CN109708712B - Device and method for measuring mass flow of fixed flow guide element based on dynamic differential pressure attenuation - Google Patents
Device and method for measuring mass flow of fixed flow guide element based on dynamic differential pressure attenuation Download PDFInfo
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Abstract
The invention discloses a device and a method for measuring the mass flow of a fixed flow guide element based on dynamic differential pressure attenuation, which have the characteristics of accuracy, high efficiency, simplicity and convenience in measuring the mass flow of an AAO fixed flow guide element. The device of the invention comprises: the system comprises an inflating device, a first valve, a container A, a first thermometer, a differential pressure transmitter, a second valve, a third valve, an AAO fixed flow guide element, a second thermometer, a container B, a fourth valve and a vacuum pump set, wherein when experimental gas flows through the AAO fixed flow guide element under the drive of differential pressure, an exponential function is fitted according to the time-dependent attenuation change of the dynamic differential pressure of an inlet and an outlet of the AAO fixed flow guide element, and then the transient mass flow of the calculated gas flowing through the fixed flow guide element is calculated.
Description
Technical Field
The invention relates to a device and a method for measuring mass flow of a fixed flow guide element based on dynamic differential pressure attenuation, and belongs to the technical field of measurement.
Background
In recent years, with the development of micro-electronic-mechanical systems (MEMS), micro-fluidic technology has gained wide attention, and many theoretical and experimental studies have been carried out to understand physical phenomena related to flow. Among them, the measurement of lean gas mass flow has been a hot topic of research. There are three commonly used measurement techniques, namely, a liquid drop method, a constant pressure method and a constant volume method. The drop method is a direct measurement technology, and the change of mass flow is obtained by measuring the moving speed of a drop in a calibration tube through a low-power microscope or a photoelectric sensor; the constant pressure method and the constant volume method are indirect measurement technologies, and have the defects that the piston moves slowly under the condition of low mass flow rate and is difficult to accurately control; the constant volume method can only measure mass flow in various quasi-steady states.
The invention introduces a new technology for measuring the mass flow of an anode porous alumina (AAO) fixed flow guide element by utilizing dynamic differential pressure attenuation, so that the measurement of the mass flow of the fixed flow guide element has the characteristics of accuracy, high efficiency and simplicity.
Disclosure of Invention
The invention provides a device and a method for measuring mass flow of a fixed flow guide element based on dynamic differential pressure attenuation, which aim to accurately measure transient mass flow of the fixed flow guide element.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention relates to a device and a method for measuring the mass flow of a fixed flow guide element based on dynamic differential pressure attenuation, which is characterized in that the device for measuring the mass flow of the fixed flow guide element based on the dynamic differential pressure attenuation comprises: the device comprises an air charging device, a first valve, a container A, a first thermometer, a differential pressure transmitter, a second valve, a third valve, an AAO fixed flow guide element, a second thermometer, a container B, a fourth valve and a vacuum pump set.
The container A is connected with the inflating device through a first valve, a first thermometer is installed on the container A, the container A is connected with the container B through a second valve, the high-pressure end of the AAO fixed flow guide element is connected with a third valve, the low-pressure end of the AAO fixed flow guide element is connected with the container B, the container B is provided with a second thermometer, the container B is connected with a vacuum pump set through a fourth valve, the high-pressure end of the differential pressure transmitter is connected with the container A, and the low-pressure end of the differential pressure transmitter is connected with the container B.
The container A and the container B are made of stainless steel, and the volume of the high-pressure end of the container A, the high-pressure end of the peripheral pipeline and the high-pressure end of the valve are V measured by a gas expansion method1＝1.34×10-2m3The volume of the low-pressure end of the container B, the peripheral pipeline and the valve is V2＝7.1×10- 4m3。
The differential pressure transmitter measures the dynamic differential pressure change at two ends of the AAO fixed flow guide element, and calculates the transient mass flow of gas flowing through the AAO fixed flow guide element by adopting a least square function fitting and differentiating method according to a deduced theoretical formula
The AAO material model of the AAO fixed flow guide element is AAO-DP-25 produced by the offshore wood technology company Limited, the aperture is 13mm, nitrogen, helium and argon are respectively used as experimental gases and are always in a molecular flow state when flowing through the AAO fixed flow guide element, and the flow guide of the AAO fixed flow guide element is kept constant from vacuum to atmospheric pressure.
The method for measuring the mass flow of the fixed flow guide element is completed according to the following steps:
1. closing the first valve, opening the second valve, the third valve andfourth valve, vacuum pump set is used to pump the system to 1 × 10-3Pa below, then opening the first valve, closing the fourth valve, introducing the test gas into the containers A and B to a pressure p0. And then closing the second valve and the third valve, and filling the experimental gas into the container A again to ensure that the pressure in the container A rises again, and closing the first valve when the reading of the differential pressure at two ends of the differential pressure transmitter is increased from 0Pa to 1200 Pa. Waiting for about 15 minutes to enable the temperature and the pressure of the containers A and B to reach a stable state, opening the third valve again, enabling the gas in the container A to flow through the AAO fixed flow guide element to enter the container B due to the existence of the pressure difference, and finally enabling the pressure in the two containers to reach an equilibrium state, wherein the time for the pressure difference delta P between the two ends of the differential pressure transmitter to be reduced from 1200Pa to 0Pa is t.
2. The mass flow of the AAO fixed flow guide element can be derived by the following procedure:
the gas mass flow through the AAO fixed flow guide element is related to the change in gas mass between the vessels A, B, the change in mass being related to the change in pressure within the vessels over time, according to the ideal gas equation of state:
p1V1＝M1RT，p2V2＝M2RT (1)
wherein T is temperature, R is gas constant, ViIs the total volume of the containers A, B and their surrounding piping and valves, piAnd MiIs the pressure and gas mass of the container A, B and their surrounding piping and valves. The vessel temperature was kept constant throughout the experiment. Wherein, the gas mass changes of the container B, the peripheral pipelines and the valve are as follows:
throughout the experiment, the change in temperature dT/T is 10-3Left and right, the variation of the average pressure is dpp/p is 10-1Left and right and therefore negligible. The mass of gas in vessel B and surrounding piping and valves can be derived from equation (2):
according to the mass conservation law, the mass flow is obtained:
thus, from equations (3) and (4), one can simply derive:
where Δ p (t) is the pressure difference between vessels a and B, Δ p (t) p2(t)-p1(t).
According to the definition of conductance, the conductance of the AAO fixed conductance element can be obtained:
in the formula Q1、Q2Respectively represent a flow through V1、V2The gas flow, the flow Q commonly used in the field of vacuum science and technology to represent the gas flow, is defined as:
as shown above, from equations (3), (6) and (7), it can be derived:
a differential equation for the pressure difference Δ p (t) between vessels a and B can thus be obtained:
since the conductance C of the conductance element is constant, the differential equation (9) can be rewritten as:
in the formula,. DELTA.p0Is the initial pressure difference when t is 0, and τ is the characteristic time of the experiment. According to equation (5), the mass flow of gas in vessel B and surrounding piping and valves can be written as:
the mass flow rate of the gas flowing through the AAO fixed flow guide element is equal, the change value delta p (t) of the pressure difference between two ends of the container A and the container B along with the time can be obtained in the experimental process, and exponential function fitting is carried out on the change value delta p (t) by using Origin software according to a formula (10); the specific function obtained by the fitting is then derived according to equation (11), where V0R and T are known and finally a time-varying mass flow function is obtained.
Compared with the prior art, the invention has the following advantages:
1. the nitrogen, helium and argon in the invention are always in a molecular flow state when flowing through the AAO fixed flow guide element, so that the mass flow of the fixed flow guide element can be measured by using various gases.
2. The device can measure the mass flow of nitrogen, helium and argon at any time when the nitrogen, the helium and the argon flow through the fixed flow guide element.
3. The conductance of the AAO fixed conductance element used in the present invention remains constant up to atmospheric conditions, and thus the method is applicable from vacuum conditions to atmospheric conditions.
4. The device of the invention has the advantages of simple structure, convenient processing, low cost, strong anti-interference capability and accurate measurement result.
Drawings
FIG. 1 is a schematic diagram of a fixed conductance element mass flow measurement device based on dynamic differential pressure decay;
the system comprises an air charging device 1, a first valve 2, a container 3, a first thermometer 4, a differential pressure transmitter 5, a second valve 6, a third valve 7, an AAO (anodic porous alumina) fixed flow guide element 8, a second thermometer 9, a container B10, a fourth valve 11 and a vacuum pump group 12.
Detailed Description
As shown in fig. 1, the present invention relates to a device and a method for measuring mass flow of a fixed flow guide element based on dynamic differential pressure attenuation, comprising: the device comprises an air charging device 1, a first valve 2, a container A3, a first thermometer 4, a differential pressure transmitter 5, a second valve 6, a third valve 7, an AAO fixed flow guide element 8, a second thermometer 9, a container B10, a fourth valve 11 and a vacuum pump set 12.
The container A3 is connected with the air charging device 1 through the first valve 2, the container A is provided with the first thermometer 4, the container A3 is connected with the container B10 through the second valve 6, the high-pressure end of the AAO fixed flow guide element 8 is connected with the third valve 7, the low-pressure end of the AAO fixed flow guide element 7 is connected with the container B10, the container B10 is provided with the second thermometer 9, the container B10 is connected with the vacuum pump set 12 through the fourth valve 11, the high-pressure end of the differential pressure transmitter 5 is connected with the container A3, and the low-pressure end is connected with the container B10.
The container A3 and the container B10 are both made of stainless steel, and the volume of the high-pressure end of the container A3, the high-pressure end of the peripheral pipeline and the high-pressure end of the valve are measured to be V by a gas expansion method1＝1.34×10-2m3The volume of the low-pressure end of the container B10, the peripheral pipeline and the valve is V2＝7.1×10-4m3。
The differential pressure transmitter 5 measures the dynamic differential pressure change across the AAO fixed conductance element 8.
The AAO material model of the AAO fixed flow guide element 8 is AAO-DP-25 produced by the offshore wood technology company Limited, the aperture is 13mm, nitrogen, helium and argon are respectively used as experimental gases and are always in a molecular flow state when flowing through the AAO fixed flow guide element, and the flow guide of the AAO fixed flow guide element is kept constant from vacuum to atmospheric pressure.
The method for measuring the mass flow of the fixed flow guide element is completed according to the following steps:
1. the first valve 2 is closed, the second valve 6, the third valve 7 and the fourth valve 11 are opened, and the system is evacuated to 1 × 10 using the vacuum pump group 12-3Pa, then the first valve 2 is opened, the fourth valve 11 is closed, and the test gas is introduced into the vessel A3 and the vessel B10 to reach a certain pressure p0. Then, the second valve 6 and the third valve 7 were closed, and the vessel A3 was filled with the test gas again, so that the pressure in the vessel A3 was increased again, and when the reading of the differential pressure across the differential pressure transmitter 5 was increased from 0Pa to 1200Pa, the first valve 2 was closed. After waiting about 15 minutes for the temperature and pressure in the vessels A3 and B10 to reach a steady state, the third valve 7 is opened again, the gas in the vessel A3 flows through the AAO fixed flow guide element 8 into the vessel B10 due to the pressure difference, and finally the pressure in the two vessels reaches an equilibrium state, at which time the time it takes for the pressure difference Δ P across the differential pressure transmitter 5 to decrease from 1200Pa to 0Pa is t.
2. The mass flow of the AAO fixed conductance element 8 can be derived by the following procedure:
the gas mass flow through the AAO fixed flow guide 8 is related to the mass change between the vessels a3, B10, which is related to the change in pressure inside the vessel over time. According to an ideal gas state equation:
p1V1＝M1RT，p2V2＝M2RT (1)
wherein T is temperature, R is gas constant, ViIs the total volume of vessels A3, B10 and their surrounding piping and valves, piAnd MiAre the pressure and gas mass of vessels a3, B10 and their surrounding piping and valves. The vessel temperature was kept constant throughout the experiment. Wherein, the gas mass changes of the container B10, the peripheral pipelines and the valves are as follows:
throughout the experiment, the change in temperature dT/T is 10-3Left and right, the variation of the average pressure is dpp/p is 10-1Left and right and therefore negligible. The mass of gas in vessel B10 and surrounding piping and valves can be derived from equation (2):
according to the mass conservation law, the mass flow is obtained:
thus, from equations (3) and (4), one can simply derive:
where Δ p (t) is the pressure difference between vessels a3 and B10, Δ p (t ═ p)2(t-p1(t.
The conductance of the AAO fixed conductance element 8 can be obtained according to the definition of conductance:
in the formula Q1、Q2Respectively represent a flow through V1、V2The gas flow, the flow Q commonly used in the field of vacuum science and technology to represent the gas flow, is defined as:
as shown above, from equations (3), (6) and (7), it can be derived:
the pressure difference Δ p between the containers a3 and B10 can thus be obtained (differential equation of t:
since the conductance C of the conductance element is constant, the differential equation (9) can be rewritten as:
in the formula,. DELTA.p0Where t is the initial pressure differential at 0, τ is the characteristic time of the experiment, and the mass flow of gas in vessel B10 and surrounding piping and valves can be written as:
it is equal to the mass flow of the gas flowing through the AAO fixed flow guide element 8, and in the experimental process, the change value delta p (t) of the pressure difference between the two ends of the containers A3 and B10 along with the time can be obtained, and according to the formula (10), the exponential function fitting is carried out on the change value delta p (t) by using Origin software; the specific function obtained by the fitting is then derived according to equation (11), where V0R and T are known and finally a time-varying mass flow function is obtained.
Claims (5)
1. A fixed conductance element mass flow measurement device based on dynamic differential pressure decay, characterized by: the device comprises an air charging device (1), a first valve (2), a container A (3), a first thermometer (4), a differential pressure transmitter (5), a second valve (6), a third valve (7), an AAO fixed flow guide element (8), a second thermometer (9), a container B (10), a fourth valve (11) and a vacuum pump set (12);
container A (3) link to each other with aerating device (1) through first valve (2), install first thermometer (4) on the container A, container A (3) link to each other through second valve (6) with container B (10), the high-pressure side of the fixed flow of AAO leads component (8) links to each other with third valve (7), the low pressure end of the fixed flow of AAO leads component (8) links to each other with container B (10), install second thermometer (9) on container B (10), container B (10) link to each other with vacuum pump group (12) through fourth valve (11), differential pressure transmitter (5) high-pressure side links to each other with container A (3), the low-pressure side links to each other with container B (10).
2. The device of claim 1, wherein the vessel A (3) and the vessel B (10) are made of materials of the same materialThe quality is stainless steel, and the volume of the container A (3), the high-pressure end of the peripheral pipeline and the high-pressure end of the valve are measured to be V by using a gas expansion method1＝1.34×10-2m3The volume of the low-pressure end of the container B (10), the peripheral pipeline and the valve is V2＝7.1×10-4m3。
3. The dynamic differential pressure decay-based fixed conductance element mass flow measurement device of claim 1, wherein: the differential pressure transmitter (5) measures the dynamic differential pressure change at two ends of the AAO fixed flow guide element (8), and calculates the transient mass flow of the gas flowing through the AAO fixed flow guide element (8) by adopting a least square function fitting and differentiating method according to a deduced theoretical formula.
4. The dynamic differential pressure decay-based fixed conductance element mass flow measurement device of claim 1, wherein: the AAO material model of the AAO fixed flow guide element (8) is AAO-DP-25 produced by offshore wood technology limited company, the aperture is 13mm, nitrogen, helium and argon are respectively used as experimental gases and are always in a molecular flow state when flowing through the AAO fixed flow guide element (8), and the flow guide of the AAO fixed flow guide element is kept constant from vacuum to atmospheric pressure.
5. The device of claim 1, wherein the device comprises the following specific steps:
first, close the first valve, open the second valve, the third valve and the fourth valve, use the vacuum pump group to vacuumize the system to 1 × 10-3Pa below, then opening the first valve, closing the fourth valve, introducing the test gas into the containers A and B to a pressure p0Then closing the second valve and the third valve, filling the experimental gas into the container A again to ensure that the pressure in the container A rises again, closing the first valve when the reading of the differential pressure at two ends of the differential pressure transmitter is increased from 0Pa to 1200Pa, waiting for about 15 minutes to ensure that the temperature and the pressure of the containers A and B reach a stable state, and opening the second valve againThree valves, because of the existence of differential pressure, the gas in the container A flows through the AAO fixed flow guide element and enters the container B, and finally the pressure in the two containers reaches a balanced state, and at the moment, the time for the pressure difference delta P at the two ends of the differential pressure transmitter to be reduced from 1200Pa to 0Pa is t;
secondly, the mass flow of the AAO fixed flow guide element can be obtained by the following process:
the gas mass flow through the AAO fixed flow guide element is related to the change in mass between the vessels A, B, which is related to the change in pressure within the vessels over time, according to the ideal gas equation of state:
p1V1＝M1RT，p2V2＝M2RT (1)
wherein T is temperature, R is gas constant, ViIs the total volume of the containers A, B and their surrounding piping and valves, piAnd MiIs the pressure and gas mass of the vessel A, B and its surrounding piping and valves, the vessel temperature remained constant throughout the experiment, where the vessel B and surrounding piping and valves gas mass changes were:
throughout the experiment, the change in temperature dT/T is 10-3Left and right, the variation of the average pressure is dpp/p is 10-1Left and right, and therefore negligible, the mass of gas in vessel B and surrounding piping and valves can be derived from equation (2):
obtaining mass flow according to mass conservation law
Therefore, from equations (3) and (4), it can be simply derived
Where Δ p (t) is the pressure difference between vessels a and B, Δ p (t) p2(t)-p1(t).
The conductance of the AAO fixed conductance element can be obtained according to the definition of the conductance
In the formula Q1、Q2Respectively represent a flow through V1、V2Is used to represent the gas flow rate in the field of vacuum science and technology
Is defined as
As shown above, from equations (3), (6) and (7), it can be derived
A differential equation for the pressure difference Δ p (t) between vessels a and B can thus be obtained:
since the conductance C of the conductance element is constant, the differential equation (9) can be rewritten as:
in the formula,. DELTA.p0Is the initial pressure difference when t is 0, τ is the characteristic time of the experiment, and according to equation (5), the capacityThe mass flow of gas in vessel B and surrounding piping and valves can be written as:
the mass flow rate of the gas flowing through the AAO fixed flow guide element is equal, the change value delta p (t) of the pressure difference between two ends of the container A and the container B along with the time can be obtained in the experimental process, and exponential function fitting is carried out on the change value delta p (t) by using Origin software according to a formula (10);
the specific function obtained by the fitting is then derived according to equation (11), where V0R and T are known and finally a time-varying mass flow function is obtained.
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