J. Phys. III France
Volume 6, Number 7, July 1996
Page(s) 975 - 989
DOI: 10.1051/jp3:1996166
J. Phys. III France 6 (1996) 975-989

Experimental Determination of the Geometry of Real Drops on Transparent Materials

J.G. Pieters1, J.M. Deltour2 and M.J. Debruyckere1

1  University of Ghent, Departement of Agricultural Engineering, Coupure Links 653, 9000 Gent, Belgium
2  Faculté Universitaire des Sciences Agronomiques de Gembloux, UER de Physique et de Chimie Physique, Avenue de la Faculté 8, 5030 Gembloux, Belgium

(Received 21 December 1995, revised 1 April 1996, accepted 16 April 1996)

An experimental method for the determination of real drop geometries on transparent supports is developed. The method offers the possibility to obtain the general form of a drop by using commonly available instruments, such as a photo camera with bellow, a digitizer or a scanner. By means of this method, a set of isoclinal lines of the drop registered by a camera. By integration, the map of isoclinal lines is then mathematically transformed into a relief-map of the drop, revealing all geometric information about the drop profile. A trial and error method for the correction of the measuring equipment alignment errors is also developed. For a series of 15 drops on a vertical PE film and whose geometries are determined by means of the above mentioned method, light transmission and diffusion are then simulated. It is shown that the light transmittance of flat drops is somewhat lower than the light transmittance for dry PE but much higher than for hemispherical drops. Light diffusion is shown to be nearly independent of the drop shape. Nearly all the light is diffused in a small solid angle. For an evaporating drop on a vertical PE film, the evolutions of the drop geometry and the light transmittance are followed in time. It is also demonstrated that during evaporation, the drop becomes mainly flatter so that the light transmittance increases.

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