Thermal flow meter

Abstract

A thermal flow meter is provided, comprising: a measuring tube 11 having an inlet port into which a liquid flows, and an outlet port from which the liquid flowing in from the inlet port can flow out, and having an internal flow channel 10c extending along an axis, and a temperature sensing substrate 12 in which a heating resistance element 12a and a temperature sensing resistance element are formed on a sensing surface 12A along the axis and the sensing surface 12A is connected to the measuring tube 11 along the axis, and the measuring tube 11 is formed from a thermally conductive fluorinated resin material, which contains a fluorinated resin material and a thermally conductive material dispersed in the fluorinated resin material and having a higher thermal conductivity than the fluorinated resin material.

Description

BACKGROUND 1. TECHNICAL AREA

[0001] The present invention relates to a thermal flow meter. 2. DESCRIPTION OF THE STATE OF THE ART

[0002] Thermal flow meters are known in which a heating resistance element and a temperature sensing resistance element are attached to a measuring tube in a liquid flow direction and the flow rate of a liquid flowing through the measuring tube is measured on the basis of a time of heating of the liquid by the heating resistance element and a time of temperature sensing of the liquid by the temperature sensing resistance element (see, for example, Japanese patent no. 6539458).

[0003] In the thermal flow meter disclosed in Japanese patent application No. 6539458, the sensing surface of a glass temperature sensing substrate, on which the heating resistance element and the temperature sensing resistance element are formed, is connected to a flat surface of the glass measuring tube.

[0004] Such a thermal flow meter instantly heats the heating resistance element to heat a liquid via the measuring tube and detects the heat transferred via the measuring tube to the temperature sensing resistance element as a voltage signal when the heated liquid flows through a section of the measuring tube to which the temperature sensing resistance element is connected.

[0005] Since silicon dioxide, the main component of glass, and an alkaline liquid undergo a neutralization reaction, a glass measuring tube suffers from the disadvantage of low corrosion resistance to the alkaline liquid. Therefore, to measure the flow rate of an alkaline liquid, it is advantageous to use a tubular flow channel made of a resin material with high corrosion resistance to alkaline liquids.

[0006] However, since resin materials have a lower thermal conductivity than glass, it is not possible to adequately heat a liquid via the measuring tube if the thickness of a flow channel made of resin material is essentially the same as the thickness of a flow channel made of glass. In such a case, it may not be possible to accurately determine the temperature of a liquid using a temperature-sensing resistance element. SUMMARY

[0007] The present invention was developed taking such circumstances into account and aims to provide a thermal flow meter that can adequately measure the flow rate of a liquid using a temperature sensing substrate on which a temperature sensing resistance element is formed on a sensing surface, while simultaneously increasing the corrosion resistance to alkaline or acidic liquids.

[0008] To solve the problem described above, the present invention uses the following solutions.

[0009] A thermal flow meter according to one aspect of the present invention comprises the following: a measuring tube having an inlet port and an outlet port and having an internal flow channel extending along an axis, wherein a liquid flows into the inlet port and the liquid flowing in from the inlet port can flow out of the outlet port; and a temperature sensing substrate comprising a heating resistance element and a temperature sensing resistance element formed on a sensing surface along the axis, wherein the sensing surface is connected to the measuring tube along the axis, and the measuring tube is formed from a thermally conductive fluorinated resin material comprising a fluorinated resin material and a thermally conductive material, wherein the thermally conductive material is dispersed in the fluorinated resin material and has a higher thermal conductivity than the fluorinated resin material.

[0010] According to the thermal flow meter as described in one aspect of the present invention, the corrosion resistance to alkaline or acidic liquids can be increased because the measuring tube, in which the inner flow channel through which a liquid can flow is formed, is made of a thermally conductive fluorinated resin material. Since the thermally conductive material, having a higher thermal conductivity than the fluorinated resin material, is dispersed in the thermally conductive fluorinated resin material forming the measuring tube, the thermal conductivity of the measuring tube, which contains the fluorinated resin material with a lower thermal conductivity than glass, can be further increased.This makes it possible to ensure better thermal conductivity between the measuring tube and a liquid and to measure the flow rate of the liquid appropriately using the temperature sensing substrate, in which the temperature sensing resistance element is formed on the sensing surface, while simultaneously increasing corrosion resistance to alkaline or acidic liquids.

[0011] In the thermal flow meter according to one aspect of the present invention, a preferred configuration consists in the thermally conductive material being composed of carbon nanotubes and the thermally conductive fluorinated resin material containing the carbon nanotubes in a ratio of 0.020 wt.% or more and 0.060 wt.% or less.

[0012] According to the thermal flow meter of the present configuration, the thermal conductivity of the measuring tube can be increased because the carbon nanotubes are dispersed in the fluorinated resin material at a weight fraction of 0.020% or more. This is because the use of tubular carbon nanotubes, which have a predetermined length compared to the thermally conductive material, can add thermal conductivity even at a lower quantity than when using other granular thermally conductive materials such as carbon black or iron powder. Furthermore, since the ratio of carbon nanotubes contained in the thermally conductive fluorinated resin material is very low at 0.060% by weight or less, contamination of the liquid through contact between the measuring tube and the liquid can be suppressed, unlike with other granular thermally conductive materials such as carbon black or iron powder.

[0013] In the thermal flow meter according to one aspect of the present invention, a preferred configuration is such that the sensing surface is a planar surface and a flat surface is formed on an outer circumferential surface of the measuring tube, wherein the sensing surface of the temperature sensing substrate faces the flat surface and is arranged on it.

[0014] According to the thermal flow meter of the present configuration, a wide contact area can be ensured to improve the connectivity between them, since the flat surface formed on the outer circumferential surface of the measuring tube and the flat sensing surface are connected to each other.

[0015] In the thermal flow meter according to one aspect of the present invention, a preferred configuration is such that the thermal flow meter includes a metal sheet which is arranged between the flat surface of the measuring tube and the sensing surface of the temperature sensing substrate in order to cover the flat surface, a first side of the sheet being connected to the flat surface of the measuring tube and a second side of the sheet being connected to the sensing surface of the temperature sensing substrate.

[0016] According to the thermal flow meter of the present configuration, even if some corrosive gas, which has evaporated from a liquid flowing in the measuring tube, enters the measuring tube, it is possible to prevent the corrosive gas from corroding the heating resistance element and the temperature sensing resistance element in a suitable manner, since 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.

[0017] In the thermal flow meter of the above configuration, a preferred configuration is such that the first side of the sheet and the flat surface of the measuring tube are connected to each other via a hot-welding film which creates the connection when heated, and the second side of the sheet and the sensing surface of the temperature sensing substrate are connected to each other via an adhesive.

[0018] According to the thermal flow meter of the present configuration, by using hot-welding foil to connect the first side of the sheet, which is susceptible to corrosive gas penetrating the measuring tube, and the flat surface of the measuring tube, it is possible to create a suitable connection while simultaneously preventing the effects of corrosive gas. Furthermore, it is possible to bond the second side of the sheet and the sensing surface of the temperature-sensing substrate appropriately using adhesive.

[0019] In the thermal flow meter of the above configuration, a preferred configuration is such that the sheet metal is made of a nickel alloy containing nickel as a major component.

[0020] According to the thermal flow meter of the present configuration, the use of the sheet metal, which is made of a nickel alloy having nickel as the main component, can reliably prevent a corrosive gas from corroding the heating resistance element and the temperature sensing resistance element.

[0021] In the thermal flow meter according to one aspect of the present invention, a preferred configuration is such that a first distance from the sensing surface of the temperature sensing substrate to an inner circumferential surface of the inner flow channel is shorter than a second distance from the top of the measuring tube to the inner circumferential surface of the inner flow channel.

[0022] According to the thermal flow meter of the present configuration, since the first distance is shorter than the second distance, the heating power exerted on a fluid within the internal flow channel by the heating resistance element and the temperature sensing power exerted on a fluid by the temperature sensing resistance element can be increased compared to a case where the first and second distances are the same.

[0023] In the thermal flow meter according to one aspect of the present invention, a preferred configuration is such that the temperature sensing substrate consists of glass.

[0024] According to the thermal flow meter of the present configuration, any bending that may occur during the attachment of the temperature sensing substrate to the measuring tube or during its use can be suppressed, since the temperature sensing substrate is made of glass, which is less susceptible to deformation due to heating.

[0025] According to the present invention, it is possible to provide a thermal flow meter which can suitably measure the flow rate of a liquid by using a temperature sensing substrate comprising a temperature sensing resistance element formed on a sensing surface, while at the same time increasing the corrosion resistance to alkaline or acidic liquids. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a longitudinal sectional view of a thermal flow meter according to a first embodiment of the present invention. Fig. 2 is a longitudinal section view of a Fig. 1 sensor unit shown. Fig. 3A is a top view of a measuring tube and a sensor substrate, which are in Fig. 2 are shown. Fig. 3B is a longitudinal section view of the in Fig. 2 shown measuring tube and sensor substrate. Fig. 3C is a lower-level view of the in Fig. 2. Measuring tube and sensor substrate shown. Fig. 4 is an end-surface view of the in Fig. 2. Sensor unit shown along the direction of arrow AA. Fig. 5 is an end-face view of the in Fig. 3B shown measuring tube and sensor substrate along line BB. Fig. 6 is a top view of the in Fig. 3B shows the sensor substrate as seen from the side of the detection surface. Fig. Figure 7 is a partially enlarged view of part C of the measuring tube and sensor substrate, which is shown in Fig. 4 are shown. Fig. Figure 8 is a diagram illustrating a relationship between the amount of carbon nanotubes added and the volume resistance of a mixed fluorinated resin material. Fig. Figure 9 is a diagram illustrating a relationship between the duration of the water flow and the number of particles. DETAILED DESCRIPTION

[0026] In the following, a thermal flow meter 100 according to an embodiment of the present invention is described with reference to the drawings. Fig. Figure 1 is a longitudinal sectional view of the thermal flow meter 100 according to the first embodiment of the present invention. Fig. 2 is a longitudinal section view of a Fig. 1 sensor unit shown 10.

[0027] The thermal flow meter 100 of the present embodiment is a thermal flow meter configured to heat a liquid flowing through an internal flow channel and to determine the temperature of the heated liquid in order to measure the flow rate of the liquid. The thermal flow meter 100 of the present embodiment is suitable for measuring a very small flow rate of, for example, 0.1 cm³ / h. 3 / min up to 30 cm 3 / min. The liquid whose flow rate is to be measured with the thermal flow meter 100 of the present embodiment comprises a corrosive liquid, such as an alkaline liquid or an acidic liquid. The corrosive liquid is a chemical solution used in a semiconductor manufacturing device, such as ammonia solution, hydrofluoric acid, or hydrochloric acid.

[0028] As in the Fig. 1 and Fig. As shown in Figure 2, the thermal flow meter 100 of the embodiment includes a sensor unit 10, a control substrate 20, a relay substrate 30, an upper housing 40 and a lower housing 50.

[0029] The sensor unit 10 allows the fluid flowing in through an inlet 10a connected to an external pipe (not shown) to flow out through an outlet 10b connected to an external pipe (not shown) and simultaneously measures the flow rate of the fluid flowing through an internal flow channel 10c. The sensor unit 10 does not directly calculate the fluid flow rate, but instead detects the temperature of the fluid, which is heated by a heating resistance wire 12a (a heating resistance element), described later by temperature sensing resistance wires 12b, 12c, 12d, and 12e (temperature sensing resistance elements), and transmits a temperature sensing signal indicating the detected temperature to the control substrate 20 via a signal cable (not shown). The sensor unit 10 will be described in detail later.

[0030] The control substrate 20 is a device that transmits a voltage signal to the heating resistance wire 12a of the sensor unit 10 to heat the heating resistance wire 12a and also calculates a flow rate of the liquid based on the temperatures transmitted by the temperature-sensing resistance wires 12b, 12c, 12d, 12e. The control substrate 20 outputs the voltage signal for heating the heating resistance wire 12a via a flexible substrate 60 (see Figure 1). Fig. 6) to a sensor substrate 12. In addition, the control substrate 20 outputs a voltage signal to the sensor substrate 12 via the flexible substrate 60 in order to detect resistance values ​​of the temperature sensing resistance wires 12b, 12c, 12d, 12e.

[0031] The control substrate 20 outputs the voltage signal to the heating resistance wire 12a to periodically repeat a heating cycle to heat the heating resistance wire 12a and a non-heating cycle to prevent the heating resistance wire 12a from heating. The heating cycle is set to be shorter than the non-heating cycle. That is, the heating cycle is set to a rate of less than 0.5 of a cycle, which is the sum of the heating cycle and the non-heating cycle. The heating cycle rate can be set to less than 0.4.

[0032] The relay substrate 30 forwards various signals that are sent and received between the control substrate 20 and an external device (not shown). A cable 200 for sending and receiving the various signals to and from the external device (not shown) is connected to the relay substrate 30.

[0033] The upper housing 40 serves as a housing for an upper area of ​​the thermal flow meter 100 and accommodates the control substrate 20 inside.

[0034] The lower housing 50 serves as a housing for a lower section of the thermal flow meter 100 and accommodates the sensor unit 10 inside. When the sensor unit 10 is inserted into the lower housing 50, a stopper 70 is inserted between the lower housing 50 and the sensor unit 10 from the side of the inlet 10a of the sensor unit 10.

[0035] When the sensor unit 10 is inserted into the lower housing 50, a stopper 70 is inserted between the lower housing 50 and the sensor unit 10 from the side of the outlet 10b of the sensor unit 10. The sensor unit 10 is fixed to the lower housing 50 by means of the stopper 70. The lower housing 50 has mounting holes 50a on its underside and is fastened to a mounting surface (not shown) with mounting screws (not shown) that are inserted from below the mounting surface.

[0036] Next, sensor unit 10 will be described in detail. As in the Fig. As shown in Figure 2, the sensor unit 10 comprises a measuring tube 11, a sensor substrate (temperature detection substrate) 12, a nut 15, an inlet-side body 16, an outlet-side body 17, an inlet-side ferrule 18 and an outlet-side ferrule 19.

[0037] The measuring tube 11 is a tube having an inlet port 11a into which a liquid flows, and an outlet port 11b from which the liquid flowing in from the inlet port 11a can flow out. The internal flow channel 10c, which is circular in cross-section and extends along the axis X, is formed in the measuring tube 11. The measuring tube 11 is made of a mixed fluoropolymer material that exhibits corrosion resistance to alkaline or acidic liquids. The mixed fluoropolymer material will be described later.

[0038] The inlet-side body 16 is an element into which the inlet connection 11a of the measuring tube 11 is inserted and in whose interior a connecting flow channel 16a (a first connecting flow channel) is formed, which has a circular cross-section. An external thread 16b is formed on the outer circumferential surface of the end on the side of the outlet connection 10b of the inlet-side body 16.

[0039] The outlet-side body 17 is an element into which the outlet port 11b of the measuring tube 11 is inserted and in whose interior a connecting flow channel 17a (a second connecting flow channel) is formed, which has a circular cross-section. An external thread 17b is formed on the outer circumferential surface of the end on the side of the inlet port 10a of the outlet-side body 17. The inlet-side body 16 and the outlet-side body 17 are made of a plastic material with high corrosion resistance (for example, polytetrafluoroethylene (PTFE)).

[0040] The nut 15 consists of an inlet-side nut 15a, which is attached to the inlet-side body 16, and an outlet-side nut 15b, which is attached to the outlet-side body 17. The inlet-side nut 15a is a circular cylindrical element that extends from the inlet-side body 16 along the outer circumferential surface of the measuring tube 11 on the side of the outlet port 11b. An internal thread 15g is formed in the inner circumferential surface of the end on the side of the inlet port 10a of the inlet-side nut 15a. Furthermore, the outlet-side nut 15b is a circular cylindrical element that extends from the outlet-side body 17 along the outer circumferential surface of the measuring tube 11 on the side of the inlet port 11a. An internal thread 15h is formed in the inner circumferential surface of the end on the side of the outlet connection 10b of the outlet-side nut 15b.

[0041] The internal thread 15g of the inlet-side nut 15a and the external thread 16b of the inlet-side body 16 are connected, thereby securing the inlet-side nut 15a to the inlet-side body 16. Similarly, the internal thread 15h of the outlet-side nut 15b and the external thread 17b of the outlet-side body 17 are screwed together, thereby securing the outlet-side nut 15b to the outlet-side body 17.

[0042] A recess 15e (a first recess) is formed at the end on the side of the outlet port 10b of the inlet-side nut 15a, extending towards the inlet port 10a. The end on the side of the inlet port 11a of the sensor substrate 12, which contains an adhesive 81, is inserted into the recess 15e. The recess 15e is filled with a filler material 15i. The end on the side of the inlet port 11a of the sensor substrate 12 is secured to the inlet-side nut 15a by the filler material 15i.

[0043] A recess 15f (a second recess) is formed at the end on the inlet side 10a of the outlet-side nut 15b, extending towards the outlet port 10b. The end of the sensor substrate 12 on the outlet port 11b side, which contains an adhesive 82, is inserted into the recess 15f. The recess 15f is then filled with a filler material 15j. The filler material 15j secures the end of the sensor substrate 12 on the outlet port 11b side to the outlet-side nut 15b.

[0044] The inlet ferrule 18 is a plastic element (e.g., PTFE) formed in a circular cylindrical shape and inserted between the outer circumferential surface of the measuring tube 11 and the inner circumferential surface of the end on the side of the outlet port 10b of the inlet-side body 16. The outlet ferrule 19 is a plastic element (e.g., PTFE) formed in a circular cylindrical shape and inserted between the outer circumferential surface of the measuring tube 11 and the inner circumferential surface of the end on the side of the inlet port 10a of the outlet-side body 17.

[0045] The sensor unit 10 of the thermal flow meter 100 of the present embodiment is manufactured by attaching the internal thread 15g of the inlet-side nut 15a to the external thread 16b of the inlet-side body 16, wherein the inlet port 11a of the measuring tube 11 and the inlet-side ferrule 18 are inserted into the end on the side of the outlet port 10b of the inlet-side body 16, and by attaching the internal thread 15h of the outlet-side nut 15b to the external thread 17b of the outlet-side body 17, wherein the outlet port 11b of the measuring tube 11 and the outlet-side ferrule 19 are inserted into the end on the side of the inlet port 10a of the outlet-side body 17.

[0046] When the tip on the inlet port side 10a of the inlet nut 15a comes into contact with a projecting part 16d of the inlet body 16, the fastening between the internal thread 15g of the inlet nut 15a and the external thread 16b of the inlet body 16 is complete. When the tip on the outlet port side 10b of the outlet nut 15b comes into contact with a projecting part 17d of the outlet body 17, the fastening between the internal thread 15h of the outlet nut 15b and the external thread 17b of the outlet body 17 is complete.

[0047] Fig. Figure 3A is a top view of the measuring tube 11 and the sensor substrate 12, which are located in Fig. 2 are shown. Fig. Figure 3B is a longitudinal sectional view of the measuring tube 11 and the sensor substrate 12, which is shown in Fig. 2 are shown. Fig. 3C is a bottom view of the measuring tube 11 and the sensor substrate 12, in Fig. 2 are shown.

[0048] As in Fig. 3B and Fig. As shown in Figure 3C, the end on the side of the inlet port 11a of the sensor substrate 12 and the end on the side of the inlet port 11a of the flat surface 11c formed on the measuring tube 11 are connected to each other via the adhesive 81, and the end on the side of the outlet port 11b of the sensor substrate 12 and the end on the side of the outlet port 11b of the flat surface 11c are connected to each other via the adhesive 82. For example, an epoxy resin-based adhesive can be used as the adhesive 81 and adhesive 82.

[0049] Fig. 4 is an end-surface view of the in Fig. 2. Sensor unit 10 shown along the direction of arrow AA. As in Fig. As shown in Figure 4, the upper surface of the measuring tube 11 is substantially circular in cross-section along a plane perpendicular to the X axis at the position where the sensor substrate 12 is attached. The outer circumferential surface of the measuring tube 11 forms a flat surface 11c on which the sensing surface 12A of the sensor substrate 12 is in contact. The sensing surface 12A and the flat surface 11c are connected to each other at their respective positions along the X axis.

[0050] Fig. 5 is an end-face view of the in Fig. 3B shows the measuring tube 11 and the sensor substrate 12 along the direction of arrow BB. As in Fig. As shown in Figure 5, the cross-section in the measuring tube 11 is circular along a plane perpendicular to the axis X at a position where the sensor substrate 12 does not adhere.

[0051] As in Fig. As shown in Figure 4, the distance D1 (the first distance) from the sensing surface 12A of the sensor substrate 12 to the inner circumferential surface 10d of the internal flow channel 10c is shorter than the distance D2 (the second distance) from the top surface 11d of the measuring tube 11 to the inner circumferential surface 10d of the internal flow channel 10c. This serves to make the distance D1 from the sensing surface 12A of the sensor substrate 12 to the inner circumferential surface 10d of the internal flow channel 10c shorter than the distance D2, in order to improve the thermal conductivity of the heating resistance wire 12a to the liquid and to improve the temperature sensing characteristic provided by the temperature sensing resistance wire 12b and the temperature sensing resistance wire 12d. The distance D1 is preferably 0.2 mm or less, for example 0.1 mm.

[0052] Fig. 6 is a top view of the in Fig. Figure 3B shows the sensor substrate 12, viewed from one side of the sensing surface 12A. The sensor substrate 12 is a glass substrate (e.g., quartz glass with a high silicon dioxide content) with the temperature sensing resistance wire (temperature sensing resistance element) 12e, the temperature sensing resistance wire (temperature sensing resistance element) 12c, the heating resistance wire (heating resistance element) 12a, the temperature sensing resistance wire (temperature sensing resistance element) 12b, and the temperature sensing resistance wire (temperature sensing resistance element) 12d formed on the sensing surface 12A along the X axis.

[0053] The sensing surface 12A is a flat surface extending along the X axis. The heating resistance wire 12a, the temperature sensing resistance wire 12b, and the temperature sensing resistance wire 12c are each formed from a metal layer, for example platinum, which is vapor-deposited onto the glass substrate.

[0054] The liquid flowing through the measuring tube 11 flows along the axis X in a flow direction FD from left to right. Fig. 6. When the heating resistance wire 12a is briefly heated, the heated liquid flows accordingly along the X axis to a position of the temperature sensing resistance wire 12b and then to a position of the temperature sensing resistance wire 12d. The control substrate 20 detects the electrical resistance values ​​of the temperature sensing resistance wire 12b and the temperature sensing resistance wire 12d, which change with temperature, in order to measure the temperatures of the temperature sensing resistance wire 12b and the temperature sensing resistance wire 12d.

[0055] As in Fig. As shown in Figure 6, there is a position P1, at which the heating resistance wire 12a is arranged in the sensor substrate 12, on the side of the outlet 11b of an intermediate position at an equal distance from both an end region of the inlet 11a of the sensor substrate 12 and from an end region of the outlet 11b of the sensor substrate 12.

[0056] A distance L1 (see Fig. The distance from the inlet 11a of the measuring tube 11 to the heating resistance wire 12a on the axis X is greater than the distance L2 (see Fig. 3A) from the outlet 11b of the measuring tube 11 to the heating resistance wire 12a on the axis X. Consequently, the distance from the inlet 11a of the measuring tube 11 to the heating resistance wire 12a can be increased, and turbulence or similar disturbances of the liquid flowing into the inlet 11a of the measuring tube 11 can be sufficiently reduced before the liquid is heated.

[0057] The control substrate 20 can calculate the flow velocity of the liquid flowing into the measuring tube 11 from the time at which the heating resistance wire 12a was briefly heated and the times at which the temperature sensing resistance wire 12b and the temperature sensing resistance wire 12d subsequently detect the temperature of the heated liquid. Furthermore, the control substrate 20 can calculate the flow rate of the liquid from the determined flow velocity and the cross-sectional area of ​​the measuring tube 11.

[0058] When the heating resistance wire 12a is briefly heated, the heat transferred from the heating resistance wire 12a to the sensing surface 12A is transferred along the X axis in a direction opposite to the flow direction FD of the liquid, reaching a position of the temperature sensing resistance wire 12c and then reaching a position of the temperature sensing resistance wire 12e. The control substrate 20 detects the electrical resistance values ​​of the temperature sensing resistance wire 12c and the temperature sensing resistance wire 12e, which change with temperature, in order to measure the temperatures of the temperature sensing resistance wire 12c and the temperature sensing resistance wire 12e.

[0059] The control substrate 20 subtracts the temperature of the temperature sensing resistance wire 12c from the temperature of the temperature sensing resistance wire 12b. The temperature detected by the temperature sensing resistance wire 12c upstream of the heating resistance wire 12a in the flow direction FD corresponds to heat that is transferred from the heating resistance wire 12a to the measuring tube 11 and not to the liquid, but rather via the measuring tube 11 to the temperature sensing resistance wire 12c. The temperature sensing resistance wire 12b and the temperature sensing resistance wire 12c are arranged at the same distance from the heating resistance wire 12a.

[0060] For this reason, the temperature of temperature sensing resistance wire 12c is subtracted from the temperature of temperature sensing resistance wire 12b, so that the temperature of the liquid passing the position of temperature sensing resistance wire 12b can be measured. Similarly, the control substrate 20 can subtract the temperature of temperature sensing resistance wire 12e from the temperature of temperature sensing resistance wire 12d to measure the temperature of the liquid passing the position of temperature sensing resistance wire 12d.

[0061] As in Fig. As shown in Figure 6, 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 in the sensing area 12A. Additionally, a wiring pattern 12h, connected to one end of the temperature sensing resistance wire 12b, a wiring pattern 12i, connected to the other end of the temperature sensing resistance wire 12b, and a wiring pattern 12j, connected to one end of the temperature sensing resistance wire 12d, are formed in the sensing area 12A. The other end of the temperature sensing resistance wire 12d is connected to wiring pattern 12i.

[0062] Furthermore, in the sensing area 12A, a wiring pattern 12k, connected to one end of the temperature sensing resistance wire 12c, a wiring pattern 12l, connected to the other end of the temperature sensing resistance wire 12c, and a wiring pattern 12m, connected to one end of the temperature sensing resistance wire 12e, are formed. The other end of the temperature sensing 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 from a metal layer, for example, platinum, which is vapor-deposited onto the glass substrate.

[0063] The end regions of the wiring patterns 12f, 12g, 12h, 12i, 12j, 12k, 12l, 12m are each connected to metal wiring patterns 60f, 60g, 60h, 60i, 60j, 60k, 60l, 60m, which are arranged in the flexible substrate (the external connection terminal) 60, formed from film resin. Each of the wiring patterns 60f, 60g, 60h, 60i, 60j, 60k, 60l, 60m of the flexible substrate 60 is electrically connected to the control substrate 20.

[0064] Fig. Figure 7 is a partially enlarged view of part C of the measuring tube 11 and the sensor substrate 12, which is shown in Fig. 4 are shown. As in Fig. As shown in Figure 7, the thermal flow meter 100 of the present embodiment comprises a metal gas permeation barrier 13 arranged between the flat surface 11c and the sensing surface 12A to cover the entire area connected to at least the sensing surface 12A in the flat surface 11c of the measuring tube 11. The gas permeation barrier 13 has a constant thickness T. For example, the thickness T is set to a range of 0.01 mm or more and 0.03 mm or less. The gas permeation barrier 13 is made of a nickel alloy whose main component is nickel (for example, Hastelloy (registered trademark)).

[0065] The top surface (the first side) 13a of the gas permeation barrier film 13 is connected to the flat surface 11c of the measuring tube 11 via a hot-welding film 80a. The hot-welding film 80a is heated above a predetermined welding temperature, softened, and then cooled and solidified until the top surface 13a and the flat surface 11c are joined together.

[0066] The heat-sealing foil 80a is preferably made of a fluoropolymer material such as ethylenetetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), or tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA). Making the heat-sealing foil 80a from a fluoropolymer material improves its resistance to corrosive gases that may have penetrated from the measuring tube 11.

[0067] The underside (a second side) 13b of the gas permeation barrier film 13 is connected to the sensing surface 12A of the sensor substrate 12 via the adhesive 80b. It should be noted that in an area where the temperature-sensing resistance wires 12e, 12c, 12b, 12d and the heating resistance wire 12a are formed on the sensing surface 12A, the underside 13b is connected to these resistance wires.

[0068] Suitable adhesives include, for example, epoxy resin-based adhesives, UV-curable resin-based adhesives, thermally curable resin-based adhesives, low-melting-point glass, or similar materials. Adhesive 80b is an insulating material with insulating properties and thus serves to prevent electrical conduction between the metallic gas permeation barrier film 13 and the heating resistance wire 12a and the temperature sensing resistance wires 12b, 12c, 12d, 12e.

[0069] Next, the mixed fluorinated resin material (the thermally conductive fluorinated resin material) that integrally forms the measuring tube 11 of the present embodiment is described.

[0070] The measuring tube 11 of the present embodiment is formed from a mixed fluorinated resin material containing a fluorinated resin material and carbon nanotubes (the thermally conductive material) dispersed in the fluorinated resin material. The fluorinated resin material can be, for example, PTFE, PCTFE, PFA, or the like. Powdered materials (for example, PTFE G163, manufactured by AGC Inc.) can be used as the fluorinated resin material.

[0071] Furthermore, it is desirable to use carbon nanotubes that have, for example, the following properties: - have a fiber length of 50 µm or more and 150 µm or less; - have a fiber diameter of 5 nm or more and 20 nm or less; - a bulk density of 10 mg / cm³ 3 or more and 70 mg / cm² 3 or less; - have a G / D ratio of 0.7 or more and 2.0 or less; - have a purity of 99.5% or more; - are made up of several layers (for example, 4 to 12 layers).

[0072] The reason why carbon nanotubes preferably have a fiber length of 50 µm or more is to achieve sufficient thermal conductivity with a small amount of carbon nanotubes when the carbon nanotubes are dispersed in the fluorinated resin material.

[0073] Furthermore, the G / D ratio is a value representing the ratio between a peak in the G-band and a peak in the D-band of the Raman spectrum of carbon nanotubes. The G-band originates from the graphite structure, while the D-band originates from a defect. The G / D ratio represents the ratio of crystal purity to defect concentration of carbon nanotubes.

[0074] The inventors investigated the relationship between the amount [wt%] of carbon nanotubes dispersed in the fluorinated resin material and the volume resistance [Ω·cm] of the mixed fluorinated resin material containing the fluorinated resin material and the carbon nanotubes dispersed therein, thereby examining the Fig. The result shown in section 8 was obtained. Fig. The result shown in Figure 8 was obtained by measuring the volume resistance of a test piece based on the “Test method for the resistance of conductive plastics using a four-point probe arrangement” defined in JIS K 7194.

[0075] A large number of test pieces were produced by melting and kneading pieces with a kneading machine, then pressing and shaping them with a compression molding machine, and finally machining them to a size conforming to JIS K 7194. The fluoropolymer material used to produce the test pieces was PTFE G163, manufactured by ACG Inc.

[0076] To measure the specific volume resistivity, a resistance meter was used that operates according to JIS K 7194 using the four-point probe method. The four-point probe method is a procedure in which four needle-like probes (electrodes) are brought into contact with a test piece, and the resistance of the test piece is determined based on the current flowing between the two outer probes and the potential difference occurring between the two inner probes. The specific volume resistivity was calculated by averaging the measured values ​​obtained at multiple points on the numerous test pieces.

[0077] According to the in Fig. The result shown in Figure 8 is that, if the amount of carbon nanotubes added is in the range of greater than or equal to 0.020 wt.% and less than or equal to 0.030 wt.%, the specific volume resistivity of the mixed fluorinated resin material is in the range of greater than or equal to 1.0 × 103 wt.% Ω·cm and less than 1.0 × 10 4 Ω·cm. The value of the specific volume resistivity is, in comparison to the value of the specific volume resistivity of the fluorinated resin material in which no carbon nanotubes are dispersed (10 18 Ω·cm), sufficiently low. If the amount of carbon nanotubes added is increased further above 0.03 wt%, the specific volume resistivity is further reduced.

[0078] Furthermore, the inventors have discovered that in the mixed fluororesin material, where carbon nanotubes are added to the fluororesin material that does not contain carbon nanotubes, there is a negative correlation between the volume resistance and the thermal conductivity. That is, the inventors have discovered that if the amount of carbon nanotubes added is increased and the volume resistance is reduced, the thermal conductivity is correspondingly increased. Furthermore, the inventors have confirmed that if the amount of carbon nanotubes added to the mixed fluororesin material forming the measuring tube 11 is in the range of 0.020 wt.% or greater and 0.060 wt.%, the thermal conductivity is increased accordingly.-% or less, a liquid flowing through the inner flow 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 suitably determined by the temperature detection resistance wires 12b, 12c, 12d, 12e.

[0079] Accordingly, in the present embodiment, the amount of carbon nanotubes added to the mixed fluoropolymer material forming the measuring tube 11 is in the range of 0.020 wt.% or greater and 0.060 wt.% or less. It should be noted that when using PTFE as the fluoropolymer material, the thermal conductivity of the measuring tube 11 without the addition of carbon nanotubes is 0.53 W / m·K, while the thermal conductivity of the measuring tube 11 with a carbon nanotube addition of 0.05 wt.% is 0.64 W / m·K.

[0080] Furthermore, the inventors measured fine particles contained in a liquid flowing through a flow channel formed from the mixed fluororesin material in which the amount of carbon nanotubes added is 0.025 wt.%. Fig. Figure 9 represents a measurement result illustrating the relationship between the duration of water flow during which pure water can flow and the number of particles measured by a particle counter (not shown).

[0081] Here, the number of particles refers to the number of particles with a size of 0.04 µm or larger contained per 1 ml of pure water. In the Fig. In the measurement shown in Figure 9, the flow rate of the pure water flowing through the flow channel was 0.5 liters / minute. Furthermore, the system switched every 5 seconds between a blocked state to stop the flow of pure water and a flow state in which pure water could pass through. The temperature of the pure water was 25 °C.

[0082] Although in Fig. Figure 9 (not shown) shows that the number of particles at the beginning of the measurement (with a water flow time of zero) was approximately 340. Subsequently, the number of particles gradually decreased with the water flow time, and after the water flow time exceeded 4 hours, the number of particles remained at 10 or less. Therefore, if the measuring tube 11 is formed from a mixed fluororesin material containing carbon nanotubes in a ratio of 0.020 wt% or more and 0.060 wt% or less as an additive, and the measuring tube 11 is sufficiently washed with pure water or the like and then manufactured as a product, the number of particles that mix from the measuring tube 11 into a liquid during use can be sufficiently low.

[0083] It should be noted that, although Fig.Figure 9 shows the result of the mixed fluororesin material with an added amount of carbon nanotubes of 0.025 wt.%. The inventors have confirmed that even with an added amount of carbon nanotubes of 0.060 wt.%, the number of particles does not increase excessively. As explained above, in the measuring tube 11 of the present embodiment, since the proportion of carbon nanotubes contained in the mixed fluororesin material is a negligible 0.060 wt.% or less, contamination of a liquid by contact with the liquid can be suppressed, unlike with other granular conductive substances such as soot or iron powder.

[0084] The effects and advantages achieved by the thermal flow meter 100 of the present embodiment described above are explained below.

[0085] According to the thermal flow meter 100 of the present embodiment, the corrosion resistance to alkaline or acidic liquids can be increased because the measuring tube 11, in which the inner flow channel 10c is formed through which a liquid can flow, is made of a mixed fluororesin material containing a fluororesin material. Furthermore, since the thermally conductive material, having a 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 the fluororesin material having a lower thermal conductivity than glass, can be increased.Thus, it is possible to ensure better thermal conductivity between the measuring tube 11 and a liquid and to measure the flow rate of the liquid using the sensor substrate 12, on whose sensing surface 12A the temperature sensing resistance wires 12b, 12c, 12d, 12e are formed, while simultaneously increasing the corrosion resistance to alkaline or acidic liquids.

[0086] According to the thermal flow meter 100 of the present embodiment, the thermal conductivity of the measuring tube 11 can be increased because the carbon nanotubes are dispersed in the fluorinated resin material with a weight fraction of 0.020% or more. This is because the use of tubular carbon nanotubes having a predetermined length compared to the thermally conductive material can increase the thermal conductivity even at a lower quantity than when using other granular thermally conductive materials such as carbon black or iron powder. Furthermore, since the ratio of carbon nanotubes contained in the thermally conductive fluorinated resin material is very low at 0.060% by weight or less, contamination of a liquid through contact between the measuring tube 11 and the liquid can be suppressed, unlike with other granular thermally conductive materials such as carbon black or iron powder.

[0087] According to the thermal flow meter 100 of the present embodiment, a wide contact area can be ensured in order to increase the connectivity between the flat surface 11c formed on the outer circumferential surface of the measuring tube 11 and the flat detection surface 12A, since these are connected to each other.

[0088] According to the thermal flow meter 100 of the present embodiment, a metallic gas permeation barrier film 13 is arranged between the flat surface 11c of the measuring tube 11 and the sensing surface 12A of the sensor substrate 12 such that it covers the flat surface 11c, even if some of a corrosive gas that has evaporated from a liquid flowing in the measuring tube 11 enters the measuring tube 11, thus preventing the corrosive gas from corroding the heating resistance wire 12a and the temperature sensing resistance wires 12b, 12c, 12d, 12e.

[0089] According to the thermal flow meter 100 of the present embodiment, the use of the hot-welding film 80a to connect the upper surface 13a of the gas permeation barrier film 13, which is susceptible to corrosive gas penetrating the measuring tube 11, to the flat surface 11c of the measuring tube 11 makes it possible to establish a suitable connection and simultaneously prevent the ingress of corrosive gas. Furthermore, it is possible to suitably connect the lower surface 13b of the gas permeation barrier film 13 and the sensing surface 12A of the sensor substrate 12 using the adhesive 80b.

[0090] According to the thermal flow meter 100 of the present embodiment, the use of the gas permeation barrier foil 13, which is made of a nickel alloy with nickel as the main component, can reliably prevent a corrosive gas from corroding the heating resistance wire 12a and the temperature sensing resistance wires 12b, 12c, 12d, 12e.

[0091] According to the thermal flow meter 100 of the present embodiment, since the distance D1 from the sensing surface 12A of the sensor substrate 12 to the inner circumferential surface 10d of the inner flow channel 10c is shorter than the distance D2 from the top 11d of the measuring tube 11 to the inner circumferential surface 10d of the inner flow channel 10c, the heating properties for a liquid in the inner flow channel 10c generated by the heating resistance wire 12a and the temperature sensing property for a liquid generated by the temperature sensing resistance wires 12b, 12c, 12d, 12e can be increased compared to a case in which the first and second distances are the same.

[0092] According to the thermal flow meter 100 of the present embodiment, since the glass sensor substrate 12 is used which is less easily deformed by heating, a bending that may occur during the attachment of the sensor substrate 12 to the measuring tube 11 or during its use can be suppressed. [Other embodiments]

[0093] Although the thermal flow meter 100 includes the metal gas permeation barrier 13, which is arranged between the flat surface 11c and the sensing surface 12A to cover the entire area connected to at least the sensing surface 12A in the flat surface 11c of the measuring tube 11, as described above, other shapes can also be used. For example, if a liquid flowing through the inner flow channel 10c of the measuring tube 11 does not generate any corrosive gas or generates only an extremely small amount of corrosive gas that permeates the measuring tube 11 to the outside, a gas permeation barrier 13 can be omitted.

[0094] In such a case, the flat surface 11c of the measuring tube 11 and the sensing surface 12A of the sensor substrate 12 are joined together by the heat-welding film 80a or the adhesive 80b. Since there is no gas permeation barrier film 13 between the flat surface 11c and the sensing surface 12A, the thermal conductivity between the flat surface 11c and the sensing surface 12A is improved. If the heat-welding film 80a, made of fluoropolymer material, is used, a reduction in the bonding force between the flat surface 11c and the sensing surface 12A can be suppressed even if a corrosive gas penetrates from the measuring tube 11. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 6539458 [0002, 0003]

Claims

Thermal flow meter (100) comprising: a measuring tube (11) having an inlet port and an outlet port and having an internal flow channel extending along an axis, wherein a fluid flows into the inlet port and the fluid flowing in from the inlet port can flow out of the outlet port; and a temperature sensing substrate (12) comprising a heating resistance element and a temperature sensing resistance element formed on a sensing surface (12A) along the axis, wherein the sensing surface (12A) is connected along the axis to the measuring tube (11), wherein the measuring tube (11) is formed from a thermally conductive fluorinated resin material comprising a fluorinated resin material and a thermally conductive material, wherein the thermally conductive material is dispersed in the fluorinated resin material and has a higher thermal conductivity than the fluorinated resin material. Thermal flow meter (100) according to claim 1, wherein the thermally conductive material consists of carbon nanotubes and wherein the thermally conductive fluorinated resin material contains the carbon nanotubes in a ratio of 0.020 wt.% or more and 0.060 wt.% or less. Thermal flow meter (100) according to claim 1 or 2, wherein the sensing surface (12A) is a planar surface, and wherein a planar surface connected to the sensing surface (12A) of the temperature sensing substrate (12) is formed on an outer circumferential surface of the measuring tube (11). Thermal flow meter (100) according to claim 3, further comprising a metal sheet (13) arranged between the flat surface of the measuring tube (11) and the sensing surface (12A) of the temperature sensing substrate (12) to cover the flat surface, wherein a first side (13a) of the sheet (13) is connected to the flat surface of the measuring tube (11), and wherein a second surface (13b) of the sheet (13) is connected to the sensing surface (12A) of the temperature sensing substrate (12). Thermal flow meter (100) according to claim 4, wherein the first side (13a) of the sheet (13) and the flat surface of the measuring tube (11) are connected to each other via a hot welding film (80a), and wherein the second side (13b) of the sheet (13) and the sensing surface (12A) of the temperature sensing substrate (12) are connected to each other via an adhesive. Thermal flow meter (100) according to claim 4, wherein the sheet (13) is formed from a nickel alloy containing nickel as a major component. Thermal flow meter (100) according to claim 1 or 2, wherein a first distance from the sensing surface (12A) of the temperature sensing substrate (12) to an inner circumferential surface of the inner flow channel is shorter than a second distance from the top of the measuring tube (11) to the inner circumferential surface of the inner flow channel. Thermal flow meter (100) according to claim 1 or 2, wherein the temperature sensing substrate (12A) consists of glass.

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