JP4135432B2 - Flow measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow rate measuring device for measuring a flow rate of gas or the like.
[0002]
[Prior art]
A conventional flow measuring device of this type will be described with reference to FIG. In the figure, a flow rate detecting means 2 such as an ultrasonic type is provided in a part of the fluid passage 1 to measure the flow rate. When there is a periodic fluctuation in the flow, the flow rate measurement value varies depending on the measurement timing. For example, in a gas meter that measures household gas consumption, pressure fluctuation occurs when a gas engine is operated nearby. For this reason, in order to buffer the pressure fluctuation, a pulsation absorbing device 4 having a valve body 3 is provided to reduce the pulsation level.
[0003]
[Problems to be solved by the invention]
However, the conventional flow rate measuring device has a drawback that the flow turbulence caused by the pulsation absorbing device 4 and the deviation of the flow velocity distribution deteriorate the accuracy of the flow rate measurement. Further, when the valve body is opened, the transmission through the gap is assumed to be 1 / n of the area of the valve body in the partition wall of the area S.
TL ≒ 101ogn
For example, when the gap is 1/1000, the transmission loss does not exceed 30 db.
[0004]
Moreover, the frequency of 50HZ to 150HZ is usually a problem for the cavity resonance phenomenon of the fluid passage when the gas engine is operated. However, the shape of the fluid passage is changed for the cavity resonance, and the resonance frequency is changed. It is difficult to move the position to become a stomach.
[0005]
The present invention has been made in view of the conventional problems, and an object of the present invention is to provide a flow rate measuring device that does not have a movable part such as a valve body and improves pressure fluctuation resistance.
[0006]
[Means for Solving the Problems]
The present invention, in order to solve the above problems, a fluid passage disposed orthogonally to the inlet passage and an outlet passage, a flow rate detecting means for detecting the flow rate of the passage being disposed in said fluid passage, said fluid passage On the upstream side, it has a cross-sectional area equal to or larger than the cross section of the inlet passage, and intersects the fluid passage on the extension line in the direction of introduction of fluid from the inlet, and has a depth of 1 to 5 times the height of the fluid passage. A sound absorbing member is provided in a recess provided at one end of the fluid passage .
[0007]
The above invention suppresses pressure fluctuations and absorbs pulsation to obtain an accurate flow rate.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes a fluid passage disposed orthogonally to the inlet passage and an outlet passage, a flow rate detecting means for detecting the flow rate of the passage being disposed in said fluid passage, upstream of the fluid passage, an inlet passage section A concave portion having a cross-sectional area equal to or greater than that and extending in the direction of introduction of fluid from the inlet and intersecting with the fluid passage and having a depth of 1 to 5 times the height of the fluid passage. A sound absorbing member is provided in a recess provided at one end of the passage, and when there is pulsation, the pulsation is absorbed and the flow rate is accurately measured without causing flow disturbance. The surface of the sound absorbing member has wedge-shaped irregularities and further enhances sound absorption.
[0009]
In addition, a porous foam having a fine cell structure is provided as a sound absorbing member, and the pulsation is absorbed by this porous member to stabilize the flow rate measurement.
[0010]
Further, a bulk member is provided as a sound absorbing member, and by reducing the density of the fibrous member, pulsation is absorbed and flow measurement is stabilized.
[0011]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
[0012]
(Example 1)
FIG. 1 is a configuration diagram illustrating a flow rate measuring apparatus according to a first embodiment of the present invention. In FIG. 1, a flow rate detecting means 6 is provided in the fluid passage 5 to detect the flow rate of the passage. The flow rate detection means 6 is arranged with ultrasonic transmitters / receivers 6a and 6b on the upstream side and downstream side of the flow, respectively, and the flow rate is determined from the time difference between the ultrasonic propagation time from upstream to downstream and the ultrasonic propagation time from downstream to upstream. The details will be described later. A recess 7a having a depth of 1 to 5 times the height of the fluid passage is provided in the upstream 5a of the flow rate detection means 6. The recess 7a is provided with an absorbing member 7b to constitute the pressure fluctuation absorbing portion 7. The absorbing member 7b is press-fitted and fixed to the recess 7a using the elasticity of the absorbing member 7b . The upper end surface of the absorbing member 7b is provided to be 1/5 to 1 lower than the fluid passage height h from the lower end of the fluid passage to reduce pressure loss when passing through the bent portion. The pressure fluctuation suppressing effect is further increased by the absorbing member 7b. When a pressure fluctuation occurs, the flow momentarily causes a detour flow that flows into the recess 7a , but the absorbing member 7b suppresses the detour flow that flows into the recess 7a and can effectively absorb the pressure variation.
[0013]
Next, the operation will be described. In FIG. 1, the pressure fluctuation absorbing portion 7 is provided on the upstream side of the flow rate detecting means 6, and is configured to extend on the extension line of the fluid flow from the inlet and intersect the measurement flow path. When the fluid flows in the forward direction from the inlet to the outlet, in the case of a small flow rate, there is no flow that wraps around the concave portion 7a, and an almost shortest streamline is drawn. The recess 7a has a depth that is 1 to 5 times the height of the fluid passage. If it is less than 1 time, the effect of absorbing pressure fluctuation is small, and even if it is 5 times or more, an increase in effect is not recognized. When there is no flow, the pressure pulsation is absorbed by the recess 7a , so the pressure does not increase greatly. When a flow in the opposite direction is generated from the outlet to the inlet due to pressure fluctuation, the pressure rise is mitigated by the recess 7a .
[0014]
That is, when there is no flow in the fluid passage 5 or when the flow rate is small, the backflow generated by the pressure fluctuation is relaxed, and the forward flow is also suppressed by the pressure fluctuation absorbing portion 7, and the pulsating flow is reduced. The value of the flow rate detection means 6 does not vary greatly, and the average flow rate can be calculated. Also, if a large flow rate flows through the fluid passage 5 and a pressure fluctuation occurs at this time, the effect of suppressing the pressure fluctuation is small, so a flow rate error occurs. However, the average flow rate is large, and the error ratio is relatively small. So it doesn't matter.
[0015]
When the pressure fluctuation absorbing portion 7 is provided on the upstream side of the flow rate detecting means 6, the pressure fluctuation is suppressed in this portion, so that the influence of pulsation is further reduced on the flow rate detecting means 6.
[0016]
On the other hand, it is conceivable that the flow changes due to the provision of the pressure fluctuation absorber 7 upstream, thereby deteriorating the flow rate accuracy. However, since the fluid does not go around the recess 7a but flows on average, the influence on the flow rate detection means 6 is extremely small.
[0017]
FIG. 2 shows details of the flow rate detecting means using ultrasonic waves. In FIG. 2, the 2nd transmitter / receiver 6b which transmits / receives with the 1st transmitter / receiver 6a is arrange | positioned in the flow direction. 8 is a flow rate calculation means for processing and calculating a signal based on the ultrasonic wave, and 9 is a transmission circuit, which drives the first transmitter / receiver 6a by the trigger means 10 toward the second transmitter / receiver 6b, that is, from upstream to downstream. Send sound waves. The amplifier circuit 11 amplifies the signal received by the second transmitter / receiver 6b. The amplified signal is compared with the reference signal by the comparison circuit 12, and after the signal equal to or higher than the reference signal is detected, the repeater 13 triggers again. Transmission is performed from the means 10, and the time after the above transmission / reception is repeated a predetermined number of times is obtained by the time measuring means 14 such as a timer counter.
[0018]
Next, the switching means 15 switches the transmission / reception of the first transmitter / receiver 6a and the second transmitter / receiver 6b to transmit an ultrasonic signal from the second transmitter / receiver 6b toward the first transmitter / receiver 6a, that is, from downstream to upstream. Is repeated as described above, and the time is counted.
[0019]
Then, the flow rate calculation means 8 obtains the flow value from the time difference in consideration of the size of the pipeline and the flow state.
[0020]
(Example 2)
FIG. 3 is a block diagram showing an embodiment of the present invention, in which the pressure fluctuation absorbing portion 7 composed of the concave portion 7a and the absorbing member 7b on the upstream side of the flow rate detecting means 6 provided in the fluid passage 5 and the concave portion 16a on the downstream side are absorbed. A pressure fluctuation absorbing portion 16 composed of the member 16b is provided.
[0021]
Next, the operation will be described. When there is no flow, if a pulsation is applied from the outlet side, the pressure fluctuation absorber 16 absorbs the pulsation and the pressure does not increase greatly. Even if a local reverse flow occurs due to the pressure fluctuation, the flow is reduced by the pressure fluctuation absorber 16 . Since the pressure fluctuation absorber 16 is located downstream of the flow rate detection means 6, even if the flow is somewhat disturbed in this portion, the flow rate detection is not adversely affected.
[0022]
(Example 3)
In FIG. 3, the absorbent members 7b and 16b are provided with a porous foam, and the flow is extremely stable when the flow rate is small because the porous body absorbs pressure fluctuations. Further, by making the porous foam into a multilayer and reducing the density of the surfaces 7d and 16d in contact with the fluid, the absorption response is high and the flow rate detection accuracy is high. It is preferable that the surface layers 7d and 16d in contact with the fluid have an acoustic impedance close to that of gas and have a low density.
[0023]
Example 4
In FIG. 3, the absorbing members 7b and 16b are provided with a porous foam having a fine cell structure, and the size of the cell is preferably 1/4 to 1 of the wavelength of the ultrasonic wave.
[0024]
(Example 5)
In FIG. 4, the sound-absorbing material is bulky members 17b and 18b, and when the flow rate is small, the air flow in the bulky member absorbs pressure fluctuations and the flow is stabilized. Further, the bulk-like member has a micro tube-like hollow fiber with a hollow center, and the density is reduced to increase the absorption response. In particular, the surface on the side in contact with the fluid preferably has a low fiber density so that the acoustic impedance is close to that of gas and the density is low.
[0025]
(Example 6)
In FIG. 1, a plurality of wedge-shaped irregularities are formed on the end face of the absorbing member 7b. The absorbing member 7b is attenuated by repeating absorption and reflection in the wedge-shaped recess, and pressure fluctuation is further suppressed.
[0026]
As is clear from the above description, according to each of the embodiments described so far, the following effects can be obtained.
[0027]
(1) according to the flow rate measuring apparatus of the embodiment, the fluid passage 5, the flow rate detecting means 6 for detecting the flow rate of the fluid passage 5, and suppressing recess 7a of the pressure fluctuations on the upstream side of the fluid passage 5 Since it is provided, when there is pulsation, the pulsation is absorbed, and even when there is no pulsation, the flow rate can be accurately measured without causing flow disturbance.
[0028]
Further, since the pressure fluctuation is absorbed by the sound absorbing member 7b provided in the concave portion 7a, there is no pulsation and the flow stability can be further enhanced.
[0029]
Housing (2) further includes a fluid passage 5, the flow rate detecting means 6 for detecting the flow rate of the fluid passage 5, the upstream and downstream of the fluid passage 5, the sound absorbing member 7b is suppressed pressure fluctuations, 16b Since the concave portions 7a and 16a are provided, the flow in the downstream side 16a that suppresses the flow in the reverse direction while suppressing the flow in the reverse direction is less affected by the flow disturbance in the downstream concave portion 16a and is highly accurate. It can be measured. Furthermore, by making the upstream side and the downstream side symmetrical, the influence of the pressure fluctuation is offset and the influence on the flow rate measurement accuracy can be further reduced.
[0030]
(3) Further, since the sound absorbing members 7b and 16b are made of a porous foam, there is no pulsation, the flow stability can be improved, and the measurement accuracy is high.
[0031]
(4) Since the sound absorbing members 7b and 16b are made of a porous foam having a fine cell structure, absorption of pressure fluctuation is further increased, there is no pulsation, flow stability can be improved, and measurement accuracy is high.
[0032]
(5) Since the sound absorbing members 7b and 16b are constituted by bulk-like members, the density of the fibers can be reduced, and the flow disturbance due to the pressure fluctuation can be reduced even at a low flow rate, and measurement can be performed with high accuracy.
[0033]
(6) The surface of the sound-absorbing member 7b has wedge-shaped projections, and since absorption and reflection are repeated between the wedge-shaped projections, the sound absorption rate increases, there is no pulsation, flow stability can be further improved, and measurement accuracy is improved. high.
[0034]
【The invention's effect】
According to the present invention, the flow rate can be accurately measured.
[Brief description of the drawings]
FIG. 1 is a block diagram of a flow rate measuring device according to a first embodiment and a sixth embodiment of the present invention. FIG. 2 is a block diagram of a flow rate measuring means in the same device. FIG. 3 is an upstream side of a fluid passage according to a second embodiment of the present invention. FIG. 4 is a configuration diagram showing a porous foam having a concave portion and an absorbing member provided on the downstream side, and a fine cell structure of Examples 3 and 4. FIG. 4 is a configuration diagram of a bulk-like member of Example 5 of the present invention. ] Configuration of conventional pulsation absorber [Explanation of symbols]
5 Fluid passage 6 Flow rate detection means 7 Fluctuating pressure absorbing part 7a Recessed part 7b Absorbing member

Claims (5)

A fluid passage disposed orthogonally to the inlet passage and an outlet passage, said a flow rate detecting means for detecting the flow rate of the disposed within fluid passageway passage, upstream of the fluid passage, the inlet passage section equal to or higher than the cross-sectional A recess having an area and extending in the direction of introduction of fluid from the inlet and intersecting with the fluid passage and having a depth of 1 to 5 times the height of the fluid passage, at one end of the fluid passage A flow rate measuring device in which a sound absorbing member is provided in the provided recess. The flow rate measuring device according to claim 1, wherein the sound absorbing member is a porous foam . The flow rate measuring device according to claim 2, wherein the sound absorbing member is a porous foam having a fine cell structure . The flow rate measuring device according to claim 1, wherein the sound absorbing member is constituted by a bulk member . The flow rate measuring device according to any one of claims 1 to 3 , wherein a wedge-shaped protrusion is provided on a side of the sound absorbing member in contact with the fluid .