Thermal flow meter

Abstract

The flow rate of a liquid is appropriately measured using a temperature detection substrate with a temperature-sensing resistor formed on its detection surface, while also enhancing corrosion resistance to alkaline or acidic liquids. [Solution] A thermal flow meter is provided, comprising: a measuring tube 11 having an inlet for liquid to flow in and an outlet for the liquid that has flowed in from the inlet and having an internal flow path 10c that extends along its axis; and a temperature detection substrate 12 having a heating resistor 12a and a temperature detection resistor formed on its detection surface 12A along its axis and the detection surface 12A being joined to the measuring tube 11 along its axis, wherein the measuring tube 11 is formed of a thermally conductive fluororesin material that includes a fluororesin material and a thermally conductive material dispersed in the fluororesin material that has a higher thermal conductivity than the fluororesin material.

Description

Technical Field

[0001] The present invention relates to a thermal flow meter.

Background Art

[0002] There is known a thermal flow meter that measures the flow rate of a liquid flowing through a measurement pipe from the timing of heating the liquid by a heating resistor and the timing of detecting the temperature of the liquid by a temperature detection resistor, with the heating resistor and the temperature detection resistor adhered to the measurement pipe along the flow direction of the liquid (see, for example, Patent Document 1).

[0003] The thermal flow meter disclosed in Patent Document 1 is one in which a detection surface of a glass temperature detection substrate on which a heating resistor and a temperature detection resistor are formed is joined to a flat surface of a measurement pipe formed of glass. This thermal flow meter instantaneously heats the heating resistor to heat the liquid through the measurement pipe, and detects, as a voltage signal, the heat transmitted through the measurement pipe to the temperature detection resistor when the heated liquid passes through the portion of the measurement pipe to which the temperature detection resistor is joined.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] A measurement pipe formed of glass has a drawback in that its corrosion resistance to an alkaline liquid is low because silicon dioxide, which is the main component of glass, and the alkaline liquid undergo a neutralization reaction. Therefore, in order to measure the flow rate of an alkaline liquid, it is preferable to use a tubular flow path formed of a resin material having high corrosion resistance to the alkaline liquid. ,

[0006] However, because resin materials have lower thermal conductivity than glass, if the wall thickness of a channel formed from resin material is the same as that of a channel made from glass, the liquid cannot be properly heated through the measuring tube. In this case, the temperature of the liquid may not be properly detected by the temperature sensing resistor.

[0007] This invention has been made in view of these circumstances, and aims to provide a thermal flow meter that can appropriately measure the flow rate of a liquid using a temperature detection substrate in which a temperature detection resistor is formed on the detection surface, while improving corrosion resistance to alkaline or acidic liquids. [Means for solving the problem]

[0008] To solve the above problems, the present invention employs the following means. A thermal flow meter according to one aspect of the present invention comprises a measuring tube having an inlet into which liquid flows and an outlet for discharging the liquid that has flowed in from the inlet, and having an internal flow path extending along its axis; and a temperature detection substrate having a heating resistor and a temperature detection resistor formed on its detection surface along the axis, and the detection surface being joined to the measuring tube along the axis, wherein the measuring tube is formed of a thermally conductive fluororesin material including a fluororesin material and a thermally conductive material dispersed in the fluororesin material that has a higher thermal conductivity than the fluororesin material.

[0009] According to one aspect of the present invention, a thermal flow meter is formed from a thermally conductive fluororesin material containing a fluororesin material, which provides an internal flow path for the liquid to flow through. This enhances corrosion resistance to alkaline or acidic liquids. Furthermore, since a thermally conductive material with higher thermal conductivity than the fluororesin material is dispersed in the thermally conductive fluororesin material forming the measuring tube, the thermal conductivity of the measuring tube containing the fluororesin material, which has lower thermal conductivity than glass, can be increased. As a result, the thermal conductivity between the measuring tube and the liquid is improved, enhancing corrosion resistance to alkaline or acidic liquids, while allowing for appropriate measurement of the liquid flow rate using a temperature detection substrate with a temperature detection resistor formed on its detection surface.

[0010] In a thermal flow meter according to one aspect of the present invention, it is preferable that the thermally conductive material is a carbon nanotube, and the thermally conductive fluororesin material contains the carbon nanotube in a proportion of 0.020% by weight or more and 0.060% by weight or less.

[0011] This thermal flow meter configuration allows for increased thermal conductivity of the measuring tube by dispersing 0.020% by weight or more of carbon nanotubes in a fluororesin material. This is because using tubular carbon nanotubes of a predetermined length as the thermal conductive material allows for thermal conductivity to be imparted with a smaller amount compared to other granular thermal conductive materials such as carbon black or iron powder. Furthermore, because the proportion of carbon nanotubes in the thermal conductive fluororesin material is a minute amount of 0.060% by weight or less, unlike other granular thermal conductive materials such as carbon black or iron powder, it can suppress liquid contamination due to contact between the measuring tube and the liquid.

[0012] In a thermal flow meter according to one aspect of the present invention, the detection surface is a flat surface, and it is preferable that a flat surface is formed on the outer circumferential surface of the measuring tube, on which the detection surface of the temperature detection substrate is positioned opposite to the detection surface. With this configuration of thermal flow meter, a wide contact area can be secured and bonding performance improved by joining a flat surface formed on the outer surface of the measuring tube with a flat detection surface.

[0013] In a thermal flow meter according to one aspect of the present invention, a metal sheet is provided which is disposed between the flat surface of the measuring tube and the detection surface of the temperature detection substrate so as to cover the flat surface of the measuring tube, wherein the first surface of the sheet is bonded to the flat surface of the measuring tube and the second surface of the sheet is bonded to the detection surface of the temperature detection substrate.

[0014] With this thermal flow meter configuration, a metal sheet is placed between the flat surface of the measuring tube and the detection surface of the temperature detection substrate so as to cover the flat surface of the measuring tube. Therefore, even if some corrosive gas volatilized from the liquid flowing inside the measuring tube permeates the measuring tube, it is possible to effectively prevent the corrosive gas from corroding the heating resistor and the temperature detection resistor.

[0015] In the thermal flow meter with the above configuration, it is preferable that the first surface of the sheet and the flat surface of the measuring tube are joined by a heat-sealing film that is joined by heating, and the second surface of the sheet and the detection surface of the temperature detection substrate are joined by an adhesive.

[0016] In this thermal flow meter configuration, the first surface of the sheet, which is susceptible to the effects of corrosive gases permeating the measuring tube, and the flat surface of the measuring tube are joined using a heat-sealing film, thereby preventing the effects of corrosive gases while ensuring proper joining. Furthermore, the second surface of the sheet and the detection surface of the temperature detection substrate can be properly joined using an adhesive.

[0017] In the thermal flow meter with the above configuration, it is preferable that the sheet is made of a nickel alloy with nickel as the main component. With this thermal flow meter configuration, the sheet formed from a nickel alloy with nickel as the main component reliably prevents corrosive gases from corroding the heating resistor and the temperature sensing resistor.

[0018] In a thermal flow meter according to one aspect of the present invention, it is preferable that the first distance from the detection surface of the temperature detection substrate to the inner circumferential surface of the internal flow path is shorter than the second distance from the top of the measuring tube to the inner circumferential surface of the internal flow path. With this configuration of thermal flow meter, since the first distance is shorter than the second distance, the heating characteristics of the liquid in the internal flow path by the heating resistor and the temperature detection characteristics of the liquid by the temperature detection resistor can be improved compared to the case where these distances are equal.

[0019] In the thermal flowmeter according to one aspect of the present invention, it is preferable that the temperature detection substrate is made of glass. According to the thermal flowmeter of this configuration, since a glass temperature detection substrate with little deformation due to heating is used, it is possible to suppress the deflection that occurs when the temperature detection substrate is adhered to the measurement pipe or during use.

Advantages of the Invention

[0020] According to the present invention, it is possible to provide a thermal flowmeter capable of appropriately measuring the flow rate of a liquid by using a temperature detection substrate on which a resistor for temperature detection is formed on the detection surface while enhancing the corrosion resistance against alkaline or acidic liquids.

Brief Description of the Drawings

[0021] [Figure 1] It is a longitudinal sectional view of the thermal flowmeter according to the first embodiment of the present invention. [Figure 2] It is a longitudinal sectional view of the sensor unit shown in FIG. 1. [Figure 3A] It is a plan view of the measurement pipe and the sensor substrate shown in FIG. 2. [Figure 3B] It is a longitudinal sectional view of the measurement pipe and the sensor substrate shown in FIG. 2. [Figure 3C] It is a bottom view of the measurement pipe and the sensor substrate shown in FIG. 2. [Figure 4] It is an end view of the sensor unit shown in FIG. 2 as viewed from the A-A arrow direction. [Figure 5] It is an end view of the measurement pipe and the sensor substrate shown in FIG. 3B as viewed from the B-B arrow direction. [Figure 6] It is a plan view of the sensor substrate shown in FIG. 3B as viewed from the detection surface side. [Figure 7] It is a partially enlarged view of the C part of the measurement pipe and the sensor substrate shown in FIG. 4. [Figure 8] It is a graph showing the relationship between the addition amount of carbon nanotubes and the volume resistivity of the mixed fluororesin material. [Figure 9] It is a graph showing the relationship between the water passing time and the number of particles.

Modes for Carrying Out the Invention

[0022] Hereinafter, a thermal flow meter 100 according to one embodiment of the present invention will be described with reference to the drawings. Figure 1 is a longitudinal cross-sectional view of the thermal flow meter 100 according to the first embodiment of the present invention. Figure 2 is a longitudinal cross-sectional view of the sensor unit 10 shown in Figure 1.

[0023] The thermal flow meter 100 of this embodiment is a thermal flow meter that measures the flow rate of a liquid by heating the liquid flowing through its internal channel and detecting the temperature of the heated liquid. The thermal flow meter 100 of this embodiment is suitable for measuring minute flow rates, for example, from 0.1 cc / min to 30 cc / min. The liquid whose flow rate is measured by the thermal flow meter 100 of this embodiment includes corrosive liquids such as alkaline liquids and acidic liquids. Corrosive liquids are, for example, chemicals used in semiconductor manufacturing equipment, such as ammonia water, hydrofluoric acid, and hydrochloric acid.

[0024] As shown in Figures 1 and 2, the thermal flow meter 100 of this embodiment comprises a sensor unit 10, a control board 20, a relay board 30, an upper case 40, and a bottom case 50.

[0025] The sensor unit 10 controls the flow rate of liquid flowing in through an inlet 10a connected to an external pipe (not shown) and out through an outlet 10b connected to the external pipe (not shown), and also measures the flow rate of liquid flowing through an internal channel 10c. The sensor unit 10 does not directly calculate the liquid flow rate, but rather detects the temperature of the liquid heated by a heating resistor 12a (heating resistor), which will be described later, using temperature detection resistors 12b, 12c, 12d, and 12e (temperature detection resistors), and transmits a temperature detection signal indicating the detected temperature to the control board 20 via a signal line (not shown). Details of the sensor unit 10 will be described later.

[0026] The control board 20 is a device that transmits a voltage signal to the heating resistor wire 12a of the sensor unit 10 to heat the heating resistor wire 12a, and calculates the liquid flow rate based on the temperature transmitted from the temperature detection resistor wires 12b, 12c, 12d, and 12e. The control board 20 outputs a voltage signal for heating the heating resistor wire 12a to the sensor board 12 via the flexible board 60 (see Figure 6). The control board 20 also outputs a voltage signal for detecting the resistance values ​​of the temperature detection resistor wires 12b, 12c, 12d, and 12e to the sensor board 12 via the flexible board 60.

[0027] The control board 20 outputs a voltage signal to the heating resistor wire 12a so as to periodically repeat a heating period in which the heating resistor wire 12a is heated and a non-heating period in which the heating resistor wire 12a is not heated. The heating period is set to be shorter than the non-heating period. That is, the heating period is set to a ratio of less than 0.5 to one cycle, which is the sum of the heating period and the non-heating period. The ratio of the heating period to one cycle may also be set to less than 0.4.

[0028] The relay board 30 is a board that acts as a relay for sending and receiving various signals between the control board 20 and an external device (not shown). A cable 200 for sending and receiving various signals between the relay board 30 and the external device (not shown) is connected to the relay board 30.

[0029] The upper case 40 is a component that forms the upper housing of the thermal flow meter 100 and houses the control board 20 inside. The bottom case 50 is a component that forms the lower housing of the thermal flow meter 100 and houses the sensor unit 10 inside. With the sensor unit 10 inserted into the bottom case 50, the stopper 70 is inserted between the bottom case 50 and the sensor unit 10 from the inlet 10a side of the sensor unit 10.

[0030] With the sensor unit 10 inserted into the bottom case 50, the stopper 70 is inserted between the bottom case 50 and the sensor unit 10 from the outlet 10b side of the sensor unit 10. The stopper 70 fixes the sensor unit 10 to the bottom case 50. Fastening holes 50a are formed in the bottom surface of the bottom case 50, and it is fixed to the mounting surface (not shown) by fastening bolts (not shown) inserted from below the mounting surface (not shown).

[0031] Next, the sensor unit 10 will be described in detail. As shown in Figure 2, the sensor unit 10 includes a measuring tube 11, a sensor substrate (temperature detection substrate) 12, a nut 15, an inlet body 16, an outlet body 17, an inlet ferrule 18, and an outlet ferrule 19.

[0032] The measuring tube 11 is a tube having an inlet 11a into which liquid flows and an outlet 11b that discharges the liquid that has flowed in from the inlet 11a. The measuring tube 11 has an internal flow channel 10c that extends along axis X and has a circular cross-section. The measuring tube 11 is made of a mixed fluororesin material that has corrosion resistance to alkaline or acidic liquids. The mixed fluororesin material will be described later.

[0033] The inlet-side body 16 is a component into which the inlet 11a of the measuring tube 11 is inserted, and which has a circular connecting channel 16a (first connecting channel) formed inside in cross-section. A male thread 16b is formed on the outer circumferential surface of the end of the inlet-side body 16 on the outlet 10b side.

[0034] The outlet-side body 17 is a component into which the outlet 11b of the measuring tube 11 is inserted, and which has a circular connecting channel 17a (second connecting channel) formed inside in cross-section. A male thread 17b is formed on the outer circumferential surface of the end of the outlet-side body 17 on the inlet 10a side. The inlet-side body 16 and the outlet-side body 17 are made of a highly corrosion-resistant resin material (for example, PTFE: polytetrafluoroethylene).

[0035] The nut 15 consists of an inlet nut 15a attached to the inlet body 16 and an outlet nut 15b attached to the outlet body 17. The inlet nut 15a is a cylindrical member inserted along the outer circumferential surface of the measuring tube 11, closer to the outlet 11b than the inlet body 16. A female thread 15g is formed on the inner circumferential surface of the inlet nut 15a end on the inlet 10a side. The outlet nut 15b is also a cylindrical member inserted along the outer circumferential surface of the measuring tube 11, closer to the inlet 11a than the outlet body 17. A female thread 15h is formed on the inner circumferential surface of the outlet nut 15b end on the outlet 10b side.

[0036] The inlet nut 15a is attached to the inlet body 16 by fastening the female thread 15g of the inlet nut 15a to the male thread 16b of the inlet body 16. Similarly, the outlet nut 15b is attached to the outlet body 17 by fastening the female thread 15h of the outlet nut 15b to the male thread 17b of the outlet body 17.

[0037] A recess 15e (first recess) is formed at the outlet 10b end of the inlet nut 15a, facing the inlet 10a. The inlet 11a end of the sensor substrate 12, which contains adhesive 81, is inserted into the recess 15e. The recess 15e is filled with filler material 15i. The inlet 11a end of the sensor substrate 12 is fixed to the inlet nut 15a by the filler material 15i.

[0038] A recess 15f (second recess) is formed at the inlet 10a end of the outlet nut 15b, facing the outlet 10b. The outlet 11b end of the sensor substrate 12, which contains adhesive 82, is inserted into the recess 15f. The recess 15f is also filled with filler material 15j. The outlet 11b end of the sensor substrate 12 is fixed to the outlet nut 15b by the filler material 15j.

[0039] The inlet ferrule 18 is a cylindrical resin (e.g., PTFE) member inserted between the outer surface of the measuring tube 11 and the inner surface of the outlet 10b end of the inlet body 16. The outlet ferrule 19 is a cylindrical resin (e.g., PTFE) member inserted between the outer surface of the measuring tube 11 and the inner surface of the inlet 10a end of the outlet body 17.

[0040] The sensor unit 10 of the thermal flow meter 100 in this embodiment is assembled by inserting the inlet 11a of the measuring tube 11 and the inlet ferrule 18 into the outlet 10b end of the inlet body 16, fastening the female thread 15g of the inlet nut 15a to the male thread 16b of the inlet body 16, and inserting the outlet 11b of the measuring tube 11 and the outlet ferrule 19 into the inlet 10a end of the outlet body 17, fastening the female thread 15h of the outlet nut 15b to the male thread 17b of the outlet body 17.

[0041] When the tip of the inlet-side nut 15a on the inlet 10a side comes into contact with the projection 16d of the inlet-side body 16, the fastening of the female thread 15g of the inlet-side nut 15a and the male thread 16b of the inlet-side body 16 is completed. When the tip of the outlet-side nut 15b on the outlet 10b side comes into contact with the projection 17d of the outlet-side body 17, the fastening of the female thread 15h of the outlet-side nut 15b and the male thread 17b of the outlet-side body 17 is completed.

[0042] Figure 3A is a plan view of the measuring tube 11 and sensor substrate 12 shown in Figure 2. Figure 3B is a longitudinal cross-sectional view of the measuring tube 11 and sensor substrate 12 shown in Figure 2. Figure 3C is a bottom view of the measuring tube 11 and sensor substrate 12 shown in Figure 2.

[0043] As shown in Figures 3B and 3C, the inlet 11a side end of the sensor substrate 12 and the inlet 11a side end of the flat surface 11c formed on the measuring tube 11 are joined by adhesive 81, and the outlet 11b side end of the sensor substrate 12 and the outlet 11b side end of the flat surface 11c are joined by adhesive 82. For example, epoxy resin adhesives can be used as adhesives 81 and 82.

[0044] Figure 4 is an end view of the sensor unit 10 shown in Figure 2, taken along the AA arrow. As shown in Figure 4, the upper side of the cross-section of the measuring tube 11, defined by a plane perpendicular to the axis X, is approximately circular at the position where the sensor substrate 12 is bonded. Of the outer surface of the measuring tube 11, the surface where the detection surface 12A of the sensor substrate 12 is positioned opposite is a flat surface 11c. The detection surface 12A and the flat surface 11c are joined at various positions along the axis X.

[0045] Figure 5 is an end view of the measuring tube 11 and sensor substrate 12 as seen by arrow BB, as shown in Figure 3B. As shown in Figure 5, the measuring tube 11 has a circular cross-section defined by a plane perpendicular to axis X at the position where the sensor substrate 12 is not bonded.

[0046] As shown in Figure 4, the distance D1 (first distance) from the detection surface 12A of the sensor substrate 12 to the inner surface 10d of the internal flow channel 10c is shorter than the distance D2 (second distance) from the top 11d of the measuring tube 11 to the inner surface 10d of the internal flow channel 10c. This is to make the distance D1 from the detection surface 12A of the sensor substrate 12 to the inner surface 10d of the internal flow channel 10c shorter than the distance D2, thereby improving the heat conductivity from the heating resistance wire 12a to the liquid and improving the temperature detection characteristics of the temperature detection resistance wire 12b and temperature detection resistance wire 12d. The distance D1 is preferably 0.2 mm or less, for example, 0.1 mm.

[0047] Figure 6 is a plan view of the sensor substrate 12 shown in Figure 3B, as seen from the detection surface 12A side. The sensor substrate 12 is a glass substrate (for example, made of quartz glass with a high silicon dioxide content) on the detection surface 12A, with temperature detection resistance wires (temperature detection resistors) 12e, 12c, 12a, 12b, and 12d formed along the axis X.

[0048] The detection surface 12A is a flat surface that extends along the axis X. The heating resistance wire 12a, the temperature detection resistance wire 12b, and the temperature detection resistance wire 12c are each formed by depositing a metal film such as platinum onto a glass substrate.

[0049] The liquid flowing through the measuring tube 11 flows along axis X, following the flow direction FD from left to right in Figure 6. Therefore, when the heating resistance wire 12a is instantaneously heated, the heated liquid flows along axis X to the position of the temperature detection resistance wire 12b, and then to the position of the temperature detection resistance wire 12d. The control board 20 measures the temperatures of the temperature detection resistance wires 12b and 12d by detecting the electrical resistance values ​​of the temperature detection resistance wires 12b and 12d, which change with temperature.

[0050] As shown in Figure 6, the position P1 where the heating resistance wire 12a is placed on the sensor substrate 12 is located on the outlet 11b side, rather than at an intermediate position that is equidistant from both the inlet 11a side end and the outlet 11b side end of the sensor substrate 12.

[0051] The distance L1 (see Figure 3A) along axis X from the inlet 11a of the measuring tube 11 to the heating resistance wire 12a is longer than the distance L2 (see Figure 3A) along axis X from the outlet 11b of the measuring tube 11 to the heating resistance wire 12a. This ensures a longer distance from the inlet 11a of the measuring tube 11 to the heating resistance wire 12a, allowing the liquid to be heated only after the turbulence of the liquid flowing into the inlet 11a of the measuring tube 11 has sufficiently decreased.

[0052] The control board 20 can calculate the flow rate of the liquid flowing through the measuring tube 11 from the timing when the heating resistor wire 12a is instantaneously heated and the timing when the temperature detection resistor wire 12b and temperature detection resistor wire 12d detect the temperature of the heated liquid. Furthermore, the control board 20 can calculate the liquid flow rate from the calculated flow rate and the cross-sectional area of ​​the measuring tube 11.

[0053] When the heating resistance wire 12a is instantaneously heated, the heat transferred from the heating resistance wire 12a to the detection surface 12A is transferred along the axis X in the opposite direction of the liquid flow FD, reaching the position of the temperature detection resistance wire 12c, and then the position of the temperature detection resistance wire 12e. The control board 20 measures the temperatures of the temperature detection resistance wires 12c and 12e by detecting the electrical resistance values ​​of the temperature detection resistance wires 12c and 12e, which change with temperature.

[0054] The control board 20 subtracts the temperature of the temperature detection resistor wire 12b from the temperature of the temperature detection resistor wire 12c. The temperature detected by the temperature detection resistor wire 12c on the upstream side of the flow direction FD of the heating resistor wire 12a corresponds to the heat that was transferred from the heating resistor wire 12a to the measuring tube 11 and not transferred to the liquid, but was transferred to the temperature detection resistor wire 12c via the measuring tube 11. The temperature detection resistor wires 12b and 12c are arranged at an equidistant distance from the heating resistor wire 12a.

[0055] Therefore, by subtracting the temperature of the temperature detection resistor wire 12c from the temperature of the temperature detection resistor wire 12b, the temperature of the liquid passing through the position of the temperature detection resistor wire 12b can be measured. Similarly, the control board 20 can measure the temperature of the liquid passing through the position of the temperature detection resistor wire 12d by subtracting the temperature of the temperature detection resistor wire 12e from the temperature of the temperature detection resistor wire 12d.

[0056] As shown in Figure 6, the detection surface 12A has a wiring pattern 12f connected to one end of the heating resistance wire 12a and a wiring pattern 12g connected to the other end of the heating resistance wire 12a. The detection surface 12A also has a wiring pattern 12h connected to one end of the temperature detection resistance wire 12b, a wiring pattern 12i connected to the other end of the temperature detection resistance wire 12b, and a wiring pattern 12j connected to one end of the temperature detection resistance wire 12d. The other end of the temperature detection resistance wire 12d is connected to the wiring pattern 12i.

[0057] Furthermore, the detection surface 12A has a wiring pattern 12k connected to one end of the temperature detection resistance wire 12c, a wiring pattern 12l connected to the other end of the temperature detection resistance wire 12c, and a wiring pattern 12m connected to one end of the temperature detection resistance wire 12e. The other end of the temperature detection resistance wire 12e is connected to the wiring pattern 12l. The wiring patterns 12f, 12g, 12h, 12i, 12j, 12k, 12l, and 12m are each formed by depositing a metal film such as platinum onto a glass substrate.

[0058] The ends of the wiring patterns 12f, 12g, 12h, 12i, 12j, 12k, 12l, and 12m are joined to metal wiring patterns 60f, 60g, 60h, 60i, 60j, 60k, 60l, and 60m, respectively, which are placed on a flexible substrate (external connection terminal) 60 formed from a film-like resin. The wiring patterns 60f, 60g, 60h, 60i, 60j, 60k, 60l, and 60m on the flexible substrate 60 are electrically connected to the control board 20.

[0059] Figure 7 is a partially enlarged view of portion C of the measuring tube 11 and sensor substrate 12 shown in Figure 4. As shown in Figure 7, the thermal flow meter 100 of this embodiment includes a metallic gas permeability barrier sheet 13 positioned between the flat surface 11c and the detection surface 12A so as to cover the entire area of ​​the flat surface 11c of the measuring tube 11 that is joined to at least the detection surface 12A. The gas permeability barrier sheet 13 has a certain thickness T. The thickness T is set, for example, in the range of 0.01 mm or more and 0.03 mm or less. The gas permeability barrier sheet 13 is formed of a nickel alloy with nickel as the main component (for example, Hastelloy®).

[0060] The upper surface (first surface) 13a of the gas permeability-blocking sheet 13 is joined to the flat surface 11c of the measuring tube 11 by a heat-sealing film 80a. The heat-sealing film 80a is heated to a predetermined welding temperature or higher, softened, and then cooled and solidified, thereby joining the upper surface 13a and the flat surface 11c.

[0061] The heat-sealable film 80 is preferably formed from a fluororesin material such as ETFE (ethylene tetrafluoroethylene), PTFE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene), or PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer). By forming the heat-sealable film 80 from a fluororesin material, the durability of the heat-sealable film 80 against corrosive gases that permeate from the measuring tube 11 is improved.

[0062] The lower surface (second surface) 13b of the gas permeability-blocking sheet 13 is bonded to the detection surface 12A of the sensor substrate 12 by adhesive 80b. In addition, the lower surface 13b is bonded to the temperature detection resistance wires 12e, 12c, 12b, 12d and the heating resistance wire 12a of the detection surface 12A in the areas where these resistance wires are formed.

[0063] As the adhesive 80b, for example, epoxy resin adhesives, UV-curable resin adhesives, thermosetting resin adhesives, low-melting-point glass, etc., can be used. Since the adhesive 80b is an insulating material with insulating properties, it has the function of preventing electrical conductivity between the metal gas permeability-blocking sheet 13 and the heating resistance wire 12a, temperature detection resistance wires 12b, 12c, 12d, and 12e.

[0064] Next, the mixed fluororesin material (thermally conductive fluororesin material) used to integrally form the measuring tube 11 of this embodiment will be described. The measuring tube 11 of this embodiment is formed from a mixed fluororesin material containing a fluororesin material and carbon nanotubes (thermally conductive material) dispersed in the fluororesin material. Here, the fluororesin material is, for example, PTFE, PCTFE, PFA, etc. As the fluororesin material, a powdered form (for example, PTFE G163 manufactured by Asahi Glass) can be used.

[0065] Furthermore, it is desirable to use carbon nanotubes that possess the following properties, for example. • Having a fiber length of 50 μm or more and 150 μm or less. • The fiber has a diameter of 5 nm or more and 20 nm or less. 10 mg / cm³ 3 And 70 mg / cm³ or more 3 It has the following bulk density: The G / D ratio is 0.7 or higher and 2.0 or lower. • The purity is 99.5% or higher. It is formed in multiple layers (for example, 4 to 12 layers). The reason the carbon nanotube fiber length is set to 50 μm or more is to ensure that a small amount of carbon nanotubes provides sufficient thermal conductivity when dispersed in a fluororesin material.

[0066] Furthermore, the G / D ratio is a value that indicates the ratio of the G-band peak to the D-band peak that appear in the Raman spectrum of carbon nanotubes. The G-band peak originates from the graphite structure, while the D-band peak originates from defects. The G / D ratio represents the ratio of the purity of the crystal to the defect concentration of the carbon nanotube.

[0067] The inventors investigated the relationship between the amount of carbon nanotubes dispersed in the fluororesin material (weight %) and the volume resistivity (Ω·cm) of the mixed fluororesin material containing the fluororesin material and the dispersed carbon nanotubes, and obtained the results shown in Figure 8. The results shown in Figure 8 are the result of measuring the volume resistivity of the test specimens based on the "Resistivity Test Method for Conductive Plastics using the Four-Probe Method" specified in JIS K 7194.

[0068] Multiple test specimens were prepared by melt-kneading the material in a kneader, then compression-molding it in a compression molding machine, and finally processing them to a size conforming to JIS K 7194. The fluoropolymer material used to prepare the test specimens was PTFE G163 manufactured by Asahi Glass.

[0069] Furthermore, a resistivity meter using the four-probe method in accordance with JIS K 7194 was used to measure volume resistivity. The four-probe method involves contacting the test specimen with four needle-shaped probes (electrodes) and determining the resistance of the test specimen from the current flowing between the two outer probes and the potential difference generated between the two inner probes. Volume resistivity was calculated by averaging the measured values ​​obtained at multiple locations on each of the multiple test specimens.

[0070] As shown in Figure 8, by setting the amount of carbon nanotubes added to a range of 0.020% by weight or more and 0.030% by weight or less, the volume resistivity of the mixed fluororesin material becomes 1.0 × 10⁻⁶ 3 Greater than Ω·cm and 1.0 × 10⁻⁶ 4 The value fell within the range of less than Ω·cm. This volume resistivity value is the same as the volume resistivity of a fluoropolymer material in which carbon nanotubes are not dispersed (10 18 It is sufficiently low compared to (Ω·cm). Furthermore, increasing the amount of carbon nanotubes added beyond 0.03 wt% further reduces the volume resistivity.

[0071] The inventors then found that in a mixed fluororesin material in which carbon nanotubes are added to a fluororesin material that does not contain carbon nanotubes, there is a negative correlation between volume resistivity and thermal conductivity. In other words, they found that as the amount of carbon nanotubes added increases and the volume resistivity decreases, the thermal conductivity increases accordingly. The inventors then confirmed that by setting the amount of carbon nanotubes added to the mixed fluororesin material forming the measuring tube 11 to a range of 0.020% by weight or more and 0.060% by weight or less, the liquid flowing through the internal channel 10c of the measuring tube 11 can be heated by the heating resistance wire 12a formed on the detection surface 12A of the sensor substrate 12, and the temperature of the heated liquid can be appropriately detected by the temperature detection resistance wires 12b, 12c, 12d, and 12e.

[0072] Therefore, in this embodiment, the amount of carbon nanotubes added to the mixed fluororesin material forming the measuring tube 11 is set to be in the range of 0.020% by weight or more and 0.060% by weight or less. When PTFE is used as the fluororesin material, the thermal conductivity of the measuring tube 11 without added carbon nanotubes is 0.53 W / m·k, while the thermal conductivity of the measuring tube 11 with added carbon nanotubes of 0.05% by weight is 0.64 W / m·k.

[0073] Furthermore, the inventors measured the number of fine particles (particles) contained in a liquid flowing through a channel formed from a mixed fluororesin material with a carbon nanotube content of 0.025% by weight. Figure 9 shows the measurement results illustrating the relationship between the flow time of pure water and the number of particles measured by a particle counter (not shown).

[0074] Here, particle count refers to the number of particles with a size of 0.04 μm or larger contained in 1 ml of pure water. In the measurement shown in Figure 9, the flow rate of pure water circulating through the channel was set to 0.5 liters / minute. The system switched between a blocked state (where the flow of pure water is blocked) and a flow state (where the flow of pure water is enabled) at 5-second intervals. The temperature of the pure water was set to 25°C.

[0075] Although not shown in Figure 9, the number of particles at the start of measurement (zero water flow time) was approximately 340. Subsequently, the number of particles gradually decreased as the water flow time progressed, and after 4 hours of water flow, it was maintained at 10 or less. Therefore, by forming the measuring tube 11 from a mixed fluororesin material containing carbon nanotubes in a ratio of 0.020% by weight or more and 0.060% by weight or less, and thoroughly washing the measuring tube 11 with pure water or the like before packaging it as a product, the number of particles that enter the liquid from the measuring tube 11 during use can be kept sufficiently low.

[0076] Figure 9 shows the results for a mixed fluororesin material with a carbon nanotube content of 0.025% by weight. However, the inventors confirmed that even when the carbon nanotube content was 0.060% by weight, the number of particles did not increase excessively. Thus, in this embodiment, the measurement tube 11 contains a minute proportion of carbon nanotubes of 0.060% by weight or less in the mixed fluororesin material. Unlike other granular conductive materials such as carbon black and iron powder, it can suppress fluid contamination due to contact with the fluid.

[0077] The functions and effects of the thermal flow meter 100 of this embodiment, as described above, will now be explained. In the thermal flow meter 100 of this embodiment, the measuring tube 11, which has an internal flow path 10c through which liquid flows, is formed of a mixed fluororesin material containing a fluororesin material, thereby increasing corrosion resistance to alkaline or acidic liquids. Furthermore, since a thermally conductive material with higher thermal conductivity than the fluororesin material is dispersed in the mixed fluororesin material forming the measuring tube 11, the thermal conductivity of the measuring tube 11, which contains a fluororesin material with lower thermal conductivity than glass, can be increased. As a result, the thermal conductivity between the measuring tube 11 and the liquid is improved, and the liquid flow rate can be appropriately measured using a sensor substrate 12 on the detection surface 12A, while increasing corrosion resistance to alkaline or acidic liquids.

[0078] According to the thermal flow meter 100 of this embodiment, the thermal conductivity of the measuring tube 11 can be increased by dispersing 0.020% by weight or more of carbon nanotubes in a fluororesin material. This is because, by using tubular carbon nanotubes of a predetermined length as a thermal conductive material, thermal conductivity can be imparted with a smaller amount compared to other granular thermal conductive materials such as carbon black or iron powder. Furthermore, because the proportion of carbon nanotubes contained in the thermal conductive fluororesin material is a minute proportion of 0.060% by weight or less, unlike other granular thermal conductive materials such as carbon black or iron powder, contamination of the liquid due to contact between the measuring tube 11 and the liquid can be suppressed.

[0079] According to the thermal flow meter 100 of this embodiment, a wide contact area can be secured and bonding performance can be improved by joining the flat surface 11c formed on the outer surface of the measuring tube 11 with the flat detection surface 12A.

[0080] According to the thermal flow meter 100 of this embodiment, a metal gas permeability-blocking sheet 13 is placed between the flat surface 11c of the measuring tube 11 and the detection surface 12A of the sensor substrate 12 so as to cover the flat surface 11c of the measuring tube 11. Therefore, even if some corrosive gas volatilized from the liquid flowing inside the measuring tube 11 permeates the measuring tube 11, it is possible to appropriately prevent the corrosive gas from corroding the heating resistance wire 12a and the temperature detection resistance wires 12b, 12c, 12d, and 12e.

[0081] According to the thermal flow meter 100 of this embodiment, the upper surface 13a of the gas permeability-blocking sheet 13, which is susceptible to the effects of corrosive gases that permeate the measuring tube 11, and the flat surface 11c of the measuring tube 11 are joined using a heat-sealing film 80a, thereby enabling proper joining while preventing the effects of corrosive gases. Furthermore, the lower surface 13b of the gas permeability-blocking sheet 13 and the detection surface 12A of the sensor substrate 12 can be properly joined using adhesive 80b.

[0082] According to the thermal flow meter 100 of this embodiment, the gas permeability-blocking sheet 13, which is made of a nickel alloy with nickel as the main component, can reliably prevent corrosive gases from corroding the heating resistance wire 12a and the temperature detection resistance wires 12b, 12c, 12d, and 12e.

[0083] According to the thermal flow meter 100 of this embodiment, the distance D1 from the detection surface 12A of the sensor substrate 12 to the inner circumferential surface 10d of the internal flow path 10c is shorter than the distance D2 from the top 11d of the measuring tube 11 to the inner circumferential surface 10d of the internal flow path 10c. Therefore, compared to the case where these distances are equal, the heating characteristics of the liquid in the internal flow path 10c due to the heating resistance wire 12a and the temperature detection characteristics of the liquid due to the temperature detection resistance wires 12b, 12c, 12d, and 12e can be improved.

[0084] According to the thermal flow meter 100 of this embodiment, since a glass sensor substrate 12 that deforms less due to heating is used, it is possible to suppress the bending that occurs when bonding the sensor substrate 12 to the measuring tube 11 or during use.

[0085] [Other embodiments] In the above description, the thermal flow meter 100 is provided with a metal gas permeability-blocking sheet 13 placed between the flat surface 11c and the detection surface 12A so as to cover the entire area of ​​the flat surface 11c of the measuring tube 11 that is in contact with at least the detection surface 12A. However, other embodiments are also possible. For example, if the liquid flowing through the internal flow path 10c of the measuring tube 11 does not generate or generates very little corrosive gas that permeates to the outside of the measuring tube 11, the gas permeability-blocking sheet 13 may be omitted.

[0086] In this case, the flat surface 11c of the measuring tube 11 and the detection surface 12A of the sensor substrate 12 are joined by a heat-sealing film 80a or adhesive 80b. Since there is no gas permeation prevention sheet 13 between the flat surface 11c and the detection surface 12A, the thermal conductivity between the flat surface 11c and the detection surface 12A is improved. When a heat-sealing film 80a made of fluororesin material is used, even if corrosive gases permeate from the measuring tube 11, it is possible to suppress a decrease in the bonding strength between the flat surface 11c and the detection surface 12A. [Explanation of symbols]

[0087] 10 Sensor section 10a Inlet 10b Outlet 10c internal flow path 10d Inner surface 11 Measuring tube 11a Inlet 11b Outlet 11c flat surface 11d Top 12. Sensor board (temperature detection board) 12A Detection surface 12a Heating resistance wire (heating resistor) 12b, 12c, 12d, 12e Resistance wires for temperature detection 12f, 12g, 12h, 12i, 12j, 12k, 12l, 12m wiring pattern 13. Gas permeability barrier sheet 13a Top surface (first surface) 13b Bottom surface (2nd surface) 15 nuts 16 Inlet body 17 Outlet body 18. Inlet ferrule 19 Outflow ferrule 20 Control board 30 relay boards 40 Upper Case 50 Bottom Cases 60 Flexible circuit boards 60f, 60g, 60h, 60i, 60j, 60k, 60l, 60m wiring patterns 70 Stopper 80a heat-sealable film 80b, 81, 82 Adhesive 100 Thermal flow meter 200 Cables FD flow direction T thickness X axis

Claims

1. A measuring tube having an inlet into which liquid flows and an outlet for which the liquid flowing in from the inlet flows out, and having an internal flow path that extends along its axis, A temperature detection substrate is provided, wherein a heating resistor and a temperature detection resistor are formed on the detection surface along the axis, and the detection surface is joined to the measuring tube along the axis. A thermal flow meter in which the measuring tube is formed of a thermally conductive fluororesin material that includes a fluororesin material and a thermally conductive material dispersed in the fluororesin material that has a higher thermal conductivity than the fluororesin material.

2. The aforementioned thermally conductive material is a carbon nanotube. The thermal flow meter according to claim 1, wherein the thermally conductive fluororesin material contains carbon nanotubes in a proportion of 0.020% by weight or more and 0.060% by weight or less.

3. The detection surface is a flat surface, The thermal flow meter according to claim 1 or claim 2, wherein a flat surface is formed on the outer circumferential surface of the measuring tube, which is joined to the detection surface of the temperature detection substrate.

4. The measuring tube is provided with a metal sheet that is placed between the flat surface and the detection surface of the temperature detection substrate so as to cover the flat surface of the measuring tube, The first surface of the sheet is joined to the flat surface of the measuring tube, The thermal flow meter according to claim 3, wherein the second surface of the sheet is bonded to the detection surface of the temperature detection substrate.

5. The first surface of the sheet and the flat surface of the measuring tube are joined together by a heat-sealing film. The thermal flow meter according to claim 4, wherein the second surface of the sheet and the detection surface of the temperature detection substrate are joined together by an adhesive.

6. The thermal flow meter according to claim 4, wherein the sheet is formed of a nickel alloy having nickel as the main component.

7. The thermal flow meter according to claim 1 or claim 2, wherein the first distance from the detection surface of the temperature detection substrate to the inner circumferential surface of the internal flow path is shorter than the second distance from the top of the measuring tube to the inner circumferential surface of the internal flow path.

8. The thermal flow meter according to claim 1 or claim 2, wherein the temperature detection substrate is made of glass.

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