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

Abstract

The invention belongs to the technical field of low-temperature tests, and discloses a PIV clean particle generation and transmission system for a low-temperature environment. The system comprises a normal-temperature nitrogen pipeline, a particle generator, a liquid nitrogen flash tank, a low-temperature nitrogen pipeline, a cooling and mixing device and an ice particle conveying pipeline. The normal-temperature nitrogen pipeline provides driving airflow needed by operation of the particle generator, wet water vapor containing tiny water particles is generated through the particle generator and conveyed to the cooling mixing device, the wet water vapor is rapidly mixed with low-temperature nitrogen generated by the liquid nitrogen flash tank, and ice particles with the average particle size being about 1 mm are formed through instant cooling. Ice particles generated by the system are uniform in particle size, good in light scattering performance, low in cost and controllable in concentration, can meet PIV test requirements in low-temperature test equipment below 180K, can also be used for other low-temperature environment PIV test requirements with high requirements for trace particle pollution, and has engineering practical value.

Description

Technical Field

[0001] The invention belongs to the technical field of low temperature testing, and in particular relates to a PIV clean particle generation and transmission system for low temperature environments. 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, the 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 can produce oily particles with a particle size of about 1μm using the Laskin nozzle atomization principle; the other is based on SiO 2 Solid powders such as solid powders can be produced by using 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 PIV clean particle generation and transmission system for low-temperature environments. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a PIV clean particle generation and transmission system for low temperature environment, which is used for PIV test experiments in low temperature environment.

[0010] The normal temperature medium pressure dry nitrogen storage tank of the PIV clean particle generation and transmission system for low temperature environment of the present invention is connected to the particle generator through a normal temperature nitrogen pipeline, and the particle generator is connected to the cooling and mixing device through a wet nitrogen pipeline; the normal temperature medium pressure dry nitrogen storage tank is also connected to the liquid nitrogen flash tank through a normal temperature nitrogen pipeline, and the liquid nitrogen flash tank is connected to the cooling and mixing device through a low temperature nitrogen pipeline; a pressure flow regulating valve assembly is provided on the normal temperature nitrogen pipeline; The liquid nitrogen storage tank is connected to the liquid nitrogen flash tank via a flow regulating valve assembly, and the liquid nitrogen flash tank is connected to the cooling mixing device via a low-temperature nitrogen pipeline; The ice particles in the cooling and mixing device are transmitted to the low-temperature test environment through the ice particle transmission pipeline; the applicable temperature range is: 110K~180K; the total pressure range is: 0~450kPa.

[0011] Furthermore, the pressure flow regulating valve assembly comprises a stop valve, a flow meter, a check valve, a quick valve and a pressure reducing valve arranged in sequence from front to back along the air flow direction; the stop valve is used to manually cut off the air flow, the flow meter is used for flow feedback, the check valve is used to prevent air flow backflow, the quick valve is used to remotely control the on and off of the particle generator, and the pressure reducing valve is used to adjust the working pressure; The remote control system of the PIV clean particle generation and transmission system adjusts the valve opening in real time according to the reading feedback of the flow meter, and controls the amount of tracer particles generated by controlling the size of the air intake.

[0012] Furthermore, the flow regulating valve assembly includes a manual low-temperature stop valve, a filter, a pressure gauge, an electric regulating valve and a check valve which are sequentially arranged from front to back along the air flow direction to perform on-off and flow control on the liquid nitrogen pipeline.

[0013] Furthermore, an exhaust valve, an electric switch valve and a manual stop valve are sequentially arranged along the air flow direction from front to back on the ice particle transmission pipeline; the exhaust valve is used to discharge the remaining nitrogen and ice particles after the test; the electric switch valve and the manual stop valve are used to connect and disconnect the PIV clean particle generation and transmission system with the low-temperature test environment. After the test, the electric switch valve and the manual stop valve are in a closed state.

[0014] Furthermore, the particle generator uses pure water as the tracer particle raw material, and an electric heater is arranged in the particle generator.

[0015] Furthermore, a wire mesh packing layer is arranged inside the liquid nitrogen flash tank, and liquid nitrogen and room temperature nitrogen transfer mass and heat in the wire mesh packing layer, so that the liquid nitrogen is flashed into low-temperature nitrogen, and the uniformity of the low-temperature nitrogen is ensured; a safety valve is arranged on the top of the liquid nitrogen flash tank, and when the internal pressure of the liquid nitrogen flash tank exceeds 0.8MPa, the safety valve automatically opens to release the pressure.

[0016] The particle generator in the PIV clean particle generation and transmission system for low-temperature environment of the present invention is driven by medium-pressure nitrogen. The tank of the particle generator contains pure water as the tracer particle material. The medium-pressure nitrogen is injected into the pure water through a conventional Laskin nozzle. Its working principle is similar to that of a traditional Laskin atomizer. Since the viscosity of water is much smaller than that of oily liquids, the concentration of water particles produced by the traditional Laskin atomization method is far from meeting the test requirements. Therefore, a heating device is arranged inside the generator. Ground tests have shown that heating pure water to about 50°C can greatly increase the water vapor saturation in nitrogen, thereby increasing the particle concentration. Water vapor containing tiny water droplets enters the cooling and mixing device with the nitrogen gas flow, and is mixed with the low-temperature nitrogen formed by liquid nitrogen flash evaporation from the liquid nitrogen pipeline, thereby achieving instant condensation of tiny water droplets and water vapor. The debugging test results show that the optimized design of the cooling mixing device and the reasonably distributed mixing ratio of the normal temperature airflow and the low temperature airflow will significantly affect the condensation effect, and can control the particle size distribution of the ice particles within the ideal range of 1μm~2μm. At the same time, the nitrogen flow temperature at the outlet of the cooling mixing device can be controlled below 180K, which is conducive to maintaining the physical state of the ice particles stable for a long time.

[0017] The particle generator in the PIV clean particle generation and transmission system for low temperature environment of the present invention has the following special designs: a. Using pure water as tracer particle material solves the pollution problem of traditional oily and solid tracer particle materials; b. Installing a heating device can effectively solve the problem of low efficiency of traditional Laskin nozzle atomization water. Since the heating temperature is controllable and the nitrogen flow rate at room temperature is controllable, the concentration of tracer particles can be controlled more accurately to avoid test failure due to insufficient concentration or aggravated particle agglomeration and increased particle size due to excessive concentration. c. A cooling and mixing device is designed. By optimizing the internal structure design, water droplets or water vapor can be condensed into ice particles efficiently and evenly. By optimizing the flow design, the particle size of ice particles can be effectively controlled to avoid the problem of uncontrollable particle concentration and particle size caused by direct injection of water vapor into the low-temperature test equipment; d. Use liquid nitrogen and nitrogen as driving and cooling gases, which is consistent with the pure nitrogen environment in the cryogenic test equipment; e. The operating temperature of the suitable low temperature test environment shall not be higher than 180K.

[0018] The PIV clean particle generation and transmission system for low-temperature environments of the present invention can simultaneously meet several requirements for the characteristics of PIV tracer particles in low-temperature test environments: (1) Pure water is used as the tracer particle material. Pure water is non-corrosive and does not pollute the structure and insulation materials of the low-temperature test environment; (2) Ice particles have good physical stability at ambient temperatures below 180K. Existing research results show that when the ambient temperature is 180K, the survival period of ice particles with a diameter of 1μm is as long as 10 2 ~10 3 s, 150K, survival up to 10 5 ~10 6 s, therefore, ice particles with a diameter of 1 μm are suitable for use in an ambient temperature range of ≤180K. After the test is completed, the test environment only needs to be blown with room temperature nitrogen or air to accelerate the volatilization of water vapor and leave no residue; (3) The debugging test shows that the optimized cooling and mixing device can effectively accelerate the liquefaction-condensation process of water droplets and water vapor and prevent ice particles from agglomerating. The particle size of ice particles is about 1 μm, which is at the same level as traditional oily particles. The density of ice is basically the same as that of oil. Therefore, the tracking ability of ice particles is basically the same as that of oily tracer particles; (4) Existing research results show that the light scattering of ice particles is slightly lower than that of oily particles, but it can also meet the needs of optical measurement; (5) By heating the pure water in the particle generator, the water vapor saturation in the normal temperature nitrogen flow can be effectively increased, thereby effectively increasing the particle concentration. However, there are two points that need to be designed in detail and verified through ground debugging: First, excessive water vapor saturation will lead to excessive ice particle concentration in the cooling and mixing device, thereby accelerating the agglomeration of ice particles and increasing the particle size; second, excessive water temperature or excessive normal temperature nitrogen flow will lead to insufficient cooling and mixing, and the air flow temperature in the ice particle transmission pipeline at the outlet of the cooling and mixing device will be high, resulting in a shortened ice particle life cycle. Excessive temperature will also aggravate the agglomeration of ice particles. Therefore, key control parameters such as water temperature, normal temperature nitrogen flow, and liquid nitrogen flow must be matched and designed according to different generator specifications and verified through ground tests.

[0019] The PIV clean particle generation and transmission system for low-temperature environments of the present invention utilizes 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 PIV test experiments in low-temperature environments with an ambient temperature below 180K and high requirements on the tracer particle pollution problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the PIV clean particle generation and transmission system for low temperature environment of the present invention; Figure 2 This is the original image of tracer particles obtained by the PIV clean particle generation and transmission system for low temperature environment of the present invention.

[0021] In the figure, 1. Normal temperature medium pressure dry nitrogen storage tank; 2. Liquid nitrogen storage tank; 3. Normal temperature nitrogen pipeline; 4. Pressure flow regulating valve assembly; 5. Flow regulating valve assembly; 6. Particle generator; 7. Liquid nitrogen flash tank; 8. Wet nitrogen pipeline; 9. Cryogenic nitrogen pipeline; 10. Cooling mixing device; 11. Ice particle transmission pipeline. DETAILED DESCRIPTION

[0022] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0023] Example 1: Figure 1 As shown, the normal temperature medium pressure dry nitrogen storage tank 1 of the PIV clean particle generation and transmission system for low temperature environment of this embodiment is connected to the particle generator 6 through the normal temperature nitrogen pipeline 3, and the particle generator 6 is connected to the cooling mixing device 10 through the wet nitrogen pipeline 8; the normal temperature medium pressure dry nitrogen storage tank 1 is also connected to the liquid nitrogen flash tank 7 through the normal temperature nitrogen pipeline 3, and the liquid nitrogen flash tank 7 is connected to the cooling mixing device 10 through the low temperature nitrogen pipeline 9; the normal temperature nitrogen pipeline 3 is provided with a pressure flow regulating valve assembly 4; The liquid nitrogen storage tank 2 is connected to the liquid nitrogen flash tank 7 via the flow regulating valve assembly 5, and the liquid nitrogen flash tank 7 is connected to the cooling mixing device 10 via the low-temperature nitrogen pipeline 9; The ice particles in the cooling and mixing device 10 are transmitted to the low-temperature test environment through the ice particle transmission pipeline 11; the applicable temperature range is: 110K~180K; the total pressure range is: 0~450kPa.

[0024] Furthermore, the pressure flow regulating valve assembly 4 includes a stop valve, a flow meter, a check valve, a quick valve and a pressure reducing valve arranged in sequence from front to back along the air flow direction; the stop valve is used to manually cut off the air flow, the flow meter is used for flow feedback, the check valve is used to prevent air flow backflow, the quick valve is used to remotely control the particle generator 6 on and off, and the pressure reducing valve is used to adjust the working pressure; The remote control system of the PIV clean particle generation and transmission system adjusts the valve opening in real time according to the reading feedback of the flow meter, and controls the amount of tracer particles generated by controlling the size of the air intake.

[0025] Furthermore, the flow regulating valve assembly 5 includes a manual low-temperature stop valve, a filter, a pressure gauge, an electric regulating valve and a check valve which are sequentially arranged from front to back along the air flow direction to perform on-off and flow control on the liquid nitrogen pipeline.

[0026] Furthermore, an exhaust valve, an electric switch valve and a manual stop valve are sequentially arranged on the ice particle transmission pipeline 11 from front to back along the air flow direction; the exhaust valve is used to discharge the remaining nitrogen and ice particles after the test; the electric switch valve and the manual stop valve are used to connect and disconnect the PIV clean particle generation and transmission system with the low-temperature test environment. After the test, the electric switch valve and the manual stop valve are in a closed state.

[0027] Furthermore, the particle generator 6 uses pure water as the tracer particle raw material, and an electric heater is provided in the particle generator 6 .

[0028] Furthermore, a wire mesh packing layer is arranged inside the liquid nitrogen flash tank 7, and liquid nitrogen and room temperature nitrogen transfer mass and heat in the wire mesh packing layer, so that the liquid nitrogen is flashed into low-temperature nitrogen, and the uniformity of the low-temperature nitrogen is ensured; a safety valve is arranged on the top of the liquid nitrogen flash tank 7, and when the internal pressure of the liquid nitrogen flash tank 7 exceeds 0.8MPa, the safety valve automatically opens to release the pressure.

[0029] This embodiment obtains Figure 2 The original image is shown. It can be seen that the brightness and concentration of the ice particles are relatively uniform, and the probability of large light spots is very low, indicating that the PIV clean particle generation and transmission system for low-temperature environments of the present invention can effectively control the ice particle size and ensure the flow followability of the tracer particles; the tracer particle distribution density increases rapidly, indicating that the entire system can effectively provide the particle concentration required for PIV testing.

[0030] 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. A PIV clean particle generation and transmission system for low temperature environment, characterized in that: The normal temperature medium pressure dry nitrogen storage tank (1) of the PIV clean particle generation and transmission system is connected to the particle generator (6) via a normal temperature nitrogen pipeline (3), and the particle generator (6) is connected to the cooling and mixing device (10) via a wet nitrogen pipeline (8); the normal temperature medium pressure dry nitrogen storage tank (1) is also connected to the liquid nitrogen flash tank (7) via a normal temperature nitrogen pipeline (3), and the liquid nitrogen flash tank (7) is connected to the cooling and mixing device (10) via a low temperature nitrogen pipeline (9); a pressure flow regulating valve assembly (4) is provided on the normal temperature nitrogen pipeline (3); The liquid nitrogen storage tank (2) is connected to the liquid nitrogen flash tank (7) via a flow regulating valve assembly (5), and the liquid nitrogen flash tank (7) is connected to the cooling mixing device (10) via a low-temperature nitrogen pipeline (9); The ice particles in the cooling and mixing device (10) are transmitted to the low-temperature testing equipment via the ice particle transmission pipeline (11); the applicable temperature range is: 110K~180K; the total pressure range is: 0~450kPa.

2. A PIV clean particle generation and transmission system for low temperature environment according to claim 1, characterized in that: The pressure flow regulating valve assembly (4) comprises a stop valve, a flow meter, a check valve, a quick valve and a pressure reducing valve arranged in sequence from front to back along the air flow direction; the stop valve is used to manually cut off the air flow, the flow meter is used for flow feedback, the check valve is used to prevent air flow backflow, the quick valve is used to remotely control the on and off of the particle generator (6), and the pressure reducing valve is used to adjust the working pressure; The remote control system of the PIV clean particle generation and transmission system adjusts the valve opening in real time according to the reading feedback of the flow meter, and controls the amount of tracer particles generated by controlling the size of the air intake.

3. A PIV clean particle generation and transmission system for low temperature environment according to claim 1, characterized in that: The flow control valve assembly (5) comprises a manual low-temperature stop valve, a filter, a pressure gauge, an electric control valve and a check valve which are arranged in sequence from front to back along the air flow direction, and are used to control the on-off and flow rate of the liquid nitrogen pipeline.

4. A PIV clean particle generation and transmission system for low temperature environment according to claim 1, characterized in that: The ice particle transmission pipeline (11) is provided with an exhaust valve, an electric switch valve and a manual stop valve in order from front to back along the airflow direction; the exhaust valve is used to discharge the remaining nitrogen and ice particles after the test is completed; the electric switch valve and the manual stop valve are used to connect and disconnect the PIV clean particle generation and transmission system and the low-temperature test environment. After the test is completed, the electric switch valve and the manual stop valve are in a closed state.

5. A PIV clean particle generation and transmission system for low temperature environment according to claim 1, characterized in that: The particle generator (6) uses pure water as a tracer particle raw material, and an electric heater is provided in the particle generator (6).

6. A PIV clean particle generation and transmission system for low temperature environment according to claim 1, characterized in that: A wire mesh packing layer is arranged inside the liquid nitrogen flash tank (7), and liquid nitrogen and room temperature nitrogen transfer mass and heat in the wire mesh packing layer, so that the liquid nitrogen is flashed and converted into low-temperature nitrogen, and the uniformity of the low-temperature nitrogen is ensured; a safety valve is arranged on the top of the liquid nitrogen flash tank (7), and when the internal pressure of the liquid nitrogen flash tank (7) exceeds 0.8 MPa, the safety valve automatically opens to release the pressure.

Images