JP2008256633A - Flow rate measuring device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive, simple and highly accurate minute flowmeter hardly having necessity of maintenance. <P>SOLUTION: At first, a calibration curve for indicating the relationship of a flow rate and temperature increase due to heating is prepared. A fluid is flowed in a flow passage, and heated with a heater provided on the way of the flow passage. The heated fluid moves by being mounted on flow, and temperature is uniformed by heat diffusion. In a diffusion part provided on the way of the flow passage, the influence of acceleration due to heating by the heater is relieved, and sufficient diffusion is performed. The temperature measurement of the heated fluid is performed in a temperature detection part provided in the downstream side of the heater to find the flow rate based on the calibration curve. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a flow rate measuring device and a flow rate measuring method, and more particularly to a flow rate measuring device and a flow rate measuring method that can be used for measuring a very small flow rate.

The measurement of the flow rate is indispensable in the industrial field, and many detection methods have been devised so far. However, for micro flowmeters of 1 ml / min or less, which are in demand for semiconductor manufacturing and microfluidics, an expensive and complicated device is currently required.

For example, a means using a laser beam such as a laser Doppler velocimeter (LDV) can be cited as means for measuring a minute flow rate (see, for example, Patent Document 1). However, such a measuring apparatus using a laser beam is expensive and has a problem that the apparatus size tends to be large.

Further, as an inexpensive minute flow rate measuring means, for example, a measuring device described in JP-A-56-43559 can be mentioned. In the flow rate measuring method described in Japanese Patent Laid-Open No. 56-43559, the fluid is heated on the upstream side and the heated fluid is used as a temperature marker to measure the flow velocity from the marker moving time. Of course, if the flow velocity is obtained, the flow rate can be obtained by multiplying the cross-sectional area of the flow path, but there is a problem that the heating fluid is difficult to serve as a marker because the influence of thermal diffusion is large in the micro flow region.

Patent 3279116 JP 56-43559

  The present invention has been made in view of the above-described conventional circumstances, and a problem to be solved by the present invention is to provide a low-cost, simple, and highly accurate micro flow meter with little need for maintenance.

In order to solve the above problems, a flow rate measuring device according to the present invention includes a flow path that allows fluid to pass through, a heater that heats the fluid that flows through the flow path, and a midway in the flow path. A diffusion unit that alleviates the influence of acceleration due to heating and promotes diffusion of the fluid; and a temperature detection unit that detects the temperature of the fluid, and the heater is disposed in the flow path or in the diffusion unit, and the temperature The detection unit is provided on the downstream side of the heater.

In the present invention, when the fluid heated by the heater passes through a sensor installed downstream of the heater, the temperature rise ΔT compared to before heating is measured, and the relationship that ΔT and the flow rate Q are linear is utilized. (Based on a relational expression described later derived by the present inventor). Furthermore, according to the present invention, it is possible to stabilize the output and improve the sensitivity by providing a mechanism having a function of diffusing a fluid such as a reducer in the apparatus. Moreover, it is also possible to employ a configuration including an information processing device that controls the heater and / or performs signal processing of a detection signal from the temperature detection unit.

Furthermore, in order to solve the above-described problem, the flow rate measuring device according to the present invention may be configured such that the flow path is held so that fluid flowing through the flow path passes in a direction substantially opposite to gravity. As a result, the fluid heated by the heater is accelerated in the same direction as the main flow direction (the heated fluid is accelerated in the direction opposite to gravity due to the density change). By suppressing the acceleration of the heated fluid by the diffusion unit and promoting sufficient thermal diffusion, it can be applied to a model described later, and a minute flow rate can be measured.

The flow rate measuring device according to the present invention may be configured such that the flow path is held so that the fluid flowing through the flow path passes in substantially the same direction as gravity. Thereby, the fluid heated by the heater is accelerated in the direction opposite to the main flow direction. In other words, this means that the acceleration direction of the fluid based on heating and the main flow direction are opposed to each other, and uniform temperature is promoted by collision of each flow. In the case of such a configuration, the temperature can be made uniform without providing a temperature diffusing section, so that a micro flow meter can be realized at a lower cost. In addition, depending on the conditions (for example, the heating amount and the main flow velocity), a sufficient temperature diffusion action cannot be obtained only by the collision between the acceleration flow and the main flow. Therefore, by providing a temperature diffusion portion, accuracy and sensitivity can be improved.

Furthermore, in order to solve the above-described problem, in the flow rate measuring device according to the present invention, the diffusion unit may be configured by a reducer that reduces the tube diameter of the flow path.

In the flow rate measuring device according to the present invention, the diffusion unit may be configured such that a plate having at least one hole is inserted at a right angle to the flow direction.

Further, it is preferable that the heating position of the fluid by the heater is configured to be substantially in the center on a virtual plane orthogonal to the fluid flow direction.

Furthermore, in the flow rate measuring device according to the present invention, measurement is possible even when the flow rate of the fluid flowing through the flow path is 1 ml / min or less.

The flow rate measurement method of the present invention is a method for measuring the flow rate of a fluid flowing through a flow path having a diffusion part that alleviates the influence of acceleration due to heating and promotes diffusion of the fluid, and heats a part of the fluid. And a step of measuring a temperature of the heating fluid, a step of measuring a flow rate of the fluid using a calibration curve indicating a relationship between a rising temperature of the heating fluid and a flow rate of the fluid, It is characterized by providing.

The flow rate measurement method of the present invention is a method for measuring the flow rate of a fluid flowing through a flow path having a diffusion part that alleviates the influence of acceleration due to heating and promotes diffusion of the fluid, and heats a part of the fluid. Creating a calibration curve indicating the relationship between the rising temperature of the heated fluid and the flow rate of the fluid, heating a part of the fluid to be a heated fluid, and the temperature of the heated fluid And measuring the flow rate of the fluid using the calibration curve.

According to the present invention, it is possible to provide an inexpensive and simple micro flow meter with little need for maintenance.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. However, it should be noted that the drawings are schematic and different from the actual ones. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings. Further, the embodiment described below exemplifies an apparatus and a method for embodying the technical idea of the present invention. The technical idea of the present invention is the arrangement of each component as described below. It is not something specific. The technical idea of the present invention can be variously modified within the scope of the claims.

[First embodiment]
First, a flow rate measuring device according to a first embodiment of the present invention will be described with reference to FIG. The flow rate measuring device according to this embodiment connects an upstream flow path 1 having a large cross-sectional area that allows fluid to pass through, a downstream flow path 3 having a small cross-sectional area, and a flow path 1 and the flow path 3 to each other. A reducer 2 that reduces the pipe diameter of the path 1 to the pipe diameter of the flow path 3, a heater 4 that heats the fluid, and a temperature detection unit 5 that includes a thermocouple are provided as main components.

  The channel 1 has a circular cross-sectional shape, and the inside thereof is formed so as to allow fluid (liquid or gas) to pass therethrough. In this embodiment, the flow path 1 is extended in the vertical direction, so that the fluid flowing through the flow path 1 can pass in a direction substantially opposite to gravity. Here, “substantially reverse” includes not only the case where the directions are different by 180 degrees but also the case where the vector component has a direction opposite to the direction of gravity.

  The reducer 2 has a function of diffusing the fluid heated by the heater 4 (making the temperature uniform). This action makes it possible to apply the present flow meter to a model described later (the flow rate and the rising temperature have a linear relationship). Note that the reducer is a preferred embodiment as a diffusing portion for diffusing fluid. For example, an acrylic tube is used for the flow path 1 having an inner diameter of 6 mm, synthetic resin parts are used for the other portions, and the parts of the flow path 1, the reducer 2, and the flow path 3 are bonded to each other with an adhesive. A reducer part can be provided in the middle of a flow path. In addition to this, for example, a seamless tube in which the reducer portion is formed in advance may be used.

  The flow path 3 is provided on the downstream side of the reducer 2. The inner diameter of the channel 3 is the same as the diameter of the outlet portion of the reducer, and the other configurations are the same as those of the channel 1 described above.

  The heating heater 4 is provided on the upstream side of the temperature detection unit 5. Considering the diffusion action by the reducer described above, the heater 4 for heating is preferably provided near the entrance of the reducer in order to obtain this effect sufficiently. As shown in FIG. 2, the heater 4 includes a ring portion 4a formed in an annular shape, and a conductive wire 4b connected to the ring portion 4a. The ring portion 4a is installed so that the axial direction and the fluid flow direction are substantially parallel. Moreover, the ring part 4a is arrange | positioned so that the heating position of a fluid may become a substantially center in the virtual surface orthogonal to the flow direction of a fluid. As a result, the heater 4 is disposed in the vicinity of the position that is the maximum flow velocity point of the fluid.

As is well known, when the Reynolds number is about 2000 or less, the flow of fluid in the straight pipe becomes a Poiseuille flow as shown in FIG. 3 regardless of the flow state at the straight pipe inlet. As shown in Fig. 3, the Poiseuille flow is a laminar flow with a parabolic flow velocity distribution whose flow velocity distribution does not change in the flow direction. In particular, in the case of a pipe flow having a small Reynolds number Re, it is known that a Poiseuille flow is obtained with a very short approach distance L. The approach distance L is obtained by the following equation.
L = 0.065Re × d
However,
Re≡Ud / γ: Reynolds number d: Diameter of the flow path (m)
U: Average pipe flow velocity (m / s)
γ: Kinematic viscosity coefficient of fluid (m 2 / s)
It is.

  Since the Poiseuille flow is well known from the past, it will not be described any more, but what is important in the present invention is that the velocity distribution is as shown in FIG. That is, the flow velocity of the fluid flowing through the flow path 1 is maximized near the center where the heater 4 is located. As a result, the Poiseuille flow, which is an axially symmetric flow, can be heated axisymmetrically by a heater provided near the center of the flow path, and diffusion also occurs symmetrically, so that the temperature can be made uniform throughout the flow path. it can.

Heater 4 is heated for a time t _h by a square wave voltage from the pulse voltage generator 41. FIG. 4 is an example of an apparatus used for pulse heating the heater 4 for heating. The apparatus includes a heater 4 for heating, a pulse voltage generator 41, a constant voltage power supply 42, and a resistance circuit 43 for current control. Although the pulse voltage generator is not a feature of the present invention and will not be described in detail, for example, an astable multivibrator circuit using a timer IC is operated by the constant voltage power supply 42, and the magnitude of the resistance in the circuit is changed. it is the waiting time t ₁ between the pulse current can be adjusted pulse energization time t _h. Further, when the output from the pulse voltage generator 41 is constant, the current intensity can be controlled using the current control resistor circuit 43 shown in FIG. 4 to adjust the heating amount of the heater 4 for heating. it can. In this way, the heating heater 4 can be energized at an arbitrary interval to heat the fluid in pulses. Note that by connecting the constant voltage power source to the information processing device 54, the information processing device 54 can control not only the collection of temperature measurement data but also the heater for heating.

  The heating fluid heated by the heating heater 4 moves along the flow while performing thermal diffusion. And the temperature measurement is performed by the temperature detection part 5 in the downstream, and the temperature rise ΔT before and after heating is measured.

  FIG. 5 shows an example of the device configuration of the temperature detection unit 5. In this example, in order to configure the present apparatus at low cost, the temperature detection unit 5 is configured using a thermocouple. The temperature detection unit 5 includes an information processing device 54 including a thermocouple 5, a thermocouple output amplifier circuit 52, a low-pass filter circuit 53, an A / D conversion board, a data storage medium, a data processing unit, and the like (not shown). As a main component. The output of the thermocouple is enlarged by the thermocouple output amplifier circuit 52 and taken into the information processing device 54 via the low-pass filter circuit 53.

  In some embodiments, the distance L between the heater 4 and the temperature detector 5 is assumed to be close. In such a case, the non-insulated nichrome wire heater and the measurement part of the thermocouple are present at a position close to each other, and a leakage current is generated between the heater and the thermocouple while the heater is energized. Since the output of the thermocouple itself is small and the gain of the amplifying device is large, even if the leakage current is weak, the output of the device during and immediately after energizing the heater is greatly affected. In particular, the influence of leakage current becomes significant in water having a higher conductivity than air. Therefore, in this embodiment, as a measure against leakage current, the thermocouple measurement part is covered with the insulating tape 51, and the electric potential of the thermocouple is made equal to the average electric potential of the nichrome wire heater during the energization and standby of the pulse energization. A circuit 55 is provided.

  Next, an operation method of the flow rate measuring device according to the present embodiment will be described. First, it is assumed that fluid flows in the direction of the arrow in FIG. Then, a part of the fluid is first pulse-heated by the heater 4 provided near the entrance of the reducer. The heated fluid is uniformly diffused while being thermally diffused in the reducer section, and moves downstream along the flow.

  Then, the heated fluid reaches a temperature detection unit provided on the downstream side of the heater, and temperature measurement is performed. Since the temperature of the fluid before heating is known, the temperature rise ΔT is calculated by the information processing device 54, and the flow rate is calculated from a previously determined calibration curve (representing the relationship between the fluid rise temperature ΔT and the fluid flow rate Q). Can know. As described above, since the flow rate measuring device according to the present invention has a very simple configuration, it can be manufactured at low cost. Estimating the manufacturing cost on the assumption that this flow meter is used as a single unit, for example, the manufacturing cost of the heater part (manufacturing cost of the pulse generation circuit and constant voltage power supply: ~ \ 2000), the manufacturing cost of the temperature sensor part (thermoelectric Considering the pair and amplifier for amplification: ~ \ 500, DC voltmeter for output measurement: ~ \ 2000), one flow meter can be manufactured within 5000 yen.

  Next, a method for creating a calibration curve showing the relationship between the fluid rising temperature ΔT and the fluid flow rate Q will be described. Since this calibration curve is based on the following relational expression derived by the present inventor, this relational expression will be described first. Hereinafter, the qualitative relationship between the flow rate Q and the fluid rising temperature ΔT will be described based on a simplified model of the flow system.

If the amount of heating Δq by the heater is constant, the amount of ΔT is the total volume V _h of the volume of fluid to which heat is transferred from the start of heating by the heater until the heated fluid reaches the sensor. (Equation (1)). However, heat diffusion outside the measuring tube and the measuring tube shall not be considered. Here, ρ represents the density of the fluid, and Cp represents the constant pressure specific heat.

Here, for simplification of the model, the following conditions (i) to (iii) are used.

(i) Replace the reducer model with a straight tube model with the same volume (see Fig. 6). Here, when the time required for the fluid having the average flow velocity U _{m in} the pipe to pass through the length L (distance between the heater and the sensor) is Δt, it takes the time of Δt to pass through the same volume. The length of the inner straight tube is L ′, and the volume of the length L reducer and the length L ′ of the straight tube is equal. For example, an inner diameter of 6 between length L
Applying the reducer reduced from 3 mm to 3 mm and a straight tube with an inner diameter of 6 mm of length L 'to the above relationship, L' = 7L / 12, so that the reducer of length L and the length of L ' The volume of the circular tube is equal. In the following, it is assumed that the measurement tube is a straight tube having a heater-sensor length of L ′, and this result is applicable to a reducer model of length L.
(ii) The flow velocity U _m is uniformly in the pipe cross section. That is, the formation of the velocity boundary layer due to the viscosity in the tube and the acceleration due to the buoyancy of the fluid accompanying the rise in the temperature of the fluid are not considered.
(iii) Heating is performed uniformly over the entire heater installation cross section. An actual heater has a finite width in the axial direction and the cross-sectional direction of the tube, but here, a heater that uniformly heats the entire cross-section of the heater-installed cross section having a thickness of 0 is assumed.

FIG. 7 is a model of V _h derived from the above conditions. The order of V _h depends on h ₀ and δ _T , and is expressed by equation (2). Here, h ₀ is the length of the fluid passing through the heater section in the heater, [delta] _T represents the length of the heat heater gave fluid is diffused by thermal conduction (see FIG. 7).

h ₀ is the axial length of the fluid that passes through the section where the heater is installed at the flow velocity U _m during the heater heating time t _h , and is given by Equation (3).

The [delta] _T at the time the heating fluid reaches the sensor, the length of the thermal diffusion (see Fig. 8). The heated fluid moves along the main stream (Fig. 8 (a)), and heat diffusion occurs in the flow direction due to heat conduction during the movement of the heated fluid (Fig. 8 (b)), and Δt [s After that, the heated fluid reaches the sensor ((c) in the figure). Let δ _T be the length of thermal diffusion that has occurred so far.

The order evaluation of δ _T is given by Equation (5) from Equation (4) of thermal diffusion from a point heat source placed in an infinite static space. Note that the representative amount of time includes the time Δt during which the fluid having a flow velocity U _m moves between the heat source and the sensor L ′ for easy analysis.
(= L '/ U _m ) is used.

As can be seen from equation (2), the order of V _h is proportional to the order of (h ₀ + 2δ _T ). Further, Equation (2), (3), from (5), the order of V _h is, Q is [delta] _T affects the dominant at sufficiently small area, Q is the influence of h ₀ is a sufficiently large area It turns out that it becomes dominant. That, Q is a sufficiently large area, since the faster the min flow rate, travel time Δt of the heating fluid is shortened, resulting in [delta] _T is also reduced. On the other hand, the Q is a small region (micro-flow region), the moving time Δt heated fluid increases, [delta] _T increases.

From the equations (1) to (4), the order of ΔT is a function of U _m (equation (6)). Here, a, b, c, a ′, b ′, and c ′ are constants.

From equation (6)
It turns out that it becomes. Also,

The maximum value of ΔT occurs at U _m .

  FIG. 9 shows the relationship of Q−ΔT according to the equation (6). Referring to FIG. 9, the relationship between Q−ΔT appears in the region A where the flow rate is small, and in the region B where the flow rate is high, the relationship where the right shoulder is lowered. In the present invention, a calibration curve is created using the relationship of the region A (the portion where the Q-ΔT relationship can be approximated linearly) to realize a micro flowmeter.

As described above, since the influence of thermal diffusion becomes dominant in the minute flow rate region, it is difficult to realize a method in which the heating fluid is used as a temperature marker and the flow velocity is obtained from the moving time. On the other hand, the present invention also utilizes the equalizing effect of the temperature due to thermal diffusion, in order to apply the model represented by the equation (6), due to the fact that the length [delta] _T of the thermal diffusion becomes dominant There is no inconvenience. The above is the basic principle of the present invention.

  Now, a calibration curve creation method will be described. A calibration curve can be created by using an apparatus as shown in FIG. The apparatus shown in FIG. 10 is obtained by adding a device 61 (hereinafter referred to as a constant flow rate generator) capable of generating a constant flow rate to the configuration shown in FIG.

  An example of the constant flow rate generator 61 is shown in FIG. In the example shown here, the supply of the water flow at a constant flow rate uses a traverse device with a speed reducer that pushes the water in the syringe at a constant speed. First, the motor 62 with a speed reducer is driven by an external power source (not shown). The rotation obtained by driving the motor 62 is converted into a linear motion of the pedestal 64 by the traverse device 63. The pedestal 62 is provided with at least one syringe, and the syringe 65 also moves linearly as the pedestal 62 moves linearly (in the direction of the arrow 66). This linear movement of the syringe 65 pushes the piston of the syringe and pushes the fluid at a constant speed. Furthermore, the flow rate can be adjusted according to the type and number of syringes used. In FIG. 11, as an example, a total of four syringes are shown on the base 64.

For example, when the motor speed is 60 rev / min, the reduction gear reduction ratio is 12.5: 1, and the traverse device pitch is 3 mm / rev, a linear motion of 14.4 mm / min is obtained. When a 1 mL plastic medical syringe (inner diameter: 4.5 mm) is used as the syringe,
For mL / min and 5mL (inner diameter 13mm), the flow rate can be adjusted in units of 1.9 mL / min.

  In order to create a calibration curve, first, a known flow rate generated by the constant flow rate generator 61 is passed through the flow path 1. When the fluid flows through the flow path 1, the Poiseuille flow shown in FIG. 3 is obtained at the position of the heater 4, and the flow velocity becomes maximum near the center where the heater 4 is located. Subsequently, the density of the fluid (heated fluid) in the heated portion that is pulse-heated by the heater 4 is smaller than that before heating. Then, the flow of the heated portion is accelerated in the direction opposite to gravity due to the buoyancy based on the density difference from the surrounding non-heated fluid. Then, the heated fluid moves along the flow, passes through the reducer unit 2, and reaches the temperature detection unit 5. The temperature of the heated fluid is measured in the temperature detection unit.

  The temperature measured here is only the temperature of the heated fluid (the temperature rise ΔT can be calculated from this temperature). Therefore, the relationship with the actual fluid flow rate Q (or flow velocity) is unknown. Therefore, by changing the flow rate with a constant flow rate generator, measuring the rising temperature for each experiment, and plotting the results of this experiment, a calibration curve showing the relationship between them can be obtained.

  For example, an experimental result as shown in FIG. 12 is obtained. In the figure, the upper graph shows an experimental result in the case of a normal circular tube without a reducer, and the lower graph shows a test result in the case of a tube with a reducer. Although there are a plurality of experimental results at the same flow rate in the figure, the variation in the experimental results can be eliminated by optimizing the whole by changing the design of the inner diameter of the tube, the heater shape, and the like. Thereby, the measurement accuracy can be further improved. The experimental conditions are as follows.

(A) Inner diameter of pipe / channel 1 with reducer: 6 mm
・ Inner diameter of channel 2: 3mm
Reducer length L: 18mm
・ Heater material: Nichrome wire (wire diameter 0.12mm)
-Heater diameter D = 0.5mm, length in the flow direction: 3mm
・ Heater power: 1.7W
(Heating time t _h = 1.8 s, heating amount Δq = 3J)
・ Flow rate: 0.00 to 1.95 (mL / min)
・ Water temperature: 19 ℃
(B) Straight pipe, pipe inner diameter: 6mm
・ L ': 10.5
mm
・ Water temperature: 18 ℃
As can be seen from the graph of the pipe with reducer (a) in FIG. 12, the relationship of Q−ΔT is a linear relationship (relation represented by a linear function) when the flow rate Q is in the range of 0 to 1 (ml / min). (Refer to the broken line in the figure). This agrees well with the area A of the analytical result shown in FIG. By using this as a calibration curve, the actual fluid flow rate can be accurately measured from the rise temperature ΔT. If the relationship between the heating flow rate and the fluid flow rate is complicated and nonlinear, the accuracy will deteriorate even if a calibration curve is created. That is, it becomes difficult to perform accurate interpolation from the experimental results that are finite. On the other hand, if the relationship between the two is linear, the value between the measurement points at the time of creating the calibration curve can be accurately interpolated. From the experimental results shown in FIG. 12, it can be seen that according to the present invention, measurement is possible even with a minute flow rate of 1 (ml / min) or less.

  On the other hand, the graph (b) in the case of a circular pipe shown as a comparative example has a lower sensitivity (amount of increase in temperature with respect to flow rate change) than in the case of (a) a pipe with a reducer. Further, a linear relationship is not obtained between 0 and about 0.5 (ml / min). This is because, since there is no reducer, acceleration of the heated fluid by buoyancy becomes dominant, and the heated fluid reaches the sensor before the thermal diffusion sufficiently proceeds. That is, it is considered that because the temperature is not uniformized, the above-mentioned condition (iii) is not satisfied, and it cannot be applied to the simplified model shown in Equation (6). Although this is actually partial heating, it is possible to apply to the condition (iii) in which the diffusion of the temperature field and velocity field in the tube progresses due to the effect of introducing the reducer, and the entire cross section is heated uniformly. It shows that it becomes. By introducing a reducer, there is an advantage that sensitivity is improved and measurement accuracy is increased, and a linear relationship is obtained in a wider flow rate range, so that the measurement range is widened.

This can be understood from the experimental results shown in FIG. The graph shown in FIG. 13 is a temperature measurement result (when Q = 0.5 ml / min) in the temperature detection unit. In the figure, the horizontal axis is time scale 1 scale 10
s, vertical axis is temperature and 1 scale is 1 K. In the figure, it means that the heated fluid has reached the position indicated by the arrow. Here, it is considered that the heated fluid has reached the sensor with the peak value of the temperature of the fluid. However, in the case of a tube with a reducer, since a clear peak value cannot be read due to thermal diffusion, the temperature when the temperature becomes almost constant is used. Thus, unlike the case of the straight circular tube, the peak value appears for a long time, so that there is an advantage that the peak value can be easily measured and the reproducibility of the experimental result is improved. Furthermore, since the present invention does not require a time from when the fluid is heated until it reaches the sensor in order to measure the flow rate, there is no need to provide a mechanism for measuring the time.

In the case of a normal circular tube, as shown in FIG. 13 (b), the time Δt _B at which the heated fluid reaches the sensor after heating is started is the time for the main flow velocity to move between the heater and the sensor. It can be seen that it is much shorter than that. When heating is not performed, the fluid passes between the heater and the temperature detection sensor in 35 seconds, whereas in the case of a straight tube without a reducer (b), the heated fluid reaches in 3.7 seconds. . On the other hand, in the case of the pipe with the reducer (a), the arrival of the heated fluid is delayed for about 7 seconds compared with the case of the straight pipe (b), and it can be seen that the influence of acceleration is suppressed by the reducer.

  In addition, in the case of (b) straight circular pipe, a clear temperature peak appears in a short time, while in the case of (a) pipe with reducer, almost the same temperature is measured over a long period of time. . This indicates that since the time until the heated fluid reaches the temperature detecting portion is increased by introducing the reducer, the thermal diffusion length ΔT is increased, and the temperature is sufficiently uniformed.

In addition, as can be seen by comparing the experimental results shown in Fig. 13 (when Q = 0.50 ml / min) with the experimental results shown in Fig. 14 (when Q = 0.25 ml / min), the case of a normal straight pipe The value of Δt _B does not change much even if the magnitude of Q changes. From this, it can be seen that in the case of a straight pipe, the acceleration by buoyancy is dominant in the flow rate of the heated fluid, rather than the main flow rate before heating. In a straight circular tube, it is considered that the flow rate of the heating fluid becomes almost constant regardless of the flow rate before heating due to the buoyancy generated by heating. Further, comparing both experimental results, it can be seen that the acceleration of the heated fluid is suppressed by the reducer as the flow rate Q is smaller (the average flow velocity Um is smaller). In particular, in the case where Um is small (Um to 0 mm / s), acceleration of the heated fluid is suppressed by the reducer. For this reason, since sufficient time can be taken for temperature diffusion, the uniformization of the fluid temperature is promoted. As a result, in the case of a pipe with a reducer, it is considered that a linear relationship was obtained between the temperature rise ΔT and Um of the uniform fluid including a small range of Um.

  Further, as can be seen from the equation (6), the temperature rise amount ΔT decreases as Um decreases. In this phenomenon, acceleration due to buoyancy is dominant in the absence of a reducer, so that sufficient diffusion time cannot be obtained and the temperature distribution is non-uniform, whereas in the presence of a reducer, acceleration is suppressed and sufficient diffusion is achieved. It is because it is done. Furthermore, when there is no reducer, sufficient time for temperature diffusion cannot be taken. Therefore, the temperature sensor installed in the center of the pipe shows a high ΔT compared to the case with the reducer, and between ΔT and Um, The linear relationship is no longer valid.

  From this experimental result, the usefulness of the diffusion effect by providing the reducer can be seen. The heated fluid is moved by mass transfer of the fluid and heat conduction by heat diffusion in the fluid, but in a system with a small flow velocity, an increase in temperature is observed at the sensor position before reaching the main flow due to the influence of heat conduction. . Therefore, the reducer relaxes the effect of acceleration by heating, promotes thermal diffusion, and improves sensitivity.

  Further, as in this example, when a minute flow rate is set as a measurement target, the flow velocity of the fluid becomes small. Therefore, since the Reynolds number Re is also small, a Poiseuille flow is formed even if the run-up distance of the fluid is short. Therefore, according to the flow rate measuring device or the flow rate measuring method according to the present invention, since the run-up distance of the fluid (the straight circular pipe portion to the heater for heating) can be shortened, there is an advantage that the device can be miniaturized.

  Furthermore, as can be seen from the experimental results shown in FIG. 12, according to the present invention, since the flow rate can be measured even when the flow rate is close to zero, for example, a gas leak in which a very small amount continues to leak is accurately detected. It is also possible. That is, the flow measuring device or the flow measuring method according to the present invention can be applied to a gas leak detector.

In the present embodiment, since the measurement method is as described above, the flow rate of the unsteady minute flow rate is substantially continuously (that is, a short time) by shortening the time interval Δt _h of pulse heating. It can also be measured (at intervals).

  Furthermore, in the present embodiment, since the fluid is heated at substantially the center in the cross section of the fluid, heat exchange between the heated fluid and the tube wall can be suppressed to a low level. If the temperature of the heating fluid is affected by the heat exchange between the fluid and the tube wall, it is difficult to apply to the above simplified model and the measurement accuracy may be deteriorated. However, according to the present embodiment, since the fluid is heated at substantially the center in the cross section of the fluid, almost all of the heating amount is given to the fluid, and deterioration in measurement accuracy due to heat exchange with the tube wall is reduced. Can be suppressed.

  However, the position of the heater 4 is not limited to the vicinity of the center of the flow path 1, but can be shifted in the radial direction as long as it is not affected by heat exchange with the tube wall. Even if the heater for heating is not arranged near the center, in the present invention, temperature measurement is performed after sufficient temperature diffusion is performed, so the arrangement position of the temperature detector and the heater for heating is virtual. Even if it is slightly deviated in the plane, there is no possibility that the measurement accuracy is lowered. However, considering that the temperature is made uniform by the reducer provided on the downstream side of the heater, the diffusion of the Poiseuille flow, which is an axially symmetric flow, is generated symmetrically when heated axially symmetrically. It is preferable to be provided in the vicinity.

  In addition, in a device that heats a fluid and obtains a flow rate from the moving time of the heated fluid, if the measured flow rate is excessively slow, heat diffuses before temperature detection is performed, resulting in inaccurate measurement. There is a fear. That is, in such a case, it is difficult for the heated fluid to serve as a marker. However, since the present invention is based on a principle that also considers the influence of thermal diffusion, measurement can be performed accurately without being affected by thermal diffusion.

  Further, in this embodiment, the ring-shaped heater is arranged near the center of the flow path, but as another example, by arranging the grid-like conductors in the entire virtual plane orthogonal to the flow, the fluid is almost uniformly distributed. It is also possible to heat.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIG. The flow rate measuring device according to this embodiment mainly includes a flow path 71 that is held so that fluid passes in substantially the same direction as gravity, a heater 72 that heats the fluid, and a temperature detection unit 73 that includes a thermocouple. As a major component. Unlike the first embodiment, this embodiment is held such that the fluid flowing through the flow path passes in substantially the same direction as gravity. Here, “substantially the same direction” means not only the case where the directions are exactly the same, but also the case where the vector component has the same direction as gravity. Since the flow path 71, the heater 72, and the temperature detection unit 73 have the same configuration as the flow path 1, the heating heater 4, and the temperature detection unit 5, they will not be described in detail here.

  As described above, the density of the fluid (heating fluid) in the portion heated by the heater for heating is smaller than that before heating. Then, the flow of the heated portion is accelerated in the direction opposite to gravity due to the buoyancy based on the density difference from the surrounding non-heated fluid. In the present embodiment, since the flow path is held so that the fluid flows in the same direction as gravity, the acceleration direction of the fluid accelerated by heating differs from the main flow direction. Therefore, since the heated fluid tends to accelerate against the main flow, the main flow and the acceleration flow collide with each other, and a good diffusing action can be obtained without providing a diffusion portion such as a reducer. That is, the forced flow that flows in the same direction as gravity is destabilized by the upward buoyancy flow based on heating, so that a diffusion action due to convective mixing occurs and the temperature of the heated fluid is made uniform.

A non-dimensional number representing the magnitude of forced flow, called Reynolds number (Re number), with constant heating (the dimensionless number representing the size of natural convection called the Grashof number (Gr number) is constant). ), The ratio of both dimensionless numbers, Gr / Re ² (representing the relative magnitude of natural convection and forced flow) produces various flow patterns. For example, if the Gr / Re ² value is designed to be close to 1, the effects of buoyancy due to heating and the mainstream inertial force are almost the same, and a good mixing effect can be obtained. It is preferable to do.

  The calibration curve may be created by plotting the relationship between an arbitrary flow rate and an elevated temperature, as in the case of the first embodiment. If the linear relationship in the calibration curve is used, the accurate flow rate Q can be known only by measuring the rising temperature ΔT.

[Third embodiment]
Next, a third embodiment will be described with reference to FIG. The flow rate measuring device according to this embodiment includes a flow path 81 that is held so that the fluid passes in a direction substantially opposite to gravity, a heating heater 82 that heats the fluid, and a heating heater 82.
A plate 83 having at least one hole arranged on the downstream side thereof and a temperature detection unit 84 made of a thermocouple are provided as main components. In this embodiment, the plate 83 serves to suppress the influence of acceleration due to heating and diffuse the fluid.

  Here, “substantially opposite direction” has the same meaning as in the first embodiment. The other flow paths, the heater for heating, and the temperature detection unit are the same as in the other embodiments.

  The plate 83 is “a plate having a plurality of holes” or “a plate having one hole near the center (referred to as an orifice plate)”. The plate 83 is provided on the downstream side of the heater and is inserted at a right angle to the flow direction of the circular pipe. By providing the plate 83, mixing and diffusion of the fluid are promoted, and application to the above simplified model becomes possible. In the embodiment shown in FIG. 16, as an example, a plate having one hole in the center is provided.

  The calibration curve may be created by plotting the relationship between an arbitrary flow rate and an elevated temperature, as in the case of the first embodiment. If the linear relationship in the calibration curve is used, the accurate flow rate Q can be known only by measuring the rising temperature ΔT.

  In this embodiment, the flow path is held so that the fluid passes almost in the opposite direction to the gravity. However, even in the case where the fluid passes in the same direction as the gravity as in the second embodiment, it is added. In particular, it is useful to provide a plate with a hole on the downstream side of the heater to promote mixing.

It is a figure explaining the basic composition of the present invention. (First embodiment) FIG. 2 is an enlarged view in the A direction in FIG. It is a figure for demonstrating a Poiseuille flow. It is a figure explaining the structure of the heater for a heating. It is a figure explaining the structure of a temperature detection part. It is a figure for demonstrating the basic principle of this invention. It is a figure for demonstrating the basic principle of this invention. It is a figure for demonstrating the behavior of a heating fluid. It is a figure explaining the relationship between a flow volume and rising temperature. It is a figure explaining the basic composition of the device for calibration curve creation. It is a figure explaining the structure of a fixed flow generator. It is a graph which shows an example of a calibration curve. It is a graph which shows time until a heating fluid reaches | attains a temperature detection part. It is a graph which shows time until a heating fluid reaches | attains a temperature detection part. It is a figure explaining the basic composition of the present invention. (Second embodiment) It is a figure explaining the basic composition of the present invention. (Third embodiment)

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 3, 71, 81 ... Flow path 2 ... Reducer 4, 72, 82 ... Heating heater 5, 73, 84 ... Thermocouple 4a ... Ring part 4b ... Conductor 41 ... Pulse voltage generator 42 ... Constant voltage power supply 43 ... Current adjusting resistor circuit 51 ... Insulating tape 52 ... Thermocouple amplifier circuit 53 ... LP filter circuit 54 ... Information Processing device 55 ... Leakage current countermeasure circuit 61 ... Constant flow rate generator 62 ... Motor with speed reducer 63 ... Traverse device 64 ... Base for syringe 65 ... Syringe 83 ... Perforated plate

Claims (10)

A flow path through which fluid passes;
A heater for heating the fluid flowing through the flow path;
A diffusion part provided in the middle of the flow path, which alleviates the influence of acceleration by heating in the heater and promotes fluid diffusion;
A temperature detection unit that is provided downstream of the heater and detects the temperature of the heating fluid;
The flow rate measuring apparatus according to claim 1, wherein the heater is disposed in the flow path or the diffusion portion.   2. The flow rate measuring device according to claim 1, further comprising an information processing device that performs control of the heater and / or signal processing of a detection signal from the temperature detection unit.   3. The flow rate measuring device according to claim 1, wherein the flow path is held so as to pass a fluid flowing through the flow path in a direction substantially opposite to gravity.   3. The flow rate measuring device according to claim 1, wherein the flow path is held so that the fluid flowing through the flow path passes in substantially the same direction as gravity.   5. The flow rate measuring device according to claim 1, wherein the diffusion unit is a reducer that reduces the tube diameter of the flow path.   5. The flow rate measuring device according to claim 1, wherein the diffusion part has a plate having at least one hole inserted at a right angle to the flow direction.   7. The flow rate measuring device according to claim 1, wherein the heating position of the fluid by the heater is substantially in the center on a virtual plane orthogonal to the flow direction of the fluid. The flow rate of the fluid is 1ml
8. The flow rate measuring device according to claim 1, wherein the flow rate measuring device is equal to or less than / min. A method of measuring the flow rate of a fluid flowing through a flow path having a diffusion part that reduces the influence of acceleration due to heating and promotes diffusion of the fluid,
Heating a portion of the fluid to form a heated fluid;
Measuring the temperature of the heated fluid;
And a step of measuring the flow rate of the fluid using a calibration curve indicating the relationship between the rising temperature of the heated fluid and the flow rate of the fluid. A method of measuring the flow rate of a fluid flowing through a flow path having a diffusion part that reduces the influence of acceleration due to heating and promotes diffusion of the fluid,
Heating a part of the fluid to form a heated fluid, and creating a calibration curve indicating the relationship between the rising temperature of the heated fluid and the flow rate of the fluid;
Heating a portion of the fluid to form a heated fluid;
Measuring the temperature of the heated fluid;
And a step of measuring the flow rate of the fluid using the calibration curve.