Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Surface tension
Patent
1994-03-04
1995-10-17
Williams, Hezron E.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Surface tension
73 5401, G01N 1302
Patent
active
054579872
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a surface tension measuring device for a liquid, and relates more particularly to the surface tension measuring of a liquid flow on an horizontal or slightly inclined plane. This device according to the invention is particularly adapted for measuring the surface tension of a photographic emulsion on the inclined plane of a coating device, or of a surfactant solution.
BACKGROUND OF THE INVENTION
According to a known technique, known as WILHELMY technique, the surface tension of a static liquid is measured by means of a very thin and rectangular platinum blade passing through the surface to be studied. The platinum blade is suspended at one end of a wire and brought into contact of the liquid surface. FIG. 1 to which is now referred to, schematically illustrates a device carrying out the WILHELMY technique. The device comprises a platinum blade 1, the dimensions of which, by way of example, can be of 2 cm wide, 1 cm high and 0.01 cm thick. This blade is coupled to a balance 2 or a strain gauge by means of a wire 3.
Let us sum up briefly the theory which governs the operation of such a surface tension sensor. When a perfectly wettable platinum blade 1 is dipped into a liquid 4, this blade is subjected to capillary forces S and to buoyancy P.sub.A. The buoyancy corresponds to the volume immerged multiplied by the density. In the case of a conventional surface tension measuring of a static liquid, the immersion height of the blade is null; the P.sub.A force is thus null. In order to extract this blade out of the liquid, a vertical outwardly oriented force f must be exerted, proportional to the blade perimeter and to the liquid surface tension .sigma.. This last parameter depends on the liquid, and is constant for a pure liquid, for a given temperature. For surfactant solutions, this parameter depends on the concentration and the age of the surface.
The equation governing the equilibrium of the forces is the following: the solid/liquid wetting angle is equal to zero. So, we have cos .theta.=1. of the blade portion in contact with the liquid. ##EQU1##
This technique is perfectly satisfactory when it deals with the surface tension measuring of a static liquid but raises problems for the surface tension measuring of a flow on a horizontal or slightly inclined plane, the measures being in fact erroneous due to the drag force acting on the blade. This was demonstrated in an Article of R. DEFAY and J. HOMMELEN published in the journal de l'industrie Belge (23, Jun. 1958, pages 597-614). On page 602, paragraph 6, it is mentioned that the ascending and drag forces have always been too important to be able to provide for an even approximative measure of the surface tension.
According to another known method which raises the same problems, the rectangular blade was replaced by a ring.
Thus, it is an object of the present invention to provide a device allowing an experimenter to measure the surface tension of a liquid, particularly adapted to a flow on a horizontal or slightly inclined plane.
SUMMARY OF THE INVENTION
Other objects of the present invention will appear during the detailed following disclosure. The objects of the present invention will be achieved by means of a surface tension sensor for a liquid flow including a means allowing an experimenter to measure a force, and a probe which is brought into contact with the liquid, said probe being hooked to the means measuring the force by means of an appropriate member, said device being characterized in that the probe, at least in its portion being into contact with the liquid, is comprised of a wettable cylinder, the cross section circumference of which does not exhibit any concave portion and whose distance between the cross section isobaricenter and any point on the circumference is less than 3 mm, the ratio between the maximum distance of a point on the circumference to the isobaricenter and the minimum distance of a point on the circumference to the isobaricenter being less or equal to 2.
According to an emb
REFERENCES:
patent: 2756587 (1956-07-01), Doble
patent: 3415109 (1968-12-01), Sucker et al.
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patent: 4437337 (1984-03-01), Fenrick
patent: 4646562 (1987-03-01), Cronan
patent: 4970893 (1990-11-01), Reid
Article re precise measurement of density and surface tension at temps up to 1000.degree. C. Review of Scientific Instruments, vol. 31, No. 1, Jan. 1960, pp. 18-22 Article from the Journal of Physics E. Scientific Instruments.
Bulou Jacques
Raynal Jean-Marie
Eastman Kodak Company
Ruoff Carl F.
Wiggins J. David
Williams Hezron E.
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