CN109839961A - A kind of low reynolds number zone gas mass flow control method and control calibrating installation - Google Patents
A kind of low reynolds number zone gas mass flow control method and control calibrating installation Download PDFInfo
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Abstract
A kind of low reynolds number zone gas mass flow control method and control calibrating installation, in Re≤104Low reynolds number region, corresponding efflux coefficient C under 5 different Reynolds number Re is at least demarcated to the critical fluid element that is jammedd, to obtain the efflux coefficient C of the critical fluid element that is jammeddWith the functional relation of reynolds number Re；The air-flow for keeping critical choked flow components upstream is T0Constant temperature, flow a gas over it is critical be jammed fluid element and reach critical state of being jammed；The gas mass flow by the critical fluid element that is jammed is set as qm, calculate reynolds number Re, efflux coefficient Cd, then calculate stagnation pressure target value p at critical choked flow element inlet0；The inlet pressure for adjusting the critical fluid element that is jammed is p0, it is at this time setting value q by the real gas mass flow value of the critical fluid element that is jammedm.This method and device can provide accurate mass flow for gas equipment, it is also possible to make traffic alignment device and implement to calibrate to common flow meters.
Description
Technical field
The present invention relates to low reynolds number gas mass flow control field, more particularly to one kind are former based on critical choking flow
The low reynolds number zone gas mass flow control method of reason and control calibrating installation, control calibration system and carry out control or
The method of calibration.
Background technique
Requirement of the fields such as industrial production, technology controlling and process, medicine bioengineering to gas flow control technology is higher and higher.Example
Such as, semiconductor manufacturing industry, needs to control the growth of film on chip using accurate process gas flow, this is directly affected
The yield rate and productivity of semiconductor chip.Wound healing is promoted by control oxygen flow in pharmaceuticals industry, passes through oxygen
Or the flow of inert gas controls the cultivation of cell or bacterium.Therefore, in order to control gas flow rate under such working condition, no
Accurate mass flow is only needed, and measuring instrumentss need to have higher repdocutbility and stability.
Currently, the flowing of process gas is mainly controlled by thermal mass flow meter, wherein thermal type gas quality flow is passed
Sensor is the critical component for realizing flow control, and heat type gas flow sensor internal opaque film on piece has heating unit
Part, temperature are consistently higher than ambient temperature.When air-flow passes through, heat is taken away because of fluid forced convertion in temperature field leads to air-flow
Upstream and downstream generate temperature change, and this asymmetry detection and implementation procedure are all completed in a CMOS silicon on piece, are integrated in silicon
Its Temperature Distribution of the temperature sensor measurement of on piece is calculated current by special signal processing circuit and gas flow number model
The mass flow of air-flow.
However, the working principle of thermal mass flow meter determines that its accuracy and repdocutbility are difficult to further increase.It is existing
There is thermal type gas quality flow sensor accuracy to be up to 0.5 grade, it is common that 1.0 grades.Gas mass flow rate sensors include
The devices such as thermal insulation diaphragm, heating element, temperature sensor, are all movable member or wearing detail, and acquisition signal also occurs to be easy
Drift.
Summary of the invention
Technical problem to be solved by the present invention lies in provide a kind of low reynolds number area based on critical choking flow principle
Domain gas mass flow amount control method and control calibrating installation, control calibration system and the method for being controlled or being calibrated, tool
There is the advantages that accuracy is high, stability and good repdocutbility.
The present invention is achieved by the following technical solutions:
A kind of low reynolds number zone gas mass flow control method, it is characterised in that:
The first step, in reynolds number Re≤104Low reynolds number region, 5 differences are at least demarcated to the critical fluid element that is jammed
Corresponding efflux coefficient C under reynolds number Red, to derive the efflux coefficient C of the critical fluid element that is jammeddExist with reynolds number Re
The functional relation in low reynolds number region:
Cd=f (Re)； (Ⅰ)
Functional expression obtained by calibrating will not be just the same each time, such as:
Or
Second step, keeping the air-flow of critical choked flow components upstream is T0Constant temperature flows a gas over the critical fluid element that is jammed,
Keep the inlet pressure p of the critical fluid element that is jammed1It is constant, reduce the outlet back pressure p of the critical fluid element that is jammed2, make back pressure ratio p2/
p1Reduce, is increased by the gas mass flow of the critical fluid element that is jammed, until p2/p1When reaching critical backing pressure ratio, gas is facing
Boundary's fluid element throat velocity of being jammed reaches local velocity of sound, and the gas for flowing through the critical fluid element that is jammed reaches critical state of being jammed, this
When further decrease back pressure ratio p2/p1, gas mass flow remains unchanged, and keeps p2/p1It is consistently less than and is equal to critical backing pressure ratio；
Third step sets the gas mass flow by the critical fluid element that is jammed as qm, (II) calculates according to the following formula
Gas mass flow qmCorresponding reynolds number Re:
In formula:
D: the larynx diameter of the critical fluid element that is jammed,
μ0: aerodynamic force viscosity is tabled look-up acquisition according to gas temperature, and aerodynamic force viscosity hardly follows pressure change under normal pressure
Change and changes, by taking air as an example, under normal circumstances, air viscosity (1.81 × 10-5~1.84 × 10-5)Pa·s；
Re≤104；
Reynolds number Re calculated in formula (II) is substituted into formula (I), to calculate the corresponding stream of the reynolds number Re
Coefficient C outd, the inlet pressure target value p of the critical fluid element that is jammed is calculated further according to following formula (III)0:
In formula:
Ant: critical fluid element throat section product of being jammed, Ant=0.25 π d2, d is the larynx diameter of the critical fluid element that is jammed；
R: universal gas constant；
M: the molal weight of gas；
p0: the absolute stagnation pressure of critical choked flow components upstream；
T0: the absolute stagnation temperature of critical choked flow components upstream；
Cd: efflux coefficient, by Cd=f (Re), which is calculated, to be obtained, and Cd<1；
C*: the critical flow of real gas, calculation formula are shown in JJG620-2008 critical flow venturi nozzle P.15 formula
(B.1):
In formula each parameter only need to according to gas property, temperature, pressure is tabled look-up can be obtained, will not be introduced using the equation
Any significantly additional uncertainty；
4th step is keeping back pressure ratio p2/p1Under the premise of critical backing pressure ratio, the critical fluid element that is jammed is adjusted
Inlet pressure p1Until p1=p0, it is at this time setting value q by the real gas mass flow value of the critical fluid element that is jammedm。
Gas mass flow amount control method in the present invention is not based on the hot principle art of existing amount of heat transfer, but base
Critical choking flow principle in aerodynamics, the critical choking flow of gas refer under given initial conditions, gas
Mobility status of the body in runner no longer changes with downstream conditions, and mass flowrate reaches maximum value, i.e. critical flow at this time.
By formula I, II, III it is found that critical flow venturi nozzle (i.e. back pressure ratio p under critical stream mode2/p1Less than critical pressure
Power ratio), mass flow value is determined by upstream stagnation pressure p0, stagnation temperature T0, unrelated with the variation of downstream pressure p2.It examines
Considering control temperature accurately to change relatively difficult therefore of the invention thinking is that a mass flow is preset under critical stream mode
Qm first passes through formula II and calculates the corresponding reynolds number Re of acquisition, then calculated by formula I and obtain corresponding efflux coefficient Cd, then lead to
It crosses formula III and calculates acquisition inlet pressure target value p0 (i.e. the absolute stagnation pressure p0 of upstream), finally adjusted according to the calculated value
Swim entrance actual pressure p1Until p1=p0, to make the actual mass flow and preset value q of gas flow pathmIt is identical, to realize standard
True flow control then still assumes again that another mass flow q by above-mentioned thinking if necessary to mass-flow changem, control
Upstream stagnation pressure p0Variation, to change the actual mass flow of gas flow path.
Further, the critical fluid element that is jammed is critical flow venturi nozzle, or is based on critical choked flow principle
Nozzle, spray orifice, jet pipe etc..Critical flow venturi nozzle has two kinds of patterns of cylindrical throat and circular ring shape throat, and production adds
Work, calibration test have specific standard to support [1], and critical flow venturi nozzle has very compared with other flow controllers
Clear advantage: first is that interference of the thermal type gas quality flow sensor vulnerable to disturbances, and critical flow venturi sprays
After mouth reaches critical stream mode, flow is not influenced by the disturbance of instrument downstream pressure, so when critical flow venturi nozzle is set to
In the upstream of gas equipment, no matter gas equipment pressure disturbance has the stabilization that how acutely all will not influence flow, this is other
The characteristic that flow controller does not have；Second is that be all 0.2 grade by the critical flow venturi nozzle of assay approval, additional temp,
The device of the measuring appliances such as pressure, humidity composition, opposite expanded uncertainty are no more than 0.3%, and critical flow venturi nozzle is
The measurement instrument of Transfer Standards rank, and gas mass flow rate sensors are the measurement instruments of work grade, the two accuracy has aobvious
Write difference；Third is that critical flow venturi nozzle is the stainless steel cylindrical body of a perforation, without mechanical movable component or electronics device
Part is stability and the best flow measurement utensil of repdocutbility, and meter characteristic data are nearly constant, normal use almost without
Abrasion, therefore stability and repdocutbility are far superior to thermal type gas quality flow sensor.
Certainly, it if alternative solution does not use critical flow venturi nozzle, but uses based on critical choked flow principle
Nozzle, spray orifice or jet pipe etc. (air-flow can reach in throat or hole and keep velocity of sound), also may be implemented mass flow
It adjusts, but there is no concerned countries standards and legality measurement technical body to support for the uncertainty of its calibration and measurement result,
There is certain difficulty in actual operation.
Further, the gas is air or oxygen, nitrogen, argon gas, methane, carbon dioxide, is suitable for ISO-
Several common pure gas and dry air that 9300:2005 is listed, if working media is not wherein, it is necessary to ensure that this kind of gas
The calculating accuracy of critical flow, the mass flow otherwise exported can introduce additional uncertainty.
A kind of gas mass flow control calibrating installation, it is characterised in that:
Stream pressure control element and the critical fluid element that is jammed including gas circuit connection, at critical choked flow element inlet and
Exit is respectively equipped with inlet pressure transmitter and outlet back pressure transmitter；
Temperature transmitter is additionally provided at critical choked flow element inlet；
Temperature transmitter, inlet pressure transmitter, outlet back pressure transmitter are electrically connected central processor CPU, center
Processor CPU is electrically connected stream pressure control element, and display module, input module and memory are electrically connected centre
Manage device CPU；
Formula I, II and III is pre-stored in the memory.
Further, the gas mass flow control calibrating installation further includes being set to stream pressure control element upstream
Filter, impurity that may be present in pre-filtering gas avoids the accuracy for influencing gas mass flow control.
Further, the critical fluid element that is jammed is one or n in parallel.Each critical choked flow element quality
Flow has a certain amount journey range, and the range of device can be adjusted flexibly in the critical fluid element that is jammed by replacing different larynx diameters
Range, also can use the additive property of gas mass flow, and multiple critical fluid elements that are jammed used in parallel expand whole device
Range ability.
Further, the n critical fluid elements that are jammed of the parallel connection share a set of outlet back pressure transmitter and temperature pick-up
Independent inlet pressure transmitter and stream pressure control element is respectively set in device, corresponding each critical fluid element that is jammed；And
For formula I, it is pre-stored with the efflux coefficient C of each critical fluid element that is jammed in memorydWith reynolds number Re in low Reynolds
The functional relation C in number regiond1=f1(Re), Cd2=f2(Re) ..., Cdn=fn(Re).This kind of parallel-connection structure, it is contemplated that Mei Gelin
Be jammed the efflux coefficient C of fluid element on boundarydFunctional relation from reynolds number Re in low reynolds number region is different, and (even specification is complete
The critical fluid element that is jammed of the same two, the C calibratedd=f (Re) will not be completely the same), it is therefore desirable to respectively calibration and
It is pre-stored, further, since reaching outlet back pressure after critical stream mode does not influence gas mass flow, therefore one can be shared
A outlet back pressure transmitter, if back pressure value can guarantee all critical fluid elements that are jammed all in critical stream mode, most
Afterwards, it is contemplated that the basic constant temperature of the temperature of gas, therefore need to only arrange that a temperature transmitter carries out temperature monitoring.
Further, the gas mass flow control calibrating installation further includes being set to stream pressure control element upstream
Filter.It will be re-fed into device after gas pre-filtering, avoid impurity effect monitoring data.
Further, the temperature transmitter, inlet pressure transmitter and outlet back pressure transmitter pass through temperature A/D respectively
Converter connects central processor CPU with pressure A/D converter, and central processor CPU is controlled by circuit connection stream pressure
Element, the memory are erasable programmable read-only memory EPROM.In the present invention, stream pressure cannot be manipulated with CPU
Control element, CPU are only sent to it pressure target value p0, worked by stream pressure control element complete independently pressure regulation.
Further, the gas mass flow control calibrating installation is Integral box type, and display module is LCD panel,
Input module is point contact type input panel, and point contact type input panel and LCD panel pass through input and output processing circuit respectively and connect
Connect central processor CPU.Cassette arrangement is easy to carry, and access is simple, and good appearance is neat.
Further, the gas mass flow control calibrating installation is assembly type, further includes two coaxial installing pipes,
Upstream installing pipe is equipped with inlet pressure transmitter pressure port and temperature transmitter takes warm hole, and downstream installing pipe is equipped with outlet back
Critical fluid element installation of being jammed is respectively equipped on pressure transmitter pressure port, upstream installing pipe and the opposite one end of downstream installing pipe to connect
Mouthful, air circuit connection interface is respectively equipped on opposite one end.In certain current paths for being not easy to integrally access, by each component
Grafting respectively, clamping are designed to to the split type structure in installing pipe, scene dismounts.
Further, the stream pressure control element is preferably that automatic pressure controller is had using other similar to gas
The pressure control of pressure adjusting control function and adjustment equipment (or instrument), can equally complete goal of the invention, it is contemplated that the present apparatus
Degree of regulation and pressure that accurate mass flow additionally depends on the stream pressures control element such as automatic pressure controller can be obtained
The accuracy of power measurement, automatic pressure controller are built-in with piezoelectric type ratio adjusting valve, are adjusted pressure by central processor CPU
Target value be sent to ratio adjusting valve, by its own control algolithm adjust output pressure.Also it is quasi- to can according to need selection
The pressure controller of exactness higher (control range 20~350kPa absolute pressure, stability are less than ± 5Pa), such as FLUKE are public
Take charge of PPC4 gas pressure regulator/calibrator.But if adjusting flow by valve opening, precision can be can control not
It is enough.
A kind of gas mass flow control calibration system, including gas mass flow as described above control calibrating installation.
Further, further include the vacuum generating device for controlling calibrating installation downstream set on gas mass flow, be set to gas
Gas source (such as pressure steel cylinder), regulating valve and the vacuum tank of weight flow control calibrating installation upstream.
A method of gas mass flow calibration being carried out using above-mentioned gas mass flow control calibration system, it will be to
Calibrating flow meter air circuit connection controls calibrating installation downstream in gas mass flow, then carries out as follows:
Whole system is placed in the laboratory environment of a constant temperature by the first step；
Second step opens gas source, vacuum tank, uses regulating valve coarse adjustment gas pressure, it is ensured that enters gas mass flow control
The gas pressure of calibrating installation processed is no more than the pressure-resistant upper limit of stream pressure control element, avoids damage instrument；
Third step opens gas mass flow control calibrating installation and flowmeter to be calibrated, makes it into normal work shape
State；
4th step starts vacuum generating device, reduces critical choked flow component outlet back pressure p2, until being jammed by critical
The air-flow back pressure ratio of fluid element is less than or equal to critical backing pressure ratio, and the fluid element that is jammed critical at this time is under critical stream mode, gas
Mass flow is stablized, into the adjustable stage；
5th step, by required gas mass flow magnitude qmIt is inputted by input module；
6th step, central processor CPU is according to mass flow set point qm, reynolds number Re, then root are calculated by formula II
Corresponding efflux coefficient C is calculated according to formula Id, combination temperature transmitter actual measurement critical choked flow element inlet at temperature T0, root
Pressure target value p is calculated according to formula III0；
7th step, under critical stream mode, central processor CPU is by pressure target value p0It is sent to stream pressure control member
Part makes the inlet pressure p of inlet pressure transmitters monitor by its separately adjustable inlet pressure1Equal to target value p0, critical at this time
The real gas mass flow of the fluid element that is jammed output is setting value qm；
Whether the meter readings to be calibrated that mass flow value at this time can be used for calibrating downstream are accurate；
8th step repeats the 5th step~the 7th step, and the flowmeter to be calibrated for calibrating downstream is read in different quality flow point
It is whether accurate；
After use, vacuum generating device, gas source, vacuum tank are successively closed；Close gas mass flow control calibration
Device and flowmeter to be calibrated.
A method of gas mass flow control being carried out using above-mentioned gas mass flow control calibration system, will be used
Gas equipment is connected to gas mass flow control calibrating installation downstream, then carries out as follows:
Whole system is placed in the laboratory environment of a constant temperature by the first step；
Second step opens gas source, vacuum tank, uses regulating valve coarse adjustment gas pressure, it is ensured that enters gas mass flow control
The gas pressure of calibrating installation processed is no more than the pressure-resistant upper limit of stream pressure control element, avoids damage instrument；
Third step opens gas mass flow control calibrating installation and gas equipment, makes it into normal operating conditions；
4th step starts vacuum generating device, reduces critical choked flow component outlet back pressure p2, until being jammed by critical
The air-flow back pressure ratio of fluid element is less than or equal to critical backing pressure ratio, and the fluid element that is jammed critical at this time is under critical stream mode, gas
Mass flow is stablized, into the adjustable stage；
5th step, by required gas mass flow magnitude qmIt is inputted by input module point contact type panel；
6th step, central processor CPU is according to mass flow set point qm, reynolds number Re, then root are calculated by formula II
Corresponding efflux coefficient C is calculated according to formula Id, combination temperature transmitter actual measurement critical choked flow element inlet at temperature T0, root
Pressure target value p is calculated according to formula III0；
7th step, under critical stream mode, central processor CPU adjusts inlet pressure by stream pressure control element,
Make the inlet pressure p of inlet pressure transmitters monitor1Equal to target value p0, the real gas of fluid element output of being jammed critical at this time
Mass flow is setting value qm；
Mass flow value at this time is the real gas mass flow value of gas equipment, if necessary to change by using gas
The gas mass flow of equipment repeats the 5th step~the 7th step, after use, successively closes vacuum generating device, gas
Source, vacuum tank；Close gas mass flow control calibrating installation and gas equipment.
Further, in the method for above-mentioned progress gas mass flow calibration, or gas mass flow control is carried out
Method in, if the critical fluid element that is jammed in gas mass flow control calibrating installation is n in parallel, and at least two
It is a in above-mentioned 4th step, to need to adjust all critical fluid elements that is jammed and be under critical stream mode when working at the same time, the 6th
Need to calculate separately the pressure target value p of each critical fluid element that is jammed in step0, need to adjust each critical be jammed in the 7th step
The inlet pressure of fluid element is equal to respective pressure target value p0。
It infuses, the part reference source and explanation of technical terms in specification and claims are as follows:
[1] technical standard of critical flow venturi nozzle and scaling method are referring to following three standards:
(1)ISO 9300:2005Measurement of gas flow by means of critical flow
venturi nozzles；
(2) GB-T 21188-2007 measures gas flow with critical flow venturi nozzle；
(3) JJG 620-2008 critical flow venturi nozzle vertification regulation；
[2] nozzle: for measure gas flow, entrance hole diameter gradually decreases to throat or is gradually expanded again by throat
Measurement pipe；
[3] critical flow venturi nozzle: throat can reach the nozzle with diffuser of local velocity of sound；
[4] throat: the smallest position of diameter in nozzle, diameter become larynx diameter；
[5] stagnation state: fluid under stagnation, that is, reaches state of the speed equal to zero when in flowing；
[6] stagnation absolute pressure: gas absolute pressure when stagnation state；
[7] stagnation temperature: gas temperature when stagnation state；
[8] critical flow: when reaching critical backing pressure ratio, the gas mass flow for flowing through nozzle reaches maximum, and gas is in throat
Reach local velocity of sound, flowing at this time is known as critical flow, further decreases back pressure ratio, and the flow for flowing through nozzle remains unchanged；
[9] reynolds number Re: being the ratio between inertia force and viscous force for characterizing the dust suppression by spraying of fluid viscosity influence.
The beneficial effects of the present invention are:
1, the measurement instrument of the present apparatus, system and control method based on Transfer Standards is able to solve gas Tiny Mass stream
The control problem of amount, flux lower limit is up to 0.2g/min, it might even be possible to it is lower (depending on nozzle efflux coefficient capacity rating and
Pressure controls to adjust ability)；
2, the present apparatus, system and control method can provide accurate mass flow for gas equipment and (extend relatively not true
Fixed degree≤0.3%), it on the other hand can be used as traffic alignment device and school implemented to common flow meters (usually thermal mass flow meter)
It is quasi-；The accuracy that can be improved gas mass flow as mass flow timing can guarantee work when as traffic alignment device
The magnitude of grade flowmeter is accurately and uniformly；
3, critical flow venturi nozzle is as the element for saving magnitude, and stability and repdocutbility are very good, accuracy, stabilization
Property, repdocutbility and anti-interference aspect be better than existing thermal mass flow meter；
4, the critical flow venturi nozzle of different larynx diameters can be matched according to range, and nozzle and pressure controller are easy to
Replacement, flexibly, whole equipment is placed in Portable instrument box, easy to use, reliable for configuration.
Detailed description of the invention
Fig. 1 is the control structure schematic diagram of existing thermal mass flow meter
Fig. 2 is the upstream and downstream pressure schematic diagram of critical flow venturi nozzle
Fig. 3 is efflux coefficient CdWith the graph of relation of reynolds number Re
Fig. 4 is low reynolds number region efflux coefficient CdWith the relational graph of reynolds number Re
Fig. 5 is a kind of preferred structure schematic diagram that gas mass flow controls calibrating installation
Fig. 6 is the structural schematic diagram of upstream installing pipe, downstream installing pipe
Fig. 7 is the attachment structure schematic diagram that a kind of gas mass flow controls calibration system
Fig. 8 is a kind of mounting structure schematic diagram of critical flow venturi nozzle
Fig. 9 is the corresponding mass flow of critical flow venturi nozzle and reynolds number range of different larynx diameters
In Fig. 1~9: 1 is heat type gas flow sensor, and 2 be flow control component, and 3 be proportion valve body, and 4 be gas stream
Road, 5 be stream pressure control element, and 6 be the critical fluid element that is jammed, and 7 be inlet pressure transmitter, and 8 be outlet back pressure transmitter,
9 be central processor CPU, and 10 be memory, and 11 be temperature transmitter, and 12 be filter, and 13 be display module, and 14 be input mould
Block, 15 be upstream installing pipe, and 151 be inlet pressure transmitter pressure port, and 152 take warm hole for temperature transmitter, and 16 pacify for downstream
Tubulature, 161 be outlet back pressure transmitter pressure port, 17 for it is critical be jammed fluid element install interface, 18 be air circuit connection interface, 19
It is gas source for vacuum generating device, 20,21 be vacuum tank, and 22 be flowmeter to be calibrated, and 23 be gas equipment, and 24 be gaseous mass
Flow control calibrating installation, 25 be regulating valve, and 26 be temperature A/D converter, and 27 be pressure A/D converter, and 28 be installation connection
Part, 29 be knob, and 30 be critical choked flow mounting blocks.
Specific embodiment
The present invention will be further explained below with reference to the attached drawings.
The flowing of process gas mainly controls mass flow by thermal mass flow meter at present.As shown in Figure 1, hot type matter
Amount flowmeter mainly includes heat type gas flow sensor 1, flow control component 2, proportion valve body 3 and gas flow path 4 etc., is such as schemed
Shown in 1.Wherein thermal type gas quality flow sensor 1 is the critical component of flow control.It utilizes hot between air-flow and heat source
Exchange principle is measured, heat source is set in inside, the variation of heat when flowing through heat source according to gas obtains the mass flow of gas.
The output signal of heat type gas flow sensor 1 is by data processing (including Data Linearization, temperature-compensating etc.
Reason), gas flow control is realized using Closed loop Control.In feedback control system, regardless of (being disturbed outside for what reason
The variation of dynamic or internal system), as long as controlled variable gas flow deviates scheduled setting value, it will use preposition proportion valve body 3
Flow is adjusted to reach the mass flow of setting, so by heat type gas flow sensor 1, proportion valve body 3, control unit group
At closed loop feedback system, corresponding adjusting is made according to the indicating value of heat type gas flow sensor 1, to realize automatic flow control
System.
Gas mass flow amount control method in this hair is not based on the hot principle art of existing amount of heat transfer, but is based on
Critical choking flow principle in aerodynamics, the control system based on gas mass flow amount control method of the present invention are constituted simultaneously
It does not include Closed loop Control, but by the independent function of implementing to adjust of stream pressure control element 5, that is, stream pressure control
Element 5 does not need to constitute control loop with flow sensor/indicator.
It in the specific implementation, is a kind of preferred embodiment of the critical fluid element that is jammed using critical flow venturi nozzle,
Critical flow venturi nozzle primarily as standard appliance applications gas flow metering.Critical flow venturi nozzle is utilized
The flow behavior of Laval nozzle (tapered divergent nozzle).As shown in Fig. 2, since critical flow venturi nozzle structure is simple, nothing
Movable member, detection piece are profile part, and no passivation defect, sound construction is light, durable, convenient for accurate duplication, are belonged to semipermanent
Property detection piece, thus the Transfer Standards of flow measurement are suitable as, as a result the nozzle accuracy after gauging calibration is generally ok
Reach 0.2 grade, multiple nozzles (range extension) in parallel can establish (the extension of critical flow venturi nozzle method gas flow standard device
Uncertainty: 0.25%~0.33%), it can be used as STANDARD MEASURING APPARATUS FOR and flowmeter examined and determine or calibrated.
As shown in Figure 2, if nozzle inlet pressure p1It remains unchanged, reduces jet expansion back pressure p2, that is, reduce back pressure ratio
p2/p1, it was continuously increased before this by the gas flow of critical flow venturi nozzle, when reaching critical pressure ratio, gas is critical
Stream Venturi nozzle throat velocity reaches local velocity of sound, and the gas mass flow for flowing through critical flow venturi nozzle reaches maximum,
Back pressure ratio is further decreased, flow will remain unchanged, this state is critical stream mode.
When gas passes through critical flow venturi nozzle and reaches critical flow condition, mass flow is calculated by formula IV
[1] (i.e. the deformation of formula III):
In formula:
Ant: critical flow venturi nozzle throat section product (m2), Ant=0.25 π d2, d is the larynx of critical flow venturi nozzle
Diameter (m)；
R: universal gas constant (Jmol-1·K-1)；
M: the molal weight (kgmol of gas-1)；
p0: the absolute stagnation pressure (Pa) of critical flow venturi nozzle upstream；
T0: the absolute stagnation temperature (K) of critical flow venturi nozzle upstream；
Cd: efflux coefficient, by Cd=f (Re), which is calculated, to be obtained, due to practical not proper by the air-flow of nozzle
One dimensional isentropic flow is influenced by viscosity there are a boundary-layer, so introducing efflux coefficient CdAs what is flowed to real gas
Amendment, and Cd<1；
C*: the critical flow of real gas, the critical flow of real gas, it is gas property and stagnant condition
Dimensionless function, it is artificial to assign one meaning of stream function for the convenience of magnitude tracing, i.e., so that C* is related with medium, and Cd
It is unrelated with medium.
Efflux coefficient C is removed in formula IIIdExcept, all be can measure or can calculation amount.Only efflux coefficient CdNeed practical mark
It is fixed, the efflux coefficient C of the nozzle is obtained through legal measurement technology mechanism calibrationd, then, by measurement gas on critical flow text mound
In nozzle upstream stagnation pressure p0, stagnation temperature T0, and the critical flow C for giving gas is calculated by formula* [1], can obtain
Mass flow of the critical flow venturi nozzle under actual condition.
And efflux coefficient CdIt is with the qualitative variation of reynolds number Re:
As shown in figure 3, with Re=2 × 105It is divided into low reynolds number region and high reynolds number region for boundary, in high reynolds number area
Domain, usually 106Or bigger region, in the case where being normally applied environment (pressure change is not violent), efflux coefficient CdIt is almost fixed
Value, and variation range is within ± 0.1%.Therefore, in medium or more large Reynold number region, critical flow venturi nozzle only has
There is single efflux coefficient calibration value, constant flow rate standard can only be used as, the adjustable control of gas mass flow can not be carried out.
But in low reynolds number region (Re < 2 × 105), especially Re≤104Region, efflux coefficient CdWith reynolds number Re
Nonlinear change it is very big, pass through reynolds number Re influence efflux coefficient Cd, to finally realize the adjusting to gas mass flow.
So in Re≤104The extremely low region of flow in, critical flow venturi nozzle is not re-used as constant current device use, and is used as controlling
The variable-quality flow element of mass flow processed.
Studies have shown that efflux coefficient C in low reynolds number regiondA simple nonlinear function can be used with reynolds number Re
It indicates, thus in range ability, at least need to demarcate corresponding efflux coefficient C under five different Reynolds number Red, to be fitted
Obtain the efflux coefficient C of the critical flow venturi nozzledFunctional relation with reynolds number Re in low reynolds number region:
Cd=f (Re) I
In practical calibration, functional expression obtained by calibrating will not be just the same each time, such as:
Or
As shown in figure 4, being as directed to respectively in low reynolds number region to two critical flow venturi nozzles of Q1 and A6 more
Corresponding efflux coefficient C under a different Reynolds number RedRelational graph can respectively obtain two critical flow texts according to the calibration result
The efflux coefficient C of nozzle in mounddWith reynolds number Re in low reynolds number region (Re≤104) functional relation.
After the completion of critical flow venturi nozzle manufacture, larynx diameter is it is known that can demarcate acquisition through legal measurement technology mechanism
Formula I.
Reynolds number Re and mass flow also have following functional relation:
In formula:
D: the larynx diameter of critical flow venturi nozzle；
μ0: aerodynamic force viscosity is tabled look-up acquisition according to gas temperature, and aerodynamic force viscosity hardly follows pressure change under normal pressure
Change and changes, by taking air as an example, under normal circumstances, air viscosity (1.81 × 10-5~1.84 × 10-5)Pa·s；
By formula I, II, III it is found that critical flow venturi nozzle (i.e. back pressure ratio p under critical stream mode2/p1Less than critical pressure
Power ratio), mass flow value is by upstream stagnation pressure p0, stagnation temperature T0It determines, with downstream pressure p2Variation it is unrelated.It examines
Considering control temperature accurately to change relatively difficult therefore of the invention thinking is that a mass flow is preset under critical stream mode
qm, first pass through formula II and calculate the corresponding reynolds number Re of acquisition, then calculated by formula I and obtain corresponding efflux coefficient Cd, then pass through
Formula III, which calculates, obtains inlet pressure target value p0(the i.e. absolute stagnation pressure p of upstream0), upstream is finally adjusted according to the calculated value
Entrance actual pressure p1Until p1=p0, to make the actual mass flow and preset value q of gas flow pathmIt is identical, it is accurate to realize
Flow measurement, if necessary to control mass-flow change, then still reset another mass flow q by above-mentioned thinkingm, control
Stagnation pressure p in upstream processed0Variation, thus finally change gas flow path actual mass flow.
Gas mass flow as shown in Figure 5 controls calibrating installation, filter 12, stream pressure control including gas circuit connection
Element 5 processed and the critical fluid element 6 that is jammed, it is critical to be jammed 6 inlet of fluid element and exit is respectively equipped with inlet pressure transmitter 7
With outlet back pressure transmitter 8；Critical 6 inlet of fluid element of being jammed is additionally provided with temperature transmitter 11；Temperature transmitter 11, entrance pressure
Power transmitter 7 and outlet back pressure transmitter 8 connect centre by temperature A/D converter 26 and pressure A/D converter 27 respectively
Device CPU9 is managed, central processor CPU 9 passes through circuit connection stream pressure control element 5, display module 13,14 and of input module
Memory 10 is electrically connected central processor CPU 9；In the present embodiment, memory 10 is erasable programmable read-only memory
EPROM10；Stream pressure control element 5 is automatic pressure controller；The critical fluid element 6 that is jammed is critical flow venturi nozzle.
Formula I, II and III is pre-stored in memory 10, in actual operation, central processor CPU 9 receives setting
Mass flow value qm, reynolds number Re is calculated by formula II according to the stagnation state parameter measured, is obtained flowing out system accordingly by formula I
Number Cd, under more stable environment temperature, p is obtained by formula III0, as pressure controlled target, final use is from dynamic pressure
Force controller realizes that accurate mass flow is adjusted.The present apparatus and system are suitable for low reynolds number flow range (Re < 2 × 105),
Usually in Re≤104Region, critical flow venturi nozzle are current limiting elements, and automatic pressure controller is regulating element, flow tune
The lower limit of section depends on critical flow venturi nozzle efflux coefficient CdCapacity rating and automatic pressure controller pressure control
Regulating power.In use process, it is necessary to ensure that the ratio between critical flow venturi nozzle outlet back pressure and inlet pressure, which are consistently lower than, to be faced
Boundary's back pressure ratio, air-flow reaches velocity of sound by the speed of critical flow venturi nozzle throat at this time.
Integrated boxlike gas mass flow as shown in Figure 7 controls calibrating installation 24, and display module 13 is LCD panel,
Input module 14 is point contact type input panel, and point contact type input panel and LCD panel pass through input and output processing circuit respectively
Connect central processor CPU 9.
As shown in fig. 6, further including two coaxial peaces if gas mass flow control calibrating installation 24 is component assembly type
Tubulature, upstream installing pipe 15 is equipped with inlet pressure transmitter pressure port 151 and temperature transmitter takes warm hole 152, is respectively used to
Fast Installation inlet pressure transmitter 7 and temperature transmitter 11, downstream installing pipe 16 are equipped with outlet back pressure transmitter pressure port
161, it is used for Fast Installation outlet back pressure transmitter 8, is set respectively on upstream installing pipe 15 and the opposite one end of downstream installing pipe 16
There is the critical fluid element installation interface 17 that is jammed, is respectively equipped with air circuit connection interface 18 on opposite one end.
The mass flow of each critical flow venturi nozzle has a certain amount journey range, to adjust or changing when needed
The whole range ability for becoming gas mass flow control calibrating installation 24, can pass through the critical choked flow mounting blocks 30 in Fig. 8
The critical flow venturi nozzle or multiple critical flow venturi nozzles in parallel of different larynx diameters are replaced, the nozzle of different larynx diameters is corresponding
Mass flow adjustable range it is as shown in Figure 9.
When need replacing it is different it is critical be jammed fluid element 6 or it is in parallel multiple when, it is contemplated that single critical choked flow member
6 small volume of part, to be easily installed, mounting structure as shown in Figure 8 can use knob 29 and installation connecting element 28,
The critical fluid element 6 that is jammed is sent into the mounting hole in critical choked flow mounting blocks 30 one by one and is fixed, critical choked flow installation
It is equipped with independent gas circuit in each mounting hole of block 30, only built-in critical 6 gas circuit of fluid element of being jammed can be just connected to, and installation is solid
After fixed, knob 29 and 28 entirety of installation connecting element are detached from the critical fluid element 6 that is jammed.
When the critical fluid element 6 that is jammed is installed in parallel, all critical fluid elements 6 that are jammed share a set of outlet back pressure transmitter 8
With temperature transmitter 11, independent inlet pressure transmitter 7 and stream pressure is respectively set in corresponding each critical fluid element 6 that is jammed
Control element 5；And for formula I, the efflux coefficient C of each critical fluid element 6 that is jammed is pre-stored in memory 10dWith
Functional relation C of the reynolds number Re in low reynolds number regiond1=f1(Re), Cd2=f2(Re) ..., Cdn=fn(Re)。
Gas mass flow as shown in Figure 7 controls calibration system, including is set to gas mass flow and controls calibrating installation
24, and set on vacuum generating device 19 downstream, it is provided thereon gas source 20, regulating valve 25 and the vacuum tank 21 of trip, this reality
It applies in example, vacuum generating device 19 is vacuum pump.
When carrying out gas mass flow calibration using this gas mass flow control calibration system, by flowmeter 22 to be calibrated
Air circuit connection controls 24 downstream of calibrating installation in gas mass flow, then carries out as follows:
Whole system is placed in the laboratory environment of a constant temperature by the first step；
Second step opens gas source 20, vacuum tank 21, uses 25 coarse adjustment gas pressure of regulating valve, it is ensured that enters gaseous mass
The gas pressure of flow control calibrating installation 24 is no more than the pressure-resistant upper limit of stream pressure control element 5, avoids damage instrument；
Third step opens gas mass flow control calibrating installation 24 and flowmeter to be calibrated 22, makes it into normal work
Make state；
4th step starts vacuum generating device 19, reduces the critical 6 outlet back pressure p of fluid element that is jammed2, until by critical
The air-flow back pressure ratio of fluid element 6 of being jammed is less than or equal to critical backing pressure ratio, and the fluid element 6 that is jammed critical at this time is in critical stream mode
Under, gas mass flow is stablized, into the adjustable stage；
5th step, by required gas mass flow magnitude qmIt is inputted by input module 14；
6th step, central processor CPU 9 is according to mass flow set point qm, reynolds number Re, then root are calculated by formula II
Corresponding efflux coefficient C is calculated according to formula Id, the critical 6 inlet temperature T of fluid element that is jammed of the actual measurement of combination temperature transmitter 110,
Pressure target value p is calculated according to formula III0；
7th step, under critical stream mode, central processor CPU 9 is by pressure target value p0It is sent to stream pressure control
Element 5, by its separately adjustable inlet pressure, the inlet pressure p for monitoring inlet pressure transmitter 71Equal to target value p0, at this time
The critical real gas mass flow for being jammed the output of fluid element 6 is setting value qm；
Whether the reading of flowmeter to be calibrated 22 that mass flow value at this time can be used for calibrating downstream is accurate；
8th step repeats the 5th step~the 7th step, and the flowmeter to be calibrated 22 for calibrating downstream is read in different quality flow point
Whether number is accurate；
After use, vacuum generating device 19, gas source 20, vacuum tank 21 are successively closed；Close gas mass flow control
Calibrating installation 24 and flowmeter to be calibrated 22 processed；
If the critical fluid element 6 that is jammed in gas mass flow control calibrating installation 24 is n in parallel, and at least
Two when working at the same time, in above-mentioned 4th step, need to adjust all critical fluid elements 6 that is jammed and are under critical stream mode,
Need to calculate separately the pressure target value p of each critical fluid element 6 that is jammed in 6th step0, need to adjust each face in the 7th step
Boundary be jammed fluid element 6 inlet pressure be equal to respective pressure target value p0。
When carrying out gas mass flow control using this gas mass flow control calibration system, gas equipment 23 is connected
24 downstream of calibrating installation is controlled in gas mass flow, is then carried out as follows:
Whole system is placed in the laboratory environment of a constant temperature by the first step；
Second step opens gas source 20, vacuum tank 21, uses 25 coarse adjustment gas pressure of regulating valve, it is ensured that enters gaseous mass
The gas pressure of flow control calibrating installation 24 is no more than the pressure-resistant upper limit of stream pressure control element 5, avoids damage instrument；
Third step opens gas mass flow control calibrating installation 24 and gas equipment 23, makes it into normal work shape
State；
4th step starts vacuum generating device 19, reduces the critical 6 outlet back pressure p of fluid element that is jammed2, until by critical
The air-flow back pressure ratio of fluid element 6 of being jammed is less than or equal to critical backing pressure ratio, and the fluid element 6 that is jammed critical at this time is in critical stream mode
Under, gas mass flow is stablized, into the adjustable stage；
5th step, by required gas mass flow magnitude qmIt is inputted by input module 14；
6th step, central processor CPU 9 is according to mass flow set point qm, reynolds number Re, then root are calculated by formula II
Corresponding efflux coefficient Cd, critical 6 inlet temperature of fluid element that is jammed that combination temperature transmitter 11 is surveyed are calculated according to formula I
T0, pressure target value p is calculated according to formula III0；
7th step, under critical stream mode, central processor CPU 9 is by pressure target value p0It is sent to stream pressure control
Element 5, by its separately adjustable inlet pressure, the inlet pressure p for monitoring inlet pressure transmitter 71Equal to target value p0, at this time
The critical real gas mass flow for being jammed the output of fluid element 6 is setting value qm；
Mass flow value at this time is the real gas mass flow value of gas equipment 23, passes through use if necessary to change
The gas mass flow of gas equipment 23 repeats the 5th step~the 7th step, after use, successively closes vacuum generating device
19, gas source 20, vacuum tank 21；Close gas mass flow control calibrating installation 24 and gas equipment 23；
If the critical fluid element 6 that is jammed in gas mass flow control calibrating installation 24 is n in parallel, and at least
Two when working at the same time, in above-mentioned 4th step, need to adjust all critical fluid elements 6 that is jammed and are under critical stream mode,
Need to calculate separately the pressure target value p of each critical fluid element 6 that is jammed in 6th step0, need to adjust each face in the 7th step
Boundary be jammed fluid element 6 inlet pressure be equal to respective pressure target value p0。
Claims (17)
1. a kind of low reynolds number zone gas mass flow control method, it is characterised in that:
The first step, in reynolds number Re≤104Low reynolds number region, 5 different thunders are at least demarcated to the critical fluid element that is jammed (6)
Corresponding efflux coefficient C under promise number Red, to derive the efflux coefficient C of the critical fluid element that is jammed (6)dExist with reynolds number Re
The functional relation in low reynolds number region:
Cd=f (Re)； (Ⅰ)
Second step, keeping the air-flow of the critical fluid element that is jammed (6) upstream is T0Constant temperature flows a gas over the critical fluid element that is jammed
(6), the inlet pressure p of the critical fluid element that is jammed (6) is kept1It is constant, reduce the outlet back pressure p of the critical fluid element that is jammed (6)2, make
Back pressure ratio p2/p1Reduce, is increased by the gas mass flow of the critical fluid element that is jammed (6), until p2/p1Reach critical backing pressure
Than when, gas reaches local velocity of sound in the critical fluid element that is jammed (6) throat velocity, flows through the gas of the critical fluid element that is jammed (6)
Reach critical state of being jammed, further decreases back pressure ratio p at this time2/p1, gas mass flow remains unchanged, and keeps p2/p1Always
Less than or equal to critical backing pressure ratio；
Third step sets the gas mass flow by the critical fluid element that is jammed (6) as qm, (II), which calculates, according to the following formula is somebody's turn to do
Gas mass flow qmCorresponding reynolds number Re:
In formula:
D: the larynx diameter of the critical fluid element that is jammed (6),
μ0: aerodynamic force viscosity is tabled look-up acquisition according to gas temperature, under normal pressure aerodynamic force viscosity hardly follow pressure change and
Variation；
Re≤104；
Reynolds number Re calculated in formula (II) is substituted into formula (I), to calculate the corresponding outflow system of the reynolds number Re
Number Cd, the inlet pressure target value p of the critical fluid element that is jammed (6) is calculated further according to following formula (III)0:
In formula:
Ant: the critical fluid element that is jammed (6) throat section product, Ant=0.25 π d2, d is the larynx diameter of the critical fluid element that is jammed (6)；
R: universal gas constant；
M: the molal weight of gas；
p0: the absolute stagnation pressure of the critical fluid element that is jammed (6) upstream；
T0: the absolute stagnation temperature of the critical fluid element that is jammed (6) upstream；
Cd: efflux coefficient, by Cd=f (Re), which is calculated, to be obtained, and Cd<1；
C*: the critical flow of real gas, calculation formula:
In formula each parameter only need to according to gas property, temperature, pressure is tabled look-up can be obtained；
4th step is keeping back pressure ratio p2/p1Under the premise of critical backing pressure ratio, the critical fluid element that is jammed (6) is adjusted
Inlet pressure p1Until p1=p0, it is at this time setting value by the real gas mass flow value of the critical fluid element that is jammed (6)
qm。
2. low reynolds number zone gas mass flow control method according to claim 1, it is characterised in that: described critical
It is jammed fluid element (6) for critical flow venturi nozzle, or nozzle, spray orifice or jet pipe based on critical choked flow principle.
3. low reynolds number zone gas mass flow control method according to claim 1, it is characterised in that: the gas
For air or oxygen, nitrogen, argon gas, methane, carbon dioxide.
4. a kind of gas mass flow controls calibrating installation, it is characterised in that:
Stream pressure control element (5) and the critical fluid element that is jammed (6) including gas circuit connection, the critical fluid element that is jammed (6) enter
At mouthful and exit is respectively equipped with inlet pressure transmitter (7) and outlet back pressure transmitter (8)；
The critical fluid element that is jammed (6) inlet is additionally provided with temperature transmitter (11)；
Temperature transmitter (11), inlet pressure transmitter (7), outlet back pressure transmitter (8) are electrically connected central processor CPU
(9), central processor CPU (9) is electrically connected stream pressure control element (5), display module (13), input module (14) and
Memory (10) is electrically connected central processor CPU (9)；
Formula (I), (II) and (III) is pre-stored in the memory (10).
5. gas mass flow according to claim 4 controls calibrating installation, it is characterised in that: the critical choked flow member
Part (6) is one or n in parallel.
6. gas mass flow according to claim 5 controls calibrating installation, it is characterised in that: n of the parallel connection face
Boundary's fluid element (6) that is jammed shares a set of outlet back pressure transmitter (8) and temperature transmitter (11), corresponding each critical choked flow member
Independent inlet pressure transmitter (7) and stream pressure control element (5) is respectively set in part (6)；
And for formula (I), the efflux coefficient C of each critical fluid element that is jammed (6) is pre-stored in memory (10)dWith
Functional relation C of the reynolds number Re in low reynolds number regiond1=f1(Re), Cd2=f2(Re) ..., Cdn=fn(Re)。
7. gas mass flow according to claim 4 controls calibrating installation, it is characterised in that: the gas mass flow
Controlling calibrating installation (24) further includes the filter (12) for being set to stream pressure control element (5) upstream.
8. gas mass flow according to claim 4 controls calibrating installation, it is characterised in that: the temperature transmitter
(11), inlet pressure transmitter (7) and outlet back pressure transmitter (8) are turned by temperature A/D converter (26) and pressure A/D respectively
Parallel operation (27) connects central processor CPU (9), and central processor CPU (9) passes through circuit connection stream pressure control element (5),
The memory (10) is erasable programmable read-only memory EPROM (10).
9. gas mass flow according to claim 4 controls calibrating installation, it is characterised in that: the gas mass flow
Controlling calibrating installation (24) is Integral box type, and display module (13) is LCD panel, and input module (14) is point contact type input
Panel, point contact type input panel pass through input and output processing circuit respectively with LCD panel and connect central processor CPU (9).
10. gas mass flow according to claim 4 controls calibrating installation, it is characterised in that: the gas mass flow
Amount control calibrating installation (24) is component assembly type, further includes two and is co-axially mounted pipe, upstream installing pipe (15) is equipped with entrance
Pressure transmitter pressure port (151) and temperature transmitter take warm hole (152), and downstream installing pipe (16) is equipped with outlet back pressure pick-up
Critical choked flow member is respectively equipped on device pressure port (161), upstream installing pipe (15) and the opposite one end of downstream installing pipe (16)
Part installs interface (17), is respectively equipped with air circuit connection interface (18) on opposite one end.
11. gas mass flow according to claim 4 controls calibrating installation, it is characterised in that: the stream pressure control
Element (5) processed is automatic pressure controller.
12. a kind of gas mass flow controls calibration system, it is characterised in that: including such as any institute of the claims 4~12
Gas mass flow control calibrating installation (24) stated.
13. gas mass flow according to claim 12 controls calibration system, it is characterised in that: further include being set to gas
Mass flow controls the vacuum generating device (19) in calibrating installation (24) downstream, is set to gas mass flow and controls calibrating installation
(24) gas source (20) of upstream, regulating valve (25) and vacuum tank (21).
14. gas mass flow according to claim 13 controls calibration system, it is characterised in that: the vacuum fills
Setting (19) is vacuum pump or vacuum generator.
15. a kind of carry out gas mass flow using any gas mass flow control calibration system of claim 13~14
Flowmeter to be calibrated (22) air circuit connection is controlled calibrating installation (24) downstream in gas mass flow, so by the method for measuring calibration
It carries out as follows afterwards:
Whole system is placed in the laboratory environment of a constant temperature by the first step；
Second step opens gas source (20), vacuum tank (21), uses regulating valve (25) coarse adjustment gas pressure, it is ensured that enters gas matter
The gas pressure for measuring flow control calibrating installation (24) is no more than the pressure-resistant upper limit of stream pressure control element (5)；
Third step opens gas mass flow control calibrating installation (24) and flowmeter to be calibrated (22), makes it into normal work
Make state；
4th step starts vacuum generating device (19), reduces the critical fluid element that is jammed (6) outlet back pressure p2, until passing through critical heap soil or fertilizer over and around the roots
The air-flow back pressure ratio of plug flow element (6) is less than or equal to critical backing pressure ratio, and the fluid element that is jammed (6) critical at this time is in critical stream mode
Under, gas mass flow is stablized, into the adjustable stage；
5th step, by required gas mass flow magnitude qmIt is inputted by input module (14)；
6th step, central processor CPU (9) is according to mass flow set point qm, reynolds number Re, then root are calculated by formula (II)
Corresponding efflux coefficient C is calculated according to formula (I)d, the critical fluid element that is jammed (6) inlet of combination temperature transmitter (11) actual measurement
Temperature T0, pressure target value p is calculated according to formula (III)0；
7th step, under critical stream mode, central processor CPU (9) is by pressure target value p0It is sent to stream pressure control element
(5), by its separately adjustable inlet pressure, the inlet pressure p for monitoring inlet pressure transmitter (7)1Equal to target value p0, at this time
The real gas mass flow of the critical fluid element that is jammed (6) output is setting value qm；
Whether flowmeter to be calibrated (22) reading that mass flow value at this time can be used for calibrating downstream is accurate；
8th step repeats the 5th step~the 7th step, and the flowmeter to be calibrated (22) for calibrating downstream is read in different quality flow point
It is whether accurate；
After use, vacuum generating device (19), gas source (20), vacuum tank (21) are successively closed；Close gas mass flow
Control calibrating installation (24) and flowmeter to be calibrated (22).
16. a kind of carry out gas mass flow using any gas mass flow control calibration system of claim 13~14
Gas equipment (23) is connected to gas mass flow control calibrating installation (24) downstream, then by as follows by the method for measuring control
Step carries out:
Whole system is placed in the laboratory environment of a constant temperature by the first step；
Second step opens gas source (20), vacuum tank (21), uses regulating valve (25) coarse adjustment gas pressure, it is ensured that enters gas matter
The gas pressure for measuring flow control calibrating installation (24) is no more than the pressure-resistant upper limit of stream pressure control element (5)；
Third step opens gas mass flow control calibrating installation (24) and gas equipment (23), makes it into normal work shape
State；
4th step starts vacuum generating device (19), reduces the critical fluid element that is jammed (6) outlet back pressure p2, until passing through critical heap soil or fertilizer over and around the roots
The air-flow back pressure ratio of plug flow element (6) is less than or equal to critical backing pressure ratio, and the fluid element that is jammed (6) critical at this time is in critical stream mode
Under, gas mass flow is stablized, into the adjustable stage；
5th step, by required gas mass flow magnitude qmIt is inputted by input module (14)；
6th step, central processor CPU (9) is according to mass flow set point qm, reynolds number Re, then root are calculated by formula (II)
Corresponding efflux coefficient Cd, the critical fluid element that is jammed (6) inlet of combination temperature transmitter (11) actual measurement are calculated according to formula (I)
Temperature T0, pressure target value p is calculated according to formula (III)0；
7th step, under critical stream mode, central processor CPU (9) is by pressure target value p0It is sent to stream pressure control element
(5), by its separately adjustable inlet pressure, the inlet pressure p for monitoring inlet pressure transmitter (7)1Equal to target value p0, at this time
The real gas mass flow of the critical fluid element that is jammed (6) output is setting value qm；
Mass flow value at this time is the real gas mass flow value of gas equipment (23), if necessary to change by using gas
The gas mass flow of equipment (23) repeats the 5th step~the 7th step, after use, successively closes vacuum generating device
(19), gas source (20), vacuum tank (21)；Close gas mass flow control calibrating installation (24) and gas equipment (23).
17. the method according to claim 15 for carrying out gas mass flow calibration, or according to claim 1 described in 6
Progress gas mass flow control method, it is characterised in that:
If it is n in parallel that gas mass flow, which controls the critical fluid element that is jammed (6) in calibrating installation (24), and at least
Two when working at the same time, in above-mentioned 4th step, need to adjust all critical fluid elements that is jammed (6) and are in critical stream mode
Under, need to calculate separately the pressure target value p of each critical fluid element that is jammed (6) in the 6th step0, need to adjust in the 7th step every
The inlet pressure of a critical fluid element that is jammed (6) is equal to respective pressure target value p0。
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Cited By (1)
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| CN115259692A (en) * | 2022-07-14 | 2022-11-01 | 四川天马玻璃有限公司 | High-precision gas delivery system |
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Application publication date: 20190604 |