Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
2000-12-22
2002-11-05
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
active
06474175
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a mass flowmeter operating by the Coriolis principle and incorporating a straight Coriolis measuring tube through which flows a fluid or medium, at least one oscillator associated with and exciting the Coriolis measuring tube, and at least one detector associated with the Coriolis measuring tube for capturing the Coriolis force values and/or the Coriolis-force-induced oscillations.
The above description states that the mass flowmeter discussed incorporates, inter alia, at least one oscillator “associated” with the Coriolis measuring tube, and at least one detector “associated” with the Coriolis measuring tube. It is common for the oscillator(s) or, in any event, part of the oscillator(s) and the detector(s) or, in any event, part of the detector(s) to be directly connected to the Coriolis measuring tube. However, since that is not absolutely necessary, the term “associated” is being used instead of “connected”.
For mass flowmeters operating by the Coriolis principle, one fundamentally distinguishes between those with an at least essentially straight Coriolis measuring tube and those with a looped Coriolis measuring tube. In the case of the mass flowmeters discussed here, one also distinguishes between designs employing only one Coriolis measuring tube and those with two Coriolis measuring tubes. Where two Coriolis measuring tubes are used, these may be connected in-line or positioned parallel to each other for the desired flow path.
In recent times, mass flowmeters with only one, essentially straight, Coriolis measuring tube have gained in popularity. Mass flowmeters operating by the Coriolis principle and equipped with one straight Coriolis measuring tube offer considerable advantages over mass flowmeters employing either two straight Coriolis measuring tubes or one looped Coriolis measuring tube. Compared to mass flowmeters with two straight Coriolis measuring tubes, their main advantage is that they obviate the need for a flow divider and a flow combiner, required in the case of mass flowmeters with two Coriolis measuring tubes. Compared to mass flowmeters employing one looped Coriolis measuring tube or two looped Coriolis measuring tubes, their main advantage lies in the fact that a straight Coriolis measuring tube is easier to manufacture than a looped Coriolis measuring tube, that in the case of a straight Coriolis measuring tube there is less of a pressure drop than in a looped Coriolis measuring tube, and that a straight Coriolis measuring tube can be cleaned more thoroughly than a looped Coriolis measuring tube.
Their advantages notwithstanding, mass flowmeters with only one straight Coriolis measuring tube also have drawbacks. For example, longitudinal expansion due to thermal effects can cause stress patterns in straight Coriolis tubes which, in extreme cases, may lead to mechanical damage to the Coriolis measuring tube, such as stress fissures and breaks. The reason is that in straight Coriolis measuring tubes, unlike for instance looped Coriolis measuring tubes, stress patterns caused by thermal expansion are not absorbed by a varied radius of curvature of the tube.
Another problem, albeit peculiar to all mass flowmeters operating by the Coriolis principle regardless of whether these mass flowmeters employ one Coriolis measuring tube or several Coriolis measuring tubes and regardless of whether the Coriolios measuring tubes are straight or looped, consists in the fact that, depending on the material used for the Coriolis measuring tube(s), chemical substances which would tend to corrode that material cannot be measured in the Coriolis mass flowmeter concerned. This might possibly impose severe limitations on the range of applications of the individual Coriolis mass flowmeter, necessitating the use of a different type of Coriolis mass flowmeter, meaning the replacement of the built-in Coriolis mass flowmeter.
SUMMARY OF THE INVENTION
In view of the above, it is the objective of this invention to provide a mass flowmeter, operating by the Coriolis principle, with one Coriolis measuring tube which displays only minor thermal expansion and corresponding stress patterns while at the same time offering high chemical resistance to corrosive substances.
The mass flowmeter according to this invention which solves the above-mentioned problem is characterized in that the Coriolis measuring tube consist of a ceramic material. A Coriolis measuring tube made from a ceramic material offers the advantage of permitting operation in a very wide temperature range including very high temperatures, displaying only moderate thermal expansion throughout the said wide operational temperature range. At the same time, ceramic materials are not affected, or temperatures, displaying only moderate thermal expansion throughout the said wide operational temperature range. At the same time, ceramic materials are not affected, or barely so, by corrosive substances such as chloric gases or liquids, which opens up a broad spectrum of possible applications for the Coriolis flowmeter according to this invention.
It is basically possible to use virtually any ceramic material for the Coriolis measuring tube in the Coriolis-type mass flowmeter according to this invention. Particular preference, however, is given to ceramic materials with especially high chemical resistance and with a low thermal expansion coefficient. Preferably, then, the Coriolis measuring tube consists of zirconium oxide or aluminum oxide and, according to a particularly preferred embodiment of this invention which allows the use of the Coriolis mass flowmeter for virtually all chemical compounds save for hydrofluoric acid (HF), of zirconium-stabilized aluminum oxide containing in excess of 5% zirconium. As an alternative, the Coriolis measuring tube for the mass flowmeter according to this invention preferably uses nitride ceramics.
The mass flowmeter of this invention, operating by the Coriolis principle, can be structured along essentially any conventional mass flowmeter design employing a single straight Coriolis measuring tube. However, in a preferred embodiment of this invention, a design is used whereby the mass flowmeter is provided with an outer enclosure which features a flange permitting installation in a pipe system. It is particularly desirable in this case to decouple the Coriolis measuring tube from any longitudinal forces in the pipe system in which it is installed. Such decoupling is preferably obtainable by firmly attaching the two ends of the Coriolis measuring tube to the outer enclosure while dimensioning and positioning it in such fashion that the Coriolis measuring tube is slightly set back from the lateral surfaces of the Coriolis mass flowmeter so that, when installed in the pipe system, it does not make direct contact with the latter.
As an alternative, it is also possible to connect only one end of the Coriolis measuring tube to the outer enclosure, allowing the Coriolis measuring tube to be longitudinally moved in relation to the outer enclosure. This approach serves as well to decouple the Coriolis measuring tube from the pipe system with respect to longitudinal forces.
To keep the Coriolis measuring tube in its proper position despite its longitudinal movability, elastic mounts are provided between the faces of the Coriolis measuring tube and the flange of the pipe system in which the Coriolis mass flowmeter can be installed, preferably in the form of O-ring gaskets which serve as an elastic support for the end section of the Coriolis measuring tube that is movable relative to the outer enclosure. In terms of the problem of longitudinal forces which are present in the longitudinal direction of, and bear on, the Coriolis measuring tube, it should be stated that ceramic components offer a certain resistance to longitudinal pressure while longitudinal tractive forces can much more readily lead to problems, meaning damage to the ceramic component. In view of this fact, the measures described above are intended to essentially decouple the Coriolis measuri
Davies Lawrence
Hussain Yousif
Rolph Chris N.
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