Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
1999-06-30
2001-12-18
Noori, Max (Department: 2855)
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
C073S861354
Reexamination Certificate
active
06330832
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a casing enclosing a Coriolis flowmeter. More particularly, the present invention relates to a veneer on the outside of the casing that allows the casing to be used in sanitary applications. Still more particularly, the present invention relates to a veneer that encloses a casing and that provides a sanitary and/or corrosion proof surface for the casing.
PROBLEM
It is known to use Coriolis effect mass flowmeters to measure mass flow and other information of materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flowmeters have one or more flow tubes of a curved or a straight configuration. Each flow tube configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending, torsional, radial, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled systems are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a vibrational force to the flow tube. The force causes the flow tube to oscillate. When there is no material flowing through the flowmeter, all points along a flow tube oscillate with an identical phase. As a material begins to flow through the flow tube, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Sensors at two different points on the flow tube produce sinusoidal signals representative of the motion of the flow tube at the two points. A phase difference of the two signals received from the sensors is calculated in units of time. The phase difference between the two sensor signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes.
The flow tubes are typically enclosed in a casing. The casing prevents damage to the flow tubes from outside forces. The casing may also be used to contain material when a flow tube ruptures and may also be used as a spacer to maintain the distance between flanges connecting the flow tube to a pipeline.
It is a problem that customers sometimes require the casing to be made out of sanitary or corrosion resistant material. The casing must be made out of sanitary material that is easy to clean when the flowmeter is used in a system, such as an ingredient delivery system in food processing. The casing must be made of a corrosion resistant material when the flowmeter is inserted into an environment that may contain a corrosive material such as an acid.
In a conventional dual loop Coriolis flowmeter, it is not a problem to make a casing of sanitary or corrosion resistant material. A spacer bears the structural load of the flowmeter to reduce external vibrations and maintains proper spacing between the inlet and the outlet. The loop configuration of the flow tubes allows the middle section of the flow tube to expand outward and inward to account for expansion and contraction. Thus, the casing must have enough space between the casing and the tube to allow expansion and contraction of the flow tube. For these reasons, the casing and spacer may be made from or coated with a sanitary material in order to provide a sanitary surface for the flowmeter.
However, it is a problem to make a casing out of sanitary or corrosion resistant material for a straight tube Coriolis flowmeter. In a straight tube flowmeter, the casing and spacer are combined and provide the same function of bearing the structural load of the flowmeter. As the flow tube heats up and expands, the length of the flow tube increases because the straight tube must expand radially and axially.
The casing will be subjected to the same net axial loading of the flow tube, although the axial loading of the casing will be opposite in sign to that of the flow tube. However, the stress on the flow tubes will be much greater than the casing due to its smaller cross section. Therefore, the axial expansion of the flow tube is a problem because the casing is affixed to the flow tube at the ends of the flow tube and if the casing does not expand at the same rate as the tube, the flow tube will be subjected to stresses that will damage the integrity of the flow tube.
One solution may be to make the casing and the flow tube out of the same sanitary and corrosion resistant material. However, the cost of a corrosion resistant material such as titanium is prohibitive. Therefore, there is a need to make a casing that can withstand the stress applied by the thermal expansion of dissimilar metals while being cost efficient to produce. This will allow less expensive straight flow tube Coriolis flowmeters to be produced.
SOLUTION
The above and other problems are solved and an advance in the art is made by the provision of a casing for a Coriolis flowmeter enclosed in a veneer of sanitary or corrosion resistant material. For purposes of this invention, a veneer is a layer of material that encloses or is layered onto a surface of a casing to cover the material of the surface. The veneer of this invention allows a casing to carry the structural load of a flowmeter while a function of providing a sanitary surface is accomplished by the veneer.
A first advantage of this invention is that the use of a veneer of sanitary or corrosion resistant material to enclose the casing reduces the amount of sanitary or corrosion resistant material needed to produce a Coriolis flowmeter which reduces the cost of production. The amount of sanitary material needed is reduced because the casing does not have to be made of sanitary or corrosion resistant material. A second advantage is that the casing material may have a coefficient of thermal expansion that is substantially equal to the flow tube. Therefore, expansion and contraction of the casing and flow tube occur at substantially the same rate which reduces structural stress caused by thermal expansion.
The casing of this invention is constructed in the following manner to provide the above advantages. A casing encloses a flow tube of a Coriolis flowmeter. The casing is affixed to the opposing ends of the flow tube. The outer surface of the casing is enclosed by a veneer. The veneer is affixed to case ends made of a material having substantially the same properties as the veneer material to allow affixing. Further expansion and contraction of the veneer may be independent of the expansion and contraction of the casing.
In order for the expansion and contraction of the veneer to be independent of the expansion and contraction of the casing, there may be a space defined by a gap between an inner surface of the veneer and an outer surface of the casing. The space allows the casing to expand and contract freely inside the veneer.
Alternatively or in conjunction with the gap, a veneer may have bellows around the perimeters of opposing ends of the veneer. Bellows are bends in the surface veneer which may bent as the material of the veneer expands and may be pulled straight as the veneer contracts.
The gap between the veneer and the outer surface of the casing may be filled with insulation. The insulation keeps the temperature of the flow tube more uniform. The gap could also house heating elements that provide a heating jacket for the flow tube. Another possibility is that steam or other fluid could flow through the gap to regulate the temperature of the flow tube. All of these alternatives could be used to reduce axial stress on the flow tube due temperature gradients through the flow tube.
REFERENCES:
patent: 4823614 (1989-04-01), Dahlin
Normen David F.
Overfeldt Michael Leon
Chrisman Bynum & Johnson, P.C.
Micro Motion Inc.
Noori Max
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