Immersion Depth and Cavity Span During Droplet Impact Onto a Liquid Pool

Abstract

Abstract. Droplet impact dynamics are vital in various industries, including spray cooling, oil spill cleanup, and industrial heat recovery systems. Understanding the droplet dynamics is crucial for optimizing applications ranging from material processing to efficient thermal management systems. This study examines droplet impact dynamics near the surface of a water pool, including the cavity formation and jet dynamics for various immiscible liquid droplets (water, silicone oils, and rapeseed oil). Experiments were conducted over a range of Froude numbers (Fr from 24 to 700) and Weber numbers (We from 61 to 2400). The droplets, with diameters ranging from 3 to 5 mm and impact velocities from 1 to 4.2 m/s, were examined using high-speed imaging. The cavity depth and jet height both increased with the Froude number (Fr). At higher Froude numbers of Fr = 390, water showed the longest jet initiation time and the smallest jet height, while silicone oil 5 cSt showed the highest jet with the shortest jet initiation time. At moderate Froude numbers of Fr = 260, silicone oil 5 cSt kept the highest jet height. In contrast, at lower Froude numbers of Fr = 160, water exhibited the highest jet, and the rapeseed oil jet displayed the shortest jet initiation time. An energy analysis demonstrated that around 80% of the impact energy was utilized in cavity formation, while 40% of the cavity energy was used in the formation of jet. New empirical correlations for cavity depth and horizontal span of the impact droplets are derived as a function of the Froude number, Weber number, and viscosity ratio between the droplet and the pool liquid. This study emphasizes the effect of fluid properties and impact regimes on the droplet dynamics, providing useful insight for applications in heat transfer, mixing, and immiscible fluid dynamics.