Flowmeter, flow rate measurement method, and flow rate measurement device

Abstract

Provided are a thermal flowmeter and a flow rate measurement method for measuring, from outside a pipe, the flow rate of a fluid flowing through the pipe.　The thermal flowmeter comprises: an insulating wiring substrate that can be bonded to an outer peripheral part of the pipe; a conductive wiring pattern that is provided on the insulating wiring substrate; a thermal stimulus generation unit that heats or cools the outer surface of the pipe; and at least two thin-film-like peripheral thermosensitive elements that are disposed at positions which are separated from the thermal stimulus generation unit by a prescribed distance. The peripheral thermosensitive elements are disposed at positions that are on a straight line which passes through the center position of the thermal stimulus generation unit and that are symmetrical, with the thermal stimulus generation unit being sandwiched therebetween. The flow rate measurement method employs the thermal flowmeter and comprises: a step for giving a thermal stimulus to the pipe by heating or cooling the thermal stimulus generation unit; and a step for using a temperature difference measured by the peripheral thermosensitive element to determine the flow rate.

Description

Flowmeter, Flow Measurement Method, and Flow Measurement Device

[0001] The present invention relates to a flowmeter, a flow measurement method, and a flow measurement device for measuring the flow rate of a fluid flowing in a pipe from outside the pipe.

[0002] A general thermal flowmeter includes a measurement unit having at least one or more heating devices and at least one or more thermal sensors provided at a position separated from the heating device by a predetermined distance. This measurement unit is inserted between the pipe through which the fluid to be measured flows and the pipe, or is installed inside an existing pipe, so that the velocity and / or flow rate of the fluid flowing in the pipe can be measured (for example, see Patent Documents 1 to 3).

[0003] Also, by applying the same principle, a biosensor for non-invasively measuring the flow rate of a fluid flowing in a living body such as blood by attaching it to the skin is also known (for example, Patent Documents 4 and 5).

[0004] Japanese Patent Application Laid-Open No. 2024-32149, Japanese Patent Application Laid-Open No. 2020-008339, Japanese Patent Application Laid-Open No. 2002-71413, Japanese Patent Application Laid-Open No. 2021-519641, Japanese Patent Application Laid-Open No. 2017-532079

[0005] In the thermal flowmeter for a pipe as described above, when the heating device or the thermal sensor directly touches the fluid to be measured, in the case of a fluid composed of a corrosive liquid, the life may be significantly shortened. That is, there are restrictions on the fluid to be measured. Also, when inserting the measurement unit of the flowmeter between the pipes to be measured and the pipes, it is necessary to process the pipes for installation, and extra costs are incurred during installation. Therefore, a flowmeter that can measure the flow rate of the fluid flowing in the pipe from outside the pipe has been demanded.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a flowmeter and a flow measurement method for measuring the flow rate of a fluid flowing in a pipe from outside the pipe.

[0007] The thermal calorimeter according to the present invention is a thermal flow meter for measuring the flow rate of a fluid flowing in a pipe, comprising: an insulating wiring board that can be attached to the outer circumference of the pipe; a conductive wiring pattern wired on the insulating wiring board; a thermal stimulation generating unit for heating or cooling the outer surface of the pipe; and at least two thin-film peripheral thermal sensing elements positioned at a predetermined distance from the thermal stimulation generating unit, wherein the peripheral thermal sensing elements are arranged symmetrically on a straight line passing through the center of the thermal stimulation generating unit, with the thermal stimulation generating unit in between.

[0008] These features allow the device to be attached to the outside of a pipe to measure the flow rate of fluid flowing inside the pipe. It does not require any processing of the pipe, and the flow rate of fluid flowing inside the pipe can be measured without any modifications.

[0009] In the above-described invention, the thermal stimulation generating portion may be characterized by having an axis passing through its central position and being symmetrical with respect to a line perpendicular to the axis at the central position. Furthermore, the thermal stimulation generating portion may be characterized by having a circular, rectangular, or elliptical planar shape.

[0010] The invention described above may be characterized by having a central region in the center of the thermal stimulation generating portion that does not generate thermal stimulation. Furthermore, the central region may be characterized by being symmetrical with respect to a line perpendicular to the axis passing through the center of the thermal stimulation generating portion. Additionally, a thin-film central thermal element may be disposed in the central region, and the surrounding thermal element and the central thermal element may be arranged in a straight line. Furthermore, it may be characterized by being located inside a heat insulating cover.

[0011] In the invention described above, the central thermal element and the peripheral thermal element may be characterized by being thin-film thermistors. Furthermore, the thin-film thermistor may be trimmed to make the electrical characteristics of the peripheral thermal element and the central thermal element identical. Furthermore, the thin-film thermistor may include a substrate and a thermal thin film and electrode layer formed on the substrate, and the thermal thin film and electrode layer may be arranged to face the contact surface of the object to be measured. Moreover, the thin-film thermistor may be formed by directly depositing the thermal thin film and electrode layer onto the insulating wiring substrate.

[0012] In the invention described above, the thermal stimulation generating unit may be characterized by being a heater. Furthermore, the heater may be characterized by having a meander structure.

[0013] In the above-described invention, the thermal stimulation generating unit may be characterized by being made of a Peltier element.

[0014] In the invention described above, the wiring pattern may be characterized by having a wiring extension portion made of a conductive thin film on which the central heat-sensitive element and / or the peripheral heat-sensitive element are placed.

[0015] The flow rate measurement method according to the present invention is a flow rate measurement method using a thermal flow meter comprising: an insulating wiring board that can be attached to the outer circumference of a pipe; a conductive wiring pattern wired on the insulating wiring board; a thermal stimulation generating unit for heating or cooling the outer surface of the pipe; and at least two peripheral thermal sensing elements positioned at a predetermined distance from the thermal stimulation generating unit, wherein the peripheral thermal sensing elements are arranged symmetrically on a straight line passing through the center of the thermal stimulation generating unit, and the method is characterized by comprising the steps of: heating or cooling the thermal stimulation generating unit to apply thermal stimulation to the pipe; and determining the flow rate using the temperature difference measured by the peripheral thermal sensing elements.

[0016] With these features, the device can be attached to the outside of a pipe to measure the flow rate of fluid flowing inside the pipe without requiring any processing of the pipe.

[0017] In the above-described invention, the distance from the center position to the outer circumference position of the thermal stimulation generating part with respect to the fluid flow direction in the pipe may be one-quarter or more of the inner diameter of the pipe.

[0018] The invention described above may be characterized by including a step of measuring the viscosity of the fluid in the piping. Alternatively, it may be characterized by the viscosity of the fluid in the piping being 1500 mPa·s or less.

[0019] The above invention may also be characterized by detecting the presence or absence of bubbles in the fluid inside the piping. Furthermore, the bubbles may have a dimension of 5 mm or more in the direction of fluid flow.

[0020] In the above-described invention, the thermal stimulation generating portion may be characterized by having a shape that is symmetrical with respect to a line perpendicular to a line passing through the center of the thermal stimulation generating portion.

[0021] The above-described invention may be characterized by having a central region in the center of the thermal stimulation generating portion that does not generate thermal stimulation. Alternatively, a single thin-film central thermal sensor may be disposed in the central region, and the peripheral thermal sensor and the central thermal sensor may be arranged in a straight line.

[0022] The invention described above may be characterized in that the temperature difference between the fluid temperature inside the piping and the temperature of the thermal stimulation generating part is 5°C or more.

[0023] The flow rate measuring device according to the present invention includes an insulating wiring board that can be attached to the outer circumference of a pipe, a conductive wiring pattern wired on the insulating wiring board, a thermal stimulation generating unit for heating or cooling the outer surface of the pipe, and at least two peripheral thermal sensing elements positioned at a predetermined distance from the thermal stimulation generating unit, wherein the peripheral thermal sensing elements are arranged at symmetrical positions on a straight line passing through the center of the thermal stimulation generating unit, and the device has a control processing unit that incorporates a program for executing a flow rate measuring method which includes the steps of heating or cooling the thermal stimulation generating unit to apply thermal stimulation to the pipe, and determining the flow rate using the temperature difference measured by the peripheral thermal sensing elements.

[0024] With these features, the device can be attached to the outside of a pipe to measure the flow rate of fluid flowing inside the pipe without requiring any processing of the pipe.

[0025] This is a plan view showing a thermal flow meter according to the first embodiment. This is a diagram of the configuration of a thin-film thermistor used as the thin-film thermal element of the thermal flow meter. This is a plan view showing a thermal flow meter according to the second embodiment. This is a plan view showing a thermal flow meter with an insulating cover attached. This is a perspective view of the insulating cover. This is a schematic diagram of a thermal flow meter attached to the outside of a pipe. This is a graph showing the temperature difference between the upstream and downstream thermal elements when a thermal flow meter is installed on the outside of a resin pipe. This is a graph showing the temperature difference between the upstream and downstream thermal elements when a thermal flow meter is installed on the outside of a metal pipe. This is a graph showing the temperature difference between the upstream and downstream thermal elements when a thermal flow meter (using a cooling element) is installed on the outside of a resin pipe. This is a graph simulating the temperature change of the central thermal element in the thermal flow meter of the second embodiment. This is a graph simulating the temperature change of the central thermal element for each thermal resistance. This is a graph of the temperature response of the central, upstream, and downstream thermal elements when air bubbles pass through the pipe. This is a graph showing the temperature difference between the upstream and downstream thermosensitive elements when glycerin is used as the fluid. This is a flowchart showing the processing of the control unit.

[0026] Embodiments of the present invention will be described with reference to Figures 1 to 5. Note that in each figure, the scale of each component has been appropriately changed for illustrative purposes in order to make each component recognizable. Also, the same reference numerals are used for identical or corresponding parts, and redundant explanations are omitted.

[0027] The thermal flow meter 1 described here is a device used by attaching it to the outside of a pipe, and includes a thermal stimulation generating unit 20, which is a heat source that provides heating or cooling, and a thin-film thermal sensing element 4 surrounding it. The thermal flow meter 1 is a device that measures the flow rate of fluid flowing inside a pipe based on temperature information measured by the thermal sensing element 4. These components are mounted on an insulating wiring board and controlled by a control device (not shown). In addition to the flow rate, the fluid velocity can also be measured from the inner diameter of the pipe, etc.

[0028] (First Embodiment, Peripheral Heat Sensing Element Only) A thermal flow meter according to the first embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a plan view showing a thermal flow meter according to the first embodiment, and Figure 2 is a configuration diagram illustrating a thin-film thermistor that can be used as a heat sensing element in a thermal flow meter.

[0029] The insulating wiring board 5 is made of polyimide resin and has a flow rate sensing section 5a and a wiring section 5b extending from a part thereof. The insulating wiring board 5 is preferably flexible to improve adhesion to the piping, but it may also be a hard substrate. The back side of the flow rate sensing section 5a serves as the temperature sensing section and constitutes the contact surface that comes into contact with the object to be measured (piping). A double-sided adhesive sheet (not shown) is provided on this contact surface so that it can be attached to the object to be measured. Although the flow rate sensing section 5a in this embodiment is rectangular, there are no restrictions on its shape; it may also be circular or other shapes.

[0030] The heater 2, which serves as the thermal stimulation generating unit 20, is a meandering wiring structure made using fine copper wires 2a, and is positioned on the flow detection unit 5a of the insulating wiring substrate 5. By using a meandering wiring structure, heat dissipation can be suppressed and sensitivity can be improved. The heater 2 is entirely made of copper wiring so that the wiring covers the entire surface of a predetermined area and no areas without wiring are formed. Its shape is not particularly limited, but when the fluid velocity in the pipe is zero, it is preferable to have a symmetrical planar shape such as a rectangle, circle, or ellipse, which has a center, an axis passing through this center, and is symmetrical with respect to a line perpendicular to this axis at the center, so that the heat is propagated uniformly to the thin film-like heat-sensitive element 4 in the surrounding area, which will be described later.

[0031] The thermal stimulation generating unit 20 is not limited to a heater that provides thermal stimulation, but can use various positive or negative heat supply means. For example, when the temperature of the fluid flowing through the pipe is high, or when using pipes or fluids that are easily altered by heating, a cooling element such as a Peltier element can also be suitably used as the thermal stimulation generating unit 20. The difference between the heating or cooling temperature of the thermal stimulation generating unit 20 and the temperature of the fluid being measured is preferably 5°C or more, and more preferably 10°C or more. A temperature difference of 5°C or more results in good sensitivity.

[0032] Two thin-film thermal elements 4 are arranged around the heater 2, positioned opposite each other at a constant distance from the heater 2. In other words, they are positioned point-symmetrically with respect to the heater 2. More specifically, the thermal elements 4 around the heater 2 are on a straight line passing through the center of the heater 2 and are positioned near the edge of the flow detection section 5a on the insulating wiring board 5. Therefore, the center of the heater 2 and the two thermal elements 4 are arranged in a straight line at equal intervals, and the distance between the thermal elements 4 and the periphery of the heater 2 is constant. Note that there only need to be at least two thermal elements 4, but there may be multiple, for example, four or more, forming multiple pairs. If there are more than two thermal elements 4, for example, it becomes possible to detect the flow velocity of fluid flowing through a bent pipe.

[0033] As shown in Figure 2, a thin-film thermistor 41 can be used as the heat-sensitive element 4. The thin-film thermistor 41 has an insulating substrate 42, and is constructed by forming a heat-sensitive thin film 43, a pair of electrode layers 43a and 43b, and a protective film 44 on the insulating substrate 42.

[0034] The insulating substrate 42 is substantially rectangular in shape, with dimensions of 1 mm in width and 0.5 mm in height, a thickness of 200 μm or less, preferably 150 μm or less, and is formed from a glass material, ceramic material, or the like.

[0035] The thermal thin film 43 is a thermoresistive thin film that functions as a temperature sensor, and is an NTC thermistor thin film made of an oxide semiconductor having a negative temperature coefficient. The thermal thin film 43 is located on the insulating substrate 42 and is formed by sputtering onto the electrode layers 43a and 43b, so as to straddle the electrode layers 43a and 43b, and is electrically connected to the electrode layers 43a and 43b.

[0036] The thermistor thin film is composed of a thermistor material that mainly contains a composite metal oxide having a spinel structure, which is composed of two or more elements selected from transition metal elements such as manganese (Mn), nickel (Ni), cobalt (Co), and iron (Fe). Furthermore, minor components may be included to improve properties. The composition and content of the main and minor components can be appropriately determined according to the desired properties.

[0037] The pair of electrode layers 43a and 43b are formed on the insulating substrate 42 and are the portion to which the thin-film thermistor 3 is electrically connected. They are arranged facing each other with a predetermined distance between them. Specifically, the pair of electrode layers 43a and 43b are formed by directly depositing a metal thin film onto the insulating substrate 42 by sputtering. The metal material can be a precious metal such as platinum (Pt), gold (Au), silver (Ag), palladium (Pd), ruthenium (Ru), or an alloy thereof, such as an Ag-Pd alloy. In this embodiment, the electrode layers 43a and 43b are formed beneath the heat-sensitive thin film 43, but they may also be formed on or within the heat-sensitive thin film 43.

[0038] The protective film 44 covers the region where the heat-sensitive thin film 43 is formed, and also covers the electrode layers 43a and 43b by forming an exposed portion so that at least a part of the electrode layers 43a and 43b is exposed. The protective film 44 is made of silicon dioxide (SiO ２ ), silicon nitride (Si ３ N ４ These can be formed by depositing films of the following materials by sputtering, or by forming lead glass, borosilicate glass, and lead borosilicate glass by printing.

[0039] Furthermore, the thin-film thermistor 41 may be formed by depositing a heat-sensitive thin film 43, electrode layers 43a and 43b, and a protective film 44 on an insulating wiring substrate 5. In other words, the thin-film thermistor 41 may be formed directly on the insulating wiring substrate 5 without using an insulating substrate 42.

[0040] The thin film thermistor 41 is subjected to processing means such as trimming and adjusted so that its electrical characteristics become substantially constant, thereby providing a thermal flowmeter with high accuracy and high reliability. The thin film thermistor 41 is mounted on the insulating wiring board 5 such that the heat-sensitive thin film 43 formed on the surface of the insulating substrate 42 and the pair of electrode layers 43a and 43b face the side of the measurement object, that is, the surface side of the pipe serving as the contact surface. Therefore, the thin film thermistor 41 is arranged to be face-down mounted on the insulating wiring board 5. Note that it may be arranged by face-up mounting.

[0041] Further, a conductive wiring pattern 51 is formed on the insulating wiring board 5. The wiring pattern 51 is a conductive pattern that connects the heater 2 and the heat-sensitive element 4 and leads them to the wiring portion 5b. The end portion of the wiring pattern 51 functions as a connector connection portion 52. The connection portion 53 for obtaining an electrical connection between the wiring pattern 51 and the heat-sensitive element 4 is preferably a wiring extension portion having an area (size) large enough to place the entire thin film-shaped heat-sensitive element 4 in order to make the heat transmitted to the thin film-shaped heat-sensitive element 4 uniform. That is, the wiring extension portion on which the heat-sensitive element 4 is placed is a conductive thin film such as a metal thin film having a surface that is slightly larger than the size of the main surface of the thin film-shaped heat-sensitive element 4.

[0042] The width of the contact surface with the measurement object (pipe) is preferably at least the same as or larger than that of the connection portion 53. If the width of the contact surface is equal to or greater than the width of the connection portion 53, the heat of the pipe propagates uniformly to the heat-sensitive elements 4 in the peripheral portion.

[0043] (Second Embodiment, with Central Heat-Sensitive Element) Referring to FIG. 3, the thermal flowmeter according to the second embodiment of the present invention will be described. FIG. 3 is a plan view showing the thermal flowmeter according to the second embodiment.

[0044] As shown in FIG. 3, in the thermal flowmeter according to the present embodiment, a central region 21 that does not have wiring of the heater 2 and does not generate a thermal stimulus, that is, a central region that does not include wiring, is formed in the central portion of the heater 2 as the thermal stimulus generation unit 20. A thin-film heat-sensitive element 4b in the central portion is disposed at the center of the central portion of the heater 2, that is, at the center of the central region 21. Note that the heat-sensitive element 4b in the central portion has basically the same electrical characteristics as the heat-sensitive elements 4a in the peripheral portion. When the heat-sensitive element 4b is arranged, it is possible to detect an abnormality due to poor contact between the pipe and the thermal flowmeter 1. This is because when the pipe and the sensor are not sufficiently in close contact, the heat of the heating device is not sufficiently transmitted to the pipe and concentrates on the central heat-sensitive element 4b, and as a result, the temperature of the central heat-sensitive element 4b rises significantly.

[0045] Further, when the heat-sensitive element 4b is arranged in the central portion, it is possible to detect the presence of bubbles in the fluid flowing through the pipe. This is because the thermal conductivities of the liquid and the gas are significantly different. That is, in the bubble portion, the heat of the heater 2 is less likely to propagate than in the fluid portion, and the amount of heat propagated to the central heat-sensitive element 4b increases, so that the temperature detected by the central heat-sensitive element 4b becomes higher. Bubbles that can be detected with a sufficient S / N ratio are, for example, those having a dimension in the flow direction of the fluid of 5 mm or more.

[0046] Similar to the first embodiment, two heat-sensitive elements 4a are arranged in the peripheral portion of the heater 2 and are positioned so as to face each other at a certain distance on the peripheral portion. That is, they are arranged at symmetric positions that are point-symmetric with the thin-film heat-sensitive element 4b in the central portion as the center. More specifically, the three thin-film heat-sensitive elements including the heat-sensitive element 4b in the central portion and the heat-sensitive elements 4a in the peripheral portion thereof are linearly arranged at equal intervals, and the distances between the two heat-sensitive elements 4a in the peripheral portion and the heater 2 are constant.

[0047] When the thin-film heat-sensitive element 4b in the central portion is the thin-film thermistor 41, the structure of the heat-sensitive element 4b is the same as the configuration shown in FIG. 2. By applying processing means such as trimming to the thin-film heat-sensitive element 4b in the central portion and the heat-sensitive element 4a (thin-film thermistor 41) in the peripheral portion thereof and adjusting them so that their electrical characteristics are substantially the same, it is possible to provide a highly accurate and reliable thermal flowmeter.

[0048] The thermal element 4b is mounted on the insulating wiring board 5 in the same way as the surrounding thermal element 4a, with the thermal thin film 43 and the pair of electrode layers 43a and 43b formed on the surface of the insulating substrate 42 facing toward the object to be measured, i.e., toward the pipe surface which will be the contact surface. Therefore, the thin-film thermistors 41 of the thermal elements 4a and 4b are mounted face down on the insulating wiring board 5. Alternatively, they may be mounted face up.

[0049] Furthermore, the connection portion 53 that provides an electrical connection between the wiring pattern 51 and the central heat-sensitive element 4b is preferably a wiring extension portion that is large enough to accommodate the entire central thin-film heat-sensitive element 4b, similar to the case of the wiring pattern 51 and the surrounding heat-sensitive element 4a, in order to uniformly distribute the heat transmitted to the thin-film heat-sensitive element. That is, it is a conductive thin film such as a metal thin film having a main surface slightly larger than the central heat-sensitive element 4b.

[0050] (Third Embodiment, with Insulating Cover) A thermal flow meter according to a third embodiment of the present invention will be described with reference to Figures 4 and 5. Here, Figure 4 is a plan view showing the thermal flow meter installed inside the insulating cover, and Figure 5 is a perspective view showing the insulating cover.

[0051] As shown in Figures 4 and 5, in the third embodiment, the thermal flow meter 1 is mounted and arranged so as to be covered by an insulating cover 10, and is provided inside the insulating cover 10. The insulating cover 10 is made of an insulating material such as urethane foam, and by covering it with the insulating cover 10, heat loss when the heater 2 is heated and heat dissipation from the piping to which the thermal flow meter 1 is attached can be prevented, thereby improving the temperature detection accuracy of the heat sensing elements 4a and 4b and the flow rate measurement accuracy.

[0052] The heat-insulating cover 10 has a thickness of about 1 mm and is provided with a substantially rectangular recess 10a on its bottom side that can accommodate the flow detection unit 5a. The outer shape of the heat-insulating cover 10 is also substantially rectangular to match the shape of the recess 10a. By housing the flow detection unit 5a in the recess 10a, the heat-insulating cover 10 can cover the heater 2, the central heat-sensitive element 4b, and the surrounding heat-sensitive elements 4a of the thermal flow meter 1, thereby suppressing heat dissipation from the flow detection unit 5a. A groove is formed extending from the recess 10a toward the outer circumference to guide the wiring unit 5a to the outside, but it is also preferable to make this groove tightly in contact with the wiring unit 5a and close the side to improve heat insulation.

[0053] (Method for Measuring Pipe Flow Velocity According to This Embodiment) The method for measuring pipe flow velocity in a thermal flow meter will be explained with reference to Figures 6 to 10. Here, Figure 6 is a schematic diagram of a thermal flow meter attached to the outside of a pipe 6, Figure 7 is a graph showing the temperature difference between the upstream and downstream thermal elements 4 (surrounding thermal elements 4a) when a thermal flow meter 1 is placed on the outside of a resin pipe, Figure 8 is a graph showing the temperature difference between the upstream and downstream thermal elements 4 (surrounding thermal elements 4a) when a thermal flow meter 1 is placed on the outside of a metal pipe, Figure 9 is a graph showing the temperature difference between the upstream and downstream thermal elements 4 with respect to flow rate when a thermal flow meter 1 using a Peltier element in the thermal stimulation generating unit 20 is placed on the outside of a resin pipe, and Figure 10 is a graph simulating the temperature change of the central thermal element 4 (central thermal element 4b) in the thermal flow meter 1 of the second embodiment.

[0054] As shown in Figure 6, a thermal flow meter is attached to the outer circumference of the pipe 6 to measure the flow rate of the fluid inside the pipe. Then, with the heater 2 sufficiently heated, the flow rate of the fluid inside the pipe can be measured by measuring the temperature difference between the upstream thermal element 4a1 and the downstream thermal element 4a2.

[0055] In other words, as fluid flows through the pipe, heat from the heater 2 is transported according to the flow, so the temperature detected by the downstream heat-sensitive element 4a2 is higher than the temperature detected by the upstream heat-sensitive element 4a1. Furthermore, this temperature difference depends on the velocity of the fluid flowing through the pipe. That is, the slower the fluid velocity in the pipe, the greater the temperature rise of the fluid due to the heat transferred from the heater 2, and the larger the temperature difference between the heat-sensitive elements 4a1 and 4a2 around the heat-sensitive elements 4a. Conversely, the faster the fluid velocity, the smaller the temperature difference.

[0056] The same applies when a cooling element such as a Peltier element is used in place of the heater 2 in the thermal stimulation generating unit 20. However, when a cooling element is used, the fluid flowing through the piping acts as a coolant and is transported, causing the temperature detected by the downstream thermal sensing element 4a2 to be lower than the temperature detected by the upstream thermal sensing element 4a1.

[0057] Here, by creating a table data in advance that correlates the temperature difference between the thermal elements 4a1 and 4a2 with the fluid velocity, it is also possible to determine the fluid velocity from the temperature difference calculated during measurement. Furthermore, if the inner diameter of the pipe 6 is known, the flow rate can also be calculated from the fluid velocity and the inner diameter of the pipe.

[0058] Figures 7 and 8 show the results of measuring fluid velocity by attaching a thermal flow meter 1 to the outer surface of various pipes. Figure 7 shows the measurement results when water (temperature 23°C) was flowed as the fluid in a resin pipe (outer diameter 5 mm, inner diameter 3 mm). Figure 8 shows the measurement results when water (temperature 23°C) was flowed as the fluid in a metal pipe (outer diameter 3 mm, inner diameter 2.4 mm). The thermal flow meter 1 used here is the second embodiment described above, and the distance in the fluid flow direction of the pipe from the center of the heater 2 to the outer circumference of the heater 2 is 2.6 mm. The heating temperature of the heater 2 was 35°C. In all cases of pipe material, the temperature difference between the thermal elements 4a1 and 4a2 when there was no flow in the pipe, i.e., zero flow velocity, was corrected to 0°C.

[0059] When heater 2 was heated and fluid was flowed through the piping, a temperature difference was created between the upstream thermal element 4a1 and the downstream thermal element 4a2. Furthermore, when the fluid flow rate was changed, the temperature difference between thermal elements 4a1 and 4a2 also changed accordingly. That is, the lower the flow rate and the slower the flow velocity, the larger the temperature difference, and the higher the flow rate and the faster the flow velocity, the smaller the temperature difference. From these results, it was found that this thermal flow meter is able to detect changes in flow velocity well. It was also found that accurate measurement of flow velocity is possible regardless of whether the piping is metal or resin, and even when the thermal flow meter 1 is attached to the outside of the piping.

[0060] Figure 9 shows the measurement results of the temperature difference between the surrounding heat-sensitive elements 4a1 and 4a2 in relation to the flow rate when a Peltier element, which is a cooling element, is used in the heat stimulation generation unit 20. The resin pipe used for the measurement had an outer diameter of 5 mm and an inner diameter of 3 mm, and water at a temperature of 24°C was flowed inside as the fluid. The thermal flow meter 1 used here is the same as the first embodiment described above, and a Peltier element was placed in the heat stimulation generation unit 20. The distance in the direction of fluid flow in the pipe from the center of the Peltier element to the outer circumference of the Peltier element is 10 mm. A Peltier element with a resistance of 1.05 Ω and a maximum temperature difference of 77°C was used. A current of 0.5 A was applied to the Peltier element during the measurement. In this case as well, the temperature difference between the heat-sensitive elements 4a1 and 4a2 when there was no flow in the pipe, i.e., zero flow velocity, was corrected to 0°C. Even with this, it was confirmed that the temperature difference tends to decrease as the flow velocity increases. In other words, it can be said that, as described above, it is possible to accurately measure the flow rate even if the thermal flow meter 1 using a Peltier element is attached to the outside of the pipe.

[0061] Figure 10 shows the results of a simulation of the temperature difference between the upstream thermal element 4a1 and the downstream thermal element 4a2 when water (temperature 37°C) is flowed as the fluid at a flow velocity of 1 m / min through a metal pipe made of carbon steel with an outer diameter of 46 mm and an inner diameter of 40 mm, and the distance in the direction of fluid flow in the pipe from the center of the heater 2 of the thermal flow meter 1 to the outer circumference is changed. Note that the shape of the thermal flow meter 1 used in the simulation is that of the second embodiment described above.

[0062] The simulation results in Figure 10 show that as the distance in the fluid flow direction (direction A) of the piping from the center of the heater 2 to the outer circumference increases, the temperature difference between the upstream thermal element 4a1 and the downstream thermal element 4a2 increases, and the sensitivity tends to improve. Furthermore, when the distance in direction A from the center of the heater 2 to the outer circumference is 10 mm or more, the change in the temperature difference between the upstream thermal element 4a1 and the downstream thermal element 4a2 slows down (there is an inflection point at 10 mm). In other words, if the distance in the fluid flow direction from the center of the heater 2 to the outer circumference of the heater 2 is one-quarter or more of the inner diameter of the piping, a good signal-to-noise ratio can be obtained, and therefore it is possible to measure the flow rate of the piping with accuracy.

[0063] (Detection of poor contact between thermal flow meter and piping according to this embodiment) Figure 11 shows the results of a simulation of the temperature change of the thermal element 4b for 60 seconds from the start of heating of the heater 2, with the thermal element 4b placed in the center surrounded by the heater 2, as shown in the second embodiment.

[0064] Thermal resistance represents the contact condition between the thermal flow meter 1 and the pipe 6. A lower thermal resistance indicates better contact, while a higher resistance indicates worse contact. The thermal resistance must be within a certain value (<0.001 m). ２ Up to kW, the temperature changes exhibit almost the same behavior, but the thermal resistance is 0.005 m ２ - At kW or higher, a significant temperature rise is observed in the heat-sensitive element 4b located in the center. In other words, by observing the temperature behavior of the heat-sensitive element 4b in the center, it is possible to quickly detect abnormalities caused by poor contact between the thermal flow meter 1 and the piping 6.

[0065] (Detection of bubbles in fluid flowing through piping according to this embodiment) Figure 12 shows the temperature responses of the central thermal flow meter 1, the upstream peripheral thermal element 4a1, and the downstream peripheral thermal element 4a2 when water (temperature 25°C) is flowed as the fluid through a resin pipe (outer diameter 5 mm, inner diameter 3 mm) and bubbles with a dimension of approximately 10 to 30 mm in the fluid flow direction are generated along the way, as shown in the second embodiment, with the central thermal flow meter 1 having a central thermal element 4b surrounded by a heater 2. The distance in the fluid flow direction of the piping from the center of the heater 2 to the outer circumference is 2.6 mm, and the heating temperature of the heater 2 at this time was 33°C.

[0066] In particular, as shown in Figure (b), the temperature response of the central heat-sensitive element 4b shows a temperature rise when a bubble passes through it. The larger the bubble size, the greater the temperature rise of the central heat-sensitive element 4b. This is because the thermal conductivity of liquids and gases differs significantly, and heat from the heater 2 is less easily transferred to bubbles compared to the fluid. In other words, when a bubble is present in the fluid, the amount of heat transferred from the heater 2 to the fluid decreases, and instead, the amount of heat transferred to the central heat-sensitive element 4b increases, raising the temperature detected by the central heat-sensitive element 4b. The response when a bubble passes through is extremely fast, and even small bubbles can be detected. However, considering the signal-to-noise ratio, it is suitable for detecting bubbles with a dimension of 5 mm or more in the direction of fluid flow. The upstream peripheral heat-sensitive elements 4a1 and the downstream peripheral heat-sensitive elements 4a2 also show a similar temperature rise response, but their temperature changes are smaller than those of the central heat-sensitive element 4b, and their impact on flow rate measurement is limited.

[0067] (Influence of viscosity of fluid flowing through piping according to this embodiment) Figure 13 shows the measurement results of the temperature difference between the surrounding heat-sensitive elements 4a1 and 4a2 when glycerin is used as the fluid. As shown in the second embodiment, a thermal flow meter 1 was used in which the heat-sensitive element 4b was placed in the center surrounded by the heater 2. Glycerin (viscosity approximately 1500 mPa·s (@20℃)) was flowed as the fluid through a resin pipe (outer diameter 5 mm, inner diameter 3 mm) and measurements were taken. The distance in the direction of fluid flow in the pipe from the center of the heater 2 to the outer circumference was 2.6 mm, the heating temperature of the heater 2 at this time was 32℃, and the temperature of the glycerin was 25℃.

[0068] Similar to the case where the fluid is water (viscosity approximately 1 mPa·s (at 20°C)), when glycerin is used as the fluid, the temperature difference between the surrounding heat-sensitive elements 4a1 and 4a2 also changed in accordance with the change in flow velocity. In other words, it can be seen that the thermal flow meter of the present invention shows good response even to changes in the flow velocity of high-viscosity fluids.

[0069] (Fourth Embodiment) The flow rate measuring device according to the fourth embodiment of the present invention will be described below. The flow rate measuring device comprises a thermal flow meter 1 shown in Figure 1 and a controller (not shown). The thermal flow meter 1 can be a thermal flow meter as shown in the first to third embodiments described above.

[0070] The controller has a built-in control processing unit that calculates the flow velocity or flow rate of the piping fluid by processing the output value of the thermal flow meter 1.

[0071] Specifically, as shown in Figure 14, the process includes the steps of measuring the fluid temperature (S1), setting the temperature at which the thermal stimulation generating unit 20 heats or cools based on the fluid temperature (S2), calculating the temperature difference between the upstream and downstream thermal sensing elements 4a (S3), and comparing the calculated temperature difference with a pre-created database that correlates the temperature difference between the upstream and downstream thermal sensing elements 4a with the pipe flow velocity (S4), thereby measuring the flow velocity of the pipe fluid (S5). Furthermore, a step of measuring the flow rate from the information of the inner diameter of the pipe (S6) may be added.

[0072] These operations are primarily controlled by a program in the control processing unit built into the controller, and the flow rate measurement method described above is executed.

[0073] As described above, this embodiment provides a thermal flow meter that can measure the flow rate of fluid flowing inside a pipe and can be installed from the outside without modifying the existing piping. This eliminates the extra cost of installing a flow meter through pipe modification, and because it is installed on the outside of the pipe, it does not interfere with the fluid flow, allowing for more accurate measurements. Furthermore, it can measure corrosive and contaminating liquids as well. In addition, the inclusion of a thin-film thermal element in the center allows for the detection of poor contact between the pipe and the thermal flow meter.

[0074] Furthermore, if air bubbles are present in the fluid flowing through the pipe, this method has little effect on flow rate measurement and can detect the presence or absence of bubbles. In addition, the flow rate can be similarly measured for high-viscosity fluids with a viscosity of several thousand mPa·s at room temperature.

[0075] Although embodiments and modifications based thereon have been described, the present invention is not necessarily limited to these examples. Furthermore, those skilled in the art will be able to find various alternative embodiments and modifications without departing from the spirit of the present invention or the scope of the attached claims.

[0076] 1 Thermal flow meter 2 Heater (20: heat stimulation generating part) 4 Thermal element 4a (4a1, 4a2) Thermal element (surrounding thermal element) 4b Thermal element (central thermal element) 5 Insulated wiring board 6 Piping 51 Wiring pattern

Claims

1. A thermal flow meter for measuring the flow rate of a fluid flowing in a pipe, comprising: an insulating wiring board that can be attached to the outer circumference of the pipe; a conductive wiring pattern wired on the insulating wiring board; a thermal stimulation generating unit that heats or cools the outer surface of the pipe; and at least two thin-film peripheral thermal elements positioned at a predetermined distance from the thermal stimulation generating unit, wherein the peripheral thermal elements are arranged symmetrically on a straight line passing through the center of the thermal stimulation generating unit, with the thermal stimulation generating unit in between.

2. The thermal flow meter according to claim 1, characterized in that the thermal stimulation generating part has an axis passing through the central position and is symmetrical with respect to a straight line perpendicular to the axis at the central position.

3. The thermal flow meter according to claim 2, characterized in that the planar shape of the thermal stimulation generating section is one of a circle, a rectangle, or an ellipse.

4. The thermal flow meter according to claim 1, characterized in that the central part of the thermal stimulation generating section has a central region in which thermal stimulation is not generated.

5. The thermal flow meter according to claim 4, characterized in that the central region is symmetrical with respect to a straight line perpendicular to the axis passing through the center position of the thermal stimulation generating portion.

6. The thermal flow meter according to claim 4 or 5, characterized in that a thin film-like central thermal element is disposed in the central region, and the peripheral thermal element and the central thermal element are arranged in a straight line.

7. The thermal flow meter according to claim 6, characterized in that it is located inside an insulating cover.

8. The thermal flow meter according to claim 6, characterized in that the central thermal element and the peripheral thermal element are thin-film thermistors.

9. The thermal flow meter according to claim 8, characterized in that the thin film thermistor is trimmed to make the electrical characteristics of the peripheral thermal element and the central thermal element the same.

10. The thermal flow meter according to claim 8, characterized in that the thin-film thermistor includes a substrate and a heat-sensitive thin film and electrode layer formed on the substrate, and the heat-sensitive thin film and electrode layer are arranged to face the contact surface of the object to be measured.

11. The thermal flow meter according to claim 8, characterized in that the thin-film thermistor is formed by directly depositing a heat-sensitive thin film and an electrode layer onto the insulating wiring substrate.

12. The thermal flow meter according to claim 1, characterized in that the thermal stimulation generating unit is a heater.

13. The thermal flow meter according to claim 12, characterized in that the heater has a meander structure.

14. The thermal flow meter according to claim 1, characterized in that the thermal stimulation generating unit consists of a Peltier element.

15. The thermal flow meter according to claim 6, characterized in that the wiring pattern has a wiring expansion portion made of a conductive thin film on which the central thermal element and / or the peripheral thermal element are placed.

16. A flow rate measurement method using a thermal flow meter comprising: an insulating wiring board that can be attached to the outer circumference of a pipe; a conductive wiring pattern wired on the insulating wiring board; a thermal stimulation generating unit for heating or cooling the outer surface of the pipe; and at least two peripheral thermal sensing elements positioned at a predetermined distance from the thermal stimulation generating unit, wherein the peripheral thermal sensing elements are arranged symmetrically on a straight line passing through the center of the thermal stimulation generating unit, and the method comprises the steps of: heating or cooling the thermal stimulation generating unit to apply thermal stimulation to the pipe; and determining the flow rate using the temperature difference measured by the peripheral thermal sensing elements.

17. The flow rate measurement method according to claim 16, characterized in that the distance from the center position to the outer circumference position of the thermal stimulation generating part with respect to the fluid flow direction in the pipe is one-quarter or more of the inner diameter of the pipe.

18. The flow rate measurement method according to claim 16, characterized in that it includes a step of measuring the viscosity of the fluid in the piping.

19. The flow rate measurement method according to claim 18, characterized in that the viscosity of the fluid in the piping is 1500 mPa·s or less.

20. The flow rate measurement method according to claim 16, characterized in that it also detects the presence or absence of air bubbles in the fluid inside the piping.

21. The flow rate measurement method according to claim 20, characterized in that the bubble has a dimension of 5 mm or more in the direction of fluid flow.

22. The flow rate measurement method according to claim 16, characterized in that the thermal stimulation generating unit has a shape that is symmetrical with respect to a line perpendicular to a line passing through the center of the thermal stimulation generating unit.

23. The flow rate measurement method according to claim 16, characterized in that the central part of the thermal stimulation generating section has a central region in which thermal stimulation is not generated.

24. The flow rate measurement method according to claim 23, characterized in that a thin film-like central thermal element is disposed in the central region, and the peripheral thermal element and the central thermal element are arranged in a straight line.

25. The flow rate measurement method according to claim 16, characterized in that the temperature difference between the fluid temperature inside the piping and the temperature difference between the thermal stimulation generating part is 5°C or more.

26. A flow rate measuring device using a thermal flow meter, comprising: an insulating wiring board that can be attached to the outer circumference of a pipe; a conductive wiring pattern wired on the insulating wiring board; a thermal stimulation generating unit for heating or cooling the outer surface of the pipe; and at least two peripheral thermal sensing elements positioned at a predetermined distance from the thermal stimulation generating unit, wherein the peripheral thermal sensing elements are arranged symmetrically on a straight line passing through the center of the thermal stimulation generating unit, and the device has a control processing unit that incorporates a program for executing a flow rate measuring method comprising: heating or cooling the thermal stimulation generating unit to apply thermal stimulation to the pipe; and determining the flow rate using the temperature difference measured by the peripheral thermal sensing elements.

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