JPH0334651Y2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a thermal mass flowmeter that determines the mass flow rate in a main channel by measuring the flow rate in a bypass channel.

Prior Art A thermal mass flowmeter that has a bypass channel that flows in a laminar flow and a main channel that flows in a laminar flow with a known flow rate, and measures the total flow rate by measuring the flow rate in the bypass channel. is known, for example, as disclosed in Japanese Patent Publication No. 54-3743. This conventional technology has a front surface, a rear surface, and an outer circumferential surface connected to both surfaces in the main flow path, and a through hole that communicates the front surface and the rear surface communicates with the outer circumferential surface, so that the fluid flowing inside forms a laminar flow. By connecting disks in parallel with at least one communication passage having a length/diameter ratio suitable for The total flow rate is calculated based on the measured value of the flow path.

Problems with the prior art In the above-mentioned prior art, the grooves, which are communication paths in the disc member, are formed into a smooth flat surface of the disc member by processing means such as chemical etching, with a width of 0.2 mm.
A groove with a height of 0.063 mm is provided, and usually
Multiple grooves are drilled in the radial direction. However, it is difficult to accurately align the machining dimensions of each of these minute communication passages, and as a result, in order to obtain the correct flow rate ratio, each disc member must be actually measured and recorded in advance. Based on the results, the correct flow rate ratio was assembled. For this reason, assembly and adjustment are inconvenient and require a large number of man-hours, and on the other hand, an accurate flow rate cannot be obtained because the correct flow rate ratio cannot be obtained.

Means for Solving the Problems In order to solve the above-mentioned problems, in the present invention, a plurality of thin tubes of equal length and equal diameter are arranged to flow in a laminar flow similar to the conventional disk member, The flow rate ratio of each thin tube to the flow rate flowing through the bypass channel is set to be an integral multiple, thereby making it possible to obtain a simple and accurate flow rate ratio.

Specific Example FIG. 1 is a diagram for explaining one embodiment of the present invention. In the figure, 1 is a main flow path, and in the main flow path 1, a thin tube 11 of equal length and equal diameter is inserted. It is attached as one piece by a fixing plate 12 that is fixed through the hole. A bypass flow path 2 is inserted into the openings 21 and 22 opening into the main flow path wall, sandwiching the thin tube bundle 10 thus obtained.
A heater 3 is provided in the bypass flow path, and coils 4 and 5 having equal resistance are wound on the upstream and downstream sides of the heater 3, respectively, and the fluid changes as the fluid is heated by the heater 3. The mass flow rate is determined from the resistance change between the coil resistance 5 and the coil resistance 4 before heating. Accordingly, in the present invention, the ratio of the flow rate flowing through the thin tube 11 to the flow rate flowing through the bypass channel 2 is set to be an integral multiple, and this is based on the following principle. That is, assuming that the flow is laminar, the flow rate Q is expressed as Q=πr ⁴ (P ₁ −P ₂ )/8 μl (1). Here, r is the radius of the tubule, P ₁ ,
P ₂ is the pressure before and after the thin tube 11, μ is the viscosity coefficient,
is the length of the tubule. Pressure P ₁ before and after the thin tube 11,
Since P ₂ is also the pressure between the openings 21 and 22 of the bypass flow path, in equation (1), (P ₁ − P ₂ )
are equal. Furthermore, in order to equalize the flow rate Q, if the length of the bypass flow path is L and the radius is R, then from equation (1) above, the length and diameter must be determined to satisfy the relationship l/L=r ⁴ /R ⁴ (2). Substantially equal flow ratios are obtained by applying the relationship . By bundling N such thin tubes, a flow rate of N+1 can be obtained. Furthermore, according to equation (2), a thin tube with an arbitrary flow rate ratio can be easily obtained by selecting the length and diameter.

Effects As is clear from the above explanation, according to the present invention, a highly accurate flow rate ratio can be obtained in a simple manner by combining thin tubes that can be manufactured with high precision, so a high-precision mass flowmeter can be produced at an inexpensive price. can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining one embodiment of the thermal mass flowmeter of the present invention, where Figure A is a side view and Figure B is a side view.
It is a sectional view taken along the line BB in the figure. 1...Main flow path, 2...Bypass flow path, 11...
Thin tube, 12... fixed plate.

Claims (1)

[Scope of utility model registration request] A main channel in which a plurality of thin tubes are inserted through which the fluid to be measured flows in a laminar flow, a bypass channel that opens at a position on the tube wall of the main channel across the thin tubes and flows in a laminar flow, and this bypass flow. A thermal mass flowmeter that has a heating means for heating a fluid flowing in a passage, and a detection means for detecting a temperature difference between the front and rear streams of the heating means, and calculates a mass flow rate from the temperature difference, the plurality of A thermal mass flowmeter characterized in that the cross-sectional areas of the thin tubes are equal and the flow rate flowing through one of the thin tubes is an integral multiple of the flow rate flowing through the bypass flow path.