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Journal articles on the topic 'Levitated droplets'

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Author: Grafiati

Published: 10 December 2022

Last updated: 28 January 2023

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1

Hasegawa, Koji, Ayumu Watanabe, Akiko Kaneko, and Yutaka Abe. "Coalescence Dynamics of Acoustically Levitated Droplets." Micromachines 11, no. 4 (March 26, 2020): 343. http://dx.doi.org/10.3390/mi11040343.

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The contactless coalescence of a droplet is of paramount importance for physical and industrial applications. This paper describes a coalescence method to be used mid-air via acoustic levitation using an ultrasonic phased array system. Acoustic levitation using ultrasonic phased arrays provides promising lab-on-a-drop applications, such as transportation, coalescence, mixing, separation, evaporation, and extraction in a continuous operation. The mechanism of droplet coalescence in mid-air may be better understood by experimentally and numerically exploring the droplet dynamics immediately before the coalescence. In this study, water droplets were experimentally levitated, transported, and coalesced by controlled acoustic fields. We observed that the edges of droplets deformed and attracted each other immediately before the coalescence. Through image processing, the radii of curvature of the droplets were quantified and the pressure difference between the inside and outside a droplet was simulated to obtain the pressure and velocity information on the droplet’s surface. The results revealed that the sound pressure acting on the droplet clearly decreased before the impact of the droplets. This pressure on the droplets was quantitatively analyzed from the experimental data. Our experimental and numerical results provide deeper physical insights into contactless droplet manipulation for futuristic lab-on-a-drop applications.

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2

YARIN, A. L., M. PFAFFENLEHNER, and C. TROPEA. "On the acoustic levitation of droplets." Journal of Fluid Mechanics 356 (February 10, 1998): 65–91. http://dx.doi.org/10.1017/s0022112097007829.

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This paper deals with the theoretical and experimental investigation of acoustically levitated droplets. A method of calculation of the acoustic radiation pressure based on the boundary element method (BEM) is presented. It is applied to predict shapes of droplets levitated in an acoustic field (and as a result, deformed by it). The method was compared with several known exact and approximate analytical results for rigid spheres and shown to be accurate (and a widely used approximate formula for the acoustic levitation force acting on a rigid sphere was found to be inaccurate for sound wavelengths comparable with the sphere radius). The method was also compared with some other theoretical approaches known from the literature.Displacement of the droplet centre relative to the pressure node is accounted for and shown to be significant. The results for droplet shapes and displacements are compared with experimental data, and the agreement is found to be rather good. Furthermore, the experimental investigations reveal a unique relationship between the aspect ratio of an oblate droplet and the sound pressure level in the levitator. This relationship agrees well with the predicted shapes. A practical link between droplet shape or droplet displacement and sound pressure level in a levitator is therefore now available.

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3

Gao, Xiaoyan, Chen Cai, Jiabi Ma, and Yunhong Zhang. "Repartitioning of glycerol between levitated and surrounding deposited glycerol/NaNO 3 /H 2 O droplets." Royal Society Open Science 5, no. 1 (January 2018): 170819. http://dx.doi.org/10.1098/rsos.170819.

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Repartitioning of semi-volatile organic compounds (SVOCs) between particles is an important process to understand the particle growth and shrinkage in the atmosphere environment. Here, by using optical tweezers coupled with cavity-enhanced Raman spectroscopy, we report the repartitioning of glycerol between a levitated glycerol/NaNO 3 /H 2 O droplet and surrounding glycerol/NaNO 3 /H 2 O droplets deposited on the inner wall of a chamber with different organic to inorganic molar ratios (OIRs). For the high OIR with 3 : 1, no NaNO 3 crystallization occurs both for levitated and deposited droplets in the whole relative humidity (RH) range, the radius of the levitated droplet decreases slowly due to the evaporation of glycerol from the levitated droplet at constant RHs. The levitated droplets radii with OIR of 1 : 1 and 1 : 3 increase with constant RHs that are lower than 45.3% and 55.7%, respectively, indicating that the repartitioning of glycerol occurs. The reason is that NaNO 3 in the deposited droplets is crystallized when RH is lower than 45.3% for 1 : 1 or 55.7% for 1 : 3. So the vapour pressure of glycerol at the surface of deposited droplets is higher than that of the levitated droplet which always remains as liquid droplet without NaNO 3 crystallization, resulting in the transfer of glycerol from the deposited ones to the levitated one. The process of the glycerol repartitioning we discussed herein is a useful model to interpret the repartitioning of SVOCs between the externally mixed particles with different phase states.

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4

Hasegawa, Koji, and Manami Murata. "Oscillation Dynamics of Multiple Water Droplets Levitated in an Acoustic Field." Micromachines 13, no. 9 (August 23, 2022): 1373. http://dx.doi.org/10.3390/mi13091373.

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This study aimed to improve and investigate the oscillation dynamics and levitation stability of acoustically levitated water droplets. Contactless sample manipulation technology in mid-air has attracted significant attention in the fields of biochemistry and pharmaceutical science. Although one promising method is acoustic levitation, most studies have focused on a single sample. Therefore, it is important to determine the stability of multiple samples during acoustic levitation. Here, we aim to understand the effect of multiple-sample levitation on levitation stability in acoustic fields. We visualized the oscillatory motion of multiple levitated droplets using a high-speed video camera. To characterize the dynamics of multiple levitating droplets, the oscillation frequency and restoring force coefficients of the levitated samples, which were obtained from the experimental data, were analyzed to quantify the droplet–droplet interaction. The oscillation model of the spring-mass system was compared with the experimental results, and we found that the number of levitating droplets and their position played an important role in the levitation stability of the droplets. Our insights could help us understand the oscillatory behavior of levitated droplets to achieve more stable levitation.

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5

YARIN, A. L., G. BRENN, O. KASTNER, D. RENSINK, and C. TROPEA. "Evaporation of acoustically levitated droplets." Journal of Fluid Mechanics 399 (November 25, 1999): 151–204. http://dx.doi.org/10.1017/s0022112099006266.

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The rate of heat and mass transfer at the surface of acoustically levitated pure liquid droplets is predicted theoretically for the case where an acoustic boundary layer appears near the droplet surface resulting in an acoustic streaming. The theory is based on the computation of the acoustic field and squeezed droplet shape by means of the boundary element method developed in Yarin, Pfaffenlehner & Tropea (1998). Given the acoustic field around the levitated droplet, the acoustic streaming near the droplet surface was calculated. This allowed calculation of the Sherwood and Nusselt number distributions over the droplet surface, as well as their average values. Then, the mass balance was used to calculate the evolution of the equivalent droplet radius in time. The theory is applicable to droplets of arbitrary size relative to the sound wavelength λ, including those of the order of λ, when the compressible character of the gas flow is important. Also, the deformation of the droplets by the acoustic field is accounted for, as well as a displacement of the droplet centre from the pressure node. The effect of the internal circulation of liquid in the droplet sustained by the acoustic streaming in the gas is estimated. The distribution of the time-average heat and mass transfer rate over the droplet surface is found to have a maximum at the droplet equator and minima at its poles. The time and surface average of the Sherwood number was shown to be described by the expression Sh = KB/√ω[Dscr ]0, where B = A0e/(ρ0c0) is a scale of the velocity in the sound wave (A0e is the amplitude of the incident sound wave, ρ0 is the unperturbed air density, c0 is the sound velocity in air, ω is the angular frequency in the ultrasonic range, [Dscr ]0 is the mass diffusion coefficient of liquid vapour in air, which should be replaced by the thermal diffusivity of air in the computation of the Nusselt number). The coefficient K depends on the governing parameters (the acoustic field, the liquid properties), as well as on the current equivalent droplet radius a.For small spherical droplets with a[Lt ]λ, K = (45/4π)1/2 = 1.89, if A0e is found from the sound pressure level (SPL) defined using A0e. On the other hand, if A0e is found from the same value of the SPL, but defined using the root-mean-square pressure amplitude (prms = A0e/√2), then Sh = KrmsBrms/ √ω[Dscr ]0, with Brms = √2B and Krms = K/√2 = 1.336. For large droplets squeezed significantly by the acoustic field, K appears always to be greater than 1.89. The evolution of an evaporating droplet in time is predicted and compared with the present experiments and existing data from the literature. The agreement is found to be rather good.We also study and discuss the effect of an additional blowing (a gas jet impinging on a droplet) on the evaporation rate, as well as the enrichment of gas at the outer boundary of the acoustic bondary layer by liquid vapour. We show that, even at relatively high rates of blowing, the droplet evaporation is still governed by the acoustic streaming in the relatively strong acoustic fields we use. This makes it impossible to study forced convective heat and mass transfer under the present conditions using droplets levitated in strong acoustic fields.

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6

Leiterer, Jork, Wolfram Leitenberger, Franziska Emmerling, Andreas F. Thünemann, and Ulrich Panne. "The use of an acoustic levitator to follow crystallization in small droplets by energy-dispersive X-ray diffraction." Journal of Applied Crystallography 39, no. 5 (September 12, 2006): 771–73. http://dx.doi.org/10.1107/s0021889806024915.

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For the investigation of small sample volumes, the use of an acoustic levitator was tested as a `sample holder' for hovering droplets in a synchrotron beam. It might be advantageous to use levitated droplets instead of samples confined in solid holders, especially for the study of crystallization processes where the influence of containing walls has to be minimized. In a first experiment, the crystallization of sodium chloride in a small droplet of aqueous solution has been followed with a time resolution of 30 s. The collected diffraction peaks are compared with data in the ICSD database.

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7

Габышев, Д. Н., Д. Н. Медведев, and К. В. Мисиюк. "Динамика капель, подброшенных над испаряющейся поверхностью воды." Журнал технической физики 91, no. 9 (2021): 1331. http://dx.doi.org/10.21883/jtf.2021.09.51211.25-21.

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The data of a ballistic experiment are analyzed, in which an intense capillary wave injects up microdroplets formed and levitated above a heated region of water due to an ascending convective steam-air flow. The drag force resisting the movement of a droplet is estimated. Using various theoretical approaches, the flow parameters (velocity at different heights, the rate of change of velocity) are estimated. The maximum size of droplets that can levitate freely has been determined. The impossibility of the stationary droplet levitation in a linearly inhomogeneous flow is shown.

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8

Leiterer, Jork, Markus Grabolle, Knut Rurack, Ute Resch-Genger, Jan Ziegler, Thomas Nann, and Ulrich Panne. "Acoustically Levitated Droplets." Annals of the New York Academy of Sciences 1130, no. 1 (May 2008): 78–84. http://dx.doi.org/10.1196/annals.1430.039.

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9

Lauber, Annika, Alexei Kiselev, Thomas Pander, Patricia Handmann, and Thomas Leisner. "Secondary Ice Formation during Freezing of Levitated Droplets." Journal of the Atmospheric Sciences 75, no. 8 (July 31, 2018): 2815–26. http://dx.doi.org/10.1175/jas-d-18-0052.1.

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Abstract The formation of secondary ice in clouds, that is, ice particles that are created at temperatures above the limit for homogeneous freezing without the direct involvement of a heterogeneous ice nucleus, is one of the longest-standing puzzles in cloud physics. Here, we present comprehensive laboratory investigations on the formation of small ice particles upon the freezing of drizzle-sized cloud droplets levitated in an electrodynamic balance. Four different categories of secondary ice formation (bubble bursting, jetting, cracking, and breakup) could be detected, and their respective frequencies of occurrence as a function of temperature and droplet size are given. We find that bubble bursting occurs more often than droplet splitting. While we do not observe the shattering of droplets into many large fragments, we find that the average number of small secondary ice particles released during freezing is strongly dependent on droplet size and may well exceed unity for droplets larger than 300 μm in diameter. This leaves droplet fragmentation as an important secondary ice process effective at temperatures around −10°C in clouds where large drizzle droplets are present.

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10

Chen, Hongyue, Yongjian Zhang, Heyi Wang, Xin Dong, and Duyang Zang. "Evaporation Caused Invaginations of Acoustically Levitated Colloidal Droplets." Nanomaterials 13, no. 1 (December 27, 2022): 133. http://dx.doi.org/10.3390/nano13010133.

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Controlled buckling of colloidal droplets via acoustic levitation plays an important role in pharmaceutical, coating, and material self-assembly. In this study, the evaporation process of PTFE colloidal droplets with two particle concentrations (60 wt% and 20 wt%) was investigated under acoustic levitation. We report the occurrence of surface invagination caused by evaporation. For the high particle concentration droplet, the upper surface was invaginated, eventually forming a bowl-shaped structure. While for the low particle concentration droplet, both the upper and lower surfaces of the droplet were invaginated, resulting in a doughnut-like structure. For the acoustically levitated oblate spherical droplet, the dispersant loss at the equatorial area of the droplet is greater than that at the two poles. Therefore, the thickness of the solid shell on the surface of the droplet was not uniform, resulting in invagination at the weaker pole area. Moreover, once the droplet surface was buckling, the hollow cavity on the droplet surface would absorb the sound energy and results in strong positive acoustic radiation pressure at bottom of the invagination, thus further prompting the invagination process.

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11

Tong, H. J., B. Ouyang, F. D. Pope, and M. Kalberer. "A new electrodynamic balance design for low temperature studies." Atmospheric Measurement Techniques Discussions 7, no. 7 (July 28, 2014): 7671–700. http://dx.doi.org/10.5194/amtd-7-7671-2014.

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Abstract. In this paper we describe a newly designed cold electrodynamic balance (CEDB) system, which was built to study the evaporation kinetics and freezing properties of supercooled water droplets. The temperature of the CEDB chamber at the location of the levitated water droplet can be controlled in the range: −40 to +40 °C, which is achieved using a combination of liquid nitrogen cooling and heating by positive temperature coefficient heaters. The measurement of liquid droplet radius is obtained by analyzing the Mie elastic light scattering from a 532 nm laser. The Mie scattering signal was also used to characterize and distinguish droplet freezing events; liquid droplets produce a regular fringe pattern whilst the pattern from frozen particles is irregular. The evaporation rate of singly levitated water droplets was calculated from time resolved measurements of the radii of evaporating droplets and a clear trend of the evaporation rate on temperature was measured. The statistical freezing probabilities of aqueous pollen extracts (pollen washing water) are obtained in the temperature range: −4.5 to −40 °C. It was found that that pollen washing water from water birch (Betula fontinalis occidentalis) pollen can act as ice nuclei in the immersion freezing mode at temperatures as warm as −22.45 (±0.65) °C.

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12

Tong, H. J., B. Ouyang, N. Nikolovski, D. M. Lienhard, F. D. Pope, and M. Kalberer. "A new electrodynamic balance (EDB) design for low-temperature studies: application to immersion freezing of pollen extract bioaerosols." Atmospheric Measurement Techniques 8, no. 3 (March 10, 2015): 1183–95. http://dx.doi.org/10.5194/amt-8-1183-2015.

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Abstract. In this paper we describe a newly designed cold electrodynamic balance(CEDB) system, built to study the evaporation kinetics and freezing properties of supercooled water droplets. The temperature of the CEDB chamber at the location of the levitated water droplet can be controlled in the range −40 to &plus;40 °C, which is achieved using a combination of liquid nitrogen cooling and heating by positive temperature coefficient heaters. The measurement of liquid droplet radius is obtained by analysing the Mie elastic light scattering from a 532 nm laser. The Mie scattering signal was also used to characterise and distinguish droplet freezing events; liquid droplets produce a regular fringe pattern, whilst the pattern from frozen particles is irregular. The evaporation rate of singly levitated water droplets was calculated from time-resolved measurements of the radii of evaporating droplets and a clear trend of the evaporation rate on temperature was measured. The statistical freezing probabilities of aqueous pollen extracts (pollen washing water) are obtained in the temperature range −4.5 to −40 °C. It was found that that pollen washing water from water birch (Betula fontinalis occidentalis) pollen can act as ice nuclei in the immersion freezing mode at temperatures as warm as −22.45 (±0.65) °C. Furthermore it was found that the protein-rich component of the washing water was significantly more ice-active than the non-proteinaceous component.

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13

Beaugnon, E., D. Fabregue, D. Billy, J. Nappa, and R. Tournier. "Dynamics of magnetically levitated droplets." Physica B: Condensed Matter 294-295 (January 2001): 715–20. http://dx.doi.org/10.1016/s0921-4526(00)00750-x.

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14

Ishikawa, Haruki, and Katsuhiro Nishinari. "Modelling levitated 2-lobed droplets in rotation using Cassinian oval curves." Journal of Fluid Mechanics 846 (May 15, 2018): 1088–113. http://dx.doi.org/10.1017/jfm.2018.262.

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A simple model of rotating 2-lobed droplets is proposed by setting the outline shape of the droplet to the Cassinian oval, a mathematical curve that closely resembles in shape. By deriving the governing equation of the proposed model and obtaining its stationary solutions, the relationship between the angular velocity of rotation and the maximum deformation length is explicitly and precisely calculated. The linear stability analysis is performed for the stationary solutions, and it is demonstrated that the stability of the solutions depends only on the ratio of the deformation length to the radius of the central cross-section of the droplet, which is independent of the physical properties of the droplet. Via comparison with an experimental study, it is observed that the calculated result is consistent with the deformation behaviour of actual 2-lobed droplets in the range where the stationary solution of the proposed model is linearly stable. Therefore, the proposed model is a suitable model for reproducing the steady deformation behaviour of 2-lobed droplets in a wide range of viscosities, surface tensions, densities and initial radii of the droplet, and especially if the viscosity of the droplet is low, the entire process of deformation of the 2-lobed droplet, including the unsteady breakup process, can be very well reproduced by the proposed model.

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15

Hunter-Brown, George, Naresh Sampara, Matthew M. Scase, and Richard J. A. Hill. "Sonomaglev: Combining acoustic and diamagnetic levitation." Applied Physics Letters 122, no. 1 (January 2, 2023): 014103. http://dx.doi.org/10.1063/5.0134297.

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Acoustic levitation and diamagnetic levitation are experimental methods that enable the contact-free study of both liquid droplets and solid particles. Here, we combine both the techniques into a single system that takes advantage of the strengths of each, allowing for the manipulation of levitated spherical water droplets (30 nl–14 μl) under conditions akin to weightlessness, in the laboratory, using a superconducting magnet fitted with two low-power ultrasonic transducers. We show that multiple droplets, arranged horizontally along a line, can be stably levitated with this system and demonstrate controlled contactless coalescence of two droplets. Numerical simulation of the magnetogravitational and acoustic potential reproduces the multiple stable equilibrium points observed in our experiments.

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16

Cao, Hui-Ling, Da-Chuan Yin, Yun-Zhu Guo, Xiao-Liang Ma, Jin He, Wei-Hong Guo, Xu-Zhuo Xie, and Bo-Ru Zhou. "Rapid crystallization from acoustically levitated droplets." Journal of the Acoustical Society of America 131, no. 4 (April 2012): 3164–72. http://dx.doi.org/10.1121/1.3688494.

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17

Cannuli, Antonio, Maria Teresa Caccamo, Giuseppe Castorina, Franco Colombo, and Salvatore Magazù. "Laser Techniques on Acoustically Levitated Droplets." EPJ Web of Conferences 167 (2018): 05010. http://dx.doi.org/10.1051/epjconf/201816705010.

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This work reports the results of an experimental study where laser techniques are applied to acoustically levitated droplets of trehalose aqueous solutions in order to perform spectroscopic analyses as a function of concentration and to test the theoretical diameter law. The study of such systems is important in order to better understand the behaviour of trehalose-synthesizing extremophiles that live in extreme environments. In particular, it will be shown how acoustic levitation, combined with optical spectroscopic instruments allows to explore a wide concentration range and to test the validity of the diameter law as a function of levitation lag time, i.e. the D2 vs t law. On this purpose a direct diameter monitoring by a video camera and a laser pointer was first performed; then the diameter was also evaluated by an indirect measure through an OH/CH band area ratio analysis of collected Raman and Infrared spectra. It clearly emerges that D2 vs t follows a linear trend for about 20 minutes, reaching then a plateau at longer time. This result shows how trehalose is able to avoid total water evaporation, this property being essential for the surviving of organisms under extreme environmental conditions.

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18

Knezic, Dragutin, Julien Zaccaro, and Allan S. Myerson. "Nucleation Induction Time in Levitated Droplets." Journal of Physical Chemistry B 108, no. 30 (July 2004): 10672–77. http://dx.doi.org/10.1021/jp049586s.

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19

Hyers, Robert W. "Fluid flow effects in levitated droplets." Measurement Science and Technology 16, no. 2 (January 20, 2005): 394–401. http://dx.doi.org/10.1088/0957-0233/16/2/010.

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20

Cummings, D. L., and D. A. Blackburn. "Oscillations of magnetically levitated aspherical droplets." Journal of Fluid Mechanics 224 (March 1991): 395–416. http://dx.doi.org/10.1017/s0022112091001817.

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In experiments to measure the surface energy of a magnetically levitated molten metal droplet by observation of its oscillation frequencies, Rayleigh's equation is usually used. This assumes that the equilibrium shape is a sphere, and the surface restoring force is due only to surface tension. This work investigates how the vibrations of a non-rotating liquid droplet are affected by the asphericity and additional restoring forces that the levitating field introduces. The calculations show that the expected single frequency of the fundamental mode is split into either three, when there is an axis of rotational symmetry, or five unequally spaced bands. Frequencies, on average, are higher than those of an unconstrained droplet; the surface tension appears to be increased over its normal value. This requires a small correction to be made in all analyses of surface energy. A frequency sum rule is derived from a simplified model of the magnetic field which allows the corresponding Rayleigh frequency to be evaluated from the observed frequencies of the fundamental and translational modes. A more detailed analysis shows a similar correction but one that is also sensitive to the position of the droplet in the field.

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21

Leiterer, J., F. Delißen, F. Emmerling, A. F. Thünemann, and U. Panne. "Structure analysis using acoustically levitated droplets." Analytical and Bioanalytical Chemistry 391, no. 4 (March 30, 2008): 1221–28. http://dx.doi.org/10.1007/s00216-008-2011-2.

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22

Westphall, Michael S., Kaveh Jorabchi, and Lloyd M. Smith. "Mass Spectrometry of Acoustically Levitated Droplets." Analytical Chemistry 80, no. 15 (August 2008): 5847–53. http://dx.doi.org/10.1021/ac800317f.

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23

Gärtner, F., S. A. Moir, A. F. Norman, A. L. Greer, and D. M. Herlach. "Texture analyses of levitated Fe69Ni30Cr1 droplets." Materials Science and Engineering: A 226-228 (June 1997): 307–11. http://dx.doi.org/10.1016/s0921-5093(97)80044-5.

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24

Aoki, K., and K. Hasegawa. "Acoustically induced breakup of levitated droplets." AIP Advances 10, no. 5 (May 1, 2020): 055115. http://dx.doi.org/10.1063/1.5143395.

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25

Biedasek, Silke, Mohammed Abboud, Hans-Ulrich Moritz, and Achim Stammer. "Online-Analysis on Acoustically Levitated Droplets." Macromolecular Symposia 259, no. 1 (December 2007): 390–96. http://dx.doi.org/10.1002/masy.200751344.

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26

Temperton, Robert H., Richard J. A. Hill, and James S. Sharp. "Mechanical vibrations of magnetically levitated viscoelastic droplets." Soft Matter 10, no. 29 (2014): 5375–79. http://dx.doi.org/10.1039/c4sm00982g.

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27

Bratz, A., and I. Egry. "Surface oscillations of electromagnetically levitated viscous metal droplets." Journal of Fluid Mechanics 298 (September 10, 1995): 341–59. http://dx.doi.org/10.1017/s002211209500334x.

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We investigate the oscillation spectrum of electromagnetically levitated metal droplets. In the case of electromagnetic levitation, gravity is compensated by a Lorentz force, which is generated by an external current. The oscillation spectrum contains information about the thermophysical properties of the liquid metal, namely surface tension and viscosity. For a correct interpretation of these spectra the influence of the external forces on the frequencies and the damping of the surface waves must be well understood. The external forces deform the droplet, so that the static equilibrium shape is aspherical. For a perfect conductor the effect of the Lorentz force and gravity on the oscillation spectrum is calculated for an arbitrary magnetic field and arbitrary values of the viscosity. The high Reynolds number limit is evaluated. Explicit results are obtained for a linear magnetic field, which describes the experimental situation well.

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28

Gauthier, Anaïs, Guillaume Lajoinie, Jacco H. Snoeijer, and Devaraj van der Meer. "Inverse leidenfrost drop manipulation using menisci." Soft Matter 16, no. 16 (2020): 4043–48. http://dx.doi.org/10.1039/c9sm02363a.

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29

Svensson, E. A., C. Delval, P. von Hessberg, M. S. Johnson, and J. B. C. Pettersson. "Freezing of water droplets colliding with kaolinite particles." Atmospheric Chemistry and Physics 9, no. 13 (July 3, 2009): 4295–300. http://dx.doi.org/10.5194/acp-9-4295-2009.

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Abstract. Contact freezing of single supercooled water droplets colliding with kaolinite dust particles has been investigated. The experiments were performed with droplets levitated in an electrodynamic balance at temperatures from 240 to 268 K. Under relatively dry conditions (when no water vapor was added) freezing was observed to occur below 249 K, while a freezing threshold of 267 K was observed when water vapor was added to the air in the chamber. The effect of relative humidity is attributed to an influence on the contact freezing process for the kaolinite-water droplet system, and it is not related to the lifetime of the droplets in the electrodynamic balance. Freezing probabilities per collision were derived assuming that collisions at the lowest temperature employed had a probability of unity. Mechanisms for contact freezing are briefly discussed.

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30

Omrane, Alaa, Sabina Santesson, Marcus Aldén, and Staffan Nilsson. "Laser techniques in acoustically levitated micro droplets." Lab Chip 4, no. 4 (2004): 287–91. http://dx.doi.org/10.1039/b402440k.

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31

Delißen, Friedmar, Jork Leiterer, Ralf Bienert, Franziska Emmerling, and Andreas F. Thünemann. "Agglomeration of proteins in acoustically levitated droplets." Analytical and Bioanalytical Chemistry 392, no. 1-2 (July 8, 2008): 161–65. http://dx.doi.org/10.1007/s00216-008-2252-0.

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32

Gorges, E., L. M. Raez, A. Schillings, and I. Egry. "Density measurements on levitated liquid metal droplets." International Journal of Thermophysics 17, no. 5 (September 1996): 1163–72. http://dx.doi.org/10.1007/bf01442003.

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33

Stindt, Arne, Merwe Albrecht, Ulrich Panne, and Jens Riedel. "CO2 laser ionization of acoustically levitated droplets." Analytical and Bioanalytical Chemistry 405, no. 22 (November 7, 2012): 7005–10. http://dx.doi.org/10.1007/s00216-012-6500-y.

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34

Chandra, S., and S. D. Aziz. "Leidenfrost Evaporation of Liquid Nitrogen Droplets." Journal of Heat Transfer 116, no. 4 (November 1, 1994): 999–1006. http://dx.doi.org/10.1115/1.2911477.

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The evaporation of a single droplet of liquid nitrogen, levitated during film boiling above a solid, impervious surface, was studied experimentally. The droplet initial diameter (1.9 mm), surface temperature (~20°C), ambient temperature (~20°C), and ambient pressure (~0.1 MPa) were held constant. The principal parameters varied were the surface material (copper or glass), and roughness (0.35 to 50 μm). Measurements were made of the droplet diameter evolution and the surface temperature variation during droplet impact. Predictions from existing models of droplets in Leidenfrost evaporation agree well with measurements of the droplet evaporation rate. The droplet lifetime was found to be slightly longer on the glass surface than it was on the copper surface, corresponding to the greater cooling of the glass surface during droplet impact. The droplet evaporation rate was unchanged by small increases in surface roughness. However, ridges on the surface with a height of the same magnitude as the thickness of the vapor film under the drop caused vapor bubble nucleation in the droplet, and significantly reduced the droplet evaporation time.

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Esen, C., T. Kaiser, and G. Schweiger. "Raman Investigation of Photopolymerization Reactions of Single Optically Levitated Microparticles." Applied Spectroscopy 50, no. 7 (July 1996): 823–28. http://dx.doi.org/10.1366/0003702963905501.

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Raman spectroscopy was used to investigate polymerization reactions in a single micrometer-sized monomer droplet. An Ar+ laser levitated the microparticles and simultaneously excited the Raman scattering. The polymerization reaction was initiated by exposing the monomer droplets to the UV radiation of a mercury arc excitation lamp. The Raman spectrum of the reacting particle was investigated on-line. The results demonstrate that the combination of the technique of optical levitation and Raman spectroscopy allows nondestructive in situ measurements of single particles and is therefore very useful for the study of fundamental processes.

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Raghuram, S., and Vasudevan Raghavan. "Thermodynamic Analysis of Evaporation of Levitated Binary and Ternary Liquid Fuel Droplets under Normal Gravity." ISRN Thermodynamics 2012 (July 8, 2012): 1–10. http://dx.doi.org/10.5402/2012/167281.

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The present study presents a thermodynamic model for predicting the vaporization characteristics of binary and ternary hydrocarbon fuel droplets under atmospheric pressure and normal gravity conditions. The model employs activity coefficients based on UNIFAC group contribution method and evaluates the vapor-liquid equilibrium of binary and ternary droplets. The gas-phase properties have been evaluated as a function of temperature and mixture molecular weight. The model has been validated against the experimental data available in literature. The validated model is used to predict the vaporization characteristics of binary and ternary fuel droplets at atmospheric pressure under normal gravity. Results show multiple slopes in the droplet surface regression indicating preferential vaporization of fuel components based on their boiling point and volatility. The average evaporation rate is dictated by the ambient temperature and also by composition of the mixture.

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Gómez Castaño, Jovanny, Luc Boussekey, Jean Verwaerde, Myriam Moreau, and Yeny Tobón. "Enhancing Double-Beam Laser Tweezers Raman Spectroscopy (LTRS) for the Photochemical Study of Individual Airborne Microdroplets." Molecules 24, no. 18 (September 12, 2019): 3325. http://dx.doi.org/10.3390/molecules24183325.

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A new device and methodology for vertically coupling confocal Raman microscopy with optical tweezers for the in situ physico- and photochemical studies of individual microdroplets (Ø ≤ 10 µm) levitated in air is presented. The coupling expands the spectrum of studies performed with individual particles using laser tweezers Raman spectroscopy (LTRS) to photochemical processes and spatially resolved Raman microspectroscopy on airborne aerosols. This is the first study to demonstrate photochemical studies and Raman mapping on optically levitated droplets. By using this configuration, photochemical reactions in aerosols of atmospheric interest can be studied on a laboratory scale under realistic conditions of gas-phase composition and relative humidity. Likewise, the distribution of photoproducts within the drop can also be observed with this setup. The applicability of the coupling system was tested by studying the photochemical behavior of microdroplets (5 µm < Ø < 8 µm) containing an aqueous solution of sodium nitrate levitated in air and exposed to narrowed UV radiation (254 ± 25 nm). Photolysis of the levitated NaNO3 microdroplets presented photochemical kinetic differences in comparison with larger NaNO3 droplets (40 µm < Ø < 80 µm), previously photolyzed using acoustic traps, and heterogeneity in the distribution of the photoproducts within the drop.

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Fernandez, Mara Otero, Richard J. Thomas, Natalie J. Garton, Andrew Hudson, Allen Haddrell, and Jonathan P. Reid. "Assessing the airborne survival of bacteria in populations of aerosol droplets with a novel technology." Journal of The Royal Society Interface 16, no. 150 (January 2019): 20180779. http://dx.doi.org/10.1098/rsif.2018.0779.

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The airborne transmission of infection relies on the ability of pathogens to survive aerosol transport as they transit between hosts. Understanding the parameters that determine the survival of airborne microorganisms is critical to mitigating the impact of disease outbreaks. Conventional techniques for investigating bioaerosol longevity in vitro have systemic limitations that prevent the accurate representation of conditions that these particles would experience in the natural environment. Here, we report a new approach that enables the robust study of bioaerosol survival as a function of relevant environmental conditions. The methodology uses droplet-on-demand technology for the generation of bioaerosol droplets (1 to greater than 100 per trial) with tailored chemical and biological composition. These arrays of droplets are captured in an electrodynamic trap and levitated within a controlled environmental chamber. Droplets are then deposited on a substrate after a desired levitation period (less than 5 s to greater than 24 h). The response of bacteria to aerosolization can subsequently be determined by counting colony forming units, 24 h after deposition. In a first study, droplets formed from a suspension of Escherichia coli MRE162 cells (10 8 ml −1 ) with initial radii of 27.8 ± 0.08 µm were created and levitated for extended periods of time at 30% relative humidity. The time-dependence of the survival rate was measured over a time period extending to 1 h. We demonstrate that this approach can enable direct studies at the interface between aerobiology, atmospheric chemistry and aerosol physics to identify the factors that may affect the survival of airborne pathogens with the aim of developing infection control strategies for public health and biodefence applications.

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Duft, D., and T. Leisner. "Laboratory evidence for volume-dominated nucleation of ice in supercooled water microdroplets." Atmospheric Chemistry and Physics 4, no. 7 (October 4, 2004): 1997–2000. http://dx.doi.org/10.5194/acp-4-1997-2004.

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Abstract. We report on measurements of the rate of homogeneous ice nucleation in supercooled water microdroplets levitated in an electrodynamic balance. By comparison of the freezing probability for droplets of radius 49µm and 19µm, we are able to conclude that homogeneous freezing is a volume-proportional process and that surface nucleation might only be important, if at all, for much smaller droplets.

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40

Svensson, E. A., C. Delval, P. von Hessberg, M. S. Johnson, and J. B. C. Pettersson. "Freezing of water droplets colliding with kaolinite particles." Atmospheric Chemistry and Physics Discussions 9, no. 1 (January 27, 2009): 2417–33. http://dx.doi.org/10.5194/acpd-9-2417-2009.

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Abstract. Contact freezing of single supercooled water droplets colliding with kaolinite dust particles has been investigated. The experiments were performed with droplets levitated in an electrodynamic balance at temperatures from 240 to 268 K. Under dry conditions freezing was observed to occur below 249 K, while a freezing threshold of 267 K was observed at high relative humidity. The effect of relative humidity is attributed to an influence on the contact freezing process for the kaolinite-water droplet system, and it is not related to the lifetime of the droplets in the electrodynamic balance. Freezing probabilities per collision were derived assuming that collisions at the lowest temperature employed had a probability of unity. The data recorded at high humidity should be most relevant to atmospheric conditions, and the results indicate that parameterizations currently used in modelling studies to describe freezing rates are appropriate for kaolinite aerosol particles. Mechanisms for contact freezing are briefly discussed.

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Jones, Stephanie H., Pascal Friederich, and D. James Donaldson. "Photochemical Aging of Levitated Aqueous Brown Carbon Droplets." ACS Earth and Space Chemistry 5, no. 4 (March 18, 2021): 749–54. http://dx.doi.org/10.1021/acsearthspacechem.1c00005.

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42

Jeong, Kwanghee, Peter J. Metaxas, Anrie Helberg, Michael L. Johns, Zachary M. Aman, and Eric F. May. "Gas hydrate nucleation in acoustically levitated water droplets." Chemical Engineering Journal 433 (April 2022): 133494. http://dx.doi.org/10.1016/j.cej.2021.133494.

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Preston, Richard E., Thomas R. Lettieri, and Hratch G. Semerjian. "Characterization of single levitated droplets by Raman spectroscopy." Langmuir 1, no. 3 (May 1985): 365–67. http://dx.doi.org/10.1021/la00063a018.

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Schenk, Jonas, Ulrich Panne, and Merwe Albrecht. "Interaction of Levitated Ionic Liquid Droplets with Water." Journal of Physical Chemistry B 116, no. 48 (November 26, 2012): 14171–77. http://dx.doi.org/10.1021/jp309661p.

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Pathak, Binita, Priti Xavier, Suryasarathi Bose, and Saptarshi Basu. "Thermally induced phase separation in levitated polymer droplets." Physical Chemistry Chemical Physics 18, no. 47 (2016): 32477–85. http://dx.doi.org/10.1039/c6cp06283k.

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Saha, Abhishek, Saptarshi Basu, and Ranganathan Kumar. "Velocity and rotation measurements in acoustically levitated droplets." Physics Letters A 376, no. 45 (October 2012): 3185–91. http://dx.doi.org/10.1016/j.physleta.2012.08.013.

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Combe, Nicole A., and D. James Donaldson. "Water Evaporation from Acoustically Levitated Aqueous Solution Droplets." Journal of Physical Chemistry A 121, no. 38 (September 13, 2017): 7197–204. http://dx.doi.org/10.1021/acs.jpca.7b08050.

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48

Amini, Shaahin, Haamun Kalaantari, Sasan Mojgani, and Reza Abbaschian. "Graphite crystals grown within electromagnetically levitated metallic droplets." Acta Materialia 60, no. 20 (December 2012): 7123–31. http://dx.doi.org/10.1016/j.actamat.2012.09.019.

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Brenn, G., L. J. Deviprasath, F. Durst, and C. Fink. "Evaporation of acoustically levitated multi-component liquid droplets." International Journal of Heat and Mass Transfer 50, no. 25-26 (December 2007): 5073–86. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2007.07.036.

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50

Duft, D., and T. Leisner. "Laboratory evidence for volume-dominated nucleation of ice in supercooled water microdroplets." Atmospheric Chemistry and Physics Discussions 4, no. 3 (June 7, 2004): 3077–88. http://dx.doi.org/10.5194/acpd-4-3077-2004.

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Abstract. We report on measurements of the rate of homogeneous ice nucleation in supercooled water microdroplets levitated in an electrodynamic balance. By comparison of the freezing probability for droplets of radius 49 µm and 19 µm, we are able to conclude that homogeneous freezing is a volume-proportional process and that surface nucleation might only be important, if at all, for much smaller droplets.

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