JP2022107940A - thermal flow meter - Google Patents

Abstract

An object of the present invention is to secure a run-up distance without affecting flow rate measurement accuracy and reproducibility. An introduction pipe (101) is connected to an upstream pipe (104a) through which a fluid to be measured is transported. Further, the measurement tube 102 is connected to the introduction tube 101 and provided with a sensor section 103 . A pipe 104 b is connected to the downstream side of the measurement pipe 102 . The tube axis of the introduction tube 101 and the tube axis of the measurement tube 102 are common and straight. In addition, the length D of the introduction tube 101 is longer than "D=inner diameter of introduction tube 101*Reynolds number*0.065". [Selection diagram] Fig. 1

Description

The present invention relates to a thermal flowmeter.

Techniques for measuring the flow rate and flow velocity of a fluid flowing through a channel are widely used in the industrial and medical fields. There are various types of devices for measuring flow rates and flow velocities, such as electromagnetic flowmeters, vortex flowmeters, Coriolis flowmeters, and thermal flowmeters. Thermal flowmeters can also measure gases, and by installing the sensor on the outer peripheral surface of the pipe, there is basically no pressure loss, and there are advantages such as being able to measure mass flow rates ( Patent document 1).

In a thermal flow meter, it is important for accurate flow rate measurement that the fluid passing through the sensor should be a flow that develops upstream from this point.

JP 2006-349577 A

Here, in order to secure the run-up distance required for the above-mentioned flow to develop, conventionally, pipes, tubes, etc. were connected to the preceding stage of the measuring pipe provided with the sensor. However, there is a problem that the method of tightening the joint for this attachment and the slight degree of bending of the attached additional pipe affect the measurement accuracy and reproducibility. In particular, in a high flow rate range, the disturbance of the flow velocity distribution becomes large, so the above-mentioned problem due to the additional pipe hinders expansion of the flow rate range.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to secure a run-up distance without affecting flow rate measurement accuracy and reproducibility.

A thermal flow meter according to the present invention includes an introduction pipe connected to a pipe through which a fluid to be measured is transported, and a measurement pipe connected to the introduction pipe and provided with a sensor section. A heater is provided in contact with the outer wall of the pipe to heat the fluid, and a temperature measuring unit is provided in contact with the outer wall of the measurement pipe to measure the temperature of the fluid. It is configured to output a sensor value corresponding to the state of heat diffusion in the fluid heated by the heater when the heater is driven so that the difference from the temperature of the fluid becomes the set temperature difference. , the axis of the introduction tube and the axis of the measurement tube are common and straight, and the length of the introduction tube is longer than the inner diameter of the introduction tube*Reynolds number*0.065.

Claim 1 In one structural example of the thermal flow meter, the introduction pipe is a circular pipe.

In one configuration example of the thermal flowmeter, the introduction pipe is a rectangular pipe, and the length of one side of the rectangle is a, the length of the adjacent side of the rectangle is b, and the inner diameter D of the introduction pipe is Let D=2ab/(a+b).

In one configuration example of the thermal flowmeter, the introduction pipe is composed of a rigid body.

In one configuration example of the thermal flow meter, the measuring pipe has the same inner diameter as that of the portion of the introduction pipe where the sensor section is provided.

In one configuration example of the thermal flow meter, the measuring pipe further includes a constriction section provided immediately before the sensor section on the upstream side.

In one configuration example of the thermal flowmeter, the measurement pipe and the introduction pipe are integrally formed.

In one configuration example of the thermal flowmeter, the temperature measurement unit measures the temperature of the fluid upstream of the heater and is not affected by the heat of the heater, and the sensor unit measures the temperature of the heater and the temperature measurement unit. The electric power of the heater when the heater is driven so that the difference from the temperature of the fluid that has been measured becomes the set temperature difference is output as the sensor value.

In one configuration example of the thermal flowmeter, the temperature measurement unit is composed of a first temperature measurement unit, a second temperature measurement unit, and a third temperature measurement unit. The second temperature measurement unit measures the temperature of the fluid at a position that is not affected by the heat of the heater upstream of the heater, and the third temperature measurement unit measures the temperature of the fluid that is affected by the heat of the heater. The temperature of the fluid is measured at a position further downstream that is affected by the heat of the heater, and the sensor unit adjusts the difference between the temperature of the heater and the temperature of the fluid measured by the first temperature measurement unit to be the set temperature difference. A temperature difference between the temperature of the fluid measured by the second temperature measuring section and the temperature of the fluid measured by the third temperature measuring section when the heater is driven is output as a sensor value.

As described above, according to the present invention, the tube axis of the introduction tube and the tube axis of the measurement tube are common and each is straight, and the tube length of the introduction tube is given by the inner diameter of the introduction tube x Reynolds number x 0.065. Since it is made longer, the run-up distance can be secured without affecting the flow rate measurement accuracy and reproducibility.

FIG. 1 is a configuration diagram showing the configuration of a thermal flowmeter according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a more detailed partial configuration of the thermal flowmeter according to the embodiment of the present invention. FIG. 3 is a configuration diagram showing a more detailed partial configuration of the thermal flowmeter according to the embodiment of the present invention. FIG. 4 is a configuration diagram showing the configuration of another thermal flowmeter according to the embodiment of the invention.

A thermal flowmeter 100 according to an embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. A thermal flow meter 100 includes an introduction tube 101 , a measurement tube 102 and a sensor section 103 . The introduction pipe 101 and the measurement pipe 102 are used by being connected to pipes 104a and 104b through which the fluid to be measured is transported. The thermal flowmeter 100 measures the flow rate of fluid such as liquid and gas flowing through the pipes 104a and 104b.

The introduction pipe 101 is connected to an upstream pipe 104a through which the fluid to be measured is transported. Further, the measurement tube 102 is connected to the introduction tube 101 and provided with a sensor section 103 . A pipe 104 b is connected to the downstream side of the measurement pipe 102 . The introduction tube 101 can be constructed from a rigid body such as plastic, glass, sapphire, metal (eg steel). The introduction tube 101, which is made of a rigid body, does not cause deformation of the tube that affects measurement accuracy and reproducibility. The measurement tube 102, like the introduction tube, can also be constructed from a rigid body.

The sensor section 103 is provided in contact with the outer wall of the measurement tube 102 . The sensor section 103 includes a temperature measurement section 111 , a heater 112 , a control section 113 and a power measurement section 114 . The temperature measurement part 111 is provided in contact with the outer wall of the measurement tube 102 . The heater 112 is provided in contact with the outer wall of the measuring pipe 102 on the downstream side of the temperature measuring section 111 . The temperature measurement unit 111 and the heater 112 are adhered and fixed to the outer wall of the measurement tube 102 with, for example, a thermally conductive adhesive. The temperature measurement unit 111 measures the temperature of fluid such as liquid and gas.

The axis of the introduction tube 101 and the axis of the measurement tube 102 are common and straight. Further, the length D of the introduction tube 101 is set longer than "D=inner diameter of the introduction tube 101*Reynolds number*0.065". The run-up distance D (pipe length D of the introduction pipe 101) required for the fluid to develop a developed flow is determined by the Reynolds number and pipe dimensions (inner diameter), and can be obtained by the above equation in the case of laminar flow. For example, the introduction tube 101 can be a circular tube.

Also, the introduction tube 101 can be a rectangular tube. In this case, if the length of one side of the rectangle inside the introduction tube 101 in cross section is a and the length of the adjacent side of the side is b, the inner diameter D of the introduction tube 101 is D=2ab/(a+b ).

Here, the measurement tube 102 can have the same inner diameter as the portion of the introduction tube 101 where the sensor section 103 is provided. For example, the measurement tube 102 and the introduction tube 101 can be integrally formed.

The sensor unit 103 includes a temperature measurement unit 111, a heater 112, a control unit 113, and a power measurement unit 114, as shown in FIG. The temperature measurement part 111 is provided in contact with the outer wall of the measurement tube 102 . The heater 112 is provided in contact with the outer wall of the measuring pipe 102 on the downstream side of the temperature measuring section 111 . The temperature measurement unit 111 and the heater 112 are adhered and fixed to the outer wall of the measurement tube 102 with, for example, a thermally conductive adhesive. A temperature measurement unit 111 measures the temperature of the fluid.

Here, the sensor unit 103 drives the heater 112 so that the difference between the temperature of the heater 112 and the temperature of the fluid at a position not affected by the heat of the heater 112 becomes the set temperature difference. A sensor value corresponding to the state of thermal diffusion in the fluid heated by the heater 112 is output. In the embodiment, the controller 113 presets the difference between the temperature of the heater 112 and the temperature of the fluid upstream of the heater 112, which is measured by the temperature measuring unit 111 and is not affected by the heat of the heater 112. The heater 112 is controlled and driven so as to achieve the preset temperature difference.

Also, the electric power measurement unit 114 measures and outputs the electric power of the heater 112 controlled by the control unit 113 . The power output from the power measuring unit 114 that constitutes the sensor unit 103 is the sensor value. The flow rate calculation unit 115 calculates the flow rate of the fluid from the power (sensor value) of the heater 112 measured and output by the power measurement unit 114 .

As is well known, when the heater 112 is driven such that the difference between the temperature of the heater 112 and the temperature of the fluid at a position not affected by the heat of the heater 112 becomes the set temperature difference, the heater 112 There is a correlation between the power being consumed and the flow rate of the fluid. Also, this correlation is repeatable for the same fluid/flow rate/temperature. Therefore, as described above, in a state in which the heater 112 is controlled by the control unit 113, the flow rate is can be calculated.

Note that, as shown in FIG. 3, a temperature measurement unit (first temperature measurement unit) 111, a heater 112, a control unit 113, a temperature measurement unit (second temperature measurement unit) 116, and a temperature measurement unit (third temperature measurement unit) 117 may constitute the sensor unit 103'. Each temperature measurement unit is provided in contact with the outer wall of the measurement tube 102 .

The control unit 113 determines that the difference between the temperature of the heater 112 and the position not affected by the heat of the heater 112 measured by the temperature measurement unit 111, for example, the temperature of the fluid upstream of the heater 112, is set to a preset temperature. The heater 112 is controlled and driven so as to make the difference.

The temperature measuring section 116 is provided downstream of the temperature measuring section 111 and upstream of the heater 112 so as to be in contact with the outer wall of the measuring pipe 102 . Also, the temperature measurement unit 117 is provided in contact with the outer wall of the measurement pipe 102 on the downstream side of the heater 112 . A temperature measurement unit 116 and a temperature measurement unit 117 measure the temperature of the fluid.

The flow rate of the fluid can be calculated from the temperature difference between the temperature of the fluid measured by the temperature measurement unit 116 and the temperature of the fluid measured by the temperature measurement unit 117 . In this example, the sensor value is the temperature difference between the fluid temperature measured by the temperature measurement unit 116 and the fluid temperature measured by the temperature measurement unit 117 .

As is well known, the heater 112 is driven so that the difference between the temperature of the heater 112 and the temperature of the fluid at a position not affected by the heat of the heater 112 becomes a preset temperature difference. There is a correlation between the temperature difference between the temperature of the fluid upstream of the heater 112 and the temperature of the fluid downstream of the heater 112 and the flow rate of the fluid. Also, this correlation is repeatable for the same fluid/flow rate/temperature. Therefore, as described above, in a state where the heater 112 is controlled by the control unit 113, the difference (temperature difference) between the temperature measured by the temperature measurement unit 116 and the temperature measured by the temperature measurement unit 117 is used to determine a predetermined phase. The flow rate can be calculated by using a relational coefficient (constant).

As described above, according to the embodiment, the tube axis of the introduction tube 101 and the tube axis of the measurement tube 102 are common and straight, and the length of the introduction tube 101 is , the inner diameter of the introduction pipe 101×Reynolds number×0.065, so that the run-up distance can be secured without affecting the measurement accuracy and reproducibility of the flow rate. If the introduction pipe 101 and the measurement pipe 102 are made of a rigid body, deformation of these pipes due to an external force can be suppressed.

In addition, if the measurement tube 102 and the introduction tube 101 are integrally formed, there is no need to connect the introduction tube 101 to the measurement tube 102 using a joint or the like, and a seamless state can be achieved. can. As a result, with the above configuration, it is possible to prevent deterioration in measurement accuracy and reproducibility due to the way joints are tightened, the existence of joints and seams, and the like.

By the way, as shown in FIG. 4, the thermal flowmeter 100 can further include a constriction section 105 provided immediately before the upstream side of the sensor section 103 of the measuring pipe 102a. By providing the narrowed portion 105, it is possible to further suppress the disturbance of the flow velocity distribution of the fluid to be measured flowing through the measurement pipe 102a in the region of the sensor portion 103. FIG.

As described above, according to the present invention, the axis of the introduction tube and the axis of the measurement tube are common and each is straight, and the length of the introduction tube is the inner diameter of the introduction tube x Reynolds number x 0.065. Since it is made longer, it becomes possible to secure the run-up distance without affecting the measurement accuracy and reproducibility of the flow rate.

It should be noted that the present invention is not limited to the embodiments described above, and many modifications and combinations can be implemented by those skilled in the art within the technical concept of the present invention. It is clear.

DESCRIPTION OF SYMBOLS 100... Thermal type flowmeter, 101... Introduction pipe, 102... Measurement pipe, 103... Sensor part, 104a, 104b... Piping.

Claims (9)

An introduction pipe connected to a pipe through which a fluid to be measured is transported, and a measurement pipe connected to the introduction pipe and provided with a sensor unit,
The sensor unit includes a heater that is provided in contact with the outer wall of the measurement tube to heat the fluid, and a temperature measurement unit that is provided in contact with the outer wall of the measurement tube and measures the temperature of the fluid. in the fluid heated by the heater when the heater is driven such that the difference between the temperature and the temperature of the fluid at a position not affected by the heat of the heater is a set temperature difference configured to output a sensor value corresponding to a state of heat diffusion;
the tube axis of the introduction tube and the tube axis of the measurement tube are common and straight,
The thermal flowmeter, wherein the length of the introduction pipe is longer than the inner diameter of the introduction pipe×Reynolds number×0.065. The thermal flow meter according to claim 1,
A thermal flow meter, wherein the introduction pipe is a circular pipe. The thermal flow meter according to claim 1,
The introduction tube is a rectangular tube,
A thermal flowmeter characterized in that the length of one side of a rectangle is a, the length of the adjacent side of the rectangle is b, and the inner diameter D of the introduction pipe is D=2ab/(a+b). . In the thermal flow meter according to any one of claims 1 to 3,
A thermal flowmeter, wherein the introduction pipe is made of a rigid body. In the thermal flow meter according to any one of claims 1 to 4,
A thermal flowmeter, wherein the measurement pipe has the same inner diameter as that of the portion of the introduction pipe where the sensor section is provided. The thermal flow meter according to claim 5,
A thermal flowmeter, further comprising a restrictor provided just before the upstream side of the sensor section of the measuring pipe. The thermal flow meter according to any one of claims 1 to 6,
A thermal flowmeter, wherein the measurement pipe and the introduction pipe are integrally formed. In the thermal flow meter according to any one of claims 1 to 7,
The temperature measuring unit measures the temperature of the fluid at a position upstream of the heater and not thermally affected by the heater,
The sensor unit measures the electric power of the heater when the heater is driven so that the difference between the temperature of the heater and the temperature of the fluid measured by the temperature measuring unit becomes the set temperature difference. A thermal flow meter characterized by outputting as a value. In the thermal flow meter according to any one of claims 1 to 7,
The temperature measurement unit is composed of a first temperature measurement unit, a second temperature measurement unit, and a third temperature measurement unit,
The first temperature measuring unit measures the temperature of the fluid at a position upstream of the heater and not thermally affected by the heater,
The second temperature measuring unit measures the temperature of the fluid at a position on the upstream side of the heater that is thermally affected by the heater,
The third temperature measuring unit measures the temperature of the fluid at a position downstream of the heater that is thermally affected by the heater,
The sensor unit detects the second temperature when the heater is driven such that the difference between the temperature of the heater and the temperature of the fluid measured by the first temperature measurement unit is the set temperature difference. A thermal flowmeter, wherein a temperature difference between the temperature of the fluid measured by the measuring unit and the temperature of the fluid measured by the third temperature measuring unit is output as the sensor value.

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