An inside and outside temperature controllable tunnel fire smoke layering characteristic experiment system and method

Abstract

The application discloses a tunnel fire smoke stratification characteristic experiment system and method with controllable inner and outer temperature. The tunnel fire smoke stratification characteristic experiment system comprises a sealed chamber, a tunnel model main body, a fire source simulation device, a temperature control device, a temperature measuring device, a video recording device and a flow field visualization device. The temperature control unit is used for controlling the temperature in the tunnel model main body and the temperature difference between the inside and outside of the tunnel model main body. The flow field visualization device is used for displaying the smoke stratification in the tunnel. The video recording device is used for real-time synthesis and transmission of the smoke movement behavior in the tunnel. The temperature measuring device is used for recording the temperature change in the tunnel axis plane.

Description

Technical Field

[0001] This invention relates to the field of tunnel fire test research, specifically to an experimental system and method for the stratification characteristics of tunnel fire smoke with controllable internal and external temperatures. Background Technology

[0002] In recent years, tunnel fires have occurred frequently. Due to the narrow and semi-enclosed structure of tunnels, once a fire breaks out, the high-temperature and highly toxic smoke is difficult to remove in time, easily causing structural damage to the tunnel, casualties, significant economic losses, and triggering severe public outcry. Statistics show that over 85% of casualties are related to the high-temperature and highly toxic smoke generated by tunnel fires. Therefore, reasonable smoke prevention and ventilation measures are crucial to reducing the hazards of tunnel fires.

[0003] Natural smoke extraction, as an important form of smoke extraction in tunnel fires, has attracted widespread attention in the industry due to its advantages such as low maintenance costs, high reliability, energy saving, and environmental protection. Therefore, many scholars have conducted research on the thermal and dynamic characteristics of smoke in naturally smoke-extracting tunnel fires through methods such as scale-up model experiments, numerical simulations, and full-scale tests, including smoke layer thickness and smoke settling distance.

[0004] On the one hand, existing tunnel fire testing equipment often assumes that the temperature inside the tunnel and the external ambient temperature are the same, which does not match reality. In hot summer weather, the external temperature of the tunnel can reach above 40 degrees Celsius, while the internal temperature is often below 10 degrees Celsius, with the internal temperature being much lower than the external ambient temperature. In cold winter weather, the external temperature of the tunnel is below 0 degrees Celsius, while the internal temperature is often much higher than the external ambient temperature. However, the characteristics of fire smoke movement (such as stratification) are mainly driven by thermal buoyancy, and the temperature difference between the inside and outside of the tunnel will have a significant impact on this. Moreover, there is currently a lack of corresponding testing equipment and platforms that can control the internal and external temperature differences and analyze the stratification characteristics of smoke.

[0005] On the other hand, in order to observe indicators such as flame morphology and smoke movement characteristics, existing tunnel models usually have transparent fireproof glass on one side of the model. This can cause a sudden change in the heat transfer performance of the wall, affecting the smoke movement process and stratification characteristics.

[0006] Existing tunnel fire tests often overlook the temperature differences between the internal and external environments, and therefore the experimental setups are not designed to control these temperatures. Furthermore, existing setups lack consideration for inconsistent wall heat transfer performance, failing to resolve the contradiction between observing fire characteristics and abrupt changes in boundary heat transfer (due to the transparent sidewalls).

[0007] Furthermore, patent research reveals a current lack of reliable experimental devices for controlling the temperature difference between the inside and outside of tunnels, indicating a gap in this technical approach.

[0008] In summary, the shortcomings of existing methods include:

[0009] Existing tunnel fire experimental setups lack consideration for internal and external temperature differences, making it impossible to adjust the internal and external temperatures of the tunnel model according to actual conditions. Furthermore, the sidewalls of existing tunnel models do not use materials with consistent thermal conductivity to reduce the impact of changes in wall heat transfer conditions on smoke movement characteristics. Therefore, to deepen the understanding of the thermal and dynamic behavior of tunnel fire smoke, it is necessary to innovate methods for controlling internal and external tunnel temperatures and observing smoke movement, and to invent corresponding experimental platforms. Summary of the Invention

[0010] The technical problem to be solved by this invention is to provide an experimental system and method for the stratification characteristics of tunnel fire smoke with controllable internal and external temperatures. This system analyzes the influence of fire source power, internal and external temperature difference, and tunnel length on the movement characteristics (stratification characteristics) of tunnel fire smoke, and measures the smoke layer thickness and the critical length of smoke settling, providing guidance for the design of practical natural smoke exhaust tunnels.

[0011] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0012] This invention first provides an experimental system for the smoke stratification characteristics of tunnel fires with controllable internal and external temperatures, including a sealed chamber, a tunnel model body, a fire source simulation device, a temperature control device, a temperature measuring device, a video recording device, and a flow field visualization device.

[0013] The sealed chamber is used to provide a simulated external environment of the tunnel. An air conditioning module for regulating the temperature of the sealed chamber is installed on the sealed chamber. The main body of the tunnel model is set in the sealed chamber. The main body of the tunnel model includes a fire source section and a temperature control section. The fire source section is used to simulate the burning area of ​​a tunnel fire. The temperature control section is used to simulate the one-dimensional spread area of ​​smoke. Multiple observation holes are evenly spaced on the temperature control section.

[0014] The fire source simulation device is used to simulate a fire source and is set inside the fire source section. The fire source simulation device includes an oil pan, a fire source support, a mass recording device, fuel, and an ignition device. The oil pan is used to hold fuel and is set on the fire source support. The fire source support passes through the bottom of the fire source section and is mounted on the mass recording device located outside the fire source section. The mass recording device is used to record the amount of fuel burning in the fire pan in real time. The ignition device is used to ignite the fuel in the fire pan.

[0015] The temperature control device is located outside the temperature control section and is used to regulate the temperature of the temperature control section. The number of video recording devices is equal to the number of observation holes on the temperature control section. Each video recording device corresponds to one observation hole and monitors the movement and stratification of smoke inside the tunnel model body through the observation hole. The flow field visualization device is used to provide the light source required to observe the internal conditions of the tunnel model body. The light source enters from the end of the temperature control section that is connected to the outside.

[0016] In a preferred embodiment of the present invention, the temperature control device includes a thermoelectric cooler, heat sink fins, a fan, a temperature control unit, and a surface-mount thermocouple. One side of the thermoelectric cooler is in close contact with the outer wall of the temperature control section, and the other side of the thermoelectric cooler is in close contact with the heat sink fins. Thermal grease is applied between the thermoelectric cooler, the temperature control section, and the heat sink fins. The surface-mount thermocouple is disposed on the inner side of the bottom of the temperature control section and is used to detect the temperature at the bottom of the temperature control section. The thermoelectric cooler, heat sink fins, fan, and surface-mount thermocouple are all connected to the temperature control unit via wires. The temperature control unit is disposed on the outer side of the tunnel model body and is used to compare the temperature measured by the surface-mount thermocouple with the set temperature, and control the thermoelectric cooler to switch on and off according to the comparison result to adjust the temperature inside the temperature control section.

[0017] As a preferred embodiment of the present invention, the temperature measuring device includes a thermocouple tree and a temperature acquisition instrument; the thermocouple tree is made by vertically binding multiple thermocouples, and the vertical spacing of the measuring points can be adjusted according to actual needs; multiple thermocouple trees are arranged at intervals along the length direction of the tunnel model body on the central axis inside the tunnel model body; the thermocouple tree is used to measure the temperature distribution inside the tunnel model body and transmit the corresponding signals to the temperature acquisition instrument, thereby analyzing the longitudinal smoke stratification of the tunnel.

[0018] The present invention also provides a method for conducting experiments using the aforementioned tunnel fire smoke stratification characteristics experimental system, comprising the following steps:

[0019] 1) Determine the fire source power, tunnel length, and temperature inside and outside the tunnel for the fire scenario to be tested;

[0020] 2) Select the size of the oil pan and the type of fuel according to the fire scenario to be tested. Move the oil pan through the operating hole of the fire source device so that it is close to the left closed surface and placed above the fire source support. Turn on the mass recording device to record the mass change of the oil pan.

[0021] 3) Activate the temperature measuring device to provide real-time feedback on the temperature distribution inside the tunnel model, and adjust the temperature of the temperature control section through the temperature control device.

[0022] 4) The external temperature of the tunnel model is adjusted by the air conditioning system of the sealed room so that the temperature difference between the inside and outside of the tunnel model reaches the target temperature difference;

[0023] 5) After the temperature difference between the inside and outside of the tunnel model body stabilizes, turn on the flow field visualization device and the recording device to confirm that the image inside the tunnel model body can be displayed in real time on the recording device.

[0024] 6) Send an ignition command to the fire source simulation device, and the oil pan burns and generates smoke and heat; each device of the tunnel fire smoke stratification characteristic experimental system records experimental data in real time. After the flame is extinguished, each experimental device is turned off and the experimental data recording is stopped. After the tunnel fire smoke stratification characteristic experimental system cools down and returns to its initial state, the next set of experiments is carried out.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention overcomes the technical deficiency of existing tunnel fire testing devices, which fail to consider the temperature difference between the inside and outside of the tunnel. Based on a hardware platform and a semiconductor cooling (heating) method, it constructs a closed-loop control logic to achieve automatic temperature control between the inside and outside of the tunnel. First, target temperatures are set for both the inside and outside. The hardware platform controls the on / off state of the semiconductor cooling system to control the temperature inside and outside the tunnel model. Furthermore, by adjusting the positive and negative wiring of the semiconductor cooling element, the temperature difference between the inside and outside of the tunnel in summer and winter can be simulated.

[0027] To address the issue that closed tunnel fire experimental devices cannot observe the movement of smoke, a real-time video transmission of smoke movement (smoke stratification) within the tunnel can be achieved using a short-focal-length wide-angle camera, wireless video transmission, and a Python script, while ensuring the stability of heat exchange conditions on the tunnel sidewalls. Attached Figure Description

[0028] Figure 1 A schematic diagram of an experimental platform for the stratification characteristics of smoke in tunnel fires with controllable internal and external temperatures.

[0029] Figure 2 A schematic diagram of the tunnel main body, fire source simulation device, and temperature control device; Figure 2 (a) is a side view. Figure 2 (b) is the front view;

[0030] Figure 3 This is a schematic diagram of an ignition device;

[0031] Figure 4 This is a schematic diagram of the temperature measuring device;

[0032] Figure 5 This is a schematic diagram of a video recording device;

[0033] Figure 6 This is a time-history curve of temperature control inside and outside the tunnel before ignition.

[0034] Figure 7 This is a time-history curve of the temperature distribution cloud map after ignition.

[0035] Among them, 1. Sealed chamber, 11. Air conditioning system, 12. Observation window, 13. Thermometer, 2. Main body of tunnel model, 21. Fire source section, 22. Temperature control section, 23. Closed end, 24. Magnesium oxide board, 25. Temperature control unit, 26. Transparent fireproof glass, 27. Operating hole of fire source device, 3. Fire source simulation device, 31. Oil pan, 32. Fuel, 33. Fire source support, 34. Mass recording device, 35. Tungsten filament, 36. Ignition wire, 37. Power supply, 38. Radio receiving module, 39. Including wireless 4. Flow field visualization device, 41. Sheet light source, 42. Sheet light source bracket, 5. Temperature measuring device, 51. Thermocouple tree, 52. Thermocouple wire, 53. Temperature acquisition instrument, 6. Temperature control device, 61. Thermal grease, 62. Semiconductor cooling chip, 63. Heat sink, 64. Fan, 65. Temperature control unit, 66. Temperature control wire, 67. Relay, 68. Surface mount thermocouple, 69. Observation hole, 71. Recording device, 72. Data cable, 73. Main unit. Detailed Implementation

[0036] The present invention will be further described and illustrated below with reference to specific embodiments. The embodiments described are merely examples of the content of this disclosure and do not limit the scope of the invention. The technical features of each embodiment in the present invention can be combined accordingly, provided that there is no mutual conflict. For example... Figures 1 to 5 As shown, this invention provides an experimental platform for the stratification characteristics of smoke in tunnel fires with controllable internal and external temperatures. By adjusting the fire source power, tunnel length, and internal and external temperatures, the movement and stratification characteristics of smoke under different experimental conditions can be observed based on temperature distribution and video recordings, providing a reference for the fire prevention design of naturally vented tunnels. The fire source power is determined by the size of the oil pan and the type of fuel.

[0037] Firstly, this invention provides an experimental system for the smoke stratification characteristics of tunnel fires with controllable internal and external temperatures, such as... Figure 1 As shown, the tunnel fire smoke stratification characteristic experimental system of the present invention includes a sealed chamber 1, a tunnel model body 2, a fire source simulation device 3, a flow field visualization device 4, a temperature measuring device 5, a temperature control device 6, and a video recording device 7.

[0038] like Figure 1 As shown, the sealed chamber 1 comprises multiple containers connected end-to-end to provide a simulated external environment for the tunnel. The number of containers in the sealed chamber 1 can be increased or decreased according to the length of the tunnel model. Observation windows 12 are provided on the side of the sealed chamber for observing the model experiment. An air conditioning system 11 is also installed inside the sealed chamber to control the temperature of the external environment of the tunnel. In addition, multiple thermometers 13 are evenly distributed inside the sealed chamber to measure the temperature inside the sealed chamber.

[0039] like Figure 2 As shown, the tunnel model body 2 consists of two parts: a fire source section 21 and a temperature control section 22. In a specific embodiment of the present invention, both the fire source section and the temperature control section are cuboid structures, each including two end faces and four side faces;

[0040] Among them, such as Figure 2 As shown in (a), one end of the fire source section 21 serves as the boundary of the tunnel body and is closed, while the other end of the fire source section is connected to one end of the temperature control section; in a specific embodiment of the present invention, the closed end 23 of the fire source section is on the left.

[0041] Magnesium oxide boards 24 are arranged on the inner side of the closed end face and the inner side of the top of the fire source section to prevent damage to the tunnel model body 2 from flames and high-temperature smoke. One side of the fire source section is made of transparent fireproof glass 26; the transparent fireproof glass is used to observe the flame combustion, and another side is provided with a closable fire source device operation hole. Except for the transparent fireproof glass side, the end faces of the closed end 23 are all made of galvanized steel plates. The temperature control section consists of multiple temperature control units 25, the length of which can be adjusted according to experimental requirements; in a specific embodiment of the present invention, the length of each temperature control unit 25 is set to 1m. One end of the temperature control section is connected to the fire source section, and the other end is connected to the outside. The other four sides are made of 7075 aluminum alloy to ensure consistent heat exchange conditions on the wall surface. The main structure of the tunnel model is connected by bolts and nuts to ensure the airtightness and stability of the structure.

[0042] The fire source simulation device 3 includes an oil pan 31, a fire source support 33, a mass recording device 34, fuel 32, and an ignition device. The oil pan 31 is attached to the end face of the closed end of the fire source section. The mass recording device 34 is located under the exterior of the tunnel model body. The oil pan 31 is mounted on the fire source support 33, which passes through a hole in the bottom of the fire source section and is positioned above the mass recording device 34. After the fuel 32 is added to the oil pan 31, it is ignited by the ignition device. To minimize disturbance to the sealed chamber, ignition is performed remotely from outside the sealed chamber; for example... Figure 3 As shown, the ignition device includes a tungsten filament 35, an ignition wire 36, a power supply 37, a radio receiving module 38, and a controller 39 containing a radio transmitting module.

[0043] The temperature control device 6 is located outside the temperature control section and includes thermal grease 61, a thermoelectric cooler 62, heat sink fins 63, a fan 64, a temperature control unit 65, temperature control wires 66, and a surface-mount thermocouple 68. The outside of the temperature control section is in close contact with the thermoelectric cooler 62 via thermal grease 61, and the heat sink fins 63 are in close contact with the other side of the thermoelectric cooler 62 via thermal grease 61. The thermoelectric cooler 62 generates a temperature difference based on the Peltier effect. Since this invention requires controlling the temperature difference between the inside and outside of the tunnel, and the Peltier effect allows for heat generation on one side and cooling on the other, this characteristic can be used to improve the efficiency of temperature difference control. When the power is connected in the correct direction, the side in contact with the temperature control section cools, while the side with the heat sink fins heats; when the power is reversed, the opposite occurs, with the side with the heat sink fins cooling. To control the internal temperature of the temperature control section to reach a set value, a surface-mount thermocouple 68 is arranged on the centerline of the tunnel ceiling. A wire passes through the right side of the temperature control section and connects to the temperature control unit. First, a target temperature is set. After comparing this temperature with the temperature measured by the surface-mount thermocouple 68, a relay 67 controls the switching of the semiconductor cooling chip to adjust the internal temperature of the temperature control section. In addition, a fan 64 is provided on the outside of the heat sink fins to improve heat dissipation or cooling efficiency. In one specific embodiment of the invention, the temperature control unit uses an Arduino temperature control unit.

[0044] like Figure 4 and Figure 2 As shown in (b), the temperature measuring device 5 includes thermocouple trees 51, thermocouple wires 52, and a temperature acquisition instrument 53. Multiple thermocouple trees 51 are spaced apart along the length of the tunnel model body on the central axis inside the tunnel model body to measure the temperature distribution inside the tunnel and transmit the corresponding signals to the temperature acquisition instrument 53 through the thermocouple wires 52, thereby analyzing the longitudinal smoke stratification of the tunnel. If the temperature rise data measured by the same thermocouple tree within the smoke spread range are not significantly different, it indicates that the smoke layer is disordered; if the temperature rise data measured by the same thermocouple tree are significantly different, and the temperature rise of the upper thermocouple is significantly higher than that of the lower thermocouple, it indicates that the smoke stratification is good.

[0045] The flow field visualization device 4 includes a sheet light source 41, a sheet light source support 42, etc., located on the outer side of the end of the temperature control section that connects to the outside. The sheet light source 41 is placed on the sheet light source support 42 at the same height as the center of the tunnel. When the sheet light source 41 is turned on, it can ensure that the entire interior of the tunnel is illuminated by the light source, and the flow field can be observed across the entire cross-section.

[0046] like Figure 5As shown, the recording device 7 is located at the center of the side of the temperature control section unit. After the flow field visualization device 4 is turned on, the recording device 7 can observe the movement and stratification of smoke inside the tunnel through the observation hole 69 on the side of the temperature control unit. The recording device includes a recording device 71, a data cable 72, a host computer 73, and other parts. The video data of multiple temperature control units captured by the recording device 71 is transmitted to the host computer through the data cable. After processing by the host computer, the flow of smoke inside the tunnel can be displayed in real time.

[0047] In one specific embodiment of the present invention: taking the fire source section as the left and the temperature control section as the right, and taking the low temperature inside the tunnel model and the high temperature inside the sealed room as an example.

[0048] Before the test, determine the fire source power, tunnel length, and internal and external temperatures of the fire scenario to be measured; if the internal temperature is cold and the external temperature is hot, the semiconductor refrigeration chip 62 is connected in the positive direction, and if the internal temperature is hot and the external temperature is cold, the semiconductor refrigeration chip 62 is connected in the reverse direction.

[0049] Based on the fire scenario, select the size of the oil pan 31 and the type of fuel 32, move the oil pan 31 through the fire source device operation hole 27 so that it is close to the left closed end 23 and placed above the fire source bracket, turn on the mass recording device 34 to record the mass change of the oil pan; adjust the number of temperature control units 25 and use bolts and nuts to fix each tunnel section; turn on the Arduino temperature control unit 65 and set the target temperature inside the tunnel.

[0050] Fuel 32 is added to oil pan 31 through ignition device operation port 27, and ignition device operation port 27 is sealed.

[0051] When the temperature measuring device 5 is turned on, the temperature collected by the thermocouple tree 51 is transmitted to the temperature acquisition instrument 53 through the thermocouple wire 52. The temperature distribution inside the tunnel can be confirmed by the temperature acquisition instrument 53.

[0052] Then, the temperature control device 6 starts working, the thermoelectric cooler 62 is powered on, the low temperature is transferred to the tunnel body 2 through the thermal grease 61, and the internal temperature is fed back through the patch thermocouple 68. When the temperature reaches the set value, the control unit 65 controls the relay 67 through the temperature control wire 66 to stop the thermoelectric cooler 62 from working; the high temperature generated on the other side of the thermoelectric cooler is transferred to the heat sink 63 through the thermal grease 61, and at the same time the fan 64 is turned on to accelerate heat dissipation and promote uniform temperature mixing in the sealed chamber 1.

[0053] At the same time, the temperature outside the tunnel is adjusted by turning on the air conditioning system 11 of the sealed chamber 1, so that the target temperature difference is gradually reached; the temperature inside the sealed chamber 1 is determined by observing the reading of the thermometer 13 through the observation window 12.

[0054] After the internal and external temperatures and temperature difference have stabilized, turn on the flow field visualization device 4 and the recording device 7 to confirm that the images inside the tunnel can be displayed in real time on the host 73 in order to record the flow field conditions inside the tunnel.

[0055] Ignition: The controller 39, which includes a radio transmitting module, sends an ignition command to the radio receiving module 38. The tungsten filament 35 heats up after being energized by the power supply 37 and the ignition wire 36, igniting the fuel 32 in the fuel pan 31. The experiment begins.

[0056] Each device records experimental data. After the flame is extinguished, each experimental device is turned off and experimental data recording is stopped. After the model cools down and returns to its initial state, the next set of experiments is conducted.

[0057] The boundary conditions for this embodiment are as follows: ambient temperature 20℃, oil pan dimensions 0.15m × 0.15m × 0.03m, fuel n-heptane, tunnel model cross-sectional dimensions 0.5m × 0.5m, tunnel model ignition source section length 2m, temperature control section length 18m, controlled tunnel main body temperature 5℃, and sealed chamber temperature 35℃. After the experiment following the above steps, the time history curves of temperature control inside and outside the tunnel before ignition are recorded as follows: Figure 6 As shown in the figure. 200 seconds after the device was started, the temperature inside the model tunnel was 5℃, and the temperature outside the tunnel was 35℃, indicating that the experimental device can control the temperature inside and outside the model tunnel to reach the set values. Furthermore, by setting different target values, this invention can further control the temperature difference between the inside and outside of the tunnel. The temperature distribution cloud map inside the tunnel after ignition changes over time as shown in the figure. Figure 7 As shown.

[0058] The above results demonstrate that the implementation method of the present invention is reasonable, and can achieve accurate control of the temperature difference between the inside and outside of the tunnel. Furthermore, by combining a temperature measuring device and a video recording device, the influence of the temperature difference on the movement pattern of the flue gas can be observed.

[0059] The above-described embodiments are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. Those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. An experimental system for the stratification characteristics of smoke in tunnel fires with controllable internal and external temperatures, characterized in that, It includes a sealed chamber, a tunnel model body, a fire source simulation device, a temperature control device, a temperature measuring device, a video recording device, and a flow field visualization device; The sealed chamber is used to provide a simulated external environment of the tunnel. An air conditioning module for regulating the temperature of the sealed chamber is installed on the sealed chamber. The main body of the tunnel model is set in the sealed chamber. The main body of the tunnel model includes a fire source section and a temperature control section. The fire source section is used to simulate the burning area of ​​a tunnel fire. The temperature control section is used to simulate the one-dimensional spread area of ​​smoke. Multiple observation holes are evenly spaced on the temperature control section. One end of the fire source section is closed, and the other end of the fire source section is connected to one end of the temperature control section; fireproof plates are provided on the inner side of the top of the fire source section and the inner side of the closed end; the fire source section also has an operating hole for the fire source device that can be sealed; the other end of the temperature control section is connected to the outside; the temperature control section includes multiple interconnected temperature control units; each temperature control unit in the temperature control section is equipped with a temperature control device; all four sides of the temperature control section are made of 7075 aluminum alloy to ensure consistent heat exchange conditions on the wall surface; The fire source simulation device is used to simulate a fire source and is set inside the fire source section. The fire source simulation device includes an oil pan, a fire source support, a mass recording device, fuel, and an ignition device. The oil pan is used to hold fuel and is set on the fire source support. The fire source support passes through the bottom of the fire source section and is mounted on the mass recording device located outside the fire source section. The mass recording device is used to record the amount of fuel burned in the fire pan in real time. The ignition device is used to ignite the fuel in the fire pan. The ignition device includes a tungsten filament, an ignition wire, a power supply, a radio receiving module, and a controller containing a radio transmitting module. The ignition device remotely ignites the fuel from outside the sealed chamber. The controller containing the radio transmitting module sends an ignition command to the radio receiving module. The tungsten filament heats up after being energized by the power supply and the ignition wire, igniting the fuel in the fire pan. The temperature control device is located outside the temperature control section and is used to regulate the temperature of the temperature control section. The temperature control device includes a thermoelectric cooler, heat sink fins, a fan, a temperature control unit, and a surface-mount thermocouple. One side of the thermoelectric cooler is in close contact with the outer wall of the temperature control section, and the other side is in close contact with the heat sink fins. Thermal grease is applied between the thermoelectric cooler, the temperature control section, and the heat sink fins. The surface-mount thermocouple is located inside the bottom of the temperature control section and is used to detect the temperature at the bottom of the temperature control section. The thermoelectric cooler, heat sink fins, fan, and surface-mount thermocouple are all connected to the temperature control unit via wires. The temperature control unit is located outside the tunnel model body and is used to compare the temperature measured by the surface-mount thermocouple with the set temperature. Based on the comparison result, it controls the thermoelectric cooler to switch on and off to regulate the temperature inside the temperature control section. The number of recording devices is equal to the number of observation holes on the temperature control section. Each recording device corresponds to one observation hole and monitors the movement and stratification of smoke inside the tunnel model through the observation hole. The recording device includes recording equipment, data cable and host. The video data of multiple temperature control units captured by the recording equipment is transmitted to the host through the data cable. After being processed by the host, the smoke flow inside the tunnel is displayed in real time. The flow field visualization device is used to provide the light source needed to observe the internal conditions of the tunnel model. The light source enters from the end of the temperature control section that is connected to the outside.

2. The experimental system for the smoke stratification characteristics of tunnel fires according to claim 1, characterized in that, The sealed chamber is also equipped with an observation window and a thermometer; the observation window is used to observe the model experiment; the thermometer is used to measure the temperature inside the sealed chamber.

3. The experimental system for the smoke stratification characteristics of tunnel fires according to claim 1, characterized in that, The temperature measuring device includes a thermocouple tree and a temperature acquisition instrument. The thermocouple tree is made by vertically binding multiple thermocouples together, and the vertical spacing of the measuring points can be adjusted according to actual needs. Multiple thermocouple trees are set at intervals along the length of the tunnel model body on the central axis inside the tunnel model body. The thermocouple trees are used to measure the temperature distribution inside the tunnel model body and transmit the corresponding signals to the temperature acquisition instrument, thereby analyzing the longitudinal smoke stratification of the tunnel.

4. The experimental system for the smoke stratification characteristics of tunnel fires according to claim 1, characterized in that, The flow field visualization device includes a light source and a light source support; the light source is mounted on the light source support, and the light source support is at the same height as the center of the tunnel body.

5. A method for conducting experiments using the tunnel fire smoke stratification characteristics experimental system described in claim 1, characterized in that, Includes the following steps: 1) Determine the fire source power, tunnel length, and tunnel interior and exterior temperatures of the fire scenario to be tested; 2) Select the size of the oil pan and the type of fuel according to the fire scenario to be tested. Move the oil pan through the operating hole of the fire source device so that it is close to the left closed surface and placed above the fire source support. Turn on the mass recording device to record the mass change of the oil pan. 3) Activate the temperature measuring device to provide real-time feedback on the temperature distribution inside the tunnel model, and adjust the temperature of the temperature control section through the temperature control device; 4) The external temperature of the tunnel model is adjusted by the air conditioning system of the sealed room so that the temperature difference between the inside and outside of the tunnel model reaches the target temperature difference; 5) After the temperature difference between the inside and outside of the tunnel model body reaches a stable level, turn on the flow field visualization device and the recording device to confirm that the image inside the tunnel model body can be displayed in real time on the recording device. 6) Send an ignition command to the fire source simulation device, and the oil pan burns, producing smoke and heat; Each device in the tunnel fire smoke stratification characteristic experimental system records experimental data in real time. After the flame is extinguished, each experimental device is turned off and the experimental data recording stops. After the tunnel fire smoke stratification characteristic experimental system cools down and returns to its initial state, the next set of experiments is carried out.

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