Thermal flowmeter

Abstract

This invention relates to a thermal flow meter. It improves the corrosion resistance to alkaline or acidic liquids and appropriately measures the flow rate of liquids using a temperature sensing substrate with a temperature sensing resistor formed on the sensing surface. A thermal flow meter is provided, comprising: a measuring tube (11) having an inlet for liquid inflow and an outlet for liquid flowing out from the inlet, and forming an internal flow path (10c) extending along an axis; and a temperature sensing substrate (12) having a heating resistor (12a) and a temperature sensing resistor formed on a sensing surface (12A) along the axis, the sensing surface (12A) being joined to the measuring tube (11) along the axis. The measuring tube (11) is formed of a thermally conductive fluororesin material comprising a fluororesin material and a thermally conductive material dispersed in the fluororesin material having a higher thermal conductivity than the fluororesin material.

Description

Technical Field

[0001] This invention relates to a thermal flow meter. Background Technology

[0002] A thermal flow meter is known in which a heating resistor and a temperature sensing resistor are bonded to a measuring tube along the direction of liquid flow, and the flow rate of the liquid flowing in the measuring tube is measured according to the timing of the heating resistor heating the liquid and the timing of the temperature sensing resistor detecting the liquid temperature (for example, see Patent Document 1).

[0003] The thermal flow meter disclosed in Patent Document 1 has its sensing surface of a glass temperature sensing substrate, which has a heating resistor and a temperature sensing resistor, joined to the flat surface of a glass measuring tube. This thermal flow meter heats the liquid via the measuring tube by instantaneously heating the heating resistor. As the heated liquid passes through the portion of the measuring tube joined with the temperature sensing resistor, the heat transferred to the temperature sensing resistor via the measuring tube is detected as a voltage signal.

[0004] Existing technical documents Patent documents Patent Document 1: Japanese Patent No. 6539458 Summary of the Invention The problem that the invention aims to solve Measuring tubes made of glass have the following disadvantages: silica, the main component of glass, undergoes a neutralization reaction with alkaline liquids, resulting in low corrosion resistance to alkaline liquids. Therefore, for measuring the flow rate of alkaline liquids, it is preferable to use a tubular flow path made of a resin material with high corrosion resistance to alkaline liquids.

[0005] However, resin materials have lower thermal conductivity than glass. Therefore, if the wall thickness of a flow path formed of resin material is set to the same level as that of a flow path made of glass, the liquid cannot be properly heated through the measuring tube. In this case, it may be impossible to properly detect the temperature of the liquid using a resistive element for temperature sensing.

[0006] The present invention was made in view of the following circumstances, and its object is to provide a thermal flow meter that can improve the corrosion resistance to alkaline or acidic liquids and properly measure the flow rate of liquids using a temperature sensing substrate with a temperature sensing resistor formed on the sensing surface.

[0007] Methods for solving problems To address the aforementioned issues, the present invention employs the following methods.

[0008] One aspect of the present invention, a thermal flow meter, comprises: a measuring tube having an inlet for liquid inflow and an outlet for liquid flowing in from the inlet to flow out, and having an internal flow path extending along an axis; and a temperature sensing substrate having a heating resistor and a temperature sensing resistor formed on a sensing surface along the axis, the sensing surface being joined to the measuring tube along the axis, the measuring tube being formed of a thermally conductive fluororesin material comprising a fluororesin material and a thermally conductive material having a higher thermal conductivity than the fluororesin material dispersed in the fluororesin material.

[0009] According to one aspect of the thermal flow meter of the present invention, the measuring tube having an internal flow path for liquid passage is formed of a thermally conductive fluororesin material containing a fluororesin material, thereby improving corrosion resistance to alkaline or acidic liquids. Furthermore, a thermally conductive material with higher thermal conductivity than the fluororesin material is dispersed in the thermally conductive fluororesin material forming the measuring tube, thereby improving the thermal conductivity of the measuring tube containing a fluororesin material with lower thermal conductivity than glass. Therefore, good thermal conductivity between the measuring tube and the liquid is achieved, improving corrosion resistance to alkaline or acidic liquids, and the liquid flow rate can be appropriately measured using a temperature sensing substrate with a temperature sensing resistor formed on the sensing surface.

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

[0011] According to the thermal flow meter of this structure, the thermal conductivity of the measuring tube can be improved by dispersing carbon nanotubes at least 0.020% by weight in a fluororesin material. This is because, by using flexible carbon nanotubes of a specified length as the thermally conductive material, thermal conductivity can be imparted with a small amount compared to other granular thermally conductive materials such as carbon black and iron powder. Furthermore, the proportion of carbon nanotubes contained in the thermally conductive fluororesin material is a very small percentage (less than 0.060% by weight), thus, unlike other granular thermally conductive materials such as carbon black and iron powder, liquid contamination caused by contact between the measuring tube and the liquid can be suppressed.

[0012] In a thermal flow meter according to one aspect of the present invention, it is preferably configured such that the detection surface is formed as a flat surface, and a flat surface is formed on the outer peripheral surface of the measuring tube, which is disposed opposite to the detection surface of the temperature detection substrate.

[0013] According to the thermal flow meter with this structure, by joining the flat surface formed on the outer circumference of the measuring tube with the flat sensing surface, a large contact area can be ensured and the bonding strength can be improved.

[0014] In a thermal flow meter according to one aspect of the present invention, it is preferably configured to include a thin metal sheet disposed between the flat surface of the measuring tube and the detection surface of the temperature sensing substrate in a manner that covers the flat surface of the measuring tube, wherein a first surface of the sheet is engaged with the flat surface of the measuring tube, and a second surface of the sheet is engaged with the detection surface of the temperature sensing substrate.

[0015] According to the thermal flow meter of this structure, a metal sheet is arranged between the flat surface of the measuring tube and the sensing surface of the temperature sensing substrate in such a way that it covers the flat surface of the measuring tube. Therefore, even if a portion of the corrosive gas evaporating from the liquid flowing inside the measuring tube passes through the measuring tube, the corrosive gas can be properly prevented from corroding the heating resistor and the temperature sensing resistor.

[0016] In the thermal flow meter with the above structure, it is preferably configured such that the first surface of the sheet and the flat surface of the measuring tube are joined by a heat-bonded film, and the second surface of the sheet and the sensing surface of the temperature sensing substrate are joined by an adhesive.

[0017] According to the thermal flow meter of this structure, by using a thermal fusion film to bond the first side of the sheet, which is easily affected by corrosive gases passing through the measuring tube, to the flat surface of the measuring tube, the influence of corrosive gases can be prevented and a proper bond can be achieved. Furthermore, an adhesive can be used to properly bond the second side of the sheet to the sensing surface of the temperature sensing substrate.

[0018] In the thermal flow meter with the above structure, it is preferable that the thin sheet is formed of a nickel alloy with nickel as the main component.

[0019] According to this structure, the thermal flow meter can reliably prevent corrosive gases from corroding the heating resistor and the temperature sensing resistor by utilizing a thin sheet made of a nickel alloy with nickel as the main component.

[0020] In a thermal flow meter according to one aspect of the present invention, it is preferably configured such that a first distance from the detection surface of the temperature detection substrate to the inner peripheral surface of the internal flow path is shorter than a second distance from the top of the measuring tube to the inner peripheral surface of the internal flow path.

[0021] According to the thermal flow meter of this structure, the first distance is shorter than the second distance. Therefore, compared with the case where these distances are equal, the heating characteristics of the heating resistor to the liquid in the internal flow path and the temperature detection characteristics of the temperature detection resistor to the liquid can be improved.

[0022] In one aspect of the thermal flow meter of the present invention, it is preferably configured such that the temperature sensing substrate is made of glass.

[0023] According to the thermal flow meter of this structure, since a glass temperature sensing substrate with minimal deformation due to heating is used, it is possible to suppress the deflection that occurs when the temperature sensing substrate is bonded to the measuring tube or during use.

[0024] Invention Effects According to the present invention, a thermal flow meter is provided that can improve the corrosion resistance to alkaline or acidic liquids and properly measure the flow rate of liquids using a temperature sensing substrate on which a temperature sensing resistor is formed on the sensing surface. Attached Figure Description

[0025] Figure 1 This is a longitudinal sectional view of the thermal flow meter according to the first embodiment of the present invention.

[0026] Figure 2 yes Figure 1 The image shows a longitudinal sectional view of the sensor section.

[0027] Figure 3A yes Figure 2 The top view of the measuring tube and sensor substrate shown.

[0028] Figure 3B yes Figure 2 The longitudinal sectional view of the measuring tube and sensor substrate shown.

[0029] Figure 3C yes Figure 2 The bottom view of the measuring tube and sensor substrate shown.

[0030] Figure 4 yes Figure 2 The sensor section shown is a cross-sectional view along line AA.

[0031] Figure 5 yes Figure 3B The BB-direction cross-sectional view of the measuring tube and sensor substrate is shown.

[0032] Figure 6 Observation from the side of the inspection surface Figure 3B The sensor substrate shown is a top view.

[0033] Figure 7 yes Figure 4 A partial enlarged view of part C of the measuring tube and sensor substrate shown.

[0034] Figure 8 This is a graph showing the relationship between the amount of carbon nanotubes added and the volume resistivity of the mixed fluororesin material.

[0035] Figure 9 It is a graph showing the relationship between water flow time and particle number.

[0036] Explanation of reference numerals in the attached figures 10. Sensor section; 10a. Inlet; 10b. Outlet; 10c. Internal flow path; 10d. Inner peripheral surface; 11. Measuring tube; 11a. Inlet; 11b. Outlet; 11c. Flat surface; 11d. Top; 12. Sensor substrate (temperature detection substrate); 12A. Detection surface; 12a. Heating resistance wire (heating resistor); 12b, 12c, 12d, 12e. Temperature detection resistance wire; 12f, 12g, 12h, 12i, 12j, 12k, 12l, 12m. Wiring pattern; 13. Air leakage prevention sheet; 13a. Upper surface ( 13b, Lower surface (2nd surface); 15, Nut; 16, Inflow side body; 17, Outflow side body; 18, Inflow side collar; 19, Outflow side collar; 20, Control board; 30, Relay board; 40, Upper housing; 50, Bottom housing; 60, Flexible board; 60f, 60g, 60h, 60i, 60j, 60k, 60l, 60m, Wiring pattern; 70, Stop; 80a, Hot melt film; 80b, 81, 82, Adhesive; 100, Thermal flow meter; 200, Cable; FD, Flow direction; T, Thickness; X, Axis. Detailed Implementation

[0037] Hereinafter, a thermal flow meter 100 according to an embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 This is a longitudinal sectional view of the thermal flow meter 100 according to the first embodiment of the present invention. Figure 2 yes Figure 1 The longitudinal sectional view of the sensor section 10 shown.

[0038] The thermal flow meter 100 of this embodiment heats the liquid flowing through its internal flow path and measures the flow rate of the liquid by detecting the temperature of the heated liquid. The thermal flow meter 100 of this embodiment is suitable for measuring minute flow rates, such as 0.1 cc / min to 30 cc / min. The liquids for which the thermal flow meter 100 of this embodiment measures flow include corrosive liquids such as alkaline liquids and acidic liquids. Examples of corrosive liquids include ammonia, hydrofluoric acid, and hydrochloric acid, which are chemical solutions used in semiconductor manufacturing equipment.

[0039] like Figure 1 and Figure 2 As shown, the thermal flow meter 100 of this embodiment includes a sensor unit 10, a control board 20, a relay board 30, an upper housing 40, and a bottom housing 50.

[0040] The sensor unit 10 allows liquid flowing in from the inlet 10a (connected to an external pipe, not shown) to flow out from the outlet 10b (also connected to an external pipe, not shown), and measures the flow rate of the liquid flowing through the internal flow path 10c. Instead of directly calculating the liquid flow rate, the sensor unit 10 detects the temperature of the liquid after it has been heated by the heating resistance wire 12a (heating resistance element, described later) using temperature detection resistance wires 12b, 12c, 12d, and 12e (temperature detection resistors). A temperature detection signal representing the detected temperature is then transmitted to the control board 20 via a signal line (not shown). Details regarding the sensor unit 10 will be described later.

[0041] The control board 20 is a device that transmits a voltage signal to the heating resistance line 12a of the sensor section 10 to heat the heating resistance line 12a, and calculates the liquid flow rate based on the temperature transmitted from the temperature detection resistance lines 12b, 12c, 12d, and 12e. The control board 20 transmits the voltage signal used to heat the heating resistance line 12a via the flexible substrate 60 (see reference 1). Figure 6 The control board 20 outputs voltage signals to the sensor substrate 12 via the flexible substrate 60, which are used to detect the resistance values ​​of the resistance lines 12b, 12c, 12d, and 12e for temperature detection.

[0042] The control board 20 outputs a voltage signal to the heating resistor 12a in a manner that periodically repeats the heating period during which the heating resistor 12a is heated and the non-heating period during which the heating resistor 12a is not heated. The heating period is set to be shorter than the non-heating period. That is, the ratio of the heating period to one cycle (which is the sum of the heating period and the non-heating period) is set to be less than 0.5. The ratio of the heating period to one cycle can also be set to be less than 0.4.

[0043] The relay board 30 is a board used for relaying various signals between the control board 20 and an external device (not shown). Cables 200 for transmitting and receiving various signals between the relay board 30 and the external device (not shown) are connected to the relay board 30.

[0044] The upper housing 40 is a component that forms the upper housing of the thermal flow meter 100, and houses the control board 20 inside.

[0045] The bottom housing 50 is a component that forms the lower part of the housing of the thermal flow meter 100, and houses the sensor unit 10 inside. With the sensor unit 10 inserted into the bottom housing 50, the stop member 70 is inserted from the flow inlet 10a side of the sensor unit 10 between the bottom housing 50 and the sensor unit 10.

[0046] With the sensor unit 10 inserted into the bottom housing 50, the stop member 70 is inserted from the outlet 10b side of the sensor unit 10 between the bottom housing 50 and the sensor unit 10. The stop member 70 fixes the sensor unit 10 to the bottom housing 50. A fastening hole 50a is formed on the bottom surface of the bottom housing 50, and a fastening bolt (not shown) inserted from below the mounting surface (not shown) fixes the sensor unit to the mounting surface.

[0047] Next, the sensor section 10 will be described in detail. For example... Figure 2 As shown, the sensor unit 10 includes a measuring tube 11, a sensor substrate (temperature detection substrate) 12, a nut 15, an inflow side body 16, an outflow side body 17, an inflow side collar 18, and an outflow side collar 19.

[0048] The measuring tube 11 is a tube having an inlet 11a for liquid to flow in and an outlet 11b for liquid flowing out from the inlet 11a. An internal flow path 10c, which is circular in cross-sectional view and extends along the axis X, is formed in the measuring tube 11. The measuring tube 11 is formed of a mixed fluoropolymer material that is resistant to corrosion by alkaline or acidic liquids. The mixed fluoropolymer material will be described later.

[0049] The inflow-side body 16 is a component into which the inlet 11a of the measuring tube 11 is inserted and into which a connecting flow path 16a (first connecting flow path) that is circular in cross-section is formed. An external thread 16b is formed on the outer peripheral surface of the end of the inflow-side body 16 on the outlet 10b side.

[0050] The outflow-side body 17 is a component into which the outlet 11b of the measuring tube 11 is inserted and has a connecting flow path 17a (second connecting flow path) that is circular in cross-section. An external thread 17b is formed on the outer peripheral surface of the end of the outflow-side body 17 at the inlet 10a side. The inflow-side body 16 and the outflow-side body 17 are formed of a highly corrosion-resistant resin material (e.g., PTFE: polytetrafluoroethylene).

[0051] Nut 15 consists of an inflow-side nut 15a installed on the inflow-side body 16 and an outflow-side nut 15b installed on the outflow-side body 17. The inflow-side nut 15a is a cylindrical member inserted along the outer circumferential surface of the measuring tube 11 to a position closer to the outlet 11b than the inflow-side body 16. An internal thread 15g is formed on the inner circumferential surface of the end of the inflow-side nut 15a at the inlet 10a side. Similarly, the outflow-side nut 15b is a cylindrical member inserted along the outer circumferential surface of the measuring tube 11 to a position closer to the inlet 11a than the outflow-side body 17. An internal thread 15h is formed on the inner circumferential surface of the end of the outflow-side nut 15b at the outlet 10b side.

[0052] The inflow-side nut 15a is installed on the inflow-side body 16 by fastening the internal thread 15g of the inflow-side nut 15a to the external thread 16b of the inflow-side body 16. Similarly, the outflow-side nut 15b is installed on the outflow-side body 17 by fastening the internal thread 15h of the outflow-side nut 15b to the external thread 17b of the outflow-side body 17.

[0053] A recess 15e (first recess) is formed at the end of the inflow-side nut 15a on the outlet 10b side, recessed toward the inflow-inlet 10a. The recess 15e is inserted into the end of the sensor substrate 12 on the inflow-inlet 11a side, which contains adhesive 81. The recess 15e is filled with filler material 15i. The end of the sensor substrate 12 on the inflow-inlet 11a side is fixed to the inflow-side nut 15a using the filler material 15i.

[0054] A recess 15f (second recess) is formed at the end of the outflow-side nut 15b on the inlet 10a side, recessed toward the outlet 10b. The end of the sensor substrate 12 on the outlet 11b side, containing adhesive 82, is inserted into the recess 15f. Additionally, a filler material 15j is filled into the recess 15f. The end of the sensor substrate 12 on the outlet 11b side is fixed to the outflow-side nut 15b using the filler material 15j.

[0055] The inflow-side collar 18 is a cylindrical resin (e.g., PTFE) component that is inserted between the outer peripheral surface of the measuring tube 11 and the inner peripheral surface of the end of the inflow-side body 16 at the outlet 10b side. The outflow-side collar 19 is a cylindrical resin (e.g., PTFE) component that is inserted between the outer peripheral surface of the measuring tube 11 and the inner peripheral surface of the end of the outflow-side body 17 at the inlet 10a side.

[0056] The sensor section 10 of the thermal flow meter 100 of this embodiment is assembled in the following manner: with the inlet 11a of the measuring tube 11 and the inflow-side collar 18 inserted into the end of the inflow-side body 16 at the outlet 10b side, the internal thread 15g of the inflow-side nut 15a is tightened to the external thread 16b of the inflow-side body 16; with the outlet 11b of the measuring tube 11 and the outlet-side collar 19 inserted into the end of the outlet-side body 17 at the inlet 10a side, the internal thread 15h of the outlet-side nut 15b is tightened to the external thread 17b of the outlet-side body 17.

[0057] The internal thread 15g of the inflow-side nut 15a is fastened to the external thread 16b of the inflow-side body 16 by contacting the top end of the inflow-side nut 15a at the inlet 10a side with the protrusion 16d of the inflow-side body 16. The internal thread 15h of the outflow-side nut 15b is fastened to the external thread 17b of the outflow-side body 17 by contacting the top end of the outflow-side nut 15b at the outlet 10b side with the protrusion 17d of the outflow-side body 17.

[0058] Figure 3A yes Figure 2 The top view of the measuring tube 11 and the sensor substrate 12 shown. Figure 3B yes Figure 2 The longitudinal sectional view of the measuring tube 11 and the sensor substrate 12 shown. Figure 3C yes Figure 2 The bottom view of the measuring tube 11 and sensor substrate 12 shown.

[0059] like Figure 3B and Figure 3C As shown, the end of the sensor substrate 12 at the inlet 11a side and the end of the sensor substrate 12 at the inlet 11a side of the flat surface 11c formed on the measuring tube 11 are joined by adhesive 81, and the end of the sensor substrate 12 at the outlet 11b side and the end of the sensor substrate 12 at the outlet 11b side of the flat surface 11c are joined by adhesive 82. For example, epoxy resin-based adhesives can be used as adhesives 81 and 82.

[0060] Figure 4 yes Figure 2 The sensor unit 10 shown is viewed in a cross-sectional view along direction AA. Figure 4 As shown, the upper side of the cross-section of the measuring tube 11, which is cut by a plane orthogonal to the axis X, at the position where it is bonded to the sensor substrate 12, is approximately circular. The surface of the outer peripheral surface of the measuring tube 11 that is disposed opposite to the detection surface 12A of the sensor substrate 12 is a flat surface 11c. The detection surface 12A and the flat surface 11c are joined at various positions along the axis X.

[0061] Figure 5 yes Figure 3B The BB-direction cross-sectional view of the measuring tube 11 and sensor substrate 12 is shown. Figure 5 As shown, the cross-section of the measuring tube 11 at the position where the sensor substrate 12 is not bonded is circular when it is cut by a plane orthogonal to the axis X.

[0062] like Figure 4As shown, the distance D1 (first distance) from the detection surface 12A of the sensor substrate 12 to the inner peripheral surface 10d of the internal flow path 10c is shorter than the distance D2 (second distance) from the top 11d of the measuring tube 11 to the inner peripheral surface 10d of the internal flow path 10c. This is to improve the thermal conductivity from the heating resistance wire 12a to the liquid by making the distance D1 shorter than the distance D2, and to improve the temperature detection characteristics of the temperature detection resistance wires 12b and 12d. The distance D1 is preferably set to 0.2 mm or less, for example, 0.1 mm.

[0063] Figure 6 Viewed from the 12A side of the inspection surface Figure 3B The sensor substrate 12 shown is a top view. The sensor substrate 12 is a glass substrate (e.g., made of quartz glass with a high silicon dioxide content) formed along the axis X on the detection surface 12A with temperature detection resistance wires (temperature detection resistors) 12e, 12c, 12a, 12b, and 12d for temperature detection on the detection surface 12A.

[0064] The detection surface 12A extends along the axis X and is formed into a flat surface. The heating resistance wire 12a, the temperature detection resistance wire 12b, and the temperature detection resistance wire 12c are formed by depositing a metal film such as platinum onto a glass substrate.

[0065] The liquid flowing through measuring tube 11 moves along the path from... Figure 6 The liquid flows in a left-to-right flow direction FD along the axis X. Therefore, when the heating resistance wire 12a is instantaneously heated, the heated liquid flows along the axis X, reaches the position of the temperature detection resistance wire 12b, and then reaches the position of the temperature detection resistance wire 12d. The control board 20 measures the temperature of the temperature detection resistance wires 12b and 12d by detecting the resistance values ​​of the temperature detection resistance wires 12b and 12d, which change according to the temperature.

[0066] like Figure 6 As shown, the position P1 of the heating resistance line 12a in the sensor substrate 12 is located at a position near the outlet 11b side, which is equidistant from the end of the sensor substrate 12 on the inlet side 11a side and the end of the sensor substrate 12 on the outlet side 11b side.

[0067] The distance L1 on the axis X from the inlet 11a of the measuring tube 11 to the heating resistance wire 12a (refer to...) Figure 3AThe distance L2 from the outlet 11b of the measuring tube 11 to the axis X of the heating resistance wire 12a (refer to...) Figure 3A The distance from the inlet 11a of the measuring tube 11 to the heating resistance wire 12a is longer, and the liquid is heated after sufficient reduction of turbulence in the liquid flowing into the inlet 11a of the measuring tube 11.

[0068] The control board 20 can calculate the flow velocity of the liquid flowing through the measuring tube 11 based on the timing of the instantaneous heating of the heating resistance wire 12a and the subsequent timing of the temperature detection of the heated liquid by the temperature detection resistance wires 12b and 12d. Furthermore, the control board 20 can calculate the liquid flow rate based on the calculated flow velocity and the cross-sectional area of ​​the measuring tube 11.

[0069] 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 in the opposite direction to the liquid flow direction FD along the axis X, reaching the position of the temperature detection resistance wire 12c, and then reaching the position of the temperature detection resistance wire 12e. The control board 20 measures the temperature of the temperature detection resistance wires 12c and 12e by detecting the resistance values ​​of the temperature detection resistance wires 12c and 12e, which change according to the temperature.

[0070] The control board 20 subtracts the temperature of the temperature sensing resistor line 12c from the temperature of the temperature sensing resistor line 12b. The temperature detected by the temperature sensing resistor line 12c upstream of the flow direction FD of the heating resistor line 12a is equivalent to the heat transferred from the heating resistor line 12a to the measuring tube 11 that was not transferred to the liquid but was transferred to the temperature sensing resistor line 12c via the measuring tube 11. The temperature sensing resistor lines 12b and 12c are arranged at equal distances relative to the heating resistor line 12a.

[0071] Therefore, by subtracting the temperature of the temperature detection resistor line 12c from the temperature of the temperature detection resistor line 12b, the temperature of the liquid passing through the position of the temperature detection resistor line 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 line 12d by subtracting the temperature of the temperature detection resistor line 12e from the temperature of the temperature detection resistor line 12d.

[0072] like Figure 6As shown, 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 are formed on the detection surface 12A. Additionally, 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 are formed on the detection surface 12A. The other end of the temperature detection resistance wire 12d is connected to wiring pattern 12i.

[0073] Furthermore, wiring patterns 12k (connected to one end of the temperature sensing resistance line 12c), 12l (connected to the other end of the temperature sensing resistance line 12c), and 12m (connected to one end of the temperature sensing resistance line 12e) are formed on the detection surface 12A. The other end of the temperature sensing resistance line 12e is connected to wiring pattern 12l. Wiring patterns 12f, 12g, 12h, 12i, 12j, 12k, 12l, and 12m are formed by depositing a metal film such as platinum onto a glass substrate.

[0074] The ends of wiring patterns 12f, 12g, 12h, 12i, 12j, 12k, 12l, and 12m are respectively bonded to metal wiring patterns 60f, 60g, 60h, 60i, 60j, 60k, 60l, and 60m disposed on a flexible substrate (external connection terminal) 60 formed of film resin. The wiring patterns 60f, 60g, 60h, 60i, 60j, 60k, 60l, and 60m of the flexible substrate 60 are electrically connected to the control substrate 20.

[0075] Figure 7 yes Figure 4 A partially enlarged view of portion C of the measuring tube 11 and sensor substrate 12 shown. (See attached image.) Figure 7 As shown, the thermal flow meter 100 of this embodiment includes a metal air-proof sheet 13 disposed between the flat surface 11c and the detection surface 12A, covering at least the entire area of ​​the flat surface 11c of the measuring tube 11 that engages with the detection surface 12A. The air-proof sheet 13 has a fixed 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 air-proof sheet 13 is formed of a nickel alloy (e.g., HASTELLOY (registered trademark)) with nickel as the main component.

[0076] The upper surface (first surface) 13a of the air-permeable sheet 13 is bonded to the flat surface 11c of the measuring tube 11 using a heat-fusion film 80a. The heat-fusion film 80a is softened by heating to above a specified welding temperature and then cooled and solidified, thereby achieving a state in which the upper surface 13a and the flat surface 11c are bonded.

[0077] The heat-fused membrane 80a is preferably formed from fluoropolymer materials such as ETFE (ethylene tetrafluoroethylene), PTFE (polytetrafluoroethylene), PCTFE (polychlorotrifluoroethylene), and PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer). By forming the heat-fused membrane 80a from fluoropolymer materials, the durability of the heat-fused membrane 80a against corrosive gases passing through the measuring tube 11 is improved.

[0078] The lower surface (second surface) 13b of the air-permeable sheet 13 is bonded to the detection surface 12A of the sensor substrate 12 using adhesive 80b. It should be noted that the portion of the lower surface 13b relating to the temperature detection resistance lines 12e, 12c, 12b, 12d and the heating resistance line 12a on which the detection surface 12A is formed is bonded to these resistance lines.

[0079] As the adhesive 80b, for example, epoxy resin adhesives, UV-curable resin adhesives, thermosetting resin adhesives, low-melting-point glass, etc., can be used. Adhesive 80b is an insulating material with insulating properties, and therefore has the function of preventing the metal air-permeable sheet 13 from conducting with the heating resistance wire 12a, and the temperature sensing resistance wires 12b, 12c, 12d, and 12e.

[0080] Next, the mixed fluoropolymer material (thermally conductive fluoropolymer material) of the measuring tube 11 in the integrated terrain cost implementation method will be described.

[0081] The measuring tube 11 in this embodiment is formed of a mixed fluororesin material comprising a fluororesin material and carbon nanotubes (thermally conductive materials) dispersed within the fluororesin material. The fluororesin material may be, for example, PTFE, PCTFE, or PFA. Powdered fluororesin materials (e.g., PTFEG 163 manufactured by Asahi Glass) can be used as the fluororesin material.

[0082] In addition, as carbon nanotubes, it is desirable to use carbon nanotubes with the following properties.

[0083] • It has a fiber length of 50μm or more and 150μm or less.

[0084] • It has a fiber diameter of 5nm or more and 20nm or less.

[0085] • With 10mg / cm 3 Above and 70mg / cm 3 The following are the bulk densities.

[0086] • The G / D ratio is above 0.7 and below 2.0.

[0087] • Purity is above 99.5%.

[0088] • Formed in multiple layers (e.g., 4 to 12 layers).

[0089] The purpose of making the carbon nanotube fiber length 50 μm or more is to impart sufficient thermal conductivity with a small amount of carbon nanotubes while dispersing them in the fluororesin material.

[0090] Furthermore, the G / D ratio refers to the ratio of the peaks of the G band to the peaks of the D band in the Raman spectrum of carbon nanotubes. The G band originates from the graphite structure, while the D band originates from defects. The G / D ratio represents the ratio of the purity of the crystals to the defect concentration of the carbon nanotubes.

[0091] 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 carbon nanotubes dispersed in the fluororesin material, and obtained the following results. Figure 8 The results are shown. Figure 8 The results shown are based on the volume resistivity of the test piece as specified in JIS K 7194, "Resistivity Test Method Based on 4-Probe Method for Conductive Plastics".

[0092] As test pieces, multiple test pieces were prepared and then compressed using a compression molding machine after being melt-mixed in a mixing mill, and processed into test pieces according to the dimensions of JIS K 7194. The fluoropolymer material used to make the test pieces was PTFE G163 manufactured by Asahi Glass.

[0093] Furthermore, the volume resistivity was measured using a resistivity meter employing the four-probe method according to JIS K 7194. The four-probe method involves contacting four needle-shaped probes (electrodes) with the test piece and determining the resistance of the test piece based on the current flowing between the two outer probes and the potential difference generated between the two inner probes. Volume resistivity is calculated by averaging measurements obtained from multiple test pieces at multiple locations.

[0094] according to Figure 8 The results show that, 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 fluoropolymer material is higher than 1.0 × 10⁻⁶. 3 Ω·cm is greater than or equal to 1.0 × 10⁻⁶ 4 The range of Ω·cm. This volume resistivity value is compared with the volume resistivity value of the fluoropolymer material with undispersed carbon nanotubes (10 Ω·cm). 18 The volume resistivity is sufficiently low compared to Ω·cm. Furthermore, by increasing the amount of carbon nanotubes added to more than 0.03 wt%, the volume resistivity is further reduced.

[0095] The inventors then realized that in mixed fluororesin materials containing carbon nanotubes but not carbon nanotubes, there is a negative correlation between volume resistivity and thermal conductivity. Specifically, they realized that if the amount of carbon nanotubes added increases and the volume resistivity decreases, the thermal conductivity increases accordingly. Furthermore, the inventors 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, it is possible to heat the liquid flowing through the internal flow path 10c of the measuring tube 11 from the heating resistance wire 12a formed on the detection surface 12A of the sensor substrate 12, and to appropriately detect the temperature of the heated liquid using the temperature detection resistance wires 12b, 12c, 12d, and 12e.

[0096] Therefore, in this embodiment, the amount of carbon nanotubes added to the mixed fluororesin material forming the measuring tube 11 is set to a range of 0.020% by weight or more and 0.060% by weight or less. It should be noted that 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, but the thermal conductivity of the measuring tube 11 with an added amount of 0.05% by weight is 0.64 W / m·K.

[0097] In addition, the inventors measured the microparticles (particles) contained in a liquid flowing through a flow path formed by a mixed fluororesin material in which carbon nanotubes were added at an amount of 0.025% by weight. Figure 9 It is a measurement result that shows the relationship between the water flow time for pure water to circulate and the number of particles measured by a particle counter (illustration omitted).

[0098] The particle number refers to the number of particles larger than 0.04 μm contained in 1 ml of pure water. Additionally, in Figure 9 In the measurements shown, the flow rate of pure water flowing through the flow path is set to 0.5 liters per minute. Furthermore, the flow of pure water is switched between a cut-off state (cut off the flow) and a flow-through state (allowing the flow of pure water) every 5 seconds. The temperature of the pure water is set to 25°C.

[0099] Although Figure 9 The diagram is omitted, but the number of particles at the start of the measurement (when the water flow time is zero) is approximately 340. Subsequently, as the water flow time progresses, the number of particles gradually decreases, remaining below 10 after 4 hours. Therefore, by forming the measuring tube 11 from a mixed fluororesin material containing carbon nanotubes at a ratio of 0.020% to 0.060% by weight, and thoroughly cleaning the measuring tube 11 with pure water, the product is manufactured, thereby ensuring that the number of particles mixed into the liquid from the measuring tube 11 during use is sufficiently small.

[0100] It should be noted that, Figure 9 The results, shown with a carbon nanotube addition amount of 0.025% by weight in the mixed fluororesin material, confirm that even when the carbon nanotube addition amount is set to 0.060% by weight, the particle number does not increase excessively. Thus, for the measuring tube 11 of this embodiment, the proportion of carbon nanotubes contained in the mixed fluororesin material is a very small proportion of less than 0.060% by weight, therefore, unlike other granular conductive materials such as carbon black and iron powder, it is possible to suppress fluid contamination caused by contact with the fluid.

[0101] The function and effect of the thermal flow meter 100 of this embodiment described above will be explained.

[0102] According to the thermal flow meter 100 of this embodiment, the measuring tube 11, which forms an internal flow path 10c for liquid flow, is formed of a mixed fluororesin material containing a fluororesin material, thus improving its corrosion resistance to alkaline or acidic liquids. Furthermore, a thermally conductive material with higher thermal conductivity than the fluororesin material is dispersed in the mixed fluororesin material forming the measuring tube 11, thus improving the thermal conductivity of the measuring tube 11, which contains a fluororesin material with lower thermal conductivity than glass. Therefore, good thermal conductivity between the measuring tube 11 and the liquid is achieved, improving corrosion resistance to alkaline or acidic liquids, and the liquid flow rate can be appropriately measured using a sensor substrate 12 with temperature detection resistance lines 12b, 12c, 12d, and 12e formed on the detection surface 12A.

[0103] According to the thermal flow meter 100 of this embodiment, the thermal conductivity of the measuring tube 11 can be improved by dispersing carbon nanotubes at least 0.020% by weight in a fluororesin material. This is because, by using a flexible carbon nanotube of a predetermined length as the thermally conductive material, thermal conductivity can be imparted with a small amount compared to other granular thermally conductive materials such as carbon black and iron powder. Furthermore, since the proportion of carbon nanotubes contained in the thermally conductive fluororesin material is a very small proportion of 0.060% by weight or less, unlike other granular thermally conductive materials such as carbon black and iron powder, liquid contamination caused by contact between the measuring tube 11 and the liquid can be suppressed.

[0104] According to the thermal flow meter 100 of this embodiment, by joining the flat surface 11c formed on the outer peripheral surface of the measuring tube 11 with the flat detection surface 12A, a large contact area can be ensured and the bonding strength can be improved.

[0105] According to the thermal flow meter 100 of this embodiment, a metal gas-proof sheet 13 is disposed between the flat surface 11c of the measuring tube 11 and the detection surface 12A of the sensor substrate 12 in such a way that it covers the flat surface 11c of the measuring tube 11. Therefore, even if a portion of the corrosive gas volatilized from the liquid flowing inside the measuring tube 11 passes through the measuring tube 11, the corrosive gas can be properly prevented from corroding the heating resistance wire 12a and the temperature detection resistance wires 12b, 12c, 12d, and 12e.

[0106] According to the thermal flow meter 100 of this embodiment, by using a heat-fusion film 80a to bond the upper surface 13a of the gas-proof sheet 13, which is easily affected by corrosive gases passing through the measuring tube 11, to the flat surface 11c of the measuring tube 11, the influence of corrosive gases can be prevented and a proper bond can be achieved. Furthermore, an adhesive 80b can be used to properly bond the lower surface 13b of the gas-proof sheet 13 and the detection surface 12A of the sensor substrate 12.

[0107] According to the thermal flow meter 100 of this embodiment, the gas-proof sheet 13 formed 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.

[0108] 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 peripheral 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 peripheral surface 10d of the internal flow path 10c. Therefore, compared with the case where these distances are equal, the heating characteristics of the heating resistance wire 12a to the liquid in the internal flow path 10c and the temperature detection characteristics of the temperature detection resistance wires 12b, 12c, 12d, and 12e to the liquid can be improved.

[0109] According to the thermal flow meter 100 of this embodiment, since a glass sensor substrate 12 with minimal deformation due to heating is used, it is possible to suppress the deflection that occurs when the sensor substrate 12 is bonded to the measuring tube 11 or during use.

[0110] [Other Implementation Methods] In the above description, the thermal flow meter 100 includes a metal air-proof plate 13, which is disposed between the flat surface 11c and the detection surface 12A in such a way that it covers at least the entire area of ​​the flat surface 11c of the measuring tube 11 that is in contact with the detection surface 12A, but other arrangements are also possible. For example, the air-proof plate 13 may be omitted if corrosive gases are not generated from the liquid flowing through the internal flow path 10c of the measuring tube 11 and permeate to the outside of the measuring tube 11, or if the amount generated is extremely small.

[0111] 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-fused film 80a or an adhesive 80b. Since there is no gas-proof sheet 13 between the flat surface 11c and the detection surface 12A, the thermal conductivity between them is improved. When using the heat-fused film 80a formed of a fluoropolymer material, even if corrosive gases permeate from the measuring tube 11, the reduction in the bonding force between the flat surface 11c and the detection surface 12A can be suppressed.

Claims

1. A thermal flow meter, wherein, The thermal flow meter has the following features: A measuring tube having an inlet for liquid to flow into and an outlet for liquid to flow out from the inlet, and forming an internal flow path extending along an axis; and A temperature sensing substrate has a heating resistor and a temperature sensing resistor formed on its sensing surface along the axis, and the sensing surface is joined to the measuring tube along the axis. The measuring tube is formed of a thermally conductive fluororesin material comprising a fluororesin material and a thermally conductive material dispersed in the fluororesin material having a higher thermal conductivity than the fluororesin material.

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

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

4. The thermal flow meter according to claim 3, wherein, The thermal flow meter includes a thin metal sheet disposed between the flat surface of the measuring tube and the sensing surface of the temperature sensing substrate in a manner that covers the flat surface of the measuring tube. The first surface of the thin sheet engages with the flat surface of the measuring tube. The second side of the thin sheet is bonded to the detection side of the temperature detection substrate.

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

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

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

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

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