Study on characteristics of fragment size distribution generated via droplet breakup by high-speed gas flow

Kamiya, Tomohiro; Asahara, Makoto; Yada, Tokiha; Mizuno, Kyohei; Miyasaka, Takeshi

doi:10.1063/5.0076448

“…Unlike the laminar transition from deformation to breakup observed in shear flow, a complex fragmentation phenomenon is noticed when a droplet encounters a gas stream (Guildenbecher, López-Rivera & Sojka 2009; Kamiya et al. 2022; Sharma et al. 2022).…”

Section: Introductionmentioning

confidence: 99%

“…Unlike the laminar transition from deformation to breakup observed in shear flow, a complex fragmentation phenomenon is noticed when a droplet encounters a gas stream (Guildenbecher, López-Rivera & Sojka 2009;Kamiya et al 2022;Sharma et al 2022). The intricate synergy between the aerodynamic forces and surface tension-based instabilities leads to varying droplet morphologies which are sensitive to the flow conditions and fluid properties.…”

Section: Introductionmentioning

confidence: 99%

Microemulsification from single laser-induced cavitation bubbles

Raman

¹

,

Rosselló

²

,

Reese

³

et al. 2022

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We study the interaction between a laser-induced cavitation bubble and a submillimetre-sized water droplet submerged in silicone oil. High-speed imaging reveals the pathways through which droplet fragmentation occurs and three distinct regimes of bubble–droplet interaction are identified: deformation, external emulsification and internal emulsification. We have observed that during the bubble collapse, the droplet elongates towards the bubble, which acts as a flow sink pulling on the droplet. For silicone oils with higher viscosity, the droplet jets into the cavitation bubble and forms a satellite water droplet in the continuous oil phase. In contrast, for lower-viscosity oils, the droplet encapsulates the collapsing bubble as it jets inside and undergoes multiple cycles of expansion and collapse. These internal bubble collapses create tiny oil droplets inside the parent water droplet. The kinematic viscosity of the silicone oil, maximum bubble diameter and centre-to-centre distance between the bubble and the droplet are varied. The regimes are separated in a parameter space set up by the non-dimensional distance and a cavitation Reynolds number.

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Comparison between shadow imaging and in-line holography for measuring droplet size distributions

Erinin

¹

,

Néel

²

,

Mazzatenta

³

et al. 2023

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A direct comparison of the droplet size and number measurements using in-line holography and shadow imaging is presented in three dynamically evolving laboratory scale experiments. The two experimental techniques and image processing algorithms used to measure droplet number and radii are described in detail. Droplet radii as low as $$r = 14$$ r = 14 µm are measured using in-line holography and $$r = 50$$ r = 50 µm using shadow imaging. The droplet radius measurement error is estimated using a calibration target (reticle) and it was found that the holographic technique is able to measure droplet radii more accurately than shadow imaging for droplets with $$r \le 625$$ r ≤ 625 µm. Using the measurements of droplet number and size we quantitatively cross-validate and assess the accuracy of the two measurement techniques. The droplet size distributions, N(r), are measured in all three experiments and are found to agree well between the two measurement techniques. In one of the laboratory experiments, simultaneous measurements of droplets ($$r \ge 14$$ r ≥ 14 µm, using holography) and dry aerosols ($$0.07 \lessapprox r \lessapprox 2$$ 0.07 ⪅ r ⪅ 2 µm, using an scanning mobility particle sizer and $$0.15 \lessapprox r \lessapprox 5$$ 0.15 ⪅ r ⪅ 5 µm using an optical particle sizer) are reported, one of the first such comparison to the best of our knowledge. The total number and volume of droplets is found to agree well between both techniques in the three experiments. We demonstrate that a relatively simple shadow imaging technique can be just as reliable when compared to a more sophisticated holographic measurement technique over their common droplet radius measurement range. The agreement in results is shown to be valid over a large range of droplet concentrations, which include experiments with relatively sparse droplet concentrations as low as 0.02 droplets per image. Advantages and disadvantages for the two techniques are discussed in the context of our results. The main advantages to in-line holography are the greater accuracy in droplet radius measurement, greater spatial resolution, larger depth of field, and the high repetition rate and short pulse duration of the laser light source. In comparison, the main advantages to shadow imaging are the simpler experimental setup, image processing algorithm, and fewer computer resources necessary for image processing. Droplet statistics like number and size are found to be very reliable between the two methods for large range of droplet densities, $${\mathcal {P}}_{r>50}$$ P r > 50 , ranging from $$10^{-4} \le {\mathcal {P}}_{r>50} \le 10^{-1}$$ 10 - 4 ≤ P r > 50 ≤ 10 - 1 cm$$^{-3}$$ - 3 , when the two techniques are implemented as shown in this paper.

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