Abstract
The Faraday forcing method in levitated liquid droplets has recently been introduced as a method for measuring surface tension using resonance. By subjecting an electrostatically levitated liquid metal droplet to a continuous, oscillatory, electric field, at a frequency nearing that of the droplet’s first principal mode of oscillation (known as mode 2), the method was previously shown to determine surface tension of materials that would be particularly difficult to process by other means, e.g., liquid metals and alloys. It also offers distinct advantages in future work involving high viscosity samples because of the continuous forcing approach. This work presents (1) a benchmarking experimental method to measure surface tension by excitation of the second principal mode of oscillation (known as mode 3) in a levitated liquid droplet and (2) a more rigorous quantification of droplet excitation using a projection method. Surface tension measurements compare favorably to literature values for Zirconium, Inconel 625, and Rhodium, using both modes 2 and 3. Thus, this new method serves as a credible, self-consistent benchmarking technique for the measurement of surface tension.
Highlights
The accurate measurement of thermophysical properties is imperative for the future of countless areas of manufacturing[1] and extends its importance into space exploration with the recent push for the Artemis program, in-space manufacturing, and in-situ resource utilization[2]
The reliability of processes like crystal growth, additive manufacturing, and welding depend on precise knowledge of thermophysical phenomena[3,4]
An important thermophysical property, can be measured using levitation technologies by exploiting the natural frequency fn at which a spherical liquid droplet comes to rest, given by[12] rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi fn 1⁄4
Summary
The accurate measurement of thermophysical properties is imperative for the future of countless areas of manufacturing[1] and extends its importance into space exploration with the recent push for the Artemis program, in-space manufacturing, and in-situ resource utilization[2]. Thermophysical property measurement of high-temperature materials like liquid metals, glasses, and oxides is difficult using conventional means because of high surface reactivity[5]. The advent of containerless material processing using aerodynamic[6], acoustic[7,8], electromagnetic[9], and electrostatic[10,11] levitation technologies has provided an avenue for further improvements in the accuracy of thermophysical property measurements and can be used to provide insights into other important material behavior like phase equilibria and solidification dynamics[9,10]. An important thermophysical property, can be measured using levitation technologies by exploiting the natural frequency fn at which a spherical liquid droplet comes to rest, given by[12] rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi fn 1⁄4. Electromagnetic levitation experiments take place in vacuum and suffer from the issue of asphericity[14]
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