Research Papers

Experimental Study of Shape Transition in an Acoustically Levitated and Externally Heated Droplet

[+] Author and Article Information
Binita Pathak

Mechanical Engineering Department,
Indian Institute of Science,
Bangalore 560012, India
e-mail: binitapathak88@gmail.com

Apratim Sanyal

Mechanical Engineering Department,
Indian Institute of Science,
Bangalore 560012, India
e-mail: sanyal6ap@gmail.com

Saptarshi Basu

Mechanical Engineering Department,
Indian Institute of Science,
Bangalore 560012, India
e-mail: sbasu@mecheng.iisc.ernet.in

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received April 30, 2014; final manuscript received October 30, 2014; published online August 11, 2015. Assoc. Editor: Suman Chakraborty.

J. Heat Transfer 137(12), 121006 (Aug 11, 2015) (8 pages) Paper No: HT-14-1275; doi: 10.1115/1.4030922 History: Received April 30, 2014

Experimental analyses of surface oscillations are reported in acoustically levitated, radiatively heated bicomponent droplets with one volatile and other being nonvolatile. Two instability pathways are observed: one being acoustically driven observed in low-vapor pressure fluid droplets and other being boiling driven observed in high-vapor pressure fluid droplets. The first pathway shows extreme droplets deformation and subsequent breakup by acoustic pressure and externally supplied heat. Also transition of instabilities from acoustically activated shape distortion regime to thermally induced boiling regime is observed with increasing concentration of volatile component in bicomponent droplets. Precursor phases of instabilities are investigated using Legendre’s polynomial.

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Fig. 1

Experimental setup and thermo-physical properties

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Fig. 2

Evolution of droplet shape with time

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Fig. 3

Droplet size regression rate

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Fig. 4

Variation of droplet AR

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Fig. 5

(a) IR images showing the surface temperatures of pure dodecane and 10DD90B droplets at the end of stage III just before breakup. (b) Graph shows the mean temperature plotted for different concentrations.

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Fig. 6

Decomposition of droplet shape into equilibrium shape and deviation from the same. O—droplet center and Oc—center of curvature of the droplet surface at the equator. (a) Nonuniform pressure across droplet surface, R0—radius of the spherical shape, R—radius at a particular θ. (b) Decomposition of equatorial radius of curvature Rc. In (b), O and Oc are coincident. The polar and equatorial radii are denoted as Rpole and Req. Fig. 6 adapted from Ref. [9].

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Fig. 7

Schematic of the stability pathways for dodecane-type and benzene-type of droplets

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Fig. 8

(a) Reconstruction of droplet shapes and (b) the first five Legendre modes

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Fig. 9

Temporal evolution of Legendre modes

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Fig. 10

Temporal variation of a0

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Fig. 11

Temporal variation of a2

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Fig. 12

Power spectral density of l0 and l2 modes for dodecane and 10DD90B droplets




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