Optics: measuring and testing – With plural diverse test or art
Patent
1999-08-17
2000-10-31
Evans, F. L.
Optics: measuring and testing
With plural diverse test or art
356372, 356379, G01B 1100, G01N 2100
Patent
active
061410888
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a method and apparatus for characterizing a modification in time of the state of condensation of liquid droplets on a target.
The method and apparatus of the invention namely allow for measuring the condensation or evaporation of droplets on the target. They also allow for measuring the parameters ruling the condensation of the droplets.
The fields of application of the invention are widely varied. By way of example, the invention can be used advantageously in the biological field for checking the state of sterilization of a surface by measuring the condensation of a germicide. In fact, it allows for determining whether the germicide is present on a surface for a sufficient time and in sufficient quantity for sterilizing it.
The invention can also be used in the field of meteorology, e.g. for measuring the characteristics of dew. It may also serve for determining the appropriateness of a preventive treatment of certain plants subject to cryptogamic diseases due to the presence of dew.
Furthermore, the invention can be used advantageously for measuring the condensation of water in dune sand.
STATE OF THE ART
For characterizing the state of condensation of liquid droplets on a target, at present, essentially two parameters are being used, which are the measure of the dew temperature and the measure of the condensed liquid mass.
In fact, a number of optical sensors, capable of determining the dew temperature for a target, and consequently the ambient vapor tension, are known. On this subject, we refer to document (1), the reference of which is mentioned at the end of this specification.
The principle for determining the dew temperature for a given substance is based on the measure of the reflection or transmission of a light beam by a plane target substrate whose temperature is lowered. When the substrate has reached the so-called dew temperature, condensation of the substance's droplets on the target occurs. The reflection or transmission of the light beam is then almost nil.
However, it can be noticed that the measured temperature at which the condensation phenomenon (dew) occurs always exceeds the dew temperature corresponding to a homogeneous condensation. This discrepancy is due to the fact that the contact angle of the condensation droplets on the target surface never equals 180.degree..
Also, apparatuses for measuring the dew temperature are known, wherein the target is designed so that the reflection of a light beam thereon is almost nil in the absence of droplet condensation.
The dew temperature is then determined by lowering the target's temperature and measuring it when the reflection of the light beam goes from zero to a non zero value due to the formation of a film of condensed liquid.
On this subject, we refer to document (2), the reference of which is mentioned at the end of the specification.
The second known method for determining the state of condensation consists in measuring the mass of the condensed liquid. This method, as described in document (3), the reference of which is mentioned at the end of the specification, is widely used in agricultural meteorology. In accordance with this method, a substrate, as condensation target, is weighed before, during and after condensation.
According to a variant, it is also known to sample part of the condensed liquid with a paper towel and to weigh this towel.
The techniques set forth above are not easy to implement and only provide little information on the condensation building up on the target.
In fact, as shown in document (4), the reference of which is mentioned at the end of this specification, the droplets formed through condensation may be characterized by other magnitudes and namely by their contact angle to the target surface.
SUMMARY OF THE INVENTION
It is an objective of the invention to provide a method and apparatus for determining the state of condensation of a liquid on a target, without the restrictions of the methods previously described, and allowing to establish, if required, a larg
REFERENCES:
Langmuir, 1995 11, "From Droplet Growth to Film Growth on a Heterogeneous Surface Condensation Associated with a Wettability Gradient", Hong Zhao and Daniel Beysens.
Optics Communications, vol. 91, No. 1/02, 1 Juillet 1992, pp. 5-8, XPOOO278055, "Determination of the Dew Point Using Laser Light and a Rough Surface," Shigeaki Matsumoto et al.
Sensors and Actuators A, vol. A42, No. 1/03, 15 Avril 1994, pp. 503-507, XPOOO449970 "Hygrometer with Fibre Optic Dew Point Detector," Jachowicz R S et al.
Bulletin du Bnm, n 89, Juillet, 1992, "Exploitation Statistique Des Resultats D'Etalonnage Des Hygrometres a Condensation a Detection Optique," B. Cretinon and L. Morin.
Agricultural and Forest Meteorology, 62 (1992) 263-274, "Estimating Dew Duration on Banana and Plantain Leaves from Standard Meteorological Observations," Jean-Paul Lhomme and Francisco Jimenez O.
Beysens Daniel
Marcos-Martin Maria
Nikolayev Vadim
Sibille Patrick
Commissariat a l''Energie Atomique
Evans F. L.
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