CN112880756B - Device and method for testing flow distribution of liquid helium in CICC conductor - Google Patents
Device and method for testing flow distribution of liquid helium in CICC conductor Download PDFInfo
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- CN112880756B CN112880756B CN202110068005.8A CN202110068005A CN112880756B CN 112880756 B CN112880756 B CN 112880756B CN 202110068005 A CN202110068005 A CN 202110068005A CN 112880756 B CN112880756 B CN 112880756B
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- G—PHYSICS
- 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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- G—PHYSICS
- 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
- G01F1/76—Devices for measuring mass flow of a fluid or a fluent solid material
- G01F1/86—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure
- G01F1/88—Indirect mass flowmeters, e.g. measuring volume flow and density, temperature or pressure with differential-pressure measurement to determine the volume flow
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
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- G—PHYSICS
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Abstract
The invention relates to a device and a method for testing the flow distribution of liquid helium in a CICC conductor. The method is suitable for measuring the flow distribution proportion of the liquid helium with different flow rates by the CICC conductor comprising the central cooling pipe at the temperature of the liquid helium. The invention provides a test method for measuring the flow distribution of liquid helium in a CICC (copper-clad CC) on the premise of not changing the structure of the CICC conductor, which can provide basic parameters for the research of the thermal hydraulic state in the CICC conductor. The invention has the advantages of reliable system and easy operation.
Description
Technical Field
The invention belongs to the field of thermal hydraulic parameter testing of cable conductor structures (CICC) in pipes, and mainly aims to measure the flow distribution proportion of liquid helium in a CICC conductor containing a central cooling pipe. The device can study the flow distribution of liquid helium with different flow rates in a CICC conductor cable area and a central cooling pipe area at the temperature of the liquid helium.
Background
Due to the excellent performance of the CICC conductor structure, most of the conventional large superconducting magnets are wound by the CICC conductor which consists of a group of annular superconducting wire bundles and a central cooling channel separated by a spiral pipe and is sealed in a steel leakage-proof armor. Since the superconducting materials such as Nb3Sn and NbTi need to be in a superconducting state at the temperature of liquid helium, in order to ensure the safe operation of the superconducting magnet constructed by the cic conductor, the thermal hydraulic behavior and characteristics of the superconducting magnet must be studied in detail, and the flow distribution of the liquid helium in the cable area and the central cooling tube area is one of the important thermal parameters.
Because the CICC conductor central cooling tube and the cable zone are both sealed within the conductor armor, none of the devices currently have the capability of directly measuring the flow distribution of the cooling medium in the cable zone and the central cooling tube zone. The invention can more intuitively reflect the flowing state of the cooling medium in the conductor according to the measurement results of the flow distribution of the cooling medium in the conductor in the cable area and the central cooling pipe area. The device can accurately measure the flow state of the liquid helium in the CICC conductor and provide guidance for the design optimization of the CICC conductor.
Disclosure of Invention
The invention aims to establish a device and a method for testing liquid helium flow distribution in a CICC conductor, which are used for researching the flow distribution problem of liquid helium with different flow rates in a cable area and a central cooling pipe area in the CICC conductor at the temperature of the liquid helium, thereby providing theoretical basis and guidance for the conductor design of the CICC and the cooling design of a superconducting magnet wound by the CICC.
The invention is realized by the following technical scheme: a testing device for liquid helium flow distribution in a CICC conductor comprises a liquid helium source, a liquid nitrogen source, a cryostat, a first flow control valve, a second flow control valve, a third flow control valve, a fourth flow control valve, a first mass flow meter, a second mass flow meter, a first thermometer, a second thermometer, a third thermometer, a fourth thermometer, a fifth thermometer, a sixth thermometer, a first pressure transmitter, a second pressure transmitter, a data acquisition system, a liquid nitrogen and liquid helium recovery device and a sample to be tested; the liquid helium source is connected with the cryostat through a first liquid helium pipeline, and a first flow control valve is arranged on the first liquid helium pipeline to control the flow of the liquid helium;
after the liquid helium is connected to the cryostat through the first liquid helium pipeline, the first liquid helium pipeline is sequentially provided with a first mass flow meter, a first pressure transmitter and a first thermometer respectively, and is connected to the first liquid helium pipeline in a welding manner; the first liquid helium pipeline is a stainless steel pipeline;
two ends of the sample to be detected are respectively connected with the first horn-shaped cavity and the second horn-shaped cavity through welding, and the thin ends of the first horn-shaped cavity and the second horn-shaped cavity are respectively connected to the first liquid helium pipeline and the second liquid helium pipeline for welding;
a second thermometer and a second pressure transmitter are sequentially welded on a second liquid helium pipeline, then the second liquid helium pipeline is led out of the cryostat and is input into the liquid helium recovery device through the second liquid helium pipeline, and a second flow control valve is arranged on the second liquid helium pipeline at the tail end of the cryostat and controls the liquid helium flow of the sample to be detected together with the first flow control valve at the inlet end;
the liquid nitrogen source is sequentially connected with a third flow control valve and a first liquid nitrogen mass flow meter through a first liquid nitrogen pipeline, then enters a cold screen for circulating heat exchange, and finally is connected with a liquid nitrogen recovery device through a second liquid nitrogen pipeline through a fourth flow control valve at the tail end;
the tested sample is a CICC conductor containing a central cooling pipe, a plurality of holes are arranged on the CICC conductor at preset intervals, a plurality of point heaters are arranged in an upstream first hole and are respectively positioned in a central cooling pipe area and a cable area, and third to sixth thermometers are arranged in a middle hole and a downstream hole.
Further, the cryostatComprises an outer vacuum Dewar and a middle radiation-proof cold shield, wherein the outer vacuum Dewar needs to ensure that the vacuum degree reaches 10-3Pa, keeping the temperature of the cold shield to be 80-85K, wherein the cold shield is a copper plate provided with cooling pipelines, and flowing liquid nitrogen is introduced into the cooling pipelines; and the liquid nitrogen flowing out of the cold shield enters a liquid nitrogen recovery device for cyclic utilization.
Further, the tested sample is a CICC conductor containing a central cooling pipe, three holes are drilled in the radial direction of the conductor, the axial distance between the holes is a twisting pitch or an integral multiple of the twisting pitch, and the holes are kept on a straight line in the axial direction; 2 500 Ω, 1/8W resistors as point heaters in the first hole upstream, located in the central cooling tube zone and the cable zone, respectively; third to sixth thermometers are arranged in the middle hole and the downstream hole and used for capturing marked liquid helium micelles, the thermometers are arranged in a cable area and a central cooling pipe area, and the thermometers adopt Cernox SD thermometers;
punching a hole on the sample to be tested, installing a point heater and a thermometer, and sealing and fixing by using a heat-conducting pouring sealant;
the sample under test is wrapped with several layers of super-insulating material before it is installed in the test facility to reduce the inflow or outflow of heat.
Furthermore, the data acquisition system is used for acquiring and recording numerical values of the pressure transmitter and the thermometer in the device.
Further, the liquid helium source device is used for providing a stable liquid helium source with the stable mass flow rate of 0.1-10 g/s;
the liquid nitrogen source device is used for providing liquid nitrogen with stable flow rate for cooling a cold shield in the cryostat.
Furthermore, the inlet and outlet thermometer is a Cernox-1050 thermometer, and is bonded to a stainless steel liquid helium pipeline through VGE-7031 varnish, and the liquid helium flowmeter is a low-temperature Venturi flowmeter.
According to another aspect of the invention, a method for performing distribution test of supercritical helium flow in a CICC conductor by using the device is provided, which comprises the following steps:
step 1, a system preparation stage, connecting and debugging equipment, and controlling the flow temperature of liquid helium;
step 2, realizing direct measurement of the liquid helium flow velocity of different areas in the conductor by using a point heater to mark liquid helium fluid micelles, applying pulse current to electric heaters of an upstream central cooling pipe area and a cable area respectively during measurement, and simultaneously monitoring the temperature change of a thermometer of a downstream corresponding area in real time; during the pulse duration, the current pulse heats the liquid helium flowing around the resistor, thereby "marking" a small amount of liquid helium fluid micelles;
and 3, processing the data of the acquisition system by combining the time delay from the heater pulse to the temperature rise of one or more sensors at the downstream and the distance from the point heater to the thermometer, calculating the liquid helium flow velocity of the corresponding area, and calculating the flow distribution proportion of the liquid helium in different areas in the CICC conductor according to the flow sectional areas of the cable area and the central cooling tube area.
Further, step 1 specifically includes the following steps:
A. assembling the device, and connecting the components;
B. debugging and connecting a measuring instrument of the testing device and a signal line testing system;
C. performing airtightness detection on the device, vacuumizing the cryostat, performing pressurization test on a liquid nitrogen loop and a liquid helium loop, closing a valve at the initial stage, introducing nitrogen of more than 0.5Mpa, closing a valve at the gas inlet end, keeping for more than 5 hours, and judging that the airtightness of the device meets the requirements when the vacuum degree of the cryostat and the pressure value of a liquid nitrogen and liquid helium pipeline are unchanged;
D. opening a control valve at the tail end of the device, and releasing pressure gas of the liquid nitrogen and liquid helium loop;
E. introducing nitrogen pressure into the liquid nitrogen loop, and cooling the cold screen;
F. introducing cold helium gas into the liquid helium loop to cool the CICC conductor;
G. when the temperature of the CICC conductor is reduced to the target temperature, liquid helium is introduced into the liquid helium loop, and liquid helium circulation is realized;
H. and adjusting the inlet and outlet valves of the conductor to control the liquid helium to be in a stable flow.
Further, step 2 further comprises:
I. respectively introducing pulse current to point heaters in the cable area and the central tube area;
J. recording the temperature changes of four downstream thermometers;
K. adjusting to different liquid helium flow rates, and repeating the I, J step;
l, ending the experiment, returning the conductor to the temperature, disassembling the experimental sample, and arranging the experimental device in a position;
further, the step 3 specifically includes:
the method comprises the steps of drawing a curve of temperature change of a thermometer along with time by reading experimental data recorded by an acquisition system, marking a time period for applying a pulse, calculating a flow velocity V of liquid helium according to a time delay tau from the starting time of applying the pulse to the starting of a temperature rising edge of a downstream thermometer and a distance L from a corresponding thermometer to a point heater, calculating a corresponding mass flow according to L/tau, calculating a corresponding mass flow according to a liquid helium flow cross section area A and a liquid helium density rho of a corresponding area, and obtaining a flow distribution proportion k of the liquid helium in a CICC conductor according to the following formula:
the invention has the advantages that:
the method has the advantages that the small fluid micro-cluster is marked by the point heater, the flowing condition of the liquid helium in the CICC is measured according to the moving speed of the fluid micro-cluster, the direct measurement of the flowing speed of the liquid helium in the CICC can be realized, the system is reliable, the measurement is accurate, and the method is suitable for testing the CICC conductors with different sections and the flow distribution condition of the liquid helium with different flow rates in the CICC conductors under the temperature of the liquid helium. The device can accurately measure the flowing state of the liquid helium in the CICC conductor and provide guidance for the design optimization of the CICC conductor.
Drawings
FIG. 1 is a schematic diagram of a CICC conductor structure;
FIG. 2 is a schematic diagram of a testing apparatus for flow distribution of liquid helium in a CICC conductor;
FIG. 3 is a schematic view showing the installation of a heater and a thermometer at an inner point of a sample to be measured.
Description of reference numerals: a-a central spiral pipe, b-a superconducting cable, c-a stainless steel armor; 1-a first flow control valve, 2, a first liquid helium pipeline, 3-a first mass flowmeter, 4-a first pressure transmitter, 5-a first thermometer, 6-a tested sample, 7-a cryostat cold screen, 8-a cryostat, 9-a second liquid helium pipeline, 10-a second thermometer, 11-a second pressure transmitter, 12-a second flow control valve, 13-a third flow control valve, 14, a first liquid nitrogen pipeline, 15-a second mass flowmeter, 16-a fourth flow control valve, 17-a liquid helium source, 18-a liquid nitrogen source, 19-a liquid nitrogen recovery device, 20-a liquid helium recovery device, 21, a first horn-shaped cavity, 22-a second horn-shaped cavity, 23-a data acquisition system and 24-a second liquid nitrogen pipeline; h1-spot heater at cable zone, H2-spot heater at central cooling tube, T1, T2, T3, T4-third, fourth, fifth, sixth thermometer.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person skilled in the art based on the embodiments of the present invention belong to the protection scope of the present invention without creative efforts.
As shown in fig. 1, the cic c conductor structure of the present invention includes: a central spiral pipe a, a superconducting cable b and a stainless steel armor c. As shown in fig. 2 and 3, the device comprises a liquid helium source 17, a liquid nitrogen source 18, a cryostat, a first flow control valve 1, a second flow control valve 12, a third flow control valve 13, a fourth flow control valve 16, a first mass flow meter 3, a second mass flow meter 15, a first thermometer 5, a second thermometer 10, a third thermometer T1, a fourth thermometer T2, a fifth thermometer T3, a sixth thermometer T4, a first pressure transmitter 4, a second pressure transmitter 11, a data acquisition system, liquid nitrogen and liquid helium recovery devices 19 and 20 and a sample 6 to be measured; the liquid helium source 17 is connected with the cryostat 8 through a first liquid helium pipeline 2, and a first flow control valve 1 is arranged on the first liquid helium pipeline 2 and used for controlling the flow of the liquid helium;
after the liquid helium is connected to the cryostat through the first liquid helium pipeline, the first liquid helium pipeline is sequentially provided with a first mass flow meter, a first pressure transmitter and a first thermometer respectively, and is connected to the first liquid helium pipeline in a welding manner; the first liquid helium pipeline is a stainless steel pipeline;
two ends of the sample to be detected are respectively connected with the first horn-shaped cavity and the second horn-shaped cavity through welding, and the thin ends of the first horn-shaped cavity and the second horn-shaped cavity are respectively connected to the first liquid helium pipeline and the second liquid helium pipeline 9 for welding;
a second thermometer and a second pressure transmitter are sequentially welded on a second liquid helium pipeline, then the second liquid helium pipeline is led out of the cryostat and is input into the liquid helium recovery device through the second liquid helium pipeline, and a second flow control valve is arranged on the second liquid helium pipeline at the tail end of the cryostat and controls the liquid helium flow of the sample to be detected together with the first flow control valve at the inlet end;
the liquid nitrogen source is sequentially connected with a third flow control valve and a first liquid nitrogen mass flow meter through a first liquid nitrogen pipeline, then enters a cold screen for circulating heat exchange, and finally is connected with a liquid nitrogen recovery device through a second liquid nitrogen pipeline through a fourth flow control valve at the tail end;
the tested sample is a CICC conductor containing a central cooling pipe, a plurality of holes are arranged on the CICC conductor at preset intervals, a plurality of point heaters are arranged in an upstream first hole and are respectively positioned in a central cooling pipe area and a cable area, and third to sixth thermometers are arranged in a middle hole and a downstream hole.
The liquid helium source can stably provide a stable liquid helium source of 0.1-10 g/s.
Two ends of the tested conductor are welded with the stainless steel liquid helium pipeline after passing through the horn-shaped cavity, and the horn-shaped cavity is used for enabling liquid helium to enter the CICC conductor through the horn-shaped cavity and then to be distributed more uniformly;
the low temperature and the constant temperatureThe device comprises an outer vacuum Dewar and an inner radiation-proof cold shield, wherein the vacuum degree in the Dewar is kept at 10 during the test-3And Pa, arranging a liquid nitrogen cooling coil on the cold shield, wherein the temperature of the cold shield is about 80K in the normal operation process, so as to reduce the radiant heat of the Dewar at the room temperature to the 4.2K tested sample.
The liquid helium flowmeter is a low-temperature venturi flowmeter, and mass flow is calculated by measuring the pressure difference between an inlet and a throat;
the inlet and outlet thermometer is a Cernox-1050 thermometer, is adhered to the stainless steel liquid helium pipeline through VGE-7031 varnish, and is used for measuring the temperature of the inlet and outlet liquid helium.
The installation schematic diagram of the point heater and the temperature sensor in the tested sample is shown in FIG. 3, the point heater is arranged in the upstream direction of liquid helium inflow, and a 500 Ω, 1/8W commercial resistor is respectively arranged in the cable area and the central cooling tube area as the point heater;
two pairs of thermometers are arranged in the downstream direction of the sample point heater to be measured and are respectively used for monitoring the temperature change of the liquid helium in the cable area and the central tube area, and a Cernox SD thermometer is adopted as the thermometers;
punching a hole on the sample to be tested, installing a point heater and a temperature sensor, and then sealing and fixing by using Stycast;
wrapping the sample under test with several layers of super-insulating material before it is installed in the test facility to minimize the inflow or outflow of heat;
the pressure transmitter, the differential pressure transmitter and the thermometer are connected with the signal acquisition system through signal lines, and real-time data acquisition is carried out through the acquisition system, so that the post-processing of data is facilitated;
the supercritical helium flow distribution test method in the CICC conductor is realized based on the measurement of liquid helium fluid micelles marked by temperature. As shown in fig. 2, a point heater, which is a 500 Ω, 1/8W commercial resistor according to one embodiment of the present invention, is installed upstream of the flow of liquid helium in the cic c conductor; h1-a point heater at the cable zone, H2-a point heater at the central cooling pipe, H1 and H2 are respectively used for heating the liquid helium in the cable zone and the central cooling pipe zone, and the flow speed of the liquid helium micelles is obtained according to the index change of downstream T1, T2, T3 and T4 thermometers, and the specific implementation principle is as follows:
when the flow rate of the liquid helium in the central cooling pipe area is measured, the flow rate of the liquid helium in the CICC conductor is adjusted to be a constant value and is supplied to H2The point heater is connected with pulse current; the method is mainly used for marking fluid micelles by heating, heating the liquid helium flowing around a resistor by current pulses during the pulse duration, so as to mark a small amount of the liquid helium fluid micelles, calculating the flow velocity V of the liquid helium according to the time delay tau from the starting time of applying the pulses to the starting of the temperature rising edge of a downstream thermometer and the distance L from the corresponding thermometer to a point heater by using the L/tau, calculating the corresponding mass flow according to the flow cross section area A of the liquid helium in the corresponding area and the density rho of the liquid helium, and obtaining the flow distribution ratio k of the liquid helium in the CICC conductor according to the following formula.
In the formula, the subscript b represents the parameters of the cable zone and the subscript h represents the parameters of the central cooling zone.
In consideration of the influence of the twisting of the superconducting strands on the flow state of the liquid helium in the cable area, the spacing between the H1, the T1 and the T3 is one twisting pitch or an integral multiple of the twisting pitch. With sufficient pulse energy, temperature increases were detected in the T1 and T3 thermometers even though only pulses were applied in H2.
According to the embodiment of the invention, the supercritical helium flow distribution test method in the CICC conductor comprises the following steps:
step 1, a system preparation stage, connecting and debugging equipment, and controlling the flow temperature of liquid helium;
step 2, realizing direct measurement of the liquid helium flow velocity of different areas in the conductor by using a point heater to mark liquid helium fluid micelles, applying pulse current to electric heaters of an upstream central cooling pipe area and a cable area respectively during measurement, and simultaneously monitoring the temperature change of a thermometer of a downstream corresponding area in real time; during the pulse duration, the current pulse heats the liquid helium flowing around the resistor, thereby "marking" a small amount of liquid helium fluid micelles;
and 3, processing the data of the acquisition system by combining the time delay from the heater pulse to the temperature rise of one or more sensors at the downstream and the distance from the point heater to the thermometer, calculating the liquid helium flow velocity of the corresponding area, and calculating the flow distribution proportion of the liquid helium in different areas in the CICC conductor according to the flow sectional areas of the cable area and the central cooling tube area.
Further, step 1 specifically includes the following steps:
A. assembling the device according to the attached figure 2, wherein all parts are connected in sequence;
B. debugging and connecting a measuring instrument of the testing device and a signal line testing system;
C. performing airtightness detection on the device, vacuumizing the cryostat, performing pressurization test on a liquid nitrogen loop and a liquid helium loop, closing a valve at the initial stage, introducing nitrogen of more than 0.5Mpa, closing a valve at the gas inlet end, keeping for more than 5 hours, and judging that the airtightness of the device meets the requirements when the vacuum degree of the cryostat and the pressure value of a liquid nitrogen and liquid helium pipeline are unchanged;
D. opening a control valve at the tail end of the device, and releasing pressure gas of a liquid nitrogen and liquid helium loop;
E. introducing liquid nitrogen into the liquid nitrogen loop, and cooling the cold screen;
F. introducing cold helium gas into the liquid helium loop to cool the CICC conductor;
G. when the temperature of the CICC conductor is reduced to the target temperature, liquid helium is introduced into the liquid helium loop, and liquid helium circulation is realized;
H. adjusting the flow control valves 1 and 12 to control the liquid helium to a stable flow;
further, step 2 further comprises:
I. pulse current is supplied to H1, and the time delay until the temperature rising edge of a T1 and T3 thermometer is recorded;
J. pulse current is supplied to H2, and the time delay of the temperature rising edge of the T2 and T4 thermometers is recorded;
K. adjusting the flow control valves 1 and 12 to different liquid helium flows, and repeating I, J;
l, repeating the step K until the measurement of the target flow interval is finished;
m, ending the experiment, returning the temperature of the conductor, returning the pressure of the cryostat Dewar, disassembling the experimental sample, and returning to the experimental device;
and N, exporting the experimental data recorded by the data acquisition system, and processing the data.
Although illustrative embodiments of the present invention have been described above to facilitate the understanding of the present invention by those skilled in the art, it should be understood that the present invention is not limited to the scope of the embodiments, but various changes may be apparent to those skilled in the art, and it is intended that all inventive concepts utilizing the inventive concepts set forth herein be protected without departing from the spirit and scope of the present invention as defined and limited by the appended claims.
Claims (9)
1. A testing device for liquid helium flow distribution in a CICC conductor comprises a liquid helium source, a liquid nitrogen source, a cryostat, a first flow control valve, a second flow control valve, a third flow control valve, a fourth flow control valve, a first mass flow meter, a second mass flow meter, a first thermometer, a second thermometer, a third thermometer, a fourth thermometer, a fifth thermometer, a sixth thermometer, a first pressure transmitter, a second pressure transmitter, a data acquisition system, a liquid nitrogen and liquid helium recovery device and a sample to be tested; the method is characterized in that: the liquid helium source is connected with the cryostat through a first liquid helium pipeline, and a first flow control valve is arranged on the first liquid helium pipeline to control the flow of the liquid helium;
after the liquid helium is connected to the cryostat through the first liquid helium pipeline, the first liquid helium pipeline is sequentially provided with a first mass flow meter, a first pressure transmitter and a first thermometer respectively, and is connected to the first liquid helium pipeline in a welding manner; the first liquid helium pipeline is a stainless steel pipeline;
two ends of the sample to be measured are respectively connected with the first horn-shaped cavity and the second horn-shaped cavity through welding, and the thin ends of the first horn-shaped cavity and the second horn-shaped cavity are respectively connected to the first liquid helium pipeline and the second liquid helium pipeline for welding;
a second thermometer and a second pressure transmitter are sequentially welded on a second liquid helium pipeline, then the second liquid helium pipeline is led out of the cryostat and is input into the liquid helium recovery device through the second liquid helium pipeline, and a second flow control valve is arranged on the second liquid helium pipeline at the tail end of the cryostat and controls the liquid helium flow of the sample to be detected together with the first flow control valve at the inlet end;
the liquid nitrogen source is sequentially connected with a third flow control valve and a first liquid nitrogen mass flow meter through a first liquid nitrogen pipeline, then enters a cold shield for circulating heat exchange, and finally is connected with a liquid nitrogen recovery device through a fourth flow control valve at the tail end through a second liquid nitrogen pipeline;
the tested sample is a CICC conductor containing a central cooling pipe, a plurality of holes with preset intervals are arranged on the tested sample, a plurality of point heaters are arranged in an upstream first hole, the point heaters are respectively positioned in a central cooling pipe area and a cable area, and third to sixth thermometers are arranged in a middle hole and a downstream hole;
the tested sample is a CICC conductor containing a central cooling pipe, three holes are drilled in the radial direction of the conductor, the axial distance between the holes is a twist pitch or an integral multiple of the twist pitch, and the axial distance is kept on a straight line; 2 500 Ω, 1/8W resistors as point heaters in the first hole upstream, located in the central cooling tube zone and the cable zone, respectively; third to sixth thermometers are arranged in the middle hole and the downstream hole and used for capturing marked liquid helium micelles, the thermometers are arranged in a cable area and a central cooling pipe area, and the thermometers adopt Cernox SD thermometers;
punching a hole on the sample to be tested, installing a point heater and a thermometer, and sealing and fixing by using a heat-conducting pouring sealant;
the sample under test is wrapped with several layers of super-insulating material before it is installed in the test facility to reduce the inflow or outflow of heat.
2. The apparatus of claim 1, wherein the apparatus comprises:
the cryostat comprises an outer vacuum Dewar and a middle radiation-proof cold shield, wherein the outer vacuum Dewar needs to ensure that the vacuum degree reaches 10-3Pa, keeping the temperature of the cold shield to be 80-85K, wherein the cold shield is a copper plate provided with cooling pipelines, and flowing liquid nitrogen is introduced into the cooling pipelines; and the liquid nitrogen flowing out of the cold shield enters a liquid nitrogen recovery device for cyclic utilization.
3. The apparatus of claim 1, wherein the apparatus comprises:
the data acquisition system is used for acquiring and recording numerical values of the pressure transmitter and the thermometer in the device.
4. The apparatus of claim 1, wherein the apparatus comprises:
the liquid helium source device is used for providing a stable liquid helium source with the stable mass flow rate of 0.1-10 g/s;
the liquid nitrogen source device is used for providing liquid nitrogen with stable flow rate for cooling a cold shield in the cryostat.
5. The apparatus of claim 1, wherein the apparatus comprises:
the first thermometer and the second thermometer are Cernox-1050 thermometers, and are bonded to a stainless steel liquid helium pipeline through VGE-7031 varnish, and the liquid helium flowmeter is a low-temperature Venturi flowmeter.
6. A method for performing supercritical helium flow distribution testing within a CICC conductor using the apparatus of any of claims 1-5, comprising the steps of:
step 1, a system preparation stage, connecting and debugging equipment, and controlling the flow temperature of liquid helium;
step 2, realizing direct measurement of the liquid helium flow velocity of different areas in the conductor by using a point heater to mark liquid helium fluid micelles, applying pulse current to electric heaters of an upstream central cooling pipe area and a cable area respectively during measurement, and simultaneously monitoring the temperature change of a thermometer of a downstream corresponding area in real time; during the pulse duration, the current pulse heats the liquid helium flowing around the resistor, thereby "marking" a small amount of liquid helium fluid micelles;
and 3, processing the data of the acquisition system by combining the time delay from the heater pulse to the temperature rise of one or more sensors at the downstream and the distance from the point heater to the thermometer, calculating the liquid helium flow velocity of the corresponding area, and calculating the flow distribution proportion of the liquid helium in different areas in the CICC conductor according to the flow sectional areas of the cable area and the central cooling tube area.
7. The method for supercritical helium distribution testing within a cic c conductor of claim 6, wherein step 1 specifically comprises the steps of:
A. assembling the device, and connecting the components;
B. debugging and connecting a measuring instrument of the testing device and a signal line testing system;
C. performing airtightness detection on the device, vacuumizing the cryostat, performing pressurization test on a liquid nitrogen loop and a liquid helium loop, closing a valve at the initial stage, introducing nitrogen of more than 0.5Mpa, closing a valve at the gas inlet end, keeping for more than 5 hours, and judging that the airtightness of the device meets the requirements when the vacuum degree of the cryostat and the pressure value of a liquid nitrogen and liquid helium pipeline are unchanged;
D. opening a control valve at the tail end of the device, and releasing pressure gas of the liquid nitrogen and liquid helium loop;
E. introducing nitrogen pressure into the liquid nitrogen loop, and cooling the cold screen;
F. introducing cold helium gas into the liquid helium loop to cool the CICC conductor;
G. when the temperature of the CICC conductor is reduced to the target temperature, liquid helium is introduced into the liquid helium loop, and liquid helium circulation is realized;
H. and adjusting the inlet and outlet valves of the conductor to control the liquid helium to be in a stable flow.
8. The method for testing the distribution of supercritical helium within a cic c conductor according to claim 6, wherein step 2 further comprises:
I. respectively introducing pulse current to point heaters in the cable area and the central tube area;
J. recording the temperature changes of four thermometers at the downstream;
K. adjusting to different liquid helium flow rates, and repeating the I, J step;
l, finishing the experiment, returning the conductor to the temperature, disassembling the experimental sample, and arranging the experimental device in a home.
9. The method for testing distribution of supercritical helium in a CICC conductor according to claim 6, wherein the step 3 specifically comprises:
the method comprises the steps of drawing a curve of temperature change of a thermometer along with time by reading experimental data recorded by an acquisition system, marking a time period for applying a pulse, calculating a flow velocity V of liquid helium according to a time delay tau from the starting time of applying the pulse to the starting of a temperature rising edge of a downstream thermometer and a distance L from a corresponding thermometer to a point heater, calculating a corresponding mass flow according to L/tau, calculating a corresponding mass flow according to a liquid helium flow cross section area A and a liquid helium density rho of a corresponding area, and obtaining a flow distribution proportion k of the liquid helium in a CICC conductor according to the following formula:
in the formula, the subscript b represents the parameters of the cable zone and the subscript h represents the parameters of the central cooling zone.
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