Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Vapor pressure
Patent
1983-08-01
1985-04-23
Birmiel, Howard A.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Vapor pressure
356445, G01N 1302
Patent
active
045121834
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of measuring and/or monitoring the surface tension of fluids, in which standing capillary waves are produced on the surface of the fluid by means of an oscillation generator of a known frequency and are optically evaluated.
The surface tension of many organic substances is reduced when they are dissolved in water. This applies for example to alcohols, organic acids and salts thereof. Even small quantities of such substances make themselves clearly noticeable in their effect on the surface tension. Therefore by measuring the surface tension it is possible to determine the presence and the quantity of certain substances in the fluid.
For measuring the surface tension of fluids the capillary wave method is known amongst others (cf. in this connection MULLER-POUILLET, Lehrbuch der Physik, Vol. III/1, pages 548 to 551). In this known method a tuning fork of known period of oscillation has two fine points which dip into the fluid and is used to produce waves on the surface of the fluid which interfere with each other and therefore produce distinct standing waves in their connecting lines. Their length can be determined by means of a microscope with a long focal distance.
With a known frequency and wavelength, the surface tension can be calculated using the formula developed from the theory of capillary waves: ##EQU1## .sigma.=surface tension .chi.=density
A significant disadvantage of this known method lies in the very complicated optical evaluation of the standing capillary waves by means of a microscope.
The object of the invention, therefore, is to avoid this disadvantage and provide a method of the type described in the introduction which is distinguished by its particularly simple operation and is also suitable for automatic monitoring of the surface tension of fluids.
This object is achieved according to the invention by the following features: peripherally by the oscillation generator; the excited circular surface region is altered until a system of circular standing capillary waves is produced; measuring the intensity of light radiation reflected on the surface of the fluid.
The central or peripheral excitation of the circular region of the surface of the fluid used for the measurement (conveniently in a measuring vessel with a circular wall) results at a certain wavelength of the capillary waves in a system of circular standing waves. These occur when the radius of the circular measuring vessel is an integral multiple of half the wavelength.
The occurrence of these circular standing capillary waves can be determined in a simple manner according to the invention by monitoring the intensity of light radiation reflected on the surface of the fluid. At the frequency at which the circular standing capillary waves occur, a minimum defined as a sharp peak is produced in the intensity of the reflected light radiation.
This makes it possible either to monitor the surface tension of the fluid for any deviations from a predetermined original or theoretical value or--after prior calibration of the measuring device--to make a quantitative measurement of the surface tension.
It is a considerable advantage of the method according to the invention that the measurement and/or monitoring of the surface tension of the fluid does not require any complicated optical evaluation of the surface appearance by means of a microscope. The measuring method according to the invention is therefore also suitable for remote measurement or remote monitoring--an invaluable advantage for many applications.
One sphere of application of the method according to the invention is in the monitoring of the purity of water within the framework of environmental protection.
Another technical sphere of application is in the control of the alcohol content in the moistening means in offset printing.
In order to achieve standing capillary waves, the wavelength of the generated waves can be altered according to the invention by altering the frequency of the oscillation generator--whilst keeping the diameter of the excit
REFERENCES:
patent: 3068687 (1962-12-01), Kleine et al.
Birmiel Howard A.
Roskos Joseph W.
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