CN110873591A - Gas micro-flow sensing device based on molecular flow transmission - Google Patents

Abstract

The invention relates to a gas micro-flow sensing device based on molecular flow transmission: the purpose of the invention is ^to solve the problem that the existing gas sensing device cannot measure ^10-8 Pam ³ s ^{- 1-10-10- 3} Pam ³ s ^-1 level gas flow problem, the gas micro-flow sensing device based on molecular flow transmission provided by the present invention includes a differential pressure transmitter, a gas micro-flow sensing element, a first valve, a side Through the valve and bypass pipeline, the conductance C of the gas micro-flow sensing device can be passed through.

Determine, the measured gas flow Q can be calculated and determined by the formula Q=C×ΔP. The gas micro-flow sensing device based on molecular flow transmission has constant and controllable conductance in the range of atmospheric pressure, and the manufacturing process is simple and flows through it. The gas flow state is in the molecular flow state and so on. The present invention also provides a method for measuring gas micro-flow using the above-mentioned molecular flow transmission-based gas micro-flow sensing device.

Description

A gas micro-flow sensing device based on molecular flow transmission

technical field

The invention belongs to the field of gas micro-flow measurement, in particular to a gas micro-flow sensing device based on molecular flow transmission.

Background technique

In metering experiments, most of the gas flow rate is measured by high-precision gas flow meters. For example, when measuring the gas flow of the order of 10 ^-2 Pam ³ s ^-1 or more, a constant pressure gas flow meter is used, and when measuring the gas flow of the order of 10 ^-8 Pam ³ s ^-1 or less, a quadrupole mass spectrometer is used. When measuring the gas micro-flow of the order of 10 ^-8 -10 ^-3 Pam ³ s ^-1 , it takes a long time to measure the gas flow with a constant pressure gas flowmeter, the accuracy is poor, and the measurement range is narrow; the cost of measuring the gas flow with a quadrupole mass spectrometer It is very high and the device layout is complicated. Therefore, there is an urgent need for a gas sensing device that can quickly, accurately and cost-effectively measure the micro-flow of gas in the order of 10 ^-8 -10 ^-3 Pam ³ s ^-1 .

The invention discloses a gas micro-flow sensing device based on molecular flow transmission, which can be used to accurately measure the gas micro-flow, so that the gas flow states flowing through it are all in the molecular flow state, and the gas micro-flow measurement has high precision, high precision and high accuracy. Features of high efficiency and simplicity.

SUMMARY OF THE INVENTION

A gas micro-flow sensing device based on molecular flow transmission includes a differential pressure transmitter, a gas micro-flow sensing element, a first valve, a bypass valve, and a bypass pipeline.

The gas micro-flow sensing element is connected with the differential pressure transmitter through the first valve, and the bypass pipeline is connected with the differential pressure transmitter through the bypass valve; the conductance C of the gas micro-flow sensing element can be determined by calculation .

The differential pressure transmitter measures the dynamic differential pressure at both ends of the gas micro-flow sensing element.

The function of the bypass pipeline is that when the bypass valve is opened, the gas to be tested can quickly pass through the bypass pipeline.

The material used in the gas micro-flow sensing element is double-pass porous alumina, the specification is AAO-DP-12, the pore diameter is 70nm, the pore spacing is 110nm, the pore depth is 50-70μm, and the conductance is maintained under the condition of vacuum to atmospheric pressure. constant.

The gas micro-flow sensing device based on molecular flow transmission can ensure that the gas flow state flowing through it is in the molecular flow state when measuring the gas flow rate.

The gas micro-flow sensing device based on molecular flow transmission is an all-metal vacuum system, which can reduce measurement errors caused by small molecular gas permeation.

The conductance C of the gas micro-flow sensing element can be determined by the following formula:

where A is the exposed area of the gas micro-flow sensing element, σ is the number of nanopores per unit area, R is the gas constant of the experimental gas, T is the ambient temperature, μ is the molar mass of the gas, and d is the gas micro-flow transmission rate. The sensing element adopts the nanopore diameter of the material, and l is the depth of the nanopore of the material used for the gas micro-flow sensing element.

The system for measuring gas micro-flow by the gas micro-flow sensing device based on molecular flow transmission includes: a differential pressure transmitter, a gas micro-flow sensing element, a first valve, a bypass valve, a bypass pipeline, and a second valve , The gas to be tested flows into the pipeline, the third valve, and the dry pump.

The gas inflow pipeline to be measured is connected to the gas micro-flow sensing device based on molecular flow transmission through a second valve, and the dry pump is connected to the gas micro-flow sensing device based on molecular flow transmission through a third valve.

The first valve, the bypass valve, the second valve and the third valve are all Swagelok ball valves.

The gas micro-flow sensing device based on molecular flow transmission can ensure that the gas flow state flowing through it is in the molecular flow state when measuring the gas flow rate.

The range of the gas micro-flow sensing device based on molecular flow transmission is the product of the range of the differential pressure transmitter and the conductance of the gas micro-flow sensing element.

The gas micro-flow sensing device based on molecular flow transmission measures the gas micro-flow through the following steps: opening the bypass valve and the third valve, opening the dry pump, opening the second valve and closing the bypass valve after a period of stability , and record the indication after the differential pressure transmitter is stable.

The gas flow Q measured by the gas micro-flow sensing device based on molecular flow transmission can be determined by the following formula:

Q=C×ΔP (2)

Among them, C is the conductance of the gas micro-flow sensing element, and ΔP is the indication displayed by the differential pressure transmitter.

Compared with the prior art, the beneficial effects of the present invention are embodied in:

1. When any gas flows through the present invention, it is always in the state of molecular flow, and the present invention can be used to measure the micro-flow rate of any gas only by obtaining the flow conductance of the present invention under the gas to be measured.

2. The present invention can keep the conductance constant under the condition of vacuum to atmosphere, so it can measure a wide range of gas micro-flow.

3. The invention takes a short time to measure the gas micro-flow, and can be used for accurate measurement of the gas micro-flow.

4. The present invention is not only simple in structure, convenient in processing, low in cost, easy in installation and strong in anti-interference ability.

Description of drawings

1 is a schematic diagram of a gas micro-flow sensing device based on molecular flow transmission;

Fig. 2 is the system schematic diagram that utilizes the present invention to measure gas micro-flow;

Fig. 3 is a certain measurement time-gas micro-flow curve that utilizes the present invention to measure gas micro-flow;

Among them, 1-differential pressure transmitter, 2-gas micro-flow sensing element, 3-first valve, 4-bypass valve, 5-bypass pipeline, 6-second valve, 7-inflow of gas to be measured Pipeline, 8-third valve, 9-dry pump.

Detailed ways

The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

Referring to FIG. 1, a gas micro-flow sensing device based on molecular flow transmission provided by the first embodiment of the present invention includes a differential pressure transmitter 1, a gas micro-flow sensing element 2, a first valve 3, a bypass Valve 4, bypass line 5.

The gas micro-flow sensing element 2 is connected with the differential pressure transmitter 1 through the first valve 3, and the bypass pipeline 5 is connected with the differential pressure transmitter 1 through the bypass valve 4; the flow of the gas micro-flow sensing element is The derivative C can be determined by calculation. The gas micro-flow sensor element 2 provided in this embodiment can be used not only in the fields of gas micro-flow measurement and leak rate measurement, but also in the fields of providing micro-flow gas and the like.

The differential pressure transmitter 1 measures the dynamic differential pressure at both ends of the gas micro-flow sensing element 2 . The function of the bypass line 5 is that when the bypass valve 4 is opened, the gas to be tested can quickly pass through the bypass line 5 . The material used in the gas micro-flow sensing element 2 is double-pass porous anodized aluminum, the specification is AAO-DP-12, the pore size is 70 nm, the pore spacing is 110 nm, the pore depth is 50-70 μm, and the conductance is under the condition of vacuum to atmospheric pressure. keep constant. When measuring the gas flow, the gas micro-flow sensing device based on molecular flow transmission can ensure that the gas flow state flowing through it is in the molecular flow state and is an all-metal vacuum system, which can reduce the measurement error caused by the infiltration of small molecular gas.

The calculation of the conductance of the gas micro-flow sensor element 2 provided in this embodiment will be specifically described below. For example, under the condition of atmospheric pressure nitrogen, the molecular mean free path of nitrogen gas is λ=65nm at 20°C. The conductance C of the gas micro-flow sensing element 2 to nitrogen is determined by the following formula:

In this embodiment, A is the exposed area of the gas micro-flow sensor element 2 : take A=4.0×10 ⁷ μm ² , σ is the number of nanopores per unit area: σ=95.42/μm ² , R is the experimental gas The gas constant: 8.315J/(K*mol), T is the ambient temperature: T=293K, μ is the molar mass of the gas: μ=2.8×10 ^-2 kg/mol, d is the gas micro-flow sensor element 2 adopts The diameter of the material: d=7×10 ⁻⁸ m, and l is the depth of the nanopore of the material used in the gas micro-flow sensing element 2: l=7×10 ⁻⁵ m.

By controlling the exposed area of the gas micro-flow sensing element 2, precise control of the conductance of the gas micro-flow sensing element can be achieved.

Referring to FIG. 2 , the system for measuring gas micro-flow using the present invention provided by the first embodiment of the present invention includes a differential pressure transmitter 1 , a gas micro-flow sensing element 2 , a first valve 3 , a bypass valve 4 , and a bypass valve 4 . The pipeline 5, the second valve 6, the inflow pipeline 7 of the gas to be measured, the third valve 8, and the dry pump 9.

The gas inflow pipeline 7 is connected to the gas micro-flow sensing device based on molecular flow transmission through the second valve 6 , and the dry pump 9 is connected to the gas micro-flow sensing device based on molecular flow transmission through the third valve 8 .

Among them, the first valve 3, the bypass valve 4, the second valve 6, and the third valve 8 are all Swagelok ball valves. The range of the gas micro-flow sensing device based on molecular flow transmission is the product of the range of the differential pressure transmitter 1 and the conductance of the gas micro-flow sensing element 2, in this embodiment, it is 2.3×10 ^-6 Pam ³ s ^{- 1} -4.6×10 ^-3 Pam ³ s ^-1 .

The steps of measuring gas micro-flow using the gas micro-flow sensing device based on molecular flow transmission provided in this embodiment will be specifically described below. Open the bypass valve 4 and the third valve 8, open the dry pump 9, and open the second valve 6 after 10s, so that the gas to be measured flows into the gas micro-flow sensing device through the gas inflow pipeline 7 to be measured. After 20s, open the first valve 3 and close the bypass valve 4 at the same time, and record the indication of the differential pressure transmitter 1 after it is stable.

The gas flow rate Q measured by the gas micro-flow sensing device based on molecular flow transmission can be determined by the following formula:

Q=C×ΔP (2)

In this embodiment, C is the conductance of the gas micro-flow sensor element 2 to nitrogen: C=2.3×10 ^-6 m ³ s ^-1 , ΔP is the indication displayed by the differential pressure transmitter: in this embodiment, ΔP =21Pa.

Q=C×ΔP=2.3×10 ⁻⁶ ×21=4.83×10 ⁻⁵ Pam ³ s ^−l

3 is a gas micro-flow-time curve obtained by the molecular flow gas micro-flow sensing device provided in the above embodiment in the process of measuring the gas micro-flow. It can be seen that the measurement time is very short.

In addition, those skilled in the art can make other changes within the spirit of the present invention. For example, the gas micro-flow sensing element 2 is designed with other materials. Of course, these changes made according to the spirit of the present invention should all be included within the scope of the claimed protection of the present invention.

Claims (7)

1. A gas micro-flow sensing device based on molecular flow transmission is characterized in that: the device comprises a differential pressure transmitter (1), a gas micro-flow sensing element (2), a first valve (3), a bypass valve (4) and a bypass pipeline (5).

The gas micro-flow sensing element (2) is connected with the differential pressure transmitter (1) through the first valve (3), and the bypass pipeline (5) is connected with the differential pressure transmitter (1) through the bypass valve (4).

2. A gas micro-flow sensing device based on molecular flow transmission according to claim 1, wherein: the differential pressure transmitter (1) measures the differential pressure at two ends of the gas micro-flow sensing element (2).

3. A gas micro-flow sensing device based on molecular flow transmission according to claim 1, wherein: the bypass pipeline (5) has the function that when the bypass valve (3) is opened, the gas to be measured can rapidly pass through the bypass pipeline (5).

4. A gas micro-flow sensing device based on molecular flow transmission according to claim 1, wherein: the gas micro-flow sensing element (2) is made of bi-pass porous alumina, the specification is AAO-DP-12, the aperture is 70nm, the hole distance is 110nm, the hole depth is 50-70 mu m, and the flow conductance is kept constant under the condition from vacuum to atmospheric pressure.

5. A gas micro-flow sensing device based on molecular flow transmission according to claim 1, wherein: when the gas micro-flow sensing device based on molecular flow transmission is used for measuring the gas flow, the gas flow state flowing through the gas micro-flow sensing device can be ensured to be in the molecular flow state.

6. A gas micro-flow sensing device based on molecular flow transmission according to claim 1, wherein: the measuring range of the gas micro-flow sensing device based on molecular flow transmission is the product of the measuring range of the differential pressure transmitter (1) and the conductance of the gas micro-flow sensing element.

7. A gas micro-flow sensing device based on molecular flow transmission according to claim 1, wherein: the gas flow measured by the gas micro-flow sensing device based on molecular flow transmission is the product of the indication of the differential pressure transmitter and the gas micro-flow sensing element (2).

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