Control system and method for PIV clean particle generation and transmission system in low-temperature environment

Abstract

The invention belongs to the technical field of low-temperature tests, and discloses a control system and method for a low-temperature environment PIV clean particle generation and transmission system. The control system comprises a basic sensing layer, a basic control layer, a network transmission layer and an application service layer which are arranged from bottom to top. The layers are connected through pipelines, cables and a network. The control method comprises the steps of control system checking; a control system performs self-inspection; carrying out a PIV test experiment; controlling the system to be shut down; and the control system emergently stops. According to the control system and the control method, purified water is used as a tracer particle material, the problem that a low-temperature test environment heat insulation material is polluted by traditional oily tracer particles and solid tracer particles is avoided, generated ice particles are uniform in particle size, good in light scattering performance, low in cost and controllable in concentration, the environment temperature below 180K can be met, and the energy consumption is low. And meanwhile, the low-temperature environment PIV test requirement with relatively high requirement on the tracer particle pollution problem is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of low temperature testing, and in particular relates to a control system and method for a PIV clean particle generation and transmission system in a low temperature environment. Background Art

[0002] PIV technology uses a double-pulse laser to irradiate the object to be measured, spread tracer particles in the object to be measured, obtain two consecutive particle images, and use the cross-correlation algorithm to obtain the particle displacement, thereby obtaining the tracer particle velocity. Since the tracer particles move with the object to be measured, the measured tracer particle velocity can be considered as the velocity of the object to be measured (provided that the particles can truly follow the object to be measured). In the PIV test, the tracking ability, light scattering characteristics and concentration of the tracer particles play a decisive role in the quality of the test data.

[0003] The tracking and light scattering properties of tracer particles mainly depend on the density and particle size of the tracer particle material. For the same tracer particle material, the smaller the particle size of the tracer particle, the better the tracking and the higher the data credibility. However, too small a particle size will cause the particle brightness to deteriorate, affecting the signal-to-noise ratio of the original image. Conversely, the larger the particle size, the higher the particle brightness, the better the image signal-to-noise ratio, but the tracking will deteriorate. In the PIV test, it is necessary to select appropriate tracer particles according to the actual application requirements to ensure that the tracer particles achieve a good balance in terms of tracking and light scattering.

[0004] PIV test technology has been widely used in room temperature environments. At present, traditional tracer particles used in room temperature environments are mainly divided into two categories: one is based on oily liquids such as DEHS and vegetable oil, which uses the Laskin nozzle atomization principle to produce oily particles with a particle size of about 1μm; the other is based on solid powders such as SiO2, which uses the fluidized bed principle to produce stable nano-scale solid powder particles.

[0005] When conducting PIV tests in certain low-temperature environments, the above-mentioned traditional tracer particle generation technology is no longer applicable. The main reason is the contamination problem of traditional tracer particles: the low-temperature pipeline test environment is often surrounded by a large amount of insulation materials, and oily particles or solid powder particles will contaminate the insulation materials, causing changes in the physical properties of the materials and leading to material failure. At the same time, the physical properties of oily liquids and solid particles are very stable. After the test, they will stick to the inner wall of the low-temperature pipeline and the insulation material for a long time and cannot evaporate or degrade.

[0006] Therefore, to carry out PIV test research in a low-temperature test environment, it is necessary to adopt a new clean particle generation and transmission system, and it must meet the following technical requirements at the same time: 1) Use clean tracer particle materials; 2) The physical properties of the tracer particles are stable and easy to clean after the test is completed; 3) The particle size and density of the tracer particles meet the flow field followability requirements; 4) The scattering properties of the tracer particles meet the optical measurement requirements; 5) The tracer particle concentration is high and controllable.

[0007] In summary, using water as a tracer particle material can effectively solve the problem of test environment pollution. However, how to convert water into a tracer particle flow with controllable particle size and concentration is a problem that needs to be solved. Literature research and ground research have found that there are three main ways to generate micro water droplets: one is to use the principle of ultrasonic atomization. This device is easy to buy on the market. Its water mist concentration is very large and easy to control, but the average measured value of the particle size is basically 5μm~10μm. For PIV tests, the followability does not meet the standards; the second is to use the principle of micro atomization nozzles. This device is also easy to buy on the market and is inexpensive. Its technical indicators often claim that the particle size reaches 1μm or even lower. However, the measured results show that its particle size is often greater than 20μm or even 100μm, and the particle size uniformity is poor, which cannot meet the requirements of PIV tests; the third method is to condense water vapor instantly. In this way, the author successfully generated water particles or ice particles with a particle size of about 1μm during ground debugging. From the principle of generation, it can meet the requirements of tracer particle fluidity and followability. However, to be successfully used in PIV tests in low-temperature environments, the entire tracer particle generation process needs to be under control.

[0008] Currently, there is an urgent need to develop a control system and method for a low-temperature environment PIV clean particle generation and transmission system. Summary of the invention

[0009] One technical problem to be solved by the present invention is to provide a control system for a PIV clean particle generation and transmission system in a low temperature environment. Another technical problem to be solved by the present invention is to provide a control method for a PIV clean particle generation and transmission system in a low temperature environment.

[0010] The control system of the low-temperature environment PIV clean particle generation and transmission system of the present invention includes a basic perception layer, a basic control layer, a network transmission layer and an application service layer arranged from bottom to top; each layer is connected by pipelines, cables and networks; The basic sensing layer includes the normal pressure pipeline subsystem, the cooling air flow pipeline subsystem, the tracer particle generator subsystem, the cooling mixing device and the particle transmission pipeline subsystem; The basic control layer includes programmable controller CPU, programmable controller expansion module, touch screen, switch, signal isolator, intermediate relay, low-voltage circuit breaker, button indicator light and uninterruptible power supply; The network transmission layer includes industrial electrical port switches and network cables; The application service layer includes host computers, system software, monitoring software and databases.

[0011] Furthermore, the atmospheric pressure pipeline subsystem is connected to the medium pressure nitrogen source and the tracer particle generator through the atmospheric pressure gas source pipeline; the atmospheric pressure gas source pipeline is provided with a manual valve, a filter, an electronic pressure regulating valve, a check valve, a temperature sensor and a pressure sensor; The atmospheric pressure pipeline subsystem introduces the medium-pressure nitrogen from the medium-pressure nitrogen source into the tracer particle generator through the interface reserved in the test hall. It is used to drive the tracer particle generator and also serves as the driving airflow for the PIV tracer particle flow. It is also used to monitor the medium-pressure nitrogen at the front end of the particle generator to ensure that the temperature and pressure of the medium-pressure nitrogen entering the particle generator are within the design range.

[0012] Furthermore, the cooling air flow pipeline subsystem is connected to the liquid nitrogen interface of the liquid nitrogen tank and the cooling mixing device through the cooling air flow pipeline; the cooling air flow pipeline is provided with a safety valve, a filter, an electric pressure regulating valve, a temperature sensor, a pressure sensor, a flow sensor and a liquid nitrogen flash tank; The cooling gas flow pipeline converts the liquid nitrogen from the test site into deep-cold dry nitrogen and transmits it to the cooling mixing device as a cooling gas source; the specific process is as follows: The liquid nitrogen for the cooling air flow pipeline is provided by the low-temperature nitrogen source at the test site, i.e., the liquid nitrogen tank; the pressurized gas for the cooling air flow pipeline is provided by the medium-pressure nitrogen source in the plant; the cooling air flow pipeline sprays liquid nitrogen into the liquid nitrogen flash tank to cool the medium-pressure nitrogen at room temperature, and mixes the liquid nitrogen with the medium-pressure nitrogen in the liquid nitrogen flash tank to form deep-cold dry nitrogen; the deep-cold dry nitrogen enters the cooling mixing device through the cooling air flow pipeline.

[0013] Furthermore, the main body of the tracer particle generator subsystem is the tracer particle generator, which is provided with a pressure sensor, a temperature transmitter, a check valve, an electric heater and a manual valve; the tracer particle generator subsystem generates a humidified airflow in the tracer particle generator container by passing dry nitrogen through a Laskin nozzle, and the humidified airflow contains gas with water vapor particles with an average diameter of 1 μm to 3 μm or nearly saturated water vapor at room temperature.

[0014] Furthermore, the main body of the cooling and mixing device is a cooling tank, and a temperature transmitter and a regulating valve are provided on the cooling tank; The humid airflow generated by the tracer particle generator subsystem and the deep-cold dry nitrogen generated by the cooling airflow pipeline subsystem are mixed in the cooling tank of the cooling mixing device. The water vapor particles in the humid airflow are instantly condensed into ice particles with an average diameter of 1μm~3μm. The ice particles are injected into the inner flow channel of the particle transmission pipeline subsystem through the insulation pipe as PIV tracer particles.

[0015] Furthermore, the particle transmission pipeline subsystem includes a particle transmission pipeline, on which a manual valve and an electric valve are arranged; the particle transmission pipeline subsystem transmits the PIV tracer particles generated by the cooling mixing device to the inner flow channel of the low-temperature test device.

[0016] The control method of the low temperature environment PIV clean particle generation and transmission system of the present invention comprises the following steps: S10. Control system inspection; The administrator checks and confirms that the instrument cables, control cables, power cables and aviation plugs are connected correctly and function properly; After the administrator checks that all electric valves are closed, he manually opens all manual valves that need to be opened in advance to full open; The administrator checks all mechanical pointer meters to ensure they are in good condition and the readings are within the set normal range; After the administrator completes the inspection, he or she will manually record the inspection results; S20. Control system self-check; Power on the control system; Turn on the host computer of the control system, log in with the correct user name, and enter the operation interface; The control system performs self-check to confirm that the medium-pressure nitrogen pressure is within the set range; The control system performs self-check to confirm that the medium-pressure nitrogen temperature is within the set range; The control system performs self-check to confirm that the liquid nitrogen pressure is within the set range; The control system performs self-check to confirm that the liquid level in the tracer particle generator is within the set range; The control system performs self-check to confirm that the temperature of the liquid in the tracer particle generator is within the set range; The control system is ready; S30. Conduct PIV test experiments; S301. Control system drying and purge; Click the drying and purge start button on the upper computer operation interface; The control system opens the main valve of the medium-pressure nitrogen source; The control system opens the regulating valve of the medium-pressure nitrogen source by 50%; The control system opens the regulating valve of the cryogenic nitrogen source by 50%; The control system opens the electric gate valve of the particle transmission pipeline to dry and purge the particle transmission pipeline; After the drying and purge time reaches the set time, the control system closes the electric gate valve of the particle transmission pipeline, and then delays closing the main valve of the medium-pressure nitrogen source and the regulating valve of the medium-pressure nitrogen source; Drying and purge is completed; S302.PIV test preparation; The control system turns on the electric heater of the tracer particle generator, heating the water temperature to 60°C and keeping it warm; The control system adjusts the pressure at the rear end of the tracer particle generator to 0.6 MPa through the regulating valve of the medium-pressure nitrogen source; The control system adjusts the pressure at the rear end of the cooling tank to 0.55MPa through the regulating valve of the medium-pressure nitrogen source; The control system opens the electric gate valve of the particle transmission pipeline; S303. Turn on liquid nitrogen; The control system opens the electric regulating valve of the liquid nitrogen tank delivery pipeline; The control system determines that the temperature, pressure and flow rate of the liquid nitrogen tank delivery pipeline are within the design range; The control system determines that the temperature and pressure of the cooling air flow pipeline are within the design range; The cryogenic dry nitrogen enters the cooling mixing device through the cooling air flow pipeline, and the flow rate of the cryogenic dry nitrogen is ensured to be stable; S304. Open the Laskin nozzle; When the temperature of the cooling air flow pipeline drops to the set range, the control system opens the electric regulating valve; The control system opens the electric valve of the Laskin nozzle pipeline, and the dry nitrogen passes through the Laskin nozzle to generate a humid air flow in the tracer particle generator container. The humid air flow contains gas with water vapor particles with an average diameter of 1μm~3μm or nearly saturated water vapor at room temperature; The moist airflow generated by the tracer particle generator subsystem and the deep-cold dry nitrogen generated by the cooling airflow pipeline subsystem are mixed in the cooling tank of the cooling mixing device, and the water vapor particles in the moist airflow are instantly condensed into ice particles with an average diameter of 1μm~3μm; The control system detects whether the particle size and concentration of ice particles meet the requirements of the PIV test, and adjusts the subsystems of the basic sensing layer until PIV tracer particles that meet the requirements of the PIV test are obtained; S305. The control system generates stable PIV tracer particles; After the control system reaches a steady state, it continuously generates PIV tracer particles that meet the requirements of the PIV test. At the same time, it automatically adjusts the opening of the electric control valves of each subsystem of the basic sensing layer to ensure the generation of stable PIV tracer particles. S306. Control system before shutdown; After the PIV test is completed, click the shutdown button on the upper computer operation interface; The control system closes the regulating valve of the medium-pressure nitrogen source; The control system closes the regulating valve of the cryogenic nitrogen source; The control system automatically turns on the electric heating cable of the particle transmission pipeline to heat the particle transmission pipeline and maintain the temperature for 10 minutes; The control system automatically turns on the electric heater in the liquid nitrogen flash tank to heat the residual liquid nitrogen and maintain the temperature for 10 minutes; The control system is dried and purged for 10 minutes; The control system closes the electric gate valve at the rear end of the particle transmission pipeline, the electric valve of the medium-pressure nitrogen source, the electric heating belt of the particle transmission pipeline, and the electric heater in the liquid nitrogen flash tank; The upper computer operation interface shows that the shutdown is complete; Manually close all manual valves to full close; S40. Control system shutdown; Shut down the host computer of the control system; Turn off the power in the PLC control cabinet and the control system power supply; Turn off the UPS power supply host in the PLC control cabinet and turn off the UPS power supply; S50. Emergency stop of control system; Emergency stop buttons are set on the operation interface of the upper computer and on the door of the control cabinet. The control system can stop in an emergency with one button. When the emergency stops, the control system will close all electric valves, electric regulating valves and all auxiliary devices at the same time. After the control system stops in an emergency, the administrator restores and checks the control system. After confirming that it is correct, the administrator re-enters the correct password on the operation interface of the host computer to cancel the emergency stop command.

[0017] The control system and method of the low-temperature environment PIV clean particle generation and transmission system of the present invention utilize pure water as the tracer particle material, avoiding the pollution problem of traditional oily tracer particles and solid tracer particles on the insulation materials of the low-temperature test environment. The generated ice particles have uniform particle size, good light scattering properties, low cost, and controllable concentration, which can meet the needs of low-temperature environment PIV testing experiments with ambient temperatures below 180K and high requirements on tracer particle pollution issues. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The control system topology diagram for the PIV clean particle generation and transmission system in a low-temperature environment; Figure 2This is a flow chart of the control method for the PIV clean particle generation and transmission system in a low temperature environment. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0020] Example: Figure 1 As shown, the control system of the low-temperature environment PIV clean particle generation and transmission system of this embodiment includes a basic perception layer, a basic control layer, a network transmission layer and an application service layer arranged from bottom to top; each layer is connected by pipelines, cables and networks; The basic sensing layer includes the normal pressure pipeline subsystem, the cooling air flow pipeline subsystem, the tracer particle generator subsystem, the cooling mixing device and the particle transmission pipeline subsystem; The basic control layer includes programmable controller CPU, programmable controller expansion module, touch screen, switch, signal isolator, intermediate relay, low-voltage circuit breaker, button indicator light and uninterruptible power supply; The network transmission layer includes industrial electrical port switches and network cables; The application service layer includes host computers, system software, monitoring software and databases.

[0021] Furthermore, the atmospheric pressure pipeline subsystem is connected to the medium pressure nitrogen source and the tracer particle generator through the atmospheric pressure gas source pipeline; the atmospheric pressure gas source pipeline is provided with a manual valve, a filter, an electronic pressure regulating valve, a check valve, a temperature sensor and a pressure sensor; The atmospheric pressure pipeline subsystem introduces the medium-pressure nitrogen from the medium-pressure nitrogen source into the tracer particle generator through the interface reserved in the test hall. It is used to drive the tracer particle generator and also serves as the driving airflow for the PIV tracer particle flow. It is also used to monitor the medium-pressure nitrogen at the front end of the particle generator to ensure that the temperature and pressure of the medium-pressure nitrogen entering the particle generator are within the design range.

[0022] Furthermore, the cooling air flow pipeline subsystem is connected to the liquid nitrogen interface of the liquid nitrogen tank and the cooling mixing device through the cooling air flow pipeline; the cooling air flow pipeline is provided with a safety valve, a filter, an electric pressure regulating valve, a temperature sensor, a pressure sensor, a flow sensor and a liquid nitrogen flash tank; The cooling gas flow pipeline converts the liquid nitrogen from the test site into deep-cold dry nitrogen and transmits it to the cooling mixing device as a cooling gas source; the specific process is as follows: The liquid nitrogen for the cooling air flow pipeline is provided by the low-temperature nitrogen source at the test site, i.e., the liquid nitrogen tank; the pressurized gas for the cooling air flow pipeline is provided by the medium-pressure nitrogen source in the plant; the cooling air flow pipeline sprays liquid nitrogen into the liquid nitrogen flash tank to cool the medium-pressure nitrogen at room temperature, and mixes the liquid nitrogen with the medium-pressure nitrogen in the liquid nitrogen flash tank to form deep-cold dry nitrogen; the deep-cold dry nitrogen enters the cooling mixing device through the cooling air flow pipeline.

[0023] Furthermore, the main body of the tracer particle generator subsystem is the tracer particle generator, which is provided with a pressure sensor, a temperature transmitter, a check valve, an electric heater and a manual valve; the tracer particle generator subsystem generates a humidified airflow in the tracer particle generator container by passing dry nitrogen through a Laskin nozzle, and the humidified airflow contains gas with water vapor particles with an average diameter of 1 μm to 3 μm or nearly saturated water vapor at room temperature.

[0024] Furthermore, the main body of the cooling and mixing device is a cooling tank, and a temperature transmitter and a regulating valve are provided on the cooling tank; The humid airflow generated by the tracer particle generator subsystem and the deep-cold dry nitrogen generated by the cooling airflow pipeline subsystem are mixed in the cooling tank of the cooling mixing device. The water vapor particles in the humid airflow are instantly condensed into ice particles with an average diameter of 1μm~3μm. The ice particles are injected into the inner flow channel of the particle transmission pipeline subsystem through the insulation pipe as PIV tracer particles.

[0025] Furthermore, the particle transmission pipeline subsystem includes a particle transmission pipeline, on which a manual valve and an electric valve are arranged; the particle transmission pipeline subsystem transmits the PIV tracer particles generated by the cooling mixing device to the inner flow channel of the low-temperature test device.

[0026] like Figure 2 As shown, the control method of the low temperature environment PIV clean particle generation and transmission system of this embodiment includes the following steps: S10. Control system inspection; The administrator checks and confirms that the instrument cables, control cables, power cables and aviation plugs are connected correctly and function properly; After the administrator checks that all electric valves are closed, he manually opens all manual valves that need to be opened in advance to full open; The administrator checks all mechanical pointer meters to ensure they are in good condition and the readings are within the set normal range; After the administrator completes the inspection, he or she will manually record the inspection results; S20. Control system self-check; Power on the control system; Turn on the host computer of the control system, log in with the correct user name, and enter the operation interface; The control system performs self-check to confirm that the medium-pressure nitrogen pressure is within the set range; The control system performs self-check to confirm that the medium-pressure nitrogen temperature is within the set range; The control system performs self-check to confirm that the liquid nitrogen pressure is within the set range; The control system performs self-check to confirm that the liquid level in the tracer particle generator is within the set range; The control system performs self-check to confirm that the temperature of the liquid in the tracer particle generator is within the set range; The control system is ready; S30. Conduct PIV test experiments; S301. Control system drying and purge; Click the drying and purge start button on the upper computer operation interface; The control system opens the main valve of the medium-pressure nitrogen source; The control system opens the regulating valve of the medium-pressure nitrogen source by 50%; The control system opens the regulating valve of the cryogenic nitrogen source by 50%; The control system opens the electric gate valve of the particle transmission pipeline to dry and purge the particle transmission pipeline; After the drying and purge time reaches the set time, the control system closes the electric gate valve of the particle transmission pipeline, and then delays closing the main valve of the medium-pressure nitrogen source and the regulating valve of the medium-pressure nitrogen source; Drying and purge is completed; S302.PIV test preparation; The control system turns on the electric heater of the tracer particle generator, heating the water temperature to 60°C and keeping it warm; The control system adjusts the pressure at the rear end of the tracer particle generator to 0.6 MPa through the regulating valve of the medium-pressure nitrogen source; The control system adjusts the pressure at the rear end of the cooling tank to 0.55MPa through the regulating valve of the medium-pressure nitrogen source; The control system opens the electric gate valve of the particle transmission pipeline; S303. Turn on liquid nitrogen; The control system opens the electric regulating valve of the liquid nitrogen tank delivery pipeline; The control system determines that the temperature, pressure and flow rate of the liquid nitrogen tank delivery pipeline are within the design range; The control system determines that the temperature and pressure of the cooling air flow pipeline are within the design range; The cryogenic dry nitrogen enters the cooling mixing device through the cooling air flow pipeline, and the flow rate of the cryogenic dry nitrogen is ensured to be stable; S304. Open the Laskin nozzle; When the temperature of the cooling air flow pipeline drops to the set range, the control system opens the electric regulating valve; The control system opens the electric valve of the Laskin nozzle pipeline, and the dry nitrogen passes through the Laskin nozzle to generate a humid air flow in the tracer particle generator container. The humid air flow contains gas with water vapor particles with an average diameter of 1μm~3μm or nearly saturated water vapor at room temperature; The moist airflow generated by the tracer particle generator subsystem and the deep-cold dry nitrogen generated by the cooling airflow pipeline subsystem are mixed in the cooling tank of the cooling mixing device, and the water vapor particles in the moist airflow are instantly condensed into ice particles with an average diameter of 1μm~3μm; The control system detects whether the particle size and concentration of ice particles meet the requirements of the PIV test, and adjusts the subsystems of the basic sensing layer until PIV tracer particles that meet the requirements of the PIV test are obtained; S305. The control system generates stable PIV tracer particles; After the control system reaches a steady state, it continuously generates PIV tracer particles that meet the requirements of the PIV test. At the same time, it automatically adjusts the opening of the electric control valves of each subsystem of the basic sensing layer to ensure the generation of stable PIV tracer particles. S306. Control system before shutdown; After the PIV test is completed, click the shutdown button on the upper computer operation interface; The control system closes the regulating valve of the medium-pressure nitrogen source; The control system closes the regulating valve of the cryogenic nitrogen source; The control system automatically turns on the electric heating cable of the particle transmission pipeline to heat the particle transmission pipeline and maintain the temperature for 10 minutes; The control system automatically turns on the electric heater in the liquid nitrogen flash tank to heat the residual liquid nitrogen and maintain the temperature for 10 minutes; The control system is dried and purged for 10 minutes; The control system closes the electric gate valve at the rear end of the particle transmission pipeline, the electric valve of the medium-pressure nitrogen source, the electric heating belt of the particle transmission pipeline, and the electric heater in the liquid nitrogen flash tank; The upper computer operation interface shows that the shutdown is complete; Manually close all manual valves to full close; S40. Control system shutdown; Shut down the host computer of the control system; Turn off the power in the PLC control cabinet and the control system power supply; Turn off the UPS power supply host in the PLC control cabinet and turn off the UPS power supply; S50. Emergency stop of control system; Emergency stop buttons are set on the operation interface of the upper computer and on the door of the control cabinet. The control system can stop in an emergency with one button. When the emergency stops, the control system will close all electric valves, electric regulating valves and all auxiliary devices at the same time. After the control system stops in an emergency, the administrator restores and checks the control system. After confirming that it is correct, the administrator re-enters the correct password on the operation interface of the host computer to cancel the emergency stop command.

[0027] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and implementation modes. For those familiar with the art, all features disclosed in the present invention, or steps in all methods or processes disclosed, except for mutually exclusive features and / or steps, can be combined in any way without departing from the principles of the present invention. The present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. The control system of the low temperature environment PIV clean particle generation and transmission system is characterized by: The control system includes a basic perception layer, a basic control layer, a network transmission layer and an application service layer arranged from bottom to top; each layer is connected by pipelines, cables and networks; The basic sensing layer includes the normal pressure pipeline subsystem, the cooling air flow pipeline subsystem, the tracer particle generator subsystem, the cooling mixing device and the particle transmission pipeline subsystem; The basic control layer includes programmable controller CPU, programmable controller expansion module, touch screen, switch, signal isolator, intermediate relay, low-voltage circuit breaker, button indicator light and uninterruptible power supply; The network transmission layer includes industrial electrical port switches and network cables; The application service layer includes host computers, system software, monitoring software and databases.

2. The control system of the low temperature environment PIV clean particle generation and transmission system according to claim 1, characterized in that: The atmospheric pressure pipeline subsystem is connected to the medium pressure nitrogen source and the tracer particle generator through the atmospheric pressure gas source pipeline; the atmospheric pressure gas source pipeline is provided with a manual valve, a filter, an electronic pressure regulating valve, a check valve, a temperature sensor and a pressure sensor; The atmospheric pressure pipeline subsystem introduces the medium-pressure nitrogen from the medium-pressure nitrogen source into the tracer particle generator through the interface reserved in the test hall. It is used to drive the tracer particle generator and also serves as the driving airflow for the PIV tracer particle flow. It is also used to monitor the medium-pressure nitrogen at the front end of the particle generator to ensure that the temperature and pressure of the medium-pressure nitrogen entering the particle generator are within the design range.

3. The control system of the low temperature environment PIV clean particle generation and transmission system according to claim 2, characterized in that: The cooling air flow pipeline subsystem is connected to the liquid nitrogen interface of the liquid nitrogen tank and the cooling mixing device through the cooling air flow pipeline; the cooling air flow pipeline is provided with a safety valve, a filter, an electric pressure regulating valve, a temperature sensor, a pressure sensor, a flow sensor and a liquid nitrogen flash tank; The cooling gas flow pipeline converts the liquid nitrogen from the test site into deep-cold dry nitrogen and transmits it to the cooling mixing device as a cooling gas source; the specific process is as follows: The liquid nitrogen for the cooling air flow pipeline is provided by the low-temperature nitrogen source at the test site, i.e., the liquid nitrogen tank; the pressurized gas for the cooling air flow pipeline is provided by the medium-pressure nitrogen source in the plant; the cooling air flow pipeline sprays liquid nitrogen into the liquid nitrogen flash tank to cool the medium-pressure nitrogen at room temperature, and mixes the liquid nitrogen with the medium-pressure nitrogen in the liquid nitrogen flash tank to form deep-cold dry nitrogen; the deep-cold dry nitrogen enters the cooling mixing device through the cooling air flow pipeline.

4. The control system of the low temperature environment PIV clean particle generation and transmission system according to claim 3, characterized in that: The main body of the tracer particle generator subsystem is the tracer particle generator, which is provided with a pressure sensor, a temperature transmitter, a check valve, an electric heater and a manual valve; the tracer particle generator subsystem generates a humid air flow in the tracer particle generator container by passing dry nitrogen through a Laskin nozzle, and the humid air flow contains gas with water vapor particles with an average diameter of 1μm~3μm or nearly saturated water vapor at room temperature.

5. The control system of the low temperature environment PIV clean particle generation and transmission system according to claim 4, characterized in that: The main body of the cooling and mixing device is a cooling tank, on which a temperature transmitter and a regulating valve are provided; The humid airflow generated by the tracer particle generator subsystem and the deep-cold dry nitrogen generated by the cooling airflow pipeline subsystem are mixed in the cooling tank of the cooling mixing device. The water vapor particles in the humid airflow are instantly condensed into ice particles with an average diameter of 1μm~3μm. The ice particles are injected into the inner flow channel of the particle transmission pipeline subsystem through the insulation pipe as PIV tracer particles.

6. The control system of the low temperature environment PIV clean particle generation and transmission system according to claim 5, characterized in that: The particle transmission pipeline subsystem comprises a particle transmission pipeline, on which a manual valve and an electric valve are arranged; the particle transmission pipeline subsystem transmits the PIV tracer particles generated by the cooling mixing device to the inner flow channel of the low temperature test device.

7. A method for controlling a PIV clean particle generation and transmission system in a low temperature environment, characterized in that: The control method comprises the following steps: S10. Control system inspection; The administrator checks and confirms that the instrument cables, control cables, power cables and aviation plugs are connected correctly and function properly; After the administrator checks that all electric valves are closed, he manually opens all manual valves that need to be opened in advance to full open; The administrator checks all mechanical pointer meters to ensure they are in good condition and the readings are within the set normal range; After the administrator completes the inspection, he or she will manually record the inspection results; S20. Control system self-check; Power on the control system; Turn on the host computer of the control system, log in with the correct user name, and enter the operation interface; The control system performs self-check to confirm that the medium-pressure nitrogen pressure is within the set range; The control system performs self-check to confirm that the medium-pressure nitrogen temperature is within the set range; The control system performs self-check to confirm that the liquid nitrogen pressure is within the set range; The control system performs self-check to confirm that the liquid level in the tracer particle generator is within the set range; The control system performs self-check to confirm that the temperature of the liquid in the tracer particle generator is within the set range; The control system is ready; S30. Conduct PIV test experiments; S301. Control system drying and purge; Click the drying and purge start button on the upper computer operation interface; The control system opens the main valve of the medium-pressure nitrogen source; The control system opens the regulating valve of the medium-pressure nitrogen source by 50%; The control system opens the regulating valve of the cryogenic nitrogen source by 50%; The control system opens the electric gate valve of the particle transmission pipeline to dry and purge the particle transmission pipeline; After the drying and purge time reaches the set time, the control system closes the electric gate valve of the particle transmission pipeline, and then delays closing the main valve of the medium-pressure nitrogen source and the regulating valve of the medium-pressure nitrogen source; Drying and purge is completed; S302.PIV test preparation; The control system turns on the electric heater of the tracer particle generator, heating the water temperature to 60°C and keeping it warm; The control system adjusts the pressure at the rear end of the tracer particle generator to 0.6 MPa through the regulating valve of the medium-pressure nitrogen source; The control system adjusts the pressure at the rear end of the cooling tank to 0.55MPa through the regulating valve of the medium-pressure nitrogen source; The control system opens the electric gate valve of the particle transmission pipeline; S303. Turn on liquid nitrogen; The control system opens the electric regulating valve of the liquid nitrogen tank delivery pipeline; The control system determines that the temperature, pressure and flow rate of the liquid nitrogen tank delivery pipeline are within the design range; The control system determines that the temperature and pressure of the cooling air flow pipeline are within the design range; The cryogenic dry nitrogen enters the cooling mixing device through the cooling air flow pipeline, and the flow rate of the cryogenic dry nitrogen is ensured to be stable; S304. Open the Laskin nozzle; When the temperature of the cooling air flow pipeline drops to the set range, the control system opens the electric regulating valve; The control system opens the electric valve of the Laskin nozzle pipeline, and the dry nitrogen passes through the Laskin nozzle to generate a humid air flow in the tracer particle generator container. The humid air flow contains gas with water vapor particles with an average diameter of 1μm~3μm or nearly saturated water vapor at room temperature; The moist airflow generated by the tracer particle generator subsystem and the deep-cold dry nitrogen generated by the cooling airflow pipeline subsystem are mixed in the cooling tank of the cooling mixing device, and the water vapor particles in the moist airflow are instantly condensed into ice particles with an average diameter of 1μm~3μm; The control system detects whether the particle size and concentration of ice particles meet the requirements of the PIV test, and adjusts the subsystems of the basic sensing layer until PIV tracer particles that meet the requirements of the PIV test are obtained; S305. The control system generates stable PIV tracer particles; After the control system reaches a steady state, it continuously generates PIV tracer particles that meet the requirements of the PIV test. At the same time, it automatically adjusts the opening of the electric control valves of each subsystem of the basic sensing layer to ensure the generation of stable PIV tracer particles. S306. Control system before shutdown; After the PIV test is completed, click the shutdown button on the upper computer operation interface; The control system closes the regulating valve of the medium-pressure nitrogen source; The control system closes the regulating valve of the cryogenic nitrogen source; The control system automatically turns on the electric heating cable of the particle transmission pipeline to heat the particle transmission pipeline and maintain the temperature for 10 minutes; The control system automatically turns on the electric heater in the liquid nitrogen flash tank to heat the residual liquid nitrogen and maintain the temperature for 10 minutes; Control system to dry and purge for 10 minutes; The control system closes the electric gate valve at the rear end of the particle transmission pipeline, the electric valve of the medium-pressure nitrogen source, the electric heating belt of the particle transmission pipeline, and the electric heater in the liquid nitrogen flash tank; The upper computer operation interface shows that the shutdown is complete; Manually close all manual valves to full close; S40. Control system shutdown; Shut down the host computer of the control system; Turn off the power in the PLC control cabinet and the control system power supply; Turn off the UPS power supply host in the PLC control cabinet and turn off the UPS power supply; S50. Emergency stop of control system; Emergency stop buttons are set on the operation interface of the upper computer and on the door of the control cabinet. The control system can stop in an emergency with one button. When the emergency stops, the control system will close all electric valves, electric regulating valves and all auxiliary devices at the same time. After the control system stops in an emergency, the administrator restores and checks the control system. After confirming that it is correct, the administrator re-enters the correct password on the operation interface of the host computer to cancel the emergency stop command.

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