The Impact of Single- and Multicomponent Liquid Drops on a Heated Wall: Child Droplets

Abstract

This paper presents the experimental research into the impingement of single-and multicomponent liquid drops on a solid wall. We focus on studying the conditions and characteristics of two impact scenarios: rebound and breakup. We performed a comprehensive analysis of the effect of a group of factors on the drop transformation and fragmentation characteristics. These factors include the drop velocity and size, Weber number, impinging angle, wall temperature, thermophysical properties of the wall material, surface roughness, hydrophilic and hydrophobic behavior of the surface, homogeneity and inhomogeneity of the drop composition, as well as viscosity and surface tension of the liquid. We compared the outcomes of one, two, and three drops with the same total volume on a wall. Histograms were plotted of the number and size distribution of the emerging secondary droplets. The results include the critical conditions for the intense breakup of drops. Such factors as wall heating, its roughness, impinging angle, drop size and velocity affected the breakup conditions most notably. The variation of a group of these factors could provide a 2-25-fold increase in the liquid surface area as a result of the impact. up after impinging on the surface. If We < 30, drop rebound took place. At 50 < We < 80, the drop spread over the surface and the resulting lamella disintegrated to form secondary droplets. Moreover, Liang and Mudawar [1] demonstrated the snapshots illustrating details of the drop spreading over a heated surface.The contact time of a drop with a surface also depends on its hydrophobicity. For example, Tang et al. [5] studied the behavior of a water drop when interacting with superhydrophobic surfaces in the presence of a cold airflow. Experimental studies were carried out at an ambient temperature ranging from −10 • C to 30 • C to investigate the effect of the airflow on a water drop. In the case of superhydrophobic surfaces, a decrease in the contact time of a drop with a surface was observed.Liang and Mudawar [2] and Šikalo et al.[3] studied heat transfer mechanisms when a drop impinged on a heated surface. An increase in the impact velocity accelerated the spreading velocity during film boiling. In turn, this led to a decrease in the size of secondary droplets. However, the elevated viscosity contributed to an increase in the size of secondary droplets, while a reduction in the surface roughness decreased their size by more than 15%. Moreover, the factor of changing an impingement angle was examined. In particular, the size of child droplets did not depend much on the impingement angle, when it was ϕ > 45 • . However, at ϕ < 15 • , secondary droplets became much smaller.An experimental study by Clavijo et al. [6] considered the effect of the surface inclination angle on the propagation dynamics of a drop over the surface after an impact. After the drop spreads and reaches its maximum diameter, reverse processes occur, i.e., a drop is formed from the film. For example, a surface slope angle of 67.4 • provides ma...

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