Impact dynamics of a heterogeneous droplet striking cylindrical surfaces

Abstract

Heterogeneous (or compound) fluids consist of multiple immiscible components and are commonly encountered in industrial applications. Due to the diversity of their constituents and the complex structure of their interfaces, their fluid dynamics behavior differs significantly from that of typical homogeneous fluids. This paper systematically investigates the impact dynamics of heterogeneous droplets (HTDs) on cylindrical surfaces with different surface temperatures, providing a deep understanding of how temperature and cylindrical scale influence the impact dynamics of HTD. Firstly, microinjectors were employed to produce HTDs, comprising an inner core of deionized water (ICDW) and an outer shell of silicone oil (OSSO), which were then allowed to free-fall onto cylindrical surfaces maintained at various temperatures. The impact dynamics of HTDs striking cylindrical surfaces were quantitatively compared to those of HTDs impacting a horizontal metallic flat plate where Weber number was observed to produce differing effects on the inner and outer spreading diameters across the two surface geometries. Furthermore, temperature affects the degree of retraction of ICDW where cryogenic cylinders inhibit the suspension of ICDW and alter the bounce-separation behavior, regardless of the eccentricity. Utilizing a pressure transducer to measure the freezing strength of ICDW, it was found that its freezing behavior differs significantly from that of homogeneous water, providing important guidance for engineering design. Finally, an analytical expression for the maximum spreading diameter of ICDW as a function of temperature was derived by simultaneously applying the first law of thermodynamics and Fourier’s law.