JPH09280916A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand rangeability by highly accurate measurement regardless of laminar layer and turbulence. SOLUTION: An ultrasonic pulse is transmitted or received between ultrasonic elements 2 and 3 provided on a wall of a flow pipe 1 to measure a linear average flow velocity Ve on an axis 4. The ultrasonic pulse is transmitted or received between ultrasonic elements 5 and 6 provided within a fluid to measure the maximum flow velocity Va on an axis 7. When the flow velocity ratio Va/Ve is geater than 1.2, a laminar flow is determined and when the ratio is below 1.2, turbulence is determined. A calculation formula for converting the linear average flow velocity Ve to an average flow velocity at the cross section of the flow pipe is altered between the laminar flow and the turbulence. A flow rate is calculated based on the average flow velocity at the cross section of the flow pipe.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an improvement of an ultrasonic flowmeter.

[0002]

2. Description of the Related Art In a conventional ultrasonic flowmeter, an ultrasonic beam is emitted obliquely to a flow of a fluid, and the average line velocity of the ultrasonic beam on the axis is measured. The average flow velocity is calculated and the flow rate is calculated by multiplying this by the flow tube cross-sectional area.

[0003]

Since the flow velocity distribution in the flow tube differs between laminar flow and turbulent flow, it is necessary to change the calculation formula depending on whether the flow state is laminar or turbulent in order to obtain an accurate flow velocity. . However, in the above-mentioned conventional technique, there is no means for discriminating whether the flow in the flow tube is a laminar flow or a turbulent flow, and therefore there are problems that the flow rate measurement accuracy cannot be improved and the rangeability cannot be expanded.

Therefore, an object of the present invention is to provide an ultrasonic flowmeter capable of solving these problems.

[0005]

In order to achieve the above-mentioned object, the invention of claim 1 emits an ultrasonic beam obliquely with the flow of a fluid flowing in a flow tube having a circular cross section,
Linear average flow velocity (Ve) on the axis (4) of the ultrasonic beam
In an ultrasonic flowmeter that calculates the flow rate on the basis of the value obtained by measuring the flow rate of the flow tube (1) in the direction parallel to the flow on the central axis (X) of the flow tube (1). The ultrasonic wave beam 2 is emitted to measure the maximum flow velocity (Va), and it is determined whether the flow is laminar flow or turbulent flow based on the ratio between the maximum flow velocity (Va) and the linear average flow velocity (Ve). Then, the calculation formula for converting the linear average flow velocity (Ve) into the average flow velocity in the cross section of the flow tube is changed, which is an ultrasonic flowmeter.

According to a second aspect of the invention, in the ultrasonic flowmeter according to the first aspect, the flow is laminar when the ratio (Va / Ve) of the maximum flow velocity (Va) to the linear average flow velocity (Ve) exceeds a certain value. And that the flow is turbulent when the ratio (Va / Ve) is equal to or less than a certain value.

According to the invention of claim 3, in the ultrasonic flowmeter according to claim 1 or 2, the linear average flow velocity (Ve) on the axis (4) of the beam is determined by the ultrasonic beam in the flow and oblique directions. Two ultrasonic elements (2), (3) provided on the pipe wall for measurement, and two ultrasonic elements provided in the flow for measuring the maximum flow velocity (Ve) by the second ultrasonic beam. It is characterized by comprising (5) and (6).

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a preferred embodiment of the present invention, in which 1 is a flow tube having a circular cross section, and a fluid flows in the flow tube (1) in the horizontal direction in the drawing.

Reference numerals 2 and 3 are ultrasonic elements provided on the wall of the flow tube 1, and by transmitting and receiving ultrasonic pulses between the elements, the linear average flow velocity Ve of the ultrasonic beam on the axis 4 is measured. It is an element for.

The linear average flow velocity Ve on the axis 4 is the propagation time of ultrasonic waves from one ultrasonic element 2 to the other ultrasonic element 3 and the other ultrasonic element 3 to one ultrasonic element 2. It is measured by a well-known method that is obtained independently of the speed of sound using the time reciprocal difference method from the propagation time of the ultrasonic wave.

Reference numerals 5 and 6 denote ultrasonic elements arranged apart from each other on the central axis X-X of the flow tube 1, and by transmitting and receiving ultrasonic pulses between the elements, the maximum of the ultrasonic beam on the axis 7 is obtained. The flow velocity Va is measured.

The maximum flow velocity Va is obtained from the forward propagation time and the backward propagation time of the ultrasonic wave by using the time reciprocal difference method regardless of the speed of sound. As shown in FIG. 2, when the coordinate in the axial direction of the flow tube 1 is χ and the coordinate in the radial direction is r, the flow velocity v (r) in the flow tube 1 having a circular cross section is laminar (Reynolds number). R
e ≦ 2300), v (r) = (R ² / 4μ) (− dp / dχ) {1- (r / R) ² } ... (1)

Where R is the radius of the flow tube 1, μ is the viscosity of the fluid, and dp / dχ is the friction loss due to the tube wall.

From the above equation (1), the maximum flow velocity V on the axis 7
a becomes Va = (R ² / 4μ) (− dp / dχ) (2).

The linear average velocity Ve on the axis 4 is Ve = (R ² / 6μ) (− dp / dχ) (3).

Therefore, the maximum flow velocity Va when the flow is laminar
And the linear average flow velocity Ve, that is, the flow velocity ratio K is K = Va / Ve = (R ² / 4μ) (− dp / dχ) / {(R ² / 6μ) (− dp / dχ)} = 1. 5 ... (4), which is constant.

FIG. 3A shows the flow velocity distribution when the flow is laminar.
Shown in Next, Fig. 3 shows the flow velocity distribution when the flow is turbulent.
As shown in (b), the flow velocity distribution is different from the laminar flow.

The flow velocity distribution v (r) in the case of turbulent flow is expressed by the following equation (5) when expressed by the exponential law equation which is an empirical equation. v (r) = Va {1- (r / R)} ^{1 / n} (5) However, n = 2.1 log Re-1.9.

Solving the equation (5), the axis line 4 of the ultrasonic beam
When the upper linear average flow velocity Ve is calculated, Ve = {n / (n + 1)} Va ... (6) Therefore, the flow velocity ratio K is K = Va / Ve = (n + 1) / n (7)

Here, the minimum Reynolds number R that causes turbulence
Considering e = 2300, n = 5.16, and the flow velocity ratio K becomes K ≦ 1.2 (8).

As described above, the values of the flow velocity ratio K are clearly different between the laminar flow and the turbulent flow as shown in the equations (4) and (8).
The value of the flow velocity ratio K determines whether the flow state is laminar or turbulent.

The linear average flow velocity Ve is converted into an average flow velocity in the cross section of the flow tube 1 by using different calculation formulas for laminar flow and turbulent flow, and the flow rate is converted based on the converted average flow velocity. To calculate.

The linear mean flow velocity Ve is calculated in the case of laminar flow or turbulent flow.
A well-known formula can be used as a calculation formula for converting into the average flow velocity in the cross section of the flow tube. A well-known calculation is also used to calculate the flow rate by multiplying the average flow velocity in the flow pipe cross section thus obtained by the flow pipe cross sectional area.

[0024]

Since the ultrasonic flowmeter of the present invention is configured as described above, the calculation formula of the cross-sectional average flow velocity can be changed depending on the laminar flow or the turbulent flow, which enables more accurate flow measurement. Measurement accuracy is improved.

Since highly accurate measurement can be performed regardless of laminar flow or turbulent flow, measurement can be performed in a wide flow rate range, which is useful for expanding rangeability.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a flow velocity distribution.

FIG. 3A is a diagram showing a laminar flow velocity distribution, and FIG. 3B is a diagram showing a turbulent flow velocity distribution.

[Explanation of symbols]

 1 ... Flow tube 2, 3, 5, 6 ... Ultrasonic element 4, 7 ... Axis line of ultrasonic beam X ... Central axis of flow tube Va ... Maximum flow velocity Ve ... Linear average flow velocity

Claims (3)

[Claims] 1. A linear average flow velocity (Ve) on an axis (4) of the ultrasonic beam is measured by emitting an ultrasonic beam obliquely to the flow of a fluid flowing in a flow tube having a circular cross section. Then, in the ultrasonic flowmeter that calculates the flow rate based on the value converted into the average flow velocity in the cross section of the flow tube, in the direction parallel to the flow on the central axis (X) of the flow tube (1),
Of the ultrasonic beam to measure the maximum flow velocity (Va), and determine whether the flow is laminar flow or turbulent flow from the ratio of the maximum flow velocity (Va) and the linear average flow velocity (Ve). The ultrasonic flowmeter is characterized in that the calculation formula for converting the linear average flow velocity (Ve) into the average flow velocity in the cross section of the flow tube is changed. 2. Maximum flow velocity (Va) and linear average flow velocity (Ve)
When the ratio (Va / Ve) to and exceeds a constant value, the flow is determined to be laminar flow, and when the ratio (Va / Ve) is equal to or less than a constant value, the flow is determined to be turbulent. The ultrasonic flowmeter according to claim 1. 3. Two ultrasonic elements (2) provided in the pipe wall for measuring the linear mean flow velocity (Ve) on the axis (4) of the beam by the flow and oblique ultrasonic beams,
(3), and two ultrasonic elements (5) provided in the flow for measuring the maximum flow velocity (Ve) by the second ultrasonic beam,
The ultrasonic flowmeter according to claim 1 or 2, further comprising (6).