TinyLev acoustically levitated water: Direct observation of collective, inter-droplet effects through morphological and thermal analysis of multiple droplets

McElligott, Adam; Guerra, André; Wood, Michael J.; Rey, Alejandro D.; Kietzig, Anne‐Marie; Servio, Phillip

doi:10.1016/j.jcis.2022.03.082

Cited by 6 publications

(53 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This characteristic shape is caused by several forces present in the field. These primarily include gravity (downward), a counteracting acoustic pressure from the lower TinyLev array to maintain droplet stability and acoustic pressure from the upper array that is used to prevent the droplets from leaving the acoustic region. ,, The combination of these forces creates acoustic streamlines at the boundary layer just before the droplet surface (the air–liquid interface) which determines the droplet boundary by creating vortices on its upper and lower halves. , The droplet’s shape is caused by the balance of these outer normal forces and the surface tension and hydrostatic forces within the droplet . Acoustic streaming likely caused the solution to flow steadily at the surface, resulting in a small amount of evaporation and convective cooling .…”

Section: Resultsmentioning

confidence: 99%

“…Therefore, it provides a stronger force on the closest droplet (position 3), which may allow it to have a higher volume without experiencing fragmentation. In turn, the larger surface area of the droplet would allow for greater acoustic streaming and so more evaporation at the surface . This could lead to a further reduced initial temperature.…”

Section: Resultsmentioning

confidence: 99%

“…Furthermore, protrusions were not factored into the frozen volume; only the spherical “core” of the droplet was taken. This was because previous water studies also only looked at the “core” expansion for comparison, which is essentially an examination of the elongation of the hydrate–air interface, and it could not be determined if the protrusions consisted only of hydrate . The volumetric expansion increase is likely the result of nonideal environmental factors present in open levitated systems (i.e., droplet purity and acoustic pressure-induced oscillation).…”

Section: Resultsmentioning

confidence: 99%

“…A total of 15 replicates were performed for each nodal position and configuration. Note that melting was only examined for position 2 droplets, as previous studies have suggested that the position and configuration in an acoustic field do not affect melting dynamics . Therefore, 105 replicates were performed and analyzed for this study, of which 15 included melting.…”

Section: Methodsmentioning

confidence: 99%

“…By using a custom cryogun rather than a cooling chamber for freezing, the configuration of the levitator can remain open with no obstructing interface and allow for direct and clear image capture from digital or infrared (IR) cameras. Moreover, the droplet size and location (called nodes) can be controlled . Therefore, this system is ideal for further investigation into levitated nucleation and crystallization in hydrate systems free of solid interfaces.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Interfacial Effects during Phase Change in Multiple Levitated Tetrahydrofuran Hydrate Droplets

et al. 2023

Self Cite

View full text Add to dashboard Cite

Recent strategies developed to examine the nucleation of crystal structures like tetrahydrofuran (THF) hydrates without the effects of a solid interface have included acoustic levitation, where only a liquid−gas interface initially exists. However, the ability now exists to levitate and freeze multiple droplets simultaneously, which could reveal interdroplet effects and provide further insight into interfacial nucleation phenomena. In this study, using direct digital and infrared imaging techniques, the freezing of up to three simultaneous THF hydrate droplets was investigated for the first time. Nucleation was initiated at the aqueous solution−air interface. Two pseudo-heterogeneous mechanisms created additional nucleation interfaces: one from cavitation effects entraining microbubbles and another from subvisible ice particles, also called hydrate-nucleating particles (HNPs), impacting the droplet surface. For systems containing droplets in both the second and third positions, nucleation was statistically simultaneous between all droplets. This effect may have been caused by the high liquid−solid interfacial pressures that developed at nucleation, causing some cracking in the initial hydrate shell around the droplet and releasing additional HNPs (now of hydrate) into the air. During crystallization, the THF hydrate droplets developed a completely white opacity, termed optical clarity loss (OCL). It was suggested that high hydrate growth rates within the droplet resulted in the capture of tiny air bubbles within the solid phase. In turn, light refraction through many smaller bubbles resulted in the OCL. These bubbles created structural inhomogeneities, which may explain how the volumetric expansion of the droplets upon complete solidification was 23.6% compared with 7.4% in pure, stationary THF hydrate systems. Finally, the thermal gradient that developed between the top and bottom of the droplet during melting resulted in a surface tension gradient along the air−liquid interface. In turn, convective cells developed within the droplet, causing it to spin rapidly about the horizontal axis.

show abstract