Bubble dynamics and atomization in evaporating polymeric droplets

Gannena, KSR and Rao, DCK and Roy, D and Kumar, A and Basu, S (2022) Bubble dynamics and atomization in evaporating polymeric droplets. In: Journal of Fluid Mechanics, 951 .

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Abstract

We investigate the interaction of an aqueous polymeric droplet with a tuneable continuous laser in an acoustically levitated environment. The effect of laser irradiation intensity and polymeric concentration on various spatio-temporal parameters is unearthed using high-speed shadowgraphy and theoretical scaling analysis. We observe four temporal phases: droplet evaporation, vapour bubble growth followed by membrane inflation, bubble/membrane rupture through hole nucleation and droplet breakup. During the initial droplet evaporation phase, concentration build-up at the droplet surface beyond a critical limit leads to the formation of a skin layer. It is revealed that, at a given location inside the droplet, hot spots occur, and the maximum temperature at the hot spots scales linearly with irradiation intensity until a bubble nucleates. The low-intensity laser interaction leads to symmetric membrane inflation that eventually forms holes at droplet poles and cracks on the shell surface. On the contrary, high intensity causes early bubble nucleation followed by asymmetric membrane inflation that eventually ruptures through multiple hole formation. Furthermore, the growth and rupture of the membrane is followed by a catastrophic breakup of the droplet. Two dominant atomization modes are reported at significantly high irradiation intensities: stable sheet collapse and unstable sheet breakup. The evolution of droplets into a stable/unstable sheet follows universally observed ligament and hole dynamics. A regime map is shown to describe the influence of polymer concentration and irradiation intensity on the strength and mode of droplet atomization.

Item Type:	Journal Article
Publication:	Journal of Fluid Mechanics
Publisher:	Cambridge University Press
Additional Information:	The copyright for this article belongs to Cambridge University Press.
Keywords:	Atomization; Bubbles (in fluids); Crystallization; Drop breakup; Evaporation; Irradiation; Nucleation, Bubble dynamics; Continuous lasers; Droplet evaporation; High Speed; Hotspots; Irradiation intensity; Polymeric droplets; Scaling analysis; Shadowgraphy; Spatio-temporal, Membranes, bubble; droplet; evaporation; irradiation; membrane; polymer
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	30 Dec 2022 10:02
Last Modified:	30 Dec 2022 10:02
URI:	https://eprints.iisc.ac.in/id/eprint/78637

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