CN101858764B - Coriolis mass flowmeter - Google Patents

Abstract

The invention provides a Coriolis mass flowmeter, comprising a measuring tube capable of rotating around a rotation axis and a pair of vibrating sensors; wherein the measuring tube is made by metal glass, the measuring tube is provided with an inlet straight tube section which is coaxial with the rotation axis and guides the fluid to be measure to flow in, an outlet straight tube section which is coaxial with the rotation axis and guides the fluid to be measured to flow out as well as a curved tube section which is arranged between the inlet straight tube and the outlet straight tube and is communicated with the two; and the vibrating sensor is arranged at the two ends of the curved tube of the measuring tube. The mass flowmeter of the invention has high sensibility and can be applied to mass flow measuring in small flow or in large flow regulating range.

Description

Coriolis mass flow meter

technical field

The present invention relates to a kind of flowmeter, is used for measuring the mass flow rate of fluid, specifically, relates to a kind of Coriolis flowmeter with very high sensitivity, it can measure the mass flow rate of very small flow rate, or in the flow adjustment range Measure flow in very large cases.

Background technique

In the pharmaceutical, food and other industrial fields, it is very important to determine the flow in the pipeline for the monitoring, control and production of the process. The mass flow in pipelines is usually measured by flowmeters. The flowmeters commonly used in closed pipeline systems can be divided into electromagnetic flowmeters, ultrasonic flowmeters, matrix flowmeters and Coriolis flowmeters.

Coriolis flow meters have many advantages over other flow meters. First, it can measure mass flow very accurately by a direct method, while other types of flow meters can only measure volume flow and require additional calculations to convert to mass flow. In addition, Coriolis flow meters can be used for the measurement of almost all kinds of fluids, such as liquids, gases, slurries and mixed phase fluids. Finally, the measurement principle of the Coriolis flowmeter has nothing to do with the physical properties of the fluid, it will not be affected by the pressure, density and temperature changes of the fluid. Therefore, Coriolis flowmeters are widely used in various fields.

A typical Coriolis flowmeter includes a measuring tube for measuring fluid and a drive head for vibrating the measuring tube at the resonant frequency of the measuring tube. When the measuring tube vibrates, the mass of the fluid hits the wall of the measuring tube, generating Coriolis force, which causes the measuring tube to deform elastically. The movement of multiple measuring tubes amplifies the deformation to calculate the Coriolis force and thus the mass flow rate of the fluid.

One problem with this type of Coriolis flow meter is that the sensitivity of the measurement cannot be significantly improved. Most of the measuring tubes are made of stainless steel or Hastelloy. These metals have limited elasticity, so it is difficult to further improve the sensitivity of the measurement. In addition, the shape of the measuring tube is usually U-shaped or S-shaped. Although such a shape can increase the elastic deformation of the measuring tube caused by the Coriolis force, it is also easy to cause the fluid to flow to the welded elbow or shunt Pressure loss, resulting in reduced measurement accuracy. In this kind of flowmeter, it is very difficult to comprehensively consider the sensitivity and accuracy of measurement when designing the shape of the measuring tube.

Another problem with current Coriolis flowmeters is the design for vibrations in the measuring tube. As a fluid carrier, the measuring tube will bend when subjected to vibration, which means that the measuring tube must have sufficient thickness and strength to withstand the fluid pressure and the fatigue of the measuring tube material. On the other hand, the measuring tube is measured by elastic deformation, so the tube wall of the measuring tube should be as thin as possible, so that it can produce a significant deformation under the action of Coriolis force. Obviously, these two conflicting requirements also limit the improvement of measurement sensitivity.

Due to the above problems, the current Coriolis flowmeter is not suitable for the following occasions:

Measure the gas flow with a wide adjustment range in the petrochemical industry (that is, the ratio of the maximum flow to the minimum flow>2000:1), the gas flow in the pipeline can vary from 4 g/min to 8 kg/min;

Measure the mass flow rate of liquids and gases with very low flow rate (flow rate <50 g/min), such as chemical vapor deposition (CVD) and physical vapor deposition (PVD) in the semiconductor industry, product development and laboratory analysis in the pharmaceutical industry.

As the core component of the Coriolis flowmeter, the measuring tube plays a decisive role in the performance of the flowmeter. In recent years, efforts have been made to design measuring tubes of different shapes to improve the performance of flowmeters.

A Coriolis flowmeter is disclosed in US 6684716 B2, and Figure 1 shows a typical structure of this type of flowmeter. This flowmeter comprises a straight measuring tube 71 and two straight rods 72a and 72b positioned on both sides of the straight tube in parallel, the measured fluid flows through the measuring tube 71, and the measuring tube 71 and the straight rod 72a are driven to vibrate by a vibration generator 73a , another vibration generator 73b drives the measuring tube 71 and the straight rod 72b to vibrate on the other side, and the vibration frequencies of the measuring tube 71 and the straight rods 72a and 72b are the same. The ends of the measuring tube 71 and the ends 72a and 72b of the two straight rods are fastened to common support blocks 74a and 74b. Vibration sensors 75 a and 75 b are provided on both sides along the straight pipe direction to detect the amount of deformation of the measuring pipe 71 .

Although this structure is simple, compact and robust, the measurement sensitivity of this straight tube Coriolis flow meter is not high. In the state of resonance, the measuring tube can only produce a small bend. When the fluid flows through the straight tube, the Coriolis force generated in the direction perpendicular to the straight tube is very small, and the deformation of the measuring tube is also very small. Therefore, it is necessary to optimize the structure of the measuring tube to increase the range of deformation of the measuring tube.

US 2007/0034019 A1 discloses another type of Coriolis flowmeter, as shown in Figure 2, it has a curved measuring tube 81, and the electromagnetic excitation coil 83 is fixed below the center 82 of the front end of the U-shaped measuring tube 81 , to drive the measuring tube to vibrate slightly. As shown in Figure 2, fluid flows in from the left and flows out from the right, creating opposing Coriolis forces on both sides, twisting the U-shaped measuring tube. At the bend, the force of the fluid is concentrated, so the vibration of the measuring tube is amplified, and the two measuring coils 84 arranged on the left and right measure the resulting deformation.

The above-mentioned existing Coriolis flowmeters are all designed based on the vibration of the measuring tube. In order to meet the requirements of bearing fluid pressure, the measuring tube needs to have sufficient strength, so it should not be made too thin, but this affects the measurement Increased sensitivity. In order to solve the design problem of measuring tube vibration, US 5728951 A proposes a rotary type Coriolis flowmeter, as shown in Figure 3, which has a phase measuring rotor system with an outer rotor 91, A coaxial inner rotor 92 (also called a Coriolis rotor) and an elastic torsion bar 93 , the elastic torsion bar 93 is connected with the outer rotor 91 and the inner rotor 92 . The mass flow rate of the passing flow can be determined by measuring the rotational displacement between the outer rotor 91 and the Coriolis rotor 92 . However, the structure of the measuring tube of this flowmeter is complicated, and the design of the fluid flow divider will also cause the pressure loss of the fluid, thereby causing measurement errors.

Contents of the invention

Therefore, the purpose of the present invention is to provide a Coriolis mass flowmeter that can overcome the above disadvantages, specifically to provide a Coriolis flowmeter with high sensitivity.

Another object of the present invention is to provide a durable Coriolis flowmeter that can reduce external influences on measurement accuracy.

To achieve the above object, the present invention provides a Coriolis mass flowmeter, comprising a measuring tube rotatable around a rotating shaft and a pair of vibration sensors, the measuring tube is made of metallic glass, the measuring tube has: A section of inlet straight pipe coaxial with the rotation axis for the measured fluid to flow in, a section of outlet straight pipe coaxial with the rotation axis for the measured fluid to flow out, and a section between the inlet straight pipe and the outlet straight pipe and communicated with both Arc bend pipe; the vibration sensor is arranged at both ends of the arc bend pipe of the measuring tube.

Another Coriolis flowmeter according to the present invention further includes an arc rod, which is axially symmetrical with the arc bend of the measuring tube in the same plane along the rotation axis, and the arc The two ends of the rod are respectively fixed on two supporting blocks with the measuring tube.

Another Coriolis flowmeter according to the present invention, wherein a motor drives the measuring tube to rotate around the rotation axis, and the rotor of the motor clamps the inlet of the measuring tube directly at the inlet end of the measured fluid or at the outlet end of the measured fluid. Pipe or outlet straight pipe, the stator of the motor is fixed on the housing of the flowmeter.

Still another Coriolis flowmeter according to the present invention, wherein the housing of the flowmeter supports the measuring tube at the measured fluid inlet end and the measured fluid outlet end of the measuring tube through bearings, respectively.

Still another Coriolis flowmeter according to the present invention, wherein the metallic glass for manufacturing the measuring tube is zirconium (Zr)-based metallic glass.

The measuring tube of the Coriolis flowmeter of the present invention is made of metallic glass. Because the metallic glass has high strength, high elasticity and good mechanical properties, it can be manufactured with better performance than existing stainless steel or Hastelloy. measuring tube. In addition, since the measuring tube also has an arc-shaped bend, a large Coriolis force can be generated when the fluid flows through the arc-shaped bend, and the two vibration sensors arranged radially symmetrically can increase the measured The variable amplitude, so this flowmeter of the present invention has very high measurement sensitivity.

In addition, since the measuring tube of the metallic glass of the present invention does not need to be welded, the pressure loss of the measuring tube caused by welding is eliminated, and the measurement accuracy is ensured.

In order to further improve the measurement accuracy, an arc-shaped rod that can balance the measuring tube is provided in one embodiment of the present invention, which can reduce the external vibration received by the measuring tube when it rotates.

In the present invention, the stator of the rotating motor is fixed on the casing of the flowmeter, and the rotor clamps the straight part of the measuring tube, which can eliminate the bending and twisting of the measuring tube and greatly reduce the possibility of breaking the metallic glass measuring tube , Improve the reliability of the flow meter used.

Description of drawings

The following drawings only illustrate and explain the present invention schematically, and do not limit the scope of the present invention. in:

Fig. 1 is the structural representation of a kind of existing Coriolis flowmeter with straight pipe;

Fig. 2 is a three-dimensional schematic diagram of an existing Coriolis flowmeter with a U-shaped tube;

Fig. 3 is a structural schematic diagram of an existing rotary Coriolis flowmeter;

Fig. 4 is the schematic diagram of a kind of rotating measuring tube in the Coriolis flow meter of the present invention;

Fig. 5 is a structural representation of a Coriolis flowmeter of the present invention;

Figure 6 is a distribution diagram of mechanical properties of steel, titanium alloy, wood, polymer and metallic glass;

Fig. 7 has represented the distribution curve of the distortion that produces because of Coriolis force along the measuring tube length direction shown in Fig. 4 of the present invention;

Figure 8 shows the difference in sensitivity between a metallic glass measuring tube and a stainless steel measuring tube when measuring flow.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation manners of the present invention will now be described with reference to the accompanying drawings, in which the same symbols represent the same parts.

Figure 4 shows the working principle of the Coriolis flowmeter using the rotating measuring tube of the present invention. As shown in FIG. 4 , the measuring tube 1 includes a section of straight inlet pipe 11 , a section of straight outlet pipe 12 and a section of curved curved pipe 13 . A stream of fluid with mass m flows in from the inlet end of the straight inlet pipe 11 at a velocity V and flows out from the outlet end of the straight outlet pipe 12 . The measuring tube 1 rotates clockwise at a constant angular velocity ω about an axis of rotation defined by the straight tubes 11 and 12 (see also the axis of rotation indicated by the dashed line in FIG. 5 ). When the fluid is in the straight inlet pipe 11 or the straight outlet pipe 12 of the measuring tube 1, since the moving direction of the fluid is in the same direction as the rotation axis, no Coriolis force will be generated. And when this stream of fluid flows in the curved pipe 13 of the measuring tube 1 (for example, at position 15), the velocity V of the fluid can be decomposed into a velocity component V _x parallel to the axis of rotation and a direction perpendicular to the axis of rotation and to The outer velocity component V _y . At this time, the fluid has an acceleration that makes it deviate from the axis of rotation. Under the action of this acceleration, the wall surface of the curved pipe 13 is subjected to a Coriolis force F _c , which can be expressed by the equation (1 )inferred:

F _c = mA _c (1)

in:

F _c represents the Coriolis force acting on the measuring tube,

m represents the mass of the fluid,

_Ac represents Coriolis acceleration.

According to the laws of physics, the Coriolis acceleration _Ac can be expressed as:

A _c =2(ω×V _y ) (2)

in:

ω represents the rotational angular velocity of the measuring tube,

V _y represents the velocity component of the fluid velocity V in the direction perpendicular to the axis of rotation.

Assuming that the inclination angle of the measuring tube at position 15 is θ, then:

V _y =V ×cosθ (3)

After substituting Equation (2) and Equation (3) into Equation (1), the Coriolis force at position 15 can be obtained as:

F _c =2×m×(ω×V×cosθ) (4)

The Coriolis force F _c shown in Fig. 4 can be calculated from equation (4), which is proportional to the mass m of the fluid, proportional to the velocity V of the fluid of these masses passing through the measuring tube 1, and proportional to the velocity V of the measuring tube 1 proportional to the rotational angular velocity ω. According to this principle, at the position 16 which is symmetrical to the position 15, the Coriolis force F _c is equal in magnitude and opposite in direction. Under the combined action of these two forces, the measuring tube 1 is deformed, and two vibration sensors are installed at positions 15 and 16 to measure the magnitude of the deformation caused by the Coriolis force, and then determine the fluid Mass Flow.

Fig. 5 shows a specific application embodiment of a Coriolis flowmeter of the present invention adopting the above principle. As shown in the figure, the measuring tube 1 of the flowmeter of this embodiment includes a section of inlet straight pipe 11, a section of outlet straight pipe 12, and a section of arc-shaped elbow 13 between the two straight pipe parts. The inlet end of the straight pipe 11 flows in, passes through the curved pipe 13, and finally flows out from the outlet end of the outlet straight pipe 12. A rotary motor 3 is installed on the fluid inlet end or the fluid outlet end of the measuring tube 1 , and in the example shown in FIG. 5 , the rotary motor is installed on the fluid outlet end. The rotary motor 3 includes a rotor 31 and a stator 32. The stator 32 is fixed on the casing 5 of the flowmeter. The rotor 31 clamps the tube wall of the straight tube of the measuring tube 1, thereby driving the measuring tube 1 to rotate at a certain angular velocity. The casing 5 of the flowmeter can respectively support the measuring tube 1 through bearings. As shown in the figure, the bearings can be arranged at the inlet end and the outlet end of the measured fluid of the measuring tube 1 .

In the flowmeter shown in Figure 5, there is also an arc rod 7, which is axially symmetrical with the arc portion 13 of the measuring rod 1 in the same plane along the rotation axis, so as to balance the arc of the measuring tube 1. The force received when the elbow 13 rotates. The two ends of the arc rod 2 and the measuring rod 1 are respectively supported by support blocks 41, 42 to ensure a more stable rotation.

When the fluid flows through the rotating measuring tube 1, the fluid in the curved bend 13 of the measuring tube 1 generates a Coriolis force, which deforms the measuring tube. The two ends of the arc portion 13 of the measuring tube 1 are respectively equipped with vibration sensors 14a and 14b, and these two sensors are arranged symmetrically along the radial direction of the measuring tube to measure the amplitude of the deformation of the tube wall.

In the case of the same Coriolis force, the greater the range of elastic deformation of the measuring tube, the higher the measurement sensitivity of the flowmeter. Glass has such excellent mechanical properties, it has high strength and high elasticity. In the present invention, the measuring tube 1 is made of metallic glass, and this Coriolis tube made of metallic glass can measure the mass flow rate of the fluid in a large flow adjustment range and at an extremely low flow rate.

According to one embodiment of the invention, the measuring tube with the curved bend is made of Zr-based metallic glass. Metallic glass is stronger and more elastic than measuring tubes made of stainless steel. For example: the tensile yield strength of Zr-based metal glass tube is 1.6 times that of stainless steel tube, the Young's modulus of Zr-based metal glass tube is two-fifths of that of stainless steel, and the thickness of Zr-based metal glass tube can only be the thickness of stainless steel tube a quarter of. Moreover, the Zr-based metal glass tube is also very resistant to chemical corrosion of chlorine gas and liquid chloride.

In the invention, the stator 32 of the rotating motor is fixed on the casing 5 of the flowmeter, while the rotor 31 clamps the straight pipe part of the measuring tube 1, which eliminates the bending and twisting of the measuring tube 1 and greatly reduces the measurement of metallic glass Possibility of tube breakage.

FIG. 7 shows the deformation distribution diagram of the measuring tube 1 along the x-axis direction (ie, the x-axis direction in FIG. 4 ) under the action of Coriolis force. It can be seen from the figure that the deformation caused by Coriolis force is different at different positions of the measuring tube 1 , but on the arc bend 13 , the deformation of the measuring tube 1 has increased significantly. In order to improve the sensitivity of the measurement, the vibration sensor should be set at the position where the maximum deformation can occur, that is, close to the two ends of the curved pipe. Vibration sensors can use piezoelectric elements.

Fig. 8 compares the measurement sensitivity when making the measuring tube with glass metal and stainless steel, wherein the solid line part represents the metallic glass measuring tube of the present invention, and the dotted line part represents the stainless steel measuring tube. The Coriolis mass flowmeter mainly determines the mass flow rate of the fluid by measuring the amplitude δ of the elastic deformation of the tube. The larger the deformation amplitude δ, the more sensitive the measuring meter is. The deformation amplitude can be calculated by equation (5):

δ＝4F _c L ³ /3πE(d ₂ ⁴ -d ₁ ⁴ ) (5)

in:

F _c represents the Coriolis force,

E stands for Young's modulus,

d ₁ represents the inner diameter of the measuring tube,

d ₂ represents the outer diameter of the measuring tube,

L represents the length of the measuring tube.

In actual use, since the length of the measuring tube is limited by the volume of the measuring instrument, the vibration amplitude δ is mainly affected by the wall thickness and Young's modulus of the measuring tube. In other words, the thinner the material used for the measuring tube in the flowmeter and the smaller the Young's modulus, the higher the measurement sensitivity of the flowmeter. The Young's modulus of metallic glass measuring tube is about 2/5 of stainless steel measuring tube at present, and the thickness of measuring tube of the present invention is 1/4th of stainless steel tube thickness, according to the calculation of equation (5), metallic glass measuring tube The measurement sensitivity can reach more than 30 times that of stainless steel tubes.

The series of detailed descriptions listed above are only specific descriptions for feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiment or All changes should be included within the protection scope of the present invention.

Claims (5)

1. A Coriolis mass flow meter, comprising a measuring tube and a pair of vibration sensors that can rotate around a rotating shaft, is characterized in that: the measuring tube is made of metallic glass, and the measuring tube has: A section of straight inlet pipe for the measured fluid to flow in and coaxial with the rotation axis, a section of outlet straight pipe for the measured fluid to flow out and coaxial with the rotation axis, and a section between the inlet straight pipe and the The curved curved pipe between the outlet straight pipes and the two connected; the pair of vibration sensors are symmetrically arranged radially along the measuring pipe, and are arranged at both ends of the curved curved pipe of the measuring pipe. 2. The Coriolis flowmeter as claimed in claim 1, further comprising an arcuate rod, which is in the same plane as the arcuate bend of said measuring tube along said axis of rotation The inner axis is symmetrical, and the two ends of the arc rod are respectively fixed on the two support blocks with the measuring tube. 3. The Coriolis flowmeter as claimed in claim 2, wherein a motor drives said measuring tube to rotate around said rotation axis, the rotor of said motor clamps the inlet straight tube of said measuring tube Or outlet straight pipe, the stator of the motor is fixed on the casing of the flowmeter. 4. The Coriolis flowmeter as claimed in claim 3, wherein the casing of the flowmeter supports the said measuring tube at the inlet end of the measured fluid and the outlet end of the measured fluid through bearings respectively. measuring tube. 5. The Coriolis flowmeter of claim 1, wherein the metallic glass from which the measuring tube is made is a zirconium-based metallic glass.

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