Air bubble detection method and air bubble detection device

Abstract

To provide a bubble detection method and a bubble detection device capable of quantitatively detecting mixing of bubbles into a fluid flowing through a pipe in real time.SOLUTION: A bubble detection method for detecting mixing of bubbles into a fluid flowing through piping includes the steps of: measuring flow rates by a propagation time difference type ultrasonic flowmeter installed at least on an inlet side and an outlet side of the piping; calculating normal flow rates that are not affected by the bubbles of the fluid flowing through the piping from the flow rates; calculating a difference between an inlet side normal flow rate and an outlet side normal flow rate among the normal flow rates; and determining that bubbles are mixed into the fluid flowing through the piping from the difference and estimating an amount of the mixed bubbles.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an air bubble detection method and an air bubble detection device for detecting the presence of air bubbles in a fluid flowing through a pipe. [Background technology]

[0002] To cool the blast furnace body, cooling staves (CS), which are cooling water pipes cast into the base material, are used to prevent the steel shell on the exterior of the furnace body from overheating, and cooling water is circulated through the cooling pipes that run throughout the furnace body. If the base material protecting the cooling pipes becomes detached due to the heat inside the furnace or the raw materials being charged into the furnace, the cooling pipes may be damaged. When a cooling pipe is damaged, the impact varies depending on the relative magnitude of the pressure inside the furnace (hereinafter referred to as furnace pressure) and the water pressure of the cooling water (hereinafter referred to as CS water pressure). If the CS water pressure is greater than the furnace pressure at the time of damage, cooling water will leak into the furnace. Conversely, if the CS water pressure is less than the furnace pressure, gases inside the furnace will be mixed into the cooling pipes (Figure 1).

[0003] Conventionally, detection of gas that has entered the piping from inside the furnace in damaged cooling piping has been carried out using a gas catcher that captures and accumulates the gas that has entered from inside the furnace in a detection pipe in the cooling water system (Patent Document 1), and the level of gas accumulated in the detection pipe is checked visually or by the output of a level switch, etc.

[0004] Furthermore, Patent Document 2 discloses a method for detecting air bubbles in cooling pipes using an ultrasonic flowmeter as a method for directly detecting air bubbles in the pipes. In the method of Patent Document 2, the sensitivity of the received ultrasonic signal decreases when air bubbles are present, and so air bubbles are detected based on this phenomenon. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 57-125337 [Patent Document 2] Patent No. 5070446 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the gas catcher in Patent Document 1 has a time delay until gas accumulates in the detection pipe, and is therefore unable to detect gas contamination in real time. Therefore, if a cooling pipe is damaged and there is a delay in identifying the damaged cooling pipe, proper treatment for the cooling pipe will not be taken, and cooling water will flood into the reactor.

[0007] On the other hand, commercially available (general-purpose) ultrasonic flow meters only have a flow rate (flow velocity) output, and therefore the method of detecting bubbles based on a decrease in the sensitivity of the received signal of the ultrasonic flow meter, as in Patent Document 2, does not fully grasp the sensitivity of the received signal, and in practice it is difficult to determine whether or not bubbles are present, and it is also not possible to quantitatively grasp the amount of bubbles present.

[0008] Therefore, the present invention provides a bubble detection method and bubble detection device that can detect in real time the presence of bubbles in a fluid flowing through a pipe. The present invention also provides a bubble detection method and bubble detection device that can quantitatively detect in real time the presence of bubbles in a fluid flowing through a pipe. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides the following [1] to

[10] .

[0010] [1] A bubble detection method for detecting the inclusion of air bubbles in a fluid flowing through a pipe, comprising: measuring the flow rate with a transit time ultrasonic flowmeter installed in the piping; detecting hunting based on a change in the measured flow rate over time; determining that air bubbles have been mixed into the fluid when hunting is detected; A bubble detection method comprising:

[0011] [2] The change in the measured flow rate over time is a method for monitoring that the time rate of change is greater than a threshold; a method for monitoring that the standard deviation of the flow rate over a period of time is greater than a threshold; and a method for monitoring the rate at which flows below a threshold occur over a period of time; The bubble detection method according to [1], wherein the bubble is detected by any one of the methods described above.

[0012] [3] A bubble detection method for detecting the presence of bubbles in a fluid flowing through a pipe, comprising: measuring the flow rate using a transit time ultrasonic flowmeter installed at least on the inlet and outlet sides of the piping; calculating a normal flow rate of the fluid flowing through the pipe that is not affected by bubbles from the flow rate; calculating a difference between the normal flow rate on the inlet side and the normal flow rate on the outlet side of the normal flow rate; determining whether air bubbles have been mixed into the fluid flowing through the pipe based on the difference and estimating the amount of mixed air bubbles; A bubble detection method comprising:

[0013] [4] When measuring the normal flow rate, A bubble detection method according to [3], in which a flow rate above a threshold value for a certain period of time is considered to be a flow rate not affected by bubbles, and its moving average value is considered to be the normal flow rate.

[0014] [5] A bubble detection method for detecting the presence of bubbles in a fluid flowing through a pipe, comprising: measuring the flow rate with a transit time ultrasonic flowmeter installed at least on the inlet and outlet sides of the piping; detecting hunting based on a change in the measured flow rate over time; calculating a normal flow rate of the fluid flowing through the pipe that is not affected by bubbles from the measured flow rate; calculating a difference between the normal flow rate on the inlet side and the normal flow rate on the outlet side of the normal flow rate; determining that there are air bubbles when hunting is detected, and / or determining that air bubbles have been mixed into the fluid flowing through the pipe from the difference and estimating the amount of mixed air bubbles; A bubble detection method comprising:

[0015] [6] The air bubble detection method according to any one of [1] to [5], further comprising outputting an abnormality based on the result of the air bubble determination.

[0016] [7] A bubble detection device that detects the presence of bubbles in a fluid flowing through a pipe, a transit time ultrasonic flowmeter installed in the piping; a flow rate capturing unit that captures the flow rate measured by the ultrasonic flow meter; a hunting determination unit that detects hunting based on a change over time in the measured flow rate; an air bubble detection unit that detects hunting and determines that air bubbles are present in the fluid; An air bubble detection device having:

[0017] [8] A bubble detection device that detects the presence of bubbles in a fluid flowing through a pipe, a transit time type ultrasonic flowmeter installed at least on the inlet and outlet sides of the piping; a normal flow rate calculation unit that calculates a normal flow rate of the fluid flowing through the piping that is not affected by bubbles; a bubble flow rate calculation unit that calculates a difference between the inlet normal flow rate and the outlet normal flow rate among the normal flow rates; an air bubble intrusion determination unit that determines whether air bubbles have been mixed into the fluid flowing through the pipe based on the difference and estimates the amount of mixed air bubbles; An air bubble detection device having:

[0018] [9] A bubble detection device that detects the presence of bubbles in a fluid flowing through a pipe, a transit time type ultrasonic flowmeter installed at least on the inlet and outlet sides of the piping; a flow rate capturing unit that captures the flow rate measured by the ultrasonic flow meter; a hunting determination unit that detects hunting based on a change over time in the measured flow rate; a normal flow rate calculation unit that calculates a normal flow rate of the fluid flowing through the piping that is not affected by bubbles; a bubble flow rate calculation unit that calculates a difference between the inlet normal flow rate and the outlet normal flow rate among the normal flow rates; an air bubble detection unit that determines that there are air bubbles when hunting is detected and / or determines that air bubbles have been mixed into the fluid flowing through the pipe based on the difference; An air bubble detection device having:

[0019]

[10] An air bubble detection device according to any one of [7] to [9], further comprising an abnormality output unit that outputs an abnormality based on the determination result of the air bubble detection unit. [Effects of the Invention]

[0020] According to the present invention, a transit time flow meter is installed in a pipe, and when hunting is detected from the change in the measured flow rate over time, it is determined that there are bubbles, making it possible to detect in real time that bubbles have been mixed into the fluid flowing through the pipe.

[0021] Furthermore, according to the present invention, a transit time flow meter is installed at the inlet and outlet of a pipe, and the amount of bubbles in the fluid flowing through the pipe is estimated from the difference between the flow rate at the inlet and the flow rate at the outlet, making it possible to detect bubbles mixed in the fluid flowing through the pipe in real time and quantitatively.

[0022] Therefore, by applying the present invention to cooling water piping used in the cooling staves of a blast furnace, for example, it is possible to detect damage to the cooling water piping early and take appropriate measures at an appropriate time, thereby preventing cooling water from flooding into the furnace. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a diagram illustrating the influence of the relationship between the furnace pressure and the CS water pressure in a conventional blast furnace CS when a pipe breaks. [Figure 2] FIG. 1 is a functional block diagram showing an example of a bubble detection device that detects the inclusion of bubbles in cooling water flowing through the piping of a blast furnace CS. [Figure 3] 3 is a flowchart for explaining the flow of an air bubble detection method in the air bubble detection device of FIG. 2. [Figure 4] FIG. 10 is a diagram for explaining hunting determination. [Figure 5] FIG. 1 is a diagram for explaining a method for detecting the presence of air bubbles using a transit time ultrasonic flowmeter based on the difference between the supply water flow velocity (flow rate) and the drain water flow velocity (flow rate). [Figure 6] FIG. 1 is a diagram for explaining the principle of a method for detecting the inclusion of air bubbles based on the difference between the supply water flow rate (flow rate) and the drain water flow rate (flow rate). DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0025] <Air bubble detector> First, the air bubble detector will be described. FIG. 2 is a functional block diagram showing an example of an air bubble detection device that detects air bubbles entering cooling water flowing through the piping of a blast furnace CS.

[0026] A blast furnace 100 is provided with cooling staves (CS) 102, which are cooling water pipes 103 cast from the base material, to prevent overheating of the steel shell 101 on the outer surface of the furnace body. The air bubble detection device 1 detects the presence of air bubbles in the cooling water flowing through the cooling water pipe 103, and includes two transit time ultrasonic flowmeters 10 installed on the inlet side (feedwater side) and outlet side (drainage side) of the cooling water pipe 103, and a determination unit 20. The determination unit 20 imports and processes the results (flow velocity and flow rate) of the two ultrasonic flowmeters 10 to determine the presence of air bubbles and calculate the amount of air bubbles present, and includes a calculation unit 30 and a memory unit 40.

[0027] The calculation unit 30 comprises a performance acquisition unit 31, a hunting determination unit 32, a normal flow rate calculation unit 33, an air bubble flow rate calculation unit 34, an air bubble intrusion determination unit 35, and an abnormality output unit 36. The memory unit 40 also stores an alarm for air bubble intrusion and trends in the amount of air bubbles in the system.

[0028] The result acquisition unit 31 acquires the flow velocity and flow rate results of the ultrasonic flowmeters 10 provided on the inlet and outlet sides of the cooling water pipe 103 .

[0029] The hunting determination unit 32 determines whether hunting has occurred based on the rate of change over time of the flow rate measured by the ultrasonic flowmeter 10 .

[0030] The normal flow rate calculation unit 33 calculates a normal flow rate that is not affected by bubbles from the flow rate measured by the ultrasonic flowmeter 10.

[0031] The bubble flow rate calculation unit 34 calculates the difference (range) between the actual inlet (supply water) flow rate and the actual outlet (drainage water) flow rate measured by the normal flow rate calculation unit 33 .

[0032] The air bubble presence determination unit 35 determines whether air bubbles are present in the cooling water flowing through the cooling water pipe 103 based on the hunting determination result of the hunting determination unit 32 and / or the calculation result of the air bubble flow rate calculation unit 34. Specifically, when hunting is detected by the hunting determination unit 32, the air bubble presence determination unit 35 determines that air bubbles are present in the cooling water flowing through the cooling water pipe 103, or determines whether air bubbles are present in the cooling water flowing through the cooling water pipe 103 based on the calculation result of the air bubble flow rate calculation unit 34, and estimates the amount of air bubbles that have been present. The determination of air bubble presence may be made using both the hunting determination result of the hunting determination unit 32 and the calculation result of the air bubble flow rate calculation unit 34.

[0033] When only the hunting determination result of the hunting determination unit 32 is used, it is possible to detect in real time whether or not there are bubbles in the cooling water flowing through the cooling water pipe 103. When the calculation result of the bubble flow rate calculation unit 34 is used, it is possible to detect not only the presence or absence of bubbles but also the amount of bubbles in real time. Furthermore, when both of these are used, it is possible to detect both the presence or absence of bubbles based on the hunting determination result and the amount of bubbles based on the calculation result of the bubble flow rate calculation unit 34.

[0034] The hunting determination and the estimation of the amount of bubbles using the difference (range) between the actual flow rates will be described in detail later.

[0035] If the air bubble detection unit 35 determines that air bubbles have been mixed into the cooling water flowing through the cooling water pipe 103, or if the estimated amount of air bubbles exceeds a threshold, the abnormality output unit 36 ​​outputs an alarm to the outside (such as a host computer or PATLITE (registered trademark)) and stores necessary information in the memory unit 40 (for example, the alarm, time, amount of mixed air bubbles, etc.).

[0036] In the above-described air bubble detection device 1, the calculation unit 30 is configured with the result acquisition unit 31, hunting determination unit 32, normal flow rate calculation unit 33, air bubble flow rate calculation unit 34, air bubble detection unit 35, and abnormality output unit 36, but the device can also be configured without the normal flow rate calculation unit 33 and air bubble flow rate calculation unit 34, and can only determine the presence or absence of bubbles based on the hunting determination result of the hunting determination unit 32. In such a device configuration, the presence or absence of bubbles can be determined by simply installing one ultrasonic flowmeter 10 on the inlet or outlet side.

[0037] In addition, the calculation unit 30 can be configured to exclude the hunting determination unit 32, and the bubble flow rate calculation unit 34 can calculate the difference between the actual inlet flow rate and the actual outlet flow rate measured by the normal flow rate calculation unit, thereby making it possible to determine whether bubbles have been mixed into the cooling water and estimate the amount of bubbles that have been mixed into the cooling water.

[0038] <Air bubble detection method> Next, a flow of the air bubble detection method in the air bubble detection device 1 configured as shown in Fig. 2 will be described. Fig. 3 is a flowchart for explaining the flow of the air bubble detection method.

[0039] First, the flow velocity and flow rate results of the ultrasonic flowmeters 10 provided on the inlet and outlet sides of the cooling water pipe 103 are input to the result input unit 31 (step ST1).

[0040] Next, the hunting determination unit 32 performs hunting determination based on the time rate of change of the flow rate measured by the ultrasonic flowmeter 10 (step ST2).

[0041] Next, normal flow rate calculation unit 33 calculates a normal flow rate that is not affected by air bubbles from the value measured by ultrasonic flowmeter 10 that does not hit air bubbles so as to eliminate the influence of air bubbles mixed in (step ST3).

[0042] Next, the bubble flow rate calculation unit 34 calculates the difference between the actual inlet flow rate and the actual outlet flow rate obtained in step ST3, and estimates the amount of bubbles mixed in the cooling water flowing through the cooling water pipe 103 (step ST4).

[0043] Next, the air bubble intrusion determination unit 35 determines whether air bubbles are present in the cooling water flowing through the cooling water pipe 103 based on the hunting determination result of the hunting determination unit 32 and / or the calculation result of the air bubble flow rate calculation unit 34 (step ST5). Specifically, in step ST5, if the hunting determination unit 32 detects hunting, it determines that air bubbles are present in the cooling water flowing through the cooling water pipe 103, or determines whether air bubbles are present in the cooling water flowing through the cooling water pipe 103 based on the calculation result of the air bubble flow rate calculation unit 34, and estimates the amount of air bubbles that have been mixed in. The determination of whether air bubbles are present may be made using both the hunting determination result of the hunting determination unit 32 and the calculation result of the air bubble flow rate calculation unit 34.

[0044] If it is determined in step ST5 that hunting is occurring, or if it is determined that the amount of mixed air bubbles is equal to or greater than the threshold, an alarm is output from the abnormality output unit 36, and necessary information such as the amount of mixed air bubbles is stored in the memory unit 40 (step ST6).

[0045] <Hunting detection> Next, the hunting determination will be described in detail. A method for detecting the presence of air bubbles by detecting hunting using a transit time ultrasonic flowmeter is shown in Figure 4. In Figure 4, a transit time ultrasonic flowmeter 200 is configured by arranging a pair of sensors, namely, an oscillator 200a and a receiver 200b, in a pipe 300, which emit and receive ultrasonic waves.

[0046] The transit time type ultrasonic flowmeter 200 calculates the flow rate by determining the flow velocity of the fluid from the difference in the propagation speed of the ultrasonic waves in the sensor measurement range (direction in which the ultrasonic waves pass) shown in Figure 4 (the difference between the propagation speed from the transmitting unit 200a to the receiving unit 200b and the propagation speed from the receiving unit 200b to the transmitting unit 200a). The flow rate is calculated by multiplying this by the cross-sectional area of ​​the pipe.

[0047] If gas is mixed into the fluid (cooling water) in the pipe 300, bubbles will intermittently pass through the sensor measurement range (ultrasonic wave propagation range). In this case, the difference in density between the bubbles and the fluid causes the ultrasonic wave to propagate at different speeds, resulting in a sudden increase in the rate of change over time of the flow rate indication, which can be considered to be hunting due to the mixing of bubbles. The rate of change over time can be determined, for example, by sequentially calculating the change in data between sampling periods and determining whether it exceeds a threshold. Note that a sampling period of 1 Hz or higher is desirable in order to capture the sudden change that occurs when bubbles are mixed in.

[0048] Other methods include monitoring the variation (fluctuation) of the flow rate and the frequency of bubble measurements. The method of monitoring the variation (fluctuation) of the flow rate is to monitor whether the standard deviation of the flow rate readings sampled over a certain period of time in the past exceeds a threshold. The method of monitoring the frequency of bubble measurements is to constantly calculate the occurrence rate of flow rate readings below a threshold, which can be considered to be bubble measurements, over a certain period of time in the past, and monitor whether the occurrence rate exceeds the threshold.

[0049] <Determining air bubble contamination based on the difference (gaps) between the flow rate / flow velocity readings on the water supply side (inlet) and the drainage side (outlet)> Next, the determination of air bubble inclusion based on the difference (range) between the indicated values ​​of the flow rate / flow velocity on the water supply side (inlet side) and the water discharge side (outlet side) will be described in detail. Figure 5 shows a method for detecting air bubble intrusion using a transit time ultrasonic flowmeter based on the difference between the water supply flow velocity (flow rate) and the drainage flow velocity (flow rate). This method requires the installation of ultrasonic flowmeters, each equipped with a pair of sensors (a transmitter and a receiver) that transmit and receive ultrasonic waves, on both the water supply and drainage sides to capture changes before and after air bubbles are introduced into the fluid. These ultrasonic flowmeters constantly monitor the flow rate and flow velocity readings of the fluid (cooling water) in the water supply and drainage pipes 300, and the difference between the readings on the ultrasonic flowmeters on the water supply and drainage sides is determined. If there is no difference, as in Figure 5(a), it is determined that air bubbles are not present. If there is a difference, as in Figure 5(b), it is determined that air bubbles are present.

[0050] Hereinafter, a case will be considered in which the pipe 300 is broken and external gas flows into the pipe. As shown in FIG. 5(b), the volume of the fluid on the upstream (supply water) side from the broken part of the pipe is V k , the volume of the fluid on the downstream (drain) side is V h The volume of gas flowing in from the broken part is V g Then, V h =V k +V g >V kFurthermore, the mixed gas acts to hinder the flow of fluid on the water supply side, slowing down the flow rate. Considering that the cross-sectional area of ​​the piping 300 is constant, the flow rate on the drain side increases when viewed from the water supply side.

[0051] In other words, as shown in Figure 6, when gas gets mixed into the piping, the gas disperses within the fluid and turns into bubbles, which cause the flow velocity on the supply side to decrease and the flow velocity on the drain side to increase, resulting in an increase in the flow velocity on the drain side relative to the supply side.Since an increase in flow velocity directly means an increase in flow rate, the increase in the flow rate on the drain side relative to the supply side can be considered the amount of mixed air bubbles.

[0052] Here, when air bubbles are mixed in, as described in (Hunting Determination), the output of a general-purpose transit time type ultrasonic flowmeter may hunt, so the following logic is used to handle the measurement value that correctly measures only the fluid velocity.

[0053] When air bubbles are present, the emitted ultrasonic waves collide with the bubbles, resulting in a flow rate measurement of 0 or an underestimated value. However, if there are not many bubbles, the ultrasonic waves propagate without hitting the bubbles, allowing for normal flow rate measurement, so if a normal measured signal can be determined, it is possible to detect the velocity of the fluid without the influence of bubbles.

[0054] In this case, flow rate indication values ​​above a threshold for a certain period of time can be measured without the ultrasonic waves hitting any bubbles, so it can be assumed that the fluid velocity has been measured at that time, and a method can be used in which the moving average value of the flow rate at that time is used as the measured value of the fluid flow rate excluding the influence of bubbles.

[0055] Alternatively, as the velocity of the fluid excluding the influence of bubbles, a group of flow rates concentrated at the top may be statistically extracted using a clustering (stratification) technique from the flow rate indication values ​​within a certain period of time.

[0056] <Effects of the embodiment> As described above, according to this embodiment, a transit time ultrasonic flowmeter is installed in a pipe, and when hunting is detected from the time change in the measured flow rate of the fluid (cooling water), it is determined that there are bubbles, thereby making it possible to detect in real time that bubbles have been mixed into the fluid (cooling water) flowing through the pipe. Furthermore, by installing transit time ultrasonic flowmeters on the inlet and outlet sides of the cooling water pipe and estimating the amount of bubbles in the fluid flowing through the pipe from the difference between the inlet flow rate and the outlet flow rate, it is possible to quantitatively detect bubbles mixed into the cooling water flowing through the pipe in real time. Furthermore, by performing both of these, it is possible to perform more accurate bubble detection in real time and quantitatively.

[0057] By using this method to detect bubbles in the cooling water in the cooling water piping used in blast furnace CS, if the cooling water piping is damaged, it is possible to detect the damage early and take action at the appropriate time, thereby preventing cooling water from flooding into the furnace.

[0058] <Other applications> Although the embodiments of the present invention have been described above, these are merely examples and should not be considered limiting. The above embodiments may be omitted, substituted, or modified in various ways without departing from the spirit of the present invention.

[0059] For example, in the above embodiment, an example was shown in which two transit time type ultrasonic flow meters were installed on the inlet and outlet sides, but if only hunting judgment is performed as described above, only one flow meter may be used. Also, if the piping is long and early detection of air bubble contamination is required, more ultrasonic flow meters may be installed. For example, if the purpose is to quickly identify damage to the cooling water piping of the entire blast furnace, several hundred ultrasonic flow meters must be installed throughout the piping.

[0060] Furthermore, in the above embodiment, an example was given of detecting bubbles mixed in cooling water flowing through the piping of a blast furnace CS, but this is not limited to this and the invention can be applied to any piping through which a fluid flows. [Explanation of symbols]

[0061] 1. Air bubble detector 10 Transit time ultrasonic flowmeter 20 Bubble detection unit 30 Arithmetic section 40 Storage section 100 blast furnace 101 Ironhide 102 Cooling Stave (CS) 103 Cooling water piping (piping)

Claims

1. A bubble detection method for detecting air bubbles mixed into a fluid flowing through a pipe, comprising: measuring the flow rate using a transit time ultrasonic flowmeter installed at least on the inlet and outlet sides of the piping; calculating a normal flow rate of the fluid flowing through the pipe that is not affected by bubbles from the flow rate; calculating a difference between the normal flow rate on the inlet side and the normal flow rate on the outlet side of the normal flow rate; determining whether air bubbles have been mixed into the fluid flowing through the pipe based on the difference and estimating the amount of mixed air bubbles; A bubble detection method comprising:

2. When measuring the normal flow rate, 2. The air bubble detection method according to claim 1, wherein a flow rate equal to or greater than a threshold value for a certain period of time is regarded as a flow rate not affected by air bubbles, and a moving average value of the flow rate is regarded as the normal flow rate.

3. A bubble detection method for detecting air bubbles mixed into a fluid flowing through a pipe, comprising: measuring the flow rate with a transit time ultrasonic flowmeter installed at least on the inlet and outlet sides of the piping; detecting hunting based on a change in the measured flow rate over time; calculating a normal flow rate of the fluid flowing through the pipe that is not affected by bubbles from the measured flow rate; calculating a difference between the normal flow rate on the inlet side and the normal flow rate on the outlet side of the normal flow rate; determining that there are air bubbles when hunting is detected, and / or determining that air bubbles have been mixed into the fluid flowing through the pipe from the difference and estimating the amount of mixed air bubbles; A bubble detection method comprising:

4. The air bubble detection method according to claim 1 , further comprising outputting an abnormality signal based on the result of the air bubble determination.

5. An air bubble detection device that detects air bubbles mixed into a fluid flowing through a pipe, a transit time type ultrasonic flowmeter installed at least on the inlet and outlet sides of the piping; a normal flow rate calculation unit that calculates a normal flow rate of the fluid flowing through the piping that is not affected by bubbles; a bubble flow rate calculation unit that calculates a difference between the inlet normal flow rate and the outlet normal flow rate among the normal flow rates; an air bubble intrusion determination unit that determines whether air bubbles have been mixed into the fluid flowing through the pipe based on the difference and estimates the amount of mixed air bubbles; An air bubble detection device having:

6. An air bubble detection device that detects air bubbles mixed into a fluid flowing through a pipe, a transit time type ultrasonic flowmeter installed at least on the inlet and outlet sides of the piping; a flow rate capturing unit that captures the flow rate measured by the ultrasonic flow meter; a hunting determination unit that detects hunting based on a change over time in the measured flow rate; a normal flow rate calculation unit that calculates a normal flow rate of the fluid flowing through the piping that is not affected by bubbles; a bubble flow rate calculation unit that calculates a difference between the inlet normal flow rate and the outlet normal flow rate among the normal flow rates; an air bubble inclusion determination unit that determines the presence of air bubbles when hunting is detected, and / or determines that air bubbles have been mixed into the fluid flowing through the pipe from the difference and estimates the amount of mixed air bubbles; An air bubble detection device having:

7. 7. The air bubble detection device according to claim 5, further comprising an abnormality output unit that outputs an abnormality signal based on the determination result of the air bubble detection unit.

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