JPH0620100Y2 - Karman vortex flowmeter - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is a Karman vortex flowmeter for determining the flow velocity and flow rate of a fluid to be measured, such as a gas, from a Karman vortex train by using a sensor such as a hosistar or thermistor More specifically, the present invention relates to a Karman vortex flowmeter which improves the sensitivity of detecting the Karman vortex street.

<Prior Art> Conventionally, as this type of Karman vortex flowmeter, those shown in FIG. 4 to FIG. 6 are known (for example, Jikken Sho 58).
-Reference 54746).

FIG. 4 is a schematic perspective view showing the principle configuration of the Karman vortex flowmeter.

FIG. 5 is a view in which the vortex detection mechanism is cut along the plane AA ′ in FIG.

FIG. 6 is a diagram for explaining FIG.

In FIGS. 4 to 5, 1 is a flow tube through which the fluid to be measured flows, 2 is a vortex generator (hereinafter referred to as “shedder”) arranged across the flow tube 1 at right angles to the flow direction of the fluid, and 3 is The vortex detection mechanism is provided on the downstream side of the shedder 2 and detects the Karman vortex train formed by the shedder 2. The vortex detection mechanism 3 includes, for example, a vortex detection mechanism housing (hereinafter referred to as “housing”) 3a fixed to the flow tube 1 and a housing 3a.
The sensor probe 3b, which is a sensor holder, has a sensor (heat-sensitive element, for example, a chip-type heat sensor) 3d attached to the tip detachably attached to the housing 3a by using a potting material or the like, and the housing 3a. A slit (3c) is provided at the center so as to be orthogonal to the flow direction of the fluid. The housing 3a has a slit 3c from one end thereof.
There is a hole leading to the sensor probe 3b.
Is inserted. The lead wire 3e from the sensor 3d is led to the outside through the inside of the sensor probe 3b.

By the way, it is said that the sensitivity of the Karman vortex train detection of the sensor 3d is proportional to the fluid temperature, proportional to the square root of the fluid density, inversely proportional to the Kalman frequency, etc. It is an external condition. Therefore, in order to change the sensitivity of Karman vortex street detection depending on the internal condition of the sensor itself, the only method is to change the physical properties of the sensor itself or to make the shape of the thermal sensor highly efficient in heat exchange.

The relationship between the sensor 3e and the sensor probe 3b is actually as shown in FIG.

In FIG. 6, the sensor 3d is exposed to the fluid to be measured in order to improve the thermal efficiency in the slit 3c, and its shape is
Since it is better to be thin and small, normally, for example, on the sensor probe 3b having a sensor mounting hole radius r = φ4 mm provided on the surface of the probe radius R = φ7.05 mm, the shedder 2
1/10 to 1/100 of the size (for example, l = 1m
The sensor 3e is mounted in the embedded form as shown in the figure, which is formed small as m, d = 2 mm and t = 0.4 mm. Then, at this time, the sensor surface and the sensor probe surface are formed flush with each other. The reason is that if only the sensor protrudes from the sensor probe surface, the entire surface will be in contact with the external environment, the mounting force will be weak, vibration will occur and the temperature change of the measured fluid will affect the measurement result. Because it will adversely affect Incidentally, FIG. 6 (B)
The arrow F indicates the direction in which the fluid to be measured flows.

With such a configuration, the Karman vortex train generated by the shedder 2 is made to flow downstream while growing, and the Karman vortex train reaching the vortex detection mechanism 3 causes fluid movement in the slit 3c. The flow rate can be measured by detecting the change as the resistance change of the sensor 3d.

<Problems to be Solved by the Invention> By the way, with such a sensor mounting structure, there is a problem that the surface area is reduced and the sensitivity is reduced. However, changing the physical properties of the sensor requires cost time for new material development. In addition, in order to improve the heat exchange efficiency of the sensor, it is necessary to take measures such as making it thin and small, and specializing the shape so that the shape has a large surface area, but this makes handling difficult. Or inferior in terms of environmental resistance, thin / small /
At present, it has not been put to practical use because forming a complex shape or the like is expensive. Especially when considering it as an aeronautical detection end, it was particularly difficult to adopt it in terms of environmental resistance.

The present invention has been made in view of the above problems of the conventional technology. The purpose of the present invention is to achieve the same Kalman sensor without deteriorating the environmental resistance of the sensor while having a simple structure. A Karman vortex flowmeter capable of improving detection sensitivity under vortex train conditions.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the present invention provides a vortex generator across a fluid to be measured in a flow tube through which the fluid to be measured is arranged, and the vortex generator causes the vortex to be generated. A row is generated, and the vortex row is detected by a vortex detection mechanism having a sensor that is arranged downstream of the vortex generator across the fluid to be measured and is exposed to the fluid to be measured. In the Karman vortex flowmeter, a micro vortex generator is provided around the sensor while maintaining the environment resistance without completely exposing the sensor alone in the fluid to generate turbulence at the level of the sensor. It is characterized in that the heat exchange efficiency is improved.

<Operation> When viewed from the minute part of the sensor, the Reynolds number becomes 1/10 to 1/100 of the whole measurement system, and even if it is turbulent at the level of the sheder size, it becomes laminar flow around the minute sensor. It is thought to be close.

Therefore, a micro vortex generator (micro vortex generator: hereinafter abbreviated as "MVG") is provided around the sensor to generate turbulence at the sensor size level for the purpose of increasing the heat exchange rate around the sensor, Improve heat exchange efficiency,
Increase detection sensitivity.

<Example> An example will be described with reference to the drawings.

In the following drawings, the same parts as those in FIGS. 4 to 6 are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a view showing a concrete embodiment of the Karman vortex flowmeter of the present invention.

FIG. 2 is a diagram for explaining FIG. 1.

In FIGS. 1 and 2, 4 is an MVG. In FIG. 1, the MV provided on the sensor probe 3b
The structure of G4 does not expose the sensor 3e to the fluid completely, and keeps the environment resistance equivalent to the conventional one,
A groove having the size of the sensor (here, a groove having a similar length) is provided around the.

With such a structure, the flow of the fluid on the conventional sensor, which is close to the laminar flow at the level of the size of the sensor, as shown in FIG. A turbulent flow is seen above the sensor at the size level of the sensor, and the heat exchange efficiency with respect to the sensor 3e can be improved, resulting in an increase in detection sensitivity.

The experimental results are shown. In the experiment, as shown in FIG. 2 (B), a posistor is used as a sensor of the vortex detection mechanism 3, a constant voltage is applied from the drive circuit 5 to this posistor, and the detection output (voltage change) of the posistor due to the change of fluid. Is amplified by an amplifier 6 and is indicated by an indicator 7, which is obtained. As a result, when the sensor resistance R ₁ = 182.0Ω was measured, when the frequency due to Karman vortex was 30 Hz,
The detection output is 0.2 to 0.3 V in the prior art.
When the present invention is adopted, a detection output of about 0.6 Vrms can be obtained when only about rms can be obtained. or,
Regarding the sensor resistance R ₂ = 216.2Ω, the detection output when the frequency due to the Karman vortex is 30 Hz can obtain only about 0.4 to 0.5 Vrms in the prior art, and the present invention is adopted. 0.6 to 0.7
It was confirmed that the detection output was about Vrms. Therefore, by adopting the present invention, the sensor sensitivity can be surely increased.

By the way, the present invention is not limited to the configuration shown in FIG. For example, it can be configured as shown in FIG. 3 showing another embodiment.

FIG. 3 (A) shows a structure in which a groove array is provided in place of the groove of FIG. 1, and FIG. 3 (B) shows the structure around the sensor (here, the entire surface of the sensor is against the flow of fluid). In this case, the same effect as in FIG. 1 can be obtained by providing an MVG composed of smaller projections (or a row of projections).

<Effects of the Invention> Since the present invention is configured as described above, it has the following effects.

: The sensor sensitivity can be increased.

: It is possible to obtain a superior detection result due to the turbulent flow generation effect without impairing the high cost and deterioration of the environmental resistance of the sensor.

: It has a great effect on measurement such as an air flow sensor that can obtain only a minute output, and the effect of implementation is extremely high.

[Brief description of drawings]

FIG. 1 is a diagram showing a concrete embodiment of the Karman vortex flowmeter of the present invention, FIG. 2 is a diagram used for explaining FIG. 1, FIG. 3 is a diagram showing other embodiments, and FIG. A schematic perspective view showing the principle configuration of the Karman vortex flowmeter, FIG. 5 is A in FIG.
FIG. 6 is a diagram in which the vortex detection mechanism is cut along the −A plane, and FIG. 6 is a diagram for explaining FIG. 5. 1 ... Flow tube, 2 ... Vortex generator (shedder), 3 ... Vortex detection mechanism, 4 ... Micro vortex generator (MVG).

Claims (1)

[Scope of utility model registration request] 1. A vortex generator is arranged in a flow tube through which the fluid to be measured flows across the fluid to be measured, and a vortex row is generated by the vortex generator, and the vortex row is placed downstream of the vortex generator. In a Karman vortex flowmeter for detecting by a vortex detection mechanism having a sensor arranged so as to be exposed to the fluid to be measured, the sensor alone being completely immersed in the fluid. A Karman vortex characterized by improving the heat exchange efficiency of the sensor by providing a minute vortex generator around the sensor while maintaining environmental resistance without exposing it to generate turbulence at the level of the sensor. Type flow meter.