JP2956805B2 - Ultrasonic flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter for measuring the flow rate of a fluid by measuring the flow velocity in a pipe using ultrasonic waves .

[0002]

2. Description of the Related Art In general, the surface average flow velocity V ₀ which tubes flow of the fluid in the tube, is obtained by multiplying the Kandan area, etc.,
As one of the flow rate measuring means, for example, as shown in FIG. 3, the ultrasonic flow meter 1 has a pair of ultrasonic transducers 2 attached to the tube wall 3 and alternately transmits ultrasonic pulses. It is a flow rate measuring type flow meter that measures the flow velocity by propagating. The measured flow velocity is the linear average flow velocity V ₁ of the ultrasonic wave propagation path (measuring line). The surface average flow velocity distribution of the fluid in the pipe is obtained from Re = V ₀ · D / ν (1) (where Re: Reynolds number, D: pipe inner diameter, and ν: kinematic viscosity coefficient). Here, a flow with Re <2320 is a laminar flow, and a flow with Re ≒ 4000 or more is called a turbulent flow, and FIG. 4 shows an example of the distribution. In laminar flow,
Assuming that the ratio between the linear average flow velocity V ₁ and the surface average flow velocity V ₀ is κ, κ = V ₁ / V ₀ (2) In this case, κ = 4/3, which is constant. In turbulence,
There are several reports, but here we apply the one by Gay Virgel. Reynolds number Re and κ
5 is as shown in FIG.

[0003] In the actual flow rate measurement, usually, it becomes a measure of the turbulent basin, the flow rate Q in the turbulent _{basin, Q = V 0 · S ·} 3600 = V 1 / κ · πD 2/4 · 3600 ( m ³ / H) (3) (where V ₀ : average surface velocity, S: cross-sectional area, V ₁ : average linear velocity, κ: velocity correction coefficient corresponding to Reynolds number).

[0004]

However, in the turbulent flow region, κ in the equation (3) changes depending on the Reynolds number Re, that is, the surface average flow velocity V _{0, and} therefore, over a wide flow rate range. It is difficult to obtain a value with high accuracy. The present invention has been made in view of such a problem, and has an object to improve the accuracy of a measured value of a flow rate by configuring an ultrasonic flowmeter so that measurement can be performed in a laminar flow region where κ is constant. I do.

[0005]

In order to solve the above-mentioned problems, the present invention provides a main pipe through which a fluid flows, a branch pipe, and a pair of ultrasonic transducers respectively provided in the main pipe and the branch pipe. The branch pipe has an inner diameter of 23
20> Re = V ₀ · d / ν (where V ₀ : plane average flow of the pipe)
Speed, Re: Reynolds number, d: pipe inner diameter, ν: kinematic viscosity of fluid
(Sex coefficient). Further, in the ultrasonic flow meter, the measurement is performed by switching the ultrasonic flow in the main pipe and the branch pipe according to the flow velocity. The invention further main pipe for circulating the fluid, a branch pipe provided in the main pipe and branch pipes, respectively disposed relative to the pair of ultrasonic transducer, the branch
The ultrasonic transducer installed in the tube is opposed to the tube axis.
And the inner diameter of the branch pipe is set to 2320> Re = V ₀ .d /
ν (where, V ₀ : average surface flow velocity of tube, Re: Reynolds
Number, d: pipe inner diameter, ν: kinematic viscosity coefficient of fluid)
Was set to .

[0006]

[Function] In the laminar flow range where the flow velocity in the main pipe is small,
The definitive ultrasonic transducer, the flow rate measurement, the flow rate is increased and becomes turbulent, 2320> Re = V ₀ ·
Since the measurement was performed by the ultrasonic transducer in the branch pipe set so as to satisfy d / ν, the measurement under laminar flow was performed.
Measurement, and a highly accurate flow rate can be obtained.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an ultrasonic flow meter according to the present invention will be described with reference to the accompanying drawings. In FIG. 1, reference numeral 10 denotes an ultrasonic flowmeter 10 according to the first embodiment. This ultrasonic flowmeter 10 is provided with a branch pipe 12 in a main pipe 11 through which a fluid flows, and the main pipe 11 and the branch pipe. Ultrasonic transducers 13 and 14 are provided in a tube 12, respectively. In this case, in the branch pipe 12, the introduction part 15 is formed so as to be branched at right angles to the pipe axis of the main pipe 11, the branch part 16 is parallel to the pipe axis of the main pipe 11,
The reflux portion 17 is formed at right angles to the pipe axis of the main pipe 11. The ultrasonic transducers 13 and 14 are attached so that the ultrasonic wave propagation path forms a predetermined angle θ with respect to the tube axis. Note that the inner diameter d of the flow dividing portion 16 is 2320> R
It is set so as to satisfy e = V ₀ · d / ν.

In the ultrasonic flow meter 10, a procedure for switching the ultrasonic transducers 13 and 14 in the main pipe 11 and the branch pipe 12 in accordance with the flow velocity by a suitable control means (not shown) to perform measurement. Has adopted. That is, when the flow velocity is small and the flow is laminar, the main pipe 11
The flow is measured by the ultrasonic transducer 13 in the above, and if the flow velocity is large and the flow is in a turbulent region, the procedure is performed so as to be measured by the ultrasonic transducer 14 in the branch pipe 12.

In the above ultrasonic flow meter 10,
Re = V ₀ · D / ν (in this case, D is
From the relationship ( diameter) , in the range where the flow velocity in the main pipe 11 is small and laminar flow is constant, κ is constant, so that measurement can be performed by the ultrasonic transducer 13 in the main pipe 11. When the flow velocity increases and the turbulent flow occurs, the turbulence is measured by the ultrasonic transducer 14 in the branch pipe 12 having a small inner diameter, so that a highly accurate flow rate can be obtained.

Next, FIG. 2 shows a second embodiment. In the ultrasonic flow meter 20 in this case, the ultrasonic transducer 14 is disposed at both ends of the branching section 16 of the branch pipe 12 so that the ultrasonic propagation path is aligned with the pipe axis direction. Things. The ultrasonic wave propagation path length L formed between the ultrasonic transducers 14 has a distance corresponding to the length of the branching section 16.

According to such an ultrasonic flowmeter 20, the resolution of time measurement can be increased and the measurement can be performed with higher accuracy by adopting a longer ultrasonic wave propagation path length L.

(Effects of the Invention) As described above, according to the present invention, ultrasonic transducers are provided in both the main pipe and the branch pipe,
By operating any of the ultrasonic transducers according to the flow velocity, flow measurement in a laminar flow region can be performed. Therefore, since the ratio between the linear average flow velocity and the surface average flow velocity is measured based on a constant value, a highly accurate flow measurement value can be obtained.

[0013]

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing one embodiment of an ultrasonic flowmeter according to the present invention.

FIG. 2 is a schematic explanatory view showing a second embodiment of the ultrasonic flowmeter according to the present invention.

FIG. 3 is a schematic explanatory view of a conventional ultrasonic flowmeter.

FIG. 4 is a graph showing a flow velocity distribution in a circular pipe.

FIG. 5 is a graph showing a relationship between a flow velocity in a circular pipe and a flow velocity correction coefficient.

[Explanation of symbols]

 10, 20 Ultrasonic flowmeter 11 Main pipe 12 Branch pipe 13, 14 Ultrasonic transducer 15 Introducing section 16 Dividing section 17 Reflux section

Claims (3)

(57) [Claims] To 1. A main pipe for circulating the fluid, a branch pipe provided in the main pipe and branch pipes, respectively disposed relative to the pair of ultrasonic transducer, the internal diameter of the branch pipe, 232
0> Re = V ₀ · d / ν (where V ₀ : plane average flow of the pipe)
Speed, Re: Reynolds number, d: pipe inner diameter, ν: kinematic viscosity of fluid
( Ultrasonic coefficient) . 2. The ultrasonic flowmeter according to claim 1, wherein the measurement is carried out by switching between ultrasonic transducers in the main pipe and the branch pipe according to the flow velocity. To 3. A main pipe for circulating the fluid, ultrasonic the branch pipe provided in the main pipe and branch pipes, respectively disposed relative to the pair of ultrasonic transducer, is disposed in the branch pipe
Wave transmitters and receivers should face each other in the direction of the pipe axis.
The diameter is 2320> Re = V ₀ · d / ν (where V ₀ : tube
, Re: Reynolds number, d: tube inner diameter, ν:
An ultrasonic flowmeter which is set so as to satisfy a kinetic viscosity coefficient of a fluid .