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Research Papers: SPECIAL SECTION PAPERS

Transient Effects in Evaporating Sessile Drops: With and Without Heating

[+] Author and Article Information
Liu Bin

Tianjin Key Lab of Refrigeration Technology,
Tianjin University of Commerce,
Tianjin 300134, China

Rachid Bennacer

LMT-Cachan/ENS-Cachan/CNRS/Université
Paris Saclay,
61 Avenue du Président Wilson,
Cachan 94235, France;
Tianjin Key Lab of Refrigeration Technology,
Tianjin University of Commerce,
Tianjin 300134, China
e-mail: rachid.bennacer@ens-cachan.fr

Khellil Sefiane

School of Engineering,
University of Edinburgh,
Kings Buildings Mayfield Road,
Edinburgh EH9 3JL, UK;
Tianjin Key Lab of Refrigeration Technology,
11 Tianjin University of Commerce,
12 Tianjin 300134, China

Annie Steinchen

MADIREL UMR 7246
Bd Escadrille Normandie Niemen,
Marseille 13397, France

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 19, 2014; final manuscript received March 27, 2015; published online June 1, 2016. Assoc. Editor: Ziad Saghir.

J. Heat Transfer 138(9), 091009 (Jun 01, 2016) (6 pages) Paper No: HT-14-1690; doi: 10.1115/1.4032954 History: Received October 19, 2014; Revised March 27, 2015

The evaporation phenomenon of sessile drops has been recently subject to an extensive interest by industry and researchers. This is stimulated by new developments in exploiting this basic process for more industrial technologies and biological applications. The underlying mechanisms to this apparently simple, yet elusive phenomenon as well as its complete description are still far from being achieved. Many theoretical models describe the phenomenon by neglecting some important physical aspects of the problem. Transient thermal effects can indeed be very crucial, nonetheless very often neglected. In a recent work, a new approach was adopted to model the physical process taking into account the thermal resistance of the substrate. This was, however, limited to the investigation of cases where steady-state assumption is adopted. In such pseudo steady-state, a controlling nondimensional SB number was identified. The evaporation of sessile drops deposited on a substrate is found to exhibit various regimes. These latter are related to the wetting and spreading behavior of the drop, depending on whether the drop is pinned with a decreasing contact angle, with a receding contact line and constant angle or a mixed behavior. Most modeling attempts have considered vapor diffusion in the gas phase as the limiting mechanism for evaporation. However, the heat and mass transfer in the solid, liquid, and gas phases describe the problem and predict droplets evaporation. It is worth noting that most theoretical and numerical models proposed so far assume the quasi steady-state hypothesis and neglect transient effects. It is essential to acknowledge that not only the three phases (gas, solid, and liquid) take part in mass and energy transport but also the interfaces between these phases are equally important. The liquid–vapor interface, for instance is the surface through which phase change takes place. This interface is subjected to evaporative cooling effects, depending on the physical dimensions, properties as well as experimental conditions. In the present paper, we propose to extend this approach to account for transient effects. The results of this investigation demonstrate that in some cases transient effects can extend beyond the lifetime of the drop, making the entire process transitory. These effects are quantified and the implications for modeling wetting drops are discussed.

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References

Bonn, D. , Eggers, J. , Indekeu, J. , Meunier, J. , and Rolley, E. , 2009, “ Wetting and Spreading,” Rev. Mod Phys., 81(2), pp. 739–805. [CrossRef]
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Girard, F. , Antoni, M. , and Sefiane, K. , 2008, “ On the Effect of Marangoni Flow of Evaporation Rates of Heated Water Drops,” Langmuir, 24(17), pp. 9207–9210. [CrossRef] [PubMed]
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Sefiane, K. , and Bennacer, R. , 2011, “ An Expression for Droplet Evaporation Incorporating Thermal Effects,” J. Fluid Mech., 667, pp. 260–271. [CrossRef]
Ruiz, O. E. , and Black, W. Z. , 2002, “ Evaporation of Water Droplets Placed on a Heated Horizontal Surface,” ASME J. Heat Transfer, 124(5), pp. 854–863. [CrossRef]
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Girard, F. , Antoni, M. , Faure, S. , and Steinchen, A. , 2006, “ Evaporation and Marangoni Driven Convection in Small Heated Water Droplets,” Langmuir, 22(26), pp. 11085–11091. [CrossRef] [PubMed]
Bin, L. , Bennacer, R. , and Bouvet, A. , 2011, “ Evaporation of Methanol Droplet on the Teflon Surface Under Different Air Velocities,” Appl. Therm. Eng., 31(17–18), pp. 3792–3798. [CrossRef]

Figures

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Fig. 1

Illustrating drawing of the energy balance and thermal resistances

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Fig. 2

Temperature change versus time for methanol drop at various substrate thicknesses and the gas thermal effect

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Fig. 3

Normalized simulation results and analytical trends

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Fig. 4

The transitory time as a function of substrate thickness for a 1 mm methanol droplet

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Fig. 5

Temperature change versus time for different liquids (e = 1 mm)

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Fig. 6

Temperature change versus time for different liquids resistance decrease

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