Infrared temperature measurement calibration method for closed pyrolysis device and weighing anti-interference method

Abstract

This invention discloses an infrared temperature measurement calibration method and a weighing anti-interference method for a closed pyrolysis device, relating to the field of materials fire safety technology. The infrared temperature measurement calibration method mainly includes: dynamically calibrating the lumped transmittance using a non-steady-state heating process based on the infrared optical measurement path, calibration components, and the closed pyrolysis device, to obtain the equivalent lumped transmittance. The weighing anti-interference method mainly includes: operating the closed pyrolysis device, with no sample placed, according to the same heater heating program, gas flow rate, and water cooling conditions as in a formal experiment, and obtaining the curve of the electronic balance reading changing over time. Implementing the infrared temperature measurement calibration method and weighing anti-interference method for a closed pyrolysis device provided by this invention enables accurate non-contact temperature measurement, and the system identifies and comprehensively reduces weighing interference.

Description

Technical Field

[0001] This invention relates to the field of materials fire safety technology, and more specifically, to an infrared temperature measurement calibration method and a weighing anti-interference method for a closed pyrolysis device. Background Technology

[0002] In the field of materials fire safety research, medium-scale closed-environment pyrolysis devices can more realistically reproduce the heat transfer gradient and pyrolysis behavior of solid materials in a fire, and are therefore widely used to obtain pyrolysis kinetic parameters. However, the extreme environment created by these devices—closed, high-temperature, and continuously ventilated—poses a severe challenge to the accurate measurement of key sample parameters. Currently, there are two problems with parameter acquisition: ① contact temperature measurement interferes with high-precision weighing, and ② closed airflow and thermal radiation severely affect the stability of the mass baseline.

[0003] Traditional contact thermocouple methods for sample temperature measurement have inherent limitations. Thermocouples and their leads can interfere with the weighing results of high-precision electronic balances due to mechanical stress, making it difficult to simultaneously and accurately obtain mass and temperature on the same sample. Placing multiple thermocouples at the bottom of the sample to monitor the evolution of the two-dimensional temperature field not only amplifies the interference from weighing but also compromises the overall gas tightness of the device. To achieve non-invasive temperature measurement, researchers have attempted to introduce infrared thermal imagers. However, for sealed vaporization chambers, quartz or ordinary glass optical windows strongly absorb radiation in the mid-to-far infrared band (8-13 μm), blocking a significant amount of infrared signals and making non-contact temperature measurement impossible. Even when using single-crystal germanium with high infrared transmittance as the window material, its lumped transmittance over a wide temperature measurement range is affected by various factors such as wavelength and sample temperature, and is not a known constant. Without precise calibration, infrared temperature readings will exhibit significant deviations. Currently, a systematic infrared optical path design and transmittance calibration method suitable for sealed pyrolysis devices is lacking.

[0004] In sample mass measurement, the impact of a closed environment on the weighing stability of an electronic balance is far greater than that of an open device, primarily due to the coupled effects of airflow dynamics and thermal radiation. The high-temperature heater creates a significant temperature gradient between the vaporization chamber and the lower balance chamber, resulting in thermal buoyancy and a pressure difference between the upper and lower chambers. These factors create nonlinear changes that affect the sample tray, causing the weighing baseline to drift over time. Simultaneously, the continuously supplied purge gas, flowing through an poorly structured sample tray, induces eddy currents and airflow deflections at its raised edges, causing some gas to rush into the lower chamber where the balance is located, directly impacting the load cell. Furthermore, the intense thermal radiation from the upper heater causes the local temperature around the balance to exceed its normal operating range, further affecting measurement accuracy, especially for the mass testing of thin and light samples.

[0005] While some existing devices employ high-temperature resistant balances or simple heat insulation measures, there is a lack of a method that can systematically identify and comprehensively reduce weighing interference. Therefore, there is an urgent need to develop a non-contact temperature measurement calibration method specifically for closed pyrolysis environments, as well as a comprehensive weighing anti-interference method. Summary of the Invention

[0006] The purpose of this invention is to provide an infrared temperature measurement calibration method and a weighing anti-interference method for a closed pyrolysis device, which can accurately measure temperature without contact and systematically identify and comprehensively reduce weighing interference.

[0007] This invention provides an infrared temperature measurement calibration method for a closed pyrolysis apparatus, comprising the following steps: S11: A gold mirror at a 45° angle is installed directly below the sample holder of the sealed pyrolysis device. An optical window is opened on the outer wall of the vaporization chamber of the sealed pyrolysis device corresponding to the height of the gold mirror. The optical window is used to allow the infrared radiation signal from the bottom of the sample to penetrate the sealed wall and be received by an external infrared thermal imager to obtain an infrared optical measurement path. S12: The same black paint as the bottom of the formal experimental sample is uniformly sprayed onto the surface of a high thermal conductivity copper block with the same diameter as the sample to be tested. Holes with the same diameter as the thermocouple are set at the center and half radius of the high thermal conductivity copper block for thermocouples. The thermocouples are used to measure the true internal temperature of the high thermal conductivity copper block to obtain a calibration piece. S13: Based on the infrared optical measurement path, calibration component and sealed pyrolysis device, the lumped transmittance is dynamically calibrated using the unsteady heating process to obtain the equivalent lumped transmittance, which is used for accurate non-contact temperature measurement in real sample experiments.

[0008] Furthermore, the gold mirror is used to deflect the infrared path emitted downwards from the bottom of the sample by 90°; the reflectivity of the gold mirror is not less than 0.96.

[0009] Furthermore, the optical window is made of single-crystal germanium, which has high transmittance in the mid- and far-infrared bands.

[0010] Furthermore, the height of the high thermal conductivity copper block is 5mm.

[0011] Furthermore, the emissivity of the black paint is not less than 0.95.

[0012] Furthermore, the method for dynamically calibrating lumped transmittance using a non-steady-state heating process includes: Place the calibration component in the sample tray of the closed pyrolysis device, and start the heater of the closed pyrolysis device to heat up according to the predetermined program. The readings of the infrared thermal imager and the thermocouple of the calibration component along the infrared optical measurement path are obtained. The optical transmittance parameter of the infrared thermal imager is continuously adjusted until the maximum deviation between the reading of the infrared thermal imager and the reading of the thermocouple does not exceed a preset difference within the full range. The current optical transmittance parameter of the infrared thermal imager is then used as the equivalent lumped transmittance of the infrared optical measurement path within the practical temperature measurement range.

[0013] Furthermore, the preset difference value is ±5K.

[0014] The present invention also provides a weighing anti-interference method for a closed pyrolysis apparatus, comprising the following steps: S21: Construct an internal flow field and temperature field model for a closed pyrolysis device using computational fluid dynamics, and obtain simulation results of temperature field, airflow, and pressure difference between the upper and lower surfaces of the sample tray using the internal flow field and temperature field model. S22: Based on the simulation results of the temperature field, airflow, and pressure difference between the upper and lower surfaces of the sample tray, the structure of the closed pyrolysis device is optimized to obtain the optimized closed pyrolysis device. S23: Based on the optimized closed pyrolysis device, without placing any sample, run the closed pyrolysis device according to the same heater heating program, gas flow rate and water cooling conditions as the formal experiment, obtain the curve of the electronic balance reading changing over time, and obtain the mass baseline under the formal experimental conditions.

[0015] Furthermore, the internal flow field temperature field model includes a full-size simplified geometric model of the sealed vaporization chamber, sample tray, lower cavity, and balance mounting area of ​​the sealed pyrolysis device. The model is coupled with gas flow, pressure field, and temperature field.

[0016] Furthermore, the quality baseline is used to: in the quality test of the formal sample, subtract the baseline value at the corresponding moment from the real-time collected balance reading to obtain the true dynamic quality loss data of the sample.

[0017] The infrared temperature measurement calibration method and weighing anti-interference method for a closed pyrolysis device provided by the present invention have the following beneficial effects: This invention addresses the shortcomings of existing technologies, such as interference with weighing by contact temperature measurement and the lack of calibration methods for inaccurate infrared temperature measurement. It proposes a non-contact infrared temperature measurement calibration method for a closed pyrolysis device. This method solves the problem of mechanical stress interference to high-precision electronic balances caused by the invasive structure of contact thermocouples, while avoiding the problem of multiple thermocouple arrangements compromising the device's airtightness, thus meeting the requirements for controlled closed pyrolysis atmosphere. Furthermore, it solves the problem of inaccurate infrared temperature measurement caused by the non-constant lumped transmittance of the single-crystal germanium window, enabling accurate non-contact measurement of the sample bottom temperature and meeting the requirements for temperature monitoring during the pyrolysis process.

[0018] Specifically, this invention constructs a special infrared light path with a 45° high reflectivity gold mirror. A gold mirror with a 45° tilt angle and high reflectivity (0.96) is arranged directly below the sample holder to refract the infrared radiation emitted downward from the bottom of the sample by 90°. A single-crystal germanium optical window is opened on the outer wall of the vaporization chamber at the height corresponding to the gold mirror to replace the traditional glass / quartz window. This is mainly to address the shortcomings of existing technologies where infrared temperature measurement requires opening a window on the top wall of the vaporization chamber, which would damage the airtightness of the O-ring seal and also require the introduction of an invasive structure. The gold mirror folding design of this invention allows infrared radiation to penetrate only the single-crystal germanium window on the side wall, eliminating the need for a window on the top wall. This completely preserves the sealed structure of the vaporization chamber and completely eliminates invasive temperature measuring elements such as thermocouples. This fundamentally eliminates the interference of mechanical stress on the balance and directly solves the root cause of contact temperature measurement interfering with weighing and compromising airtightness in the prior art.

[0019] Furthermore, this invention establishes a non-steady-state heating dynamic lumped transmittance calibration process. A high-thermal-conductivity copper calibration component is prepared, with the same diameter (70 mm) as the sample to be tested, a surface coated with the same high-emissivity (0.95) black paint as the official sample, and K-type thermocouples embedded in the center and half the radius. The calibration component is placed on the sample tray, and heating is performed according to a real pyrolysis heating program (heating rate 20 K / min, from 313 K to 1073 K, covering the target temperature range of 313-800 K). Simultaneously, infrared thermal imager readings and the actual measured temperature of the copper block by the thermocouples are acquired. The transmittance parameters of the infrared thermal imager are dynamically adjusted until the full-range temperature measurement deviation is ≤ ±5 K. The equivalent lumped transmittance of this optical path system addresses the root cause of inaccurate infrared temperature measurement in existing technologies, which is the failure to consider the dynamic changes in transmittance of single-crystal germanium with temperature and wavelength, assuming a constant transmittance. This invention simulates the heating process of real pyrolysis and uses the actual temperature measured by thermocouples as a true reference within the temperature range corresponding to the actual temperature measurement. It dynamically calibrates and obtains the equivalent lumped transmittance of the current optical path system within the practical temperature measurement range. The non-constant transmittance that changes with temperature is equivalent to a constant parameter applicable to the current temperature measurement range. In principle, this eliminates the temperature measurement deviation caused by the non-constant transmittance and directly solves the root cause of inaccurate infrared temperature measurement in existing technologies.

[0020] This invention completely eliminates the mechanical stress of thermocouples and leads from interfering with the weighing of the electronic balance. At the same time, it eliminates the need for opening windows in the top wall of the vaporization chamber, fully preserving the airtightness of the O-ring rubber seal of the device and meeting the atmosphere control requirements of closed pyrolysis. The calibrated equivalent lumped transmittance of the optical path enables precise measurement of the sample bottom temperature with extremely low error across the entire range, meeting the accuracy requirements for temperature monitoring during the pyrolysis process.

[0021] This invention addresses the shortcomings of existing technologies, such as baseline drift caused by multi-source coupling interference in closed pyrolysis environments and the lack of systematic anti-interference methods. It proposes an anti-interference method for the weighing system of closed pyrolysis devices, which solves the problem of baseline drift in electronic balances caused by airflow dynamic disturbances and thermal radiation coupling in closed pyrolysis environments, improves the stability and repeatability of the weighing baseline, and solves the problem that existing technologies cannot cope with multi-source coupling interference by using only simple measures. It enables high-precision dynamic mass measurement of thin samples and meets the need to obtain the mass loss rate during pyrolysis.

[0022] Specifically, this invention employs full-scale CFD simulation to identify multiple interference sources. It performs full-scale simplified modeling of the sealed vaporization chamber, sample tray, lower chamber, and balance mounting area, coupling gas flow, pressure field, and temperature field. It quantitatively analyzes the pressure distribution, temperature gradient, and airflow streamlines in the space above and below the sample tray, clarifying the generation mechanism and coupling relationship of interference. This addresses the shortcomings of existing technologies, which fail to clearly define the coupling mechanism of multi-source interference and can only resort to blind, simple insulation measures. This invention quantitatively identifies three core interference sources through computational fluid dynamics (CFD) simulation: the nonlinear force resulting from the thermal buoyancy and pressure difference caused by the temperature difference between the upper and lower chambers; the airflow deflection and eddies induced by the raised tray; and the thermal radiation from the heater. It clarifies the generation mechanism of each interference source, providing a theoretical basis for subsequent targeted optimization and solving the root cause of the lack of a systematic anti-interference method.

[0023] This invention implements three synergistic structural optimizations to fundamentally weaken interference sources. First, it increases the exhaust port diameter and shortens the exhaust pipe: the exhaust port diameter is increased from 28.5mm to 48mm, while the exhaust pipe length is shortened. The principle is that increasing the exhaust port diameter and shortening the pipe reduces exhaust resistance, suppressing gas seepage from the upper chamber to the lower chamber due to poor exhaust flow, thus fundamentally weakening the interference source of airflow impacting the balance and solving the problem of baseline drift caused by pressure difference / airflow seepage between the upper and lower chambers. Second, it lowers the sample tray installation height: the sample tray is lowered by 20mm, making its upper surface basically flush with the connection opening of the vaporization chamber. The principle is that it eliminates the raised edge structure of the tray, avoiding the vortex effect and airflow deflection induced by high-speed airflow impacting the raised edge, ensuring smooth airflow into the exhaust channel, fundamentally eliminating the airflow impact interference induced by the tray structure, and solving the problem of baseline drift caused by vortex / airflow impact induced by the tray protrusion. Third, an anti-radiation shield is added directly above the balance: it is made of 1.5mm thick polished stainless steel sheet, and the outer surface is polished to reduce the radiation absorption rate. A 16mm air gap is maintained between the outer surface and the upper surface of the balance. The principle is that the low absorption rate of polished stainless steel can block the heat radiation of the upper heater. At the same time, the shield can shield the residual micro-airflow. The air gap further blocks heat conduction, controlling the temperature fluctuation of the working environment around the balance within a stable range of ≤5K. This fundamentally weakens the coupling interference between heat radiation and residual airflow, and solves the problem of the balance working environment overheating caused by heat radiation.

[0024] This invention implements dynamic calibration of the mass baseline under blank operating conditions. After structural optimization, without placing a sample, the entire device is run under the same heater heating program, gas flow rate, and water cooling conditions as the formal experiment, and the change curve of the electronic balance reading over time is recorded synchronously to obtain the mass baseline under this operating condition (reflecting only residual reproducible environmental interference). During formal sample testing, the baseline value at the same moment is subtracted from the real-time collected balance reading to obtain the true dynamic mass loss data of the sample. Thus, the interference remaining after structural optimization is reproducible environmental interference and is unrelated to the actual mass change of the sample. This invention directly eliminates the coupling effect of residual interference on the mass signal by subtracting the blank baseline under the same operating conditions, further improving weighing accuracy without additional hardware, and solving the problem of insufficient measurement accuracy caused by residual interference.

[0025] This invention clarifies the generation mechanism of multi-source coupling interference through CFD simulation, providing a reusable theoretical analysis framework for the anti-interference design of closed pyrolysis devices. The synergistic effect of three structural optimizations significantly suppresses the influence of airflow impact and thermal radiation on the balance. The improved mass baseline enters a slow linear descent mode at 50 seconds, which can be uniformly described by piecewise linear equations, and the repeatability of the mass baseline is significantly improved. The blank baseline correction method further eliminates residual reproducible interference, fully meeting the accuracy requirements for obtaining pyrolysis kinetic parameters in materials fire safety research. Attached Figure Description

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a flowchart of the infrared temperature measurement calibration method for a closed pyrolysis device provided by the present invention; Figure 2 This is a flowchart of the weighing anti-interference method for a closed pyrolysis device provided by the present invention; Figure 3 This is a schematic diagram of the closed pyrolysis device provided by the present invention; Figure 4 This is a schematic diagram of the infrared optical path provided by the present invention; Figure 5 This is a schematic diagram of real-time calibration of optical transmittance during the experimental process provided by the present invention. Figure 6 This is a schematic diagram comparing calibrated infrared thermometry and thermocouple data provided by the present invention. Figure 7 This is a simplified schematic diagram of the model structure provided by the present invention; Figure 8 This is a schematic diagram of the temperature field distribution of the closed pyrolysis device during the heating process provided by the present invention; Figure 9 This is a schematic diagram of the airflow streamline distribution of the closed pyrolysis device provided by the present invention; Figure 10 This is a schematic diagram of the air pressure difference between the upper and lower spaces of the sample tray inside the device during the heating process provided by the present invention. Figure 11 This is a schematic diagram of the improved device structure based on simulation results provided by the present invention; Figure 12 This is a schematic diagram comparing the quality baselines of the transpose structure before and after optimization provided by the present invention; Figure 13 This is a schematic diagram of the pyrolysis experimental results of PMMA samples in the closed thermal control device provided by the present invention. Detailed Implementation

[0027] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0028] Figure 1 A schematic diagram of the infrared temperature measurement calibration method for a closed pyrolysis apparatus according to this embodiment is shown. In this embodiment, the infrared temperature measurement calibration method for a closed pyrolysis apparatus includes the following steps: S11: A gold mirror at a 45° angle is installed directly below the sample holder of the sealed pyrolysis device. An optical window is opened on the outer wall of the vaporization chamber of the sealed pyrolysis device corresponding to the height of the gold mirror. The optical window is used to allow the infrared radiation signal from the bottom of the sample to penetrate the sealed wall and be received by an external infrared thermal imager to obtain an infrared optical measurement path. In one exemplary embodiment, the gold mirror is used to fold the infrared path emitted downwards from the bottom of the sample by 90°.

[0029] In one exemplary embodiment, the reflectivity of the gold mirror is not less than 0.96.

[0030] In one exemplary embodiment, the optical window is made of single-crystal germanium, which has high transmittance in the mid- and far-infrared bands.

[0031] S12: The same black paint as the bottom of the formal experimental sample is uniformly sprayed onto the surface of a high thermal conductivity copper block with the same diameter as the sample to be tested. Holes with the same diameter as the thermocouple are set at the center and half radius of the high thermal conductivity copper block for embedding thermocouples. The thermocouples are used to measure the true internal temperature of the high thermal conductivity copper block to obtain a calibration piece.

[0032] In one exemplary embodiment, the height of the high thermal conductivity copper block is 5 mm.

[0033] In one exemplary embodiment, the emissivity of the black paint is not less than 0.95.

[0034] In one exemplary embodiment, the thermocouple is a type K thermocouple.

[0035] S13: Based on the infrared optical measurement path, calibration component and sealed pyrolysis device, the lumped transmittance is dynamically calibrated using the unsteady heating process to obtain the equivalent lumped transmittance, which is used for accurate non-contact temperature measurement in real sample experiments.

[0036] In one exemplary embodiment, the method for dynamically calibrating lumped transmittance using a non-steady-state heating process includes: Place the calibration component in the sample tray of the closed pyrolysis device, and start the heater of the closed pyrolysis device to heat up according to the predetermined program. The readings of the infrared thermal imager and the thermocouple of the calibration component along the infrared optical measurement path are obtained. The optical transmittance parameter of the infrared thermal imager is continuously adjusted until the maximum deviation between the reading of the infrared thermal imager and the reading of the thermocouple does not exceed a preset difference within the full range. The current optical transmittance parameter of the infrared thermal imager is then used as the equivalent lumped transmittance of the infrared optical measurement path within the practical temperature measurement range.

[0037] In one exemplary embodiment, the preset difference is ±5K.

[0038] Figure 2 A schematic diagram of a weighing anti-interference method for a closed pyrolysis apparatus according to this embodiment is shown. In this embodiment, the weighing anti-interference method for a closed pyrolysis apparatus includes the following steps: S21: Construct an internal flow field and temperature field model for a closed pyrolysis device using computational fluid dynamics. Use the internal flow field and temperature field model to obtain simulation results of temperature field, airflow, and pressure difference between the upper and lower surfaces of the sample tray.

[0039] In one exemplary embodiment, the internal flow field temperature field model includes a full-size simplified geometric model of the sealed vaporization chamber, sample tray, lower cavity, and balance mounting area of ​​the sealed pyrolysis device, and the model is coupled with gas flow, pressure field, and temperature field.

[0040] S22: Based on the simulation results of the temperature field, airflow, and pressure difference between the upper and lower surfaces of the sample tray, the structure of the closed pyrolysis device is optimized to obtain the optimized closed pyrolysis device.

[0041] S23: Based on the optimized closed pyrolysis device, without placing any sample, run the closed pyrolysis device according to the same heater heating program, gas flow rate and water cooling conditions as the formal experiment, obtain the curve of the electronic balance reading changing over time, and obtain the mass baseline under the formal experimental conditions.

[0042] In one exemplary embodiment, the quality baseline is used to: in the quality test of the formal sample, subtract the baseline value at the corresponding moment from the real-time collected balance reading to obtain the true dynamic quality loss data of the sample.

[0043] In some embodiments, the infrared temperature measurement calibration method and the weighing anti-interference method for a closed pyrolysis device described above can also be implemented in the following ways.

[0044] This invention is based on Figure 3 The experimental setup is described below. The closed-loop controlled atmosphere pyrolysis apparatus mainly consists of four key modules: a heater, a vaporization chamber, a parameter monitoring module, and a gas sampling module. Figure 3 (a) shows the heater, vaporization chamber, and parameter monitoring module. Figure 3 (b) is the gas sampling module. Figure 3 The image in (c) is an actual photograph.

[0045] The heater of the closed-loop controlled atmosphere pyrolysis apparatus (see...) Figure 3 The design (green box in (a)) is similar to a cone calorimeter, consisting of an electric heating coil. It can rotate left and right and move up and down, making it easy to remove highly expandable samples. Before the experiment, the heater is preheated to the set temperature on an insulated tray next to it; during the experiment, the heater and the vaporization chamber are closed, and the gap between them is sealed by an O-ring rubber seal to precisely control the composition and concentration of the purge gas.

[0046] like Figure 3 As shown in the red box in (a), the vaporization chamber consists of an inner and outer wall, both coated with black paint (Rust-Oleum Specialty High Heat 7778830), a coating proven to have stable thermal properties and a high emissivity of 0.95. The distance between the inner and outer walls is 30 mm, and gas can be introduced into the chamber through a rectifier plate. A sample holder with an inner diameter of 100 mm and a sample diameter of 70 mm is housed inside the inner wall, surrounded by ceramic fiberboard for thermal insulation. The bottom of the sample is covered with a 0.03 mm thick high thermal conductivity copper foil, bonded to the sample with a thin layer of Poxy Pak EA9017 epoxy adhesive. The sample is supported by a diamond-shaped aluminum mesh inside the sample holder; both the aluminum mesh and the bottom of the copper foil are also coated with black paint. Three stainless steel columns connect the sample holder to the electronic balance; there is no contact between the sample holder and the inner wall of the vaporization chamber to avoid interference with mass measurement.

[0047] The inner and outer walls of the vaporization chamber are designed with water-cooled jackets to reduce heat accumulation on the chamber walls and secondary radiation to the sample. The flow rate of the water-cooled jackets is set to 1.5 L·min. -1 Regarding gas introduction, three independent gas channels supply gas to the vaporization chamber according to the set gas composition and flow rate to ensure an oxygen-free environment within the chamber. A 25 mm thick layer of glass beads is installed above the rectifier plate to ensure uniform airflow distribution into the vaporization chamber.

[0048] Parameter monitoring module (see) Figure 3(a) Blue box indicates that the sample mass, bottom surface temperature, sample shape, and purge gas temperature can be measured simultaneously. Sample mass is measured using an AND GF-1003A electronic balance with an accuracy of ±0.001 g. To achieve non-contact measurement of the sample bottom surface temperature, a FLIR A400 infrared thermal imager and a high-reflectivity (0.96) gold mirror are used. Notably, due to the closed system design of the sealed controlled atmosphere pyrolysis apparatus, a germanium window with high infrared transmittance is integrated into the system, instead of a traditional glass window. Furthermore, a quartz viewing window is installed on the outer wall of the vaporization chamber to record sample shape changes via a camera. At the glass bead layer outlet, two 1 mm diameter thermocouples are installed at the same height as the sample to measure the gas flow temperature near the sample.

[0049] Gas analysis module (see) Figure 3 (b) (shown in the brown box) is connected to the exhaust pipe, and has a gas sampling and processing capacity of 7 L·min. -1 The heat tracing pipe uses a corrugated metal tube with an inner diameter of 8 mm and is maintained at 350 °C to prevent premature condensation of the gas and avoid secondary reactions. The transparent water-cooled condenser is made of borosilicate glass and has a built-in 300 mm long condensation coil; the tar produced during condensation is collected through a conical flask. The gas analysis module also includes a flue gas filter and a drying cylinder, with a vacuum pump downstream. The flue gas filter removes particulate matter from the flue gas, and the drying cylinder removes moisture. The system has three gas sampling ports, which can be connected in parallel to a flue gas analyzer, an online gas mass spectrometer, and a sampling gas bag to achieve simultaneous analysis of gas and solid-phase pyrolysis data. In addition, an extra exhaust port is provided for the safe discharge of excess gas. Each sampling port is equipped with a corresponding float flowmeter to adjust and read the gas sampling flow rate.

[0050] In some embodiments, the infrared temperature measurement calibration method for a closed pyrolysis apparatus described above can also be implemented in the following ways.

[0051] In this embodiment, through a special combination of optical path media and a dynamic calibration process for lumped transmittance, non-contact and accurate measurement of the sample bottom temperature is achieved under completely sealed conditions. The infrared temperature measurement calibration method for the sealed pyrolysis device includes the following steps: Step 1: Construct the infrared optical measurement path. For example... Figure 4 As shown, a high-reflectivity (0.96) gold mirror is installed at a 45° angle directly below the sample holder. This gold mirror can deflect the infrared path emitted downwards from the bottom of the sample by 90°. An optical window is opened on the outer wall of the vaporization chamber corresponding to the height of the gold mirror. The window material is single-crystal germanium, which has high transmittance in the mid- and far-infrared bands, to replace the traditional quartz or ordinary glass window, so that the infrared radiation signal from the bottom of the sample can effectively penetrate the sealed wall and be received by the external infrared thermal imager.

[0052] Step 2: Prepare a dedicated contact-non-contact combined calibration component. Take a high thermal conductivity copper block (70 mm in diameter and 5 mm in height) with the same diameter as the sample to be tested. Evenly spray its surface with the same high emissivity (0.95) black paint as the bottom of the actual experimental sample to ensure its surface radiation characteristics are stable and known. Drill holes of the same diameter as the thermocouples at the center and half the radius of the copper block, and insert K-type thermocouples to accurately measure the true internal temperature of the copper block at the corresponding locations.

[0053] Step 3: Dynamically calibrate the lumped transmittance during the unsteady-state heating process. Place the calibration piece prepared in Step 2 in the sample tray and start the heater to heat according to the predetermined program. Move the heater directly above the sample and set the heater temperature to 20K / min. -1 The heating rate increased from 313 K to 1073 K, with the copper block temperature continuously varying within a target range of 313 K to 800 K to simulate the temperature and rapid heating process during the pyrolysis of a real sample. Infrared thermal imager temperature measurement points were positioned next to the thermocouple embedding locations, simultaneously recording both infrared thermal imager readings and thermocouple readings. Figure 5 As shown, during the entire heating process, the optical transmittance parameter of the infrared thermal imager is continuously adjusted until the maximum deviation between the infrared temperature measurement value and the thermocouple measurement value does not exceed ±5 K across the entire range. The transmittance value set at this point is the equivalent lumped transmittance of the optical path system within the practical temperature measurement range, which can be used for accurate non-contact temperature measurement in subsequent real sample experiments.

[0054] The final test results are shown below. Figure 6 By comparing and calibrating with copper block thermocouples, the optical transmittance parameter was finally determined to be 0.72, so that the error of infrared temperature measurement does not exceed ±5 K in the full range.

[0055] 2. Anti-interference methods for the weighing system of a closed pyrolysis apparatus This method identifies interference sources in mass measurement through simulation and optimizes the internal structure of the device accordingly, thereby reducing the impact of airflow dynamic disturbances and thermal radiation on the weighing of the electronic balance in the closed pyrolysis device.

[0056] Step 1: Establish a flow and temperature field model within the device and identify sources of interference in the balance weighing. Using computational fluid dynamics (CFD), a full-size simplified model of the sealed vaporization chamber, sample tray, lower chamber, and balance mounting area is created. The geometric model is as follows: Figure 7 As shown, the model couples gas flow, pressure field, and temperature field, focusing on the analysis of the pressure distribution and temperature gradient in the space above and below the sample tray.

[0057] Figure 8The results show the simulation of the internal temperature field of the device. During the heating process, the upper chamber is heated to a significantly higher temperature than the lower chamber, and the sample tray in the middle is affected by thermal buoyancy. Figure 9 The results show the simulated airflow inside the device. The streamlines indicate that due to the continuous introduction of nitrogen into the upper chamber and the inability to expel the gas in a timely manner, gas flows into the lower chamber, disturbing the balance's operating environment. Combined with the analysis of the protruding sample tray in reality, the high-speed airflow impacts the tray's sidewall, then deflects downwards and surges into the lower chamber, creating turbulence on the balance. Figure 10 This is a simulation result of the pressure difference between the upper and lower surfaces of the sample tray. The combined effect of airflow lift and thermal buoyancy causes the pressure in the upper chamber to be lower than that in the lower chamber, creating a pressure difference that changes non-linearly over time. Furthermore, the temperature fluctuation of the balance's operating environment should not exceed 5 K. However, in actual experiments, it was found that the balance operates in an unsteady environment due to the thermal radiation from the high-temperature sample tray and the downward infiltration of hot airflow from the upper chamber, severely affecting the weighing results.

[0058] Step 2: Implement three targeted structural optimizations based on the simulation analysis results. Figure 11 The diagram shows the structure of the device before and after the improvements. The first optimization is to increase the exhaust port diameter from 28.5 mm to 48 mm, while simultaneously shortening the exhaust pipe length to suppress gas seepage into the lower chamber due to poor exhaust flow. The second optimization is to lower the sample tray installation height by 20 mm, making its upper surface almost flush with the connection opening of the vaporization chamber. This eliminates the airflow deflection and vortex effect induced by the tray's protruding edges, ensuring smooth entry of high-speed airflow into the exhaust channel. The third optimization is to add a radiation shield directly above the balance. This shield is made of 1.5 mm thick polished stainless steel sheet, with a polished outer surface to reduce radiation absorption, and maintains a 16 mm air gap with the upper surface of the balance. This radiation shield can simultaneously block high-temperature thermal radiation from the upper chamber and shield residual micro-airflow that may exist due to structural gaps, controlling the ambient temperature fluctuations around the balance within the stable operating range allowed by the electronic balance.

[0059] Step 3: Implement dynamic calibration of the mass baseline under blank operating conditions. After completing the above structural optimization, without placing any samples, run the entire apparatus according to the exact same heater heating program, gas flow rate, and water cooling conditions as in the formal experiment, and simultaneously record the change curve of the electronic balance reading over time. This is the mass baseline under this operating condition. This baseline only reflects the residual and reproducible environmental interference effects after structural optimization. In the mass testing of the formal samples, subtracting the baseline value at the same moment from the real-time collected balance readings will yield the true dynamic mass loss data of the samples.

[0060] The airflow / radiation interference resistance method for the weighing system of the closed pyrolysis device described in this invention systematically combines CFD simulation and experimental verification to identify the key interference factors on the weighing baseline in the closed pyrolysis device as the pressure difference between the upper and lower chambers, airflow disturbance on the balance and sample tray, and thermal radiation. Through three synergistic improvement measures—expanding the exhaust gas outlet, reducing the tray height, and adding a radiation shield—this method achieves [the desired effect]. Figure 12 The results are shown. The improved quality baseline enters a slow linear decline mode at 50 s, and can be described by a piecewise linear equation. Furthermore, the error band in the figure shows that the improved quality baseline has higher repeatability.

[0061] Example 1: 1. Sample Preparation: Take a black polymethyl methacrylate (PMMA) disc sample, 70 mm in diameter, with an initial thickness of 5.7 mm and an initial mass of approximately 26 g (the exact value may vary slightly depending on the batch). The bottom of the sample is treated in the same way as in Example 1 (copper foil, aluminum mesh, black paint coating). The sample is placed in a ceramic fiber insulated sample holder.

[0062] 2. Experimental conditions: The radiative heat flux of the heater was set to 60 kW·m. -2 (Corresponding heater temperature 718 ℃). Nitrogen flow rate is 150 L / min. -1 Pre-purge for 3 minutes. Water jacket flow rate is 1.5 L / min. -1 .

[0063] 3. Measurement and Data Acquisition: Mass measurement was performed using an AND GF-1003A electronic balance (accuracy ±0.001 g, sampling 1 Hz), with real-time subtraction of the calibrated mass baseline (60 kW·m). -2 (Linear baseline model under the given conditions). Bottom temperature measurement was performed using a FLIR A400 infrared thermal imager, a high infrared transmittance germanium window (calibrated transmittance 0.72), and a 45° gold mirror. Multiple temperature monitoring points were set up to collect the average temperature of the sample bottom. To verify the accuracy of the test data from the device of this invention, the obtained PMMA MLR and bottom temperature data were compared with publicly available data from a non-sealed device in the literature (CAPA II, Fiola et al., Comparison of pyrolysis properties of extruded and cast poly, 2021).

[0064] 4. Experimental Results: Figure 13 These are the test results for PMMA in a closed, controlled atmosphere pyrolysis apparatus. Figure 13 In the middle (a), mass is represented. Figure 13 (b) represents the temperature at the bottom of the sample.

[0065] Mass loss rate (MLR): The experimentally obtained MLR curve over time is in good agreement with the literature data. The peak MLR occurs at approximately 236 s, and the peak value measured by this device is approximately 0.012 kg·m. - ²·s - ¹, differing from the literature value by 5.8%. Between 80 and 240 s, small bubbles and slight arching were observed on the sample surface in the video images, causing slight fluctuations in the MLR curve.

[0066] Bottom temperature evolution: The bottom temperature gradually rises from room temperature to approximately 660 K. The entire heating curve highly coincides with literature data, with an average temperature difference of less than 5 K. Especially in the main pyrolysis stage (200-400 s), the temperature plateau characteristics are consistent.

[0067] Repeatability verification: Three repeated experiments were conducted, and the standard deviations of the MLR peak and bottom temperature curves were less than 6% and 2.1%, respectively, indicating that the experimental data have good repeatability.

[0068] 5. Results of the Example: This example compares the PMMA pyrolysis data measured by the closed pyrolysis device with the results of the non-closed device. The test results of the closed device after temperature calibration and mass weighing improvement are highly consistent with the results of the non-closed device, with an average error of only 5.8%.

[0069] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. An infrared temperature measurement calibration method for a closed pyrolysis apparatus, characterized in that, Includes the following steps: S11: A gold mirror at a 45° angle is installed directly below the sample holder of the sealed pyrolysis device. An optical window is opened on the outer wall of the vaporization chamber of the sealed pyrolysis device corresponding to the height of the gold mirror. The optical window is used to allow the infrared radiation signal from the bottom of the sample to penetrate the sealed wall and be received by an external infrared thermal imager to obtain an infrared optical measurement path. S12: The same black paint as the bottom of the formal experimental sample is uniformly sprayed onto the surface of a high thermal conductivity copper block with the same diameter as the sample to be tested. Holes with the same diameter as the thermocouple are set at the center and half radius of the high thermal conductivity copper block for thermocouples. The thermocouples are used to measure the true internal temperature of the high thermal conductivity copper block to obtain a calibration piece. S13: Based on the infrared optical measurement path, calibration component and sealed pyrolysis device, the lumped transmittance is dynamically calibrated using the unsteady heating process to obtain the equivalent lumped transmittance, which is used for accurate non-contact temperature measurement in real sample experiments.

2. The method according to claim 1, characterized in that, The gold mirror is used to refract the infrared path emitted downwards from the bottom of the sample by 90°; the reflectivity of the gold mirror is not less than 0.

96.

3. The method according to claim 1, characterized in that, The optical window is made of single-crystal germanium, which has high transmittance in the mid- and far-infrared bands.

4. The method according to claim 1, characterized in that, The height of the high thermal conductivity copper block is 5mm.

5. The method according to claim 1, characterized in that, The emissivity of the black paint is not less than 0.

95.

6. The method according to claim 1, characterized in that, The method for dynamically calibrating lumped transmittance using an unsteady heating process includes: Place the calibration component in the sample tray of the closed pyrolysis device, and start the heater of the closed pyrolysis device to heat up according to the predetermined program. The readings of the infrared thermal imager and the thermocouple of the calibration component along the infrared optical measurement path are obtained. The optical transmittance parameter of the infrared thermal imager is continuously adjusted until the maximum deviation between the reading of the infrared thermal imager and the reading of the thermocouple does not exceed a preset difference within the full range. The current optical transmittance parameter of the infrared thermal imager is then used as the equivalent lumped transmittance of the infrared optical measurement path within the practical temperature measurement range.

7. The method according to claim 1, characterized in that, The preset difference is ±5K.

8. A weighing anti-interference method for a closed pyrolysis apparatus, characterized in that, Includes the following steps: S21: Construct an internal flow field and temperature field model for a closed pyrolysis device using computational fluid dynamics, and obtain simulation results of temperature field, airflow, and pressure difference between the upper and lower surfaces of the sample tray using the internal flow field and temperature field model. S22: Based on the simulation results of the temperature field, airflow, and pressure difference between the upper and lower surfaces of the sample tray, the structure of the closed pyrolysis device is optimized to obtain the optimized closed pyrolysis device. S23: Based on the optimized closed pyrolysis device, without placing any sample, run the closed pyrolysis device according to the same heater heating program, gas flow rate and water cooling conditions as the formal experiment, obtain the curve of the electronic balance reading changing over time, and obtain the mass baseline under the formal experimental conditions.

9. The method according to claim 8, characterized in that, The internal flow field and temperature field model includes a full-size simplified geometric model of the sealed vaporization chamber, sample tray, lower cavity, and balance mounting area of ​​the sealed pyrolysis device. The model is coupled with gas flow, pressure field, and temperature field.

10. The method according to claim 8, characterized in that, The quality baseline is used to: in the quality test of the formal sample, subtract the baseline value at the corresponding moment from the real-time collected balance reading to obtain the true dynamic quality loss data of the sample.

Images