JPH0143886B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flow rate detector that detects the flow rate of a fluid object using heat transfer between a heating element and a fluid object. The present invention relates to a heat-sensitive flow rate detector that detects the amount of flowing fluid, such as flow rate or flow rate, based on the amount of heat transfer.

An example of a conventional flow rate detector of this kind is shown in FIG. 1. In the figure, 1 is a bulk heating element made of a silicon semiconductor, and 2 is a function of supplying power to and supporting the bulk heating element 1. 3 is a support corresponding to a transistor package that holds this electrode lead 2, 4 is an extraction lead, 5 is a stainless steel piping pipe, and 6 is a fluid passing through the inside of this piping pipe 5. 7 is a detection circuit including a differential bridge and an amplifier connected to the extraction lead 4, and 8 is a detection output signal obtained from this detection circuit 7.

The operation of the device configured in this way will be explained. First, the power to be supplied to the bulk heating element 1 is
If Pin is the amount of heat transfer between the bulk heating element 1 and the mineral spirits 6, then Pout is the amount of heat transferred between the bulk heating element 1 and the mineral spirits 6. In a state of thermal equilibrium, Pin=Pout=h.As.ΔT holds true. Here, h is the transmission rate between the bulk heating element 1 and the mineral spirits 6, As is the surface area of the bulk heating element 1, and ΔT is the temperature difference between the bulk heating element 1 and the mineral spirits 6. .

Generally, under laminar flow conditions where the Reynolds number Re is |<Re<2000, the heat transfer coefficient h can be approximated by the experimental formula h=a+b·v ^0.5 , where a and b are constants. Here, v means the average flow velocity of the fluid.

The power Pin supplied to the bulk heating element 1 is expressed as Pin=Is ²・Rs=Vs ² /Rs, where the resistance of the bulk heating element 1 is Rs, the current is Is, and the voltage is Vs. By measuring the electrical impedance of the bulk heating element 1 with the detection circuit 7, the flow velocity v or flow rate Q of the fluid is obtained as the detection output signal 8.

Here, the bulk heating element 1 is 0.7×0.7×0.15mm ³
It is a silicon chip made of N-type homogeneous material doped with 10 ¹⁵ cm ^-3 of P. The support body 3 is a TO-46 transistor package, and the stainless steel piping 5 has a diameter of 0.767 cm and a length of 30 cm, and the bulk heating element 1
is located 25.3cm behind.

However, this heat-sensitive flow rate detector should be set under conditions where the Reynolds number is 2000 to 3000, avoiding the transition region from laminar flow to turbulent flow where the flow becomes unstable. Therefore, a low value for the heat transfer coefficient and a laminar state for the flow must be used. moreover,
Since the silicon chip serving as the heating element 1 is a homogeneous bulk heating element, it has a drawback that the heat capacity is large and the thermal time constant for reaching a thermal equilibrium state is also relatively large. In addition, the bulk heating element 1 has a certain size and becomes an external element that disturbs the flow together with the electrode lead 2, which not only lowers the responsiveness as a flow rate detector but also causes problems when the flow rate is small or large. It had unstable characteristics depending on the flow rate.

In view of the above points, the present invention has been made in order to solve such problems and eliminate such drawbacks.The purpose of the present invention is to form a jet flow and make it collide with a diaphragm, thereby creating a gap between a heating element and a flowing fluid. A heat-generating flow rate detector that can measure heat transfer and diaphragm deformation to provide a small, lightweight, high-performance flow rate sensor at a low price that can measure flow rates close to the true mass flow rate. Our goal is to provide the following.

In order to achieve such an object, the present invention includes a flow rate increasing means using a throttle mechanism such as a throttle or a nozzle that narrows the flow path of the flowing fluid to increase the flow rate, and a flow rate increasing means placed behind the flow rate increasing means to increase the flow rate of the flowing fluid. a diaphragm that deforms under pressure according to the flow velocity of the diaphragm; a heating element embedded in or bonded to the diaphragm; a strain detection element embedded in or bonded to the diaphragm; and a support that supports a peripheral portion of the diaphragm and is made of a thermally poor conductor. Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 2 is a configuration diagram showing an embodiment of the exothermic flow rate detector according to the present invention. In this Figure 2, the same numbers as in Figure 1 indicate corresponding parts, and 9 is P
A heating element made of a low-resistance impurity layer of type silicon,
Similarly, the strain sensing element 10 is made of a high-resistance impurity layer of P-type silicon, and the heating element 9 and the strain sensing element 10 are configured to be embedded or bonded to a pressure receiving diaphragm, which will be described later. Reference numeral 11 denotes a pressure receiving diaphragm made of an N-shaped silicon substrate whose central portion has been etched to make it thinner.This pressure receiving diaphragm 11 is placed behind a flow rate increasing means using a throttle mechanism such as a throttle or nozzle, and is adapted to adjust the flow rate of the flowing fluid. It constitutes a diaphragm that deforms under pressure. Here, the pressure receiving diaphragm 11 is not particularly limited to silicon, but may be made of Ge or a compound semiconductor such as InSb or GaAs as long as it can form a resistance layer.

Reference numeral 12 denotes a hollow portion, which is sealed under a constant pressure such as a vacuum state, and is configured to deform due to the total pressure that is the sum of static pressure and dynamic pressure of the mineral spirits 6. ing. 13 is
This oxide film insulating layer 13 is not limited to SiO ₂ , but may be Si ₃ N ₄ or Al ₂ O ₃ as long as it is made of _an electrically insulating material. Reference numeral 14 denotes an aluminum electrode layer, and this electrode layer 14 is not particularly limited to aluminum, but may be made of known electrode materials such as Au, Ni, and Pt. 15 is a bonding wire, 16 is a bonding post, and 17 is an adhesive layer made of glass solder, for example. ZnO--B ₂ O, which has a coefficient of thermal expansion similar to that of silicon, is attached to this adhesive layer 17 for airtight sealing at a relatively low temperature. ₃ -V ₂ O _5- based glass solder is used, but alloys such as An--Si, or synthetic resins such as epoxy and silicon may also be used. Reference numeral 18 denotes a support base made of, for example, borosilicate glass. This support base 18 is preferably made of a material with a coefficient of thermal expansion close to that of the pressure receiving diaphragm 11, and if it is similar, it is not limited to borosilicate glass, but may also be a ceramic material. . This ceramic material includes cordierite, zircon,
Porcelain such as Lithia is suitable. The support stand 18 supports the peripheral portion of the pressure receiving diaphragm 11 and constitutes support means made of a thermally poor conductor.

19 is a package made of Kovar, 20 is an insulator made of an electrically insulating material such as ceramic, which insulates and supports the bonding post 16, 21 is a housing, and 22 is a nozzle. A flow rate increasing means is constituted by a throttle mechanism that increases the flow rate by narrowing the tube.

Although mineral spirits 6 is used as the flowing fluid, the present invention is not limited to this, and can be applied to most fluids such as fuel oil, water, and air, and is particularly suitable for insulating properties. Suitable for fluids. Furthermore, it is fully applicable to non-insulating fluids by coating the aluminum electrode layer 14, bonding wire 15, and bonding post 16 with an insulating film.

As is clear from the above, the pressure receiving diaphragm 11 is made of a semiconductive material,
Further, the pressure receiving diaphragm 11 is made of a silicon material, and as shown in FIG. 2, the pressure receiving diaphragm 11 has a structure in which the center portion thereof is thinner than the peripheral portion. The heating element 9 is arranged in the thinned part of the pressure receiving diaphragm 11, and this heating element 9 is arranged in the center of the pressure receiving diaphragm 11. Also, this heating element 9 is used as an impurity diffusion layer, and the pressure receiving diaphragm 11 is The structure is such that it can be buried inside 11.

Then, the strain detection element 10 is made into an impurity diffusion layer,
The strain detection element 10 is embedded in the pressure receiving diaphragm 11.
The strain sensing element 10 is arranged at the periphery of the thinned part of the pressure receiving diaphragm 11.

Next, the operation of the embodiment shown in FIG. 2 will be explained. First, the mineral spirits 6 are accelerated by the nozzle 22 and collide with the pressure receiving diaphragm 11 in the form of a jet stream. Then, part or all of this jet collides with the heating element 9, and cooling heat transfer is performed as expressed by the following equation (1).

Pin=Pout=0.94Pr ^0.4 ReD ^0.5 k/D ・As・ΔT…(1) Here, D is the nozzle diameter, Pr is the Prandtl number,
ReD is Reynolds number and k is thermal conductivity. Note that Pin is the power supply, and Pout is the amount of heat transfer. Transforming this, Pin=0.94Pr ^0.4 (U _j /ν・D) ^0.5・k・As・ΔT …(2) =0.94Pr ^0.4 (ρU _j /μD) ^0.5・k・As・ΔT …(3) becomes. Here, U _j is the ejection velocity, ν is the kinematic viscosity coefficient, and μ is the viscosity coefficient.

In the above equation (2), the Prandtl number Pr, the thermal conductivity k, the kinematic viscosity coefficient ν, and the temperature difference ΔT between the fluid and the heating element 9 depend on the temperature of the fluid. Then, if a known constant temperature difference operation is performed in the hot wire, 0.94・As・ΔT/D ^0.5 becomes a constant, and under a certain constant temperature, the input power (supply power) Pin to the heating element 9 becomes the ejection speed U _j ^1/2
This means that a nonlinear relationship exists, that is, it is proportional to .

Generally, in a liquid, as the temperature of the fluid increases, the Prandtl number Pr and the kinematic viscosity coefficient ν decrease, and the thermal conductivity k does not change much. Furthermore, in the case of a gas, as the temperature of the fluid increases, the kinematic viscosity coefficient ν and conductivity k increase, but the Prandtl number Pr does not change much. Therefore, according to equation (2) above, whether the fluid is liquid or gas, in general, the Prandtl number is
When Pr and the kinematic viscosity coefficient ν are gases, the kinematic viscosity coefficient ν and thermal conductivity k have the effect of offsetting the temperature dependence of the input power (supplied power) Pin, and in a narrow operating temperature range, other than constant temperature difference operation, For example, there is no need to perform temperature compensation such as adding a temperature detection element.

However, there is a limit to the above-mentioned offsetting effect.
When the operating temperature range is wide, it is desirable to provide a separate temperature detection element and perform characteristic compensation for the temperature of the fluid.

The collision of the jets exerts pressure on the pressure receiving diaphragm 11 in addition to the cooling heat transfer, causing the pressure receiving diaphragm 11 to deform. As mentioned above, this transformation is
It is based on the total pressure, which is the sum of dynamic pressure, which corresponds to kinetic energy per unit volume of fluid, and static pressure, which corresponds to potential energy per unit volume of fluid.
Therefore, similar to the principle of Pitot-Venture tube combination, if the static pressure value of the fluid at any other location is known, the dynamic pressure 1/2ρU ² _j can be determined.

On the other hand, the strain detection element 10 constitutes a full bridge with four elements that are often employed in known semiconductor diffusion type pressure detectors, and has linear pressure conversion characteristics. Therefore, the characteristics of the dynamic pressure 1/2ρU ² _j are directly measured as the output of a detection circuit such as a differential amplifier.

As mentioned above, since the mass flow rate ρUj density-corrected by cooling heat transfer using the heating element 9 is determined as ρU ² _j by pressure conversion using the strain detection element 10, appropriate arithmetic processing is performed in the detection circuit section. By doing so, it is possible to measure something even closer to the true mass flow rate. Even in the case of a two-phase flow such as a liquid flow containing bubbles or a gas flow containing droplets, there are two functional relationships that determine the flow velocity, so the true mass flow rate can be measured.

In the embodiment shown in FIG. 2, the fluid flow is configured such that after colliding with the pressure receiving diaphragm 11, the fluid flow is bent 90 degrees and discharged. Therefore, the heat capacity in the heat generating part is small, and high-speed response on the order of milliseconds is possible. In addition, the flow near the pressure receiving diaphragm 11 is in a turbulent region with a Reynolds number of 3000 or more due to the nozzle 22, and is set to always be in a turbulent state within the measured flow rate range, so not only can a stable output be obtained. It has the advantage of being much smaller and lighter than conventional ones. Furthermore, the collision energy of the jet and the pressure receiving diaphragm 1
Since the vortices are generated in the vicinity of 1, "dust" and other deposits are difficult to adhere to, the characteristics change less over time, and the material is excellent in durability. Also, as shown in Figure 2,
This flow rate detector has a structure that allows easy installation and replacement.

Furthermore, since semiconductor materials are applied, it is excellent in mass production and can be produced at low cost and with high performance. Although the explanation has been given here by taking an N-type silicon substrate as an example, the same can be said for a P-type silicon substrate as well.

FIG. 3 is a configuration diagram showing another embodiment of the present invention,
This shows an example of a structure in which a heat generating element 9 and a strain detecting element 10 are laminated on a pressure receiving diaphragm 11, that is, are bonded.

In FIG. 3, the same reference numerals as in FIG. 2 indicate corresponding parts, and 23 is an insulating film that covers the entire surface or a part of the pressure receiving diaphragm 11 and is made of an electrically and thermally insulating material. The material of this insulating film 23 may be a metal oxide film, a heat-resistant polymer film, or
These include vapor-deposited thin films of SiO, SiO ₂ , MgF ₂ , CaF ₂ , ZnS, etc.

The heating element 9 is made of a thermistor, carbon film, SnO ₂ , etc., which is a stackable temperature-sensitive resistance material.
TiO ₂ oxide thin film, or noble metal thin film such as Pt, Au, Pd, or Ti, Cr, Zr, Mo, Ta,
Metal thin film such as W, or Ni-Cr, Au-
It consists of a thin film of alloys such as Cr, Cr-Ti, and manganese.
Further, as the strain detection element 10, a known resistance wire strain gauge or semiconductor strain gauge is used. Further, the pressure receiving diaphragm 11 on which the heating element 9 and the strain sensing element 10 are stacked is made of a metal such as stainless steel, which is a magnetic material capable of forming a membrane, or a semiconductor such as silicon.

As is clear from the foregoing, the pressure receiving diaphragm 11 is made of a metal material, and as shown in FIG. 3, the pressure receiving diaphragm 11 has a structure in which the central portion is thinner than the peripheral portion. The heating element 9 is a pressure receiving diaphragm 11.
The pressure receiving diaphragm 11 has a structure that can be adhered onto the surface of the pressure receiving diaphragm 11. Further, the strain detection element 10 is also bonded onto the surface of the pressure receiving diaphragm 11.

Next, the operation of the embodiment shown in FIG. 3 will be explained. In the embodiment shown in FIG. 3, the manufacturing method and material of the element are different from those in FIG. 2, but the operation is basically the same as in the embodiment shown in FIG. It operates almost the same as the embodiment shown.

Here, the difference from FIG. 2 is that in the embodiment shown in FIG. 3, the responsiveness of cooling heat transfer is improved compared to the embodiment shown in FIG.

This is because the pressure receiving diaphragm 11 and the heating element 9 are thermally insulated by the insulating film 23, so that leakage of heat flow to the pressure receiving diaphragm 11 is suppressed.

Further, by using a material with a high temperature coefficient of resistance such as a thermistor for the heating element 9, the output can be increased and the burden on an external detection circuit such as a differential amplifier can be reduced.

FIG. 4 is a block diagram showing still another embodiment of the present invention. In FIG. 4, parts that are the same as those in FIG. 2 are given the same reference numerals and explanations will be omitted.

The embodiment shown in FIG. 4 differs from the embodiment shown in FIG. 2 in that the static pressure of the fluid is introduced into the back surface of the pressure receiving diaphragm 11. This is because a port 24 is provided, and this inlet port 24 is configured so that fluid is introduced through the support base 18. Note that the other configurations are completely similar to the embodiment shown in FIG.

In the flow rate detector configured in this way, first, the total pressure of the fluid is applied to the surface of the pressure receiving diaphragm 11 that collides with the mineral spirits 6, as described above, but the static pressure of the fluid is applied to the back surface of the pressure receiving diaphragm 11. Since pressure is applied, the amount of deformation of the pressure receiving diaphragm 11 depends on the dynamic pressure 1/2ρU ² _j of the fluid.

Therefore, as in the embodiments shown in FIGS. 2 and 3, dynamic pressure can be directly measured without using other static pressure measuring means. The basic principle of this operation is similar to that of a pitot static pressure tube, and can be realized in an extremely narrow local space. In this way, except for directly measuring the amount of dynamic pressure, the other operations are similar to those of the embodiment shown in FIG. 2, so a description thereof will be omitted here.

As described above, in the embodiment shown in Fig. 4, mass measurement including up to two-phase flow is possible just by using a narrow space, and high-performance flow rate detection is possible using a small, lightweight, and inexpensive detector. can be realized.

FIG. 5 is a block diagram showing still another embodiment of the present invention. In FIG. 5, the same parts as in FIG. 2 are given the same reference numerals, and their explanation will be omitted.

The difference between the embodiment shown in FIG. 5 and the embodiment shown in FIG. It is configured such that pressure is applied to the back surface of the pressure receiving diaphragm 11. The method for forming such an inlet 24 is based on a known etching process and can be easily obtained.

FIG. 6 shows an enlarged view of only the portion related to the pressure receiving diaphragm 11 in the embodiment shown in FIG. 5. This figure 6 shows the pressure receiving diaphragm 11.
This is a bottom view when viewed directly from below, and in this figure, four inlet ports 24 are bored by etching.

The basic operation of the flow rate detector configured as described above is the same as that of the embodiment shown in FIG. can do. In addition to the fact that the stress is affected by the discontinuity caused by the introduction port 24 as the square of the film thickness and that the introduction port is extremely small, the strain detection element 10 is arranged so as to avoid the introduction port 24. Therefore, it can be almost ignored.

As is clear from the foregoing, in the embodiment shown in FIGS. 4 and 5, one surface of the pressure receiving diaphragm 11 is configured to receive the total pressure of the flowing fluid, and the other surface is configured to receive the total pressure of the flowing fluid. The pressure receiving diaphragm 11 is configured to receive static pressure, and is configured to be deformed by the dynamic pressure of the flowing fluid.

Note that this configuration can also be applied to the embodiments shown in FIGS. 2 and 3 by providing an inlet.

As is clear from the above description, according to the present invention, true mass measurement is possible with a simple configuration in which a heating element and a strain sensing element are formed on the same diaphragm without using complicated means. Since a small, lightweight, and high-performance flow rate detector can be realized at a low cost, the practical effects are extremely large. In addition, due to the impact energy of the jet and the vortices generated near the pressure receiving diaphragm, it is difficult for dust and other deposits to adhere to it, resulting in less change in characteristics and excellent durability.In addition, the detector is easy to install and replace. The present invention is extremely effective in that it enables mass flow measurement including up to two-phase flow.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of a conventional heat-sensitive flow rate detector, Fig. 2 is a block diagram showing an embodiment of a heat-sensitive flow rate detector according to the present invention, and Fig. 3 is a block diagram showing another embodiment of the present invention. FIGS. 4 and 5 are configuration diagrams showing still other embodiments of the present invention, and FIG. 6 is an explanatory diagram showing an enlarged portion of the pressure-receiving diaphragm in the embodiment of FIG. 5. be. 6... Mineral spirits, 9... Heat generating element, 10... Strain detection element, 11... Pressure receiving diaphragm, 18... Support stand, 22... Nozzle.

Claims (1)

[Claims] 1. In a heat-sensitive flow rate detector that detects the flow velocity or flow rate of a flowing fluid from the amount of heat transfer between a heating element and a flowing fluid, the cross-sectional area of the flow path of the flowing fluid is narrowed. A flow velocity increasing means using a throttle mechanism that increases the flow velocity, a diaphragm placed behind the flow velocity increasing means and deforming under pressure according to the flow velocity of the flowing fluid, a heating element embedded in or bonded to the diaphragm, and a heating element embedded in or bonded to the diaphragm. 1. A heat-sensitive flow rate detector comprising a strain detecting element that is buried or bonded, and supporting means that supports a peripheral portion of the diaphragm and is made of a thermally poor conductor. 2. The heat-sensitive flow rate detector according to claim 1, wherein the diaphragm that deforms under pressure is made of a semiconductive material. 3. The heat-sensitive flow rate detector according to claim 2, wherein the diaphragm that deforms under pressure is made of silicone material. 4. The heat-sensitive flow rate detector according to claim 2 or 3, wherein the diaphragm that deforms under pressure has a structure in which a central portion of the diaphragm is thinner than a peripheral portion. 5. A heat-sensitive flow rate detector according to any one of claims 2, 3, or 4, characterized in that the heating element is disposed in a thinned portion of the diaphragm. 6. The heat-sensitive flow rate detector according to claim 5, characterized in that the heating element is disposed in the center of the diaphragm. 7. A heat-sensitive flow rate detector according to any one of claims 2, 3, 4, 5, or 6, characterized in that the heating element is an impurity diffusion layer and is embedded in a diaphragm. 8. The heat-sensitive flow rate detection according to any one of claims 2, 3, 4, 5, 6, or 7, characterized in that the strain detection element is an impurity diffusion layer and is embedded in a diaphragm. vessel. 9. The thermosensitive type according to claim 2, 3, 4, 5, 6, 7 or 8, characterized in that the strain detection element is arranged in a thinned part of the diaphragm. Flow rate detector. 10. The heat-sensitive flow rate detector according to claim 9, characterized in that the strain detection element is disposed around the periphery of the thinned portion of the diaphragm. 11. The heat-sensitive flow rate detector according to claim 1, wherein the diaphragm that deforms under pressure is made of a metal material. 12. The heat-sensitive flow rate detector according to claim 11, wherein the diaphragm that deforms under pressure has a structure in which a central portion of the diaphragm is thinner than a peripheral portion. 13 Claim 1 characterized in that the heating element is arranged in the center of the diaphragm without having a structure in which the heating element is bonded on the diaphragm surface.
The heat-sensitive flow rate detector according to item 1 or 12. 14 Claim 1 characterized in that the strain detection element is structured to be bonded onto the diaphragm surface.
1. The heat-sensitive flow rate detector according to any one of Items 1, 12 and 13. 15 One surface of the diaphragm that deforms under pressure is configured to receive the total pressure of the flowing fluid, the other surface is configured to receive the static pressure of the flowing fluid, and the diaphragm is configured to receive the total pressure of the flowing fluid, and the diaphragm is configured to receive the static pressure of the flowing fluid. Claims 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 characterized in that it is configured to deform under pressure.
1, 12, 13 or 14.