Controlled condensation and frosting visualization experimental device during gas flow in ultra-low temperature environment

Abstract

This invention belongs to the field of phase change heat transfer technology, specifically disclosing a controlled condensation and frosting visualization experimental device for gas flow in ultra-low temperature environments. Addressing the problems of current condensation and frosting visualization experimental devices, this invention designs a multifunctional experimental device capable of observing the gas-liquid-solid phase change process and measuring heat transfer performance. This device can not only observe the gas-liquid-solid phase change process during low-temperature gas flow under different operating conditions, but also investigate the effects of various factors such as fluid velocity, initial temperature, pressure, gas composition, and wall materials on the gas frosting process, frost crystal morphology, and frost layer properties, as well as the influence of different factors on the gas phase change heat transfer performance. Conducting phase change heat transfer experiments with different low-temperature fluids using the condensation and frosting visualization experimental device proposed in this invention can provide data support for the optimized design of heat exchangers for different fluids and the design of CO2 capture devices.

Description

Technical Field

[0001] This invention belongs to the field of phase change heat transfer technology, specifically relating to a controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment. Background Technology

[0002] Gas-liquid-solid phase change is a common physical phenomenon in nature and industrial production, playing a vital role in refrigeration, food processing, petrochemicals, aerospace, and other fields. Understanding the specific process of gas-liquid-solid phase change and clarifying the key factors affecting the phase change process and heat transfer efficiency is of great significance for achieving efficient control of phase change heat transfer efficiency, improving energy utilization efficiency, ensuring safe equipment operation, and guiding the development of functional materials.

[0003] Existing experimental devices for observing gas condensation and frosting are mostly built to observe the phase change process of water vapor condensation and frosting. The temperature of the condensation surface is relatively high, generally not lower than -20℃. Moreover, most visualization experimental devices can only study the phase change process of gas in a closed space, and cannot study the phase change process under flow conditions. For example, the "Multifunctional Steam Condensation Heat Exchange and Frosting Process Visualization Experimental Device" disclosed in patent application No. 201810229255.3 uses deionized water heated by a boiler as condensable steam, and the cooling system uses cooling water with uncontrollable water temperature. The gas undergoes a phase change in a sealed chamber. The "Controlled Liquefaction and Solidification Process Visualization Experimental Observation Device Based on a Cryogenic Refrigerator" disclosed in patent application No. 201610964667.2 can only meet the visualization observation of the liquefaction or solidification process of cryogenic fluids, and cannot measure the heat transfer coefficient of the fluid heat exchange process under different operating conditions. Moreover, the phase change process is also completed in a closed chamber.

[0004] In actual industrial production, such as in natural gas liquefaction, CCUS (Concentrated Gas-Liquid-Solid State Gas), and microscale heat transfer and phase change processes, the main areas of focus are the gas-liquid-solid phase change processes of fluids like light alkanes and CO2. These fluids have relatively low phase change temperatures; for example, methane has a liquefaction temperature of -161.5℃ at atmospheric pressure, and CO2 has a frosting temperature of -78.5℃. Furthermore, fluid phase changes occur during flow, and their phase change and heat transfer processes are significantly influenced by fluid flow. Importantly, these fluids differ significantly from water in their physical properties. For instance, light alkanes and CO2 have significantly lower surface tensions than water, leading to drastically different phase change behaviors. Therefore, the gas-liquid-solid phase change process of water cannot be used to characterize the phase change process of low surface tension fluids, nor can experimental data on water phase change be used to guide the design of heat exchangers suitable for low surface tension fluids. Additionally, anti-icing and de-icing technologies for water may not be applicable to CO2.

[0005] Furthermore, existing experimental devices for observing gas condensation and frosting suffer from the difficulty of measuring the heat transfer coefficient between fluids under controlled phase change conditions, i.e., when the cold source temperature is controllable. For example, the cooling system of the "Multifunctional Steam Condensation Heat Exchange and Frosting Process Visualization Experimental Device" disclosed in patent application number 201810229255.3 lacks a temperature control device, making it impossible to investigate the influence of the cold source temperature on the steam phase change process. Although the "Controlled Fluid Liquefaction and Solidification Process Visualization Experimental Observation Device Based on a Cryogenic Refrigerator" disclosed in patent application number 201610964667.2 can achieve controlled steam phase change, this device can only achieve visual observation and cannot measure the heat transfer performance under different operating conditions through experimental data. Summary of the Invention

[0006] The purpose of this invention is to provide a controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment. This device is used to realize the condensation and frosting experiments of various steams in the flow process under ultra-low temperature conditions. Through this device, the phase change process can be visualized and observed, and the influence of different factors on the phase change process and heat transfer performance can be explored.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment includes a cooling system, a visualization testing system, a gas supply system, and a vacuum system;

[0009] The cooling system includes a nitrogen storage tank, a liquid nitrogen cooling device, and a pre-cooling heat exchanger;

[0010] The visualization testing system includes a dual-tube test pipeline and a camera. The dual-tube test pipeline includes an outer tube and an inner tube, and a visualization window is provided on the outer tube of the dual-tube test pipeline.

[0011] The outlet of the nitrogen storage tank is connected to the gas cooling inlet of the liquid nitrogen cooling device, the gas cooling outlet of the liquid nitrogen cooling device is connected to the inner tube inlet of the double-tube test pipeline, the inner tube outlet of the double-tube test pipeline is connected to the refrigerant inlet of the precooling heat exchanger, and the refrigerant outlet of the precooling heat exchanger is connected to the inlet of the nitrogen storage tank.

[0012] The gas supply system includes a high-pressure gas cylinder group, a mixed gas buffer tank, and a mixed gas recovery tank;

[0013] The outlet of the high-pressure gas cylinder group is connected to the first inlet of the mixed gas buffer tank. The outlet of the mixed gas buffer tank or the outlet of the mixed gas recovery tank is connected to the experimental medium inlet of the precooling heat exchanger. The experimental medium outlet of the precooling heat exchanger is connected to the outer pipe inlet of the double-tube test pipeline. The outer pipe outlet of the double-tube test pipeline is connected to the inlet of the mixed gas recovery tank or the second inlet of the mixed gas buffer tank.

[0014] A vacuum system includes a vacuum chamber and a vacuum pump;

[0015] The dual-tube test line, camera, and pre-cooling heat exchanger are located in the vacuum chamber;

[0016] The side of the vacuum chamber is equipped with a vacuum port and a first sealing door. The vacuum pump is connected to the vacuum port, and a vacuum valve is installed on the connecting pipeline between the vacuum pump and the vacuum port.

[0017] Preferably, a first nitrogen heater is installed on the connecting pipeline between the gas cooling outlet of the liquid nitrogen cooling device and the inner tube inlet of the double-tube test pipeline;

[0018] A second nitrogen heater is installed on the connecting pipeline between the inner tube outlet of the double-tube test pipeline and the refrigerant inlet of the precooling heat exchanger. The second nitrogen heater is located in the vacuum chamber.

[0019] Preferably, a first compressor, a first pressure reducing valve, and a first MFC mass flow meter are installed on the connecting pipeline between the outlet of the nitrogen storage tank and the gas cooling inlet of the liquid nitrogen cooling device.

[0020] A second compressor, a second pressure reducing valve, and a second MFC mass flow meter are installed on the connecting pipeline between the outlet of the mixed gas buffer tank / the outlet of the mixed gas recovery tank and the experimental medium inlet of the precooling heat exchanger.

[0021] Preferably, the controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment also includes a data acquisition and control system, which includes a temperature sensor, a pressure sensor, a data acquisition card, and a data acquisition terminal.

[0022] Temperature and pressure sensors are installed at the inner tube inlet, inner tube outlet, outer tube inlet, and outer tube outlet of the double-tube test pipeline;

[0023] Temperature sensor, pressure sensor, first MFC mass flow meter, second MFC mass flow meter and camera are respectively connected to the input terminal of data acquisition card, and the output terminal of data acquisition card is connected to the data acquisition terminal.

[0024] Preferably, the data acquisition terminal is a computer.

[0025] Preferably, valves are provided at the second inlet and outlet of the mixed gas buffer tank;

[0026] Valves are installed at the inlet and outlet of the mixed gas recovery tank;

[0027] When the valve at the outlet of the mixed gas buffer tank and the valve at the inlet of the mixed gas recovery tank are open, and the valve at the second inlet of the mixed gas buffer tank and the valve at the outlet of the mixed gas recovery tank are closed, the mixed gas buffer tank is used to supply experimental gas to the experimental medium inlet of the precooling heat exchanger, and the mixed gas recovery tank is used to recover experimental gas from the outer pipe outlet of the double-tube test pipeline.

[0028] When the valve at the outlet of the mixed gas buffer tank and the valve at the inlet of the mixed gas recovery tank are closed, and the valve at the second inlet of the mixed gas buffer tank and the valve at the outlet of the mixed gas recovery tank are open, the mixed gas buffer tank is used to recover experimental gas from the outer pipe outlet of the double-tube test pipeline, and the mixed gas recovery tank is used to supply experimental gas to the experimental medium inlet of the precooling heat exchanger.

[0029] Preferably, the liquid nitrogen cooling device includes a liquid nitrogen chamber, a cooling coil, a level gauge, and a pressure gauge;

[0030] The liquid nitrogen chamber is equipped with a liquid nitrogen filling port and a pressure relief port, and a pressure relief valve is installed at the pressure relief port;

[0031] The liquid nitrogen chamber is also equipped with a gas cooling inlet and a gas cooling outlet;

[0032] The cooling coil is located inside the liquid nitrogen chamber. One end of the cooling coil is connected to the gas cooling inlet, and the other end of the cooling coil is connected to the gas cooling outlet.

[0033] The level gauge and pressure gauge are located outside the liquid nitrogen chamber, with their detection ends extending into the interior of the liquid nitrogen chamber.

[0034] Preferably, the inner tube of the double-tube test pipeline is a square tube, and the outer wall of the inner tube is coated with black paint.

[0035] The outer tube of the double-tube test pipeline is a square tube, and a second sealing door is installed on the outer tube;

[0036] There are multiple visualization windows, which are respectively set on the side of the outer tube and the second sealing door.

[0037] Preferably, the vacuum system also includes a light strip and a camera movement track, which are disposed within the vacuum chamber;

[0038] The camera movement tracks are arranged along the circumference and axial direction of the outer tube of the double-tube test pipeline, respectively.

[0039] The side of the vacuum chamber is equipped with a refrigerant pipeline inlet, a refrigerant pipeline outlet, an experimental gas pipeline inlet, an experimental gas pipeline outlet, and a sensor bundle outlet.

[0040] Preferably, a bypass line is provided between the outlet of the nitrogen storage tank and the inlet of the inner tube of the double-tube test pipeline, and between the refrigerant outlet of the precooling heat exchanger and the inlet of the experimental medium, and a bypass valve is provided on the bypass line.

[0041] A vent valve is also installed on the connecting pipeline between the outer pipe outlet of the double-tube test pipeline and the second inlet of the mixed gas buffer tank;

[0042] Valves are installed at the inlet and outlet of the nitrogen storage tank, and at the gas cooling inlet and outlet of the liquid nitrogen cooling device.

[0043] The present invention has the following advantages:

[0044] As described above, this invention proposes a controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment. This device uses nitrogen as the refrigerant and liquid nitrogen from a liquid nitrogen cooling system as the cold source to cool the nitrogen, ensuring the refrigerant's minimum temperature approaches that of liquid nitrogen. This facilitates phase change experiments on low-boiling-point, low-surface-tension fluids such as light alkanes and CO2. The experimental device also uses a nitrogen heater for temperature control to achieve controlled phase change of the low-temperature gas. It can control the temperature of the refrigerant before it enters the double-tube test pipeline and the pre-cooling heat exchanger, and achieve controlled condensation and frosting of the experimental gas by adjusting the refrigerant temperature.

[0045] The experimental apparatus of the present invention can also observe the condensation and frosting process of low-temperature gas in a flowing state and obtain convective heat transfer data during the experiment. Compared with the experimental apparatus for conducting condensation and frosting phase change experiments of fluids in a closed space, the experimental apparatus of the present invention can keep the experimental medium in a flowing state during the experiment and record the heat transfer data between fluids in real time, so as to analyze the influence of liquid film and frost layer on heat exchange efficiency.

[0046] Furthermore, the experimental apparatus of this invention possesses strong functionality, enabling it to conduct phase change and heat transfer performance tests under various operating conditions, thus having wide applicability. This apparatus can perform experiments on the effects of experimental gas composition and content, experimental gas flow rate, initial experimental gas temperature, initial experimental gas pressure, cold source temperature, cold source pressure, cold source flow rate, and wall material on the low-temperature gas phase change process and heat transfer efficiency. It can also be used to test the anti-condensation and anti-frost performance of different materials and surface structures.

[0047] Furthermore, the experimental apparatus of this invention enables the recycling of experimental gases and refrigerants, resulting in lower costs. In this experimental apparatus, the cooling system forms a complete loop through pipelines and the inner tube of the double-tube test pipeline, allowing for the recycling of the refrigerant. Simultaneously, the apparatus can also achieve the recycling of the experimental medium through valve switching, further reducing experimental costs. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of the controlled condensation and frosting visualization experimental device during gas flow in an ultra-low temperature environment, as described in an embodiment of the present invention.

[0049] Figure 2 This is a cross-sectional view of the liquid nitrogen cooling device in an embodiment of the present invention.

[0050] Figure 3 This is a top view of the liquid nitrogen cooling device in an embodiment of the present invention.

[0051] Figure 4 This is a schematic diagram of the structure of the double-tube test pipeline in an embodiment of the present invention.

[0052] Figure 5 This is a front view of the double-tube test pipeline in an embodiment of the present invention.

[0053] Figure 6 This is a schematic diagram of the precooling heat exchanger in an embodiment of the present invention.

[0054] Figure 7 This is a cross-sectional view of the precooling heat exchanger in an embodiment of the present invention.

[0055] Figure 8 This is a cross-sectional view of the vacuum chamber in an embodiment of the present invention.

[0056] Figure 9 This is a left view of the vacuum chamber in an embodiment of the present invention.

[0057] Figure 10 This is a right view of the vacuum chamber in an embodiment of the present invention.

[0058] Among them, 1-nitrogen storage tank.

[0059] 2-Liquid nitrogen cooling device, 21-Liquid nitrogen chamber, 211-Gas cooling inlet, 212-Gas cooling outlet, 213-Liquid nitrogen filling port, 214-Pressure relief port, 22-Cooling coil, 23-Level gauge, 24-Pressure gauge, 25-Pressure relief valve, 26-Handrail.

[0060] 3-Precooling heat exchanger, 31-Refrigerant flow chamber, 311-Refrigerant inlet, 312-Refrigerant outlet, 32-Experimental medium flow chamber, 321-Experimental medium inlet, 322-Experimental medium outlet.

[0061] 4-Double-tube test pipeline, 41-Outer tube, 411-Visualization window, 412-Outer tube inlet, 413-Outer tube outlet, 414-Second sealing door, 42-Inner tube, 421-Inner tube inlet, 422-Inner tube outlet.

[0062] 5. Camera.

[0063] 61-High-pressure gas cylinder group, 62-Mixed gas buffer tank, 63-Mixed gas recovery tank.

[0064] 7-Vacuum chamber, 71-Vacuum extraction port, 72-First sealed door, 73-Light strip, 74-Camera moving track, 75-Refrigerant line inlet, 76-Refrigerant line outlet, 77-Experimental gas line inlet, 78-Experimental gas line outlet, 79-Sensor harness outlet.

[0065] 8 - Vacuum pump, 81 - Vacuum valve.

[0066] 91 - First nitrogen heater, 92 - Second nitrogen heater.

[0067] 101 - First compressor, 102 - First pressure reducing valve, 103 - First MFC mass flow meter, 104 - Second compressor, 105 - Second pressure reducing valve, 106 - Second MFC mass flow meter.

[0068] 111-Temperature sensor, 112-Pressure sensor, 113-Data acquisition terminal.

[0069] 121 - First bypass line, 122 - First bypass valve, 123 - Relief valve, 124 - Second bypass line, 125 - Second bypass valve. Detailed Implementation

[0070] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. Certain embodiments of the invention will be described more fully below with reference to the accompanying drawings, and some, but not all, of these embodiments will be shown. In fact, various embodiments of the invention can be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to enable the invention to meet applicable legal requirements.

[0071] In the description of this invention, it should be noted that the terms "inner," "outer," "upper," "lower," "front," and "rear," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0072] Example

[0073] To address the shortcomings of current visualization experimental devices for condensation and frosting, this invention proposes a multifunctional experimental device capable of observing gas-liquid-solid phase change processes and measuring heat transfer performance. This device not only enables the observation of gas-liquid-solid phase change processes during low-temperature gas flow under different operating conditions, but also allows for the investigation of the effects of various factors such as fluid velocity, initial temperature, pressure, gas composition, and wall materials on the gas frosting process, frost crystal morphology, and frost layer properties, as well as the investigation of the influence of different factors on gas phase change heat transfer performance. This experimental device can observe the controlled gas-liquid-solid phase change processes of gases with low freezing points in ultra-low temperature environments. Conducting phase change heat transfer experiments with different low-temperature fluids using this visualization experimental device can provide data support for the optimized design of heat exchangers for different fluids and the design of CO2 capture devices.

[0074] The structure of the controlled condensation and frosting visualization experimental device during gas flow in an ultra-low temperature environment is described below.

[0075] like Figures 1 to 10 As shown in the figure, this embodiment describes a controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment, which includes a cooling system, a visualization testing system, a gas supply system, a vacuum system, and a data acquisition and control system.

[0076] First, the cooling system and visualization testing system in the condensation and frosting visualization experimental device of this invention are introduced.

[0077] The cooling system includes a nitrogen storage tank 1, a liquid nitrogen cooling device 2, and a pre-cooling heat exchanger 3. Nitrogen is used as the refrigerant in the cooling system, and liquid nitrogen in the liquid nitrogen cooling device 2 is used to supply the nitrogen, so that the minimum temperature of the refrigerant can be close to the temperature of liquid nitrogen.

[0078] The visualization testing system includes a dual-tube test pipeline 4 and a camera 5. The dual-tube test pipeline 4 includes an outer tube 41 and an inner tube 42. The camera 5 is preferably a high-speed camera.

[0079] The outlet of nitrogen storage tank 1 is connected to the gas cooling inlet 211 of liquid nitrogen cooling device 2. A first compressor 101, a first pressure reducing valve 102, and a first MFC mass flow meter 103 are installed on the connecting pipeline between the outlet of nitrogen storage tank 1 and the gas cooling inlet 211 of liquid nitrogen cooling device 2. The gas cooling outlet 212 of liquid nitrogen cooling device 2 is connected to the inner tube inlet 421 of double-tube test pipeline 4. A first nitrogen heater 91 is installed on the connecting pipeline between the gas cooling outlet 212 of liquid nitrogen cooling device 2 and the inner tube inlet 421 of double-tube test pipeline 4.

[0080] The inner tube outlet 422 of the double-pipe test line 4 is connected to the refrigerant inlet 311 of the precooling heat exchanger 3. A second nitrogen heater 92 is installed on the connecting pipeline between the inner tube outlet 422 of the double-pipe test line 4 and the refrigerant inlet 311 of the precooling heat exchanger 3. The refrigerant outlet 312 of the precooling heat exchanger 3 is connected to the inlet of the nitrogen storage tank 1.

[0081] The following is a detailed description of the double-tube test pipeline 4 in the condensation and frosting visualization experimental device of the present invention.

[0082] During the experiment, the fluid in the inner tube 42 of the double-tube test pipeline 4 is a refrigerant, and the fluid in the outer tube 41 of the double-tube test pipeline 4 is the experimental medium. The fluids in the inner tube 42 and outer tube 41 flow in opposite directions, i.e., they flow counter-currently. The inner tube inlet 421 is connected to the first nitrogen heater 91 upstream of it, and the inner tube outlet 422 is connected to the second nitrogen heater 92 downstream of it. The outer tube inlet 412 is connected to the experimental medium outlet 322 of the pre-cooling heat exchanger 3, and the outer tube outlet 413 is connected to the inlet of the mixed gas recovery tank 63 via a pipeline.

[0083] The inner tube 42 of the double-tube test pipeline 4 is preferably a square tube, and the outer tube 41 of the double-tube test pipeline 4 is preferably a square tube. The cross-sections of the inner tube 42 and the outer tube 41 in the double-tube test pipeline 4 are both rectangular, which facilitates the horizontal and vertical placement of experimental samples to carry out condensation and frosting phase change experiments of gases on the surface of different materials.

[0084] To facilitate the handling of experimental samples, a second sealing door 414 is provided on the outer tube 41 of the double-tube test pipeline 4.

[0085] The outer tube 41 of the double-tube test pipeline 4 is also provided with a visualization window 411. In this embodiment, the visualization window 411 is a visualization optical window, and preferably multiple visualization windows 411 are provided. Multiple visualization windows 411 are respectively provided on the sides around the outer tube 41 and on the second sealing door 414.

[0086] The top of the outer tube 41 of the double-tube test pipeline 4 is preferably connected to a second sealing door 414 with a visualization window 411 via a hinge. Experimental samples are taken out and put in through the second sealing door 414 to realize phase change experiments of mixed gas on different material surfaces. This allows for the investigation of the influence of different materials and surface microstructures on the morphology and properties of droplets and frost crystals during the phase change process, as well as their influence on gas heat transfer efficiency. It can also be used to experimentally test the anti-dew and anti-frost performance of different material and structural surfaces.

[0087] In addition, the outer wall of the inner tube 42 is coated with black paint to facilitate observation of the morphology and structure of condensed droplets, condensed film and frost crystals.

[0088] The liquid nitrogen cooling device 2 in the condensation and frosting visualization experimental device of the present invention will be described in detail below.

[0089] The liquid nitrogen cooling device 2 includes a liquid nitrogen chamber 21, a cooling coil 22, a level gauge 23, and a pressure gauge 24.

[0090] The liquid nitrogen chamber 21 is filled with a sufficient amount of liquid nitrogen. The liquid nitrogen chamber 21 is provided with a liquid nitrogen filling port 213 and a pressure relief port 214. A pressure relief valve 25 is provided at the pressure relief port 214. The level gauge 23 and the pressure gauge 24 are located on the outside of the liquid nitrogen chamber 21, and the detection ends of the level gauge 23 and the pressure gauge 24 extend into the interior of the liquid nitrogen chamber 21.

[0091] Cooling coil 22 is located inside liquid nitrogen chamber 21 and is immersed in liquid nitrogen. Liquid nitrogen chamber 21 is also provided with gas cooling inlet 211 and gas cooling outlet 212. One end of cooling coil 22 is connected to gas cooling inlet 211, and the other end of cooling coil 22 is connected to gas cooling outlet 212.

[0092] In this embodiment, the cooling system forms a loop with the inner tube 42 of the double-tube test line 4 through the nitrogen flow pipeline, so that the refrigerant can be circulated. The following is a detailed description of the refrigerant flow loop.

[0093] The outlet of nitrogen storage tank 1 is connected to the inlet of first compressor 101 via a pipeline. The outlet of first compressor 101 is connected to one end of first pressure reducing valve 102 via a pipeline. The other end of first pressure reducing valve 102 is connected to the inlet of first MFC mass flow meter 103. The outlet of first MFC mass flow meter 103 is connected to the gas cooling inlet 211 of liquid nitrogen cooling device 2. Gas cooling inlet 211 on liquid nitrogen cooling device 2 is connected to one end of cooling coil 22. Liquid nitrogen cooling device 2 is filled with a sufficient amount of liquid nitrogen. Cooling coil 22 is immersed in liquid nitrogen. The low temperature of liquid nitrogen is used to reduce nitrogen to an extremely low temperature. The other end of cooling coil 22 is connected to gas cooling outlet 212 on liquid nitrogen cooling device 2. In addition, liquid nitrogen cooling device 2 is equipped with a level gauge 23, a pressure gauge 24, a liquid nitrogen filling port 213, a pressure relief port 214, and a pressure relief valve 25 on top.

[0094] The gas cooling outlet 212 on the liquid nitrogen cooling device 2 is connected to the inlet of the first nitrogen heater 91 via a pipeline. The outlet of the first nitrogen heater 91 is connected to one end of the inner tube 42 of the double-tube test pipeline 4 via a pipeline. The first nitrogen heater 91 is set up to ensure that the temperature of the refrigerant entering the visualization test system is controllable and to ensure that the experimental medium undergoes controlled condensation and frosting in the double-tube test pipeline 4.

[0095] The other end of the inner tube 42 of the double-tube test pipeline 4 is connected to the inlet of the second nitrogen heater 92 via a pipeline. The outlet of the second nitrogen heater 92 is connected to the refrigerant inlet 311 of the precooling heat exchanger 3. The purpose of setting up the precooling heat exchanger 3 is to make full use of the cooling capacity of the low-temperature nitrogen and exchange heat with the experimental mixed gas before entering the visualization test system to precool the experimental mixed gas, i.e., the experimental medium. However, the precooling process needs to avoid the experimental mixed gas from undergoing a phase change in advance. Therefore, the second nitrogen heater 92 is used to further increase the refrigerant temperature to above the temperature at which the experimental mixed gas undergoes a phase change.

[0096] The precooling heat exchanger 3 is designed for counter-current heat exchange, and its refrigerant outlet 312 is connected to the inlet of the nitrogen storage tank 1 via a pipeline. The entire nitrogen flow pipeline described above forms a complete loop, enabling the refrigerant to be circulated and reused, saving costs and protecting the environment.

[0097] The gas supply system in the condensation and frosting visualization experimental device of the present invention will be described in detail below.

[0098] The gas supply system includes a high-pressure gas cylinder group 61, a mixed gas buffer tank 62, and a mixed gas recovery tank 63.

[0099] The mixed gas buffer tank 62 is provided with two inlets and one outlet, and the two inlets of the mixed gas buffer tank 62 are defined as the first inlet and the second inlet, respectively. The mixed gas recovery tank 63 is provided with one inlet and one outlet.

[0100] The outlet of the high-pressure gas cylinder group 61 is connected to the first inlet of the mixed gas buffer tank 62. The outlet of the mixed gas buffer tank 62 or the outlet of the mixed gas recovery tank 63 is selectively connected to the experimental medium inlet 321 of the precooling heat exchanger 3. The experimental medium outlet 322 of the precooling heat exchanger 3 is connected to the outer pipe inlet 412 of the double-tube test pipeline 4. The outer pipe outlet 413 of the double-tube test pipeline 4 is connected to the inlet of the mixed gas recovery tank 63 or the second inlet of the mixed gas buffer tank 62.

[0101] The condensation and frosting visualization experimental device of this invention realizes the recycling of experimental media through valve switching.

[0102] Valves are installed at the first inlet, second inlet, and outlet of the mixed gas buffer tank 62. Valves are also installed at the inlet and outlet of the mixed gas recovery tank 63. The valve at the first inlet of the mixed gas buffer tank 62 is used to control whether the high-pressure gas cylinder group 61 is connected to the mixed gas buffer tank 62.

[0103] When the valve at the outlet of the mixed gas buffer tank 62 and the valve at the inlet of the mixed gas recovery tank 63 are open, and the valve at the second inlet of the mixed gas buffer tank 62 and the valve at the outlet of the mixed gas recovery tank 63 are closed, the mixed gas buffer tank 62 supplies experimental gas to the experimental medium inlet 321 of the precooling heat exchanger 3, and the mixed gas recovery tank 63 recovers experimental gas from the outer pipe outlet 413 of the double-tube test pipeline 4. When the experimental medium needs to be recycled, the valves are switched. When the valve at the outlet of the mixed gas buffer tank 62 and the valve at the inlet of the mixed gas recovery tank 63 are closed, and the valve at the second inlet of the mixed gas buffer tank 62 and the valve at the outlet of the mixed gas recovery tank 63 are open, the mixed gas buffer tank 62 recovers experimental gas from the outer pipe outlet 413 of the double-tube test pipeline 4, and the mixed gas recovery tank 63 supplies experimental gas to the experimental medium inlet 321 of the precooling heat exchanger 3.

[0104] In this embodiment, a second compressor 104, a second pressure reducing valve 105, and a second MFC mass flow meter 106 are installed on the connecting pipeline between the outlet of the mixed gas buffer tank 62 / the outlet of the mixed gas recovery tank 63 and the experimental medium inlet 321 of the precooling heat exchanger 3. The outlet of the mixed gas buffer tank 62 or the outlet of the mixed gas recovery tank 63 is selectively connected to the inlet of the second compressor 104.

[0105] When the mixed gas buffer tank 62 is used to supply experimental gas to the experimental medium inlet 321 of the precooling heat exchanger 3, a second compressor 104, a second pressure reducing valve 105, and a second MFC mass flow meter 106 are installed on the connecting pipeline between the outlet of the mixed gas buffer tank 62 and the experimental medium inlet 321 of the precooling heat exchanger 3. The outlet of the mixed gas buffer tank 62 is connected to the inlet of the second compressor 104, the outlet of the second compressor 104 is connected to one end of the second pressure reducing valve 105, the other end of the second pressure reducing valve 105 is connected to the inlet of the second MFC mass flow meter 106, and the outlet of the second MFC mass flow meter 106 is connected to the experimental medium inlet 321 of the precooling heat exchanger 3.

[0106] When the mixed gas recovery tank 63 is used to supply experimental gas to the experimental medium inlet 321 of the precooling heat exchanger 3, a second compressor 104, a second pressure reducing valve 105, and a second MFC mass flow meter 106 are installed on the connecting pipeline between the outlet of the mixed gas recovery tank 63 and the experimental medium inlet 321 of the precooling heat exchanger 3. The outlet of the mixed gas recovery tank 63 is connected to the inlet of the second compressor 104, the outlet of the second compressor 104 is connected to one end of the second pressure reducing valve 105, the other end of the second pressure reducing valve 105 is connected to the inlet of the second MFC mass flow meter 106, and the outlet of the second MFC mass flow meter 106 is connected to the experimental medium inlet 321 of the precooling heat exchanger 3.

[0107] In this embodiment, the gas supply system supplies the experimental medium through the experimental gas flow pipeline and the outer pipe 41 of the double-tube test pipeline 4, and the experimental medium can be recycled by switching valves. The specific details are as follows.

[0108] The high-pressure gas cylinder group 61 is composed of all the gas cylinders corresponding to the gas to be tested connected in parallel. The outlet of the high-pressure gas cylinder group 61 is connected to the first inlet of the mixed gas buffer tank 62. During the experiment, the mixed gas buffer tank 62 is used to prepare mixed gases with different compositions and contents. The outlet of the mixed gas buffer tank 62 is connected to the inlet of the second compressor 104. The outlet of the second compressor 104 is connected to one end of the second pressure reducing valve 105. The other end of the second pressure reducing valve 105 is connected to the inlet of the second MFC mass flow meter 106. The outlet of the second MFC mass flow meter 106 is connected to the experimental medium inlet 321 of the precooling heat exchanger 3 through a pipeline. The experimental medium outlet 322 of the precooling heat exchanger 3 is connected to the outer pipe inlet 412 of the double-tube test pipeline 4 of the visualization test system. The outer pipe outlet 413 of the double-tube test pipeline 4 is connected to the inlet of the mixed gas recovery tank 63 and the second inlet of the mixed gas buffer tank 62 through pipelines respectively. The outlet of the mixed gas recovery tank 63 is connected to the inlet of the second compressor 104 through a pipeline. The above design enables the recycling of experimental gases when conducting experiments on the effects of other factors on phase change processes and heat transfer performance, while ensuring that the composition and content of the experimental gas are constant, thus greatly saving costs.

[0109] The vacuum system in the condensation and frosting visualization experimental device of the present invention will be described in detail below.

[0110] The vacuum system includes a vacuum chamber 7, a vacuum pump 8, a light strip 73, and a camera movement track 74.

[0111] The double-tube test pipeline 4, camera 5, pre-cooling heat exchanger 3, and second nitrogen heater 92 are located in the vacuum chamber 7.

[0112] The side of the vacuum chamber 7 is provided with a vacuum port 71 and a first sealing door 72. The vacuum pump 8 is connected to the vacuum port 71, and a vacuum valve 81 is provided on the connecting pipeline between the vacuum pump 8 and the vacuum port 71.

[0113] The light strip 73 and the camera movement track 74 are disposed inside the vacuum chamber 7. The camera movement track 74 is preferably arranged circumferentially and axially along the outer tube 41 of the double-tube test pipeline 4, respectively.

[0114] The side of the vacuum chamber 7 is provided with a refrigerant pipeline inlet 75, a refrigerant pipeline outlet 76, an experimental gas pipeline inlet 77, an experimental gas pipeline outlet 78, and a sensor harness outlet 79.

[0115] In this embodiment, the vacuum chamber 7 is cylindrical, and the dual-tube test pipeline 4 of the visualization test system and the pre-cooling heat exchanger 3 of the cooling system are both located inside the vacuum chamber 7. Two rings of light strips 73 are provided on the inner surface of the vacuum chamber 7, and a camera moving track 74 is provided around the visualization window 411 of the outer tube 41 of the dual-tube test pipeline 4. The sides of the vacuum chamber 7 are respectively provided with a refrigerant pipeline inlet 75, a refrigerant pipeline outlet 76, an experimental gas pipeline inlet 77, an experimental gas pipeline outlet 78, a sensor harness outlet 79, a vacuum port 71, and a first sealing door 72, etc. The vacuum port 71 is connected to one end of a vacuum valve 81, and the other end of the vacuum valve 81 is connected to a vacuum pump 8. The vacuum valve 81 controls whether the inlet of the vacuum pump 8 is connected to the vacuum chamber 7, and the vacuum pump 8 is used to extract the air from the vacuum chamber 7. The vacuum system ensures a high vacuum within the vacuum chamber 7, preventing condensation and frost formation on the outer surface of the outer tube 41 of the double-tube test line 4, which would affect visual observation. It also prevents heat exchange between the external ambient air and the fluid within the double-tube test line 4 and the pre-cooling heat exchanger 3, thus avoiding interference with the testing and recording of heat exchange data during the experiment. Furthermore, the first sealing door 72 is preferably hinged, allowing the vacuum chamber 7 to be opened for sample replacement and for manual adjustment of the position of the light strip 73 and the high-speed camera on the camera movement track 74.

[0116] The data acquisition and control system in the condensation and frosting visualization experimental device of the present invention will be described in detail below.

[0117] The data acquisition and control system includes a temperature sensor 111, a pressure sensor 112, a data acquisition card (not shown), and a data acquisition terminal 113.

[0118] Temperature sensor 111 and pressure sensor 112 are installed at the inner tube inlet 421, inner tube outlet 422, outer tube inlet 412 and outer tube outlet 413 of the double-tube test pipeline 4 to obtain phase change heat transfer experimental data.

[0119] Temperature sensor 111, pressure sensor 112, first MFC mass flow meter 103, second MFC mass flow meter 106 and camera 5 are respectively connected to the input terminal of data acquisition card, and the output terminal of data acquisition card is connected to the data acquisition terminal 113.

[0120] The data acquisition terminal 113 is preferably a computer. In this embodiment, the statistical data of the first MFC mass flow meter 103 and the second MFC mass flow meter 106, the data of the temperature sensor 111 and the pressure sensor 112, and the images captured by the high-speed camera are all acquired and transmitted to the computer through a data acquisition card, thereby realizing real-time recording of experimental data.

[0121] In addition, the condensation and frosting visualization experimental device of the present invention also includes a bypass pipeline, a bypass valve and a relief valve 123.

[0122] A bypass line is provided between the outlet of nitrogen storage tank 1 and the inner pipe inlet 421 of the double-pipe test pipeline 4, and between the refrigerant outlet 312 of precooling heat exchanger 3 and the experimental medium inlet 321. A bypass valve is provided on the bypass line. In this embodiment, the bypass line between the outlet of nitrogen storage tank 1 and the inner pipe inlet 421 of the double-pipe test pipeline 4 is defined as the first bypass line 121, and the bypass valve provided on the first bypass line 121 is defined as the first bypass valve 122; the bypass line between the refrigerant outlet 312 of precooling heat exchanger 3 and the experimental medium inlet 321 is defined as the second bypass line 124, and the bypass valve provided on the second bypass line 124 is defined as the second bypass valve 125.

[0123] A vent valve 123 is also installed on the connecting pipeline between the outer pipe outlet 413 of the double-pipe test pipeline 4 and the second inlet of the mixed gas buffer tank 62. Valves are installed at the inlet and outlet of the nitrogen storage tank 1, and at the gas cooling inlet 211 and gas cooling outlet 212 of the liquid nitrogen cooling device 2.

[0124] The working principle of the controlled condensation and frosting visualization experimental device during gas flow in an ultra-low temperature environment is described in detail below.

[0125] This invention employs a high-pressure gas cylinder group 61 to prepare mixed gases with different compositions and contents, which are then stored in a mixed gas buffer tank 62 to provide the required experimental gases for the entire experiment. The pressure and flow rate of the experimental gases are controlled by a second compressor 104 and a second MFC mass flow meter 106, respectively. The temperature of the experimental gases is regulated by a pre-cooling heat exchanger 3. The experimental gases and refrigerant flow in the outer tube 41 and inner tube 42 of the double-tube test pipeline 4, respectively, exchanging heat to induce a phase change in the experimental medium. This invention uses a liquid nitrogen cooling device 2 to cool nitrogen gas as the experimental refrigerant. The pressure and flow rate of the nitrogen gas are controlled by a first compressor 101 and a first MFC mass flow meter 103, respectively, and the temperature of the nitrogen gas is controlled by a first nitrogen heater 91, thereby achieving controlled condensation or frosting of the experimental medium in the double-tube test pipeline 4. The specific process of gas condensation and frosting is observed using a high-speed camera during the experiment. This invention employs a second nitrogen heater 92 to regulate the temperature of the refrigerant flowing from the double-tube test line 4. Heating the refrigerant with the second nitrogen heater 92 prevents the experimental gas from undergoing a phase change before entering the double-tube test line 4 due to excessively low refrigerant temperature. The pre-cooling heat exchanger 3 initially cools the experimental gas to reduce the temperature difference between the experimental gas and the refrigerant, ensuring condensation and frosting occur during the flow of the mixed gas in the double-tube test line 4. This invention uses a vacuum chamber 7 to meet the environmental conditions required for experimentation and visualization. A vacuum pump 8 is used to evacuate the vacuum chamber 7. This avoids heat exchange between the experimental medium and the external environment, thus obtaining accurate heat exchange experimental data. It also prevents frost formation on the outer wall of the visualization window 411, which would affect the observation of the condensation and frosting process. The pre-cooling heat exchanger 3, the second nitrogen heater 92, the double-tube test line 4, and the high-speed camera are all located inside the vacuum chamber 7, with the high-speed camera mounted on a camera movement track 74.

[0126] This invention uses a liquid nitrogen cooling device 2 to provide the low temperature required for the experiment, such as... Figure 2 and Figure 3As shown, in this embodiment, the liquid nitrogen cooling device 2 includes a liquid nitrogen chamber 21, a cooling coil 22, a level gauge 23, a pressure gauge 24, and a handrail 26. A gas cooling inlet 211 is connected to one end of the cooling coil 22, and the other end of the cooling coil 22 is connected to a gas cooling outlet 212. The liquid nitrogen chamber 21 is filled with cryogenic liquid nitrogen. Nitrogen gas enters the cooling coil 22 from the gas cooling inlet 211 and exchanges heat with the liquid nitrogen in the liquid nitrogen chamber 21, lowering the nitrogen temperature to an extremely low value. A pressure relief port 214 and a pressure gauge 24 are provided at the top of the liquid nitrogen cooling device 2. A pressure relief valve 25 is installed at the pressure relief port 214. As heat exchange proceeds, the liquid nitrogen gradually vaporizes, causing the pressure in the liquid nitrogen chamber 21 to gradually rise. When the pressure gauge 24 displays a pressure value exceeding a preset pressure value, the pressure relief valve 25 will automatically open to release pressure. In addition, the top of the liquid nitrogen cooling device 2 is equipped with a liquid nitrogen filling port 213 and a liquid level gauge 23. During the experiment, the liquid nitrogen level in the liquid nitrogen chamber 21 is measured by the liquid level gauge 23. The initial liquid nitrogen level can be adjusted according to the temperature requirements of the experiment. As the experiment continues, when the liquid nitrogen gradually vaporizes and is discharged, the liquid nitrogen level in the liquid nitrogen chamber 21 gradually decreases. In order to ensure that the nitrogen can still be cooled to the preset low temperature in subsequent experiments, liquid nitrogen will be added to the liquid nitrogen chamber 21 through the liquid nitrogen filling port 213.

[0127] This invention uses a double-tube test line 4 to conduct flow heat transfer experiments on mixed gas and refrigerant, such as... Figure 4 and Figure 5 As shown, the dual-tube test line 4 includes an outer tube 41 and an inner tube 42. The experimental gas and refrigerant flow continuously through the outer tube 41 and inner tube 42 of the dual-tube test line 4, respectively, and exchange heat driven by the temperature difference. During the flow, the experimental gas undergoes a phase change on the low-temperature wall surface, i.e., the outer wall of the inner tube 42 of the dual-tube test line 4. Visualization windows 411 are provided on the top and both sides of the outer tube 41 of the dual-tube test line 4 for real-time observation and recording of the condensation and frosting process of the mixed gas. Furthermore, to ensure that the morphology of the condensate droplets and frost crystals captured by the high-speed camera is clearly distinguishable, the outer wall of the inner tube 42 of the dual-tube test line 4 in this invention is coated with black paint. The top of the outer tube 41 of the double-tube test pipeline 4 is provided with a second sealing door 414 with a viewing window 411 connected by a hinge. Experimental samples can be placed and removed from the top and side outer wall of the inner tube 42 of the double-tube test pipeline 4 through the second sealing door 414, thereby realizing phase change experimental testing of mixed gas on different material surfaces in the horizontal and vertical directions. To facilitate the placement of experimental samples, both the inner tube 42 and the outer tube 41 of the double-tube test pipeline 4 are designed as square tubes.

[0128] This invention employs a pre-cooling heat exchanger 3 to pre-cool the experimental mixed gas, reducing the temperature difference between the experimental gas and the refrigerant to ensure that the mixed gas can condense or frost during its flow in the double-tube test pipeline 4. Figure 6 and Figure 7As shown, the precooling heat exchanger 3 includes a refrigerant flow chamber 31 and an experimental medium flow chamber 32. The refrigerant flow chamber 31 has a refrigerant inlet 311 and a refrigerant outlet 312, while the experimental medium flow chamber 32 has an experimental medium inlet 321 and an experimental medium outlet 322. In this embodiment, the experimental medium flow chamber 32 is a circular tube, and the refrigerant flow chamber 31 completely surrounds the experimental medium flow chamber 32. During the experiment, the experimental gas flows in the experimental medium flow chamber 32 of the precooling heat exchanger 3, while the low-temperature nitrogen gas heated to a preset temperature by the second nitrogen heater 92 flows in the refrigerant flow chamber 31. The two gases exchange heat under the effect of temperature difference to initially reduce the temperature of the experimental gas.

[0129] This invention uses a vacuum chamber 7 to meet the environmental conditions required for experiments and visual observation, such as... Figures 8 to 10 As shown, the vacuum chamber 7 is equipped with a vacuum extraction port 71, a first sealing door 72, a light strip 73, a camera movement track 74, a refrigerant pipeline inlet 75, a refrigerant pipeline outlet 76, an experimental gas pipeline inlet 77, an experimental gas pipeline outlet 78, and a sensor harness outlet 79. The pre-cooling heat exchanger 3, the second nitrogen heater 92, the double-tube test pipeline 4, and the high-speed camera are all located inside the vacuum chamber 7, with the high-speed camera mounted on the camera movement track 74. The vacuum chamber 7 is cylindrical, with one circular side having a refrigerant pipeline inlet 75, a refrigerant pipeline outlet 76, and an experimental gas pipeline inlet 77, providing channels for the entry and exit of the cryogenic nitrogen pipeline and the experimental gas pipeline. In addition, the circular side of the vacuum chamber 7 is equipped with a vacuum port 71 and a first sealed door 72 connected by a hinge. Before the experiment, a vacuum pump 8 is used to evacuate the vacuum chamber 7 through a pipeline connected to the vacuum port 71. During the experiment, the first sealed door 72 is opened, followed by the second sealed door 414 with a visualization window 411 on the double-tube test pipeline 4, thereby enabling the loading and unloading of experimental samples. Another circular side of the vacuum chamber 7 has an experimental gas pipeline outlet 78 and a sensor harness outlet 79. Data transmission lines of all sensors contained in the vacuum chamber 7 are led out through the sensor harness outlet 79 and connected to the data acquisition terminal 113. LED strips 73 are installed at both ends of the circular side of the vacuum chamber 7 to provide light for the high-speed camera. A camera movement track 74 is installed on the top and circumference of the circular side of the vacuum chamber 7, directly opposite the visualization window 411 of the double-tube test pipeline 4. The high-speed camera can move along the camera movement track 74 during the experiment, enabling real-time observation of condensation and frosting at different locations in the horizontal, vertical, and gas flow directions.

[0130] The following is a detailed description of the experimental process using the controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment proposed in this invention.

[0131] First, the pipeline purging before the experiment is introduced. The specific procedure is as follows: open the valve at the outlet of nitrogen storage tank 1, start the first compressor 101 to send nitrogen to the pipeline of the cooling system, namely the nitrogen cooling pipeline, then use the first pressure reducing valve 102 to control the nitrogen pressure to the preset pressure of the experimental conditions, and then use the first MFC mass flow meter 103 to adjust the nitrogen flow to the preset flow of the experimental conditions. Close the valves at the upstream pipeline of the gas cooling inlet 211 and the downstream pipeline of the gas cooling outlet 212 of the liquid nitrogen cooling device 2. Open the first bypass valve 122 to connect the outlet of the nitrogen storage tank 1 with the inner tube inlet 421 of the double-tube test pipeline 4 through the first bypass pipeline 121, allowing nitrogen to bypass the liquid nitrogen cooling device 2 and directly enter the inner tube 42 of the double-tube test pipeline 4 in the vacuum chamber 7. The nitrogen flowing out of the inner tube 42 will enter the refrigerant flow chamber 31 in the precooling heat exchanger 3. Then close the valve at the inlet of the nitrogen storage tank 1 and open the second bypass valve 125 to allow the refrigerant in the precooling heat exchanger 3 to flow through the inner tube 421. The outlet 312 and the experimental medium inlet 321 are connected via a second bypass pipeline 124. At this time, the nitrogen flow pipeline is connected to the experimental gas flow pipeline, allowing nitrogen to flow sequentially through the experimental medium circulation chamber 32 in the pre-cooling heat exchanger 3 and the outer pipe 41 of the double-tube test pipeline 4. The valves at the second inlet of the mixed gas buffer tank 62 and the inlet of the mixed gas recovery tank 63 are closed, and the vent valve 123 on the experimental pipeline is opened to complete the venting. In this embodiment, the vent valve 123 is located on the connecting pipeline between the outer pipe outlet 413 of the double-tube test pipeline 4 and the second inlet of the mixed gas buffer tank 62. Pipeline purging can prevent impurities in the pipeline from interfering with the experimental results during the experiment.

[0132] The following describes the specific process of using the device of this invention to conduct experiments on the effects of various factors on condensation, frosting phenomena, and heat exchange performance. These various factors include the composition and content of the experimental gas, the flow rate of the experimental gas, the initial temperature of the experimental gas, the initial pressure of the experimental gas, the temperature of the cold source, the pressure of the cold source, and the flow rate of the cold source. The specific experimental procedure is as follows: After the pipeline is purged, the valve of the high-pressure gas cylinder group 61 is opened. According to the experimental conditions, the gas composition and content are configured in the mixed gas buffer tank 62. The gas in the mixed gas buffer tank 62 is sampled and tested to ensure that it meets the experimental conditions. After the gas composition configuration is completed, the valve of the high-pressure gas cylinder group 61 is closed. The vacuum pump 8 is started, the vacuum valve 81 is opened, and the vacuum chamber 7 is evacuated. When the pressure gauge near the vacuum port 71 shows a pressure of less than 1 Pa, the vacuum valve 81 and the vacuum pump 8 are closed in sequence to complete the vacuuming process.

[0133] Open the valve at the outlet of nitrogen storage tank 1, start the first compressor 101 to send nitrogen to the pipeline, use the first pressure reducing valve 102 to control the nitrogen pressure to the preset pressure of the experimental conditions, and then use the first MFC mass flow meter 103 to adjust the nitrogen flow rate to the preset flow rate of the experimental conditions. Close the first bypass valve 122 to disconnect the first bypass pipeline 121 between the outlet of nitrogen storage tank 1 and the inner pipe inlet 421 of the double-tube test pipeline 4. Open the valve at the gas cooling inlet 211 and the valve at the gas cooling outlet 212 of the liquid nitrogen cooling device 2. Nitrogen enters the cooling coil 22 immersed in liquid nitrogen from the gas cooling inlet 211 for cooling. Then, use the first nitrogen heater 91 to heat the nitrogen flowing out of the gas cooling outlet 212 to ensure that the nitrogen temperature is the temperature required for the experimental conditions. After being heated by the first nitrogen heater 91, the low-temperature nitrogen gas then enters the inner tube 42 of the double-tube test pipeline 4 in the vacuum chamber 7 to cool the pipeline. The second nitrogen heater 92 is then activated to regulate the temperature of the nitrogen gas flowing out of the inner tube 42. Subsequently, the nitrogen gas enters the refrigerant circulation chamber 31 in the pre-cooling heat exchanger 3. The valve at the inlet of the nitrogen storage tank 1 is opened, and the nitrogen gas flowing out of the refrigerant outlet 312 of the pre-cooling heat exchanger 3 enters the nitrogen storage tank 1, completing the refrigerant circulation.

[0134] Open the valve at the outlet of the mixed gas buffer tank 62, start the second compressor 104 to send the experimental gas to the pipeline of the visualization test system, i.e., the experimental pipeline. Use the second pressure reducing valve 105 to control the experimental gas pressure to the preset pressure of the experimental conditions, and then use the second MFC mass flow meter 106 to adjust the experimental gas flow rate to the preset flow rate of the experimental conditions. Close the second bypass valve 125 and disconnect the second bypass pipeline 124 between the refrigerant outlet 312 and the experimental medium inlet 321 of the precooling heat exchanger 3. The experimental gas enters the experimental medium flow chamber 32 in the precooling heat exchanger 3 in the vacuum chamber 7 and exchanges heat with the low-temperature nitrogen in the refrigerant flow chamber 31 for preliminary precooling. Then, the experimental gas enters the outer pipe 41 of the double-tube test pipeline 4 for the experiment. Close the vent valve 123 and open the valve at the inlet of the mixed gas recovery tank 63. The experimental gas flowing out of the outer pipe outlet 413 of the double-tube test pipeline 4 enters the mixed gas recovery tank 63.

[0135] The experiment used LED strips 73 installed at both ends of the inner chamber of vacuum chamber 7 to provide light. A high-speed camera recorded and observed the condensation and frosting process of the mixed gas through the visualization window 411 of the double-tube test pipeline 4. The high-speed camera was moved along a camera track 74 installed at the top and around the circumference of vacuum chamber 7. Through the visualization window 411, the phase change of the mixed gas at different locations, including the horizontal direction, the vertical direction, and along the gas flow direction, could be observed. The temperature and pressure of the refrigerant flowing through the inner tube inlet 421 and inner tube outlet 422 of the double-tube test pipeline 4, as well as the temperature and pressure of the experimental gas flowing through the outer tube inlet 412 and outer tube outlet 413 of the double-tube test pipeline 4, were recorded during the experiment to obtain the flow and heat transfer data of the fluid. During the experiment, the liquid nitrogen level is observed through the liquid nitrogen level gauge 23 in the liquid nitrogen cooling device 2. As the experiment continues, the liquid nitrogen gradually vaporizes and is discharged, and the liquid nitrogen level in the liquid nitrogen chamber 21 will gradually decrease. In order to ensure that the nitrogen can still be cooled to the preset temperature in subsequent experiments, liquid nitrogen needs to be added through the liquid nitrogen filling port 213 during the experiment to provide sufficient cooling capacity for nitrogen.

[0136] During the experiment, the gas composition and content distribution were adjusted by controlling the opening of the high-pressure gas cylinder group 61 to realize the effect of different mixed gas compositions and contents on the condensation, frosting and heat exchange performance of the mixed gas. After completing the experiment under this influencing factor, the gas in the mixed gas recovery tank 63 was recovered and treated. Then, experiments under other influencing factors can be carried out.

[0137] During the experiment, other parameters were kept constant. The initial pressure of the experimental gas was changed by controlling the second pressure reducing valve 105 on the experimental pipeline to investigate the effect of the initial pressure of the experimental gas on the condensation, frosting, and heat transfer performance of the mixed gas. The flow rate of the experimental gas was changed by controlling the second MFC mass flow meter 106 on the experimental pipeline to investigate the effect of the flow rate of the experimental gas on the condensation, frosting, and heat transfer performance of the mixed gas. The temperature of the experimental gas was changed by controlling the second nitrogen heater 92 to investigate the effect of the temperature of the experimental gas on the condensation, frosting, and heat transfer performance of the mixed gas. The pressure of the cold source was changed by controlling the first pressure reducing valve 102 on the nitrogen cooling pipeline to investigate the effect of the cold source pressure on the condensation, frosting, and heat transfer performance of the mixed gas. The flow rate of the actual nitrogen was changed by controlling the first MFC mass flow meter 103 on the nitrogen cooling pipeline to investigate the effect of the cold source flow rate on the condensation, frosting, and heat transfer performance of the mixed gas. The temperature of the cold source was changed by controlling the first nitrogen heater 91 to investigate the effect of the temperature of the cold source on the condensation or frosting and heat transfer performance of the mixed gas.

[0138] When conducting experimental studies on factors other than the composition and content of the mixed gas, when the gas in the mixed gas buffer tank 62 decreases to the point where subsequent experiments cannot be carried out for a long time, the valve at the upstream pipeline of the gas cooling inlet 211 of the liquid nitrogen cooling device 2 and the valve at the downstream pipeline of the gas cooling outlet 212 are closed, and the first bypass valve 122 is opened, allowing nitrogen to bypass the liquid nitrogen cooling device 2 and directly enter the inner tube 42 of the double-tube test pipeline 4 in the vacuum chamber 7. Room temperature nitrogen is introduced into the inner tube 42 of the double-tube test pipeline 4 so that the condensed droplets and frost layer in the outer tube 41 of the double-tube test pipeline 4 are completely vaporized and flow into the mixed gas recovery tank 63. This can ensure the consistency and uniformity of the gas composition in the previous and subsequent experiments. Then, open the valve at the outlet of the mixed gas recovery tank 63, close the valve at the outlet of the mixed gas buffer tank 62, open the valve at the second inlet of the mixed gas buffer tank 62, and close the valve at the inlet of the mixed gas recovery tank 63, so that the mixed gas recovery tank 63, containing a sufficient amount of gas, serves as the experimental gas supply device, while the original mixed gas buffer tank 62 serves as the experimental gas recovery device. Then, open the valve on the upstream pipeline of the gas cooling inlet 211 and the valve on the downstream pipeline of the gas cooling outlet 212 of the liquid nitrogen cooling device 2, close the first bypass valve 122, and disconnect the first bypass pipeline 121 between the outlet of the nitrogen storage tank 1 and the inner pipe inlet 421 of the double-tube test pipeline 4, so that the nitrogen is cooled and used as a cold source to continue the experiment, realizing the recycling of experimental gas.

[0139] The following describes the process of using the device of the present invention to conduct experiments on the effects of materials or surface structures on the condensation, frosting phenomena, and heat transfer performance of mixed gases. The experimental procedure is as follows: Open the first sealing door 72 of the vacuum chamber 7 and open the second sealing door 414 of the outer tube 41 of the double-tube test pipeline 4. Install the experimental sample of a specific material or with a specific surface structure on the upper surface or side of the outer wall of the inner tube 42 of the double-tube test pipeline 4, directly facing the visualization window 411. Close the second sealing door 414 and the first sealing door 72, and conduct the relevant experiments according to the above procedure. Record and observe the condensation and frosting process of the mixed gas on different materials or surface structures through the visualization window 411 of the double-tube test pipeline 4 using a high-speed camera.

[0140] The following describes the process of using the device of the present invention to conduct tests on the anti-condensation and anti-frost properties of materials or surface structures. The experimental scheme is as follows: Open the first sealing door 72 of the vacuum chamber 7 and open the second sealing door 414 of the outer tube 41 of the double-tube test pipeline 4. Install different experimental samples of specific materials or processed with specific surface structures on the upper surface or side of the outer wall of the inner tube 42 of the double-tube test pipeline 4, facing the visualization window 411. Close the second sealing door 414 and the first sealing door 72, and conduct relevant phase change experiments according to the above scheme. After the experiment is completed, close the valve of the upstream pipeline of the gas cooling inlet 211 of the liquid nitrogen cooling device 2 and the valve of the downstream pipeline of the gas cooling outlet 212. Open the first bypass valve 122 to allow nitrogen gas to bypass the liquid nitrogen cooling device 2 and directly enter the inner tube 42 of the double-tube test pipeline 4 in the vacuum chamber 7. Introduce room temperature nitrogen gas into the inner tube 42 of the double-tube test pipeline 4 to increase the temperature of the surface where the liquid film, droplets, and frost layer are located, and start the decondensation and defrosting experiment. The process of desorption of liquid film, droplets and frost layer on different samples is recorded and observed through the visualization window 411 of the double-tube test pipeline 4 using a high-speed camera, and the anti-condensation and anti-frost performance of different materials or surface structures is compared.

[0141] This concludes the detailed description of this embodiment in conjunction with the accompanying drawings. Based on the above description, those skilled in the art should have a clear understanding of the controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment according to the present invention.

[0142] This invention discloses a controlled condensation and frosting visualization experimental device for gas flow in an ultra-low temperature environment. The device includes a cooling system, a visualization testing system, a gas supply system, a vacuum system, and a data acquisition and control system. This experimental device enables the visualization observation of the condensation and frosting process of different low-temperature gas mixtures during flow, the acquisition of heat transfer data during the experiment, and the investigation of the influence of different factors on the phase change of low-temperature gases and the heat transfer performance between fluids. Nitrogen is used as the refrigerant in the experiment. A liquid nitrogen cooling device 2 is used to cool the nitrogen to an extremely low temperature, and a nitrogen heater is used to control the temperature of the refrigerant. The low-temperature nitrogen then exchanges heat with the experimental medium to achieve the low-temperature phase change of the experimental medium. To fully utilize the cooling capacity of the low-temperature nitrogen, the nitrogen after heat exchange pre-cools the experimental gas mixture before it enters the visualization testing system, ensuring that the phase change of the experimental gas mixture can be observed at the visualization window 411. The specific experimental procedure for using nitrogen as a refrigerant is as follows: nitrogen flowing out of nitrogen storage tank 1 is pressurized by the first compressor 101, and then controlled by the first pressure reducing valve 102 and the first MFC mass flow meter 103 to reach the preset experimental operating condition value. After the nitrogen reaches the preset experimental operating condition value, it is sent to the liquid nitrogen cooling device 2 for cooling. When the nitrogen is cooled to an extremely low temperature, the first nitrogen heater 91 heats the low-temperature nitrogen to the preset experimental operating condition temperature and then sends it to the inner tube 42 of the double-tube test pipeline 4 in the visualization test system to perform deep cooling with the experimental medium, causing the experimental medium to undergo a phase change. The low-temperature nitrogen flowing out of the inner tube 42 of the double-tube test pipeline 4 is heated to the pre-cooling temperature by the second nitrogen heater 92 and then enters the pre-cooling heat exchanger 3 to perform preliminary pre-cooling of the experimental medium. After the pre-cooling is completed, the nitrogen flows to nitrogen storage tank 1 for circulation supply.

[0143] The experiment involves preparing a mixed gas with the required composition and content in a mixed gas buffer tank 62 using high-pressure gas cylinders containing different components. The experiment begins after the valves of the high-pressure gas cylinder group 61 are closed. After thorough mixing in the mixed gas buffer tank 62, the mixed gas is pressurized by a second compressor 104. Then, the pressure and flow rate of the mixed gas are controlled at preset experimental operating conditions by a second pressure reducing valve 105 and a second MFC mass flow meter 106. Subsequently, the experimental mixed gas exchanges heat with low-temperature nitrogen in a pre-cooling heat exchanger 3 to pre-cool the mixed gas to a preset temperature before being sent to the outer pipe 41 of the visualization testing system for the experiment. The experimental mixed gas flowing out of the outer pipe 41 of the double-tube test pipeline 4 in the visualization testing system flows into the mixed gas recovery tank 63. When the gas in the mixed gas buffer tank 62 is insufficient to continue the experiment, the valve is switched to close the valve at the inlet of the mixed gas recovery tank 63 and open the valve at the outlet of the mixed gas recovery tank 63, connecting the outlet of the mixed gas recovery tank 63 to the inlet of the second compressor 104 for gas supply; the valve at the outlet of the mixed gas buffer tank 62 is closed to disconnect the original connecting pipeline between the outlet of the mixed gas buffer tank 62 and the inlet of the second compressor 104, and the valve at the inlet of the mixed gas buffer tank 62 is opened to connect the inlet of the mixed gas buffer tank 62 to the outer pipe outlet 413 of the double-tube test pipeline 4 in the visualization test system, thereby recovering the experimental gas through the mixed gas buffer tank 62 and realizing the recycling of the experimental gas.

[0144] The side of the vacuum chamber 7 is connected to a first sealing door 72 via a hinge. The top of the outer tube 41 of the double-tube test pipeline 4 is also connected to a second sealing door 414 with a visualization window 411 via a hinge. During the experiment, the first sealing door 72 and the second sealing door 414 are opened in sequence to take out and put in the experimental samples, so as to realize the phase change experiment test of the mixed gas on different material surfaces, and then explore the influence of different materials and surface microstructures on the droplet and frost crystal morphology and properties during the phase change process, as well as the influence on the gas heat transfer efficiency. In addition, the anti-dew and anti-frost performance of different material or structural surfaces can also be tested through experiments.

[0145] The controlled condensation and frosting visualization experimental device for gas flow in ultra-low temperature environments of the present invention has several advantages. First, the experimental device uses a liquid nitrogen cooling device 2 to cool the nitrogen gas. The low temperature of the cold source enables controlled phase change of the low-temperature gas. The cold source temperature of this device is close to the temperature of liquid nitrogen, which is convenient for conducting phase change experiments on low-boiling-point, low-surface-tension fluids such as light alkanes and CO2. The experimental device of the present invention also incorporates a nitrogen heater to control the temperature of the cold source, which can control the temperature of the refrigerant before it enters the experimental test section. Controlled condensation and frosting of the experimental gas can be achieved by flexibly adjusting the refrigerant temperature.

[0146] Secondly, the experimental device of the present invention can simultaneously observe the condensation and frosting process of low-temperature gas in a flowing state and obtain convective heat transfer data during the experiment. The experimental device does not conduct the condensation and frosting phase change experiment of fluid in a closed space. The experimental medium is always in a flowing state during the experiment. The experimental device of the present invention can also record heat transfer data between fluids in real time so as to analyze the influence of liquid film and liquid frost layer on heat exchange efficiency.

[0147] Third, the experimental device of the present invention has strong functionality and can be used for multiple purposes. It can conduct phase change and heat exchange performance tests under multiple working conditions. For example, it can conduct experiments on the effects of experimental gas composition and content, experimental gas flow rate, experimental gas initial temperature, experimental gas initial pressure, cold source temperature, cold source pressure, cold source flow rate, wall material, etc. on the low-temperature gas phase change process and heat exchange efficiency. The experimental device of the present invention can also be used to test the anti-condensation and anti-frost performance of different materials or surface structures. It has strong functionality and wide applicability.

[0148] Fourth, the experimental device of the present invention can simultaneously realize the recycling of experimental gas and refrigerant, which has a low cost. The cooling pipeline of the device forms a complete loop, enabling the refrigerant to be recycled. At the same time, the experimental pipeline can also realize the recycling of experimental medium through valve switching, thereby further reducing the experimental cost.

[0149] Furthermore, the experimental apparatus of this invention employs a square sleeve structure to achieve flow heat exchange of the experimental medium and refrigerant. The outer tube 41 and inner tube 42 of the double-sleeve test pipeline 4 are preferably square tubes. By placing experimental samples horizontally and vertically on the surface of the inner tube 42, condensation and frosting phase change experiments of gases on different material surfaces can be conducted. Visualization of the gas phase change process under flow conditions can be achieved through the visualization window 411 on the outer tube 41 and the camera 5 inside the vacuum chamber 7.

[0150] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An experimental device for visualizing controlled condensation frosting in a gas flow process under cryogenic conditions, characterized in that The cooling system, the visual test system, the gas supply system and the vacuum system are included; The cooling system includes a nitrogen storage tank, a liquid nitrogen cooling device and a pre-cooling heat exchanger; The visual test system includes a double-sleeve test pipeline and a camera, the double-sleeve test pipeline includes an outer tube and an inner tube, and a visual window is arranged on the outer tube of the double-sleeve test pipeline; The outlet of the nitrogen storage tank is connected to the gas cooling inlet of the liquid nitrogen cooling device, the gas cooling outlet of the liquid nitrogen cooling device is connected to the inner tube inlet of the double-sleeve test pipeline, the inner tube outlet of the double-sleeve test pipeline is connected to the coolant inlet of the pre-cooling heat exchanger, and the coolant outlet of the pre-cooling heat exchanger is connected to the inlet of the nitrogen storage tank; The gas supply system includes a high-pressure gas cylinder group, a mixed gas buffer tank and a mixed gas recovery tank; The outlet of the high-pressure gas cylinder group is connected to the first inlet of the mixed gas buffer tank, the outlet of the mixed gas buffer tank and the outlet of the mixed gas recovery tank are selectively connected to the experimental medium inlet of the pre-cooling heat exchanger, the experimental medium outlet of the pre-cooling heat exchanger is connected to the outer tube inlet of the double-sleeve test pipeline, and the outer tube outlet of the double-sleeve test pipeline is connected to the inlet of the mixed gas recovery tank or the second inlet of the mixed gas buffer tank; The vacuum system includes a vacuum chamber and a vacuum pump; The double-sleeve test pipeline, the camera and the pre-cooling heat exchanger are located in the vacuum chamber; A vacuum port and a first sealing door are arranged on the side of the vacuum chamber, the vacuum pump is connected to the vacuum port, and a vacuum valve is arranged on the connecting pipeline between the vacuum pump and the vacuum port; A first nitrogen heater is arranged on the connecting pipeline between the gas cooling outlet of the liquid nitrogen cooling device and the inner tube inlet of the double-sleeve test pipeline; A second nitrogen heater is arranged on the connecting pipeline between the inner tube outlet of the double-sleeve test pipeline and the coolant inlet of the pre-cooling heat exchanger, and the second nitrogen heater is located in the vacuum chamber.

2. The visualization experiment device for controlled condensation frosting in gas flow process under ultra-low temperature environment according to claim 1, wherein A first compressor, a first pressure reducing valve and a first MFC mass flow meter are arranged on the connecting pipeline between the outlet of the nitrogen storage tank and the gas cooling inlet of the liquid nitrogen cooling device; A second compressor, a second pressure reducing valve and a second MFC mass flow meter are arranged on the connecting pipeline between the outlet of the mixed gas buffer tank / the outlet of the mixed gas recovery tank and the experimental medium inlet of the pre-cooling heat exchanger.

3. The visualization experiment device for controlled condensation frosting in gas flow process under ultra-low temperature environment according to claim 2, wherein The visualization experiment device for controlled condensation frosting in gas flow process under ultra-low temperature environment further includes a data acquisition and control system, and the data acquisition and control system includes temperature sensors, pressure sensors, a data acquisition card and a data acquisition terminal; The temperature sensors and the pressure sensors are arranged at the inner tube inlet, the inner tube outlet, the outer tube inlet and the outer tube outlet of the double-sleeve test pipeline; The temperature sensors, the pressure sensors, the first MFC mass flow meter, the second MFC mass flow meter and the camera are respectively connected to the input end signal of the data acquisition card, and the output end of the data acquisition card is connected to the signal of the data acquisition terminal.

4. The experimental device of claim 3, wherein the data acquisition terminal is a computer.

5. The experimental device of claim 1, wherein the second inlet and outlet of the mixed gas buffer tank are provided with valves; the inlet and outlet of the mixed gas recovery tank are provided with valves; when the valve at the outlet of the mixed gas buffer tank and the valve at the inlet of the mixed gas recovery tank are opened, and the valve at the second inlet of the mixed gas buffer tank and the valve at the outlet of the mixed gas recovery tank are closed, the mixed gas buffer tank is used to supply the experimental gas to the experimental medium inlet of the pre-cooling heat exchanger, and the mixed gas recovery tank is used to recover the experimental gas from the outlet of the outer tube of the double-tube test pipeline; when the valve at the outlet of the mixed gas buffer tank and the valve at the inlet of the mixed gas recovery tank are closed, and the valve at the second inlet of the mixed gas buffer tank and the valve at the outlet of the mixed gas recovery tank are opened, the mixed gas buffer tank is used to recover the experimental gas from the outlet of the outer tube of the double-tube test pipeline, and the mixed gas recovery tank is used to supply the experimental gas to the experimental medium inlet of the pre-cooling heat exchanger.

6. The experimental device of claim 1, wherein the liquid nitrogen cooling device comprises a liquid nitrogen chamber, a cooling coil, a liquid level meter and a pressure gauge; the liquid nitrogen chamber is provided with a liquid nitrogen filling port and a pressure relief port, and the pressure relief port is provided with a pressure relief valve; the liquid nitrogen chamber is further provided with a gas cooling inlet and a gas cooling outlet; the cooling coil is arranged in the interior of the liquid nitrogen chamber, one end of the cooling coil is communicated with the gas cooling inlet, and the other end of the cooling coil is communicated with the gas cooling outlet; the liquid level meter and the pressure gauge are located outside the liquid nitrogen chamber, and the detection ends of the liquid level meter and the pressure gauge extend into the interior of the liquid nitrogen chamber.

7. The experimental device of claim 1, wherein the inner tube of the double-tube test pipeline is a square tube, and the outer wall of the inner tube is coated with black paint; the outer tube of the double-tube test pipeline is a square tube, and the outer tube is provided with a second sealing door; the visualization window has a plurality of visualization windows, and the plurality of visualization windows are arranged on the side of the outer tube and the second sealing door.

8. The experimental device of claim 1, wherein the vacuum system further comprises a lamp strip and a camera moving track, and the lamp strip and the camera moving track are arranged in the vacuum chamber; the camera moving track is arranged along the circumferential direction and the axial direction of the outer tube of the double-tube test pipeline; the side of the vacuum chamber is provided with a refrigerant pipeline inlet, a refrigerant pipeline outlet, an experimental gas pipeline inlet, an experimental gas pipeline outlet and a sensor bundle outlet.

9. The experimental device of claim 1, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ A bypass pipeline is arranged between the outlet of the nitrogen storage tank and the inlet of the inner pipe of the double-sleeve test pipeline, and between the coolant outlet of the pre-cooling heat exchanger and the experimental medium inlet, and a bypass valve is arranged on the bypass pipeline; A relief valve is further arranged on the connecting pipeline between the outlet of the outer pipe of the double-sleeve test pipeline and the second inlet of the mixed gas buffer tank; Valves are arranged at the inlet and outlet of the nitrogen storage tank, and at the gas cooling inlet and gas cooling outlet of the liquid nitrogen cooling device.

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