Probe-type optical fiber temperature sensor based on multi-layer material encapsulation and applications thereof

Abstract

The present application relates to a probe type optical fiber temperature sensor based on a multi-layer material package and its application, and relates to the technical field of sensors. The sensor comprises a package shell, a heat dissipation structure and a fiber grating assembly. The package shell comprises an outer tube shell, a first columnar core and a second columnar core which are spliced in the outer tube shell in the axial direction, and the thermal conductivity of the first columnar core is lower than that of the second columnar core. The heat dissipation structure is at least partially embedded in the interior of the package shell and is used for guiding the heat in the interior of the package shell at the radial section where the grating is located to the outside. The fiber grating assembly is arranged in the interior of the package shell and comprises an optical fiber and a grating written on the optical fiber. The present application adopts a multi-layer material axial splicing package, combines the active heat dissipation of the heat dissipation structure, and enables the thermal regenerated fiber grating to work stably for a long time in an ultra-high temperature environment. Simulation experiments verify that the package structure can withstand 1400 DEG C ultra-high temperature and realize stable temperature measurement, breaks through the temperature measurement bottleneck of the practical application of the thermal regenerated fiber grating, solves the problem of long-term stable monitoring in a high temperature environment, and can be widely applied to temperature monitoring in an ultra-high temperature environment such as a gasifier furnace.

Description

Technical Field

[0001] This invention belongs to the field of sensors, specifically relating to a probe-type fiber optic temperature sensor based on multilayer material encapsulation and its applications. Background Technology

[0002] In large-scale coal-water slurry gasification industrial sites, the gasifier is considered a core piece of equipment, and its operating efficiency directly impacts economic benefits. To ensure the safety and reliability of the production process, it is typically necessary to monitor the internal temperature of the gasifier to assess its operating status and prevent major accidents caused by excessively high temperatures. During normal operation, the internal temperature of the gasifier can reach as high as 1000℃ to 1700℃. Excessively high temperatures will shorten the service life of the gasifier, increase equipment insecurity, and potentially lead to serious accidents. Therefore, ultra-high temperature monitoring is particularly important.

[0003] However, existing technologies have the following drawbacks when applied to temperature monitoring in ultra-high temperature gasifiers: (1) In harsh environments with high temperature and high pressure, the reliability of temperature sensing by traditional thermocouples is limited. Due to their inherent conductivity, thermocouples are susceptible to electromagnetic interference, which introduces errors into the measurement results. (2) Infrared spectroscopy provides a non-contact method for measuring temperatures above 1400℃. However, dust particles and gas absorption in the furnace can interfere with the infrared signal, often leading to increased temperature measurement errors and reduced spatial resolution. (3) Theoretical calculations and intelligent algorithms indirectly infer temperature through models based on combustion mechanisms or data-driven methods (such as temperature compensation schemes based on deep learning), thereby overcoming hardware limitations. However, these methods are highly dependent on accurate boundary condition inputs and usually have limited generalization ability under complex and dynamic conditions. (4) Thermal regeneration fiber gratings are prone to softening and failure in environments above 1200℃, and their sensing performance will drop sharply, making them difficult to use as an effective means for long-term health monitoring.

[0004] Therefore, there is an urgent need for a new type of temperature sensor that can break through the temperature measurement limit of thermally regenerated fiber Bragg gratings and adapt to harsh ultra-high temperature environments. Summary of the Invention

[0005] The purpose of this invention is to provide a probe-type fiber optic temperature sensor based on multilayer material encapsulation and its application, in order to overcome the above-mentioned technical defects.

[0006] To address the aforementioned technical problems, this invention provides a probe-type fiber optic temperature sensor based on multilayer material encapsulation, comprising: The encapsulation housing includes an outer tube shell and a first columnar core and a second columnar core axially spliced ​​within the outer tube shell, wherein the thermal conductivity of the first columnar core is lower than that of the second columnar core. A heat dissipation structure, at least partially embedded inside the encapsulation housing, is used to guide the heat inside the encapsulation housing at the radial cross-section where the grating is located to the outside. A fiber optic grating assembly, disposed inside the encapsulation housing, includes an optical fiber and a grating inscribed on the optical fiber.

[0007] According to the probe-type fiber optic temperature sensor based on multi-layer material encapsulation, the outer shell is a corundum tube, the first columnar core is a thermally protective material column, and the second columnar core is a highly oriented pyrolytic graphite column. The first columnar core and the second columnar core are fitted and spliced ​​together along their axial end faces, and both have the same outer diameter; The inner wall of the outer shell is tightly wrapped and fitted with the outer walls of the first columnar core and the second columnar core, and the outer shell wraps the entire first columnar core and at least a portion of the second columnar core.

[0008] According to the probe-type fiber optic temperature sensor based on multi-layer material encapsulation, the first columnar core is located at the front end of the outer shell and is used to approach the high-temperature heat source being measured. The second columnar core is located at the rear end of the outer shell, and is intended to be close to the heat dissipation end.

[0009] According to the probe-type fiber optic temperature sensor based on multi-layer material encapsulation, the thermal protection material of the first columnar core is ceramic fiber, and its length is greater than that of the second columnar core. The axial thermal conductivity of the second columnar core is greater than its radial thermal conductivity.

[0010] According to the probe-type fiber optic temperature sensor based on multi-layer material encapsulation, both the first columnar core and the second columnar core have multiple through or non-through mounting channels along the axial direction. The heat dissipation structure includes a heat dissipation rod that is at least partially embedded in the mounting hole.

[0011] According to the probe-type fiber optic temperature sensor based on multilayer material encapsulation, the mounting channel includes a central channel that is interconnected at the central axis of the first columnar core and the second columnar core, and a plurality of peripheral channels arranged around the central channel. The heat sink includes a first heat sink embedded in the central channel and multiple second heat sinks embedded in the peripheral channels; The first heat sink is a hollow structure, and its axial hollowness forms an optical fiber channel for accommodating the optical fiber temperature sensing component. The optical fiber channel is a partially penetrating blind hole structure.

[0012] According to the probe-type fiber optic temperature sensor based on multi-layer material encapsulation, both the first heat sink and the second heat sink are made of copper and are at least partially exposed outside the outer shell, and are cooled by forced air cooling.

[0013] According to the probe-type fiber optic temperature sensor based on multi-layer material encapsulation, the grating is a thermally regenerated fiber optic grating, and there is only one such grating, which is inscribed in the middle of the fiber, and its grating region is located inside the first columnar core.

[0014] According to the probe-type fiber optic temperature sensor based on multi-layer material encapsulation, the fiber optic cable is covered with an alumina sleeve. One end of the alumina sleeve is fixed to the fiber optic cable with high-temperature ceramic adhesive, and the other end of the alumina sleeve is sealed with high-temperature ceramic adhesive to form a single-head dispensing fixing structure.

[0015] This invention also provides an application of a probe-type fiber optic temperature sensor based on multilayer material encapsulation in gasifier furnace temperature measurement.

[0016] The beneficial effects of this invention are as follows: (1) This invention employs a multi-layer material encapsulation structure. Through the axial splicing design of thermally protective material pillars and highly oriented pyrolytic graphite pillars, as well as the embedded heat-dissipating copper rod array and forced air cooling, the external ultra-high temperature environment (1000℃-1700℃) is attenuated to the temperature range that the internal fiber grating can withstand. The thermally regenerated fiber grating does not need to directly contact the ultra-high temperature environment, and can indirectly realize the temperature measurement of the gasifier furnace by measuring the attenuated temperature, thus solving the problem of long-term stable monitoring under high temperature environment.

[0017] (2) This invention achieves stable and predictable temperature field within the encapsulation structure through axial functional partitioning of thermally protective material pillars (low thermal conductivity) and highly oriented pyrolytic graphite pillars (high axial thermal conductivity), as well as active heat dissipation via a copper rod array. The grating region of the fiber optic grating is located inside the first columnar core, avoiding the direct impact of external environmental fluctuations on the measurement results and ensuring the stability and repeatability of long-term temperature measurements.

[0018] (3) This invention uses a fiber optic grating as the temperature sensing element, and the signal is transmitted through optical fiber, which is inherently safe and unaffected by electromagnetic interference. Compared with the temperature measurement error of traditional thermocouples in strong electromagnetic environments such as gasifiers, this invention has significant advantages.

[0019] (4) The present invention uses corundum tube as outer shell, which has the characteristics of high hardness, high temperature resistance and corrosion resistance; the heat protection material column and the highly oriented pyrolytic graphite column are attached and spliced ​​along the axial end face, and the outer shell tightly wraps around it to form an integrated package. The overall structure is compact and has high mechanical strength, and can be directly inserted into the gasifier furnace for long-term online monitoring without the need for additional protection devices.

[0020] (5) The optical fiber of the present invention is covered with a corundum sleeve and fixed by single-head glue application (one end fixed and the other end suspended and sealed), which effectively releases the thermal expansion stress between the optical fiber and the corundum sleeve, avoids optical fiber breakage under high temperature environment, and improves the service life and measurement accuracy of the sensor.

[0021] (6) The present invention inserts the sensor directly into the furnace and measures the temperature after attenuation inside the encapsulation structure to characterize the actual temperature of the furnace. There is no need to open holes in the inner wall of the furnace or install complex external temperature measuring devices, which reduces the installation difficulty and maintenance cost, and avoids the direct corrosion of the temperature measuring element by the harsh environment inside the furnace.

[0022] To make the above description of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a probe-type fiber optic temperature sensor based on multi-layer material encapsulation.

[0024] Figure 2 This is a cross-sectional view along the axial direction of a probe-type fiber optic temperature sensor based on multi-layer material encapsulation.

[0025] Figure 3 This is a radial cross-sectional view of a probe-type fiber optic temperature sensor based on multilayer material encapsulation.

[0026] Figure 4 This is a schematic diagram of a measurement experimental setup for a probe-type fiber optic temperature sensor based on multilayer material encapsulation.

[0027] Figure 5 This is a fitted sensitivity curve of a probe-type fiber optic temperature sensor based on multi-layer material encapsulation.

[0028] Figure 6 It was obtained from the calibration experiment. T 1. T Temperature results graph for Figure 2.

[0029] Figure 7 It was obtained from the verification experiment. T 3 、T 4 、T 重构1 Temperature results graph.

[0030] Figure 8-1 It is obtained from the calibration experimental steps in the simulation experiment. T 5. T Temperature results graph for 6.

[0031] Figure 8-2 It is obtained from the verification experimental steps in the simulation experiment.T 7. T 8. T 重构2 Temperature results graph.

[0032] Explanation of reference numerals in the attached figures: 10. Encapsulation shell; 11. First columnar core; 12. Second columnar core; 13. Outer shell; 20. Heat dissipation structure; 21. First heat sink; 22. Second heat sink; 30. Fiber Bragg grating assembly; 31. Optical fiber; 32. Grating; 33. Corundum sleeve; 41. Tube furnace; 42. Heating controller; 43. SM125 fiber optic demodulator; 44. Computer; 45. Thermocouple acquisition device; 46. Powerful fan; 47. Type K thermocouple. Detailed Implementation

[0033] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0034] It should be noted that, in this invention, the top, bottom, left, and right in the figure are considered to be the top, bottom, left, and right of the probe-type fiber optic temperature sensor based on multi-layer material encapsulation described in this specification.

[0035] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0036] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0037] A probe-type fiber optic temperature sensor based on multi-layer material encapsulation (hereinafter referred to as the sensor).

[0038] Example 1 This embodiment relates to a probe-type fiber optic temperature sensor based on multilayer material encapsulation. Please refer to [link to relevant documentation]. Figure 1 , Figure 2 and Figure 3It includes a housing 10, a heat dissipation structure 20, and a fiber optic grating assembly 30.

[0039] The encapsulation housing 10 includes an outer shell 13, a first columnar core 11, and a second columnar core 12. The outer shell 13 serves as the external protective structure for the entire sensor, bearing the thermal radiation and thermal shock of the measured high-temperature environment and protecting the internal components from mechanical damage and chemical corrosion. The first columnar core 11 and the second columnar core 12 are axially spliced ​​inside the outer shell 13, together forming the main structure of the encapsulation housing 10. The thermal conductivity of the first columnar core 11 is lower than that of the second columnar core 12. The first columnar core 11 is made of a low thermal conductivity material to attenuate the high temperature of the furnace, significantly reducing the temperature transferred to the fiber optic grating assembly 30 inside the sensor to within the grating's tolerance range, while ensuring that temperature changes can be effectively measured by the grating 32. The second columnar core 12 is used to conduct heat transferred to the vicinity of the splicing interface between the first columnar core 11 and the second columnar core 12 axially towards the rear end, preventing heat accumulation at the front end of the sensor.

[0040] The heat dissipation structure 20 is at least partially embedded inside the encapsulation housing 10 to conduct heat from the location of the grating 32 to the outside. Specifically, the heat dissipation structure 20 is mostly embedded inside the encapsulation housing 10. Through the embedding of the heat dissipation structure 20, the heat accumulated inside the first columnar core 11 and the second columnar core 12 can be quickly conducted to the outside of the encapsulation housing 10, thereby reducing the temperature at the location of the grating 32, ensuring that the grating 32 operates within the normal operating temperature range, and preventing grating failure due to excessive temperature.

[0041] A fiber optic grating assembly 30 is disposed inside the encapsulation housing 10, including an optical fiber 31 and a grating 32 etched on the optical fiber 31. The optical fiber 31 is used to transmit optical signals, and the grating 32 is used to measure temperature changes. When the external temperature of the encapsulation housing 10 changes, heat is transferred to the interior through the encapsulation housing 10. The period and effective refractive index of the grating 32 change with the temperature, causing a shift in its reflection center wavelength. By detecting the amount of this wavelength shift, the ambient temperature at the location of the grating 32 can be obtained.

[0042] Example 2 This embodiment provides a probe-type fiber optic temperature sensor based on multilayer material encapsulation, which is a further limitation and optimization of Embodiment 1.

[0043] The outer shell 13 is a corundum tube. The corundum tube is made of 99% corundum material, which has high hardness, high temperature resistance (withstanding temperatures above 1700℃) and good thermal shock resistance. Its geometry is a cylindrical crucible structure with an inner diameter of 51mm-61mm, preferably 56mm, an outer diameter of 55mm-65mm, preferably 60mm, and a length of 85mm-95mm, preferably 90mm. It is used to withstand the ultra-high temperature environment of 1000℃-1700℃ inside the gasifier furnace and to provide structural support and preliminary thermal protection for the internal components.

[0044] The first columnar core 11 is a thermal protection material column. The thermal protection material column is made of ceramic fiber material with low thermal conductivity. Its geometric structure is a cylinder with a diameter of 51mm-61mm, preferably 56mm, and a length of 55mm-65mm, preferably 60mm. It is used to prevent heat from being rapidly transferred from the front end of the sensor to the inside, and plays a role in heat insulation and buffering.

[0045] The second columnar core 12 is a highly oriented pyrolytic graphite column. The highly oriented pyrolytic graphite column is made of highly oriented pyrolytic graphite material, and its geometry is a cylinder with a diameter of 51mm-61mm, preferably 56mm, and a length of 25mm-35mm, preferably 30mm. Highly oriented pyrolytic graphite has different thermal conductivity in different directions, with its axial thermal conductivity being much greater than its radial thermal conductivity. This anisotropic characteristic allows it to rapidly dissipate heat from the fiber grating assembly 30 along the axial direction to the rear end, preventing heat accumulation at the grating assembly 30.

[0046] In this embodiment, the axial thermal conductivity of the highly oriented pyrolytic graphite is 1700-1900 W / m·K, preferably 1800 W / m·K, and the radial thermal conductivity is 10-11 W / m·K, preferably 10.5 W / m·K.

[0047] The first columnar core 11 and the second columnar core 12 are joined together along their axial end faces, and both have the same outer diameter, such as 56mm. This end-face joining method creates a continuous heat conduction path in the axial direction between the two columnar cores. After the heat at the front end is attenuated by the first columnar core 11, it is further conducted by the second columnar core 12, thus achieving a controllable transfer of heat from the front end to the rear end of the sensor.

[0048] The inner wall of the outer shell 13 is tightly wrapped and fitted with the outer walls of the first columnar core 11 and the second columnar core 12. Preferably, the inner diameter of the outer shell 13 is 56 mm, and the outer diameters of the first columnar core 11 and the second columnar core 12 are both 56 mm. This tight-fitting design eliminates interlayer gaps, ensuring a continuous and predictable heat conduction path when heat is transferred radially. It avoids uncertainties in thermal resistance and local overheating problems caused by gaps, while also enhancing the mechanical strength and integration of the overall structure.

[0049] The first columnar core 11 is located at the front end of the outer shell 13, intended to be close to the high-temperature heat source being measured, such as the furnace. The front end is the end directly facing the high temperature when the sensor is inserted into the gasifier furnace. At this position, the first columnar core 11 first bears the high temperature of the furnace, utilizing its low thermal conductivity to significantly attenuate the high temperature before transmitting it further. The length of the first columnar core 11 is preferably 60mm, occupying two-thirds of the total 90mm length of the encapsulation shell, providing ample insulation path.

[0050] The second columnar core 12 is located at the rear end of the outer shell 13, close to the heat dissipation end. The rear end is the end of the sensor closest to the external air environment. At this location, the second columnar core 12 further conducts the remaining heat, after attenuation by the first columnar core 11, axially, thus, in conjunction with the heat dissipation structure 20, dissipating heat to the external environment and maintaining a low-temperature environment in the area where the fiber optic grating assembly 30 is located. The length of the second columnar core 12 is preferably 30 mm. Its shorter axial length facilitates rapid axial heat dissipation towards the rear end, reducing heat accumulation inside the sensor.

[0051] The length of the first columnar core 11 is preferably 60 mm, which is greater than the preferred length of the second columnar core 12 (30 mm). This length difference design provides a longer heat insulation path at the sensor front end, allowing heat to undergo more sufficient attenuation as it passes through the first columnar core 11, thereby further reducing the temperature reaching the fiber grating assembly 30. Simultaneously, the shorter second columnar core 12 facilitates the rapid axial dissipation of remaining heat towards the rear end.

[0052] Example 3 This embodiment provides a probe-type fiber optic temperature sensor based on multi-layer material encapsulation, which is a further limitation and optimization of the aforementioned embodiment, mainly involving the specific implementation of the heat dissipation structure 20.

[0053] Both the first columnar core 11 and the second columnar core 12 have multiple through or non-through mounting channels along the axial direction. These mounting channels are holes drilled along the length of the columnar core to accommodate components of the heat dissipation structure 20. Through channels are those that extend the entire length of the columnar core, while non-through channels extend only to a certain depth inside the columnar core and are not completely through. This design allows the heat dissipation structure 20 to be inserted from the rear end of the encapsulation housing 10 and extend into the front end, guiding heat from the front end of the sensor to the rear end.

[0054] The heat dissipation structure 20 includes a heat sink at least partially embedded in a mounting channel. Specifically, most of the heat sink is embedded in the mounting channel. The heat sink is made of a metal with high thermal conductivity, with at least a portion of its column embedded inside the mounting channel and the other portion exposed outside the enclosure housing 10. By directly contacting the inner wall of the mounting channel, the heat sink conducts heat accumulated inside the first columnar core 11 and the second columnar core 12 from the front end of the sensor to the rear end via thermal conduction, and finally dissipates it into the external environment.

[0055] Specifically, the mounting channels include a central channel that is interconnected and opened at the central axis of the first columnar core 11 and the second columnar core 12, and a plurality of peripheral channels arranged around the central channel. The central channel is opened along the central axis of the first columnar core 11 and the second columnar core 12. The peripheral channels are equidistantly distributed around the central channel, for example, four peripheral channels are arranged at equal angular intervals around the central channel to accommodate additional heat sinks to enhance heat dissipation.

[0056] Please see Figure 2 and Figure 3 The heat sink includes a first heat sink 21 embedded in a central channel and multiple second heat sinks 22 embedded in peripheral channels. The first heat sink 21 is a hollow structure with an outer diameter of 2.7mm-3.7mm, preferably 3.2mm, an inner diameter of 1.0mm-2.0mm, preferably 1.5mm, and a length of 115mm-125mm, preferably 120mm. Its axial hollowness forms an optical fiber channel for accommodating the optical fiber temperature sensing component 30. The second heat sinks 22 are solid structures with a diameter of 1mm-11mm, preferably 6mm, and a length of 115mm-125mm, preferably 120mm. After the first and second heat sinks 21 are embedded in their respective channels, they fit tightly against the inner wall of the channels, forming an efficient heat conduction path.

[0057] The first heat sink 21 is a hollow structure, with its axial hollowness forming an optical fiber channel for accommodating the optical fiber temperature sensing component 30. This optical fiber channel is a partially penetrating blind hole structure. Specifically, the axial hollowness of the first heat sink 21 extends from the rear end to the front end of the heat sink, but terminates before reaching the very front end, forming a blind hole. The bottom of the blind hole is located inside the first columnar core 11. This blind hole structure allows the fiber optic grating component 30 to be inserted from the rear end of the sensor and advance along the axial hollowness of the first heat sink 21 until the grating 32 reaches near the bottom of the blind hole. The bottom of the blind hole serves two purposes: firstly, it mechanically limits the optical fiber 31, ensuring that the grating 32 is accurately positioned in the predetermined location; secondly, it prevents the optical fiber 31 from exiting from the front end of the sensor and being directly exposed to the ultra-high temperature environment.

[0058] Furthermore, both the first heat sink 21 and the second heat sink 22 are made of copper. Copper has an extremely high thermal conductivity, far exceeding that of ceramic fibers and corundum tubes, enabling it to quickly dissipate heat from the interior of the first columnar core 11 and the second columnar core 12. Copper also has good processing properties, making it easy to manufacture hollow tubular and solid rod-shaped structures.

[0059] The first heat sink 21 and the second heat sink 22 are at least partially exposed outside the outer casing 13, and are cooled by forced air cooling. Specifically, the length of the first heat sink 21 and the second heat sink 22 is, for example, 120 mm, which is greater than the total length of the encapsulation housing 10, for example, 90 mm, so that the rear end of the heat sink extends from the rear end of the outer casing 13 and is exposed to the outside air. During the operation of the sensor, a powerful fan or other forced air cooling device performs forced convection cooling on the rear ends of these heat sinks exposed to the air, quickly removing the heat conducted by the heat sinks, thereby forming a continuous temperature gradient inside the heat sinks, driving heat to be continuously conducted from the front end to the rear end of the sensor, effectively maintaining the low temperature state of the area where the fiber grating assembly 30 is located.

[0060] It should be noted that, for example Figure 2 As shown, the outer shell 13 encloses the entire first columnar core 11 and at least a portion of the second columnar core 12. Specifically, the rear end face of the outer shell 13 terminates at a certain axial position of the second columnar core 12, such that the rear end portion of the second columnar core 12 is exposed outside the outer shell 13.

[0061] The purpose of this partially enclosed design is to create a stepped heat dissipation structure. Viewing along the sensor axis from front to rear, the degree of exposure of each functional component increases in a stepped manner: The first layer, or front end: the first columnar core 11 is completely wrapped by the outer shell 13. The first columnar core 11 is made of ceramic fiber material with low thermal conductivity. Its main function is to attenuate the high temperature in the furnace. Therefore, it does not need to be in direct contact with the outside air. Complete wrapping helps to maintain its structural integrity and heat insulation effect.

[0062] The second stage, or the middle and rear section, involves the rear end of the second columnar core 12 being exposed outside the outer shell 13. The second columnar core 12 is made of highly oriented pyrolytic graphite, which has a high axial thermal conductivity. Its exposed portion can directly contact the outside air, dissipating the heat conducted from the interior into the environment, thus achieving passive heat dissipation.

[0063] The third layer, the rear end: the rear ends of the first heat sink 21 and the second heat sink 22 extend the longest, significantly exposed beyond the rear end face of the second columnar core 12. Copper material has extremely high thermal conductivity, serving as the primary heat conduction channel. Its extended rear ends, in conjunction with a forced air cooling device, actively dissipate heat, quickly removing the heat accumulated inside the sensor.

[0064] The advantage of this stepped heat dissipation structure is that the closer to the rear end, the more components with higher thermal conductivity are exposed, resulting in progressively enhanced heat dissipation capacity. After entering from the sensor front end, heat sequentially passes through the thermal insulation attenuation of the first columnar core 11, the initial heat dissipation of the second columnar core 12, and the forced air cooling of the copper rod array, forming a thermal management path of insulation, conduction, and forced dissipation. This design ensures that the grating 32 located within the first columnar core 11 always operates at a temperature far below the external environment, thus overcoming the technical bottleneck of easily softening and failing thermally regenerated fiber Bragg gratings in ultra-high temperature environments.

[0065] Example 4 This embodiment provides a probe-type fiber optic temperature sensor based on multilayer material encapsulation, which is a further limitation and optimization of the aforementioned embodiment, mainly involving the specific structure and fixing method of the fiber optic grating assembly 30.

[0066] Grating 32 is a thermally regenerated fiber grating. The thermally regenerated fiber grating is obtained by subjecting a seed grating to high-temperature thermal regeneration. Specifically, a seed grating is first etched onto the core of a single-mode fiber 31 using a femtosecond laser. The grating region length of the seed grating is 8mm-12mm, preferably 10mm. Then, the seed grating is placed in a high-temperature environment for thermal regeneration, causing the refractive index modulation structure of the seed grating to be reconstructed, forming a thermally regenerated fiber grating with higher thermal stability. The thermally regenerated fiber grating can withstand high-temperature environments above 800℃, exhibiting improved thermal stability compared to ordinary fiber gratings.

[0067] There is only one grating 32, which is engraved in the middle section of the optical fiber 31. Specifically, the grating area of ​​the grating 32 is located in the middle section of the optical fiber 31 along its length, rather than near the end of the optical fiber 31. This arrangement allows the grating 32 to be naturally located deep inside the encapsulation housing 10 after the sensor is assembled, and to be fully protected by the encapsulation housing 10.

[0068] An alumina sleeve 33 is fitted around the outer surface of the optical fiber 31, and the alumina sleeve 33 is embedded within the optical fiber channel of the first heat sink 21. The alumina sleeve 33 is made of 99% alumina material, with an outer diameter of 1.0mm-2.0mm, preferably 1.3mm, and an inner diameter of 0.7mm-1.7mm, preferably 1.0mm. Its inner diameter is larger than the outer diameter of the optical fiber 31. The cladding diameter of the optical fiber 31 is 125μm, or 0.125mm, allowing the optical fiber 31 to pass freely within the alumina sleeve 33 without constraint. The alumina sleeve 33 provides mechanical and thermal protection for the optical fiber 31, preventing it from being damaged by compression, bending, or high temperatures during assembly and use.

[0069] It is worth mentioning that the high temperature heat inside the furnace acts on the outer wall of the sensor packaging housing 10, and the heat is transferred radially from the outside to the inside. The first columnar core 11 is a solid cylindrical structure, and the central channel and the front end of the first heat sink 21 are both in a closed state. Therefore, the heat is not directly transferred to the fiber grating assembly 30 through high temperature gas convection, but is indirectly transferred through the solid heat conduction path and the air heat conduction in the closed gap, which gradually attenuates.

[0070] The specific heat transfer path is as follows: The sensor is inserted into the furnace chamber of the gasifier, and the high temperature of the furnace chamber acts on the outer wall of the sensor encapsulation housing 10. The heat is transferred radially from the outside to the inside, passing through the outer shell 13, the first columnar core 11, the first heat sink 21, and the corundum sleeve 33 in sequence, and finally reaching the grating 32 located at the central axis of the encapsulation housing 10. The grating 32 measures the temperature at the center point of the radial section.

[0071] The grating 32 is located at the first columnar core 11. Part of the heat from this radial section is transferred to the front end via the first columnar core 11, and another part is transferred to the rear end via the first columnar core 11 and the second columnar core 12. Simultaneously, heat is dissipated axially to the rear end through the first heat sink 21 (i.e., the central copper tube) and the second heat sink 22 (i.e., the four peripheral copper rods) embedded within the columnar core. A forced air cooling device further dissipates heat from the rear end of the heat sink exposed to the air, creating a continuous temperature gradient within the heat sink. This continuously removes heat from the sensor's interior, maintaining a low-temperature operating environment in the area where the grating 32 is located.

[0072] The heat transfer path described above is radial and axial heat conduction: the ultra-high temperature of 1000℃-1700℃ in the furnace is transferred radially from the outside to the inside to the grating 32, allowing the grating 32 to measure the temperature attenuated by the encapsulation shell 10; simultaneously, the heat in the radial section where the grating 32 is located is conducted axially through the first columnar core 11, the second columnar core 12, and the copper heat sink array to the rear end, and then dissipated to the external environment by forced air cooling. This design ensures that the grating 32 can measure the temperature changes inside the encapsulation shell 10, and also prevents heat accumulation in the radial section where the grating 32 is located through the axial heat dissipation mechanism, ensuring that the grating 32 can operate stably for a long time in ultra-high temperature environments.

[0073] The function of the corundum sleeve 33 is to protect the optical fiber 31 and the grating 32 from mechanical damage and direct erosion by high-temperature gas, rather than to dissipate heat. Therefore, the corundum sleeve 33 is not mentioned in the heat transfer path.

[0074] One end of the corundum sleeve 33 is fixed to the optical fiber 31 using high-temperature ceramic adhesive. Specifically, at the front end of the corundum sleeve 33, high-temperature ceramic adhesive is applied between the optical fiber 31 and the inner wall of the corundum sleeve 33, fixing the optical fiber 31 relative to the corundum sleeve 33 at this end; the remaining portion maintains a gap, allowing the optical fiber 31 to pass freely within the corundum sleeve 33. The high-temperature ceramic adhesive used is a ceramic adhesive with a temperature resistance exceeding 1200℃, capable of maintaining stable bonding strength in high-temperature environments.

[0075] At the rear end of the corundum sleeve 33, high-temperature ceramic adhesive is applied to the port of the corundum sleeve 33 to completely seal the port. This port seal prevents high-temperature gas from entering the interior of the corundum sleeve 33 and directly contacting the optical fiber 31 and the grating 32, thus avoiding the grating 32 being ablated by the high-temperature gas flow.

[0076] The above-described fixing method forms a single-head adhesive fixing structure. Single-head adhesive means that the optical fiber 31 is bonded and fixed only to the front end of the corundum sleeve 33, while the rest of the optical fiber 31 inside the corundum sleeve 33 is suspended and does not contact the inner wall of the corundum sleeve 33; at the same time, the rear end of the corundum sleeve 33 is sealed with high-temperature ceramic adhesive. The advantages of this single-head adhesive fixing structure are: when the sensor operates in an ultra-high temperature environment, the corundum sleeve 33 and the optical fiber 31 will experience different degrees of thermal expansion due to their different materials (the coefficient of thermal expansion of corundum differs from that of quartz optical fiber). The single-head fixing method allows the optical fiber 31 to freely expand and contract axially within the corundum sleeve 33, thereby effectively releasing thermal expansion stress, preventing the optical fiber 31 from breaking due to tensile stress or experiencing micro-bending loss due to compressive stress, and also preventing spectral distortion of the grating 32.

[0077] In this embodiment, fiber 31 is a single-mode fiber of type SMF-28. SMF-28 is a standard single-mode fiber widely used in the fields of communication and sensing. It has excellent geometric uniformity, optical performance and mechanical strength, and is suitable for fiber grating writing and sensing applications in high-temperature environments.

[0078] The core diameter of optical fiber 31 is 8.0μm-8.4μm, preferably 8.2μm. The core is the core region in the optical fiber for transmitting optical signals, and the grating 32 is inscribed on the core. The core diameter of 8.2μm ensures single-mode transmission conditions, allowing the optical signal to be transmitted in the fundamental mode in the core, which has the characteristics of low loss and high stability.

[0079] The cladding diameter of fiber 31 is 125 μm. The cladding is an optical medium layer surrounding the fiber core, with a lower refractive index than the core. It uses the principle of total internal reflection to confine the optical signal within the core for transmission. 125 μm is the cladding diameter of standard single-mode fiber, offering good compatibility and facilitating use with standard fiber optic connectors and fusion splicing equipment.

[0080] The length of the single-mode fiber 31 is greater than 120mm. The total length of the encapsulation housing 10 is 90mm. The fact that the fiber 31 is longer than 120mm means that the fiber 31 extends at least 30mm beyond the rear end of the encapsulation housing 10, providing sufficient operating space for the connection of the fiber 31 to the external fiber demodulator.

[0081] Example 5 This embodiment provides an application and testing method of a probe-type fiber optic temperature sensor based on multi-layer material encapsulation in gasifier furnace temperature measurement.

[0082] A probe-type fiber optic temperature sensor based on multi-layer material encapsulation is inserted into the gasifier furnace chamber. The sensor transmits the ultra-high temperature of the furnace chamber to the internal fiber optic grating assembly 30 after attenuation through the encapsulation housing 10. The grating 32 measures the attenuated temperature, thereby realizing the indirect measurement of the gasifier furnace chamber temperature.

[0083] In the following steps, the radial section of grating 32 refers to the plane passing through the grating region of grating 32 and perpendicular to the sensor axis. This plane intersects with the outer shell 13 to form a closed curve, and any point on this closed curve is recorded as a point on the radial section. The temperature of the outer shell 13 at this radial section is the furnace temperature in the calibration experiment. T 2. Verify the furnace temperature in the experiment. T 4, and the temperature obtained by reverse calculation. T 重构1 .

[0084] The test method provided in this embodiment is used to calibrate and verify the performance of the above-mentioned sensor in gasifier furnace temperature measurement, and specifically includes the following steps: Step 1: Set up the test setup.

[0085] Test equipment such as Figure 4 As shown, it includes a tubular furnace 41, a heating controller 42, an SM125 fiber optic demodulator 43, a computer 44, a thermocouple acquisition device 45, a powerful fan 46, and a K-type thermocouple 47.

[0086] The heating zone of the tubular furnace 41 has a length of 280mm-320mm, preferably 300mm, to simulate the high-temperature environment of the gasifier furnace chamber. The tubular furnace 41 is fixed in the heating controller 42, which controls the heating rate and holding temperature of the tubular furnace 41.

[0087] A probe-type fiber optic temperature sensor based on multi-layer material encapsulation is placed in the tube furnace 41 to ensure uniform heating of the sensor. This ensures that the front end of the sensor, i.e. the end where the first columnar core 11 is located, is located in the center of the heating area of ​​the tube furnace 41, and the axis of the sensor is parallel to the axis of the tube furnace 41.

[0088] The optical fiber 31 at the back end of the optical fiber sensor is connected to one end of the SM125 optical fiber demodulator 43. The SM125 optical fiber demodulator 43 has a wavelength resolution of 1 pm and is used to acquire the reflection spectrum of the grating 32 in real time and calculate the center wavelength. The other end of the SM125 optical fiber demodulator 43 is connected to the computer 44 via a USB data cable to transmit the wavelength data to the computer 44 in real time.

[0089] The type-k thermocouple 47 is used to monitor the furnace temperature of the tubular furnace 41. This furnace temperature is considered to be the temperature at the same radial cross-section as the grating 32 on the outer shell 13 of the sensor, serving as a reference value for the actual external temperature. The measuring end of the type-k thermocouple 47 is placed near the sensor to ensure that the temperature it measures is consistent with the temperature experienced by the front end of the sensor. The other end of the type-k thermocouple 47 is connected to the thermocouple acquisition device 45, and the other end of the thermocouple acquisition device 45 is connected to the computer 44 via a USB data cable to transmit the furnace temperature data to the computer 44 in real time.

[0090] A powerful fan 46 is used to provide forced air cooling for the heat dissipation structure 20 at the rear of the sensor. The powerful fan 46 is directed at the first heat sink 21 and the second heat sink 22 exposed to the air at the rear of the sensor, and operates at maximum power during the test to quickly remove the heat conducted from inside the sensor.

[0091] Step 2: Fiber Bragg grating sensitivity calibration.

[0092] Before testing the packaged sensor, the sensitivity of the unpackaged grating 32 is first calibrated.

[0093] Step 201: Record the reflectance spectrum of the unencapsulated grating 32 at room temperature as a reference.

[0094] Step 202: Place the unencapsulated grating 32 into the tube furnace 41, and increase the temperature of the heating controller 42, which houses the tube furnace 41, from room temperature to 1000°C in increments of 100°C. Hold each temperature point for 15 minutes to ensure uniform temperature distribution within the tube furnace 41. After the spectrum stabilizes, record wavelength data every 100°C to obtain the temperature response spectrum. (See [link to relevant documentation]). Figure 5 .

[0095] Step 203, for grating 32, i.e. Figure 5 Linear fitting was performed on the dots in the diagram to obtain the fitted sensitivity formula. Experiments show that as the temperature increases, the reflection center wavelength of grating 32 shifts linearly towards longer wavelengths. This phenomenon is mainly caused by the thermal expansion effect and thermo-optic effect of grating 32. The fitted sensitivity formula is used to convert the wavelength changes measured in subsequent experiments into temperature changes.

[0096] like Figure 5As shown, a linear fit is performed on the wavelength-temperature response of the grating to obtain the sensitivity formula. y=0.01468x+ 1546.22973 goodness of fit R 2 =0.9967 This indicates a very strong linear relationship between wavelength and temperature, demonstrating that the temperature measurement accuracy and repeatability of grating 32 are excellent.

[0097] Step 3: Calibration Experiment.

[0098] The purpose of the calibration experiment is to establish the heat transfer balance relationship between the temperature at any point on the outer shell 13 of the sensor and the temperature at the center point of the same radial section as the grating 32 (measured by the grating 32).

[0099] Step 301: Package the fiber Bragg grating assembly 30 to assemble it into a complete unit. Figure 2 The structure shown is then followed by all the devices according to... Figure 4 Prepare for connection, start the heating controller 42, and increase the temperature from room temperature to 1000°C in increments of 100°C. Hold each temperature point for 15 minutes to ensure uniform temperature distribution in the tube furnace 41, and hold at 1000°C for 30 minutes.

[0100] In step 302, during heating, the powerful fan 46 operates at maximum power to force-cool the first heat sink 21, the second heat sink 22, the outer shell 13, and the highly oriented pyrolytic graphite column (i.e., the second columnar core 12) exposed to the air. This heat dissipation measure can effectively regulate the radial and axial heat flow inside the encapsulation shell 10 and prevent the grating 32 from overheating.

[0101] Step 303: After the calibration experiment, the wavelength information of the grating 32 is acquired by the SM125 fiber optic demodulator 43, and the temperature of the environment in which the embedded grating 32 is located is calculated using the pre-calibrated sensitivity formula. T 1 refers to the temperature at the center point of the radial section where grating 32 is located. Also, see... Figure 6 The furnace temperature outside the outer shell 13 is obtained by the k-type thermocouple 47 and the thermocouple collecting device 45. T 2. Furnace temperature T 2 represents the temperature at any point on the radial section where the grating 32 is located.

[0102] Based on internal temperature T 1. External temperature T The correspondence between 2 and 3 yields the thermal balance relationship of heat transfer from the outside to the inside. This balance relationship reflects the complete physical process of heat transfer from the furnace chamber through the encapsulation shell 10 to the internal grating 32.

[0103] Step 4: Verification Experiment.

[0104] The purpose of the verification experiment is to check the accuracy of the heat transfer equilibrium relationship obtained from the calibration.

[0105] Step 401: Once all devices are connected again, start the heating controller 42 to increase the temperature from room temperature to 1000℃ at a rate of 10℃ / min, and maintain the temperature at 1000℃ for 30 minutes. During heating, the powerful fan 46 also operates at maximum power to provide forced air cooling for the heat dissipation components.

[0106] Step 402: After the verification experiment is completed, the wavelength information of grating 32 is sampled again, and the temperature of the environment in which the embedded grating 32 is located is obtained using the sensitivity formula. T 3 refers to the temperature at the center point of the radial section where grating 32 is located. See also... Figure 7 The furnace temperature outside the outer shell 13 is obtained by the k-type thermocouple 47 and the thermocouple acquisition device 45. T 4.

[0107] Step 403: Based on the heat transfer balance relationship obtained from the calibration experiment and the temperature of the environment where the embedded grating 32 is located... T 3 refers to the temperature at the center point of the radial section where the grating 32 is located, and then the temperature of the gasifier furnace is calculated. T 重构1 The furnace temperature obtained by back-calculation T 重构1 The furnace temperature measured by thermocouple 21 of type K T 4. Compare the two and calculate the error between them.

[0108] Experimental results show that the back-calculated temperature T 重构1 Compared with the measured temperature T The average relative error between 4 is 4.369%, which is very small. This verifies that the probe-type fiber optic temperature sensor based on multi-layer material encapsulation of the present invention can accurately calculate the high temperature information of the sensor probed environment from the low temperature information of the embedded grating, thereby breaking through the technical bottleneck of the thermal regeneration fiber optic grating being prone to softening and failure in ultra-high temperature environments.

[0109] It should be noted that, due to experimental limitations, the maximum temperature in this application was 1000°C within the tube furnace 41. Under these conditions, the encapsulated grating 32 responded to approximately 600°C, and the furnace temperature was successfully calculated, verifying the attenuation heat transfer effect of the structure of this invention. Based on this attenuation ratio, the encapsulation structure of this invention can be further applied to ultra-high temperature environments of 1200°C or even 1700°C, breaking through the 1200°C temperature measurement limit of the thermally regenerated fiber grating itself.

[0110] In the test method described in this embodiment, the heat transfer balance relationship established in the calibration experiment and the specific calculation process of calculating the outer shell temperature from the grating temperature in the verification experiment can be implemented using conventional inverse heat conduction algorithms and interpolation fitting methods based on experimental data. These algorithms are existing publicly available technologies in this field and will not be elaborated upon here.

[0111] Example 6 To further verify the performance of the sensor of the present invention in ultra-high temperature environments, this embodiment supplements the COMSOL finite element simulation experiment. Unlike the tube furnace physical testing method described in Embodiment 5, the simulation experiment is not limited by the maximum temperature of the heating equipment and can apply a circumferential thermal load of up to 1400°C to the outside of the sensor.

[0112] The simulation experiment followed the steps outlined in Example 5. First, the temperature of the environment in which the embedded grating 32 was located was calculated using the sensitivity formula. T 5 refers to the temperature at the center point of the radial section where grating 32 is located. See also Figure 8-1 In the calibration experiment, a stepped circumferential thermal load was applied to the COMSOL model, and the temperature of the radial section corresponding to the outer wall of the outer shell 13 was extracted as the furnace temperature. T 6. Establish a heat transfer equilibrium. Then, refer to... Figure 8-2 In the verification experiment, a circumferential thermal load of up to 1400℃ was applied, and the temperature of the environment in which the embedded grating 32 was located was calculated using the sensitivity formula. T 7. Obtain the furnace temperature outside the outer shell 13. T 8 ， Back-calculation of gasifier furnace temperature T 重构2 With furnace temperature T 8. Compare the results and calculate the relative error.

[0113] Simulation results show that the sensor is initially feasible under extreme and complex heat flux environments, with a total time average relative error of only 1.26%. Under the condition that the sensor directly measures a temperature of approximately 958℃, the temperature measurement limit can be indirectly increased to 1400℃ through the inverse heat conduction algorithm. This simulation experiment numerically compensates for the limitation of the furnace temperature being only 1000℃ in physical testing, further demonstrating that the packaging structure of this invention can overcome the 1200℃ temperature measurement bottleneck of the thermally regenerated fiber Bragg grating.

[0114] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail may be made without departing from the spirit and scope of the present invention.

Claims

1. A probe-type fiber optic temperature sensor based on multilayer material encapsulation, characterized in that, include: The encapsulation housing (10) includes an outer tube shell (13) and a first columnar core (11) and a second columnar core (12) axially spliced ​​within the outer tube shell (13), wherein the thermal conductivity of the first columnar core (11) is lower than that of the second columnar core (12). A fiber optic grating assembly (30) is disposed inside the encapsulation housing (10) and includes an optical fiber (31) and a grating (32) inscribed on the optical fiber (31). A heat dissipation structure (20), at least partially embedded inside the encapsulation housing (10), is used to direct the heat at the location of the grating (32) to the outside.

2. The probe-type fiber optic temperature sensor based on multilayer material encapsulation according to claim 1, characterized in that, The outer shell (13) is a corundum tube, the first columnar core (11) is a thermal protection material column, and the second columnar core (12) is a highly oriented pyrolytic graphite column. The first columnar core (11) and the second columnar core (12) are joined together along the axial end face, and both have the same outer diameter; The inner wall of the outer shell (13) is tightly wrapped and fitted with the outer walls of the first columnar core (11) and the second columnar core (12), and the outer shell (13) wraps the entire first columnar core (11) and at least a part of the second columnar core (12).

3. The probe-type fiber optic temperature sensor based on multilayer material encapsulation according to claim 1 or 2, characterized in that, The first columnar core (11) is located at the front end of the outer shell (13) and is used to be close to the high-temperature heat source being measured; The second columnar core (12) is located at the rear end of the outer shell (13) and is positioned close to the heat dissipation end.

4. The probe-type fiber optic temperature sensor based on multilayer material encapsulation according to claim 2, characterized in that, The thermal protection material of the first columnar core (11) is ceramic fiber, and its length is greater than that of the second columnar core (12); The axial thermal conductivity of the second columnar core (12) is greater than its radial thermal conductivity.

5. The probe-type fiber optic temperature sensor based on multilayer material encapsulation according to claim 1, characterized in that, Both the first columnar core (11) and the second columnar core (12) have multiple through or non-through mounting holes along the axial direction; The heat dissipation structure (20) includes a heat dissipation rod that is at least partially embedded in the mounting hole.

6. The probe-type fiber optic temperature sensor based on multilayer material encapsulation according to claim 5, characterized in that, The mounting channels include a central channel that is interconnected at the central axis of the first columnar core (11) and the second columnar core (12), and a plurality of peripheral channels arranged around the central channel. The heat sink includes a first heat sink (21) embedded in the central channel and multiple second heat sinks (22) embedded in the peripheral channels. The first heat sink (21) is a hollow structure, and its axial hollow structure forms an optical fiber channel for accommodating the optical fiber temperature measurement component (30). The optical fiber channel is a blind hole structure that does not completely penetrate through the fiber.

7. The probe-type fiber optic temperature sensor based on multilayer material encapsulation according to claim 6, characterized in that, The first heat sink (21) and the second heat sink (22) are both made of copper and are at least partially exposed outside the outer shell (13) for heat dissipation in conjunction with forced air cooling.

8. The probe-type fiber optic temperature sensor based on multilayer material encapsulation according to claim 1, characterized in that, The grating (32) is a thermally regenerated fiber grating, and there is only one of it, which is inscribed in the middle of the fiber (31), and its grating area is located inside the first columnar core (11).

9. The probe-type fiber optic temperature sensor based on multilayer material encapsulation according to claim 8, characterized in that, The optical fiber (31) is fitted with a corundum sleeve (33). One end of the corundum sleeve (33) is fixed to the optical fiber (31) by high-temperature ceramic adhesive, and the other end of the corundum sleeve (33) is sealed by high-temperature ceramic adhesive to form a single-head adhesive fixing structure.

10. The application of a probe-type fiber optic temperature sensor based on multilayer material encapsulation as described in any one of claims 1-9 in temperature measurement of a gasifier furnace.

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