Generalized analysis of the deposition/splashing limit for one- and two-component droplet impacts upon thin films

Abstract

Single drop impacts on thin liquid layers are of particular interest because of the ejection of secondary droplets, the so-called splashing. Only a few studies handle the deposition/splashing limit for two-component interaction, where the liquid properties of the impacting drop and wall film differ significantly. This study aims at identifying a unified approach for one-and two-component interactions to determine the deposition/splashing limit. Therefore, a large database of both interactions is considered, which includes data from literature for one-component interactions plus the following binary combinations: hyspin-hexadecane, diesel-hexadecane and diesel-motor oil. Furthermore, a systematic study of two-component interactions with several silicon oils and hexadecane is performed. To map the outcomes, the Ohnesorge number Oh and the Reynolds number Re calculated with arithmetically averaged fluid properties between droplet and wall film fluid are chosen. The dimensionsless film thickness δ is added to form a 3D plot, where one-and two-component experiments are combined. Existing correlations from the literature are revised regarding both interactions and their consistency is checked. The investigated range of high viscosity fluids allow us to propose an improvement of the correlation for high Oh. Our results show that the arithmetically averaged fluid properties lead to a good repartition of both one-and twocomponents interactions toward the deposition/splashing limit. They also corroborate the previous findings that an increase of δ inhibits splashing but its influence is decreasing with increasing Oh. Keywords droplet impact, thin film, two-components interaction, splashing treshold. IntroductionSingle drop impact on a thin liquid layer (i.e. wall film) covers a wide range of industrial applications like coating, printing, cooling or combustion. They are of particular interest since they lead to the ejection of secondary droplets, the so-called splashing.The investigations concerning the droplet impact on wetted walls show that for a given Reynolds number (Re), Ohnesorge number (Oh) and dimensionsless wall film thickness (δ, film thickness h over droplet diameter D), the outcome of one-component droplet impact can be determined. Roughness of the wall can be neglected in the case of 0.1 ≤ δ ≤ 1 [9], when it is completely embedded in the liquid wall film. However, drop-film interactions are affected by the use of different fluids for the droplet and the liquid film. Very little is known for this two-component interaction: the available database is still sparse and therefore the validity of proposed correlations for the deposition/splashing limit cannot be yet generalized to any type of fluid combinations. In this study, we consider a droplet impact of Newtonian fluids onto a wetted, cold, horizontal, solid surface. In the following, the denomination fluid1/fluid2 means that a fluid1 droplet impacts onto a fluid2 wall film and fluid1-fluid2 that both permutations were performed. This study focuses on ...

Miscibility and wettability: how interfacial tension influences droplet impact onto thin wall films

“…the review article of Liang & Mudawar (2016)), studies on binary droplet/wall-film systems are rarely found in the literature. Originally studied in the pioneering work of Worthington & Cole (1897) with water and milk, most of the studies on binary systems are with miscible liquid pairs (Thoroddsen, Etoh & Takehara 2006;Geppert et al 2016;Bernard et al 2017;Geppert et al 2017;Kittel, Roisman & Tropea 2018b;Geppert 2019) and focus on splashing limit, crown dynamics or on the viscosities. In contrast, binary systems with exclusively immiscible droplet/wall-film systems have been investigated mainly with respect to the characteristics of the secondary droplets (Shaikh et al 2018) and to the repartition of the droplet and wall-film liquids in the crown depending on the viscosity ratio (Kittel, Roisman & Tropea 2018a).…”

Crown evolution kinematics of a camellia oil droplet impacting on a liquid layer

“…In addition to experimental investigations, researchers developed theoretical models to predict the crown evolution, looking for an accurate length scale of crown expansion and its dependence on the impact parameters (i.e., We, Fr, and/or δ * ). Bernard et al [28] concentrated on the crown radius and found an accurate length scale for the crown rim expansion. Yarin and Weiss [29] investigated crown morphology for different operating parameters, and obtained an empirical correlation of the crown radius…”

Experimental Investigation of Impinged Droplet Dynamics

“…Similarly, we have discussed another splashing criteria based on Ohnesorge number (Oh) and Reynolds number (Re) in Introduction section, which was presented by Ma et al [23] by summarizing a larger number of researchers' experimental data at various test conditions shown in Figure 11 (right). The black dash line stands for the splashing correlation of OhRe = 17 from Ma et al [23], the rest of four dash lines exhibit the correlations of OhRe 1.25 = 124.3, OhRe 1.25 = 126.7, OhRe 1.17 = 63, and OhRe 1.29 = 197.9 from Geppert et al [49], Cossali et al [50],Vander Wal et al [51], and Bernard et al [52], respectively. Most of blue points from our experiment are below these critical lines while most of red data points are above it.…”