CN111505048A - Time-varying radiation heat flow experimental system based on distance control and measuring method - Google Patents
Time-varying radiation heat flow experimental system based on distance control and measuring method Download PDFInfo
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Abstract
The invention discloses a time-varying radiant heat flow experimental system and a measuring method based on distance control, and relates to an experimental device and a testing system capable of realizing time-varying radiant heat flow (time-varying heat flow). The device comprises a radiation source, a radiation source bearing frame, a radiation source moving support, a radiation source controller, a driver, a direct-current power supply and a laboratory bench base; the radiation source moving support adopts a guide rail sliding table, and a guide rail sliding block is arranged on the guide rail sliding table; a radiation source bearing frame is arranged on the guide rail sliding block, and the radiation source is fixedly arranged below the radiation source bearing frame; the lower part of the guide rail sliding block is provided with a fixed frame, a baffle rotating rod is arranged on the fixed frame through a bolt, a baffle is fixedly connected with the baffle rotating rod and is positioned right below a radiation source, and a motor is arranged above the guide rail sliding table and drives a screw rod to rotate; the controller and the direct current power supply are respectively connected with a driver, and the driver is connected with the motor; the direct current power supply provides power for the motor; the radiation source controller is connected with the radiation source.
Description
Technical Field
The invention discloses a time-varying radiant heat flow experimental system and a measuring method based on distance control, and relates to an experimental device and a testing system capable of realizing time-varying radiant heat flow (time-varying heat flow), in particular to an experimental system and a measuring method capable of realizing time-varying radiant heat flow by controlling the distance between a radiation source and a combustible material.
Background
Solid combustibles include natural and man-made materials. Especially, synthetic materials such as high molecular polymers are widely used in the production and living of the nation because of their excellent physicochemical properties. Such as sea, land and air transportation tools, medical materials, building decoration, aerospace instruments and equipment, industrial devices, leisure and entertainment devices and the like, are important materials in the fields of industry, agriculture, national defense, science and technology and the like. However, the solid combustible material has the characteristic of easy pyrolysis and combustion when meeting high temperature or open fire, and is very easy to lose control to cause fire. The fire risk of solid combustibles is varied and includes thermal, smoke, toxicity and corrosion risks. With the development of science and technology, various natural or synthetic materials, especially novel polymer materials, are increasingly applied to various buildings (building wall insulation materials, interior decoration materials and the like) and fields (such as aerospace fields) due to good physical properties. But the research on the fire safety of the material per se is relatively lagged, and comprises the basic research on pyrolysis kinetics, the fire mechanism, the phase change influence (such as thermal deformation, expansion, melting, dripping, gasification and the like), the fire spread, the external condition influence, fire prevention and flame retardance and the like.
Currently, in the research on the thermal safety of medium-sized materials, Cone calorimeters (Cone calorimeters) developed by National Institute of Standards and Technology (NIST) based on international standards ISO 5660, ASTM E1354, etc., and FPAs (Fire Propagation apparatuses) developed based on ASTM E2058 are widely used in countries around the world as standard instruments. In a real fire scenario, the thermal radiation to which the unburned solid combustible is subjected is constantly changing over time. However, in the process of testing materials, due to the limitation of the cone calorimeter, only the pyrolysis ignition process of solid combustible materials under constant radiant heat flow can be measured, so that a great difference exists between an experimental scene and an actual fire scene.
Disclosure of Invention
The invention aims to provide a time-varying radiant heat flow experimental system and a measuring method based on distance control aiming at the defect that the existing standard instrument (such as a cone calorimeter) can not realize time-varying radiant heat flow, and particularly relates to an experimental device and a measuring method aiming at pyrolysis of solid combustible under time-varying heat flow. By designing a device for controlling the position and the moving speed of the radiation source by a program, the distance between the radiation source and the sample piece to be measured is dynamically changed, and the quantitative measurement of the temperature and the quality of the sample piece to be measured under the time-varying heat flow is realized.
The invention is realized by adopting the following technical scheme:
the time-varying radiation heat flow experiment system based on distance control comprises a radiation source, a radiation source bearing frame, a radiation source moving support, a radiation source controller, a driver, a direct-current power supply and an experiment table base;
the cross section of the platform of the experiment table base is rectangular, a square through hole is formed in the middle of the platform of the experiment table base, and the platform is used for placing the bracket to bear an electronic balance and a sample piece when in use so as to avoid the influence of vibration generated by the up-and-down movement of the radiation source on the quality measurement of the sample piece;
the radiation source moving support adopts a guide rail sliding table, the back of the guide rail sliding table is fixedly arranged on the upper half part of the longitudinal support of the experiment table base, and the bottom of the guide rail sliding table is arranged on the rectangular narrow platform; a guide rail sliding block which can move up and down on the guide rail sliding table is arranged on the guide rail sliding table;
a radiation source bearing frame is arranged on the guide rail sliding block, and the radiation source is fixedly arranged below the radiation source bearing frame; a fixed frame is fixedly arranged below the bearing frame mounting part of the guide rail sliding table, a baffle rotating rod is arranged on the fixed frame through a bolt, and the baffle rotating rod can horizontally rotate on the fixed frame; the other end of the baffle rotating rod is fixedly connected with a baffle which is positioned right below the radiation source and blocks the radiation source, and the baffle is used for preventing heat flow from preheating the sample piece in the experimental preparation stage;
the motor is arranged above the guide rail sliding table and drives the screw rod to rotate, and the screw rod is connected with the guide rail sliding block through a fine thread on the screw rod; the controller and the direct current power supply are respectively connected with a driver, and the driver is connected with the motor; the direct current power supply provides power for the motor, and the controller and the driver set and control the instantaneous rotating speed and direction of the motor by changing the pulse and current and the direction so as to achieve a preset heat flow form; the rotating speed and direction of the screw rod determine the moving direction and speed of the guide rail slide block, namely the moving direction and speed of the radiation source;
the radiation source controller is connected with the radiation source to control whether the radiation source heats and the temperature of the heating resistor.
Furthermore, the radiation source consists of a heating resistor, a stainless steel shell, a side cover and a quartz plate, wherein the quartz plate is a semitransparent quartz plate, the side cover is positioned around the quartz plate, the quartz plate is embedded in a groove of the side cover, the side cover is hollow and used for fixing the quartz plate and not blocking radiation heat flow; a semi-frame-shaped stainless steel shell with a downward opening is covered above the quartz plate, and a heating resistor connected in series is fixedly connected in the middle of the stainless steel shell; two rows of 6 threaded holes are uniformly formed in the upper part of the stainless steel shell, and each row is provided with 3 threaded holes so as to fix the stainless steel shell on the bearing frame. In order to prevent the stainless steel shell from being electrified, the inside and the outside of the stainless steel shell are covered with insulating layers and are kept grounded.
The radiation source bearing frame is composed of two L section steels and two steel wires, one end of each steel wire is connected with the long end of the L section steel, a ribbed plate is fixed at the corner of the L section steel for supporting, in order to facilitate installation of the resistance radiation source, 3 bearing frame threaded holes are formed in the upper end face of each L section steel and are used for being matched with threaded holes in a stainless steel shell of the resistance radiation source to facilitate fixing of the resistance radiation source, in order to prevent the radiation source from inclining caused by deformation of the L section steel, the outer end of the L section steel is connected with a guide rail sliding block on a guide rail sliding table through the steel wires, and the radiation source bearing frame is fixed with the guide rail sliding block through screws.
When the experiment system works, an additional part of the experiment device is required to be arranged. The experimental apparatus additional part includes sample support, electronic balance, heat-flow meter and sample, the square through-hole department that opens some in laboratory bench base platform middle part is placed to the sample support, for electronic balance and sample provide the support, avoids the radiation source to reciprocate the influence of the vibrations that produce to electronic balance mass measurement degree of accuracy. Because the height of the upper plane of the sample piece support determines the maximum heat flow value which can be reached by the radiation source in the moving process, the sample piece support adopts a support with adjustable height. The electronic balance is placed on the sample support, so that real-time mass data can be measured conveniently. During calibration, the heat flow meter is placed at the same height position with the upper surface of the sample piece, real-time heat flow data in the moving process of the radiation source is measured, the output voltage of the heat flow meter is connected with the controller, a feedback signal is provided for the change of the rotating speed of the motor, and the fact that the measured heat flow does not deviate from a set heat flow form is guaranteed. During the experiment, the calibrated time sequence of the output voltage of the heat flow meter is loaded in the controller to reproduce the target time-varying heat flow. The sample is wrapped by a sample box with a heat insulation layer, the preparation process of the sample is the same as that of other current standard instruments (such as a cone calorimeter), and the sample is placed on an electronic balance and is arranged in the center right below a radiation source.
The heat flow meter is placed below the radiation source when calibrating heat flow, is connected with the controller to feed back a heat flow signal so as to adjust the moving speed of the radiation source, thereby reducing the deviation between the actually measured heat flow and the set heat flow form, and storing the data in the controller so that the radiation heat flow changes according to the preset heat flow form during the experiment.
Compared with the prior art, the invention has the advantages that: the experimental system has reasonable design and proper volume, and is completely suitable for the mesoscale experiment of a laboratory. The device for controlling the position and the moving speed of the radiation source by a program is adopted to dynamically change the distance between the radiation source and the sample piece to be measured, so that the quantitative measurement of the temperature and the quality of the sample piece to be measured under the time-varying heat flow is realized. The device is simple and easy to operate, has high reliability, can adjust the linear, square, power function, polynomial, decay and other changing heat flow forms, and has high repeatability and recognition degree of test results.
Drawings
FIG. 1 is a schematic diagram of the structure and layout of the system of the present invention;
FIG. 2 is a front view of the radiation source of the system of the present invention (with baffles installed);
FIG. 3 is a left side view of a radiation source of the system of the present invention;
FIG. 4 is a top view of a stainless steel housing for a radiation source of the system of the present invention;
FIG. 5 is a bottom view of a radiation source of the system of the present invention;
FIG. 6 is a bottom view of the radiation source of the system of the present invention after mounting the quartz plate;
FIG. 7 is a front view of a radiation source carrier of the system of the present invention;
FIG. 8 is a top view of a radiation source carrier (without steel wires) of the system of the present invention;
FIG. 9 is a left side view (without steel wires) of the radiation source carrier of the system of the present invention;
FIG. 10 is a schematic view of a radiation source carrier and a radiation source mounting arrangement of the system of the present invention;
FIG. 11 is a front view of a laboratory bench base of the system of the present invention;
FIG. 12 is a top view of a laboratory bench base of the system of the present invention;
FIG. 13 is a schematic diagram of the horizontal heat flux calibration of the system of the present invention;
FIG. 14 is a system set-up heat flow diagram of the present invention;
FIG. 15 is a plot of the surface temperature of PMMA in the form of linear and power function heat flow for the system of the present invention;
FIG. 16 is a graph of the mass loss rate of PMMA in the form of a power function of the system of the present invention.
In the figure:
1. the radiation source comprises 1-1 parts of a radiation source, 1-2 parts of a heating resistor, 1-3 parts of a stainless steel shell, 1-4 parts of a side cover, 1-5 parts of a quartz plate and a threaded hole;
2. the radiation source comprises a radiation source bearing frame, 2-1 parts of L section steel, 2-2 parts of steel wires, 2-3 parts of ribbed plates, 2-4 parts of bearing frame threaded holes, 3 parts of a radiation source moving support (a guide rail sliding table), 4 parts of a radiation source controller, 5 parts of a controller, 6 parts of a direct-current power supply;
7. 7-1 of a experiment table base, 7-2 of a longitudinal support, 7-3 of a platform of the experiment table base, 7-4 of a rectangular narrow platform and a through hole;
8. the device comprises a driver, 9, a fixing frame, 10, a baffle rotating rod, 11, a baffle, 12, a motor, 13, a guide rail sliding block, 14, a sample support, 15, an electronic balance, 16, a heat flow meter, 17, a sample, 18, a heat flow uniform area, 19 and a heat flow attenuation area.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings 1 to 16, in conjunction with specific embodiments.
Time-varying radiation heat flow experimental system based on distance control comprises a radiation source, a radiation source bearing frame, a radiation source moving support, a radiation source controller, a driver, a direct-current power supply and an experimental table base.
The experiment table base is used for fixing the whole experiment device and a radiation source moving support and preventing the device from toppling over, the experiment table base is made of solid 304 stainless steel, the experiment table base is L-shaped integrally and used for improving the stability of the bottom of the whole experiment device, as seen from the figure, the experiment table base is provided with a longitudinal support and an experiment table base platform, the size of the horizontal plane at the lowest part of the experiment table base is 650mm × 500mm and 100mm, a protruding rectangular narrow platform is arranged at the lower part of the longitudinal support, the protruding part is 250mm high and 135mm thick and the width is the same as that of a bottom panel and used for supporting the bottom of a guide rail sliding table, the upper part of the longitudinal support is 1260mm high, 50mm thick and 150mm wide and used for fixing the back of the guide rail sliding table, the cross section of the experiment table base platform is rectangular, a square through hole is formed in the middle of the experiment table base platform, the size is 250mm × 250mm, the experiment table base is used for placing the support and bearing an electronic balance and a sample.
The radiation source moving support adopts a guide rail sliding table, the back of the guide rail sliding table is fixedly arranged on the upper half part of the longitudinal support of the experiment table base, and the bottom of the guide rail sliding table is arranged on the rectangular narrow platform; the guide rail sliding table is provided with a guide rail sliding block which can move up and down on the guide rail sliding table.
The radiation source comprises a heating resistor, a stainless steel shell, a side cover and a quartz plate, wherein the quartz plate is a semitransparent quartz plate, the embodiment takes a radiation source with the size of 300mm × 300mm as an example, if other radiation sources with other sizes are needed, the side cover with the thickness of 3mm is customized according to needs and is arranged around the quartz plate, the quartz plate is embedded in a groove of the side cover, the side cover is hollow and used for fixing the quartz plate and does not obstruct radiation heat flow, the quartz plate adopts a semitransparent quartz plate with the size of 310mm × 310mm and the thickness of 3mm, the semitransparent quartz plate is used for uniformly radiating heat flow and preventing electric shock, a semi-frame-shaped stainless steel shell with a downward opening is covered above the quartz plate, the middle of the stainless steel shell is fixedly connected with the heating resistor in series, the heating resistor is 20mm in diameter and 300mm in length, the distance between every two adjacent resistors is 40mm, the size of the stainless steel shell with the thickness of 5mm is 40mm × 300mm × 300mm, two rows of threaded holes with the same size of M6 mm are uniformly arranged on the upper part of the stainless steel shell, each row is provided with 3 threaded holes, a stainless steel shell, a stainless steel baffle plate is used for controlling the temperature of a stainless steel baffle plate, the radiation source, the stainless steel baffle is used for preventing the radiation source, the stainless steel shell, the stainless steel baffle is used for preventing the radiation source, the radiation baffle with the radiation baffle, the stainless steel baffle, the baffle is.
The radiation source support frame is arranged on a guide rail sliding block, a radiation source is fixedly arranged below the radiation source support frame, a fixed frame is fixedly arranged below the mounting position of the radiation source support frame of the guide rail sliding block, a baffle rotating rod is arranged on the fixed frame through a bolt and can horizontally rotate on the fixed frame, a baffle is fixedly connected to the other end of the baffle rotating rod and is positioned right below the radiation source and used for blocking the radiation source and preventing heat flow from preheating a sample piece in an experimental preparation stage, in order to meet the requirement of supporting the weight of the radiation source, the radiation source support frame is composed of L section steel with the length of 700mm, the width of 50mm and the thickness of 5mm and two steel wires with the diameter of 5mm, rib plates are arranged at corners of L section steel for supporting, in order to conveniently mount the radiation source, 3M 6 (the diameter of 6 mm) support frame threaded holes are arranged above L section steel, are matched with threaded holes on a stainless steel shell of the radiation source, in order to conveniently fix the radiation source, the horizontal distance of 100mm is 120mm, in order to prevent the radiation source from inclining caused by L section steel deformation, the outer end of the guide rail sliding block is connected with threaded holes of the guide rail sliding block L through screws, and the length of the side length of the.
The device comprises a guide rail sliding table, a motor, a controller, a direct current power supply, a driver, a controller and a radiation source, wherein the motor is arranged above the guide rail sliding table and drives a lead screw to rotate, the lead screw is connected with a guide rail sliding block through a fine thread on the lead screw, the controller and the direct current power supply are respectively connected with the driver, the driver is connected with the motor, the direct current power supply provides power for the motor, the controller and the driver control the instantaneous rotating speed and direction of the motor through changing the pulse and current size and direction, so that a preset heat flow form is achieved, the rotating speed and direction of the lead screw determine the moving direction and speed of the guide rail sliding block, namely the moving speed of the radiation source, a moving support for fixing the radiation source selects the guide rail sliding table with the model of GBX2010, the effective stroke is 1000mm, the size of the guide rail sliding table is 160mm × 165mm, the guide rail sliding table is used for driving the radiation source to move, so that the surface of a sample piece to be detected receives radiation heat flow changing along with time, the guide rail sliding table is.
The radiation source controller is connected with the radiation source to control whether the radiation source heats and the temperature of the heating resistor.
The sample holder, electronic balance, heat flow meter and sample are additional parts of the experimental setup for determining experimental data, as shown in fig. 1. The height-adjustable sample support is placed in the hollow part of the base of the experiment table and used for supporting the electronic balance and the sample. The influence of vibration generated by the up-and-down movement of the radiation source on the mass measurement accuracy of the electronic balance can be avoided. The electronic balance is placed on the sample support, so that real-time mass data can be measured conveniently. During calibration, the heat flow meter is placed at the same height position with the upper surface of the sample piece, real-time heat flow data in the moving process of the radiation source is measured, the output voltage of the heat flow meter is connected with the controller, a feedback signal is provided for the change of the rotating speed of the motor, and the fact that the measured heat flow does not deviate from a set heat flow form is guaranteed. During the experiment, the calibrated time sequence of the output voltage of the heat flow meter is loaded in the controller to reproduce the target time-varying heat flow. The sample is wrapped by a sample box with a heat insulation layer, the preparation process of the sample is the same as that of other current standard instruments (such as a cone calorimeter), and the sample is placed on an electronic balance and is arranged in the center right below a radiation source.
The heat flow meter is a water-cooled Schmidt-bourette (Schmidt-Boelter) heat flow meter. The sample support consists of two optical bread boards and four screw rods and provides support for the electronic balance and the sample. The direct current power supply can provide 20-50V direct current.
The experimental system can measure the pyrolysis combustion performance of solid-phase combustible materials such as polymer, wood and the like, and the measured materials are required to be cut into square or round sample pieces before the experiment, the experiment takes uniform polymer material-extruded transparent PMMA (polymethyl methacrylate) as an example, the sample pieces are cut by laser, the size is × 100mm, the thickness is 10mm, the processed and formed sample pieces are uniform in thickness, the thickness error is not more than 0.01mm, the material is transparent, uniform and free of impurities, no obvious bubbles, sand holes and small holes exist, the cut surfaces are smooth, and the sample pieces are placed in an oven to be baked for 8 hours at 70 ℃ after being cut, so that the surface of the sample pieces is ensured to be free of moisture and colloid residues.
The following examples illustrate in detail the assay method using the present system, comprising the steps of:
(1) calibrating the heat flow uniformity of a horizontal plane;
(1-1) fixing a heat flow meter at a certain height below a radiation source, and keeping the position of the radiation source and the temperature of the radiation source unchanged;
(1-2) horizontally moving the heat flow meter in four directions by taking the position right below the radiation source as a center axis, wherein the interval of each direction is 90 degrees, the height of the heat flow meter is kept unchanged during the period, and repeatedly calibrating for many times; when the heat flow attenuation is larger than 5% of the heat flow value of the central shaft position, the heat flow is not uniform; recording the horizontal distance from the central axis at a thermal decay of 5%, the horizontal distance from the central axis to this location being the radius of the thermally uniform region, as shown in fig. 13; this radius is measured to be 60mm, so the size of the sample to be tested should not be greater than 120mm (sample length or diameter).
(2) Setting and calibrating target heat flow;
(2-1) fixedly placing a heat flow meter at a certain height under the radiation source; the direct current power supply provides power support for the system, the controller controls the pulse signal and the direction signal, and the driver controls the current and the pulse; the controller and the driver jointly set the heat flow form and the change rate required by the experiment, and the motor drives the guide rail sliding block and the radiation source to move up and down to start calibration;
(2-2) adjusting the temperature of the radiation source and the opening and closing of the baffle plate by using the radiation source controller;
(2-3) in the calibration process, the heat flow meter feeds back the monitored real-time heat flow value to the controller, and the controller adjusts the rotating speed of the motor together by adjusting the pulse and the current according to the feedback data and the driver so that the radiation source continues to move under the condition that the radiation source hardly deviates from the set heat flow form and the change rate; the calibration results show that the R2 between the measured heat flow and the set heat flow is higher than 99.5%, and the fitting degree is good, as shown in FIG. 14.
The heat flow form includes linear, square, power function sum, polynomial or attenuation forms.
(3) Carrying out pyrolysis experiment of sample piece to be tested
(3-1) adjusting the height of the sample support to ensure that the height of the upper surface of the sample is consistent with that of the upper surface of the heat flow meter during calibration;
(3-2) sequentially placing the electronic balance and the sample box filled with the sample to be tested on the sample support, and setting a heat flow form and a heat flow change rate required by an experiment; and then the transient mass loss or transient surface and internal temperature measurement experiment in the sample piece pyrolysis process can be carried out.
(3-3) measuring the surface or internal temperature of the sample by using a K-type thermocouple with the diameter of 0.5mm, wherein the mass and temperature change of the material in the pyrolysis process cannot be measured simultaneously due to the existence of the thermocouple, so that the transient mass loss and the temperature of the sample in the pyrolysis process need to be measured separately under the condition of ensuring that the heat flow form is not changed.
If the synchronous data of the surface temperature and the quality need to be measured, a non-contact thermal infrared imager can be adopted to collect the change process of the surface temperature. The surface temperatures of samples in the linear and power function forms are shown in fig. 15, and the mass loss rates of samples in the power function form are shown in fig. 16.
The device effectively overcomes the defect that the existing standard instrument (such as a cone calorimeter) can not realize time-varying radiation heat flow, can control the position and the moving speed of the radiation source, dynamically changes the distance between the radiation source and the sample piece to be measured, and realizes the quantitative measurement of the temperature and the quality of the sample piece to be measured under the time-varying heat flow. The repeatability and the acceptance of the test result are high by adjusting the changing heat flow forms such as linearity, square, power function, polynomial, decay and the like.
Claims (9)
1. The utility model provides a time-varying radiation heat flow experimental system based on distance control which characterized in that: the device comprises a radiation source, a radiation source bearing frame, a radiation source moving support, a radiation source controller, a driver, a direct-current power supply and a laboratory bench base;
the cross section of the platform of the experiment table base is rectangular, a square through hole is formed in the middle of the platform of the experiment table base, and the platform is used for placing the bracket to bear an electronic balance and a sample piece when in use so as to avoid the influence of vibration generated by the up-and-down movement of the radiation source on the quality measurement of the sample piece;
the radiation source moving support adopts a guide rail sliding table, the back of the guide rail sliding table is fixedly arranged on the upper half part of the longitudinal support of the experiment table base, and the bottom of the guide rail sliding table is arranged on the rectangular narrow platform; a guide rail sliding block which can move up and down on the guide rail sliding table is arranged on the guide rail sliding table;
a radiation source bearing frame is arranged on the guide rail sliding block, and the radiation source is fixedly arranged below the radiation source bearing frame; a fixed frame is fixedly arranged below the mounting part of the radiation source bearing frame of the guide rail sliding block, a baffle rotating rod is arranged on the fixed frame through a bolt, and the baffle rotating rod can horizontally rotate on the fixed frame; the other end of the baffle rotating rod is fixedly connected with a baffle which is positioned right below the radiation source and blocks the radiation source, and the baffle is used for preventing heat flow from preheating the sample piece in the experimental preparation stage;
the motor is arranged above the guide rail sliding table and drives the screw rod to rotate, and the screw rod is connected with the guide rail sliding block through a fine thread on the screw rod; the controller and the direct current power supply are respectively connected with a driver, and the driver is connected with the motor; the direct current power supply provides power for the motor, and the controller and the driver set and control the instantaneous rotating speed and direction of the motor by changing the pulse and current and the direction so as to achieve a preset heat flow form; the rotating speed and direction of the screw rod determine the moving direction and speed of the guide rail sliding block, namely the moving speed of the radiation source;
the radiation source controller is connected with the radiation source to control whether the radiation source heats and the temperature of the heating resistor.
2. The distance control-based time-varying radiant heat flow experimental system of claim 1, characterized in that: the radiation source comprises a heating resistor, a stainless steel shell, a side cover and a quartz plate, wherein the quartz plate is a semitransparent quartz plate, the side cover is positioned around the quartz plate, the quartz plate is embedded in a groove of the side cover, and the side cover is hollow and used for fixing the quartz plate and not blocking radiation heat flow; a semi-frame-shaped stainless steel shell with a downward opening is covered above the quartz plate, and a heating resistor connected in series is fixedly connected in the middle of the stainless steel shell; two rows of 6 threaded holes are uniformly formed in the upper part of the stainless steel shell, and each row is provided with 3 threaded holes so as to fix the stainless steel shell on the bearing frame.
3. The distance control-based time-varying radiant heat flow experimental system of claim 2, characterized in that: the stainless steel shell is covered with an insulating layer inside and outside and is kept grounded.
4. The distance control-based time-varying radiation heat flow experimental system as claimed in claim 3, wherein the radiation source bearing frame is composed of L steel bars and two steel bars, one end of each steel bar is connected with the long end of the L steel bar, rib plates are fixed at the corners of the L steel bars for supporting, in order to facilitate installation of the resistance type radiation source, 3 bearing frame threaded holes are formed in the upper end face of each L steel bar and are matched with threaded holes in a stainless steel shell of the resistance type radiation source to facilitate fixing of the resistance type radiation source, and in order to prevent the radiation source from inclining caused by deformation of the L steel bars, the outer end of the L steel bars is connected with a guide rail sliding block on the guide rail sliding table through the steel bars.
5. The distance control-based time-varying radiant heat flow experimental system of claim 4, characterized in that: the radiation source bearing frame is fixed with the guide rail sliding block through screws.
6. The distance control-based time-varying radiant heat flow experimental system of claim 1, characterized in that: the experimental system is also provided with an experimental device additional part, wherein the experimental device additional part comprises a sample support, an electronic balance, a heat flow meter and a sample, and the sample support is placed at a square through hole formed in the middle of a base platform of the experimental table; the sample piece bracket adopts a bracket with adjustable height; the electronic balance is placed on the sample piece bracket, so that real-time mass data can be measured conveniently; during calibration, the heat flow meter is placed at the same height with the upper surface of the sample piece, real-time heat flow data in the moving process of the radiation source is measured, the output voltage of the heat flow meter is connected with the controller, a feedback signal is provided for the change of the rotating speed of the motor, and the fact that the measured heat flow does not deviate from a set heat flow form is guaranteed; the sample piece is wrapped by a sample piece box with a heat insulation layer, and is placed on the electronic balance and in the center right below the radiation source;
the heat flow meter is placed below the radiation source when calibrating heat flow, is connected with the controller to feed back a heat flow signal so as to adjust the moving speed of the radiation source, thereby reducing the deviation between the actually measured heat flow and the set heat flow form, and storing the data in the controller so that the radiation heat flow changes according to the preset heat flow form during the experiment.
7. The method for determining the time-varying radiant heat flow experimental system based on the distance control as claimed in claim 1, comprising the following steps:
(1) calibrating the heat flow uniformity of a horizontal plane;
(1-1) fixing a heat flow meter at a certain height below a radiation source, and keeping the position of the radiation source and the temperature of the radiation source unchanged;
(1-2) horizontally moving the heat flow meter in four directions by taking the position right below the radiation source as a center axis, wherein the interval of each direction is 90 degrees, the height of the heat flow meter is kept unchanged during the period, and repeatedly calibrating for many times; when the heat flow attenuation is larger than 5% of the heat flow value of the central shaft position, the heat flow is not uniform; recording the horizontal distance from the central shaft when the thermal attenuation is 5%, wherein the horizontal distance from the central shaft to the position is the radius of the thermal uniformity area, and the length or the diameter of the sample piece to be tested is not more than the radius;
(2) setting and calibrating target heat flow;
(2-1) fixedly placing a heat flow meter at a certain height under the radiation source; the direct current power supply provides power support for the system, the controller controls the pulse signal and the direction signal, and the driver controls the current and the pulse; the controller and the driver jointly set the heat flow form and the change rate required by the experiment, and the motor drives the guide rail sliding block and the radiation source to move up and down to start calibration;
(2-2) adjusting the temperature of the radiation source and the opening and closing of the baffle plate by using the radiation source controller;
(2-3) in the calibration process, the heat flow meter feeds back the monitored real-time heat flow value to the controller, and the controller adjusts the rotating speed of the motor together by adjusting the pulse and the current according to the feedback data and the driver so that the radiation source continues to move under the condition that the radiation source hardly deviates from the set heat flow form and the change rate; the calibration result shows that R2 between the measured heat flow and the set heat flow is higher than 99.5%, the fitting degree is good, and the calibration is finished;
(3) carrying out pyrolysis experiment of sample piece to be tested
(3-1) adjusting the height of the sample support to ensure that the height of the upper surface of the sample is consistent with that of the upper surface of the heat flow meter during calibration;
(3-2) sequentially placing the electronic balance and the sample box filled with the sample to be tested on the sample support, and setting a heat flow form and a heat flow change rate required by an experiment; the transient mass loss or transient surface and internal temperature measurement experiment in the sample piece pyrolysis process can be carried out;
(3-3) measuring the surface or internal temperature of the sample by using a K-type thermocouple with the diameter of 0.5mm, wherein the mass and temperature change of the material in the pyrolysis process cannot be measured simultaneously due to the existence of the thermocouple, so that the transient mass loss and the temperature of the sample in the pyrolysis process need to be measured separately under the condition of ensuring that the heat flow form is not changed.
8. The method for determining the time-varying radiant heat flow experimental system based on the distance control as claimed in claim 7, wherein: the heat flow form in step (2-3) includes a linear, square, power function sum, polynomial or attenuation form.
9. The method for determining the time-varying radiant heat flow experimental system based on the distance control as claimed in claim 7, wherein: in the step (3), if synchronous data of the surface temperature and the quality need to be measured, a non-contact thermal infrared imager can be adopted to collect the change process of the surface temperature.
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