A thermometer fixture suitable for transient processes in cryogenic systems

Abstract

This invention discloses a thermometer fixture suitable for transient processes in cryogenic systems, comprising a front guide tube, a rear guide tube, and a temperature measuring block with a temperature sensor mounting interface. The first end of the front guide tube and the first end of the rear guide tube are respectively connected to process piping, and the second ends of the front guide tube and the rear guide tube are respectively connected to the temperature measuring block. A heat exchange channel is formed inside the temperature measuring block, which communicates with the internal channels of the front and rear guide tubes to form a through-flow fluid channel. The fluid being measured can flow through the heat exchange channel and exchange heat with the temperature measuring block. This invention employs a through-flow structural design, combined with a temperature measuring block made of high thermal conductivity material and an optimized flow channel structure, significantly reducing the thermal inertia and thermal resistance of the temperature measuring system and improving the transient thermal response speed. It is particularly suitable for temperature measurement in cryogenic transient conditions such as superconducting cryogenic systems and modular hydrogen liquefaction equipment in the 20–30 K temperature range.

Description

Technical Field

[0001] This invention relates to the field of low-temperature temperature measurement technology, and more specifically to a thermometer fixture suitable for transient processes in low-temperature systems. Background Technology

[0002] With the rapid development of high-temperature superconducting magnets in fusion devices, particle accelerators, and high-energy physics experiments, cryogenic systems have become a crucial supporting link for maintaining superconductivity and achieving isothermal control and thermal load regulation. The electromagnetic properties of superconducting materials are extremely sensitive to temperature changes. During the operation of superconducting systems, certain conditions, such as pulsed excitation and quench loss, cause rapid changes in temperature, pressure, and flow rate. Therefore, cryogenic systems operating in this temperature range not only require high temperature measurement accuracy but also the ability to transiently monitor rapid temperature changes.

[0003] In cryogenic engineering equipment, fluid temperature is often a key operating parameter involved in system control. The applicant's authorized and published modular hydrogen liquefaction system patent CN117168087B proposes a scalable liquid hydrogen production architecture composed of multiple standardized liquefaction modules connected in parallel. This system, after multi-stage cryogenic cooling and conversion of hydrogen to ortho- and para-hydrogen, completes final depressurization liquefaction at a throttle valve. The hydrogen temperature before the throttle valve serves as an important control feedback parameter, used to dynamically adjust the throttle valve opening to maintain stable system operation.

[0004] During the operation of a modular hydrogen liquefaction system, the fluid temperature before throttling may fluctuate rapidly due to the coupling between the start-up and shutdown of the refrigeration unit, load changes, and the regeneration process. If there is a significant response lag in temperature measurement, the measured signal will lag behind the actual operating conditions, potentially leading to overshoot or oscillation in control regulation and affecting the system's operational stability. Therefore, rapid and accurate transient measurement of fluid temperature is of great importance in such cryogenic equipment.

[0005] Existing tooling structures for fluid temperature measurement in cryogenic systems mainly fall into two categories: heat trap sleeve type and tube wall-mounted type. The heat trap sleeve type typically encapsulates the temperature sensor within a pressed rod-shaped metal filler powder and embeds it within a stainless steel sleeve. Temperature measurement is achieved indirectly by inserting the sleeve into the fluid channel and utilizing the heat transfer between the sleeve wall and the metal filler layer. This type of structure is widely used in temperature measurement applications at liquid nitrogen temperatures and above. However, when applied to small-diameter, high-flow-rate fluid environments in cryogenic ranges such as liquid hydrogen or liquid helium, this type of structure presents certain structural reliability issues. Since the free end of the sleeve extends directly into the fluid, its mechanical behavior can be approximated as a cantilever beam. When the fluid bypasses the sleeve, periodic eddies may form downstream, exerting periodic lateral forces on the sleeve. Under certain conditions, this excitation frequency may approach the sleeve's natural frequency, inducing flow-induced vibration or even vortex-induced resonance, increasing the risk of structural fatigue failure. In cryogenic, high-density fluid environments and small-scale pipelines, traditional heat trap sleeve temperature measurement structures have limitations in terms of structural reliability and applicability. Another type of externally mounted structure encapsulates the temperature sensor within a heat sink block, fixing it to the outer wall of the pipe using thermally conductive adhesive, clamps, or welding. It does not directly contact the fluid but relies on the pipe wall's heat conduction for temperature measurement. Both of these structures can achieve basic temperature monitoring under steady-state conditions. However, since existing cryogenic thermometer installation structures are mostly designed for steady-state measurement, these two structures exhibit significant shortcomings when applied to transient temperature change detection in cryogenic systems. The main issue is significant thermal response hysteresis: existing temperature measurement fixtures primarily use thick-walled protective sleeves, indirect contact mounting, or high-heat-capacity encapsulation structures. While these offer mechanical reliability, they exhibit significant response hysteresis in transient measurement scenarios, making it difficult to accurately reflect rapidly changing fluid temperatures. This is especially true in the liquid hydrogen / liquid helium temperature range, where the thermal conductivity of commonly used structural materials such as stainless steel is significantly reduced, resulting in a noticeable thermal response hysteresis.

[0006] In summary, existing cryogenic temperature measurement fixtures have significant limitations in terms of structural design and application performance when applied to transient temperature measurement in cryogenic systems. Therefore, there is an urgent need to develop a thermometer fixture structure specifically designed for transient processes in cryogenic systems. This structure should significantly reduce thermal inertia and thermal resistance while ensuring cryogenic reliability and mechanical strength, and improve the thermal coupling efficiency between the sensor and the fluid. This would enable accurate capture of rapid temperature changes, meeting the engineering requirements of superconducting cryogenic systems and modular hydrogen liquefaction equipment under highly dynamic operating conditions. Summary of the Invention

[0007] To address the problems of severe hysteresis in the thermal response of existing temperature measurement technologies, which prevent accurate reflection of transient changes in fluid temperature, this invention provides a thermometer fixture suitable for transient processes in cryogenic systems. This fixture can significantly reduce the thermal time constant of the temperature measurement system and achieve a rapid and accurate response to the temperature of cryogenic fluids, enabling rapid, accurate, and reliable measurement of transient temperatures of cryogenic fluids.

[0008] A thermometer fixture suitable for transient processes in cryogenic systems includes a front guide tube, a rear guide tube, and a temperature measuring block with a temperature sensor mounting interface. The first end of the front guide tube and the first end of the rear guide tube are respectively connected to process pipelines, and the second end of the front guide tube and the second end of the rear guide tube are respectively connected to the temperature measuring block. A heat exchange channel is opened inside the temperature measuring block, and the heat exchange channel is connected to the internal channels of the front guide tube and the rear guide tube to form a through-flow fluid channel, through which the measured fluid can flow and exchange heat with the temperature measuring block.

[0009] This technical solution adopts a through-structure of "front conduit – temperature measuring block – rear conduit". The temperature measuring block has an independent flow channel inside, and the fluid flows directly through the temperature measuring area. The temperature sensor directly contacts the high thermal conductivity temperature measuring block through the side wall mounting hole, realizing a short-path heat conduction link of "fluid-temperature measuring block-sensor", which significantly reduces the thermal resistance of the heat transfer path and the thermal inertia of the temperature measuring system. The optimized heat exchange flow channel structure increases the heat exchange area between the fluid and the temperature measuring block, improving the heat transfer coefficient. Numerical simulation verification shows that the 99.9% response time of this fixture is only 0.49 s behind the actual fluid temperature, which is about 72% faster than the response speed of the traditional heat trap sleeve fixture and about 80% faster than the external tube wall fixture. It can quickly and accurately capture the transient temperature changes of the fluid, meet the high time resolution temperature measurement requirements of the cryogenic system, and effectively avoid control loop oscillation and overcompensation caused by response lag.

[0010] Preferably, the temperature measuring block is made of pure copper. Pure copper has excellent thermal conductivity, which can quickly transmit temperature changes between the fluid and the sensor, improving the temperature measurement response speed and sensitivity. At the same time, it has excellent processing and welding performance, which facilitates the precision machining of the heat exchange channel and the connection with the conduit. The front and rear conduits are made of the same material as the process pipeline, and the specifications of the connection parts of the front and rear conduits with the process pipeline match the process pipeline, ensuring connection compatibility and sealing reliability under low temperature conditions.

[0011] Preferably, the first ends of the front conduit and the rear conduit have a connection port structure that matches the process pipeline.

[0012] Preferably, when performing temperature detection, the thermometer fixture of the present invention can be installed on the process pipeline of a straight pipe section. Preferably, the front guide tube and the rear guide tube are coaxially arranged. Using this technical solution, the thermometer fixture of the present invention can be quickly and easily connected to the process pipeline of a straight pipe section. Furthermore, the thermometer fixture is symmetrically arranged along the center of the temperature measuring block.

[0013] Furthermore, the second ends of the front and rear ducts (i.e., the connection ends with the temperature measuring block) are expanded tube structures with gradually increasing inner diameters from the inside to the outside, making the cross-sectional area of ​​the heat exchange channel approximately the same as that of the process pipeline. By adopting this technical solution, the connection ends of the front and rear ducts with the temperature measuring block are selected with expanded tube structures, making the cross-sectional area of ​​the heat exchange channel approximately the same as that of the process pipeline. This reduces fluid flow resistance, maintains flow stability, and avoids pressure drop and flow disturbance caused by sudden changes in local flow resistance. This "approximate consistency" can be completely consistent or similar but not completely consistent; for example, the ratio of the cross-sectional area of ​​the heat exchange channel to the cross-sectional area of ​​the process pipeline could be 1:0.8~1.2.

[0014] Furthermore, the heat exchange channel is one of the following: a slotted channel, a wire mesh filled channel (preferably made of pure copper), or a sintered porous medium channel (preferably made of pure copper). Matching the expanded tube structure, this achieves efficient heat transfer while ensuring that the cross-sectional area of ​​the heat exchange channel is approximately the same as the cross-sectional area of ​​the process pipeline, avoiding any impact on the fluid.

[0015] Furthermore, when the heat exchange channel is a slit-type channel, the temperature sensor mounting interface is located in the central region of the slit wall extension direction, aligning the centroid of the installed temperature sensor with the main heat exchange area of ​​the slit. This technical solution shortens the heat conduction path between the sensor and the fluid, reduces the lateral heat diffusion distance, enhances the directional heat conduction effect, and lowers the thermal time constant of the temperature measurement system.

[0016] Furthermore, the heat exchange channel is a slit-type channel, with each slit being an elongated slit structure arranged along the axial direction of the heat exchange channel. Even further, the slit-type channel is composed of multiple parallel elongated slit structures.

[0017] Furthermore, the temperature sensor mounting interface is used to mount the temperature sensor, and the temperature sensor is directly thermally coupled to the temperature measuring block.

[0018] Furthermore, the number of temperature sensor mounting interfaces is at least two, and all temperature sensor mounting interfaces are arranged symmetrically with respect to the central axis of the heat exchange channel. This technical solution enables multi-point co-position temperature measurement of the same fluid cross-section, which not only improves measurement accuracy through cross-calibration of multi-sensor data but also achieves redundant arrangement. Even if a single sensor fails, the system can still maintain effective temperature measurement, enhancing the fault tolerance and data reliability of the temperature measurement system.

[0019] Preferably, heat insulation gaskets are provided between the temperature measuring block and the front and rear conduits, and sealing structures are provided between the heat insulation gaskets and the temperature measuring block and the front and rear conduits.

[0020] Preferably, the connection between the front and rear conduits and the temperature measuring block is either welding or flange connection. When welding is used, vacuum brazing is preferred to achieve an integrated connection between the temperature measuring block and the conduit, thereby improving structural rigidity. When flange connection is used, heat insulation gaskets are provided between the temperature measuring block and the front and rear conduits. The heat insulation gaskets are made of low-temperature compatible non-metallic material, and a sealing structure is provided at the heat insulation gaskets. The heat insulation gaskets can reduce the heat conduction between the process pipeline and the temperature measuring block, reduce the equivalent thermal inertia of the temperature measuring block, and the sealing structure ensures the airtightness of the fluid system.

[0021] Preferably, the connection method between the front guide tube, the rear guide tube and the process pipeline is one of welding, compression fitting, metal-face sealing, or flange connection. The connection method can be flexibly selected according to the specifications and operating conditions of the process pipeline to ensure sealing performance and connection reliability under low temperature conditions.

[0022] Preferably, the connection between the temperature measuring block and the front and rear conduits is heat-insulated to further reduce the thermal interference of the process pipeline on the temperature measuring block, so that the temperature measuring block can more sensitively reflect the true transient temperature changes of the fluid.

[0023] Preferably, the structure of the temperature sensor mounting interface matches the packaging form of the low-temperature temperature sensor, including one or both of the following: a light-hole interface for inserting a rod-shaped packaged sensor and a threaded hole interface for mounting a disc-shaped packaged sensor. Using this technical solution, while maintaining the consistency of the main structure of the temperature measuring block, a suitable interface scheme can be selected according to actual temperature measurement needs, adapting to various low-temperature thermometers such as the Lake Shore Cernox® AA type rod sensor and the Lake Shore Cernox® CU type disc sensor, thus improving the adaptability and structural flexibility of the tooling.

[0024] Preferably, a low-temperature compatible thermally conductive material is used to fill the space between the temperature sensor and its mounting interface. This material is either thermally conductive adhesive or low-temperature thermally conductive grease. This technical solution improves the thermal contact conditions between the sensor and the temperature measuring block, reduces interfacial thermal resistance, ensures stable and rapid thermal coupling between the sensor and the temperature measuring block, and further enhances the temperature measurement response speed and accuracy.

[0025] This technical solution features two centrally symmetrical temperature sensor mounting holes on the side wall of the temperature measuring block, enabling dual-point co-position temperature measurement of the same fluid cross-section. This allows for simultaneous redundant temperature monitoring and cross-calibration comparison. Compared to traditional heat trap sleeve-type structures, which struggle to achieve dual-probe arrangement, this technical solution improves the system's reliability and fault tolerance in low-temperature measurements.

[0026] The beneficial effects and technical advantages of this technical solution can be summarized as follows:

[0027] (1) The transient thermal response speed, accuracy and sensitivity are greatly improved.

[0028] This technical solution effectively reduces the thermal response time constant and the thermal resistance of the heat transfer path by directly coupling the pure copper temperature sensing block with the fluid. Simultaneously, the slit-type flow channel design significantly increases the heat exchange area between the fluid and the temperature sensing block, effectively improving the heat transfer coefficient. This structure enables the temperature sensor to quickly and accurately capture transient changes in fluid temperature, resulting in a significant improvement in transient thermal response speed, measurement accuracy, and sensitivity.

[0029] As shown in the numerical model description and verification results report below, compared with traditional heat trap sleeve type and tube wall externally attached type structures, the transient response time of this scheme is shortened by more than 70%, and the time lag of the temperature signal is significantly reduced (numerical model verification results show that the response time lags only by about 0.49 seconds behind the actual fluid temperature, which is far superior to the traditional structure). This advantage ensures high time resolution and dynamic tracking capability of temperature measurement, significantly improves the accuracy and sensitivity of measurement, effectively avoids control loop oscillation and overcompensation caused by response lag, and meets the high dynamic temperature monitoring requirements of cryogenic transient processes, especially high-temperature superconducting magnet cryogenic systems and modular hydrogen liquefaction systems in the 20–30 K temperature range. It is particularly suitable for fluid temperature measurement scenarios with rapid temperature fluctuations, such as fluids before throttle valves and superconducting magnet cooling media.

[0030] This technical solution optimizes the heat transfer path and flow channel structure, achieving a comprehensive improvement in transient thermal response speed, temperature measurement accuracy, and sensitivity. It provides a real-time and accurate temperature monitoring foundation for cryogenic systems and significantly enhances closed-loop control performance and system stability.

[0031] (2) Enhanced fault tolerance and data credibility

[0032] By setting multiple centrally symmetrical temperature sensor mounting interfaces on the side wall of the temperature measuring block, multi-point co-position temperature measurement of the same fluid cross-section can be achieved. This not only improves measurement accuracy through cross-calibration and comparison of data from multiple sensors, but also achieves temperature measurement redundancy. When a single sensor drifts or fails, the system can still maintain valid data output. Compared with the heat trap sleeve type, although this technical solution does not change the structural maintenance conditions under vacuum insulation, it enhances the fault tolerance and data reliability of the temperature measuring system without damaging the sealing system.

[0033] (3) The structure is stable and has excellent vibration resistance.

[0034] This technical solution adopts an axially symmetrical layout design, with the temperature measuring block and the conduit integrated through vacuum brazing. The flow channel ends are smoothly transitioned via an expanded tube structure, ensuring that the cross-sectional area of ​​the flow channel within the temperature measuring block is approximately the same as that of the process piping. This maintains the continuity of fluid flow and the stability of velocity distribution, avoiding pressure drop and flow disturbance caused by sudden changes in local flow resistance. Compared to heat trap sheathed structures, this design combines good mechanical rigidity with flow stability, making it suitable for low-temperature, high-velocity, or high-density fluid environments. The thermal insulation treatment at the connection between the temperature measuring block and the conduit, along with the direct temperature measurement method of the temperature measuring block, effectively avoids measurement distortion caused by factors such as heat leakage from the pipe wall and flow field interference, improving the accuracy of the measurement results.

[0035] (4) Strong applicability and integration

[0036] The front and rear guide tubes of this fixture are matched with the process piping in terms of material and specifications, and the connection method is flexible. The temperature sensor mounting interface can be designed as a smooth hole or a threaded hole according to the sensor packaging form, which is compatible with a variety of low-temperature thermometers. This technical solution can be modularized according to the process piping of different diameters, with standardized interface form, and is compatible with temperature sensors with various packaging methods. Furthermore, the heat-conducting materials and installation methods can be flexibly selected according to the working conditions, which is convenient for mass production and integrated installation of low-temperature systems, and has a wide range of applications. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram (cross-sectional view) of the overall structure of the thermometer fixture of the present invention applicable to transient processes in cryogenic systems.

[0039] Figure 2 This is a structural schematic diagram of one of the implementation schemes; the diagram shows a vacuum brazing integrated connection structure, with the front and rear conduits welded to the temperature measuring block, and the connection ends are enlarged; where A is a schematic diagram of the overall three-dimensional structure; B is an isometric sectional view; C is an orthogonal sectional view with section lines corresponding to B;

[0040] Figure 3 for Figure 2 The schematic diagram of the temperature measuring block in the embodiment shown is as follows: where A is an isometric sectional view and B is an orthogonal sectional view with section lines.

[0041] Figure 4 The diagram shows the structure of the second implementation scheme: the diagram shows a flange connection structure, with heat insulation gaskets between the temperature measuring block and the front and rear conduits, the flange being fixed by fasteners, and a threaded hole interface on the top of the temperature measuring block; where A is the overall three-dimensional structural schematic diagram; B is an isometric sectional view; C is the orthogonal sectional view with section lines corresponding to B;

[0042] Figure 5 To verify the model diagrams (cross-sectional views): A is a structural schematic diagram corresponding to Example 1; B is a structural schematic diagram of the externally attached tube wall thermometer tooling of the control scheme; C is a structural schematic diagram of the heat trap sleeve thermometer tooling of the control scheme.

[0043] Figure 6 The simulated fluid temperature and sensor response temperature curves are shown over time.

[0044] In the diagram: 11 - front conduit, 12 - rear conduit, 13 - temperature measuring block, 14 - temperature sensor mounting interface, 31 - heat exchange channel, 41 - flange, 42 - heat insulation gasket. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] like Figure 1 The diagram shows a schematic of a thermometer fixture applicable to transient processes in a cryogenic system, as per the present invention. The fixture includes a front guide tube 11, a rear guide tube 12, a temperature measuring block 13, and a temperature sensor mounting interface 14. One end of the front guide tube 11 and the rear guide tube 12 are connected to a process pipeline, and the other end is connected to the temperature measuring block 13. The temperature measuring block 13 has internal heat exchange channels to ensure sufficient heat exchange between the measured fluid and the measuring fluid as it flows through the block. A temperature sensor mounting interface 14 is provided on the temperature measuring block 13 for mounting a temperature sensor to achieve real-time measurement of the fluid temperature within the process pipeline. Overall, the front and rear guide tubes are connected to both ends of the temperature measuring block, and the temperature sensor mounting interface is located on the side wall of the temperature measuring block, corresponding to the internal heat exchange channels.

[0047] Preferably, the front conduit 11 and the rear conduit 12 can be made of the same material as the process pipeline and maintain the same specifications at the connection points with the process pipeline. For example, a standard interface structure that facilitates connection with the process pipeline can be used. The front conduit 11 and the rear conduit 12 can be fixed to the corresponding process pipeline using existing connection methods. The connection methods can be welding, compression fitting, metal-face sealing, flange connection, or other effective connection methods to ensure sealing performance and connection reliability under low-temperature conditions.

[0048] The first ends of the front conduit 11 and the rear conduit 12 are generally connected to the process pipeline by welding. When the connection is made by welding, the second ends of the front conduit 11 and the rear conduit 12 are integrated with the temperature measuring block 13 by vacuum brazing to form a through-flow fluid channel.

[0049] Preferably, the temperature measuring block 13 can be made of pure copper. The advantages of using pure copper are:

[0050] 1. Excellent thermal conductivity: Pure copper has a thermal conductivity second only to silver, but its cost is much lower than silver. It can quickly transmit temperature changes between fluids and sensors, improving temperature measurement response speed and sensitivity.

[0051] 2. Excellent processing and welding performance. Pure copper has good ductility and plasticity, which facilitates the precision machining of heat exchange channels and welding with front / rear ducts.

[0052] Preferably, the temperature measuring block 13 can be connected to the front conduit 11 and the rear conduit 12 by welding, flange connection or other effective connection methods to ensure sealing performance and connection reliability under low temperature conditions.

[0053] More preferably, a heat insulation structure or heat insulation treatment can be provided at the connection between the temperature measuring block 13 and the front conduit 11 and the rear conduit 12 to reduce the heat conduction effect between the process pipeline and the temperature measuring block. Through heat insulation treatment, the influence of thermal disturbance from the pipeline side can be effectively reduced, making the temperature measuring block more sensitive to the true transient temperature change of the fluid, thereby improving the temperature measurement response speed and measurement accuracy.

[0054] Preferably, the heat exchange channel inside the temperature measuring block 13 can be a slit-type channel, a pure copper wire mesh-filled channel, a pure copper sintered porous medium channel, or other equivalent structures, to achieve sufficient heat exchange and stable flow of the fluid within the temperature measuring area, thereby improving the response sensitivity and measurement accuracy of the temperature measurement. Figure 2As shown, a heat exchange channel is provided inside the temperature measuring block 13, through which the fluid being measured exchanges heat with the temperature measuring block 13. The heat exchange channel is a slit-type channel structure arranged axially along the temperature measuring block 13, with a long and narrow cross-section. When using the slit-type channel structure, the temperature sensor mounting interface 14 is arranged in the central area of ​​the slit wall extension direction (or projection area), so that the centroid of the installed temperature sensor is basically aligned with the main heat exchange area of ​​the slit in this extension direction, thereby shortening the heat conduction path between the sensor and the fluid.

[0055] Preferably, two temperature sensor mounting interfaces 14 can be provided on the temperature measuring block 13. More preferably, the two mounting interfaces are symmetrically arranged with respect to the central axis of the flow channel, thereby realizing multi-point co-position temperature measurement. This not only improves the accuracy and reliability of temperature measurement, but also enables redundant arrangement to ensure that effective temperature measurement can still be maintained when a single sensor fails, thereby enhancing the safety and stability of the system.

[0056] Preferably, the temperature sensor mounting interface 14 can be designed with different structural forms depending on the temperature sensor packaging method used, so as to achieve structural matching with different types of low-temperature thermometers. Specifically, one structural form is to provide a light hole interface on the side wall of the temperature measuring block for inserting devices such as Lake Shore Cernox thermometers. ® AA-type rod-shaped packaged sensor; another structural form has a threaded hole interface on the top of the temperature sensing block for mounting Lake Shore Cernox sensors. ® A CU-type disc-shaped packaged sensor. Through differentiated design of the interface structure, while maintaining the consistency of the main structure of the temperature measuring block, a suitable interface scheme can be selected according to the actual temperature measurement requirements. This enables reliable installation and stable thermal coupling of low-temperature thermometers with different packaging forms, thereby improving the adaptability and structural flexibility of the tooling.

[0057] More preferably, the space between the temperature sensor and the temperature sensor mounting interface 14 can be filled with thermally conductive adhesive, low-temperature thermally conductive grease, or other low-temperature compatible thermally conductive materials to improve the thermal contact conditions between the sensor and the temperature measuring block, reduce the interface thermal resistance, and ensure that sensors of different packaging forms can obtain stable and fast thermal coupling, thereby improving the temperature measurement response speed and measurement accuracy.

[0058] Example 1:

[0059] like Figure 2The diagram shows a schematic of a thermometer fixture suitable for transient processes in a cryogenic system. In this embodiment, the front guide tube 11 and the rear guide tube 12 are made of the same material as the process piping. The front guide tube 11 and the rear guide tube 12 are connected to the process piping by welding. The temperature measuring block 13 is made of pure copper, and the temperature measuring block 13 is connected to the front guide tube 11 and the rear guide tube 12 by vacuum brazing to form a stable sealing structure and ensure connection reliability under cryogenic conditions.

[0060] In this embodiment, at the connection points between the temperature measuring block 13 and the front conduit 11 and the rear conduit 12, the front conduit 11 and the rear conduit 12 are expanded. Specifically, the second ends of the front conduit 11 and the rear conduit 12 have a flared structure with an inner diameter gradually increasing from the inside to the outside. This ensures that the cross-sectional area of ​​the flow channel is approximately the same as the cross-sectional area of ​​the process pipeline, thereby reducing flow resistance while maintaining the temperature measurement effect, thus balancing temperature measurement performance and system flow stability. Furthermore, both the front conduit 11 and the rear conduit 12 include a connecting section a that connects to the process pipeline and a flared section b that connects to the temperature measuring block and has the aforementioned flared structure.

[0061] like Figure 3 As shown, the temperature measuring block 13 has an axially continuous slit-type heat exchange channel 31 inside. The heat exchange channel is connected to the internal channels of the front guide tube 21 and the rear guide tube 22. When the measured fluid flows through this channel, it undergoes sufficient heat exchange with the pure copper temperature measuring block 13. The heat exchange channel is a slit-type channel structure arranged axially along the temperature measuring block 13, and its cross-section is long and narrow. When using the slit-type channel structure, the temperature sensor mounting interface 14 is arranged in the central area of ​​the slit wall extension direction, so that the centroid of the installed temperature sensor (temperature sensing element) is basically aligned with the main heat exchange area of ​​the slit in this extension direction, thereby shortening the heat conduction path between the sensor and the fluid. By arranging the temperature sensing core area of ​​the sensor in a position directly opposite the high heat flux density area of ​​the slit wall, the lateral heat diffusion distance can be reduced, the directional heat conduction effect can be enhanced, and heat can be quickly transferred from the fluid to the sensor in an approximately linear direction, further reducing the thermal time constant of the temperature measuring system and improving the response speed and measurement accuracy to transient temperature changes.

[0062] Two temperature sensor mounting interfaces 14 are provided on the temperature measuring block 13. The two mounting interfaces are axially symmetrical with respect to the central axis of the flow channel to achieve multi-point co-position temperature measurement and redundant arrangement. Depending on the different thermometer packaging forms, the temperature sensor mounting interfaces 14 can be designed with different structural forms. One form is a light-perforated interface on the side wall of the temperature measuring block for inserting a rod-shaped packaged low-temperature thermometer; another form is a threaded hole interface on the top of the temperature measuring block for installing a disc-shaped packaged low-temperature thermometer. In this embodiment, a light-perforated interface is provided on the side wall of the temperature measuring block 13 for inserting a rod-shaped packaged temperature sensor. Low-temperature thermally conductive grease is filled between the temperature sensor and the interface hole wall to achieve rapid and stable thermal coupling between the thermometer and the temperature measuring block 13.

[0063] The tooling in this embodiment adopts an integrated connection structure with vacuum brazing, which has high mechanical rigidity and excellent vibration resistance. The combination of the slit-type flow channel and the pure copper temperature measuring block realizes rapid thermal coupling between the fluid and the sensor. The symmetrical design of the dual optical aperture interface realizes redundant temperature measurement. It is suitable for superconducting cryogenic systems in the 20–30 K temperature range with high requirements for structural sealing and vibration resistance.

[0064] Example 2:

[0065] like Figure 4 The diagram shown is a schematic of another type of thermometer fixture suitable for transient processes in cryogenic systems. This embodiment has the same basic structure as Embodiment 1, except that the temperature measuring block 13 is connected to the front guide tube 11 and the rear guide tube 12 using a flange connection structure.

[0066] Specifically, flanges 41 are provided at the ends of the front conduit 11 and the rear conduit 12, respectively. The temperature measuring block 13 is connected to the front conduit 11 and the rear conduit 12 through the flanges 41, respectively. A heat insulation gasket 42 is provided between the temperature measuring block 13 and the flange end faces of the front conduit 11 and the rear conduit 12. The heat insulation gasket 42 is used to reduce the heat conduction between the temperature measuring block 13 and the front and rear conduits while ensuring the structural connection, thereby reducing thermal interference from the process piping side. Through thermal isolation design, the equivalent thermal inertia of the temperature measuring block 13 can be reduced, making it more sensitive to transient temperature changes of the fluid.

[0067] The flanges on both sides are connected and fixed by fasteners through the connection holes that penetrate the temperature measuring block 13. The connection holes are located inside the temperature measuring block 13 and are independent of the flow channel structure to ensure structural strength and sealing reliability.

[0068] A sealing structure (such as a sealing ring or a sealing gasket) is provided at the heat insulation gasket 42 to ensure the airtightness of the fluid system. The heat insulation gasket 42 can be made of a low-temperature compatible non-metallic material, and a sealing ring or sealing gasket is used in conjunction with its sealing surface to balance heat insulation performance and sealing performance.

[0069] Since the flange connection structure forms a through connection hole inside the temperature measuring block 13, the installation method of the temperature sensor can be adapted according to the sensor packaging form. When a rod-shaped packaged temperature sensor is used, the temperature sensor mounting interface is preferably located on the upper wall of the temperature measuring block 13, and the sensor is inserted through a light hole; when a disc-shaped packaged temperature sensor is used, the portion of the temperature measuring block that extends above the flange height can be locally machined to form a mounting platform, and a threaded interface can be provided at this location to realize the installation of the disc-shaped packaged sensor.

[0070] In this embodiment, the temperature sensor mounting interface is a threaded hole interface, located on the mounting platform of the temperature measuring block 13 above the flange, for mounting a disc-shaped packaged low-temperature thermometer. Thermally conductive adhesive is filled between the thermometer and the threaded hole interface. The flange connection structure facilitates the disassembly and maintenance of the tooling. The setting of the heat insulation gasket further improves the sensitivity of the temperature measuring block to transient temperature changes of the fluid, making it suitable for fluid temperature measurement before the throttle valve in a modular hydrogen liquefaction system with a temperature range of 20–30 K.

[0071] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All equivalent structural transformations made based on the contents of the present invention specification and drawings under the design concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

[0072] The following is about Figure 2 The working performance of the thermometer fixture with the structure shown was verified:

[0073] I. Model Objective:

[0074] To quantitatively analyze the thermal response characteristics of three different types of thermometer fixtures under low-temperature transient conditions and to verify the advantages of the low-temperature thermometer fixture described in this invention in improving thermal response efficiency, a three-dimensional solid model was established and CFD numerical calculations were performed using fluid-structure interaction. Temperature response simulations were conducted on different structural forms (heat trap sleeve type, tube wall external type, and the low-temperature thermometer fixture described in this invention) during the linear change of fluid temperature.

[0075] II. Model Establishment and Parameter Setting:

[0076] 2.1 Three-dimensional geometric model

[0077] This study establishes a three-dimensional geometric model based on SolidWorks. When simplifying the geometric structure, the main heat transfer paths and contact surface features are retained, while secondary structural details are ignored to reduce computational load. The model is shown in Figure 5. In the figure, A, B, and C represent the low-temperature thermometer fixture, the tube-wall-mounted thermometer fixture, and the heat trap sleeve thermometer fixture models described in this invention, respectively; 51, 52, and 53 represent the temperature measurement points of the corresponding thermometer fixtures.

[0078] 1. The low-temperature thermometer fixture described in this invention:

[0079] Its main parameters / dimensions are shown in the table below:

[0080]

[0081] 2. Fixture for externally mounted tube thermometers

[0082] Its main parameters / dimensions are shown in the table below:

[0083]

[0084] 3. Fixture for heat trap sleeve thermometer

[0085]

[0086] 2.2 Physical Properties and Assumptions

[0087] The process piping uses helium gas at 20K and 20 bara. The main thermophysical properties are shown in the table below:

[0088]

[0089] 2.3 Boundary and Initial Conditions

[0090] The fluid inlet is equipped with a linear heating boundary, the outer wall is insulated, and the sensor end is in complete contact with the inner wall of the sleeve.

[0091] Fluid mass flow rate: 20 g / s.

[0092] Fluid temperature increases linearly with time:

[0093]

[0094] This indicates the process of temperature change of helium gas in a cryogenic system due to disturbance.

[0095] III. Calculation Definitions and Output Indicators

[0096] 3.1 Transient temperature distribution:

[0097] Solve for the internal temperature field of each model to obtain the temperature change curves of each temperature sensor placement point over time.

[0098] 3.2 (99.9% response time) definition:

[0099] For a given position, define For the temperature at this point to first reach its initial value To the final steady-state temperature The time it takes for the change to reach 99.9% of its range, i.e.:

[0100]

[0101] In this model, the fluid heating stage is 10–30 s, so the ideal hysteresis-free measuring point should reach 29.99 K at t ≈ 29.98 s.

[0102] IV. Simulation Results and Analysis:

[0103] 4.1 Temperature response curve:

[0104] Figure 6 The simulated fluid temperature and sensor response temperature curves over time are shown, with the left graph representing the global temperature change and the right graph showing a magnified view of the near-steady-state phase. It can be seen that the fluid temperature increases linearly according to the input, while the sensor temperature exhibits significant time lag and amplitude attenuation.

[0105] The table below shows the 99.9% response time simulation results for different thermometer fixtures. ):

[0106]

[0107] Quantitative comparison results show that, under the boundary conditions corresponding to their respective structures, the response time (τ) for the fluid's own temperature to reach a steady state is... 999 The transient thermal response time is 29.98 s; when using a slit-type pure copper fixture, the response time is 30.47 s, only 0.49 s behind the fluid; while the traditional heat trap sleeve type and the externally attached tube wall type fixtures are 31.73 s and 32.94 s respectively, 1.75 s and 2.47 s behind the fluid. It can be seen that the transient thermal response speed of the structure described in this invention is about 72% higher than that of the heat trap sleeve type and about 80% higher than that of the externally attached type, significantly reducing the time delay of the temperature signal.

[0108] It should be noted that for the heat trap sleeve thermometer fixture, the vertical distance of its fluid-solid heat transfer interface is 1.85 mm, which is less than the 3 mm vertical distance of the fluid-solid heat transfer interface of the thermometer fixture described in this invention. This structural condition is beneficial to shortening the heat conduction path and increasing the heat transfer rate to a certain extent. However, under this relatively favorable heat transfer condition, the simulated transient thermal response performance is still lower than that of the low-temperature thermometer fixture described in this invention.

[0109] VI. Conclusion and Comprehensive Analysis

[0110] This technical solution significantly reduces the thermal resistance of the heat transfer path and the thermal response time constant by employing a structure design that directly couples a high thermal conductivity pure copper temperature measuring block with the fluid. Compared to traditional heat trap sleeve-type and tube wall-mounted thermometer fixtures, this invention effectively increases the heat exchange area between the fluid and the temperature measuring block through a slit-type flow channel structure, effectively improving the heat transfer coefficient at the fluid-solid interface. This allows the temperature measuring element to respond quickly to changes in fluid temperature, achieving high-precision, low-hysteresis transient temperature measurement.

[0111] Numerical simulation results show that, under the condition of linearly increasing system temperature from 20 K to 30 K, the response time for the fluid temperature to reach steady state is 29.98 s. The response time of the slit-type pure copper fixture described in this invention is 30.47 s, with a lag of only 0.49 s. In contrast, the heat trap sleeve type and the externally attached tube wall type fixtures lag by 1.75 s and 2.47 s, respectively. Therefore, the transient thermal response speed of the thermometer fixture described in this invention is approximately 72% faster than the heat trap sleeve type and approximately 80% faster than the externally attached tube wall type, significantly reducing the time delay of the temperature signal.

[0112] By leveraging the synergistic effect of high thermal conductivity thermoelectric material and a slit-type flow channel heat exchange design, this invention achieves rapid thermal coupling between the fluid and the sensing element, avoiding the temperature response lag caused by thick-walled sleeves or thermal inertia of the tube walls in traditional structures. This thermometer fixture can operate stably in low-temperature vacuum environments and is particularly suitable for real-time measurement and control of transient temperature changes in high-temperature superconducting magnets, liquid hydrogen / liquid helium refrigeration systems, and other cryogenic devices. It boasts significant advantages such as fast thermal response, high measurement accuracy, and compact structure.

Claims

1. A thermometer fixture suitable for transient processes in cryogenic systems, characterized in that, It includes a front conduit, a rear conduit, and a temperature measuring block with a temperature sensor mounting interface; the first end of the front conduit and the first end of the rear conduit are respectively used to connect to the process pipeline, and the second end of the front conduit and the second end of the rear conduit are respectively connected to the temperature measuring block; the temperature measuring block has a heat exchange channel inside, which is connected to the internal channels of the front conduit and the rear conduit to form a through-flow fluid channel, through which the fluid being measured flows and exchanges heat with the temperature measuring block.

2. The thermometer fixture for transient processes in cryogenic systems according to claim 1, characterized in that, The second ends of the front and rear ducts are expansion tube structures with gradually increasing inner diameters from the inside to the outside, so that the cross-sectional area of ​​the heat exchange channel is approximately the same as that of the process pipeline.

3. The thermometer fixture for transient processes in cryogenic systems according to claim 1, characterized in that, The temperature measuring block is provided with heat insulation gaskets between itself and the front and rear conduits, and the heat insulation gaskets and the temperature measuring block are provided with sealing structures between themselves and the front and rear conduits.

4. The thermometer fixture for transient processes in cryogenic systems according to claim 1, characterized in that, The heat exchange channel is one of the following: slit channel, wire mesh filled channel, or sintered porous medium channel.

5. The thermometer fixture for transient processes in cryogenic systems according to claim 4, characterized in that, When the heat exchange channel is a slit channel, the temperature sensor mounting interface is arranged in the central area of ​​the slit wall extension direction, so that the centroid of the installed temperature sensor is aligned with the main heat exchange area of ​​the slit.

6. The thermometer fixture for transient processes in cryogenic systems according to claim 1, characterized in that, The temperature sensor mounting interface is used to mount the temperature sensor, and the temperature sensor and the temperature measuring block are directly thermally coupled.

7. The thermometer fixture for transient processes in cryogenic systems according to claim 1, characterized in that, The structure of the temperature sensor mounting interface is matched with the packaging form of the low-temperature temperature sensor, including one or both of the following: an optical hole interface for inserting a rod-shaped packaged sensor and a threaded hole interface for mounting a disc-shaped packaged sensor.

8. The thermometer fixture for transient processes in cryogenic systems according to claim 1, characterized in that, The front and rear guide tubes are coaxially arranged, and the thermometer fixture is symmetrically arranged along the center of the temperature measuring block.

9. The thermometer fixture for transient processes in cryogenic systems according to claim 1, characterized in that, The number of temperature sensor mounting interfaces is at least two, and all temperature sensor mounting interfaces are arranged in a centrally symmetrical manner with respect to the central axis of the heat exchange channel.

10. The thermometer fixture for transient processes in cryogenic systems according to claim 1, characterized in that, The first end of the front and rear conduits has a connection port structure that matches the process pipeline.

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