A kind of city tunnel smoke exhaust based on optical fiber internet of things control system

Abstract

The application discloses a kind of city tunnel smoke exhaust based on optical fiber's internet of things control system, in the tunnel of top transverse smoke exhaust, not only be provided with an anti-suction automatic retractable baffle at exhaust port, and the monitoring facilities of tunnel fire are provided: distributed temperature measurement optical fiber and optical fiber temperature detector;Signal transmission facilities: laser generator, the control of baffle is written with inclined fiber grating single-mode optical fiber and the heating layer coated on the surface of single-mode optical fiber;Driving facilities: directional control valve containing SAM connector: this has very important practical significance for realizing the effect of top transverse smoke exhaust in tunnel.The application is provided with an above-mentioned automatic retractable baffle at all exhaust ports of top exhaust duct, to change the flow field structure in tunnel and exhaust duct when fire occurs, inhibit the occurrence of smoke suction, improve the effect of smoke exhaust.

Description

Technical Field

[0001] This invention relates to the field of smoke extraction in tunnel fires, and more specifically to a fiber optic-based Internet of Things (IoT) control system for smoke extraction in urban tunnels. Background Technology

[0002] With social development, my country's highway tunnel construction has achieved leapfrog development, and the possibility of various tunnel traffic accidents causing fires has also increased accordingly. Tunnels, as narrow and confined spaces, have complex internal structures and harsh environments. Once a fire breaks out in a tunnel, evacuation and rescue are extremely difficult, resulting in serious casualties and property losses, with immense hazard and destructive power. Statistics show that over 85% of fire-related injuries and deaths are caused by smoke toxicity, most of which result from inhaling smoke and toxic gases and falling into a coma. Therefore, how to quickly and effectively remove smoke during tunnel fires has become an important research topic. Currently, the commonly used smoke removal modes include longitudinal smoke removal and centralized smoke removal modes (full transverse, semi-transverse, and point-type), each with different smoke control principles and applicable scopes. In a fully transverse smoke extraction system, the tunnel cross-section is divided into three parts: an air supply duct, an exhaust duct, and a roadway. The advantage of transverse ventilation is that in the event of a fire, the air supply and exhaust vents near the fire point open, while the other vents close. Airflow can only enter the tunnel from the air supply vents near the fire point and exit through the exhaust vents. Semi-transverse ventilation requires only one air supply or exhaust duct. In centralized smoke extraction systems, the tunnel has independent smoke exhaust ducts with dedicated smoke exhaust valves at intervals. During a fire, the smoke exhaust fans start, simultaneously opening several sets of smoke exhaust valves near the fire source to draw fire smoke into the exhaust ducts. Although centralized smoke extraction is more expensive, it effectively controls most fire smoke within the open exhaust vent area, ensuring the safe evacuation of personnel on both sides of the fire source and reducing damage to tunnel facilities and structures.

[0003] However, in current tunnel fire scenarios, smoke spreads horizontally along the tunnel from the fire source area in the form of a ceiling jet, forming a smoke layer of a certain thickness. Without smoke extraction, the smoke stratification within the tunnel is relatively stable. During mechanical smoke extraction, the suction force generated by the fan at the exhaust port draws some smoke into the exhaust duct, causing a depression in the smoke layer near the exhaust port, resulting in a gradual thinning of the smoke layer vertically. Due to the combined effects of the suction force at the exhaust port and the thermal buoyancy of the smoke, the depression at the exhaust port tends to deepen with distance from the fire source. This makes it difficult for smoke to form a stable smoke stratification in the centralized top-exhaust tunnel, as is the case in indoor fires. Consequently, the rate of smoke penetration at each exhaust port is not equal. Furthermore, in traditional centralized top-exhaust systems, when the smoke volume is too large, cold air at the exhaust port is vertically drawn in and mixed with the smoke, causing penetration near the exhaust port and reducing the system's smoke extraction efficiency.

[0004] Current research, using numerical simulation experiments, has revealed boundary layer separation and absorption-through phenomena during top-mounted mechanical smoke extraction. Boundary layer separation occurs at the smoke exhaust outlets farther from the fire source, significantly reducing the effective smoke extraction area and severely diminishing the effectiveness of top-mounted mechanical smoke extraction. Adding a horizontal smoke exhaust valve plate below the exhaust outlet can suppress absorption-through, and compared to traditional centralized smoke extraction methods, the smoke extraction efficiency is increased by approximately 25% after adding the horizontal smoke exhaust valve plate.

[0005] Currently, shallow-buried urban tunnels can be constructed with vertical shafts between the surface and the tunnel, spaced equidistantly along the tunnel. Valves are installed at the top of the shafts, and horizontal smoke exhaust baffles are spaced at intervals at the bottom of the shafts, away from the lower entrance, allowing for natural smoke exhaust through the chimney effect of the shafts. However, for underwater and deep-buried urban tunnels, where vertical shafts cannot be constructed, longitudinal smoke exhaust, full transverse smoke exhaust, and semi-transverse ventilation are the only options. Longitudinal smoke exhaust cannot prevent the spread of dense smoke from the fire area to non-fire areas. Full transverse and semi-transverse ventilation require valves in the exhaust ducts near the fire area to open during a fire, based on signals, while valves in exhaust ducts far from the fire area (where there is no smoke layer) remain closed. Furthermore, based on the change in the smoke layer area after the dense smoke at the tunnel top is exhausted, unnecessary smoke exhaust valves are closed.

[0006] However, to achieve the above objectives, there is still a lack of a monitoring system that can detect fires inside the tunnel and withstand high temperatures, as well as a signal transmission and control system that can open valves in high-temperature environments and close valves when the temperature returns to normal. Summary of the Invention

[0007] This invention, in tunnels employing top-mounted horizontal smoke exhaust, not only proposes adding an anti-smoke-through automatic retractable baffle at the exhaust vent, but also proposes monitoring facilities, signal transmission facilities, and baffle control facilities for fires within the tunnel. This is of great practical significance for achieving effective top-mounted horizontal smoke exhaust within tunnels. The purpose of this invention is to overcome the shortcomings of existing technologies and provide a fiber-optic IoT control system for urban tunnel smoke exhaust.

[0008] This invention is achieved through the following technical solution: a fiber-optic-based Internet of Things (IoT) control system for smoke extraction in urban tunnels, comprising:

[0009] The ventilation duct is arranged longitudinally along the top of the tunnel. On the side of the ventilation duct facing the tunnel surface, ventilation outlets are arranged at equal intervals. Each ventilation outlet is equipped with a baffle on the side facing the tunnel surface. On both sides of the ventilation duct directly above each baffle, there are multiple cylinders that can extend downwards. The piston rods of the multiple cylinders face downwards and suspend the baffle. The baffle is also sealed by the tension of the elastic body to block the ventilation outlet. The air inlet of the cylinder is connected to the compressed air pipeline through the directional control valve and the capillary tube. The capillary tube is made of high temperature resistant material. The compressed air pipeline is arranged in the longitudinal emergency passage along the tunnel.

[0010] The directional control valve has a valve chamber connected to the upper end of the valve via a channel. The radial cross-section of the channel is smaller than that of the valve chamber, and a reducing ring is provided at the top of the channel. The valve chamber and the middle side of the channel are connected to a capillary tube and a cylinder respectively through an air inlet and a working hole. A slider that can slide along the channel is provided at the upper part of the channel. The lower part of the slider is clearance-fitted with the channel and is covered with a sealing ring. The upper part of the slider is clearance-fitted with the reducing ring. An exhaust hole is provided inside the slider. The bottom end of the exhaust hole is connected to the channel, and the top end of the exhaust hole is connected to the outer side of the upper end of the slider through a transverse hole perpendicular to the channel. The valve cavity is equipped with a valve core that can slide along the channel axis. The valve core and the slider are connected by a connector. The diameter of the connector is smaller than the radial dimension of the channel. The valve core is connected to the bottom surface of the valve cavity through an SMA connector on the side facing away from the channel. When the SMA connector is heated, it shrinks, causing the transverse hole on the upper part of the slider to retract towards the lower part of the channel until it is blocked by the reducing ring. After the SMA connector cools down to room temperature, it extends. The compressed air in the cylinder pushes the slider to slide upward until the transverse hole extends to the upper end of the directional control valve to exhaust. At the same time, the slider is pulled to the upper end face of the valve core through the connector to block the lower end of the channel.

[0011] Furthermore, the SMA connector is surrounded by an optical fiber heating device, which includes a laser generator, a single-mode fiber with a tilted fiber grating, and a heating layer covering the surface of the single-mode fiber. The single-mode fiber includes a fiber core and a single-mode fiber cladding covering it. The tilted fiber grating is inscribed in the fiber core of the single-mode fiber covering the heating layer. The single-mode fiber in the direction control valve that controls the opening and closing of each baffle extends along the tunnel to the outside of the tunnel to receive the light source emitted by the laser generator.

[0012] Furthermore, it also includes: distributed temperature-measuring optical fibers arranged longitudinally along the tunnel, which are connected to the signal of an optical fiber thermometer outside the tunnel.

[0013] Furthermore, the tilt angle of the tilted fiber grating is between 4 degrees and 45 degrees.

[0014] Furthermore, the heating layer is a metal thin film or a graphite layer.

[0015] In this invention, when the laser generator does not emit laser light into the single-mode fiber inside the directional control valve, the SMA connector is heated and in an extended state. Compressed air entering from the air inlet or residual compressed air in the cylinder pushes the slider upward along the channel, expelling the gas from the cylinder. The piston rod of the cylinder can thus retract, causing the baffle to be pulled towards the exhaust port by the elastic body, blocking the exhaust port. At the same time, the slider is pulled to the lower end of the valve core blocking the channel, and the compressed air from the air inlet also exerts a thrust on the valve core at the lower end of the blocking channel, maintaining the blocking state. If the laser generator emits laser light into the single-mode fiber inside the directional control valve, or if a fire occurs below the exhaust port, the SMA connector is heated and returns to its memory state, contracting and pulling the valve core back to the bottom of the valve cavity. It also pulls the slider back to the lower end of the channel. The transverse exhaust port is blocked by the reducing ring. Compressed air entering from the air inlet enters the cylinder through the working hole, pushing the piston rod to extend, moving the baffle away from the exhaust port, and drawing in dense smoke through the exhaust port.

[0016] SMA connectors only need to be heated to 40℃ to return to their memory state. The tilted fiber grating, a short-period fiber grating, has a slight tilt between its grating plane and the fiber axis. This tilted grating couples the forward-propagating fundamental mode in the fiber core to the backward-propagating cladding and radiation modes, thus extracting energy from the fiber core. The laser energy transmitted in the fiber core is extracted, absorbed by the heating layer material, and converted into heat energy, thereby achieving the heating function. When the input laser power is 250mW, the water temperature near the heating layer increases by approximately 60℃ compared to before heating (room temperature 25℃), reaching approximately 85℃, which meets the temperature required for the SMA connector to return to its memory state. Existing research shows that when the pre-strain of a 0.4mm diameter SMA filament is 12%, its free recovery rate reaches a maximum of 6.9%, at which point the maximum restoring force also reaches a maximum of 79N. Compressed air pressure is typically 5 kg, equivalent to 46 N; therefore, a 0.4mm SMA filament is sufficient to overcome the pressure of compressed air pulling the valve core.

[0017] Through the above measures, the present invention installs an automatically retractable baffle at all exhaust outlets of the top exhaust duct to change the flow field structure in the tunnel and exhaust duct during a fire, suppress the occurrence of smoke absorption, and improve the smoke exhaust effect.

[0018] Taking a tunnel model with a length of 600 meters, a width of 11 meters, and a height of 4.5 meters, and a top ventilation duct with a width of 11 meters and a height of 1.5 meters, and a ventilation outlet with a cross-sectional dimension of 3 meters long and 3 meters wide as an example, when simulating a fire situation under this design, the automatic telescopic baffle is a horizontal plate, not a grid-shaped or conical plate, and its size is 1.5 times the size of the smoke exhaust outlet. When activated, the downward telescopic height is 0.3 meters.

[0019] The simulation results show that when the baffle is closed, the temperature at the first exhaust vent closest to the fire source changes from 20℃ to 189℃ in the 0s-1200s period. The temperature at the second exhaust vent changes from 20℃ to 100-98℃ in the same period. The temperature at the third exhaust vent changes from 20℃ to 63℃ in the same period. Therefore, due to the high temperature in the fire area, the electric devices and wires are easily burned. The fire prevention and smoke exhaust system in the tunnel is not suitable for using conventional wires to send electrical signals to control the electric mechanism to open the baffle.

[0020] When the baffle opens (the downward extension starts the cylinder to open the exhaust vent): the temperature of the first exhaust vent near the fire source changes from 20℃ to 170-164℃ in 0s-1200s; the temperature of the second exhaust vent changes from 20℃ to 80℃ in the same time; and the temperature of the third exhaust vent changes from 20℃ to 32℃ in the same time. Therefore, theoretically, when the accumulation of dense smoke weakens, the temperature at the exhaust vents far from the fire area drops to around 30℃, close to the ambient temperature of 20℃. So, the automatic upward extension cylinder retracts the baffle and closes the exhaust vent, which can improve the suction power of the exhaust vents in the dense smoke area and improve the utilization efficiency of the suction power in the exhaust duct.

[0021] Therefore, for the transverse ventilation ducts of tunnels, 30℃~40℃ can be used as a standard to distinguish between areas near a fire and areas not near a fire. This temperature is lower than the crystal phase transformation temperature when the SMA connector recovers its memory state. The directional control valve containing the SMA connector quickly and safely drives the cylinder based on the ambient temperature of the dense smoke layer and fiber optic heating. After the ambient temperature decreases, the directional control valve containing the SMA connector can automatically restore the baffle according to the ambient temperature or after the light source is turned off and the temperature drops. The baffle of this invention can automatically open and close due to ambient temperature, and can also be remotely controlled under fiber optic control.

[0022] In this invention, fire prevention and high temperature resistance are achieved through both pneumatic control of the baffle and fiber optic control, enabling remote and automatic control in complex tunnel fire environments.

[0023] This invention also includes the installation of distributed temperature-measuring optical fibers within the tunnel, which enables accurate positioning of fire zones within the tunnel, thereby providing a basis for selecting which baffles to open or close.

[0024] Furthermore, the baffle is made of a high-temperature resistant and corrosion-resistant material.

[0025] Furthermore, the size and spacing of the exhaust vents should be determined based on the actual project conditions, but the shape of the baffle and the shape of the exhaust vents should be the same and their dimensions should be 1.5 times that of each other.

[0026] The advantages and positive effects of this invention are as follows:

[0027] (1) In terms of practicality, by configuring the baffle at the exhaust port under the centralized smoke exhaust mode at the top, an enhanced anti-suction penetration automatic telescopic baffle is added to the exhaust port. Then, by analyzing and processing the data obtained from the numerical simulation study, the shape, size and telescopic distance of the automatic telescopic baffle are obtained. By forming a baffle at the exhaust port, the direction of the fan's suction force is changed, so that the smoke below the exhaust port near the fire source changes from a vertical rising state to a horizontal movement against the baffle. At the same time, the hot smoke layer and the cold air layer are separated, thereby improving the suction penetration phenomenon. In addition, the enhanced anti-suction penetration automatic telescopic baffle configuration device for the top smoke exhaust in the tunnel also includes a feedback control system. The feedback control system automatically controls the telescopic baffle to open and close, thereby improving the smoke exhaust efficiency of the entire system.

[0028] (2) In terms of safety and environmental friendliness, an enhanced anti-absorption and penetration automatic telescopic baffle is added to the ventilation outlet at the top of the tunnel. This will not affect the safety of the tunnel structure, is safe and reliable, and will not have an impact on the environment.

[0029] (3) In terms of construction operation and economic cost, whether it is an existing tunnel with top mechanical smoke exhaust or a newly built tunnel with top mechanical smoke exhaust, an efficiency-enhancing anti-suction automatic telescopic baffle is added to all exhaust outlets in the exhaust duct. It is simple to operate, low in cost and easy to implement.

[0030] This invention adds an enhanced anti-suspension automatic telescopic baffle to the exhaust vent of existing or newly constructed tunnels using top-mounted mechanical smoke extraction, suppressing the occurrence of smoke absorption and penetration. It is easy to implement, low in cost, simple to operate, and highly safe and reliable. It improves the smoke extraction effect of top-mounted mechanical smoke extraction after a tunnel fire, has broad application prospects and significant practical value, and is conducive to promoting the development and application of top-mounted mechanical smoke extraction methods. Attached Figure Description

[0031] Figure 1 A schematic diagram of a tunnel with top-mounted mechanical smoke exhaust, in which an automatic telescopic baffle is suspended directly below the exhaust vent;

[0032] Figure 2 This is a cross-sectional view of the tunnel of the device of the present invention;

[0033] Figure 3 A schematic diagram of the directional control valve's state structure when the automatic telescopic baffle retracts and extends;

[0034] Figure 4 This is a schematic diagram of the overall structure of the fiber optic heating device.

[0035] Figure 5 shows the flow field structure near the exhaust port when using top mechanical smoke exhaust without baffle and with automatic telescopic baffle. Figure 5(a) shows the flow field structure near the exhaust port without baffle, and Figure 5(b) shows the flow field structure near the exhaust port when the automatic telescopic baffle is installed and in the telescopic open state.

[0036] Figure 6 The graph shows the correlation between the downward extension height of the automatic telescopic baffle and the volumetric flow rate of CO absorbed by the exhaust vent when there is no baffle and when an automatic telescopic baffle is added. It indicates that the smoke exhaust efficiency is best when the automatic telescopic baffle extends downward by 0.3m.

[0037] Figure 7 Temperature diagram near the exhaust vent when top mechanical smoke exhaust is used, assuming there is no baffle or an automatic retractable baffle, and the exhaust vent is located far from the fire source and experiences air suction. Detailed Implementation

[0038] The invention will be further described below with reference to the accompanying drawings, taking a longitudinal section of a tunnel equipped with a top mechanical smoke exhaust system as an example.

[0039] See Figure 1 Automatic retractable baffles 4 are added to the exhaust outlets 3 inside the exhaust duct 2 at the top of tunnel 1. Tunnel 1 is 600 meters long, 11 meters wide, and 4.5 meters high. The exhaust duct 2 at the top is 11 meters wide and 1.5 meters high. The cross-sectional dimensions of the exhaust outlets 3 in the exhaust duct 2 are 3 meters long and 3 meters wide. The spacing between the exhaust outlets 3 is 60 meters. The cross-sectional dimensions of the baffles 4 are 4.5 meters long and 4.5 meters wide, which is 1.5 times the size of the exhaust outlets 3.

[0040] See Figure 2 The specific structure of the automatic telescopic baffle is as follows: the baffle 4 is a horizontal plate, not a grid-shaped or conical plate. The size of the baffle 4 is 1.5 times the size of the exhaust port 3, and the material is high-temperature resistant and corrosion resistant. Each exhaust port 3 has a baffle 4 installed on the side facing the tunnel 1 road surface. On both sides of the exhaust duct 2 directly above each baffle 4, there are multiple downward-extending cylinders 6. The cylinders 6 are fixed on both sides of the exhaust duct 2. The piston rods 62 of the multiple cylinders 6 point downward and suspend the baffle 4. The baffle 4 is also blocked by the tension of the elastic body 63 to seal the exhaust port 3. The air inlet of the cylinder 6 is connected to the compressed air pipeline 8 through the directional control valve 9 and the capillary tube. The capillary tube is made of high-temperature resistant material. The compressed air pipeline 8 is arranged in the longitudinal emergency passage 7 arranged along the tunnel 1.

[0041] See Figure 3a. A directional control valve 9 has a valve chamber 91 inside. The valve chamber 91 is connected to the upper end of the directional control valve 9 through a channel 92. The radial cross-section of the channel 92 is smaller than that of the valve chamber 91, and a reducing ring 93 is provided at the top of the channel 92. The middle side of the valve chamber 91 and the channel 92 are connected to the capillary tube and the cylinder 6 through an air inlet 94 and a working hole 95, respectively. A slider 96 that can slide along the channel 92 is provided at the upper part of the channel 92. The lower part of the slider 96 is clearance-fitted with the channel 92 and is covered with a sealing ring 96a. The upper part of the slider 96 is fitted with the reduced diameter ring 93 with a clearance. The slider 96 has an exhaust hole 97, the bottom of which connects to a channel. The top of the exhaust hole 97 connects to the outer side of the upper end of the slider 96 through a transverse hole 98 perpendicular to the channel 92. The valve cavity 91 has a valve core 99 that can slide axially along the channel. The valve core 99 is connected to the slider 96 via a connector 100, the diameter of which is smaller than the radial dimension of the channel 92. The side of the valve core 99 facing away from the channel is connected to the bottom surface of the valve cavity 91 via an SMA connector 11. Figure 3 b. When the SMA connector 11 is heated, it shrinks, causing the transverse hole 98 on the upper part of the slider 96 to retract towards the lower part of the channel 92 until it is blocked by the reducing ring 93. After the SMA connector 11 cools down to room temperature, it extends. The compressed air in the cylinder 6 pushes the slider 96 to slide upward until the transverse hole 98 extends to the upper end of the directional control valve 9 to exhaust. At the same time, the slider 96 pulls the upper end face of the valve core 99 through the rigid connector 100 to block the lower end of the channel 92.

[0042] See Figure 4An SMA connector 11 is surrounded by an optical fiber heating device 12. The optical fiber heating device 12 includes a laser generator 13, a single-mode fiber 14 inscribed with a tilted fiber grating 18, and a heating layer 15 covering the surface of the single-mode fiber 14. The single-mode fiber 14 includes a fiber core 16 and a single-mode fiber cladding 17 covering it. The tilted fiber grating 18 is inscribed within the fiber core 16 of the single-mode fiber 14 covering the heating layer 15. The single-mode fiber 14 within the direction control valve 9, which controls the opening and closing of each baffle 4, extends along the tunnel 1 to the outside of the tunnel 1 to receive the light source emitted by the laser generator 13. The tilt angle of the tilted fiber grating 18 is between 4 and 45 degrees. The heating layer 17 is a metal thin film or a graphite layer. The tilted fiber grating is a short-period fiber grating, with a slight tilt between its grating plane and the optical axis of the fiber. The tilted fiber grating can couple the forward-propagating fundamental mode in the fiber core to the backward-propagating cladding mode and radiation mode, thus extracting energy from the fiber core. The laser energy transmitted in the fiber core is extracted from the optical fiber and absorbed by the heating layer material, converting it into heat energy to achieve the heating function. When the input laser power is 250mW, the water temperature near the heating layer increases by about 60°C compared to before heating (room temperature 25°C), reaching about 85°C. The SMA connector 11 only needs to be heated to 40°C to return to its memory state. The SMA connector 11 is a titanium-nickel alloy, and its crystal structure is different above and below 40°C. It shrinks above 40°C and stretches below 40°C, causing a change in shape. The SMA wire is made into a spiral state at high temperature and forcibly straightened at room temperature. Therefore, as long as it is heated to above 40°C, it immediately returns to its spiral shape and shortens.

[0043] Taking a tunnel model measuring 600 meters long, 11 meters wide, and 4.5 meters high, with a top ventilation duct 11 meters wide and 1.5 meters high, and ventilation vents with cross-sectional dimensions of 3 meters long and 3 meters wide as an example, when simulating a fire under this design, the automatic retractable baffle is a horizontal plate, not a grid-shaped or conical plate, and its size is 1.5 times the size of the smoke vent. Upon activation, it retracts downwards by 0.3 meters. Simulation results show that when the baffle is closed, the temperature at the first ventilation vent closest to the fire source changes from 20°C to 189°C within 0s-1200s; the second ventilation vent changes from 20°C to 100-98°C within the same timeframe; and the third ventilation vent changes from 20°C to 63°C within the same timeframe. Therefore, due to the high temperature in the fire area, the electric actuators and wiring are easily burned. Conventional electrical wiring is not suitable for controlling the electric mechanism to open the baffle using conventional electrical signals to control the fire prevention and smoke extraction system within the tunnel.

[0044] When the baffle opens (the downward extension starts the cylinder to open the exhaust vent): the temperature of the first exhaust vent near the fire source changes from 20℃ to 170-164℃ in 0s-1200s; the temperature of the second exhaust vent changes from 20℃ to 80℃ in the same time; and the temperature of the third exhaust vent changes from 20℃ to 32℃ in the same time. Therefore, theoretically, when the accumulation of dense smoke weakens, the temperature at the exhaust vents far from the fire area drops to around 30℃, close to the ambient temperature of 20℃. So, the automatic upward extension cylinder retracts the baffle and closes the exhaust vent, which can improve the suction power of the exhaust vents in the dense smoke area and improve the utilization efficiency of the suction power in the exhaust duct.

[0045] Therefore, for the transverse ventilation ducts of tunnels, 30℃~40℃ can be used as a standard to distinguish between areas near a fire and areas not near a fire. This temperature is lower than the crystal phase transformation temperature when the SMA connector recovers its memory state. The directional control valve containing the SMA connector quickly and safely drives the cylinder based on the ambient temperature of the dense smoke layer and fiber optic heating. After the ambient temperature decreases, the directional control valve containing the SMA connector can automatically restore the baffle according to the ambient temperature or after the light source is turned off and the temperature drops. The baffle of this invention can automatically open and close due to ambient temperature, and can also be remotely controlled under fiber optic control.

[0046] In this invention, fire prevention and high temperature resistance are achieved through both pneumatic control of the baffle and fiber optic control, enabling remote and automatic control in complex tunnel fire environments.

[0047] This invention also includes a distributed temperature-measuring optical fiber 5 installed inside the tunnel, enabling accurate location of fire zones within the tunnel and providing a basis for selecting which baffles to open or close. The distributed temperature-measuring optical fiber is connected to a fiber optic thermometer outside the tunnel and is arranged longitudinally along the tunnel.

Claims

1. A fiber-optic-based Internet of Things (IoT) control system for smoke extraction in urban tunnels, comprising: The ventilation duct is arranged longitudinally along the top of the tunnel. On the side of the ventilation duct facing the tunnel surface, ventilation outlets are arranged at equal intervals. Each ventilation outlet is equipped with a baffle on the side facing the tunnel surface. On both sides of the ventilation duct directly above each baffle, there are multiple cylinders that can extend downwards. The piston rods of the multiple cylinders face downwards and suspend the baffle. The baffle is also sealed by the tension of the elastic body to block the ventilation outlet. The air inlet of the cylinder is connected to the compressed air pipeline through the directional control valve and the capillary tube. The capillary tube is made of high temperature resistant material. The compressed air pipeline is arranged in the longitudinal emergency passage along the tunnel. The directional control valve has a valve chamber connected to the upper end of the valve via a channel. The radial cross-section of the channel is smaller than that of the valve chamber, and a reducing ring is provided at the top of the channel. The valve chamber and the middle side of the channel are connected to a capillary tube and a cylinder respectively through an air inlet and a working hole. A slider that can slide along the channel is provided at the upper part of the channel. The lower part of the slider is clearance-fitted with the channel and is covered with a sealing ring. The upper part of the slider is clearance-fitted with the reducing ring. An exhaust hole is provided inside the slider. The bottom end of the exhaust hole is connected to the channel, and the top end of the exhaust hole is connected to the outer side of the upper end of the slider through a transverse hole perpendicular to the channel. The valve cavity is equipped with a valve core that can slide along the channel axis. The valve core and the slider are connected by a connector. The diameter of the connector is smaller than the radial dimension of the channel. The valve core is connected to the bottom surface of the valve cavity through an SMA connector on the side facing away from the channel. When the SMA connector is heated, it shrinks, causing the transverse hole on the upper part of the slider to retract towards the lower part of the channel until it is blocked by the reducing ring. After the SMA connector cools down to room temperature, it extends. The compressed air in the cylinder pushes the slider to slide upward until the transverse hole extends to the upper end of the directional control valve to exhaust. At the same time, the slider is pulled to the upper end face of the valve core through the connector to block the lower end of the channel.

2. The fiber-optic-based Internet of Things control system for smoke extraction in urban tunnels according to claim 1, characterized in that: The SMA connector is surrounded by an optical fiber heating device, which includes a laser generator, a single-mode fiber with a tilted fiber grating, and a heating layer covering the surface of the single-mode fiber. The single-mode fiber includes a fiber core and a single-mode fiber cladding covering it. The tilted fiber grating is inscribed in the fiber core of the single-mode fiber covering the heating layer. The single-mode fiber in the directional control valve that controls the opening and closing of each baffle extends along the tunnel to the outside of the tunnel to receive the light source emitted by the laser generator.

3. The fiber-optic-based Internet of Things control system for smoke extraction in urban tunnels according to claim 1, characterized in that: Also includes: Distributed temperature-measuring optical fibers are arranged longitudinally along the tunnel and are connected to the signal of an optical fiber thermometer outside the tunnel.

4. A fiber-optic-based Internet of Things control system for smoke extraction in urban tunnels according to claim 2, characterized in that: The tilt angle of the tilted fiber grating is between 4 degrees and 45 degrees.

5. A fiber-optic-based Internet of Things control system for smoke extraction in urban tunnels according to claim 2, characterized in that: The heating layer is a thin metal film or a graphite layer.

6. A fiber-optic-based Internet of Things control system for smoke extraction in urban tunnels according to claim 1, characterized in that: The baffle is made of a high-temperature and corrosion-resistant material.

7. A fiber-optic-based Internet of Things control system for smoke extraction in urban tunnels according to claim 1, characterized in that: The shape of the baffle is the same as that of the exhaust vent, and their dimensions are 1.5 times that of the vent.

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