KR101824866B1 - Thermal Micro Flow Meter and Flow Measuring Method Using Thereof - Google Patents

Abstract

The present invention relates to a thermal micro-flowmeter and a flow rate measuring method using the same. To this end, a thermal micro-flowmeter of the present invention includes: a pipe (100) through which a fluid (200) flows; a heater (300) installed in the pipe (100) and heating the fluid (200); a front temperature sensor (400) installed in an upper flow of the heater (300); a rear temperature sensor (410) installed in a lower flow of the heater (300); and a control portion (500) for calculating a flow rate of the fluid (200) based on output signals of the front temperature sensor (400) and the rear temperature sensor (410).

Description

TECHNICAL FIELD [0001] The present invention relates to a thermal micro flow meter and a flow measurement method using the micro flow meter.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter, and more particularly, to a thermal micro flow meter capable of measuring a very small flow rate and a flow measurement method using the same.

As the industry becomes more sophisticated, technologies are being developed to accurately measure the flow rate of fluids such as gas and liquid in various industries. Typical methods for measuring fluid flow include orifice, differential pressure flowmeter, vortex flowmeter, ultrasonic flowmeter, and area flowmeter. These flowmeters are volumetric flowmeters that only measure the volume of a fluid. However, if the temperature or pressure of the measurement site is different from the design value, the volume expansion and contraction There is a disadvantage that it can not compensate.

In recent years, a thermal mass flowmeter has been proposed as a method that can relatively accurately measure the mass flow rate without being influenced by the pressure or temperature around the fluid. A thermal mass flowmeter uses the fact that when a heated object is placed in a flowing fluid, heat transfer occurs between the fluid and the heated object, the heated object is cooled, and the rate of cooling is a function of the flow rate. It is a flow meter that converts to mass flow rate by measuring. A thermal mass flowmeter is often used as a mass flow controller in combination with a flow control valve.

 Typical thermal mass flowmeters include Bipass Capillary, which is widely used for low-flow gas measurement, pipe direct heating type flow meter used for measuring minute flow of liquid, and insertion type thermal flow meter suitable for large flow measurement such as large diameter duct (Insertion Thermal Mass Flow Meter).

Such a conventional thermal mass flow meter is disclosed in Korean Patent Publication No. 2005-0120922 ('mass flow rate sensor', 2005.12.26), Japanese Patent No. 3266707 (Nov. 11, 2002), Japanese Patent No. 4793098 Japanese Patent Laid-Open Publication No. 2005-172445 (June 30, 2005), Japanese Laid-Open Patent Application No. 2007-127466 (2007.5.24), Japanese Laid-Open Patent Application No. 2007-322207 (2007.12.13), US Patent No. 5,222,395 .29) and others.

In particular, a flow meter for measuring a very small (or very slow) fluid flow rate is called a thermal micro flow meter. These thermal micro flow meters are used when the flow rate of the fluid is in the range of approximately 0.001 to 0.1 m / s.

FIG. 1 is a diagram showing a schematic structure and operation principle of a conventional micro flow meter, and FIG. 2 is a graph showing a temperature according to a position of a temperature sensor in the flow meter shown in FIG. 1 and 2, the fluid 20 flows at a very slow rate inside the pipe 10, a first temperature sensor 40 is installed upstream of the heater 30, and a heater (not shown) ..., n temperature sensors 41, 42, ..., 49 are provided downstream of the first, second, third,. The temperature distribution 35 of the fluid when the heater 30 generates heat is shown through simulation.

As shown in the graph of FIG. 2, it can be seen that the temperature of the fluid 20 passes through the heater 30, and the flow rate is measured by sensing the temperature. The first temperature sensor 40 upstream of the heater 30 is used to determine the temperature of the fluid 20.

The conventional thermal type flow meter as shown in FIGS. 1 and 2 has a disadvantage in that a plurality of temperature sensors are used, and the measurement range of the flow rate is not wide.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and it is an object of the present invention to provide a thermal micro flow meter capable of measuring a flow rate of a fluid using a minimum temperature sensor, .

A second object of the present invention is to provide a thermal type micro flow meter having a wide measurement range of flow rate, which can be measured by one flow meter even if the flow rate of the fluid is low or high, and a flow rate measurement method using the same.

In order to achieve the above object, the present invention provides a thermal type flow meter, comprising: a pipe (100) through which a fluid (200) flows; A heater 300 installed in the pipe 100 to heat the fluid 200; A front temperature sensor 400 installed upstream of the heater 300; A rear temperature sensor 410 installed downstream of the heater 300; And a control unit 500 for calculating a flow rate of the fluid 200 based on the output signals of the front temperature sensor 400 and the rear temperature sensor 410.

In addition, the controller 500 can control the heater 300 to maintain a constant temperature.

In addition, the front temperature sensor 400, the heater 300, and the rear temperature sensor 410 may be installed at equally spaced intervals or at a place where the temperature difference according to the flow velocity is greatest.

In addition, the control unit 500 calculates the flow rate by multiplying the correction coefficient by the correction coefficient. The correction coefficient is calculated by the cross-sectional area of the pipe, the specific heat of the fluid, the installation interval of the front temperature sensor 400 and the heater, The installation spacing of at least one of the first,

Also, the fluid 200 preferably flows at a rate of 0.001 to 0.05 m / s.

When the speed of the fluid 200 is in the range of 0.001 to 0.01 m / s, the control unit 500 calculates the flow rate based on the output signal of the front temperature sensor 400, When it is in the range of more than 0.01 to 0.05 m / s, the control unit 500 calculates the flow rate based on the output signal of the rear temperature sensor 410.

Further, the piping 100 includes a first flow measuring unit 110 having a first cross-sectional area; And a second flow rate measuring unit 130 having a second cross sectional area different from the first cross sectional area are connected in series and the first flow rate measuring unit 110 includes a first front temperature sensor 114, The second heater 132 and the second rear temperature sensor 136 are sequentially arranged in the second flow rate measuring unit 130. The second front temperature sensor 134, the second heater 132, As shown in Fig.

In addition, a flow rate measuring section is provided continuously behind the second flow rate measuring section 130 at a ratio equal to the ratio of the first and second cross-sectional areas, and the continuously-installed flow rate measuring section is also provided with a front temperature sensor, A set of sensors can be installed in the same sequential manner.

It is further preferable that the cross-sectional areas of the first and second cross-sectional areas and the continuously-installed flow rate measuring sections are equal in height and different in width from each other.

In addition, the first cross-sectional area is relatively smaller than the second cross-sectional area.

A first transition part 120 is provided between the first flow measuring part 110 and the second flow measuring part 130 to induce a progressive change in sectional area.

The control unit 500 can determine the flow direction of the fluid 200 based on the output signals of the front temperature sensor 400 and the rear temperature sensor 410.

In another aspect of the present invention, there is provided a method of measuring flow rate of a thermal micro flow meter, comprising: a step (S100) of flowing a fluid (200) through a pipe (100); A step S120 of heating the heater 300 installed in the pipe 100 by the control unit 500; The control unit 500 receives the output of the front temperature sensor 400 provided upstream of the heater 300 and the output of the rear temperature sensor 410 installed downstream of the heater 300 (S140); The control unit 500 calculates the flow rate of the fluid 200 based on the output signals of the front temperature sensor 400 and the rear temperature sensor 410 (S160); And outputting the calculated flow rate based on the output of the front temperature sensor 400 when the flow rate is equal to or lower than the reference flow rate and outputting the flow rate calculated based on the output of the rear temperature sensor 410 when the flow rate exceeds the reference flow rate (S180). The flow rate measuring method of the thermal type micro flow meter may further comprise:

In another embodiment, in the flow rate measurement method of the thermal micro flow meter described above, the first flow rate measurement unit 110 and the second flow rate measurement unit 130 having different cross-sectional areas are connected in series to each other. A step S200 of flowing the fluid 200 whose flow rate varies through the flow path; A step S220 of heating the respective heaters installed in the pipe 100 by the control unit 500; The control unit 500 receives (S240) the output of the temperature sensors of the first flow measuring unit 110 and the temperature sensors of the second flow measuring unit 130; The control unit 500 calculates the flow rate of the fluid 200 based on the outputs of the temperature sensors of the first flow measuring unit 110 and the second flow measuring unit 130 (S260); And outputs the calculated flow rate based on the output of the temperature sensors of the first flow rate measuring unit 110 when the flow rate is equal to or less than the reference flow rate. When the flow rate exceeds the reference flow rate, And a step (S280) of outputting the calculated flow rate based on the output of the micro flow meter.

According to the embodiment of the present invention, since the two temperature sensors provided at the front and rear of the heater are used, the structure of the flow meter is simple, the manufacturing cost is low, and the number of temperature sensors is two, have.

In addition, even if the flow rate of the fluid is low or high, it is possible to measure the flow rate with one flow meter, which is advantageous in that the measurement range of the flow rate is wide. Therefore, it is not necessary to provide a flowmeter for each range of the flow rate, and even when the flow rate changes dynamically, it is possible to accurately measure the flow rate correspondingly.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description of the invention given below, serve to further understand the technical idea of the invention. And should not be construed as interpreted.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a schematic structure and operation principle of a conventional micro flow meter,
FIG. 2 is a graph showing the temperature according to the position of the temperature sensor in the flow meter shown in FIG. 1,
3 is a graph showing a result of simulating a temperature distribution while varying a flow rate around a heater,
FIG. 4 is a schematic view showing a schematic structure of a thermal micro flow meter according to a first embodiment of the present invention;
FIG. 5 is a schematic view showing a schematic structure of a thermal micro flow meter according to a second embodiment of the present invention. FIG.
FIG. 6 is a flow chart of a flow measurement method showing a schematic operation sequence of the first embodiment shown in FIG. 4;
7 is a flowchart of a flow measurement method showing a schematic operation sequence of the second embodiment shown in Fig.

Hereinafter, the configuration of the present invention will be described in detail with reference to the accompanying drawings. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail.

It is noted that the terms "comprises" or "having" in this application are intended to specify the presence of stated features, integers, steps, operations, elements, parts, or combinations thereof, , Steps, operations, components, parts, or combinations thereof, as a matter of principle.

Also, unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

1st Example  Configuration and behavior

First, FIG. 3 is a graph showing the result of simulating the temperature distribution while varying the flow rate around the heater in the thermal micro flow meter. The horizontal axis in FIG. 3 represents the distance and the vertical axis represents the temperature. In FIG. 3, distances 120 to 150 on the horizontal axis are areas where the heater is present.

Figure 3 is a flow rate of the fluid in a simulated in five flow rate of 0,0001, 0.001, 0.01, 0.1, 1 m 3 / s. As shown in FIG. 3, it can be seen that, in the front of the heater, the larger the flow rate is, the more slowly the temperature is changed, and the temperature is suddenly changed near the heater. On the other hand, at the rear of the heater, it can be seen that the larger the flow rate, the larger the temperature change (the larger the temperature difference is).

As can be seen from the simulation results shown in Fig. 3, as the flow rate in front of the heater (for example, 0.0001 to 0.001) is lower than the moving velocity of the fluid flowing from the front to the rear, Because it is faster.

Accordingly, the inventor of the present invention has focused on the simulation test result as shown in FIG. 3, and suggests that a temperature sensor installed not only in the rear of the heater but also in front of the heater can also be used for measuring the flow rate at a low flow rate. For reference, the temperature sensor installed in front of the heater in the conventional flow meter is only used to measure the temperature of the fluid.

FIG. 4 is a configuration diagram showing a schematic structure of a thermal micro flow meter according to the first embodiment of the present invention. FIG. As shown in FIG. 4, the fluid 200 flows into the piping 100. The cross section of the pipe 100 may be circular or rectangular. And the fluid may be gas or liquid. As used herein, "forward" means upstream based on the flow of fluid and "rear" means downstream.

The heater 300 is installed in the pipe 100 and may be any of the outer surface, the thickness, and the inner surface of the pipe 100 as long as it can transmit heat to the fluid 200. The heater 300 is a typical embodiment in which the temperature is controlled for precise heat generation, but may be light or other heat source.

The front temperature sensor 400 is installed upstream of the heater 300 and the rear temperature sensor 410 is installed downstream of the heater 300. It is preferable that the interval between the front temperature sensor 400, the heater 300 and the rear temperature sensor 410 is the same (for example, 10 mm to 100 mm) for accurate flow rate calculation. However, if the interval is too close, the heat transmitted directly from the heater 300 can be sensed. If the interval is too long, there is a possibility that the temperature changes due to the external influence. In particular, the front temperature sensor 400, the heater 300, and the rear temperature sensor 410 are installed in parallel along the axial direction of the pipe 100 as well as at the same interval.

The control unit 500 is connected to the front temperature sensor 400, the heater 300, and the rear temperature sensor 410, respectively. In particular, the control unit 500 receives the sensed temperature value from the front and rear temperature sensors 400 and 410, and outputs a control command to the heater 300 to control the heat generation to a desired temperature. The controller 500 may be implemented as a microcomputer or a computer.

6 is a flowchart of a flow measurement method showing a schematic operation sequence of the first embodiment shown in Fig. As shown in FIG. 6, first, the fluid 200 flows through the pipe 100 (S100).

Then, the control unit 500 heats the heater 300 installed in the pipe 100 to a predetermined temperature (S120).

Then, the control unit 500 receives the outputs of the front temperature sensor 400 and the rear temperature sensor 410 (S140).

Next, the control unit 500 calculates the flow rate of the fluid 200 based on the output signals of the front temperature sensor 400 and the rear temperature sensor 410 (S160). To this end, the control unit 500 incorporates a previously calculated correction coefficient. The correction coefficient is a constant determined by referring to the cross-sectional area of the pipe 100, the specific heat of the fluid 200, and the intervals between the front and rear temperature sensors 400 and 410 and the heater 300. Such correction factors can be determined by trial and error through simulation or experiment. The correction coefficients thus determined are stored in the control unit 500, and then multiplied by the output signals of the front temperature sensor 400 and the rear temperature sensor 410, respectively, to calculate the flow velocity. This is because the operating range is defined as the range in which the flow rate is proportional to the correction coefficient and the sensor voltage. Further, since the cross-sectional area of the pipe 100 is known, the flow rate can be calculated based on the calculated flow rate.

If the speed of the fluid 200 is in the range of 0.001 to 0.01 m / s, the control unit 500 calculates the flow rate based on the output signal of the front temperature sensor 400. The reference flow rate is defined as the flow rate at a reference speed of 0.01 m / s. When the velocity of the fluid 200 is very slow, such as in the range of 0.001 to 0.01 m / s, the linear region appears clearly from the front due to the influence of the heater as shown in FIG. In the case where the velocity of the fluid 200 is slower than 0.001 m / s, when the change of the curve is not large as shown in FIG. 3 and the velocity of the fluid 200 is faster than 0.01 m / s, And the correction factor may be inaccurate.

If the speed of the fluid 200 is in the range of more than 0.01 to 0.05 m / s, the control unit 500 calculates the flow rate based on the output signal of the rear temperature sensor 410 (S180). The flow rate calculated based on the output of the rear temperature sensor 410 is output (S180) when the speed of the fluid is comparatively sufficient (that is, not very slow) such as more than 0.01 to 0.05 m / s.

In addition, the controller 500 determines the flow direction of the fluid 200 based on the output signals of the front temperature sensor 400 and the rear temperature sensor 410. For example, since the temperature of the fluid 200 increases while passing through the heater 300, it can be determined that the fluid 200 flows from the front to the rear when the front temperature is low and the rear temperature is high. Conversely, when the temperature of the fluid 200 rises while passing through the heater 300, the front temperature is high, and when the rear temperature is low, it can be determined that the fluid 200 flows from the back to the front.

Second Example  Configuration and behavior

5 is a schematic diagram showing a schematic structure of a thermal micro flow meter according to a second embodiment of the present invention. 5, the piping 100 includes a first flow measurement unit 110, a first transition unit 120, a second flow measurement unit 130, a second transition unit 140, And the measuring unit 150 are connected in series. The cross section of the pipe 100 may be circular or may have a rectangular cross section having a constant width.

The first and second transition portions 120 and 140 are formed in a tapered shape in order to prevent a sharp change in cross section between flow measuring portions having different cross sections.

A first front temperature sensor 114, a first heater 112 and a first rear temperature sensor 116 are sequentially installed in the first flow rate measuring unit 110 in the same manner as in the first embodiment, .

The cross-sectional area of the second flow measuring part 130 is larger than the cross-sectional area of the first flow measuring part 110. A second front temperature sensor 134, a second heater 132 and a second rear temperature sensor 136 are sequentially installed in the second flow rate measuring unit 130 in the same manner as in the first embodiment, .

The sectional area of the third flow measuring part 150 is larger than the sectional area of the second flow measuring part 130. Particularly, it is preferable that the change in the sectional area size of the first, second and third flow measuring units 110, 130 and 150 is the same (for example, by 20%). A third front temperature sensor 154, a third heater 152 and a third rear temperature sensor 156 are sequentially installed in the third flow measuring unit 150 in the same manner as in the first embodiment, .

7 is a flowchart of a flow measurement method showing a schematic operation sequence of the second embodiment shown in Fig. As shown in FIGS. 5 and 7, the fluid flows through the first, second, and third flow measuring units 110, 130, and 150 (S200).

Next, the control unit 500 heats the first, second and third heaters 112, 132 and 152 to a constant temperature (S220).

Next, the control unit 500 receives the outputs of the first, second and third front temperature sensors 114, 134 and 154 and the first, second and third rear temperature sensors 116, 156 and 156 (S240).

The controller 500 then determines the flow rate and flow rate based on the outputs of the first, second and third front temperature sensors 114,134 and 154 and the first, second and third rear temperature sensors 116,136 and 156 (S260). A specific method of this is similar to that of the first embodiment, and thus a description thereof will be omitted.

Next, the three flow rates calculated by the first, second and third flow rate measuring units 110, 130, and 150 are averaged to find a range of the approximate flow rate. When the average flow rate is equal to or less than the first reference flow rate, the flow rate calculated based on the output of the temperature sensors of the first flow rate measurement unit 110 is output.

If the average flow rate is between the first reference flow rate and the second reference flow rate, the flow rate calculated based on the output of the temperature sensors of the second flow rate measurement unit 130 is output.

If the average flow rate exceeds the second reference flow rate, the flow rate calculated based on the output of the temperature sensors of the third flow rate measurement unit 150 is output.

This means that as the flow rate increases, the flow rate is made slower by passing through the pipe having a larger cross-sectional area, and the measured value of the temperature sensor at that time is used.

Modified embodiment

In the second embodiment shown in FIG. 5, the cross-sectional area gradually increases in the flow direction of the fluid. However, the cross-sectional area of the cross-sectional area gradually decreases. It should be interpreted as belonging to.

In the second embodiment shown in FIG. 5, the flow measuring unit having a change in sectional area over three stages has been shown and described, but the flow measuring unit may be composed of two stages or four or more stages. It should also be understood that this also falls within the scope of the claims of the present invention.

Although the present invention has been described in connection with the preferred embodiments set forth above, it will be readily appreciated by those skilled in the art that various other modifications and variations can be made without departing from the spirit and scope of the invention, It is obvious that all modifications are within the scope of the appended claims.

10: piping,
20: fluid,
30: heater,
35: temperature distribution,
40: first temperature sensor,
41, 42, 49: second, third, ..., n temperature sensors,
100: piping,
110: first flow measuring unit,
112: first heater,
114: first front temperature sensor,
116: first rear temperature sensor,
120: first transition portion,
130: second flow measuring unit,
132: second heater,
134: second front temperature sensor,
136: second rear temperature sensor,
140: second transition portion,
150: third flow rate measuring unit,
152: third heater,
154: third front temperature sensor,
156: third rear temperature sensor,
200: fluid,
300: heater,
400: front temperature sensor,
410: rear temperature sensor,
500:

Claims (14)

In the thermal type flow meter,
A pipe 100 in which the fluid 200 flows at a rate of 0.001 to 0.05 m / s;
The piping (100)
A first flow measuring part (110) having a first cross sectional area; And
(130) having a first cross-sectional area and a second cross-sectional area different from the first cross-sectional area are connected in series,
A first front temperature sensor 114, a first heater 112 and a first rear temperature sensor 116 are sequentially installed in the first flow rate measuring unit 110,
A second front temperature sensor 134, a second heater 132, and a second rear temperature sensor 136 are sequentially installed in the second flow rate measuring unit 130,
And a control unit 500 for calculating a flow rate of the fluid 200 based on output signals of the first and second front temperature sensors 114 and 134 and the first and second rear temperature sensors 116 and 136 ,
When the speed of the fluid 200 is in the range of 0.001 to 0.01 m / s, the control unit 500 calculates the flow rate based on the output signals of the first and second front temperature sensors 114 and 134,
When the speed of the fluid 200 is in the range of more than 0.01 to 0.05 m / s, the controller 500 calculates the flow rate based on the output signals of the first and second rear temperature sensors 116 and 136 Wherein the micro-flow meter is a micro-flow meter. The method according to claim 1,
Wherein the controller (500) controls the first and second heaters (112, 132) to maintain a constant temperature. The method according to claim 1,
Wherein the first front temperature sensor (114), the first heater (112), and the first rear temperature sensor (116) are installed at equally spaced intervals or at a position where the temperature difference according to the flow velocity is greatest. . The method according to claim 1,
The control unit 500 calculates the flow rate by multiplying the correction coefficient by the flow rate,
The correction coefficient is calculated based on a cross sectional area of the pipe, a specific heat of the fluid, an installation interval of the first front temperature sensor 114 and the first heater 112, a distance between the first rear temperature sensor 116 and the first heater 112). ≪ RTI ID = 0.0 > 11. < / RTI > delete delete delete The method according to claim 1,
A flow rate measuring part that is changed in the same ratio as the ratio of the first and second cross sectional areas is continuously provided in the rear of the second flow rate measuring part 130,
Wherein a set of a front temperature sensor, a heater, and a rear temperature sensor are also sequentially installed in the flow measuring unit continuously installed. 9. The method of claim 8,
Sectional areas of the first and second cross-sectional areas and the continuously-installed flow rate measuring sections are equal in height and different in width from each other. The method according to claim 1,
Wherein the first cross-sectional area is smaller relative to the second cross-sectional area. The method according to claim 1,
And a first transition part (120) is provided between the first flow measurement part (110) and the second flow measurement part (130) to induce a progressive change in sectional area. The method according to claim 1,
Wherein the control unit (500) determines the flow direction of the fluid (200) based on output signals of the first and second downstream temperature sensors (114, 116). delete A method for measuring flow rate of a thermal micro flow meter according to claim 1,
A step S200 of flowing a fluid 200 whose flow rate varies through a pipe 100 connected in series with a first flow measuring part 110 and a second flow measuring part 130 having different cross sectional areas;
The control unit 500 heats each of the heaters installed in the pipe 100 (S220);
The control unit 500 receives the outputs of the temperature sensors of the first flow measurement unit 110 and the temperature sensors of the second flow measurement unit 130 (S240).
The control unit 500 calculates a first flow rate based on the output of the temperature sensors of the first flow rate measurement unit 110 and outputs the second flow rate based on the output of the temperature sensors of the second flow rate measurement unit 130. [ Calculating a flow rate of the fluid 200 by an average of the first and second flow rates (S260); And
And outputs the calculated flow rate based on the output of the temperature sensors of the first flow rate measuring unit 110 when the average flow rate is equal to or less than the reference flow rate. When the average flow rate exceeds the reference flow rate, And outputting the calculated flow rate based on the output of the temperature sensors of the thermal micro flow meter.

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