JP2013142539A - Mass flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mass flowmeter which employs a curved pipe composed of a curved part and a straight part continued thereto and is not affected by a secondary flow, caused by a centrifugal force, within a pipeline cross section in the curved part.SOLUTION: A mass flowmeter uses a curved pipe composed of a curved part and a straight part continued thereto. A distortion gauge for centrifugal force detection is mounted onto an outer circumferential pipe wall of the curved part, a distortion gauge for static pressure/temperature compensation is mounted to a pipe wall of the straight part, and a flow rate is measured from an output difference therebetween. At least the curved part has a pipeline cross-sectional shape in which the curved pipe is longer in a vertical direction than in a curvature radius direction of the curved part.

Description

  The present invention relates to a mass flow meter, in particular, in a field where flow measurement is required with a small and lightweight flow meter, for example, a medical flow meter such as an artificial heart or a piping of a plant such as petroleum, petrochemical, chemical, etc. The present invention relates to a mass flowmeter suitable for measuring the flow rate of flowing fluid, and measuring the flow rate of gas, cleaning water for bottles, cleaning liquid for wafers and substrates, and chemicals.

An implantable artificial heart used outside a hospital needs to display a flow rate for pathological management, but there is no small flow meter that can be implanted. There are various types of industrial flowmeters such as vortex flowmeters, resistance flowmeters, and float flowmeters, but ultra-lightweight and simple flowmeters are required.
The inventors previously used a bending tube that generates centrifugal force as an ultra-lightweight and simple measurement type mass flow meter, a strain gauge for detecting centrifugal force at the bending portion, and a static pressure at the straight tube portion.・ We have developed and filed a mass flow meter that attaches a strain gauge for temperature compensation and measures the flow rate from the output difference (see Patent Documents 1 and 2).

JP 2007-218775 A (Japanese Patent Application No. 2006-040675) JP 2009-150671 A (Japanese Patent Application No. 2007-326761)

In the mass flowmeter using the bent pipe previously proposed by the present inventors (see Patent Documents 1 and 2), the measuring method is simple and can be reduced in size, but a bent pipe having a circular pipe cross-sectional shape is used. As a result, a secondary flow occurs in the cross section of the pipe at the bend where the centrifugal force is generated, and the flow pattern of the cross section of the pipe is different due to the influence of the secondary flow. If different calibration formulas are measured in advance for the flow rate and the high flow rate, it will not be possible to obtain accurate flow measurement results that take into account the effects of the secondary flow, and it will be necessary to perform complicated calibration work. It was.
FIG. 1 is a mass flow meter using the conventional bent pipes of Patent Documents 1 and 2 previously filed by the present inventors. As shown in the figure, the bent pipe is composed of a bent portion and a straight pipe portion connected to the bent portion. The shape of the pipe cross section of the bent pipe is circular in both the bent part and the straight pipe part. FIG. 3 is a diagram showing the secondary flow of the pipe cross section at the bent portion in the mass flowmeter having the circular pipe cross section of the bent pipe shown in FIG. Secondary flow, and the diagram on the right shows the secondary flow when the flow rate is high. At a low flow rate, the center of the vortex is close to the upper and lower surfaces of the pipe, but at a high flow rate, the flow pattern changes and the vortex center moves to a position near the center of the pipe. In order to obtain an accurate flow rate, it is necessary to measure the influence of the secondary flow in advance and obtain a calibration formula. However, as shown in Fig. 3, the secondary flow pattern is different between the high flow rate and the low flow rate. A correct calibration formula must be obtained.
In addition, since the shape of the strain gauge type sensor mounting portion of the bent pipe is a semicircular curved surface, it has been difficult to perform thin wall processing for improving measurement accuracy.
The problem to be solved by the present invention is to provide a mass flow meter using a bent pipe with a small change in flow pattern due to a secondary flow, and to easily mass-process the strain gauge sensor mounting portion of the bent pipe. To provide a flow meter.

In order to solve the above-mentioned problems, the present invention uses a bent pipe composed of a bent portion and a straight pipe portion connected to the bent portion, a strain gauge for detecting centrifugal force on the outer peripheral wall of the bent portion, and a straight pipe portion. A mass flow meter with a strain gauge for static pressure / temperature compensation attached to the pipe wall and measuring the flow rate from the output difference, where the shape of the pipe section of the bent part is the radius direction of the bent part of the bent pipe The cross-sectional shape of the pipe having a long vertical direction is used.
Further, in the present flow meter, a pipe cross section having a long vertical direction with respect to a radius direction of curvature of the pipe cross section is used only at a bent portion where the centrifugal force is measured. As the pipe cross section having a long vertical direction with respect to the radius of curvature, an ellipse, a rectangle, a rectangle with four corners R, and a rectangle with a short side replaced with a semicircle are used.

According to the present invention, in a mass flow meter using a bent pipe, the secondary flow at a high flow rate and a low flow rate is suppressed only at both ends of the pipe as compared with a conventional bent pipe having a circular cross section. The position of the vortex generated in the road section does not change. That is, since there is little change in the flow pattern of the pipe cross section between the low flow rate and the high flow rate due to the influence of the secondary flow, the calibration formula of the mass flow meter can be easily expressed by one formula.
Furthermore, when the section of the pipe line where the strain gauge sensor is attached has an elliptical shape or a rectangular shape, thin processing for improving measurement accuracy is facilitated.

It is a figure which shows the conventional mass flowmeter (refer patent document 1: Unexamined-Japanese-Patent No. 2007-218775) using the curved pipe with the circular shape of a pipe cross section. It is a figure which shows the mass flowmeter using the bending pipe | tube whose shape of the pipe cross section of this invention has a perpendicular | vertical direction long with respect to a curvature radius direction. It is a figure which shows the secondary flow (Left: Low flow rate, Right: High flow rate) in the bending part in the mass flowmeter with the circular shape of the conventional pipe line cross section shown in FIG. In the mass flow meter using the bent pipe whose shape of the pipe cross section of the present invention shown in FIG. 2 is long in the direction perpendicular to the radius of curvature, the secondary flow at the bent portion (left: low flow, right: high flow) ). FIG. 5 is a diagram showing an embodiment of the present invention, in which only a bent portion has a pipe cross-sectional shape that is long in a direction perpendicular to the radius of curvature, and a straight pipe portion has a circular pipe cross-sectional shape. It is. In the mass flowmeter which is one Example of this invention shown in FIG. 5, in order to affix a strain gauge sensor from the outer periphery of a pipe line, it is the figure explaining the shape of the sensor sticking part which processed the pipe line thinly.

The present invention uses a bent pipe composed of a bent portion and a straight pipe portion connected to the bent portion, and attaches a strain gauge for centrifugal force detection to the bent portion and a strain gauge for static pressure and temperature compensation to the straight pipe portion, Mass flow meter that measures flow rate from the output difference, characterized in that at least the shape of the pipe cross section of the bent part has a long pipe cross section perpendicular to the radius of curvature of the bent part of the bent pipe This is a mass flow meter.
As described above, in the conventional mass flow meter shown in FIG. 1, the secondary flow (left: low flow rate, right: high flow rate) as shown in FIG. At low flow rate, the center of the vortex is close to the upper surface (upper surface in the figure) and lower surface (lower surface in the figure), but at high flow rate, the flow pattern changes and the vortex center is closer to the center of the pipe line Moved to position. Here, the length of the arrow represents the magnitude of the secondary flow normalized by the maximum flow rate, and the direction of the arrow represents the direction of the secondary flow. As shown in FIG. 3, in both cases of low flow rate and high flow rate, a secondary flow is generated on the outer periphery of the bent portion, which is the strain gauge mounting position, and the influence of the secondary flow cannot be ignored. Therefore, in order to obtain an accurate mass flow rate, it is necessary to measure in advance and obtain a calibration formula. However, since the secondary flow pattern is different between the low flow rate and the high flow rate, it is difficult to calibrate the influence of the secondary flow.
On the other hand, in the mass flowmeter of the present invention shown in FIG. 2, at least the shape of the pipe cross section of the bent portion is a pipe cross section that is long in the direction perpendicular to the radius of curvature of the bent portion of the bent pipe. The secondary flow is as shown in FIG. Compared with the conventional curved pipe having the circular cross section of FIG. 3, in the present invention of FIG. 4, the secondary flow at the high flow rate and the low flow rate at the bent portion is perpendicular to the curvature radius direction of the bent portion. The flow direction is restrained only at both ends (upper and lower ends in the figure) of the long section of the pipe, the change in the flow pattern is small, and the influence of the secondary flow at the outer periphery of the curved part where the strain gauge is attached is almost insignificant. Therefore, the calibration formula of the mass flow meter can be expressed simply by one formula.
In addition, the shape of the strain gauge mounting position on the outer periphery of the bent portion is a straight line or a straight line in the cross section of the pipe, and the shape of the thin wall processing is easier than in the case of a semicircle of a conventional circular pipe.

2 and 4, the pipe cross-sectional shape of the bent portion is a rectangular cross section with an R at the corner, and the long side of the rectangle is perpendicular to the radius of curvature of the bent portion of the bent pipe. Although shown, the shape of the pipe cross section is not limited to the rectangular cross section, and may be an elliptical shape, or may be one in which the short side of the rectangle as shown in FIG. 5 is replaced with a semicircle. .
In FIG. 2, the straight pipe portion has the same pipe cross-sectional shape as the bent portion, but the straight pipe portion has a circular cross section as shown in FIGS. The pipe cross section may be long in the direction perpendicular to the radius of curvature of the bent portion of the bent pipe.

5 and 6 show an embodiment of the mass flow meter of the present invention. The bent pipe of the present embodiment is composed of a bent portion and a straight pipe portion connected to the bent portion, and the shape of the pipe cross section of the straight pipe portion is circular as shown in the figure, and the shape of the pipe cross section of the bent portion is rectangular. The short side is replaced with a semicircle, and the long side of the rectangle is perpendicular to the radius of curvature of the bent part of the bent pipe, and the cross-sectional shape is the connection part between the bent part and the straight pipe part. The flow is smoothly changed so that the flow is not disturbed by the change in the cross-sectional shape.
FIG. 6 is a diagram illustrating the shape of a sensor pasting portion in which the pipe line is thinned so that the strain gauge sensor is pasted from the outer periphery of the pipe, and a centrifugal force measuring sensor is attached to the outer circumference of the bent part. A sensor for static pressure compensation (also used for temperature compensation, hereinafter referred to as “static pressure / temperature compensation”) is attached to the section. The bending pipe is a rigid pipe that does not cause large elastic deformation due to fluid pressure, and the part to which the centrifugal force measurement sensor is attached on the outer periphery of the bending part is thinned by appropriate thinning such as grinding. The fluid flowing in the tube is easily deformed by the centrifugal force when the flow direction is changed at the bent portion. Similarly, the portion to which the static pressure / temperature compensation sensor is attached in the straight pipe portion is also thinned to be a thin portion.
The centrifugal force measurement sensor attached to the outer periphery of the bending part detects the total pressure of centrifugal force and static pressure, and the static pressure and temperature compensation sensor attached to the straight pipe part detects static pressure and temperature related pressure. The mass flow rate can be obtained from the difference between the outputs using a bridge circuit or the like commonly used in strain sensor measurement (see Patent Documents 1 and 2).

In this embodiment, the shape of the pipe cross section of the bent portion is a shape in which the short side of the rectangle is replaced with a semicircle, and the long side of the rectangle is perpendicular to the direction of the radius of curvature of the bent portion of the bent tube. Since the secondary flow is restrained only at both ends with the short side of the rectangle replaced by a semicircle, as with the secondary flow pattern in the pipe cross section shown in FIG. There is almost no influence of the secondary flow at the mounting position of the centrifugal force measuring sensor.
Further, in this embodiment, the thin wall processing at the sensor mounting position on the outer periphery of the bent portion is easier to process than the conventional circular tube shape of the tube wall at this position, and the bent portion can be bent. Since the influence of processing is less than in the case of a conventional circular tube, thin wall processing is easy.

  The mass flow meter of the present invention is suitable as a flow meter for an artificial heart for implantation in the body, but can also be applied as a flow meter for other medical devices such as a blood pump for surgery or an industrial flow meter.

Claims (3)

Using a bent pipe composed of a bent part and a straight pipe part connected to it, a strain gauge for detecting centrifugal force is provided on the outer peripheral wall of the bent part, and a strain for static pressure / temperature compensation is provided on the pipe wall of the straight pipe part. A mass flow meter that attaches a gauge and measures the flow rate from its output difference,
A mass flow meter characterized in that at least a shape of a pipe cross section of a bent portion has a pipe cross sectional shape that is long in a direction perpendicular to a curvature radius direction of a bent portion of the bent pipe.   The mass flowmeter according to claim 1, wherein the straight pipe portion has a circular cross-sectional shape.   The cross-sectional shape of the pipe having a long vertical direction with respect to the radius of curvature of the bent portion of the bent pipe is an ellipse, a rectangle, a rectangle with R at the four corners, or a rectangle with a short side replaced with a semicircle. The mass flowmeter according to claim 1 or 2, wherein

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