JPH05273022A - Measuring method for mass flow rate and mass flowmeter using the method - Google Patents

Abstract

PURPOSE:To obtain a measuring method of a mass flow rate and a mass flowmeter which enable measurement of the mass flow rate by simple processing procedures without being affected by the density of a fluid to be measured, by utilizing a Magnus effect. CONSTITUTION:In a mass flowmeter 20, a gas flow is made to run at a fixed velocity V through a passage 1a of a gas 30. A rotary cylinder 5 disposed in this gas passage is rotated at a fixed peripheral velocity (v) by a motor 18. Pressures P1 and P2 generated in the vicinity of the upper and lower places of the outer periphery of the rotary cylinder 5 by this rotation are supplied to a differential pressure detector 11 and a differential pressure DELTAP between them is determined. Based on this differential pressure DELTAP, a mass flow rate Qm is measured in an arithmetic/display circuit 12 by using the relation of P=2Qm(v/A).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mass flow rate measuring method, and more particularly to a mass flow rate measuring method utilizing the Magnus effect. The present invention also relates to a mass flow meter that employs this measuring method.

[0002]

2. Description of the Related Art Generally, volume control is used for measuring and controlling the flow rate of gas or liquid, or metering of fluid for trading. However, the actual required flow rate is often the mass flow rate.

In particular, in recent years, with the development of various industries, the need for measuring the mass flow rate has increased, and there are many fields in which manufacturing or the like cannot be performed unless the mass flow rate is measured. Examples of such fields include measurement control of various gas flows in the CVD, diffusion, etching processes and the like adopted in the semiconductor industry, and refractive index control of light by gas flow control in the manufacture of optical fibers. In such a field, it is necessary to measure and control a minute gas flow with high accuracy and high reproducibility. Various mass flow meters have been developed to meet these requirements.

[0004]

However, any of the mass flow rate measuring methods or mass flow meters proposed so far needs to be corrected by the physical properties peculiar to various gases, particularly the difference in density. For this reason, depending on the ambient conditions such as the difference in pipe diameter of the flow rate detector, temperature, pressure, etc., the measured value may be several percent of the theoretical value, and in some cases, more error may be included.

Therefore, existing mass flow meters require calibrated calibration. As the method, the gravimetric method and the volumetric method have been put into practical use. However, in such a method, the processing procedure is very complicated and it takes time. Furthermore, the ambient temperature must be kept constant during the measurement period.

Further, when a special gas such as a toxic or corrosive gas is targeted, it is practically impossible to calibrate using a real gas from the viewpoint of both safety and control of the measuring instrument. is there. Therefore, a pseudo calibration with an inert gas is performed,
The reality is that corrections based on the physical properties of gas are obtained from calculated values.

As described above, the existing mass flowmeter is very difficult to make an accurate measurement in itself. In view of this point, the object of the present invention is a method capable of measuring the mass flow rate by a simple procedure without being affected by the physical properties of the measurement gas, the ambient conditions, and the like, and the mass flow rate using the method. To propose a total.

[0008]

In order to solve the above problems, the present invention focuses on the Magnus effect, and by applying it, the mass flow rate substantially affects the density of the fluid to be measured. You can measure without being
We have realized a mass flow rate measurement method and a mass flow meter that can be used as a simple secondary calibration device.

The contents of the present invention will be described with reference to the drawings.
First, as shown in FIG. 1, it is assumed that the fluid 30 flows from the left to the right at a uniform flow velocity V. In this fluid, a sphere or cylinder 31 having a diameter R is rotated at a constant peripheral speed v around an axis 32 orthogonal to the fluid flow direction. In this case, the flow velocity on the upper side of the sphere or cylinder 31 is accelerated to (V + v), and the flow velocity on the lower side is decelerated (V + v).
-V).

At this time, the pressures P1 and P2 at points X and Y in the fluid near these upper and lower sides are given by Bernoulli's theorem, where the fluid density is ρ.

(1/2) ρ (V + v) ² + P1 = (1/2) ρ (V−v) ² + P2 (1)

[0012]

By rearranging this equation, the difference Δ between the pressures P1 and P2
If you ask for P,

ΔP = P2-P1 = 2Vvρ (2)

(Magnus effect)

Here, as shown in FIG. 2, the fluid flow path 3
Assuming that the cross-sectional area of 3 is A, the fluid 30 flowing therethrough
The mass flow rate Qm of

Qm = VρA (3)

It can be expressed as

Therefore, from the above equations (2) and (3),

ΔP = 2Qm (v / A) (4)

To obtain From this formula (4), the mass flow rate Qm
Is proportional to the pressure difference ΔP, and its sensitivity is given by v / A,
It can be seen that it is independent of the fluid density ρ. The present invention is characterized in that the pressure difference ΔP is obtained and the mass flow rate Qm is measured by using the relationship of the above equation (4).

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 and FIG. 4 show the mass flowmeter of this embodiment. First, the structure of the pressure detecting portion of the mass flowmeter 20 of this embodiment will be described. In the figure, reference numeral 1 is a case forming a passage for a gas 30 to be measured, which defines a fluid passage 1a having a rectangular cross section having a height H and a width W. The gas upstream side of the case 1 is narrowed to become a gas flow inlet 2, and the gas downstream side is also narrowed to become a gas outlet 3. A plate 4 for laminarizing the gas flow flowing into the case 1 is arranged on the downstream side of the inflow port 2 in the case 1. As this plate, for example, a mesh plate can be used.

In the case 1, a rotating cylinder 5 is arranged at a central position in the gas flow direction so as to rotate about an axis 5a orthogonal to the gas flow direction A. Then, small-diameter pipes 6 and 7 for pressure detection are connected to the portions of the case 1 located on the extension lines of the cross-sectional diameter 5b orthogonal to the gas flow direction A in the rotary cylinder 5, respectively, and the fluid passages 1a in the case are connected. Is in communication with.

As can be seen from FIG. 4, communication pipes 9 and 10 are connected to these small diameter pipes 6 and 7, respectively, and the other ends of these communication pipes are connected to a differential pressure detector 11. There is. The output side of the differential pressure detector 11 is connected to the signal line 11
It is electrically connected to the input side of the arithmetic / display unit 12 via a.

On the other hand, both ends of the rotary shaft 5c of the rotary body 5 are rotatably supported by bearings 8 mounted on the case side face 1d in an airtight manner. As such a bearing, for example, a rotating magnetic seal unit can be used. One end of the rotary shaft 5c projects outward from the bearing 8 and is connected to the output shaft 18a of the motor 18. The motor 18 is provided with a constant speed control circuit 21 for keeping the rotation speed constant. This constant speed control circuit 2
Reference numeral 1 denotes an optical rotary encoder 14 attached to a motor output shaft 18a, an F / V converter 15 for converting an encoder pulse obtained from the encoder into a voltage, a rotation speed setting unit 16, and an F / V converter. 15 and rotation speed setting unit 16
It is composed of a motor driver 17 which controls the motor drive power so that the rotation speed is set based on the output from the motor driver.

In the mass flowmeter 20 thus constructed, the gas 30 is caused to flow at the flow velocity V into the passage 1a in the case 1 while rotating the rotary cylinder 5 at a constant peripheral speed v. Internal pressures P1 and P in the inside of the case where the small diameter pipes 6 and 7 are connected
2 is supplied to the differential pressure detector 11 via the small diameter pipes 6 and 7, respectively. The differential pressure detector 11 detects the differential pressure ΔP between the supplied pressures P1 and P2. An electric signal corresponding to the detected differential pressure ΔP is supplied to the arithmetic / display circuit 12 via the signal line 11a. The calculation / display circuit 12 calculates the mass flow rate Qm based on the supplied differential pressure signal, using the relationship of the above-described equation (4). The calculation result is
It is output to a display device or the like.

Here, the present inventors have made the following measurements using the mass flowmeter 20 of this embodiment. With the width W of the gas passage 1a in the case unchanged, the height H was switched from the smaller dimension to H1, H2, and H3, and the relationship between the flow rate Qm and the differential pressure ΔP was obtained.

FIG. 5 shows the measurement results. In the figure, the characteristic line A is the case of H3 having the largest height, the characteristic line B is the case of H2, and the characteristic C is the case of H3 having the smallest height. As can be seen from the measurement results, when the height H in the case is larger than the diameter of the rotating cylinder 5, in other words, when sufficient gas passages are formed above and below the rotating cylinder, the detection sensitivity is high. Is lower than other cases, but the linearity between the flow rate Qm and the differential pressure ΔP is maintained. In this case, the flow velocity V of the fluid at the pressure detection portion
The sensitivity can be increased by increasing.

On the other hand, when the height H is small, that is, when the upper and lower gas flow portions of the rotating cylinder are small, the detection sensitivity is increased, but the linear relationship tends to be broken. This is due to the occurrence of turbulence due to fluid interference above and below the rotating body.

Therefore, the mass flow rate can be measured with sufficient detection sensitivity over a wide range of flow rates by appropriately setting the magnitude of the flow rate to be measured, the cross-sectional area of the fluid passage of the pressure detection portion, the dimensions of the rotating cylinder, etc. can do.

[0032]

As described above, in the present invention, the mass flow rate is measured by utilizing the Magnus effect. Therefore, regardless of the density of the fluid to be measured, its mass flow can be measured by a simple procedure.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the principle of the present invention.

FIG. 2 is an explanatory diagram showing the principle of the present invention.

FIG. 3 is a schematic cross-sectional view showing a pressure detecting portion of the mass flowmeter of one embodiment of the present invention.

FIG. 4 is a schematic configuration diagram showing an overall configuration of the mass flow meter of FIG.

5 is a graph showing the relationship between the mass flow rate and the differential pressure measured by the mass flow meter of FIG.

[Explanation of symbols]

 1 ... Case 1a ... Fluid passage 5 ... Rotating body 11 ... Differential pressure detector 12 ... Calculation / display circuit 18 ... Motor 21 ... Constant speed control circuit V ... Flow velocity of fluid v ・ ・ ・ Peripheral speed of rotating body P1, P2 ・ ・ ・ Pressure ΔP ・ ・ ・ Differential pressure Qm ・ ・ ・ Mass flow rate

Claims (3)

[Claims] 1. A rotary body is disposed in a fluid passage through which a fluid to be measured passes, the rotary body is rotated, and a fluid pressure difference between different points in the vicinity of the outer circumference of the rotary body is detected and detected. A mass flow rate measuring method comprising measuring a mass flow rate of a fluid passing through a fluid passage based on the fluid pressure difference. 2. A mass flowmeter using the method according to claim 1, wherein a cylindrical fluid passage through which the fluid to be measured passes and an axis orthogonal to the fluid flow direction in the fluid passage are centered. , A rotary drive mechanism that rotates the rotary body at a predetermined peripheral speed, and a pressure difference detection mechanism that detects a fluid pressure difference between two different points near the outer circumference of the rotary body. And a computing device that calculates a mass flow rate of the fluid flowing through the fluid passage based on the pressure difference detected by the pressure difference detection mechanism. 3. The fluid passage according to claim 2, wherein the fluid passage has a rectangular cross section, and the rotating body is arranged so as to have a rotation axis orthogonal to a fluid flow direction in the fluid passage. The detection mechanism has a pressure detection unit that detects a fluid pressure in the vicinity of both ends of the rotating body in the fluid circulation direction and a direction orthogonal to the rotation axis, and a differential pressure detection unit that obtains a difference between the pressures detected by these. Therefore, when the pressure difference detected by the differential pressure detection unit is Δp, the cross-sectional area of the fluid passage is A, the peripheral speed of the rotating body is v, and the mass flow rate is Qm, A mass flow meter, wherein the mass flow rate Qm is calculated from a relational expression of Δp = 2Qm · (v / A).