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Transient evolution of the heat transfer and the vapor film thickness at the drop impact in the regime of film boiling

Castanet, G. ; Chaze, W. LU ; Caballina, O. ; Collignon, R. and Lemoine, F. (2018) In Physics of Fluids 30(12).
Abstract

When a drop impinges onto a wall heated above the Leidenfrost temperature, a very thin vapor film is formed at the interface between the liquid and the solid substrate. This vapor layer modifies the impact behavior of the drop and induces a significant decrease in heat transfer. A model is proposed for the growth of this vapor layer and its resistance to the heat transfer. The main assumptions are as follows: (i) a uniform but time varying thickness of the vapor film, (ii) a quasi-steady Poiseuille flow inside the vapor film, and (iii) a constant wall temperature. Heat energy and momentum balances are employed to obtain an ordinary differential equation describing the evolution of the vapor film thickness during the drop impact. For... (More)

When a drop impinges onto a wall heated above the Leidenfrost temperature, a very thin vapor film is formed at the interface between the liquid and the solid substrate. This vapor layer modifies the impact behavior of the drop and induces a significant decrease in heat transfer. A model is proposed for the growth of this vapor layer and its resistance to the heat transfer. The main assumptions are as follows: (i) a uniform but time varying thickness of the vapor film, (ii) a quasi-steady Poiseuille flow inside the vapor film, and (iii) a constant wall temperature. Heat energy and momentum balances are employed to obtain an ordinary differential equation describing the evolution of the vapor film thickness during the drop impact. For droplets injected at a temperature sufficiently lower than the saturation temperature, this equation predicts that the impact velocity has no influence on the thickness of the vapor film. This latter is solely governed by the local heat flux transferred to the liquid, which predominates over the heat flux used for liquid evaporation. An accurate description of the droplet heating is therefore required to complement this model. As an attempt, this description is based upon a one-dimensional analysis, which includes some effects due to the complex fluid flow inside the spreading droplet. Finally, the theoretical model is validated against experiments dealing with millimeter-sized ethanol droplets. Two optical measurement techniques, based on laser-induced fluorescence and infrared thermography, are combined to characterize the heat transfer as well as the thickness of the vapor film.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physics of Fluids
volume
30
issue
12
article number
122109
publisher
American Institute of Physics
external identifiers
  • scopus:85059537780
ISSN
1070-6631
DOI
10.1063/1.5059388
language
English
LU publication?
yes
id
4ad73cdb-a250-46eb-8a96-343f6b60e82b
date added to LUP
2019-01-23 12:53:11
date last changed
2020-03-29 07:33:16
@article{4ad73cdb-a250-46eb-8a96-343f6b60e82b,
  abstract     = {<p>When a drop impinges onto a wall heated above the Leidenfrost temperature, a very thin vapor film is formed at the interface between the liquid and the solid substrate. This vapor layer modifies the impact behavior of the drop and induces a significant decrease in heat transfer. A model is proposed for the growth of this vapor layer and its resistance to the heat transfer. The main assumptions are as follows: (i) a uniform but time varying thickness of the vapor film, (ii) a quasi-steady Poiseuille flow inside the vapor film, and (iii) a constant wall temperature. Heat energy and momentum balances are employed to obtain an ordinary differential equation describing the evolution of the vapor film thickness during the drop impact. For droplets injected at a temperature sufficiently lower than the saturation temperature, this equation predicts that the impact velocity has no influence on the thickness of the vapor film. This latter is solely governed by the local heat flux transferred to the liquid, which predominates over the heat flux used for liquid evaporation. An accurate description of the droplet heating is therefore required to complement this model. As an attempt, this description is based upon a one-dimensional analysis, which includes some effects due to the complex fluid flow inside the spreading droplet. Finally, the theoretical model is validated against experiments dealing with millimeter-sized ethanol droplets. Two optical measurement techniques, based on laser-induced fluorescence and infrared thermography, are combined to characterize the heat transfer as well as the thickness of the vapor film.</p>},
  author       = {Castanet, G. and Chaze, W. and Caballina, O. and Collignon, R. and Lemoine, F.},
  issn         = {1070-6631},
  language     = {eng},
  month        = {12},
  number       = {12},
  publisher    = {American Institute of Physics},
  series       = {Physics of Fluids},
  title        = {Transient evolution of the heat transfer and the vapor film thickness at the drop impact in the regime of film boiling},
  url          = {http://dx.doi.org/10.1063/1.5059388},
  doi          = {10.1063/1.5059388},
  volume       = {30},
  year         = {2018},
}