Measuring and testing – Volume or rate of flow – By measuring transit time of tracer or tag
Reexamination Certificate
1999-11-09
2001-08-21
Oen, William (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring transit time of tracer or tag
Reexamination Certificate
active
06276217
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring the flow of fluids and more particularly to a method for measuring the velocity of fluid flow or visualizing the distribution (behavior) of a fluid or an intermingled state of two or more different fluids in an engine combustion chamber, a silencer, heat exchanger or the like.
For measurement of the velocity of fluid flow or visualization of the pattern of fluid flow within a confined space such as a pipe for observation of the state of flow, there are known laser Doppler velocimetry (LDV) (using a laser Doppler flowmeter) and particle imaging velocimetry (PIV) (photographing and image processing).
LDV is a method of measuring the flow of a fluid which comprises loading the fluid with tracer particles, projecting two laser beams against the fluid so as to form an interference figure known as “fringe” at the converging point of the beams and observing the scattered light produces as the tracer particles pass through that fringe.
In this method, however, windows of high parallelism (windows whose inner and outer planes are exactly parallel to each other) must be provided for admission of two incident laser beams and, moreover, the inevitable dead angle results in a locality which cannot be observed in the fluid body. Moreover, beyond all else, there is the problem that only the point of convergence of the two laser beams can be observed at a time (point observation).
PIV is a measuring method which comprises loading the fluid with tracer particles, irradiating the fluid using a continuous emission laser or a pulse laser and measuring the velocity of flow or visualizing the distribution of the fluid by photographing and image processing.
Unlike the method comprising the use of converging laser beams, this method does not require windows of high parallelism nor does it have the problem of a non-observable dead angle and permits a broad range of observation in one operation.
However, the scattered light mentioned above includes not only the light originating from the tracer particles, but also the light scattered by interferring objects such as the laser beam incidence window, observation window, pipe wall and suspended dust particles afloat within the pipe.
In actual observation, all of these scattered lights are observed together and the resulting high noise level (low S/N ratio) discourages attempts to measure fluid flows with high accuracy. Particularly when the scattered light from said interfering objects is high in intensity, it is even impossible to track the very tracer particles.
In observing a mixture of two or more fluids for determining the behaviors of the respective fluids or an intermingled state of the fluids, it is impossible to differentially assign the scattered radiations from tracer particles to the respective fluids. Thus, any method observing Mie scattering is not capable of measuring the flow of fluids of this sort. There may be contemplated to vary the size of tracer particles but since there is no perfectly homogeneous laser beam, it is unscrupulous to estimate the size of tracer particles from the intensity of scattered light alone. Moreover, if the size of particles supplied to the fluid is varied, the particle entrainment pattern is also varied. Therefore, the method would not be rewarded with a commensurate benefit.
SUMMARY OF THE INVENTION
Having been brought into being at the above state of the art, the present invention has for its object to provide a new technology for improving the conventional PIV method to reduce the background noise and insure an improved S/N ratio and more particularly a new method of measuring the flow of fluids with greater accuracy which comprises eliminating the scattered light from interferring objects to a large extent and selectively observing the scattered light from tracer particles.
The method of measuring fluid flows according to the present invention comprises loading the fluid to be measured with tracer particles, irradiating the fluid with light and observing scattered light from said tracer particles to measure the velocity of fluid or visualize the distribution of fluid characterized by using fluorescent tracer particles as said tracer particles, irradiating the fluid with exciting light to cause the tracer particles to produce fluorescent emissions and observing the fluid through a filter which does not transmit said exciting light but selectively transmits said fluorescent emissions to thereby permit a virtually selective observation of the fluorescence.
DETAILED DESCRIPTION OF THE INVENTION
When tracer particles are observed through a filter which does not transmit the exciting light but selectively transmits fluorescent emissions induced by said exciting light as mentioned above, the return light from interfering objects such as the light incidence window, dust, pipe wall, etc. is blocked by said filter so that the light observed is mostly the fluorescent emissions from the tracer particles. As a result, the movement of tracer particles can be clearly observed and the flow measurement error can be minimized (a higher S/N ratio can be realized).
The fluid as the object of measurement is not particularly limited and includes, inter alia, air and other gases inclusive of fuel gas and a variety of liquids such as water, liquefied gases and so on.
The term ‘fluorescent tracer particles’ is used herein to mean any of (1) porous tracer particles impregnated with a fluorescent substance, (2) tracer particles manufactured from a composition comprising a particle-forming material and a fluorescent substance and (3) tracer particles which are made of a fluorescent material or doped with a fluorescent substance. These kinds of tracer particles are now described in detail. It should be understood that the fluorescent material which can be used in the present invention is any substance that produces fluorescent emissions of wavelengths different from the wavelength of the exciting light to be used.
(1) Tracer particles impregnated with a fluorescent substance
Porous particles (e.g. porous silica particles) are impregnated with a liquid fluorescent material (e.g. a solution of Rhodamine B in anhydrous alcohol). For this purpose, a vessel is filled with the liquid fluorescent material and the porous particles are immersed for a predetermined time so that the fluorescent material diffuses gradually into the internal voids of the porous particles by capillary action. The positive entrapment of the fluorescent material in the porous particles can be achieved in a reduced time when the air within the vessel is aspirated off with a suitable suction means. The particles saturated with the fluorescent material are than dried and sieved for use as tracer particles. The tracer particles thus obtained are rich in the fluorescent material and high in the quantum yield.
When particles are impregnated with a fluorescent material for use as tracer particles as above, the substrate particles are preferably porous because (1) such particles are highly receptive to the fluorescent material, (2) the impregnated particles are rich in the fluorescent material and high in fluorescent quantum yield so that they can be used for high-velocity fluids (5~20 m/s) and even small-sized particles can be used, and (3) the bulk specific gravity of tracer particles can be decreased.
The void rate of said porous particles is not critical but is preferably about 5 to 95%. If the void rate is less than 5%, the amount of the fluorescent material that can be incorporated will not be large enough for clear observation. On the other hand, if the void rate exceeds 95%, the tracer particles may not have a sufficient mechanical strength.
(2) Tracer particles produced by adding a fluorescent material to a particle-forming material
A typical process for producing tracer particles of this type comprises dripping an aqueous solution containing both the particle precursor and the fluorescent substance directly into an organic solvent or extruding the solution through an emulsification
Hirano Akira
Ippommatsu Masamichi
Nishigaki Masashi
Ohnishi Hisao
Tsujishita Masahide
Jordan and Hamburg LLP
Oen William
Osaka Gas Company Limited
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