Low-temperature volume tube with double working modes

Abstract

The invention discloses a low-temperature volume tube with double working modes. The device comprises an inner container used for containing low-temperature fluid; the outer layer heat insulation structure is arranged outside the inner container and is used for providing heat insulation protection; the inner-layer heat insulation structure is arranged between the outer-layer heat insulation structure and the inner container and is used for further enhancing the heat insulation effect; the driving system comprises an active mode driving mechanism and a passive mode driving mechanism and is used for switching between an active mode and a passive mode so as to drive the low-temperature fluid to flow in the inner container; the control system is used for controlling the driving system to be switched between the active mode and the passive mode and monitoring and adjusting flowing parameters of the low-temperature fluid in real time. By means of a gradient heat insulation and mode switching mechanism, the low heat conductivity of vacuum is utilized, and environment heat input is greatly reduced, so that the temperature stability of low-temperature fluid in the pipe is maintained, and stable temperature control of the environment of-196 DEG C and seamless switching of active / passive working modes are achieved.

Description

Technical Field

[0001] The present invention relates to the field of fluid metering technology, and in particular to a dual-mode volume tube suitable for cryogenic media (such as liquefied natural gas, liquid nitrogen, etc.), which can be switched between active mode and passive storage mode. Background Art

[0002] In the fields of petroleum, chemical engineering, energy, etc., flow measurement of cryogenic fluids (such as liquefied natural gas (LNG) and liquid nitrogen) is a critical link in production, transportation, and trade settlement. Due to the extremely low bubble point pressure, extremely high latent heat of vaporization, and significant thermal contraction characteristics of cryogenic fluids, their flow calibration places extremely high demands on the equipment's temperature stability, drive reliability, and measurement accuracy. As the core device for flow calibration, the volume tube calibrates the flow meter by accurately measuring the displacement time of a known volume of fluid. However, in cryogenic scenarios, the design limitations of traditional volume tubes are significant and cannot meet practical requirements.

[0003] Currently, cryogenic volume tubes mainly use traditional active or passive designs. Both face the following core problems in low-temperature environments:

[0004] Active volume tubes rely on an external power source to drive fluid flow. Although they can precisely control the flow rate, their drive system has significant drawbacks at low temperatures:

[0005] The lubricating oil or rubber seals in the power unit can easily solidify and become brittle at low temperatures, leading to lubrication failure or leakage. Mechanical friction during the driving process generates Joule heat, which is directly transferred to the fluid, causing localized temperature rise and vaporization of the low-temperature fluid. Electronic sensors and electric valves are prone to signal drift and actuation obstruction at low temperatures, affecting flow control and timing accuracy.

[0006] Passive volume tubes are driven by the fluid's own pressure energy. Although they have a simple structure, they are highly dependent on the main pipeline conditions:

[0007] The flow rate is limited by the pressure difference in the main pipeline. When the upstream flow fluctuates or the downstream resistance changes, the flow rate is prone to fluctuations or even interruption, resulting in incomplete replacement of the volume tube. The thermal insulation capacity is limited. Traditional passive volume tubes only use conventional insulation layers such as polyurethane foam. The continuous transfer of ambient heat into the tube causes the fluid temperature to rise and the density to change, resulting in volume measurement errors.

[0008] Both active and passive designs struggle to adapt to the complex working conditions required for cryogenic fluid calibration. Active designs offer stable operation but consume high energy and struggle to control temperature. Passive designs, while energy-efficient, rely on mainline pressure and experience unstable flow rates. Furthermore, neither approach incorporates specific insulation solutions to address the vaporization-sensitive nature of cryogenic fluids, resulting in insufficient temperature preservation and the inability to meet the requirements of high-precision calibration. Summary of the Invention

[0009] To solve the above problems, the present invention provides a low-temperature volume tube that takes into account both active drive reliability and passive drive adaptability and has efficient vacuum insulation capabilities. It solves the working condition dependence problem of a single mode through dual-mode drive, and at the same time suppresses environmental heat input through vacuum layer insulation, ensuring that the temperature of the low-temperature fluid is stable during the displacement process, thereby achieving high-precision and high-safety flow calibration.

[0010] The present invention comprises:

[0011] An inner tank for containing a cryogenic fluid;

[0012] An outer heat-insulating structure is arranged outside the inner liner to provide heat-insulating protection;

[0013] An inner insulation structure is provided between the outer insulation structure and the inner liner to further enhance the insulation effect;

[0014] a driving system comprising an active mode driving mechanism and a passive mode driving mechanism, for switching between the active mode and the passive mode to drive the cryogenic fluid to flow in the inner tank;

[0015] The control system is used to control the switching of the drive system between the active mode and the passive mode, and to monitor and adjust the flow parameters of the cryogenic fluid in real time.

[0016] The outer insulation structure and the inner insulation structure together form a double-layer insulation structure to reduce the impact of ambient heat on the cryogenic fluid and maintain the temperature stability of the cryogenic fluid.

[0017] The driving system realizes switching between active mode and passive mode through an electromagnetic clutch mechanism. The active mode driving mechanism includes a servo motor and a transmission mechanism, and the passive mode driving mechanism drives the flow of low-temperature fluid by utilizing the pressure difference of the fluid itself.

[0018] The control system includes a temperature sensor, a pressure sensor and a flow sensor, which are used to monitor the temperature, pressure and flow of the cryogenic fluid in real time, perform dynamic compensation calculations based on the monitoring data, and output accurate flow values.

[0019] Beneficial effects of the present invention: This invention proposes a cryogenic volume tube that integrates a double-layer thermal insulation vacuum layer with a dual-mode drive system. Through gradient insulation and a mode switching mechanism, the low thermal conductivity of vacuum (approximately 0.002 W / (m·K), far lower than the 0.025 W / (m·K) of polyurethane foam) is utilized to significantly reduce ambient heat input, thereby maintaining the temperature stability of the cryogenic fluid within the tube. This achieves stable temperature control in a -196°C environment and seamless transitions between active and passive operating modes.

[0020] Engineering applicability: The modular vacuum layer design supports segmented maintenance and reduces operating costs; it is compatible with various cryogenic media such as liquid nitrogen and LNG. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of an embodiment of the present application. DETAILED DESCRIPTION

[0022] The present invention is further described below with reference to the accompanying drawings and embodiments:

[0023] The technical difficulties of the vacuum layer on the outer wall of the volume tube are concentrated on two core issues: vacuum maintenance and thermal bridge effect suppression. High manufacturing costs, low maintenance convenience, and the limitations of industry needs further hinder its large-scale application. This application solves the dependence on the working conditions of a single mode through active-passive dual-mode drive, and reduces the difficulty of vacuum maintenance by optimizing the vacuum jacket structure. At the same time, an insulating support structure is designed to reduce the thermal bridge effect of the vacuum layer, ultimately realizing the engineering implementation of the vacuum layer in the low-temperature volume tube.

[0024] An embodiment of the present application provides a structure that can freely switch the working mode of a low-temperature piston-type volume tube flow standard device. The piston-type volume tube can use a passive mode to calibrate the online low-temperature fluid flow, and can also use an active mode to controllably calibrate the offline low-temperature fluid flow.

[0025] like Figure 1 As shown, the vacuum cold box of this embodiment adopts an inner and outer double-tube composite structure design, mainly consisting of an inner liner 8, an intermediate protective layer 11, an outer vacuum insulation layer 9, an insulating support structure 13, an active-passive mode switching mechanism 1, and auxiliary systems. The core design lies in suppressing ambient heat input through the double-layer vacuum insulation structure, and achieving seamless active / passive mode switching in combination with an electromagnetic clutch-driven ball screw. At the same time, the insulating support structure 13 and radiation shielding optimization further reduce heat leakage, ensuring stable fluid temperature in the tube even at -196°C low temperatures.

[0026] To ensure constant temperature in the device, the calibrated medium range of the piston-type volume tube has been expanded. This volume tube adopts a double-layer vacuum structure with an outer vacuum insulation layer 9 and an inner high vacuum insulation layer 12. It combines multi-layer composite insulation materials with radiation shielding technology to significantly reduce environmental heat input. A purge controller is used to purge before use and adjust the local nitrogen source to prevent ice from forming on the reciprocating inlet and outlet parts of the volume tube under cold process conditions. The specific structure is as follows:

[0027] Outer vacuum insulation layer 9:

[0028] Position: Located between the outer shell 10 and the middle protective layer 11, with a thickness of 15-20 mm.

[0029] Structure: Filled with 30 layers of alternating aluminized polyester film (thickness 20μm) and glass fiber paper (thickness 50μm), the layers are bonded with low-pressure adhesive to avoid excessive interlayer compression that would increase heat conduction, effectively suppressing radiation and convection heat transfer.

[0030] Material selection:

[0031] The outer shell 10 is made of austenitic stainless steel 316L (thickness 3mm), whose low-temperature toughness (elongation ≥40% at -200°C) can resist environmental stress corrosion, and the surface polishing (Ra≤0.4μm) reduces gas adsorption and ensures vacuum sealing.

[0032] The middle protective layer 11 is a 316L stainless steel corrugated plate (thickness 1 mm), which absorbs thermal expansion and contraction stress through its wavy structure to prevent the interlayer from deforming and cracking due to temperature changes.

[0033] Inner high vacuum insulation layer 12:

[0034] Position: Located between the middle protective layer 11 and the inner liner 8, with a thickness of 10-15 mm.

[0035] Function: By removing the gas in the interlayer (vacuum degree ≤ ), suppressing the heat transfer of free molecules of residual gas; the inner wall aluminum film (thickness 50nm) and silicon oxide protective layer (thickness 2μm) are deposited by magnetron sputtering process to reduce radiation heat transfer and resist thermal cycle peeling.

[0036] Insulation support structure:

[0037] In order to avoid the generation of thermal bridges due to direct contact between the inner liner 8 and the outer shell 10 due to its own weight or fluid pressure, the volume tube is designed with a carbon fiber / polyimide composite insulation support structure 13. The specific parameters are as follows:

[0038] Materials: Carbon fiber (T700 grade, modulus 240GPa) and polyimide (PI, glass transition temperature 260°C) composite, volume ratio 7:3, with both high strength (tensile strength ≥ 3GPa) and low thermal conductivity (thermal conductivity ≤ 0.03W / (m·K)).

[0039] Structural design: The thermal insulation support structure 13 has an I-shaped cross section, and is in point contact with the inner liner 8 (contact area ≤ 5mm²), and is fixed to the intermediate protective layer 11 and the external support structure 10 by bolts.

[0040] Advantages: Compared with traditional metal supports (such as stainless steel), the contact area of ​​carbon fiber / polyimide composite materials is reduced by 90%, and heat leakage is reduced by more than 85%. At the same time, it can withstand the mechanical load of the volume tube internal pressure (≤10MPa) and its own weight (500kg level).

[0041] Inner tank 8 and fluid interface design

[0042] Inner liner 8: Made of titanium alloy, with a wall thickness of 5mm, the inner wall is electrolytically polished to ensure low-temperature impact and corrosion resistance. Flow outlets 21 are welded to both ends of the liner. The flange at the flow outlet and the inner liner 8 are welded using argon arc welding for the base and manual arc welding for the top. The welds are 100% radiographically inspected to ensure the absence of pores and cracks.

[0043] Flow outlet 21: connected to the flow meter to be tested 19, the signal end of the flow meter to be tested 19 is connected to the control system 14 through the signal line 20, and the outlet of the flow meter to be tested 19 and the flow inlet 6 are both connected to the water tank 22 through the fluid pipeline 7.

[0044] Flow inlet 6: The flow inlet flange is equipped with a quick-connect joint, which is compatible with low-temperature pipes of various specifications. The interface is filled with low-temperature sealant to prevent fluid leakage.

[0045] This volume tube achieves seamless switching between active and passive modes through the “electromagnetic clutch mechanism 18+ball screw 16+transmission system”, further:

[0046] The electromagnetic clutch mechanism 18 is installed in a sealed cabin at the bottom of the volume tube and contains a servo motor 15, a ball screw 16, and the electromagnetic clutch mechanism 18. When the electromagnet in the electromagnetic clutch mechanism is energized, it generates a magnetic force that attracts the ball screw head, rigidly connecting the ball screw to the transmission system. When the power is off, the magnetic force disappears, the piston rod is disconnected from the transmission system, and the mechanism enters a passive mode.

[0047] Ball screw 16: Made of low-temperature, high-strength titanium alloy with a polished surface, it precisely fits the inner wall of the inner liner 8 to ensure sealing. One end of the ball screw is connected to the piston 17, and the other end is linked to the transmission system through a flexible coupling.

[0048] Mode switching logic:

[0049] Active mode: The electromagnetic clutch mechanism 18 is energized, the ball screw 16 is combined with the transmission system, and the transmission system drives the ball screw 16 to reciprocate at a set speed, pushing the fluid to circulate in the volume tube, completing the flow meter calibration.

[0050] Passive mode: The electromagnetic clutch mechanism 18 is powered off, the ball screw 16 is separated from the transmission system, and the fluid relies on the pressure difference of the main pipeline to push the ball screw 16 to move (the flow rate is automatically adjusted by the main pipeline pressure). After the fluid replacement is completed, the sensor triggers a reset signal, and the system automatically switches to active mode to pull back the ball screw 16 and prepare for the next round of calibration.

[0051] Furthermore, the working process of this embodiment is as follows:

[0052] First, the device is purged with nitrogen. The purge controller regulates the local nitrogen source via the nitrogen purge cover to prevent ice accumulation in the section where the volume tube reciprocates under cold process conditions. Residual air, moisture, and other impurities in the pipeline are removed to avoid measurement errors and system instability caused by gas mixing or impurities during the experiment. During operation, a pressure sensor and flow monitoring device are used to monitor the flow of nitrogen in the pipeline in real time to ensure thorough purging.

[0053] When the passive calibration mode starts, the PLC control system first turns off the servo motor and disconnects the electromagnet, and at the same time closes the electromagnetic clutch mechanism 18; driven by the low-temperature fluid, the piston 17 moves downstream synchronously with the fluid, and the ball screw passes through the start detection photoelectric switch 2 and the end detection photoelectric switch 3 in turn to complete the test stroke. During this process, the fluid parameters collected in real time by the temperature transmitter 4 and the pressure transmitter 5 are transmitted to the control system 14, and the control system 14 performs volume correction and flow calculation; when the piston 17 reaches the downstream limit position, the piston lifting valve automatically opens, the electromagnet moves to the electromagnet suction cup and completes the adsorption, and then the servo motor reverses to drive the ball screw to reset, and the entire system enters the waiting state and prepares for the next calibration.

[0054] At the start of active mode calibration, under PLC control, the servo motor starts forward rotation, closing the electromagnet and the piston lift valve. The ball screw then pushes piston 17 downstream at a preset constant speed. During this process, the piston rod sequentially triggers start detection photoelectric switch 2 and end detection photoelectric switch 3, completing the standard test stroke. Temperature transmitter 4 and pressure transmitter 5 monitor cryogenic fluid parameters in real time and transmit them to control system 14, which calculates and outputs the precise flow rate after dynamic compensation. When piston 17 reaches its downstream limit, the piston lift valve automatically opens, and the servo motor reverses to drive the piston rod back to its initial position, preparing for the next calibration. This process implements fully automated closed-loop control, ensuring accurate and repeatable cryogenic fluid flow measurement.

[0055] The embodiment of the present application solves the technical difficulties of traditional low-temperature volume tubes in vacuum maintenance, thermal bridge effect and mode switching through the integrated design of a double-layer insulating vacuum layer, a dual-mode drive system and an insulating support structure, and achieves high-precision flow calibration in a low-temperature environment of -196°C. It is suitable for industrial measurement scenarios of cryogenic fluids such as LNG and liquid nitrogen.

[0056] The above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, but these descriptions should not be understood as limiting the scope of the present invention. The scope of protection of the present invention is defined by the appended claims, and any changes based on the claims of the present invention are within the scope of protection of the present invention.

Claims

1. A dual-working mode cryogenic volume tube, characterized in that: include: An inner tank for containing a cryogenic fluid; An outer heat-insulating structure is arranged outside the inner liner to provide heat-insulating protection; An inner insulation structure is provided between the outer insulation structure and the inner liner to further enhance the insulation effect; a driving system comprising an active mode driving mechanism and a passive mode driving mechanism, for switching between the active mode and the passive mode to drive the cryogenic fluid to flow in the inner tank; a control system for controlling the switching of the drive system between the active mode and the passive mode, and monitoring and adjusting the flow parameters of the cryogenic fluid in real time; The outer insulation structure and the inner insulation structure together form a double-layer insulation structure to reduce the impact of ambient heat on the cryogenic fluid and maintain the temperature stability of the cryogenic fluid; The drive system switches between active mode and passive mode through an electromagnetic clutch mechanism. The active mode drive mechanism includes a servo motor and a transmission mechanism. The passive mode drive mechanism drives the flow of the cryogenic fluid using the pressure difference of the fluid itself. The control system includes a temperature sensor, a pressure sensor and a flow sensor, which are used to monitor the temperature, pressure and flow of the cryogenic fluid in real time, perform dynamic compensation calculations based on the monitoring data, and output accurate flow values.

2. The dual-working mode cryogenic volume tube according to claim 1, characterized in that: The outer insulation structure is a vacuum insulation layer, the inner insulation structure is a high vacuum insulation layer, and the vacuum degree of the high vacuum insulation layer is less than or equal to .

3. The dual-working mode cryogenic volume tube according to claim 2, characterized in that: The outer vacuum insulation layer is filled with multiple layers of composite insulation material, and the composite insulation material includes aluminized polyester film and glass fiber paper stacked alternately.

4. The dual-working mode cryogenic volume tube according to claim 2, characterized in that: The inner wall of the inner high vacuum insulation layer is covered with an aluminum film and a silicon oxide protective layer deposited by magnetron sputtering, which are used to suppress radiation heat transfer and enhance the resistance to cold and hot cycles.

5. The dual-working mode cryogenic volume tube according to any one of claims 1 to 4, characterized in that: An intermediate protective layer is provided between the outer insulation structure and the inner insulation structure. The intermediate protective layer adopts a corrugated plate structure and is used to absorb thermal expansion and contraction stress to prevent the interlayer from deforming and cracking due to temperature changes.

6. The dual-operation-mode cryogenic volume tube according to claim 1, characterized in that: The transmission mechanism in the drive system is a ball screw, which is connected to the electromagnetic clutch mechanism and is used to push the piston to move in the active mode and is driven by the fluid's own pressure in the passive mode.

7. The dual-working-mode cryogenic volume tube according to claim 6, characterized in that: The ball screw is made of low-temperature high-strength titanium alloy, and the surface is polished to ensure precise matching and sealing with the inner wall of the liner.

8. The dual-operation-mode cryogenic volume tube according to claim 5, characterized in that: The inner liner is made of titanium alloy material with a wall thickness of 5 mm. The inner wall is electrolytically polished to improve impact resistance and corrosion resistance at low temperatures.

9. The dual-operation-mode cryogenic volume tube according to claim 5, characterized in that: It also includes a heat-insulating support structure, which is made of carbon fiber / polyimide composite material and is used to connect the inner liner, the middle protective layer and the outer shell to reduce the thermal bridge effect and provide mechanical support.

10. The dual-working-mode cryogenic volume tube according to claim 1, characterized in that: The flow inlet is equipped with a quick-connect joint, which is compatible with low-temperature pipes of multiple specifications. The interface is filled with low-temperature sealant to prevent fluid leakage.

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