JP2008185515A - Flow measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To continuously measure the flow of fluid in a channel with a simple constitution, and to reduce the construction cost when it is installed in the channel and facilitate periodical verification and calibration with a simple and inexpensive constitution. <P>SOLUTION: An injection pipe 1 is arranged in a duct 110 on the upstream side. A fluid pressure detection device 2 is arranged in a duct 120 on the downstream side. CO<SB>2</SB>gas is injected into the duct 110 from the injection pipe 1, and the injection amount of the CO<SB>2</SB>gas is recognized. CO<SB>2</SB>gas is sampled using, as a sampling pipe, a fluid pressure detection body 21 on the upstream side of the fluid pressure detection device 2. Flow is determined based on the concentration of the sampled CO<SB>2</SB>gas. The fluid differential pressure between the fluid pressure detection body 21 on the upstream side and a fluid pressure detection body 22 on the downstream side is detected by a differential pressure indicator 3. The relation between the flow and differential pressure determined by the gas tracer method is investigated. Then, the flow is determined based on the differential pressure detected by the fluid pressure detection device 2 and the relation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flow rate measuring method for measuring the speed and flow rate of a fluid flowing in a pipeline.

  Conventionally, there are various types of flowmeters such as a differential pressure method represented by a pitot tube and an orifice, a vortex method, a hot wire method, and an impeller method as means for continuously measuring the flow rate installed in a pipe line. However, these methods have the following problems.

  First, there is a problem of high costs associated with precision machining. Secondly, there are constraints to maintain a predetermined performance when the flow meter is actually attached. For example, a sufficiently long straight pipe portion (hereinafter referred to as a necessary straight pipe portion) is provided in the upstream and downstream areas of the measurement point, and the measurement must be performed under a condition where the fluid is rectified, which is not practical. For this reason, most of the cases where the necessary straight pipe part for demonstrating the predetermined performance of the flowmeter is not obtained in actual use sites, the initial performance in the installed state and the verification and calibration after aging are not possible There's a problem.

  In recent years, some flowmeters have built-in honeycomb-shaped rectifiers for the purpose of shortening the required straight pipe section. However, periodic maintenance work is necessary to eliminate invalid energy consumption and clogging due to pressure loss. It has become a problem in terms of workability. In addition, the attachment to the flow path generally involves a flange connection that sandwiches a dedicated pipe line with respect to the flow path, so that there is another problem that a large-scale construction cost is separately generated and expensive.

On the other hand, as another method disclosed in Non-Patent Document 1, a substance different from the fluid to be measured is injected into the flow, and a sensor for detecting the foreign substance is arranged in the downstream area, so that from injection to detection. The tracer method that calculates the velocity of the fluid to be measured based on the time and distance traveled (distance between the foreign substance injection part and the foreign substance detection part), and the initial state quantity at the time of injection (concentration and injection of the foreign substance) There is a mixed dilution method in which the velocity of the fluid to be measured is calculated on the basis of the concentration of the different substances in the downstream region diluted by mixing with the fluid to be measured. However, these methods have a problem that the speed is measured only during a period in which a foreign substance is injected, and only temporary measurement is performed.
"Flow measurement handbook", published by Nikkan Kogyo Shimbun, July 10, 1979

  Due to the problems of the conventional flow rate measurement method described above, the equipment itself is inexpensive and installation costs in the flow path can be reduced, the required straight pipe section can be shortened, initial performance and aging can be calibrated, and pressure loss is reduced. There is a demand for a continuous flow rate measurement method that can reduce maintenance work.

  In view of these points, the present invention realizes low cost by simplifying the production process, can be easily installed in the flow path, relaxes equipment installation restrictions, and performs performance verification and calibration in the equipment installation state. It is possible to reduce the energy loss due to pressure loss, reduce maintenance work such as clogging, and provide a new flow measurement method capable of continuous measurement.

  In the flow rate measuring method according to claim 1, a fluid pressure detection device whose detection pressure changes depending on the speed of the fluid is installed in the flow path, and the flow rate of the fluid can be separately obtained by a temporary flow rate measurement unit, While changing the flow rate in the channel stepwise, the relationship between the detected pressure from the fluid pressure detector and the flow rate obtained by the temporary flow rate measuring means is investigated for each flow rate, and then the detected detected pressure Based on the relationship between the flow rate and the flow rate, the temporary flow rate measuring means can continuously measure the flow rate by obtaining the diversion in the flow path from the detected pressure of the fluid pressure detection device. . The temporary flow rate measuring means obtains the flow rate by, for example, a mixed dilution method, a tracer method, or a portable ultrasonic flow meter.

A flow rate measurement method according to a second aspect is the flow rate measurement method according to the first aspect, wherein a part or all of the fluid pressure detection device also serves as a detection unit in the temporary flow rate measurement unit. In this case, the fluid pressure detection device can be, for example, a detection means (sampling tube) that detects a different substance such as CO ₂ gas injected into the flow path.

  For example, under the condition that the flow rate of the fluid is fixed and the flow rate of the fluid is kept constant by fixing the opening of the inverters and dampers and valves of the fan and pump, different substances are injected into the flow path, The flow rate is measured using a tracer method or mixed dilution method that detects the arrival time and concentration of different substances. On the other hand, the pressure difference of the fluid pressure detector (configured with two types of pressure detectors) provided in the flow path is detected, and the relationship (correlation) between the flow rate and the pressure difference is examined. The present inventor has found that a unique relationship can be obtained between the flow rate and the pressure difference by repeating this investigation while changing the flow rate. Therefore, the present invention obtains a regression curve of the flow rate and the pressure difference from this relationship, or graphs it, so that the flow rate can be obtained from the pressure difference even when different substances are not injected. As a result, a temporary flow measurement method such as a mixed dilution method can be converted into a continuous flow measurement method.

  The fluid pressure detector provided in the flow path can also serve as a sampling tube or a different substance injection tube when the flow rate is obtained by a tracer method or a mixed dilution method. The fluid pressure detector can be diverted to general-purpose pipes (round, square, rectangular, etc.) so that two types of pressure (for example, total pressure and static pressure) can be detected in the flow path so as to cross the flow. Install. The fluid pressure detector closes one end, provides a pressure outlet at the other end, and opens a fluid pressure detection hole (or a sampling hole) in a straight line (constant direction) at an appropriate interval. The fluid pressure detection device is composed of two types of pressure detectors with different directions of fluid pressure detection holes. Moreover, the two types can be paired, and a plurality of pairs can be arranged in parallel in the flow path so that the average pressure in the flow path and the sampling can be homogenized.

  As a preferable opening direction of the fluid pressure detecting hole of the fluid pressure detecting body, one type may be opened so as to be directed toward the fluid flow, and the other opening may be disposed downstream. With this arrangement, the fluid pressure detector that is opened toward the fluid flow detects the total pressure of the fluid. On the other hand, the fluid pressure detector with the opening directed downstream senses the pressure in the vortex created by itself, and detects a pressure lower than the average static pressure in the flow path. As a result, the pressure difference between them (the detected differential pressure from the fluid pressure sensing device) is greater than the dynamic pressure detected by a Pitot tube or the like, and the measurement error of the detected pressure can be reduced.

  According to the flow rate measuring method of claim 1, a new flow rate measuring method capable of continuous measurement is obtained, and each of the different substance injection pipe, the sampling pipe, and the fluid pressure detection device, which are constituent elements, is precise. Since it can be achieved with general members (general-purpose pipes, etc.) that do not involve machining, low cost can be realized. Moreover, since the structure of each component is simple, it can be easily installed in the flow path regardless of whether it is a new or existing flow path, and construction costs can be kept low. In addition, since the accurate flow rate can be measured based on the tracer method and the mixed dilution method, the installation environment of the fluid pressure detector can be greatly relaxed compared to conventional flow meters, and regular verification and calibration can also be performed. It can be done in the state attached to the channel. Further, the installation of the fluid pressure detection device in the flow path that causes the pressure loss can be reduced by minimizing the number of the fluid pressure detection bodies that constitute the fluid pressure detection device.

  According to the flow rate measuring method of the second aspect, since a separate sampling tube or the like is not required, the configuration can be simplified.

Next, an embodiment of the flow rate measuring method of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing a flow rate measuring method according to an embodiment, and FIG. 1 (B) shows an AA cross section of FIG. 1 (A). This embodiment is an example in which the fluid to be measured is air and the dissimilar substance to be injected is carbon dioxide (CO ₂ ). The air duct 10 has an upstream duct 110, a downstream duct 120, and 120 with a chamber 10 a interposed therebetween. And have. An injection pipe 1 for injecting CO ₂ gas as a different substance is disposed in the upstream duct 110, and a fluid pressure detection device 2 is disposed in the downstream duct 120.

FIG. 2 is a view showing an injection tube 1 and a method of injecting a different substance CO ₂ gas in the embodiment. By supplying CO ₂ gas from the liquefied cylinder 20, high-purity CO ₂ gas can be obtained. The CO ₂ gas emitted from the cylinder 20 reaches the injection pipe 1 via the pressure reducing valve 30 and the electromagnetic valve 40 in order. The solenoid valve 40 is on / off controlled by a timer, and the injection amount is controlled by adjusting the secondary pressure of the pressure reducing valve 30. The injection tube 1 is provided with a number of thin injection holes 11 at predetermined intervals in the longitudinal direction. As a result, the CO ₂ gas is uniformly distributed in the duct 110 on the downstream side shown in FIG. A spray nozzle or the like may be used in place of the injection hole 11.

In the example of FIG. 1, CO ₂ gas is sprayed toward the downstream side by the injection pipe 1, but it may be sprayed toward the upstream side, and the injection pipe 1 is not a square pipe as shown in FIG. 2. A highly versatile shape such as a round pipe may be used.

On the other hand, the cylinder 20 is placed on a weigh scale 50, and the weigh scale 50 is used to check the amount of CO ₂ gas injected per unit time and fluctuation. The weigh scale 50 has an output function, and the weight reduction amount of the CO ₂ cylinder 20 with the passage of time from the start of injection can be sequentially stored in a personal computer or the like, which is useful information for later analysis. In the actual injection of the different substance (CO ₂ ), the amount is preferably controlled to be negligible as compared with the flow rate of the fluid to be measured (air).

Next, FIG. 3 shows a gas sampling configuration in the downstream region where the injection gas (CO ₂ ) is mixed. In this embodiment, the fluid pressure detector 2 is used for sampling CO ₂ gas. The fluid pressure detection device 2 in the figure is composed of two fluid pressure detection bodies 21 and 21 on the upstream side (H side) and two fluid pressure detection bodies 22 and 22 on the downstream side (L side), The fluid pressure detectors 21 and 22 form one pair along the flow direction, and two pairs are provided. Each fluid pressure detector 21, 21, 22, 22 is formed by a square pipe with one end closed, and pressure extraction ports 21 a, 21 a, 22 a, 22 a are provided at the other end.

  Further, the upstream fluid pressure detectors 21 and 21 have fluid pressure detection holes 21b and 21b opened at predetermined intervals on the upstream ridge line, and both pressure extraction ports 21a and 21a are connected. . Although not shown in FIG. 3, as shown in FIG. 1 (B), the fluid pressure detection bodies 22 and 22 on the downstream side are provided with fluid pressure detection holes 22b and 22b at predetermined intervals on the ridge line on the downstream side. While being opened, both the pressure outlets 22a and 22a are connected.

In the example of FIG. 3, CO ₂ gas sampling is performed using the H-side fluid pressure detectors 21 and 21 as sampling tubes. Then, the amount of air passing through the cross section of the duct 120 per second, that is, the flow rate, is obtained from the sampled CO ₂ gas concentration.

In addition, this flow volume can be calculated | required as follows, for example. When the volume of air (attention air) passing through the infusion pipe 1 in one second with air upstream from the infusion pipe 1 is Qi and the number of CO ₂ molecules contained in the unit volume of the attention air is Ni, the attention air The total number of CO ₂ molecules present therein is Qi × Ni. Incidentally, the number of molecules Ni is determined from the CO ₂ gas concentration sampled at a sampling tube before injecting the CO ₂ gas. If the volume of the CO ₂ gas injected from the injection tube 1 is Qp and the number of CO ₂ molecules is Np, the volume Qo of the air after the CO ₂ gas is injected is Qo = Qi + Qp. Since the total number of CO ₂ before and after the cross-section of the duct 110 at the location of the injection tube 1 is unchanged, and the number of molecules obtained from the CO ₂ gas concentrations sampled at a sampling tube after injecting CO ₂ gas and No, next The formula holds.

Qi x Ni + Qp x Np = Qo x No
Therefore, Qi × Ni + Qp × Np = (Qi + Qp) × No
Therefore, (Ni-No) * Qi = Qp * No-Qp * Np

From the above equation, the amount of air Qi passing through the cross section of the duct 110 per second is
Qi = (Qp * No-Qp * Np) / (Ni-No)
Therefore, Qi = Qp (Np-No) / (No-Ni)
It becomes. That is, the flow rate can be obtained from the injection conditions (Qp, Np) of CO ₂ injected from the injection tube 1 and the measured values of the number of CO ₂ molecules (Ni, No) sampled per unit volume before and after the injection.

Note that a sampling pipe intended only for sampling of the CO ₂ gas may be used separately, or the CO ₂ gas may be sampled by the fluid pressure detectors 22 and 22 located on the downstream side (L side). . In addition, the fluid pressure detectors 21 and 22 and the separately provided sampling pipes, like the injection pipe 1, can be reduced in cost by adopting a versatile and inexpensive shape such as a square pipe or a round pipe. . Furthermore, since there is no need for rectification as long as the injection gas (foreign substances) can be mixed with respect to the mounting position, it can be installed anywhere and the restriction on the mounting position can be greatly relaxed.

  In FIG. 3, the fluid pressure detectors 21 and 21 located on the upstream side are connected to each other. Thereby, even if the mixing on the flow path is insufficient, there is an effect of increasing the mixed state by sampling evenly from the cross section of the flow path, from the injection tube 1 to the sampling (the fluid pressure detectors 21, 21). Can be shortened. That is, the size (distance) of the measurement part can be reduced. Further, regarding the position of the hole for sampling (in this example, the fluid pressure detecting hole 21b), the hole is opened toward the upstream in FIG. 3, but even if the hole is opened vertically so as to be orthogonal to the flow, You may open a hole toward it.

  Next, an embodiment in which the fluid pressure detection device 2 detects the fluid pressure is shown in FIG. The pressure outlets 21a and 21a connected to the upstream fluid pressure detectors 21 and 21 and the pressure outlets 22a and 22a connected to the downstream fluid pressure detectors 22 and 22 are respectively differential pressure indicators. The differential pressure indicator 3 detects a differential pressure between the total pressure on the upstream side of the fluid pressure detecting device 2 and a pressure lower than the average static pressure in the duct on the downstream side. As described above, since the fluid pressure detection device 2 has a simple pipe structure, it can be installed at a low cost by simple construction using the side surface of the flow path regardless of whether it is a new or existing flow path.

In the present embodiment, since gas sampling such as a mixed dilution method is performed using a part of the fluid pressure detection device 2, the detected pressure from the fluid pressure detection device 2 cannot be read simultaneously. Therefore, after the flow rate is temporarily obtained by a gas tracer method, a mixed dilution method or the like, the detected differential pressure from the fluid pressure detector 2 is read with an indicator or the like. That is, the sampling flow rate value measured by the CO ₂ concentration detection method (mixed dilution method) shown in FIG. 3 and the sampling differential pressure value measured by the method shown in FIG. repeat. Then, this data is stored in, for example, a personal computer and the regression analysis of these data is performed.

  Thus, the correlation as shown in the graph of FIG. 5 can be obtained by examining the relationship between the flow rate and the detected differential pressure step by step while changing the flow rate. Once this correlation is obtained, the flow rate can be calculated backward based on the pressure (differential pressure) from the fluid pressure detection device 2 by using an approximate expression of a graph or a regression curve.

It is a conceptual diagram which shows the flow rate method of embodiment of this invention. It is a diagram illustrating a method of injecting the injection tube and different materials CO ₂ gas in the embodiment. It is a diagram showing a sampling form of CO ₂ gas in the downstream area in the embodiment. It is a figure which shows the form which detects the pressure of the fluid with the fluid pressure detection apparatus in embodiment. It is a figure which shows an example of the correlation graph of the flow volume and detected differential pressure | voltage in embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection pipe 2 Fluid pressure detection apparatus 21, 22 Fluid pressure detection body 21b, 22b Fluid pressure detection hole 3 Differential pressure indicator

Claims (2)

  A fluid pressure detection device whose detection pressure changes depending on the speed of the fluid is installed in the flow path, and the flow rate of the fluid can be obtained separately by a temporary flow rate measuring means. While changing, investigate the relationship between the detected pressure from the fluid pressure sensing device and the flow rate obtained by the temporary flow rate measuring means for each flow rate, and then based on the relationship between the investigated detected pressure and the flow rate, A flow rate measuring method characterized in that the flow rate can be continuously measured by the temporary flow rate measuring means by obtaining diversion in the flow path from the detected pressure of the fluid pressure detecting device.   2. The flow rate measurement method according to claim 1, wherein a part or all of the fluid pressure detection device also serves as a detection unit in the temporary flow rate measurement unit.

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