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Research Papers: Heat and Mass Transfer

Effect of Particle Concentration on Shape Deformation and Secondary Atomization Characteristics of a Burning Nanotitania Dispersion Droplet

[+] Author and Article Information
Ankur Miglani

Department of Mechanical Engineering,
Indian Institute of Science,
Bangalore 560012, India

Saptarshi Basu

Department of Mechanical Engineering,
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 August 5, 2014; published online June 2, 2015. Assoc. Editor: Suman Chakraborty.

J. Heat Transfer 137(10), 102001 (Oct 01, 2015) (8 pages) Paper No: HT-14-1278; doi: 10.1115/1.4030394 History: Received April 30, 2014; Revised August 05, 2014; Online June 02, 2015

Secondary atomization characteristics of burning bicomponent (ethanol–water) droplets containing titania nanoparticles (NPs) in dilute (0.5% and 1 wt.%) and dense concentrations (5% and 7.5 wt.%) are studied experimentally at atmospheric pressure under normal gravity. It is observed that both types of nanofuel droplets undergo distinct modes of secondary breakup, which are primarily responsible for transporting particles from the droplet domain to the flame zone. For dilute nanosuspensions, disruptive response is characterized by low intensity atomization modes that cause small-scale localized flame distortion. In contrast, the disruption behavior at dense concentrations is governed by high intensity bubble ejections, which result in severe disruption of the flame envelope.

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Figures

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Fig. 1

High resolution, high speed images of dominant secondary atomization modes for nanofuel droplets with dilute concentrations (0.5% and 1 wt.%) of dispersed NPs: (a) pin/needle-type ligament ejection, (b) needle ejection with both tip-base breakup and (c) low momentum needle ligament with only tip breakup. High speed images of disrupted flame envelope corresponding to these events are shown on right.

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Fig. 2

High resolution, high speed images of dominant secondary atomization modes for nanofuel droplets with dispersed NPs at dense concentrations (5% and 7.5 wt.%): (a) very low momentum, thick ligament breakup and (b) localized catastrophic droplet fragmentation. High speed images of flame disruptions corresponding to these events are shown on right. (c) Typical sequence of flame envelope distortion following mode 5 type secondary breakup.

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Fig. 3

Time history of fluctuations in normalized, maximum flame stand-off distance for nanotitania dispersion droplets at dilute concentrations (0.5% and 1 wt.%). White dotted rectangles indicate localized distortion of diffusion flame envelope.

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Fig. 4

Temporal variation of normalized, maximum flame stand-off distance fluctuations for nanotitania dispersion droplets at dense concentrations (5% and 7.5 wt.%). White dotted rectangles indicate the distorted flame envelope.

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Fig. 5

High speed images (500 fps) showing nanofuel droplet flame at different stages of droplet lifecycle for: (a) nanotitania dispersion droplets at dilute concentration (1 wt.%) and (b) nanotitania dispersion droplets at dense concentration (5 wt.%)

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Fig. 6

Temporal variation of squared nondimensional droplet size (D/Do)2 showing slower droplet surface regression at higher particle loading rates

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Fig. 7

Regime plot showing the temporal distribution of dominant secondary breakup pathways at both dilute and dense concentrations

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