Experiments in Fluids

, Volume 53, Issue 4, pp 1045–1056 | Cite as

Experimental investigation into three-dimensional wavy liquid films under the influence of electrostatic forces

  • Wilko Rohlfs
  • Georg F. Dietze
  • Herman D. Haustein
  • Oleg Yu. Tsvelodub
  • Reinhold Kneer
Research Article

Abstract

Three-dimensional interfacial waves that develop on the free surface of falling liquid films are known to intensify heat and mass transfer. In this context, the present paper studies the effect of electrostatic forces applied to a falling film of dielectric liquid on its three-dimensional nonlinear wave dynamics. Therefore, measurements of the local film thickness using a confocal chromatic imaging method were taken, and the complex wave topology was characterized through photography. The experiments show a complex interaction between the electric field and the hydrodynamics of the falling film, whereby electrostatic forces were found to both increase and decrease wave peak height in different regions of the wave. Additionally, an electrically induced breakup of the three-dimensional wave fronts, which leads to a locally doubled frequency in streamwise direction, is found. The ability to influence the wave topology demonstrated here opens the possibility to optimize heat transfer processes in falling liquid films.

List of symbols

fs

Electrically induced surface force

g

Gravity

n

Coordinate normal to free surface

q

Volumetric flow rate per unit width

t

Coordinate tangential to free surface

t

Time

u

Phase velocity

x, y, z

Streamwise, crosswise and spanwise coordinates

yfyw

CCI measuring distance to the fluid/wall

D

Electric displacement

E

Electric field strength

H

Capacitor plate distance

α

Angle

δg

Thickness of the glass plate

δf

Film thickness

Electric permittivity

λ

Optical wavelength

ν

Kinematic viscosity

ψ

Electric potential

ρ

Density

σ

Surface tension

Λ

Wavelength of surface waves

\(Re=\frac{q}{\nu}\)

Reynolds number of the liquid film

Notes

Acknowledgments

The authors thank Anne Mettner and Norman Lahann for their contribution to the development of the three-dimensional excitation mechanism employed to obtain the experimental results. Additionally, we would like to thank the reviewers for their constructive comments and ideas on this manuscript, in particular with respect to Fig. 6. This work was financially supported by the Deutsche Forschungsgemeinschaft (grant number DFG KN 764/3-1).

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Copyright information

© Springer-Verlag 2012

Authors and Affiliations

  • Wilko Rohlfs
    • 1
  • Georg F. Dietze
    • 1
  • Herman D. Haustein
    • 1
  • Oleg Yu. Tsvelodub
    • 2
  • Reinhold Kneer
    • 1
  1. 1.Institute of Heat and Mass TransferRWTH Aachen UniversityAachenGermany
  2. 2.Institute of ThermophysicsSBRASNovosibirskRussia

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