Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Patent
1989-09-21
1990-12-11
Goldstein, Herbert
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
137826, 137833, G01F 120
Patent
active
049761552
DESCRIPTION:
BRIEF SUMMARY
This invention relates to flowmeters and flowsensors of the type utilising a fluid oscillator so arranged so that the frequency of oscillation is indicative of the flow rate being measured or indicated.
One such flowmeter is disclosed in GB-A-1 593 680 in which fluid flows through a nozzle on the centre line of a chamber which is divided by a splitter on its centre line and a C-shaped member divides each half of the divided chamber into an outer passage and a central region. If the jet from the nozzle passes on one side of the splitter facing the nozzle, it will flow into the outer passage which forms a feedback loop on that side of the chamber to arrive in a transverse direction across the mouth of the nozzle, thus urging fluid emerging from the nozzle towards the other side of the splitter so that the fluid flow then switches to the other half of the chamber. The frequency of switching is a function of the rate of flow. Transducers in the feedback conduits sense the pressure and flow perturbations to give an indication of the volumetric flow rate. All the components so far described lie in a common plane, but outlets from each of the central regions extend out of the plane to a common outlet from the device.
In GB-A-1 593 680 the chamber is divided by an approximately V-shaped splitter with a sharp apex. The apex of the splitter and the apices of the wall dividing the feedback and output channels are all at the same distance from the nozzle. The outlet conduits are separated from the splitter by the feedback channels. This is important, since as the jet deviates from the centre line of the apparatus, the first channel it passes into is the feedback channel. If the feedback channel is separated from the splitter by the outlet channel, the main flow variation from the jet will first affect the outlet and the device will be less sensitive than if the feedback channel is defined by the splitter side wall. Another parameter which affects sensitivity is the length of the feedback channel, and here it is long because it has to pass right around the outlet channel.
We have found that the relative positions of the apices of the splitter and the walls separating the feedback and output channels are important. The distance between the splitter and the apices between the outlet and feedback channels measured along the centre line of the meter from the mouth of the nozzle is preferably between 1 and 4 times the width of the nozzle. We have found that this last range gives greatest sensitivity at the lowest Reynolds numbers coupled with uniformity of response for different Reynolds numbers. The distance from the apices between the outlet and feedback channels measured along the centre line of the meter from the mouth of the nozzle is preferably between 5.6 and 12.0 times the width of the nozzle.
An optional feature of the invention is the passage of the feedback channels out of the common plane as mentioned above and back to that plane again. This enables the outlet conduits to remain in the common plane while passing from the inside to the outside of the feedback loop, and to join up into a single outlet conduit beyond the splitter while still in that plane. With this arrangement the feedback channels can run on either side of a differential pressure transducer whose output will give an indication of the frequency of variation of the flows. Another dimension which affects the sensitivity is the length of the feedback channels--the shorter they are the greater the sensitivity, and directing the channels out of the common plane enables them to be shorter than channels which have to extend around the outlet channels in the common plane. This arrangement also facilitates bleeding air from the feedback channels.
We have found from considerable experimentation that a vortex forms in the volume in front of the splitter. The direction of rotation of this vortex changes as the fluid changes direction in moving between the sides of the splitter. Another optional feature of the present invention encourages the formation and sta
REFERENCES:
patent: 3605778 (1971-09-01), Metzger
patent: 3802283 (1974-04-01), Bahrton
patent: 4085615 (1978-04-01), Haefner et al.
patent: 4838091 (1989-06-01), Markland et al.
Goldstein Herbert
Sontex, S.A.
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