CN113607246A - Calibration device and method for low-temperature flowmeter - Google Patents
Calibration device and method for low-temperature flowmeter Download PDFInfo
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- CN113607246A CN113607246A CN202110873299.1A CN202110873299A CN113607246A CN 113607246 A CN113607246 A CN 113607246A CN 202110873299 A CN202110873299 A CN 202110873299A CN 113607246 A CN113607246 A CN 113607246A
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- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
- G01F1/34—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure
- G01F1/36—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure the pressure or differential pressure being created by the use of flow constriction
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- G01F1/44—Venturi tubes
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Abstract
The invention provides a calibration device and a calibration method of a low-temperature flowmeter, which comprise a vacuum cylinder and a flange plate covering the upper end of the vacuum cylinder, wherein liquid helium is stored in the vacuum cylinder to form a liquid helium bath, at least one heat exchanger is arranged above the liquid helium bath, at least one flowmeter to be measured is connected in series in the liquid helium bath, the calibration device also comprises a compressor positioned outside the vacuum cylinder, an outlet of the compressor is sequentially connected in series with the flowmeter to be measured in the liquid helium bath through the heat exchanger, then the outlet of the compressor leaves the liquid helium bath and returns to an inlet of the compressor through the heat exchanger, a loop of the compressor is filled with helium, and a pipeline close to an inlet of the compressor is provided with a standard flowmeter positioned outside the vacuum cylinder. The invention has the advantages that: the method and the device provide liquid helium temperature zone environment for the flowmeter to be measured, realize the calibration of the flowmeter to be measured by comparing the numerical values of the standard flowmeter and the flowmeter to be measured, can calibrate a plurality of flowmeters to be measured respectively at the same time, and have high efficiency and accurate calibration result.
Description
Technical Field
The invention relates to the technical field of low-temperature flowmeters, in particular to a calibration device and method of a low-temperature flowmeter.
Background
The application of low-temperature technology in the fields of superconduction, aerospace, medical treatment and the like is more and more extensive, and the flow is used as one of the most important parameters in the process design and control of a low-temperature refrigeration system, so that the safe, efficient and stable operation of the whole system is related, and meanwhile, the flow is also an important basis for the performance analysis and optimization of the system. However, the precision of the current low-temperature flow meter, especially the flow meter in the liquid helium temperature region, can not meet the system requirement.
Since the eighties of the last century, many foreign research institutions and metering instrument companies began to research low-temperature flowmeters and build calibration platforms capable of testing various flowmeters. In recent years, domestic research on low-temperature flow measurement is continuously developed, such as optimization of a perforated plate flowmeter at Zhejiang university and research of a liquid nitrogen temperature zone Venturi flowmeter by plasma physical research institute of Chinese academy of sciences. However, most of domestic calibration research on low-temperature flowmeters is based on experiments at normal temperature, such as the calibration method of the low-temperature flowmeter disclosed in the invention patent application with the publication number of CN 108593054A; and a small part of the liquid nitrogen temperature zone is calibrated, but calibration under the flowing condition of the liquid helium temperature zone is not performed, so that the establishment of an experimental platform capable of testing and calibrating various flowmeters in the liquid helium temperature zone has important significance.
Disclosure of Invention
The invention aims to provide a device and a method for calibrating a low-temperature flowmeter in a low-temperature flowing state.
The invention solves the technical problems through the following technical scheme: the utility model provides a calibration device of low temperature flowmeter, includes the vacuum cylinder and covers the ring flange in vacuum cylinder upper end, the storage has liquid helium to form liquid helium bath in the vacuum cylinder, and liquid helium bath top is provided with at least one heat exchanger, and the interior at least one flowmeter that awaits measuring that concatenates of liquid helium bath still includes the compressor that is in the vacuum cylinder outside, the export of compressor is established ties in proper order through heat exchanger and the flowmeter that awaits measuring that is in liquid helium bath, then leaves the liquid helium bath and return the entry to the compressor through the heat exchanger, the return circuit intussuseption of compressor is filled with the helium, is provided with the standard flowmeter that is in the vacuum cylinder outside on the pipeline that is close to the compressor entry.
The liquid helium cooling device has the advantages that the low-temperature flow meter to be measured and the fluid helium are cooled by the liquid helium, the liquid helium temperature zone environment is provided for the flow meter to be measured, the numerical value measured by the standard flow meter is used as an actual value, the calibration of the flow meter to be measured is realized by comparing the numerical values of the standard flow meter and the flow meter to be measured, the calibration device can be used for simultaneously and respectively calibrating a plurality of flow meters to be measured, the efficiency is high, the calibration result is accurate, the medium-pressure path helium flowing out after passing through the flow meter to be measured transmits the cooling capacity to the high-pressure helium road roller through the heat exchanger, the influence on the temperature of the liquid helium is reduced, and the evaporation capacity of the liquid helium is reduced.
Preferably, a cooling coil in a liquid helium bath is further arranged in the vacuum cylinder, and a helium pipeline enters the flowmeter to be measured after passing through the cooling coil;
the standard flow meter is a coriolis mass flow meter.
Preferably, the inlet and outlet of the compressor are respectively provided with a first valve and a third valve, and the first valve and the third valve are both back pressure valves;
and a second valve is also arranged on a helium pipeline before the compressor enters the low-temperature cylinder, and the second valve is a flow regulating valve.
Preferably, the device also comprises a vacuum unit, a liquid helium Dewar and an air bag.
The vacuum unit is communicated with the vacuum cylinder and the helium pipeline through a fourth valve and a fifth valve respectively; the liquid helium dewar is connected with the vacuum cylinder through a sixth valve; the air bag is connected with the vacuum cylinder through a seventh valve, and a liquid level sensor is arranged in the vacuum cylinder.
Preferably, each flowmeter to be measured is provided with a differential pressure transmitter and/or two ends of the flowmeter to be measured are provided with pressure transmitters respectively; and a temperature sensor for detecting the temperature of the helium gas is arranged at least before the first flowmeter to be detected.
Preferably, at least one radiation-proof plate is further fixed between the flange plate and the vacuum cylinder.
Preferably, the heat exchanger comprises a primary sleeve heat exchanger and a secondary sleeve heat exchanger, the compressor drives helium to sequentially pass through the primary sleeve heat exchanger and the secondary sleeve heat exchanger, then enter the liquid helium bath, flow through the flowmeter to be measured, and then sequentially pass through the secondary sleeve heat exchanger and the primary sleeve heat exchanger to return to the compressor;
the size of an inner pipe of the primary double-pipe heat exchanger is 0.01m multiplied by 0.001m, the size of an outer pipe of the primary double-pipe heat exchanger is 0.022m multiplied by 0.002m, the length of the inner pipe is 103m, the size of an inner pipe of the secondary double-pipe heat exchanger is 0.007m multiplied by 0.0005m, the size of an outer pipe of the secondary double-pipe heat exchanger is 0.01m multiplied by 0.001m, and the length of the outer pipe is 17 m; returning air from the inner pipes of the first-stage double-pipe heat exchanger and the second-stage double-pipe heat exchanger, and feeding air from the outer pipes;
the cooling coil has a pipe diameter of 0.007m, a wall thickness of 0.0005m and a length of 3.18 m.
The invention also provides a low-temperature flowmeter calibrating method using the low-temperature flowmeter calibrating device, which comprises the following steps,
s1: vacuumizing the vacuum cylinder and the helium pipeline, and refilling helium into the helium pipeline;
s2: respectively connecting a liquid helium dewar storing liquid helium and a gas bag with a vacuum cylinder;
s3: adjusting the valve states of the compressor and the helium pipeline, and keeping the current state when the pressure of the helium pipeline reaches a preset value;
s4: recording pressure values of the standard flowmeter and the flowmeter to be measured and pressure difference of helium flowing through the flowmeter to be measured;
s5: adjusting the flow of the helium pipeline to adjust the pressure by a preset variable quantity, repeating the step S4 until a preset upper flow limit is reached, and closing the calibration device;
s6: and calculating the outflow coefficient of the flowmeter to be measured.
Preferably, the step of turning off the calibration means includes,
step A: closing the liquid helium dewar and stopping supplying liquid to the vacuum cylinder;
and B: the valves on the helium pipeline are closed in sequence from the inlet to the outlet, and finally the compressor is closed;
and C: opening a vacuumizing valve on the vacuum cylinder body to release the pressure in the vacuum cylinder body, wherein in the pressure release process, the pressure in the vacuum cylinder body needs to be kept higher than 1.1 bar;
step D: after 10 hours, the connection between the air bag and the vacuum cylinder was disconnected.
Preferably, the method for calculating the outflow coefficient of the flowmeter to be measured includes:
the flow meter to be measured is a Venturi tube flow meter, and the measured value q of the standard flow meter is usedmiThe measured value of the flowmeter to be measured is q 'as the actual value of the flowmeter to be measured'miThe expression is
Wherein i represents the data measured at the ith time, and C represents the outflow coefficient and the ratio of the actual flow to the theoretical flow; d is the inner diameter of the expansion section of the Venturi tube, and beta is the throat diameter ratio of the Venturi tube, and represents the ratio of the diameter D of the contraction section to the inner diameter D of the expansion section; ρ is helium density, Δ piThe pressure difference of the flowmeter to be measured;
the error functions for the standard flow meter and the flow meter under test are expressed as:
substituting formula (1) into formula (2) when the function f has minimum value, and calculating partial derivative of function f with respect to variable C
Order to
The best estimate of the outflow coefficient C is
The calibration device and method of the low-temperature flowmeter provided by the invention have the advantages that: the low-temperature flow meter and the fluid helium gas to be measured are cooled by the liquid helium, a liquid helium temperature area environment is provided for the flow meter to be measured, the numerical value of the standard flow meter is used as an actual value, the calibration of the flow meter to be measured is realized by comparing the numerical values of the standard flow meter and the flow meter to be measured, and the calibration device can be used for simultaneously calibrating a plurality of flow meters to be measured respectively, so that the efficiency is high, the calibration result is accurate, the medium-pressure path helium gas flowing out after passing through the flow meter to be measured transmits the cooling capacity to the high-pressure path helium gas through the heat exchanger, the influence on the temperature of the liquid helium is reduced, and the evaporation capacity of the liquid helium is reduced. The two sleeve heat exchangers reduce heat loss and improve heat exchange efficiency; the liquid helium using amount in the vacuum cylinder is controlled through the liquid helium dewar and the air bag, evaporated helium is stored in time, and the radiation-proof plate is arranged between the flange plate and the vacuum cylinder, so that radiation heat transfer is reduced, and heat loss is reduced.
Drawings
FIG. 1 is a schematic diagram of a calibration apparatus for a low temperature flowmeter according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of a venturi tube flowmeter calibrated by a calibration apparatus for a cryogenic flowmeter according to an embodiment of the present invention.
Detailed Description
To make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention are described below in detail and completely with reference to the accompanying drawings, and it is apparent that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, the embodiment provides a calibration apparatus for a low-temperature flowmeter, which calculates the outflow coefficient of the calibrated flowmeter in the low-temperature region corresponding to liquid helium, thereby realizing the conversion from the measurement value to the actual value of the flowmeter, specifically comprising a vacuum cylinder 1 and a flange 2 covering the upper end of the vacuum cylinder 1, liquid helium is stored in the vacuum cylinder 1 to form a liquid helium bath, at least one heat exchanger is arranged above the liquid helium bath, at least one flowmeter 3 to be tested is arranged in the liquid helium bath, a compressor 4 is also arranged on the outer side of the vacuum cylinder 1, the outlet of the compressor 4 is sequentially connected in series with at least one flowmeter 3 to be measured in the liquid helium bath through a heat exchanger, then the gas leaves the liquid helium bath and returns to the inlet of a compressor 4 through a heat exchanger, the loop of the compressor 4 is filled with helium gas, and a standard flow meter 5 which is arranged outside the vacuum cylinder 1 is arranged on a pipeline which is close to the inlet of the compressor 4.
This embodiment cools off the low temperature flowmeter and the fluid helium gas that await measuring through liquid helium, provide liquid helium warm area environment for the flowmeter 3 that awaits measuring, numerical value through standard flowmeter 5 measurement is as actual value, the calibration of flowmeter 3 that awaits measuring is realized through the numerical value of comparison standard flowmeter 5 and the flowmeter 3 that awaits measuring, and through this calibration equipment, can mark respectively a plurality of flowmeters 3 that await measuring simultaneously, high efficiency, calibration result is accurate, make the medium pressure way helium gas that flows out behind the flowmeter 3 that awaits measuring transmit cold volume for high pressure way helium gas through the heat exchanger, reduce the influence to liquid helium temperature, reduce the evaporation capacity of liquid helium. Based on the calibration device provided by the embodiment, if the low-temperature flowmeter needs to be calibrated in other low-temperature regions, the low-temperature medium in the corresponding temperature region can be used for replacing liquid helium and helium gas for testing.
The flowmeter 3 to be tested is provided with a differential pressure transmitter 31 and/or pressure transmitters 32 at the front end and the rear end of the flowmeter 3 to be tested respectively, so that the pressure change value after flowing through the flowmeter 3 to be tested can be obtained through direct measurement or calculation, the pressure difference corresponding to each flowmeter 3 to be tested is obtained, and a plurality of flowmeters 3 to be tested can be calibrated through one-time test. Still be provided with the temperature sensor 33 that detects the helium temperature before first flowmeter 3 that awaits measuring to can detect the helium temperature, start the experiment again after the helium cooling is to required experimental range. The flowmeter to be measured 3 is a Venturi tube flowmeter, and the standard flowmeter 5 is a Coriolis mass flowmeter.
A cooling coil 14 in a liquid helium bath is also arranged in the vacuum cylinder 1, and a helium pipeline enters the flow meter 3 to be tested after heat exchange is carried out on the helium pipeline through the cooling coil 14, so that helium can be fully cooled; the cooling coil 14 has a tube diameter of 0.007m, a wall thickness of 0.0005m and a length of 3.18 m.
In this embodiment, be provided with one-level double-pipe heat exchanger 11 and second grade double-pipe heat exchanger 12 in the vacuum cylinder 1, in the liquid helium bath was entered after compressor 4 drive helium passed through one-level double-pipe heat exchanger 11 and second grade double-pipe heat exchanger 12 in proper order, flow through to await measuring flowmeter 3 after again in proper order through second grade double-pipe heat exchanger 12 and one-level double-pipe heat exchanger 11 and return to compressor 4 in.
The size of the inner pipe of the primary double-pipe heat exchanger 11 is 0.01m multiplied by 0.001m, the size of the outer pipe is 0.022m multiplied by 0.002m, the length is 103m, the size of the inner pipe of the secondary double-pipe heat exchanger 12 is 0.007m multiplied by 0.0005m, the size of the outer pipe is 0.01m multiplied by 0.001m, and the length is 17 m; the primary double-pipe heat exchanger 11 and the secondary double-pipe heat exchanger 12 are both set to be inner pipe air return and outer pipe air inlet, so that the cooling and temperature return speed of helium is improved. The primary double pipe heat exchanger 11 and the secondary double pipe heat exchanger 12 both use red copper materials. The helium gas is cooled to about 6K after passing through the primary double pipe heat exchanger 11 and the secondary double pipe heat exchanger 12, and then is cooled to about 4.5K through the cooling coil 14 immersed in the liquid helium bath, so that the experiment can be started.
In order to prevent the temperature loss in the vacuum cylinder 1, at least one radiation protection plate (not shown) is further fixed between the flange plate 2 and the vacuum cylinder 1, specifically, the radiation protection plate is fixed on the flange plate 2 through fixing modes such as bolts and the like, and then the flange plate 2 and the radiation protection plate are integrally covered above the vacuum cylinder 1 and fixed, so that the liquid helium and the flange plate 2 are isolated from radiation heat exchange.
The pipeline connection mode of the compressor 4 is as follows: be provided with first valve 41 in the exit position of compressor 4, the import position is provided with third valve 43, first valve 41 and third valve 43 are the back pressure valve, can adjust pipeline pressure, and the helium pipeline of compressor 4 still is provided with second valve 42 before getting into cryobarrel 1, second valve 42 is flow control valve, mainly adjusts the pressure condition of helium pipeline through second control valve 42 to satisfy the experiment requirement. And then, helium enters the outer pipes of the first-stage double-pipe heat exchanger 11 and the second-stage double-pipe heat exchanger 12 and then enters a liquid helium bath, after being cooled to a liquid helium temperature region through the cooling coil 14, the helium sequentially flows through a plurality of serially-connected flowmeters 3 to be detected, then sequentially passes through the inner pipes of the second-stage double-pipe heat exchanger 12 and the first-stage double-pipe heat exchanger 11, and after leaving the vacuum cylinder 1, the helium is detected through the standard flowmeter 5 and then returns to the compressor 4 through the third valve 43. Wherein, be provided with temperature sensor 33 between cooling coil 14 and the flowmeter 3 that awaits measuring for the first time, after the helium temperature that detects here satisfies the experiment requirement, follow-up in liquid helium bath, the change that the helium temperature can not appear surpassing the experiment requirement.
In this embodiment, two flowmeters 3 to be tested connected in series are shown, wherein the first flowmeter 3 to be tested is connected with a differential pressure transmitter 31 to measure the pressure change condition of helium, and two ends of the second flowmeter 3 to be tested are respectively connected with a pressure transmitter 32 and simultaneously connected with the differential pressure transmitter 31, so that the repeated verification of the movement is performed by different detection modes.
Further, in order to keep the total amount of liquid helium stable in the experiment and ensure the experimental result, the vacuum cylinder 1 is also connected with a liquid helium dewar 6, a vacuum unit 7 and an air bag 8; the vacuum unit 7 is respectively connected with helium pipelines of the vacuum cylinder 1 and the compressor 4 through a fourth valve 71 and a fifth valve 72, the liquid helium Dewar 6 is connected with the vacuum cylinder 1 through a sixth valve 61, the air bag 8 is connected with the vacuum cylinder 1 through a seventh valve 81, and a liquid level sensor 13 is further arranged in the vacuum cylinder 1. Before the experiment, firstly, the vacuum unit 7 is used for vacuumizing to ensure that other gases do not exist in helium pipelines of the vacuum cylinder 1 and the compressor 4, in the experiment process, the liquid level sensor 13 is used for detecting the height of liquid helium, and the liquid helium dewar 6 is controlled to supplement the liquid helium in time, in the use process, the pressure in the liquid helium dewar 6 is gradually reduced along with the flow of liquid to the vacuum cylinder 1, and the liquid helium dewar 6 cannot be used for transfusion when the pressure is too low; in the preferred embodiment, a helium gas cylinder 62 connected to the liquid helium dewar 6 is further provided, the liquid helium dewar 6 is pressurized by the helium gas cylinder 62 to ensure normal liquid supply, and a pressurization valve 63 is provided in a connection pipe between the liquid helium dewar 6 and the helium gas cylinder 62.
The liquid level sensor 13 can be set to be always kept at a fixed height, or the upper limit and the lower limit of the liquid level are set, when the liquid helium bath reaches the lower limit of the liquid level, liquid is replenished through the liquid helium Dewar 6, and when the liquid helium bath reaches the upper limit of the liquid level, the liquid replenishment is stopped; the helium gas evaporated from the liquid helium enters the gas bag 8 for storage. In the present embodiment, the liquid level sensor 13 is a superconducting liquid level meter.
The calibration method of the calibration device of the low-temperature flowmeter provided by the embodiment comprises the following steps:
s1: vacuumizing the vacuum cylinder body 1 and the helium pipeline, and newly filling helium into the helium pipeline;
specifically, the fourth valve 71 and the fifth valve 72 are opened, the vacuum unit 7 is used for vacuumizing, helium needs to be repeatedly filled for gas replacement when the helium pipeline is vacuumized, and finally the vacuum degree is 10-3Pa。
S2: respectively connecting a liquid helium Dewar 6 and an air bag 8 which store liquid helium with the vacuum cylinder 1; in the experiment, the sixth valve 61 and the seventh valve 81 should be kept in an open state, and the liquid helium dewar 6 is controlled to start to feed liquid helium into the vacuum cylinder 1 according to the detection result of the liquid level sensor 13.
S3: adjusting the valve states of the compressor 4 and the helium pipeline, and keeping the current state when the pressure of the helium pipeline reaches a preset value;
specifically, the compressor 4 is started, the third valve 43 is completely opened, the first valve 41 is opened by 30%, then the second valve 42 is slowly opened, the pressure value in the helium pipeline is observed, when the pressure value reaches 3bar, the flow is kept stable, and the experiment is started;
s4: recording the pressure values of the standard flowmeter 5 and the flowmeter 3 to be measured and the pressure difference of helium flowing through the flowmeter 3 to be measured;
s5: adjusting the flow of the helium pipeline to adjust the pressure by a preset variable quantity, repeating the step S4 until a preset upper flow limit is reached, and closing the calibration device;
in this embodiment, the helium pipeline is adjusted at a pressure interval of 0.1bar, the experiment is repeated, and finally, when the flow rate reaches 15g/s, the last group of data is recorded, and the experiment is completed.
S6: and calculating the outflow coefficient of the flowmeter 3 to be measured.
The method for calculating the outflow coefficient of the flowmeter 3 to be measured comprises the following steps:
referring to fig. 2, the low temperature flow meter 3 is a venturi flow meter, taking the measurement q of a standard flow metermiAs an actual value of the flowmeter under test 3, the flowmeter under testMeasured value of 3 is q'miThe expression is
Wherein i represents the data measured at the ith time, and C represents the outflow coefficient and the ratio of the actual flow to the measured flow; d is the inner diameter of the expansion section of the Venturi tube, and beta is the throat diameter ratio of the Venturi tube, and represents the ratio of the diameter D of the contraction section to the inner diameter D of the expansion section; ρ is helium density, Δ piThe differential pressure of the flowmeter to be measured is the difference value between the expansion section hydraulic pressure and the contraction section hydraulic pressure of the Venturi tube under the condition of using the Venturi tube flowmeter;
the error functions for the standard flow meter and the flow meter under test are expressed as:
substituting formula (1) into formula (2) when the function f has minimum value, and calculating partial derivative of function f with respect to variable C
Order to
The best estimate of the outflow coefficient C is
Therefore, the outflow coefficient C of the flowmeter 3 to be measured can be determined only by the parameters of the Venturi tube flowmeter, the numerical value of the standard flowmeter 5 and the pressure difference of helium flowing through the flowmeter 3 to be measured.
Furthermore, after the experiment is finished, the process of closing the calibration device, namely the process of cleaning the experimental equipment, comprises,
step A: closing the liquid helium Dewar 6 and the sixth valve 61, and stopping supplying liquid to the vacuum cylinder 1;
and B: the valves on the helium pipeline are closed in sequence from the inlet to the outlet, and finally the compressor 4 is closed;
and C: opening a vacuum pumping valve on the vacuum cylinder 1, namely a fourth valve 71, releasing the pressure in the vacuum cylinder 1, wherein in the pressure release process, the pressure in the vacuum cylinder needs to be kept higher than 1.1 bar;
specifically, during pressure relief, the pressure in the vacuum cylinder is controlled to reach 1.2bar, the fourth valve 71 is closed, the vacuum cylinder 1 is waited to be heated again, the pressure in the vacuum cylinder 1 is relieved again when rising, the pressure relief is repeated, the exhaust speed of the vacuum cylinder 1 is increased, and in order to prevent air backflow, the pressure in the vacuum cylinder 1 needs to be kept above 1.1 bar.
Step D: after 10 hours, the connection between the air bag 8 and the vacuum cylinder 1 is disconnected, and the power supply of the experimental equipment is closed.
The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (10)
1. A calibration device of a low-temperature flowmeter is characterized in that: the liquid helium bath device comprises a vacuum cylinder and a flange plate covering the upper end of the vacuum cylinder, wherein liquid helium is stored in the vacuum cylinder to form a liquid helium bath, at least one heat exchanger is arranged above the liquid helium bath, at least one flowmeter to be tested is connected in series in the liquid helium bath, the liquid helium bath device further comprises a compressor arranged on the outer side of the vacuum cylinder, an outlet of the compressor is sequentially connected in series with the flowmeter to be tested in the liquid helium bath through the heat exchanger, then the outlet of the compressor is separated from the inlet of the compressor through the heat exchanger, helium is filled in a loop of the compressor, and a standard flowmeter arranged on the outer side of the vacuum cylinder is arranged on a pipeline close to an inlet of the compressor.
2. The calibration device of the low-temperature flowmeter as claimed in claim 1, wherein: a cooling coil in a liquid helium bath is also arranged in the vacuum cylinder, and a helium pipeline enters the flowmeter to be measured after passing through the cooling coil;
the standard flow meter is a coriolis mass flow meter.
3. The calibration device of the low-temperature flowmeter as claimed in claim 1, wherein: the inlet and outlet positions of the compressor are respectively provided with a first valve and a third valve, and the first valve and the third valve are both back pressure valves;
and a second valve is also arranged on a helium pipeline before the compressor enters the low-temperature cylinder, and the second valve is a flow regulating valve.
4. The calibration device of the low-temperature flowmeter as claimed in claim 1, wherein: also comprises a vacuum machine set, a liquid helium dewar and an air bag,
the vacuum unit is communicated with the vacuum cylinder and the helium pipeline through a fourth valve and a fifth valve respectively; the liquid helium dewar is connected with the vacuum cylinder through a sixth valve; the air bag is connected with the vacuum cylinder through a seventh valve, and a liquid level sensor is arranged in the vacuum cylinder.
5. The calibration device of the low-temperature flowmeter as claimed in claim 1, wherein: each flowmeter to be measured is provided with a differential pressure transmitter and/or two ends of the flowmeter to be measured are provided with pressure transmitters respectively; and a temperature sensor for detecting the temperature of the helium gas is arranged at least before the first flowmeter to be detected.
6. The calibration device of the low-temperature flowmeter as claimed in claim 1, wherein: at least one radiation-proof plate is fixed between the flange plate and the vacuum cylinder body.
7. The calibration device of the low-temperature flowmeter as claimed in claim 2, wherein: the heat exchanger comprises a primary sleeve heat exchanger and a secondary sleeve heat exchanger, helium driven by the compressor enters the liquid helium bath after sequentially passing through the primary sleeve heat exchanger and the secondary sleeve heat exchanger, flows through the flowmeter to be detected and then sequentially passes through the secondary sleeve heat exchanger and the primary sleeve heat exchanger to return to the compressor;
the size of an inner pipe of the primary double-pipe heat exchanger is 0.01m multiplied by 0.001m, the size of an outer pipe of the primary double-pipe heat exchanger is 0.022m multiplied by 0.002m, the length of the inner pipe is 103m, the size of an inner pipe of the secondary double-pipe heat exchanger is 0.007m multiplied by 0.0005m, the size of an outer pipe of the secondary double-pipe heat exchanger is 0.01m multiplied by 0.001m, and the length of the outer pipe is 17 m; returning air from the inner pipes of the first-stage double-pipe heat exchanger and the second-stage double-pipe heat exchanger, and feeding air from the outer pipes;
the cooling coil has a pipe diameter of 0.007m, a wall thickness of 0.0005m and a length of 3.18 m.
8. A method of calibrating a cryogenic flowmeter using the device of any of claims 1-7, comprising: comprises the steps of (a) preparing a mixture of a plurality of raw materials,
s1: vacuumizing the vacuum cylinder and the helium pipeline, and refilling helium into the helium pipeline;
s2: respectively connecting a liquid helium dewar storing liquid helium and a gas bag with a vacuum cylinder;
s3: adjusting the valve states of the compressor and the helium pipeline, and keeping the current state when the pressure of the helium pipeline reaches a preset value;
s4: recording pressure values of the standard flowmeter and the flowmeter to be measured and pressure difference of helium flowing through the flowmeter to be measured;
s5: adjusting the flow of the helium pipeline to adjust the pressure by a preset variable quantity, repeating the step S4 until a preset upper flow limit is reached, and closing the calibration device;
s6: and calculating the outflow coefficient of the flowmeter to be measured.
9. The method for calibrating a low-temperature flowmeter as recited in claim 8, wherein: the step of shutting down the calibration means may comprise,
step A: closing the liquid helium dewar and stopping supplying liquid to the vacuum cylinder;
and B: the valves on the helium pipeline are closed in sequence from the inlet to the outlet, and finally the compressor is closed;
and C: opening a vacuumizing valve on the vacuum cylinder body to release the pressure in the vacuum cylinder body, wherein the pressure in the vacuum cylinder body is required to be kept higher than 1.1bar in the pressure release process;
step D: after 10 hours, the connection of the air bag to the vacuum cylinder was broken.
10. The method for calibrating a low-temperature flowmeter as recited in claim 8, wherein: the method for calculating the outflow coefficient of the flowmeter to be measured comprises the following steps:
the flow meter to be measured is a Venturi tube flow meter, and the measured value q of the standard flow meter is usedmiThe measured value of the flowmeter to be measured is q 'as the actual value of the flowmeter to be measured'miThe expression is
Wherein i represents the data measured at the ith time, and C represents the outflow coefficient and the ratio of the actual flow to the measured flow; d is the inner diameter of the expansion section of the Venturi tube, and beta is the throat diameter ratio of the Venturi tube, and represents the ratio of the diameter D of the contraction section to the inner diameter D of the expansion section; ρ is helium density, Δ piThe pressure difference of the flowmeter to be measured;
the error functions for the standard flow meter and the flow meter under test are expressed as:
substituting formula (1) into formula (2) when the function f has minimum value, and calculating partial derivative of function f with respect to variable C
Order to
The best estimate of the outflow coefficient C is
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| CN113984145A (en) * | 2021-11-26 | 2022-01-28 | 华北电力大学 | Calibration platform for liquid lead-bismuth electromagnetic flowmeter and calibration method thereof |
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