Measuring and testing – Volume or rate of flow – Using turbine
Patent
1997-06-16
2000-01-04
Patel, Harshad
Measuring and testing
Volume or rate of flow
Using turbine
7386177, 454 3, 454229, 416223R, G01F 105, F23J 1308, B63H 126, F24F 7007
Patent
active
060097639
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a flow sensor, in particular suitable for use in air flow measuring, comprising an impeller suspended for free rotation in a tube section.
With known flow sensors of the above-mentioned type, a fan impeller is for instance used as impeller, arranged in a tube section so as to be freely rotatable therein. The rotations of the impeller are measured, whereupon the flow rate through the tube section is determined with some precision. With the known flow sensors, the relation between a measured speed and the flow rate through the tube section is not linear and moreover depends on the pressure drop over the measuring system. In particular at low speeds and small flow rates, and at great pressure differences over the tube section, a highly deviant behavior may be created.
A fan impeller is designed so that a rotation energy can thereby be converted into an air movement. The number of blades and the blade configuration of the fan impeller are selected to that end. When such a fan impeller is employed as a freely rotating fan impeller, i.e. a fan impeller not driven by means of a motor or a like means, the relation between the rotary speed and the flow rates through the surface covered by the impeller will deviate substantially from a linear relation, in particular at low speeds and/or great pressure differences between the two sides of the impeller, and will moreover be directly dependent on the pressure difference over the tube section.
At low speeds and great pressure differences, air will be led back through the impeller, the so-called back-flow, which causes the rotary speed of the impeller to be changed at a constant flow rate, for instance as a result of an adjacently disposed ventilating fan. Moreover, a fan impeller typically causes strong air turbulences, which also causes the action of the flow sensor to be adversely affected. This means that such flow sensors have a poor measuring characteristic, in particular at low flow rates, and that these known flow sensors are in particular not pressure-independent.
The object of the invention is to provide a flow sensor of the type described in the opening paragraph, wherein the drawbacks mentioned are avoided while the advantages are maintained.
The blade angles of the different cross sections of the blades of the impeller of the flow sensor according to the invention provide a flow sensor having an almost pressure-independent measuring characteristic within the measuring range of the flow sensor. The calibration combination to be referred to as design couple, consisting of a calibration flow rate and a calibration speed can be selected so that this measuring characteristic can readily be adapted to the measuring means and further means, if any, for the processing of the registered speeds of the impeller during use. The characteristic, given according to the invention, of the curve of the blade angles over the blades of the impeller offers the advantage that, starting from a design couple suitable for the desired use and from a suitable tube section diameter, a substantially pressure-independent flow sensor can always be obtained, i.e. for any application a flow sensor can be designed having a substantially linear measuring characteristic, which measuring characteristic comprises at least the design couple selected. Owing to its construction, in particular in combination with a suitable material selection, the flow sensor is suitable for use in dusty and corrosive environments, at strongly varying temperatures and at different humidities. The flow sensor can be used for gas flow measurement, but is also suitable for use in fluid flow measurement.
A flow sensor according to the invention is in particular suitable for use in industrial, agricultural and civil utilizations in respect of air conditioning, process control, emission control, emission measurement in practical circumstances and the like.
When a flow sensor with a freely-rotating impeller is used, it is important that the speed of the impeller during use remains within given limi
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Berckmans Daniel Albert
Goedseels Victor
Jansen Gijs
Vranken Erik Joannes
Fancom B.V.
Patel Harshad
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