Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Reexamination Certificate
2000-05-09
2002-07-02
Hellner, Mark (Department: 3662)
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
C073S861050
Reexamination Certificate
active
06414748
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for measuring the flow of fluids, herein after referred to as “flow measurement”. It should, however, be understood that the term “flow meausrement” as used throughout this specification means not only a measurement of the flow-velocity of a gas, such-as air, fuel gas, etc., or a liquid, such as water, liquefied gas, etc., but also a topological visualization of the distribution of such gas or liquid.
BACKGROUND OF THE INVENTION
Prior Art
The particles heretofore used as tracer particles in optical flow measurements are porous particles made of SiO
2
, TiO
2
, SiC or the like which are obtainable by a coprecipitation process or from a natural material such as the mineral ore. These particles generally have a mean particle diameter of about 0.5 to 150 &mgr;m.
In a measurement of the flow velocity using a laser device such as a laser Doppler velocimeter, a phase Doppler velocimeter or the like, tracer particles somewhere between 0.5 and 10 &mgr;m in mean diameter, in particular, have so far been employed.
In technologies involving a visualization of a flowing fluid by photographing the distribution of tracer particles in the fluid with the aid of an instantaneous, powerful light source, such as a flash-light or a pulse laser, and a determination of the flow pattern from the resulting picture, particles somewhere between about 5 &mgr;m and about 150 &mgr;m in mean diameter are generally employed.
Electron microphotographs of the representative tracer particles which are conventionally employed are presented in
FIGS. 3 through 14
; viz. white carbon in
FIGS. 3 and 4
, TiO
2
in
FIGS. 5 and 6
, talc in
FIGS. 7 and 8
, TiO
2
-talc in
FIGS. 9 and 10
, particles from kanto loam, and white alumina in
FIGS. 13 and 14
.
However, as apparent from these microphotographs, the conventional tracer particles have the following drawbacks, 1) through 5), which amplify the measurement error.
1) Because the tracer particles are morphologically not uniform, the sectional area of scattered light to be detected varies according to the real-time orientation of each particle.
2) Because the particle size distribution is broad and the sectional area of light scattering varies with different individual particles, the comparatively large particles scatter light in two or more fringe at a time.
3) Because the apparent specific gravity of the particulate tracer differs markedly from that of the fluid to be measured, the particles do not faithfully follow the on-going flow of,the fluid.
4) Because the particle size distribution is broad and the apparent specific gravity also has a distribution, the particles follow the fluid flow with varying efficiencies to prevent accurate quantitation of the flow measurement.
5) Because the surface of the particle is irregular, the individual particles tend to be concatenated with each other to increase the effective particle size.
The technique used generally for launching tracer particles into a fluid comprises either extruding tracer particles from a screw feeder and driving them into the body of the fluid with the aid of an air current or suspending tracer particles in a solvent and ejecting the suspension in a mist form using an ultrasonic humidifier. In any of the above methods, the rate of feed of the tracer particles is not constant so that the accuracy of flow measurement is inevitably sacrificed.
OBJECTS OF THE INVENTION
It is the object of the present invention to overcome the above-mentioned drawbacks and provide a method of flow measurement with improved accuracy.
SUMMARY OF THE INVENTION
The method of flow measurement according to the invention comprises measuring the flow of a fluid using an optical instrument and a porous particulate ceramic tracer, the diameter of which is 0.5 to 150 &mgr;m.
In another aspect, the method of flow measurement according to the invention comprises feeding a non-agglomerating particulate tracer to an optical instrument, such as a laser device, from a measuring wheel particle feeder.
The method of flow measurement according to the invention comprises measuring the flow of a fluid using an optical instrument and a porous particulate ceramic tracer, said porous particulate ceramic tracer consisting of spherical particles having a diameter of 0.5 to 150 &mgr;m. Particularly in the method of measuring the flow velocity using a laser instrument such as a laser Doppler velocimeter, spherical ceramic particles having a diameter of 0.5 to 10 &mgr;m are preferred from the viewpoint of relation with fringe. A more satisfactory spherical particle diameter range is 1.5 to 2.5 &mgr;m. In flow measurement which involves photographing, the use of spherical particles having a diameter of 5 to 150 &mgr;m is preferred from the viewpoint of detecting light and flowing the fluid flow. A more satisfactory particle diameter range is 30 to 100 &mgr;m.
When the tracer particles for use in flow measurement with an optical instrument are spherical as in the invention, the sectional area of scattered light to be detected by a photosensor or the like is constant regardless of the orientation of particles at the moment of detection. Moreover, because such particles have no surface irregularities that may cause concatenation, it does not happen that two or more tracer particles flow as concatenated through the body of the fluid. Therefore, the accuracy of flow measurement is improved.
Where the fluid to be measured is a gas, said tracer particles are preferably of hollow structure.
When the tracer particles are hollow, the specific gravity of the particles is so low that even if the particle size is not critically uniform, they may. readily follow the gas flow. Therefore, the accuracy of gas flow measurement is improved. The improved accuracy of measurement afforded by such hollow spherical particles over that attainable with solid spherical particles is more remarkable when the flow rate of the fluid is high.
The shell thickness of such hollow spherical particles is not so critical but is preferably in the range of one-third to one-tenth of the diameter of the particle. If the shell thickness is less than one-tenth of the particle diameter, the particles tend to be collapsed in use. Conversely when the shell is thicker than one-third of the particle diameter, the advantage of the hollow structure will not be fully realized.
Where the fluid to be measured is a liquid, said tracer is preferably a porous particulate ceramic tracer having closed pores with a porosity of not less than 0.1 cm
3
/g.
When the tracer particles have closed pores with a porosity of not less than 0.1 cm
1
g, the specific gravity of the tracer particles can be changed so as to minimize the differential from the specific gravity of the fluid to be measured, thereby making it easier for the particles to follow the dynamics of the fluid. In this manner, the accuracy of flow measurement can be further improved.
Where the fluid to be measured is a liquid, tracer particles coated with a metal are used with advantage.
When such metal-clad porous spherical particles are used for the flow measurement of a liquid, the intensity of reflected light is greater than it is the case when bare particles are employed so that the accuracy of flow measurement is improved. However, since such metal-clad particles are higher in specific gravity and expensive, they are preferably used where the conditions of measurement specifically call for the use of such particles.
Particularly preferred are metal-clad porous ceramic tracer particles having closed pores with a porosity of not less than 0.1 cm
3
/g. Application of a metal cladding increases the specific gravity of particles as mentioned above but the adverse effect of increased specific gravity can be minimized by using porous ceramic particles having closed pores with a porosity of not less than 0.1 cm
3
/g.
For application of a metal cladding, any of the electroless plating, electrolytic plating, CVD, vapor deposition and other techniques can be utilized but the electroless plating process
Hirano Akira
Ikeda Yuji
Ipponmatsu Masamichi
Nakajima Tsuyoshi
Nishigaki Masashi
Hellner Mark
Osaka Gas Company Limited
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