JP5336640B1 - Thermal flow meter - Google Patents

Abstract

A flow rate value with a small measurement error can be obtained even in an installation location where a sufficient length of a straight pipe cannot be secured and a flow field in a pipeline is not stable.
One heat generation and temperature sensing part M0 is located at the center of the inner peripheral surface of the sensor unit. Further, between the central part of the pipe line 13 of the sensor unit and the wall surface of the pipe line 13, five heat generating temperature sensing parts M <b> 51 to 55 of the first element are arranged at an equal angle θ. A negative error in the measured value of the heat generation and temperature sensing unit M0 disposed at the center of the pipe line and a plurality of heat generation and temperature sensing parts M51 to 55 disposed on a circle of 0.7R from the center of the line 13 By canceling out the positive error due to the sum of the measurement values, it is possible to obtain a measurement value with a small error.
[Selection] Figure 2

Description

  The present invention relates to a thermal flow meter in which a plurality of flow velocity detection elements are arranged in a flow line.

  In Patent Document 1, as shown in FIG. 25, a cylindrical sensor unit 3 in which four flow rate sensors 2 are arranged in a flow pipe 1 is installed, and the amount of heat carried away by the fluid passing through the sensor unit 3 is measured. A thermal flow meter that measures and measures the flow rate is described. By using a plurality of flow velocity sensors 2 in this way, an average value of the flow velocity can be calculated and an accurate flow rate can be obtained.

  In Patent Document 2, as shown in FIG. 26, one flow rate sensor 2 is disposed at the center portion in the flow channel tube 1, and the flow rate at the center portion of the flow channel obtained by the flow rate sensor 2 is calculated as a flow rate calculation unit. Describes a thermal flow meter that calculates the flow rate.

  Patent Document 3 describes a thermal flow meter in which four flow velocity sensors 2 are arranged on a circular cross section in a flow channel tube 1. By arranging a plurality of flow rate sensors 2, by comparing the outputs of the respective flow rate sensors 2 with each other, it is possible to easily identify the flow rate sensor 2 having deteriorated characteristics.

JP-A-8-5426 Japanese Patent Laid-Open No. 9-68448 JP 2007-192775 A

  In order to stably measure the flow velocity, a state in which the fluid velocity distribution is stable is necessary, and for that purpose, a sufficient straight pipe length is indispensable at least upstream of the installation location of the thermal flow meter. However, depending on the installation environment, it may be unavoidable to install in a place where the length of the straight pipe cannot be secured sufficiently.

  In such an environment, the velocity distribution of the fluid becomes asymmetric from the central axis in the pipe and forms a non-uniform flow field. Therefore, even if the thermal flow meter described in Patent Documents 1 to 3 is installed, Since the flow field is disturbed, there is a problem that a large error occurs in the measured flow rate value and a true value cannot be obtained.

  An object of the present invention is to provide a thermal type flow meter that solves the above-described problems and that has a plurality of flow rate detection elements arranged at predetermined positions in a fluid pipe and obtains a flow rate based on these outputs. .

  A thermal flow meter according to the present invention for solving the above-mentioned problems is a thermal flow meter having a plurality of flow rate detection elements in a pipe, and one flow rate is provided on a cross section of the pipe. A detection element is arranged at the center of the pipe line, and a plurality of other flow velocity detection elements are arranged at an equal angle between the center part and the pipe wall of the pipe line. The average is obtained as a measured value.

  By using the thermal flow meter of the present invention, it is possible to obtain a flow rate value with a small measurement error even at an installation location where the straight pipe length cannot be sufficiently secured and the flow field in the pipe is not stable.

It is a block diagram of the thermal type flow meter of a present Example. It is the layout which has arrange | positioned one heat_generation | fever temperature sensing part on the circle of 0.7R at the center part. It is explanatory drawing of the velocity distribution of the fluid in a flow-path pipe. It is the layout which has arrange | positioned one heat_generation | fever temperature sensing part on the circle of 0.7R at the center part. It is the layout which has arrange | positioned one heat generating temperature sensing part on the circle of 0.7R at the center part. It is the layout which has arrange | positioned one heat_generation | fever temperature sensing part on the circle of 0.7R at the center part. FIG. 6 is a graph showing the straight pipe length and the error between the measured value and the flow velocity value when one exothermic temperature sensing portion is arranged in the center and three on the 0.7R circle and the flow rate is 10%. FIG. 5 is a graph showing a straight pipe length and an error between a measured value and a flow velocity value when one exothermic temperature sensing unit is arranged in a central part and four exothermic temperature sensing parts are arranged on a 0.7R circle and the flow rate is 10%. FIG. 5 is a graph showing the straight pipe length and the error between the measured value and the flow velocity value when one exothermic temperature sensing part is arranged at the center and five exothermic temperature sensing parts are arranged on a 0.7R circle and the flow rate is 10%. FIG. 5 is a graph showing the straight pipe length and the error between the measured value and the flow velocity value when one exothermic temperature sensing part is arranged on the center part and six exothermic temperature sensing parts are arranged on a 0.7R circle and the flow rate is 10%. FIG. 5 is a graph showing a straight pipe length and an error between a measured value and a flow velocity value when one exothermic temperature sensing portion is arranged in the center and three on a 0.7R circle and the flow rate is 50%. FIG. 5 is a graph showing the straight pipe length and the error between the measured value and the flow velocity value when one exothermic temperature sensing part is arranged on the center part and four exothermic temperature sensing parts are arranged on a 0.7R circle and the flow rate is 50%. FIG. 5 is a graph showing a straight pipe length and an error between a measured value and a flow velocity value when one exothermic temperature sensing portion is arranged in a center portion and five on a 0.7R circle and the flow rate is 50%. FIG. 6 is a graph showing the straight pipe length and the error between the measured value and the flow velocity value when one exothermic temperature sensing portion is arranged at the center and six exothermic temperature sensing portions are arranged on a 0.7R circle and the flow rate is 50%. FIG. 6 is a graph showing the straight pipe length and the error between the measured value and the flow velocity value when one exothermic temperature sensing portion is arranged in the center and three on a 0.7R circle and the flow rate is 100%. FIG. 6 is a graph showing the straight pipe length and the error between the measured value and the flow velocity value when one exothermic temperature sensing part is arranged on the center part and four exothermic temperature sensing parts are arranged on a 0.7R circle and the flow rate is 100%. FIG. 5 is a graph showing a straight pipe length and an error between a measured value and a flow velocity value when one exothermic temperature sensing portion is arranged in a central portion and five exothermic temperature sensing portions are arranged on a 0.7R circle and the flow rate is 100%. FIG. 6 is a graph showing the straight pipe length and the error between the measured value and the flow velocity value when one exothermic temperature sensing part is arranged on the center part and six exothermic temperature sensing parts are arranged on a 0.7R circle and the flow rate is 100%. It is the graph which put together the average value of the error of exothermic temperature sensing part M0 and Mn at a flow rate of 10%. It is the graph which put together the average value of the error of exothermic temperature sensing part M0 and Mn at a flow rate of 50%. It is the graph which put together the average value of the error of exothermic temperature sensing part M0 and Mn at a flow rate of 100%. It is the graph which put together 5 exothermic temperature sensitive parts on the circle of 0.3R, 0.5R, and 0.7R at the center, and put it together by flow rate 10%. It is the graph which put together 5 exothermic temperature sensing parts on the circle of 0.3R, 0.5R, and 0.7R at the center, and put it together by flow rate 50%. FIG. 5 is a graph in which five heat-generating temperature sensing portions are arranged on a circle of 0.3R, 0.5R, and 0.7R at the center and are summarized at a flow rate of 100%. It is a block diagram which has arrange | positioned four flow velocity sensors in the flow-path pipe | tube of a prior art example. It is the block diagram which has arrange | positioned one flow velocity sensor in the flow-path pipe center of a prior art example.

The present invention will be described in detail based on the embodiment shown in FIGS.
FIG. 1 is a cross-sectional view along the direction in which a fluid flows, for example, in a thermal flow meter for gas flow measurement of an embodiment. The fluid flows in the direction of the arrow from right to left, and a cylindrical sensor unit 12 is inserted in the middle of the flow path tube 11. The inner diameter of the pipe line 13 of the sensor unit 12 is the inner diameter of the flow path pipe 11. And the same diameter.

  The sensor unit 12 includes a first element having a heat generation temperature sensing part M at the tip for heating the gas flow upstream and measuring the temperature, and a temperature sensing part m for measuring the temperature downstream. A plurality of flow velocity detection elements each including a pair of second elements provided at the tip are provided. The exothermic temperature sensing part M of the first element and the temperature sensing part m of the second element are inserted so as to protrude toward the center of the conduit 13. The first and second elements are inserted at the same depth as shown in FIG. 1, and the first element is installed on the upstream side, but the second element is arranged on the upstream side and the first element on the downstream side. These elements may be arranged. In this case, a step or the like may be provided at the insertion location so as not to be affected by the flow of the upstream element.

  Each flow rate detecting element is a pair of temperature sensing units m arranged on the upstream side and downstream side, and a current necessary for maintaining the temperature difference detected by the heating temperature sensing unit M constant by heating is a heating temperature sensing unit. The flow rate value of the fluid is measured based on this amount of current. The flow rate can be obtained by multiplying the measured flow velocity value by the cross-sectional area of the pipe 13.

  FIG. 2 is a layout diagram of the first element composed of the heat generation and temperature sensing portion M in the direction orthogonal to the direction in which the fluid flows, that is, in the cross-sectional direction of the pipe line 13. It is located in the center of the inner peripheral surface of. Further, between the central part of the pipe line 13 and the wall surface of the pipe line 13, five heat generating temperature sensing parts M 51 to 55 of the first element are arranged at an equal angle θ. In the present embodiment, it is possible to obtain a highly accurate flow rate value by combining the measurement values obtained by such a plurality of flow rate detection elements.

  FIG. 3 is an explanatory diagram of the velocity distribution of the fluid in the flow channel tube 11. Line a is a velocity distribution showing turbulent flow with a Reynolds number of about 3000, and is a velocity distribution when the flow rate per time is large, that is, when the flow velocity of the flow path tube 11 is high.

  A line b is a velocity distribution showing a laminar flow with a Reynolds number of about 2000, and is a velocity distribution when the flow rate per time is small, that is, when the flow velocity of the flow path tube 11 is low. During laminar flow, the central axis of the channel tube 11 has the fastest flow rate, and the flow rate becomes slower as it approaches the wall surface of the channel tube 11. As the flow velocity per hour flowing in the flow channel pipe 11 increases, the velocity distribution of the laminar flow of the line b changes to the velocity distribution of the turbulent flow of the line a.

  In the channel tube 11, the fluid does not flow uniformly at the same flow rate, but the flow rate that changes with time is measured. Then, the point that is least affected by the change in the flow rate per time is the intersection P of the line a and the line b.

  The intersection P between the average turbulent velocity distribution such as the line a and the average laminar velocity distribution such as the line b is a position about 0.7 times the radius R from the center of the flow channel 11. I know that When the heat generation and temperature sensing parts M51 to M55 are arranged on the circle of 0.7R and the flow velocity is measured from the average of these, the flow path 11 is changed from a laminar flow field to a turbulent flow field or a turbulent flow field. Even if the flow field changes from laminar to laminar flow field, it is possible to calculate a measurement value that is less affected by the change.

  Line c is an estimated laminar velocity distribution in a place where the length of the straight pipe cannot be sufficiently secured, and is uneven. In a portion where the straight pipe length is short immediately after the pipe is bent, a drift is likely to occur, and the velocity distribution that is symmetric with respect to the center of the laminar flow such as the line b is influenced from the center such as the line c due to the influence of the bending direction or the like. It is presumed that the drift of the velocity distribution is somewhat biased. Due to this drift, the top of the laminar flow velocity distribution shifts, and a negative error occurs in the measured value of the heat generation and temperature sensing part M0 at the center.

  When the velocity distribution of the fluid in the flow path pipe 11 is shifted at the time of laminar flow, the error between the measured value and the actual flow velocity value with a thermal flow meter in which a sensor is arranged only at the center, for example, becomes large. . On the other hand, when the velocity distribution of the fluid in the flow channel tube 11 is turbulent, the velocity distribution changes less than the laminar flow even if the center moves and becomes asymmetrical. There is little error in.

  Therefore, in this embodiment, in order to obtain a measurement value with a small error regardless of whether the flow distribution in the flow pipe 11 is a drift flow, laminar flow or turbulent flow field as indicated by the line c, In order to compensate for a negative error caused by the heat generation and temperature sensing portion M0, a plurality of heat generation and temperature sensing portions Mn are arranged on a circle of 0.7R from the center. Arrange at equal angles.

  In order to demonstrate this effect, simulation was performed using a CFD simulator employing a physical model of laminar flow and turbulent flow based on the RNGk-ε equation by a supercomputer.

  That is, on the circle of 0.7R from the central part, 3 to 6 heat-generating temperature sensing parts Mn are arranged in the pipe 13 at an equal angle, and one heat-generating temperature sensing part M0 is arranged in the central part. The error between the simulation measurement value and the assumed flow velocity value for the straight pipe length obtained in each was calculated.

  FIG. 4 is a layout diagram in which three exothermic temperature sensing parts M31 to M33 are arranged at equal angles on a circle of one exothermic temperature sensing part M0 and 0.7R in the central part, and FIG. FIG. 6 is a layout view in which four exothermic temperature sensing parts M41 to M44 are arranged at an equal angle on a circle of one exothermic temperature sensing part M0 and 0.7R, and FIG. It is the layout which has arrange | positioned the six heat_generation | fever temperature sensing parts M61-M66 on the circle of warm part M0 and 0.7R at equal angles. FIG. 2 is a layout diagram in which five exothermic temperature sensing parts M51 to M55 are arranged at an equal angle on a circle of 0.7R.

  7 to 10 show a straight pipe length in the case of one exothermic temperature sensing part M0 in the central part and 3-6 exothermic temperature sensing parts Mn installed at an equal angle on a circle 0.7R from the central part. Is a graph showing the ratio of error between the simulation measured value and the assumed flow velocity value, and shows the simulation result when the flow rate is 10% of the maximum flow rate per time. In each graph, a curve indicating an error in the simulation measurement values of the heat generation and temperature sensing portions M0 and Mn installed and an average value of these errors is described.

  Similarly, FIG. 11 to FIG. 14 are arrangements of 3 to 6 exothermic temperature sensing parts Mn on a circle of 0.7 R from the center, respectively, and the flow rate is 50% with respect to the maximum flow rate per hour. It is a graph which shows the simulation result when doing.

  FIGS. 15 to 18 show the arrangement of 3 to 6 exothermic temperature sensing parts Mn on a circle of 0.7 R from the center, where the flow rate is 100% with respect to the maximum flow rate per hour. It is a graph which shows a simulation result.

  19 to 21 are graphs in which only the average value of the errors of the heat-generating and temperature-sensitive parts M0 and Mn is extracted and the flow rates are summarized at 10%, 50%, and 100% with respect to the maximum flow rate per time.

  In these graphs, it is common that no error occurs when the straight pipe length is 40D (D is the diameter of the pipe 13). In this embodiment, error processing is performed when the straight pipe length is 40D or less. Has been applied.

  From the graphs of FIGS. 7 to 21, the error of the simulation results of the plurality of heat-sensitive parts Mn installed at the same angle on the circle of 0.7R depends on the installation position in the simulation measurement value of each simulation result. Although there are positive and negative errors, it can be seen that the total value is positive regardless of the ratio to the maximum flow rate per hour.

  From this, a negative error in the simulation measurement value of the heat generation and temperature sensing unit M0 disposed in the central portion of the pipe 13 and a plurality of heat generation sensations disposed on a circle of 0.7R from the center of the pipe 13 are obtained. It is possible to obtain a measurement value with a small error by offsetting an error that is positive in the total of the simulation measurement values of the warm part Mn.

  In particular, from the graphs of FIGS. 19 to 21, the one in which the five heat generation and temperature sensing portions M <b> 51 to M <b> 55 are arranged at the same angle on the 0.7 R circle shown in FIG. 2 has the smallest error. .

  In order to verify the simulation results, a thermal flow meter having the arrangement shown in FIG. 2 was created, and the flow rate was changed to 10%, 50% of the maximum flow rate per hour while changing the straight pipe length to 5, 10, and 15. When the measurement was performed with actual flow rates of 100% and 100% flowing, the results of the verification experiment and the simulation results described above almost coincided.

  Further, the intersection P, which is considered to have the least influence of the change in the flow field, is expected to change depending on the situation of the drift, laminar flow, or turbulent flow, so the heat generation temperature sensing part M0 shown in FIG. In the arrangement diagram of Mn, simulation was performed in the same manner with 0.5R and 0.3R in addition to 0.7R. 22 to 24 are graphs in which the flow rates are summarized at 10%, 50%, and 100% with respect to the maximum flow rate per time in the arrangements of 0.3R, 0.5R, and 0.7R, respectively.

  22 to 24, even if the velocity distribution in the pipeline 13 changes as shown by the line c, it can be seen that 0.7R that is the intersection point P of the lines a and b has the highest reliability.

  In this way, the temperature sensing part m at the center and a plurality of heat sensing parts M are arranged around it, and the average of these measured values is obtained. In particular, the arrangement of the heat sensing parts M0 and Mn shown in FIG. As a result, it is possible to obtain a flow velocity value and a flow rate value with a small measurement error even at an installation location where the length of the straight pipe cannot be sufficiently secured and the flow field in the pipeline is not stable.

  4 to 6, even if the arrangement of the heat generation and temperature sensing portions M0 and Mn is arranged, the measured value of the heat generation temperature sensing portion M0 or the heat generation temperature sensing portion Mn is multiplied by a coefficient to perform calculation. The error can be reduced as in the configuration of the arrangement of the heat generation and temperature sensing parts M0 and Mn. This coefficient can also be determined in the process of calibration with a known actual flow rate.

  Furthermore, in the configuration of the arrangement of the heat generation and temperature sensing portions M0 and Mn in FIGS. 4 to 6, the error can be reduced by adjusting 0.7R from the central portion to the optimum radius length.

11 Channel pipe 12 Sensor unit 13 Pipe line

Claims (5)

  A thermal flow meter having a plurality of flow rate detection elements in a pipe, wherein one flow rate detection element is arranged at the center of the pipe on the cross section of the pipe, A thermal flow meter, wherein a flow rate detection element is disposed at an equal angle between the central portion and the pipe wall of the pipe, and an average of measurement values obtained by these flow rate detection elements is obtained as a measurement value. .   2. The thermal flow rate according to claim 1, wherein the flow velocity detection elements arranged at the same angle are arranged at a position on a circle approximately 0.7 times the radius of the pipe line from the center of the pipe line. Total.   The thermal flow meter according to claim 1 or 2, wherein the number of flow velocity detecting elements arranged at the same angle is five.   The thermal flow meter according to any one of claims 1 to 3, wherein a coefficient is multiplied to a measured value of the flow rate detection element in the central portion or the plurality of flow rate detection elements arranged at the same angle. .   5. The thermal type flow meter according to claim 4, wherein the coefficient is determined in a process of performing calibration by flowing a known actual flow rate.

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