Coriolis mass flow meter employing non-metallic flow conduit str

Details Coriolis mass flow meter employing non-metallic flow conduit str Coriolis mass flow meter employing non-metallic flow conduit str

1989-12-23

1992-10-27

Goldstein, Herbert

Measuring and testing

Volume or rate of flow

Mass flow by imparting angular or transverse momentum to the...

G01F 184

Patent

active

051579758

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to a Coriolis mass flow meter wherein the flow conduits are fabricated from corrosion and temperature-resistant materials.
In a Coriolis type mass flow meter when fluid flows through an oscillated flow conduit, Coriolis forces are generated. The Coriolis force is represented as a vector product obtained by multiplying together two values--the rotational angular velocity of the conduit around an oscillation axis and the mass flow rate. In addition, the Coriolis force causes tiny displacements or deflections around a deflection axis of the flow conduit which is perpendicular to the oscilation axis.
The twisting torque from the deflections caused by Coriolis force is proportional to both the spring constant of the flow conduit and the twist angle around the deflection axis. Consequently, the mass flow rate is proportional to the twist angle and the spring constant. In a Coriolis flow meter comprising an oscillated flow conduit, any variation in the conduit's spring constant results in an error in the measurement value of the mass flow rate. The spring constant is inversely proportional to the Young's modulus of the flow conduit. Since the Young's modulus varies almost in inverse proportion to the temperature within a certain temperature range, the two phenomena compensate for one another.
2. Background Art
The Coriolis mass flow meters in current commercial use have flow tubes made of resilient metals and are hence susceptible to corrosion. Such corrosion may be caused by acids in flowing fluids which contact the crystal powder field in the conduit's inner surface, which field is created at the time the conduit is fabricated, as for instance, when a metal tube of stainless steel is bent during the fabrication process.
glass or ceramics have reduced susceptibility to corrosion. However, these materials in general have a low bending strength and are easily broken. In mass flow meter structures as described, e.g., in U.S. Reissue Pat. No. 31,450, the stress concentrates in the vicinity of the points at which the conduit is solidly mounted to its support. Consequently, it has been heretofore found by us to be impossible to provide a mass flow meter having long-term durability and stability which is constructed with a non-metallic flow conduit such as one of glass or ceramic material.


DISCLOSURE OF INVENTION

According to the present invention, quartz glass or similar glass, ceramic, or glass-ceramic materials of a low thermal expansion coefficient and a narrow Young's modulus range are used as the material for flow conduits and the meter design is modified to accommodate this change in the conduit material. The flow meters of this invention enable the measurement of the mass flow rate with high accuracy and without temperature compensation, even under markedly varying temperature conditions and at high temperatures. In addition, corrosion resistance can be improved.
The flow meter of the present invention exhibits satisfactory high temperature operability, improved corrosion-resistance and stress relief, and hence is durable. The present invention contemplates the use of flow conduits which are curved as constructed or which exhibit curvature when driven to oscillate, wherein the flow conduits are made of materials such as a special glass, ceramic, or hybrid glass-ceramic having suitable corrosion resistance, thermal expansion coefficient, variation in Young's modulus and appropriate service temperatures.
A flow meter embodiment of the invention was built of fused quartz, the properties of which are shown in Table 1 below. In addition, contemplated materials, examples of which are given, without limitation, in Table 2 below, are characterized by a low thermal expansion coefficient in the order of 0.5.times.10.sup.-7 /.degree. C. for titanium silicate glass, 5.6 to 7.5.times.10.sup.-7 /.degree. C. for silica glasses, 9.0.times.10.sup.-7 /.degree. C. for lithium-aluminosilicate glass-ceramic, 4 to 20.times.10.sup.-7 /.degree. C. for glass-ceramic 9608,

REFERENCES:
patent: 3729982 (1973-05-01), Senda
patent: 4187721 (1980-02-01), Smith
patent: 4217774 (1980-08-01), Agar
patent: 4793191 (1988-12-01), Flecken et al.
patent: 4845989 (1989-07-01), Titlow et al.

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