Fluid handling – Flow affected by fluid contact – energy field or coanda effect – Means to regulate or vary operation of device
Patent
1996-01-11
1997-06-17
Chambers, A. Michael
Fluid handling
Flow affected by fluid contact, energy field or coanda effect
Means to regulate or vary operation of device
137842, G01F 120
Patent
active
056388675
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a fluidic oscillator and to a flow meter for a fluid, a liquid or a gas, the meter including such a fluidic oscillator.
For several years now, meters have appeared on the market that include fluidic oscillators and that differ from conventional meters having a spinner or a membrane by the fact that they operate without using any moving parts that could wear over time. Such fluidic oscillators may be of small dimensions, and of very simple architecture, and they present very good reliability. In addition, such oscillators deliver a frequency signal which is easily converted into a digital signal, and that is particularly advantageous for reading meters remotely.
A fluidic oscillator that is symmetrical about a longitudinal plane of symmetry is described in French patent application No. 92 05 301 filed by the Applicant, and it includes a fluid inlet provided with an inlet opening of width d. Such an inlet opening enables an oscillating two-dimensional fluid jet to be formed. The fluidic oscillator includes an "oscillation" chamber in which the two-dimension fluid jet can oscillate. The oscillation chamber has walls situated on either side of the longitudinal plane of symmetry and it is connected via a first end to the fluid inlet opening, and via a second end, remote from the first, to a fluid outlet opening. The fluid inlet and outlet openings are both in alignment on the longitudinal plane of symmetry. The fluidic oscillator also includes an obstacle housed in the oscillation chamber, thus co-operating with the walls thereof to form lateral passages that are symmetrical about the longitudinal plane of symmetry so as to enable the fluid to flow towards the downstream end of the fluidic oscillator. The obstacle possesses a front portion and a rear portion, the front portion being provided with a cavity disposed facing the fluid inlet opening. The rear portion is situated facing the fluid outlet opening and it possesses an end which co-operates with said fluid outlet opening to define an empty space into which there open out the passages for allowing the fluid to flow towards the downstream end of the fluidic oscillator.
Thus, the fluid jet penetrates into the oscillation chamber via the inlet opening and it sweeps over the walls of the cavity, thereby having the effect of forming eddies on either side of said fluid jet and facing the front portion, which eddies alternate between being strong and weak, in anti-phase with the oscillation of the jet.
Flow rate is measured, for example, by detecting when the bottom of the cavity is swept over by the jet as it oscillates, with the frequency of oscillation of the jet being proportional to the flow rate of the fluid.
Fluid flow is thus exhausted towards the downstream end of the fluidic oscillator in alternation, i.e., more precisely, it passes towards the empty space and the outlet opening alternately via each of the passages disposed on either side of the obstacle.
A factor K is then defined which is equal to the ratio of frequency of oscillation of the jet to the fluid flow rate Q, and it is assumed, for example, that a fluidic oscillator used in a commercial gas meter is linear over a range of flow rates extending from 0.6 m3/h to 40 m3/h so long as relative variations in its factor K are smaller than .+-.1.5%.
For any given fluidic oscillator, its linearity is determined, as shown in FIG. 1, from a "calibration" curve of relative variations in its factor K as a function of Reynolds number Re (where Re is equal to the speed of the fluid at the inlet opening of the oscillation chamber multiplied by the width of said opening and divided by the dynamic viscosity of said fluid).
FIG. 1 shows that from a certain value of Reynolds number Re, the calibration curve no longer lies within a range corresponding to relative variation in the factor K of less than .+-.1.5%, which means that the fluidic oscillation in question is considered as being non-linear.
On each half-period of the oscillating phenomenon, the fluid flow that has taken on
REFERENCES:
patent: 4854176 (1989-08-01), Okabayashi
patent: 5181660 (1993-01-01), Stouffer et al.
patent: 5363704 (1994-11-01), Huang
Chambers A. Michael
Pojunas Leonard W.
Schlumberger Industries S.A.
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