JPH04339219A - Thermal flowmeter - Google Patents

Abstract

PURPOSE:To achieve an accurate measurement of a fluid with an S/N ratio improved by transmitting heat securely to the fluid flowing through a pipeline. CONSTITUTION:A heater 3 for heating a fluid is provided on one entire width- wise surface of a pipeline 2 formed flat in section whose width dimensions Y are larger than height dimensions X. A flow velocity distribution of the fluid flowing through the pipeline 2 can be averaged to allow uniform transmission of heat of the heater 3 to the fluid. As a result, the S/N ratio can be improved in temperature detectors 4a and 4b. In addition, higher heat exchangeability is achieved with a larger contact between the heater 3 and the pipeline 2 thereby enabling the lowering of power consumption.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention relates to a thermal flowmeter.
In particular, it relates to a thermal flowmeter with excellent measurement accuracy.

0002

2. Description of the Related Art Conventionally, a thermal flowmeter is one type of flowmeter for measuring the flow rate of fluid flowing through a pipe. This type of thermal flowmeter will be explained by taking as an example the one shown in FIGS. 3 and 4. As shown in the figure, the thermal flowmeter 11 includes a pipe 12 having a circular cross section, and a pipe wound around the outer circumference of the pipe 12 to heat the fluid flowing inside the pipe 12. a heating circuit 15 that supplies a heating current to the heater 13, temperature detection elements 14a and 14b provided in the pipe line 12 on the upstream and downstream sides of the heater 13, and these temperature detection elements 14a. ，
There is a detection circuit 16 that calculates the flow rate of the fluid based on the detection result output from the detection circuit 14b.

[0003] A thermal flowmeter 1 having the above-mentioned configuration
According to No. 1, when a flow rate occurs in the fluid in the conduit 12, a difference occurs between the detected temperatures Ta and Tb detected by the respective temperature detection elements 14a and 14b. And detection circuit 1
6 subtracts the temperature difference ΔT (ΔT=Tb−Ta) between the detected temperatures Ta and Tb of the respective temperature detection elements 14a and 14b, and based on this temperature difference ΔT, calculates the flow rate of the fluid according to the following equation. Q=κCpΔT...(1) (where κ: function including flow velocity distribution, etc., Cp: specific heat of fluid)

0004

However, since the pipe 12 has a circular cross section, the flow velocity distribution of the flowing fluid is different between the vicinity of the inner circumference and the center of the pipe 12. There is a difference in the amount of heating near the inner periphery and in the center, causing convection in the fluid, making it difficult for the temperature detection elements 14a and 14b to accurately detect the temperature. In addition, since the specific heat of the pipe line 12 is smaller than that of the fluid (it has better thermal conductivity), the heat of the heater 13 is transferred to the pipe line 12, and the transferred heat causes the temperature detection element 14a,
14b is directly heated, and these temperature detection elements 1
There was a problem in that the S/N ratio in 4a and 14b was lowered.

[0005] This invention was made in view of the above circumstances, and provides extremely good S/S by reliably transmitting heat to the fluid.
It is an object of the present invention to provide a thermal flowmeter that can detect the temperature of a fluid based on the N ratio and obtain accurate measurement data.

[0006]

[Means for Solving the Problems] The thermal flowmeter of the present invention includes a pipe constituting a flow path, a heating section that heats a fluid flowing in the pipe, and a heating section that detects the temperature of the fluid and detects the temperature of the fluid. In a thermal flowmeter comprising a detection circuit that calculates the flow rate of fluid, the pipe is formed to have a flat cross-sectional shape with a width larger than a height, and the heating part is connected to the pipe. It is characterized by being provided over the entire width of one pipe.

[0007]

[Operation] According to the thermal flowmeter of the present invention, since the cross-sectional shape of the pipe is formed into a flat shape in which the width dimension is larger than the height dimension, the flow velocity distribution of the fluid flowing in the pipe is averaged. It is possible to uniformly transfer the heat of the heating section to the fluid. In addition, since the heating part is provided over the entire width of one of the pipes, and the contact area between the heating part and the pipe is large, the heat exchange performance between the heating part and the fluid is improved. Can be done. This allows the temperature detection element to detect the temperature of the fluid extremely well.

[0008]

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. In the figure, the reference numeral 1 is the main body of the thermal flowmeter of this embodiment, and the reference numeral 2 is a pipe constituting a fluid flow path. The pipe line 2 is made of a material such as stainless steel, a resin such as a fluororesin, or a combination of these stainless steel and resin, and has a flat cross-sectional shape, that is, a rectangular shape. Here, the width dimension (horizontal dimension) Y of the flow path in conduit 2 is the height dimension (vertical dimension)
X, and the ratio of each is set to be 1:3 or higher (height X:width Y). Furthermore, a heater (heating section) 3 is provided on the upper surface side of the conduit 2 over the entire width of the conduit 2, and this heater 3 is connected to a heating circuit 5.
It is designed to be heated by supplying heating current from. Furthermore, temperature detection elements 4a and 4b are provided on the lower surface side of the conduit 2 at positions upstream and downstream of the heater 3. Further, a detection circuit 6 is connected to these temperature detection elements 4a and 4b, and the temperature detection elements 4a and 4b are connected to each other.
The detected temperature detected by the sensor 4b is input to the detection circuit 6. Then, this detection circuit 6 subtracts the temperature difference ΔT of the fluid between the upstream side and the downstream side of the heater 3 from each detected temperature, and calculates the flow rate from this temperature difference ΔT using the above-mentioned calculation formula (1). It has become.

According to the thermal flowmeter 1 configured as described above, when fluid flows through the pipe line 2, this fluid flows through the heater 3.
heated by. As a result, a difference occurs between the detected temperatures of the temperature detection element 4a provided on the upstream side of the heater 3 and the temperature detection element 4b provided on the downstream side, and this temperature difference ΔT is subtracted by the detection circuit 6. The flow rate of the fluid is calculated.

Here, in the thermal flowmeter 1 of the above embodiment, the pipe line 2 has a rectangular cross-sectional shape, compared to the pipe line 12 having a circular cross-section used in the conventional example. The flow velocity distribution of the fluid flowing in the pipe line 2 is averaged. Thereby, the heat of the heater 3 provided on the upper surface side of the pipe line 12 can be uniformly transferred to the fluid.

Further, the width dimension Y of the flow path of the conduit 2 is made larger than the height dimension X, so that the ratio of each is set to X:Y=1:3 or more, and the heater 3 is placed on the upper surface of the conduit 2. Since the temperature detection elements 4a and 4b are provided on the lower surface side through the pipe line 2, the temperature detection elements 4a and 4b are detected by the heat transferred to the pipe line 2. can reduce direct heating. As a result, temperature detection of the fluid by the temperature detection elements 4a, 4b can be made extremely good, and S
/N ratio can be improved to obtain extremely good flow rate measurement results.

Furthermore, since the heater 3 is provided over the entire width of the conduit 2 and the contact area between the heater 3 and the conduit 2 is increased, the heat exchange performance between the heater 3 and the fluid is improved. Therefore, the amount of heating by the heater 3 can be reduced compared to the conventional example. This makes it possible to reduce power consumption and provide an extremely economical thermal flowmeter.

Note that the cross-sectional shape of the pipe line 2 in the above embodiment is not limited to that in the embodiment as long as it is a flat shape, and may be, for example, an elliptical shape with a large width dimension. Further, the ratio between the height dimension X and the width dimension Y of the conduit 2 is not limited to the example. Furthermore, the specific structure of the thermal flowmeter 1 of the above embodiment is not limited to the embodiment.

[0014]

[Effects of the Invention] As explained above, according to the thermal flowmeter of the present invention, the following effects can be obtained.

Since the cross-sectional shape of the pipe is formed into a flat shape in which the width dimension is larger than the height dimension, the flow velocity distribution of the fluid flowing inside the pipe is averaged, and the heat of the heating section is uniformly distributed to the fluid. can be transmitted to Thereby, the temperature of the fluid can be detected extremely well, and the S/N ratio in the temperature detection element can be improved to obtain extremely accurate measurement data.

[0016] Furthermore, since the heating section is provided over the entire width of one of the pipes, and the contact area between the heating section and the pipe is increased, the heat exchange performance between the heating section and the fluid is improved. be able to. Therefore, compared to the conventional example, the amount of heating in the heating section can be reduced, power consumption can be reduced, and an extremely economical thermal flowmeter can be achieved.

In particular, by providing the temperature detection element on the surface opposite to the surface on which the heating section is provided, it is possible to reduce direct heating of the temperature detection element by the heat transferred to the pipe line. The S/N ratio in the temperature detection element can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a thermal flowmeter of the present invention.

FIG. 2 is a side view of the thermal flowmeter of the present invention.

FIG. 3 is a sectional view of a conventional thermal flowmeter.

FIG. 4 is a side view of a conventional thermal flowmeter.

[Explanation of symbols]

1 Thermal flowmeter body 2 Pipeline 3 Heater (heating part) 6 Detection circuit

Claims (1)

[Claims] Claim: 1. Consists of a pipe constituting a flow path, a heating section that heats a fluid flowing within the pipe, and a detection circuit that detects the temperature of the fluid and calculates the flow rate of the fluid. In the thermal flowmeter, the pipe is formed to have a flat cross-sectional shape with a width larger than a height, and the heating part is provided over the entire width of one of the pipes. Features of thermal flowmeter.