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Research Papers: Multiphase Flows

Concurrent Droplet Coalescence and Solidification on Surfaces With Various Wettabilities

[+] Author and Article Information
Sara Moghtadernejad

Department of Mechanical and
Industrial Engineering,
Concordia University,
Montreal, QC H3G 1M8, Canada
e-mail: sara.moghtadernejad@gmail.com

Mehdi Jadidi

Department of Mechanical and
Industrial Engineering,
Concordia University,
Montreal, QC H3G 1M8, Canada
e-mail: m_jadi@encs.concordia.ca

Moussa Tembely

Department of Mechanical and
Industrial Engineering,
Concordia University,
Montreal, QC H3G 1M8, Canada
e-mail: moussa.tembely@concordia.ca

Nabil Esmail

Department of Mechanical and
Industrial Engineering,
Concordia University,
Montreal, QC H3G 1M8, Canada
e-mail: esmail@encs.concordia.ca

Ali Dolatabadi

Department of Mechanical and
Industrial Engineering,
Concordia University,
Montreal, QC H3G 1M8, Canada
e-mail: ali.dolatabadi@concordia.ca

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 8, 2014; final manuscript received January 22, 2015; published online March 19, 2015. Assoc. Editor: John Abraham.

J. Fluids Eng 137(7), 071302 (Jul 01, 2015) (10 pages) Paper No: FE-14-1429; doi: 10.1115/1.4029672 History: Received August 08, 2014; Revised January 22, 2015; Online March 19, 2015

An experimental study is performed to analyze the shear driven droplet shedding on cold substrates with different airflow speeds typical of those in the flight conditions. Understanding the mechanism of simultaneous droplet shedding, coalescence, and solidification is crucial to devise solutions for mitigating aircraft in-flight icing. To mimic this scenario, the experimental setup is designed to generate shear flow as high as 90 m/s. The droplet shedding at high-speed is investigated on a cold surface (0 and −5 °C) of different wettabilities ranging from hydrophilic to superhydrophobic. Result analyses indicate that on a hydrophilic substrate, the droplets form a rivulet, which then freezes on the cold plate. In contrast, on the superhydrophobic surface, there is no rivulet formation. Instead, droplets roll over the substrate and detach from it under the effect of high shear flow.

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References

Figures

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Fig. 1

SEM image of the superhydrophobic [9] and aluminum substrates with 2500× and 5000× magnification, respectively. The specified area at the top right corner of the superhydrophobic substrate has the magnification of 15,000×.

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Fig. 2

Experimental setup

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Fig. 3

Schematic of Reff and Z of a droplet placed on: (a) aluminum and (b) superhydrophobic substrate

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Fig. 4

Schematic of the two droplets position on the substrate

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Fig. 5

Single droplet shedding sequences on aluminum substrate; airflow direction is from left to right

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Fig. 6

Normalized wetting length versus dimensionless time on aluminum substrate at different surface temperatures

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Fig. 7

Two droplets shedding sequences on aluminum substrate; airflow direction is from left to right

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Fig. 8

Variations of the normalized wetting length versus time on aluminum substrate for: (a) first droplet and (b) coalesced droplet

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Fig. 13

Variations of the normalized wetting length versus time on superhydrophobic substrate for (a) first droplet and (b) coalesced droplet

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Fig. 12

Two droplets shedding sequences on superhydrophobic substrate; airflow direction is from left to right

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Fig. 11

Dimensionless detachment time versus Reynolds number on superhydrophobic substrate

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Fig. 10

Normalized wetting length versus Dimensionless time on superhydrophobic substrate at different surface temperatures

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Fig. 9

Single droplet shedding sequences on superhydrophobic substrate; airflow direction is from left to right

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