscible liquid films 23,44 . Figure 12a also shows that the crown propagation speeds for thick films are much slower than that for thin films.…”

Section: Effect Of Film Thicknesssupporting

confidence: 93%

“…This, therefore, demonstrates that the central jet can form on a thin film, without the formation of an impact cavity. There are many scenarios to produce jets due to radially inward flows, such as the formation of a microjet on the surface of a liquid during the impact of a test tube 26 , jet formation accompanying the impact of droplets on superhydrophobic surface 27 and of a large droplet on liquid films due to the formation of a cavity on the upper side of the droplet 23 , the burst of a bubble trapped near a liquid interface 28 , and the collapse of a bubble generated due to cavitation under gravity 29 .…”

Section: Impact Of Water Droplets On Oil Films: Compound Crown and Cementioning

confidence: 99%

“…Since silicone oil can spread easily on water surfaces, the bouncing of droplets is not because the two fluids are immiscible. It has been reported that droplets can bounce even on the same fluid 12,23,40 or on hydrophilic substrates 41,42 . Here, the droplet can bounce because there is a gas layer separating the droplet and the liquid film.…”

Section: Effect Of Weber Numbermentioning

confidence: 99%

See 2 more Smart Citations

Impact of droplets on immiscible liquid films

Che

Matar

2018

Soft Matter

Self Cite

View full text Add to dashboard Cite

The impact of droplets on liquid films is a ubiquitous phenomenon not only in nature but also in many industrial applications. Compared to the widely-studied impact of droplets on films of identical fluids, the impact of droplets on immiscible films has received far less attention. In the present work, we show using high-speed imaging that immiscibility has a profound effect on the impact dynamics. The impact of a water droplet on an oil film leads to the formation of a compound crown followed by a central jet, whereas that of an oil droplet on a water film results in rapid spreading on the film surface driven by a large, positive spreading factor. In the former scenario, the central jet occurs due to the severe stretching of the droplet during the formation of the crown and then the retraction of the droplet by capillarity, which leads to the collision of fluid at the impact point. A model for the elongation dynamics of the central jet is proposed based on energy conservation. The effects of key parameters controlling the impact process are analysed, including the droplet Ohnesorge and Weber numbers, the viscosity ratio, and the dimensionless film thickness. Different impact outcomes are discussed, such as bouncing, deposition, and oscillation of the impact droplet, the formation and collapse of the compound crown, and the formation and tip-pinching of the central jet. This study not only provides physical insights into the impact dynamics, but could also facilitate the control and optimisation of the droplet impact process in a number of applications as highlighted herein.

show abstract

Section: Effect Of Film Thicknesssupporting

confidence: 93%

Section: Impact Of Water Droplets On Oil Films: Compound Crown and Cementioning

confidence: 99%

Section: Effect Of Weber Numbermentioning

confidence: 99%

See 1 more Smart Citation

Impact of droplets on immiscible liquid films

Che

Matar

2018

Soft Matter

Self Cite

View full text Add to dashboard Cite

show abstract

“…U is the wall's velocity. Bush 2012; Harris, Liu & Bush 2015) and vibrating/moving liquid surfaces (Sreenivas, De & Arakeri 1999;Couder et al 2005;Terwagne, Vandewalle & Dorbolo 2007;Gilet et al 2008;Che, Deygas & Matar 2015). The isothermal non-coalescence phenomena can be explained as follows.…”

Section: Introductionmentioning

confidence: 99%

Droplet levitation over a moving wall with a steady air film

et al. 2019

View full text Add to dashboard Cite

In isothermal non-coalescence behaviours of a droplet against a wall, an air film of micrometre thickness plays a crucial role. We experimentally study this phenomenon by letting a droplet levitate over a moving glass wall. The three-dimensional shape of the air film is measured using an interferometric method. The mean curvature distribution of the deformed free surface and the distributions of the lubrication pressure are derived from the experimental measurements. We vary experimental parameters, namely wall velocity, droplet diameter and viscosity of the droplets, over a wide range; for example, the droplet viscosity is varied over two orders of magnitude. For the same wall velocity, the air film of low-viscosity droplets shows little shape oscillation with constant film thickness (defined as the steady state), while that of highly viscous droplets shows a significant shape oscillation with varying film thickness (defined as the unsteady state). The droplet viscosity also affects the surface velocity of a droplet. Under our experimental conditions, where the air film shape can be assumed to be steady, we present experimental evidence showing that the lift force generated inside the air film balances with the droplet’s weight. We also verify that the lubrication pressure locally balances with the surface tension and hydrostatic pressures. This indicates that lubrication pressure and the shape of the free surface are mutually determined. Based on the local pressure balance, we discuss a process of determining the steady shape of an air film that has two areas of minimum thickness in the vicinity of the downstream rim.

show abstract

“…An asymmetrical crown shape was observed due to the effect of the moving film. Che et al [67] demonstrated the on inclined falling flow asymmetrical crown shape is also formed after droplet impact. Gao and Li [42] further analyzed the early evolvement of droplet impact based on experiments and theoretical model (see Figure 6c).…”

Section: Impact On Flowing Filmsmentioning

confidence: 99%

Spray Impingement Cooling: The State of the Art

Gao¹,

Li²

2019

Advanced Cooling Technologies and Applications

View full text Add to dashboard Cite

The cooling of a surface can be achieved by the impingement of spray, which is a free surface flow of droplets ejected from a spray nozzle. Spray cooling can provide uniform cooling and handle high heat fluxes in both single phase and two phases. In this chapter, spray cooling is reviewed from two aspects: the entire spray (spray level) and droplets (droplet level). The discussion on the spray level is focused on the spray cooling performance as a function of fluid properties, flow conditions, surface conditions, and nozzle positioning. The advantages and barriers of using spray cooling for engineering applications are summarized. The discussion on the droplet level is focused on the impact of droplet flow on film flow, which is the key flow mechanism in spray cooling. Droplet flow involves single droplet, droplet train (continuously droplets broke up from jet flow), and droplet burst (droplet groups affecting at a constant frequency), and local cooling enhancement due to droplet flow is discussed in details. Future work and unresolved issues in spray cooling are proposed.

show abstract

Impact of droplets on inclined flowing liquid films

Cited by 46 publications

References 63 publications

Impact of droplets on immiscible liquid films

Impact of droplets on immiscible liquid films

Droplet levitation over a moving wall with a steady air film

Spray Impingement Cooling: The State of the Art

Contact Info

Product

Resources

About