JP6229144B2 - Flow measuring device - Google Patents

Description

  The present invention relates to an ultrasonic flow rate measuring device that measures a flow rate with a multi-layered flow path.

  2. Description of the Related Art Conventionally, as this type of flow rate measuring device, a device that measures a flow rate by dividing a flow path with a partition plate is known (for example, see Patent Document 1).

  7 and 8 show a flow rate measuring device described in Patent Document 1. FIG. FIG. 7 is a cross-sectional view showing a configuration of a conventional flow rate measuring device, and FIG. 8 is a cross-sectional view taken along the line B-B ′ in FIG.

  As shown in FIG. 7, the ultrasonic flow measuring device 100 includes a flow path block 101 and a sensor block 102.

  As shown in FIG. 8, the flow path 103 having a rectangular cross section through which the fluid to be detected of the flow path block 101 flows includes a first side wall part 104, a second side wall part 105 facing the first side wall part 104, The bottom plate portion 106 spanned between the first side wall portion 104 and the second side wall portion 105 and the opening 107 facing the bottom plate portion 106 are integrally configured.

  The flow path 103 is divided by a plurality of partition plates 108 so that a plurality of flat flow paths 109 are formed.

  As shown in FIG. 7, a first ultrasonic transducer 110 and a second ultrasonic transducer 111 are arranged in the sensor block 102, and are transmitted and received by these ultrasonic transducers 110 and 111. The flow rate is measured using an ultrasonic signal.

JP 2012-103149 A

  However, in the conventional configuration, when the flow path 103 is formed by a mold, a draft angle of the mold is required on the outer wall of the flow path, that is, the first side wall portion 104 and the second side wall portion 105. It was. For this reason, even if the width of each flat flow path 109 is made uniform in the vicinity of the bottom plate portion 106 in an attempt to arrange the pitch between the partition plates 108 evenly, the upper portion, that is, in the vicinity of the opening portion 107. It wasn't even. That is, the cross-sectional area of each flow path was not constant.

  Therefore, the flow rate flowing through the flow path 103 is not evenly distributed to each flat flow path 109. Therefore, even if the flow velocity is measured in any of the flat channels 109, the average flow velocity cannot always be captured. In order to obtain the average flow velocity, a correction coefficient for multiplying the measured flow velocity value is introduced. I had to calculate. Since this correction coefficient is generally not constant, there is a possibility that an error occurs in the obtained flow rate value.

  The present invention solves the above-mentioned conventional problems, and is measured by setting the cross-sectional area of each flow path so that the relationship between the flow rate and the pressure loss is substantially the same in each divided flow path. It is an object to provide an ultrasonic flowmeter in which the flow rate of the flow channel is set to an average flow rate, and the correction coefficient is substantially 1 and constant over the entire measurement flow rate range.

  In the flow rate measuring device of the present invention, the cross-sectional shape of each layer is determined so that the relationship between the flow rate of each layer and the pressure loss is the same in the flow path divided into multiple layers, so that the flow rate flowing through each layer can be made constant.

  As a result, since the average flow velocity can be measured in the multi-layer configuration, the flow rate can be calculated with a small correction coefficient and a small error.

1 is a schematic configuration diagram of a flow path part of a flow rate measuring device according to Embodiment 1 of the present invention. A-A 'sectional view of FIG. In FIG. 1, the left side view when the width of each layer on the lower surface is constant Graph of flow rate-pressure loss characteristics in the flow path shown in FIG. In FIG. 1, the left side view when the cross-sectional area of each layer is constant Graph of flow rate-pressure loss characteristics in the flow path shown in FIG. Sectional drawing which shows the structure in the conventional flow measuring device B-B 'sectional view of the flow path block in FIG.

A first aspect of the present invention is a multilayer flow path configured by dividing a cylindrical flow path having a trapezoidal cross section in a direction perpendicular to a parallel side of the trapezoidal cross section by a plurality of partition plates, and a parallel side of the trapezoidal cross section And a pair of ultrasonic transducers arranged upstream and downstream of the multilayer flow path, a propagation time measuring means for measuring a propagation time between the pair of ultrasonic transducers, and the propagation time measurement A flow rate calculation means for calculating a flow rate based on a flow velocity obtained from the propagation time measured by the means, and the relationship between the flow rate of each layer of the multilayer flow path and the pressure loss is substantially over the entire flow rate range to be measured. By defining the cross-sectional shape of each layer, it is possible to capture the average flow velocity in the measurement flow path, maintain a constant correction coefficient over the measurement flow range, and improve accuracy. Good measurement can be realized.

  In particular, the second invention can be easily designed by configuring so that the cross-sectional areas of the respective layers of the multilayer flow path of the first invention are substantially the same.

  In the third aspect of the invention, in particular, the partition plate of the second aspect of the invention can be easily assembled by being configured to be perpendicular to the upper and lower surfaces of the multilayer flow path.

  In the fourth aspect of the invention, in particular, the pair of ultrasonic transducers is arranged at a position where the ultrasonic wave propagates to a layer of both sides of the multilayer flow path of the third aspect divided by the partition plate. As a result, the propagation of a pair of ultrasonic waves can be performed symmetrically, and the measurement characteristics can be stabilized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the present embodiment.

(Embodiment 1)
The first embodiment will be described with reference to FIGS.

  FIG. 1 is a schematic configuration diagram of a flow rate measuring apparatus according to Embodiment 1 of the present invention, and FIG. 2 is a diagram showing a vertical cross section of AA ′ in FIG.

  In FIG. 1, the flow path portion has a cylindrical flow path 2 having a trapezoidal cross section, and the cylindrical flow path 2 is constituted by a lower flow path 2a and an upper cover 2b having a concave shape. The cylindrical flow path 2 has a trapezoidal cross section because of the draft when the cylindrical flow path 2 is formed with a mold.

  The recess-shaped lower flow path 2a is integrally formed from the side walls 2c and 2d and the bottom surface 2e.

  The cylindrical flow path 2 is divided into a first layer 6, a second layer 7, a third layer 8, and a fourth layer by a first partition plate 3, a second partition plate 4, and a third partition plate 5. Divided into layers 9, the overall structure is a multilayer flow path 1. In addition, an ultrasonic transducer holding unit 10 is attached to the upper cover 2b above the third layer 8.

  The third layer 8 is a measurement channel for measuring the flow rate. Hereinafter, the third layer 8 is referred to as a measurement channel. The layers other than the measurement channel 8 are non-measurement channels.

  The ultrasonic transducer holding unit 10 includes a pair of ultrasonic transducers including a first ultrasonic transducer 11 disposed on the upstream side and a second ultrasonic transducer 12 disposed on the downstream side. The containers are held by the first holding part 13 and the second holding part 14, respectively.

  The measurement channel 8 has an upper surface 15 formed by the upper cover 2b and a lower surface 16 formed by the lower channel 2a. The upper surface 15 has a first ultrasonic transmission window 17 and a second ultrasonic transmission window 18. The lower surface 16 is configured to act as an ultrasonic reflection surface.

  The arrows indicated by P1 and P2 are propagation paths of ultrasonic waves, and propagate so as to cross the measurement flow path 8.

  Signals from the first ultrasonic transducer 11 and the second ultrasonic transducer 12 are processed by the measuring circuit 20 (propagation time measuring means) and further calculated by the arithmetic circuit 21 (flow rate calculating means). The

  The first ultrasonic transducer 11, the second ultrasonic transducer 12, the multilayer channel 1, the measurement circuit 20, and the arithmetic circuit 21 form a flow rate measuring device 19.

  Next, flow measurement using ultrasonic waves will be described with reference to FIG.

  Let V be the flow velocity of the fluid flowing through the measurement flow path 8, C be the speed of sound in the fluid, and θ be the angle between the direction in which the fluid flows and the direction of ultrasonic propagation until the ultrasonic waves are reflected by the lower surface 16. Also, let L be the effective length of the propagation path of the ultrasonic wave that propagates between the first ultrasonic transducer 11 and the second ultrasonic transducer 12.

  At this time, the propagation time t1 until the ultrasonic wave emitted from the first ultrasonic transducer 11 reaches the other second ultrasonic transducer 12 is expressed by the following equation.

t1 = L / (C + Vcos θ) (1)
Next, the propagation time t2 until the ultrasonic wave emitted from the second ultrasonic transducer 12 reaches the other first ultrasonic transducer 11 is expressed by the following equation.

t2 = L / (C−Vcos θ) (2)
When the sound velocity C of the fluid is eliminated from the equations (1) and (2), the following equation is obtained.

V = L / (2cos θ ((1 / t1) − (1 / t2))) (3)
As can be seen from Equation (3), if L and θ are known, the flow velocity V can be obtained using the propagation times t1 and t2 measured by the measurement circuit 20.

  Next, as shown in the following equation, the overall flow rate Q is calculated by multiplying the flow velocity V by the cross-sectional area S of the cylindrical flow path 2.

Q = V x S (4)
However, in general, since the flow velocity V of the measurement flow path 8 is different from the average flow speed Vave of the entire tubular flow path 2, the actual flow rate Qt is obtained by adding a correction coefficient k to this flow rate Q as shown in the following equation. Multiply to find.

Qt = k x Q (5)
In order to make this correction coefficient constant in the entire flow rate range to be measured, the flow rate in the measurement flow channel 8, that is, the flow velocity must match the overall average flow velocity with all the divided cross-sectional areas being the same. There is.

  As a method for that purpose, it is conceivable to make the flow path width of each layer constant. However, when such a flow path is created using a mold, a draft is required in the mold, and it is difficult to make the flow path width constant over the height direction of each layer.

  This situation is shown in FIG. 3 showing the left side view of FIG.

  In FIG. 3, the side walls 2 c and 2 d of the multilayer channel 1 are inclined due to the draft angle.

  On the other hand, the partition plates 3, 4, 5 of the multilayer flow path 1 are set to be perpendicular to the upper surface 15 and the lower surface 16.

  Therefore, as shown in FIG. 3, even if the flow path width of each layer is set on the lower surface 16 as shown in the following expression (6), the side walls 2c and 2d of the cylindrical flow path 2 have an inclination. The part does not have an equal flow path width.

w1 = w2 = w3 = w4 (6)
In this case, the cross-sectional areas of the layers 6, 7, 8, and 9 are S1, S2, S3, and S4, and their relationship is as follows.

S1 = S4> S2 = S3
Therefore, FIG. 4 shows the relationship between the flow rate and the pressure loss in each layer in this case.

  As shown here, for the same pressure loss (differential pressure Pi), the flow rates flowing through the layers 6 and 9 and the layers 7 and 8 are different as qi1 and qi2. In this example, the layers 6 and 9 flow more than the layers 7 and 8.

Since the average flow velocity of each layer is obtained by dividing the flow rate of each layer by its cross-sectional area, the average flow velocity of layers 6 and 9 is obtained by dividing the large flow rate (qi1) by the large cross-sectional area (S1, S4), Since the average flow velocity of 8 is divided by a small flow rate (qi2) and a small cross-sectional area (S2, S3), the average flow velocity ratio between these layers is smaller than the flow rate ratio, but the relationship between pressure loss and flow rate. Are not proportional, the average flow velocities do not match.

  As described with reference to FIG. 1, the ultrasonic transducers 11 and 12 held by the ultrasonic transducer holding unit 10 are set so as to capture only the flow velocity of the measurement flow path 8. Since this value does not give an average flow velocity, the correction coefficient is not constant when calculating the total flow rate.

  What improved such a situation is the flow path shown in FIG. 5, which shows the configuration according to the present invention.

  In FIG. 5, the width of each layer is not constant as shown in FIG. 3, and is formed so that the cross-sectional area of each layer is the same as described below.

S1 = S2 = S3 = S4 (7)
And the relationship of the flow-path width | variety of the bottom face of each layer becomes like the following Formula. That is, the second layer and the third layer are the same as those in FIG. 3, but the first layer and the fourth layer are different, and the cross-sectional shapes are set so that the cross-sectional areas of the respective layers are the same. .

w1 = w4 <w2 = w3 (8)
The relationship between the flow rate of each layer and the pressure loss at this time is as shown in FIG. That is, since the cross-sectional areas of the respective layers are the same, the resistance curves of the respective layers are substantially the same.

  Therefore, the flow rate qi at the predetermined pressure loss (differential pressure Pi) is the same in any layer. Therefore, in the measurement flow path 8, since the average flow rate, that is, the average flow velocity can be measured, the correction coefficient is constant. This state covers the entire flow rate range to be measured.

  In the present embodiment, a pair of ultrasonic transducers are arranged in the measurement flow path 8, but the same effect is exhibited even if they are arranged across other layers such as the layer 7.

  Moreover, although the inclination of the side walls 2c and 2d of the cylindrical flow path 2 is based on the draft angle of the mold, it may be intentionally higher than that.

  As described above, the flow rate measuring device according to the present invention determines the correction coefficient by determining the cross-sectional shape of each layer so that the pressure loss of each layer of the multilayer flow path is substantially the same over the entire flow rate range. Can be constant. Therefore, accurate measurement is possible. Thereby, it can be applied to a wide range of applications including gas meters that require measurement accuracy.

DESCRIPTION OF SYMBOLS 1 Multilayer flow path 2 Cylindrical flow path 3 1st partition plate 4 2nd partition plate 5 3rd partition plate 11 1st ultrasonic transducer 12 2nd ultrasonic transducer 15 Upper surface 16 Lower surface 19 Flow rate measuring device 20 Measuring circuit (Propagation time measuring means)
21 Arithmetic circuit (flow rate calculation means)

Claims (4)

A multilayer flow path configured by dividing a cylindrical flow path having a trapezoidal cross section in a direction perpendicular to parallel sides of the trapezoidal cross section by a plurality of partition plates;
A pair of ultrasonic transducers disposed on the parallel sides of the trapezoidal cross section and upstream and downstream of the multilayer flow path;
A propagation time measuring means for measuring a propagation time between the pair of ultrasonic transducers;
A flow rate calculating means for calculating a flow rate based on the flow velocity obtained from the propagation time measured by the propagation time measuring means,
A flow rate measuring device in which the cross-sectional shape of each layer is determined so that the relationship between the flow rate and pressure loss of each layer of the multilayer flow path is substantially the same over the entire flow rate range to be measured. The flow rate measuring device according to claim 1, wherein the cross-sectional areas of the layers of the multilayer flow path are substantially the same. The flow rate measuring device according to claim 2, wherein the partition plate is configured to be perpendicular to the upper and lower surfaces of the multilayer flow path. The flow rate measuring device according to claim 3, wherein the pair of ultrasonic transducers are arranged so that ultrasonic waves propagate to a layer whose both surfaces are partitioned by the partition plate among the layers of the multilayer flow path.

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