A plan of measurement of interfacial tension between Cu-rich and Fe-rich immiscible liquid phases in undercooled molten Cu–Fe alloy, using an oscillating droplet method using electromagnetic levitation, is in progress at the International Space Station. In this work, numerical simulations of an oscillating composite droplet composed of core and shell phases were performed using OpenFOAM. To determine the proper composition of the CuFe alloy to measure interfacial tension, oscillations at two specific frequencies caused by the surface and interfacial tensions appearing on the surface of the droplets have been investigated in this study. Numerical results indicate that the narrow compositional variation can be permitted as a suitable condition for determining the interfacial tension. The suitable composition of Cu for measurement of interfacial tension is 21–27at% or 67–76 at % at 1550 K – 1650 K. Especially in the case of Cu25Fe75 alloy, interfacial tension can be measured at only approximately 1600 K.
Numerical simulation of droplet migration phenomena on a temperature gradient wall was performed to realize efficient droplet behavior control by applying a temperature gradient in a microfluidic device. In order to accurately simulate such phenomena numerically, a numerical method that can capture the behavior of droplets with high accuracy without artificial treatment near the gas-liquid interface is required. To satisfy these requirements, the Conservative Phase Field method was employed to capture the gas-liquid interface. In order to capture the interfacial behavior with high accuracy, the level-set method was coupled to calculate the interfacial curvature and surface tension using a signed distance function. To simulate wettability on solid walls, wettability boundary conditions were applied to the distance function. Validation results show that the numerical method used in this study can accurately estimate the effect of surface tension on the flow field for non-isothermal gas-liquid two-phase flow problems with a small number of spatial grids and can accurately represent wettability over a very wide range of set contact angles. Finally, in the analysis of droplet migration phenomena on a temperature gradient wall conducted using this method, the results of the present study showed good agreement with the theoretical solution, confirming the improvement in accuracy from the results of previous studies.