A new hybrid ventilation method for tunnel hydrogen energy fire accident safety rescue

Abstract

The application discloses a new mixed ventilation method for tunnel hydrogen energy fire accident safety rescue, comprising: establishing a multi-verticle shaft tunnel model with a mixed ventilation system; based on the advantages and disadvantages of existing ventilation methods, a new mixed ventilation method is proposed; the influence of different new mixed ventilation methods on hydrogen jet fire back layer length and temperature in the tunnel is compared; a new mixed ventilation method with a speed prediction model for tunnel hydrogen energy fire accidents is proposed. Based on the different ventilation methods-ventilation speed-temperature distribution, the application proposes a new mixed ventilation method suitable for the tunnel to handle hydrogen energy fire accidents, establishes a dimensionless prediction model of the critical longitudinal ventilation speed, reduces the risk of hydrogen jet fire in the tunnel, realizes the quick selection of the ventilation method and the quick prediction of the ventilation speed when the hydrogen jet fire occurs in the tunnel, and the method makes up for the limitations of the traditional single ventilation method in preventing and controlling hydrogen energy fire.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of tunnel hydrogen energy fire smoke prevention and exhaust, and particularly relates to a novel hybrid ventilation method for tunnel hydrogen energy fire accident safety rescue. BACKGROUND

[0002] Tunnel is an important part of modern transportation network, which provides an efficient and convenient channel for vehicle traffic. However, hydrogen leakage of vehicles in the tunnel poses a great threat to the safe operation of the tunnel. Due to the characteristics of hydrogen, hydrogen jet fire belongs to turbulent diffusion combustion, which has the characteristics of long flame length, extremely high temperature (more than 2000℃) and strong radiation. Hydrogen leakage accidents of vehicles in tunnels will seriously threaten the safe operation of tunnels. At the same time, the difficulty of fire rescue in tunnels makes the safety of people's life and property be greatly threatened. Therefore, it is necessary to carry out in-depth research, so as to provide a theoretical basis for the related research of more complex tunnel types.

[0003] Longitudinal ventilation is an important control means to suppress smoke backflow. When a fire occurs, longitudinal ventilation can exhaust smoke from the downstream, ensuring that the upstream area of the tunnel can be safely evacuated and rescue activities can be carried out. The critical longitudinal ventilation velocity is the minimum wind speed required to suppress the diffusion of smoke to the upstream direction of the tunnel, and is also a key parameter to determine the effectiveness of longitudinal smoke exhaust. Transverse ventilation is an important means to control airflow and temperature in the tunnel. When a fire occurs, the vertical shaft can provide a fast smoke exhaust channel, and smoke will be drawn away from the top of the tunnel, so as to ensure that the smoke layer is not substantially disturbed by the airflow, and personnel evacuation is more convenient and safe.

[0004] However, due to the limited influence of single ventilation system on fire characteristics, and the more serious hazards of hydrogen jet fire compared with traditional fire, China is still in the initial stage of such research. At present, the selection of ventilation methods for hydrogen energy fire accidents in tunnels mainly has the following shortcomings:

[0005] (1) The influence of transverse ventilation system on critical longitudinal ventilation velocity is not considered

[0006] When hydrogen jet fire occurs in the tunnel, the conventional longitudinal ventilation mode can form a safe upstream channel, ensuring the safety of rescue and evacuation in the upstream. However, relying solely on longitudinal ventilation cannot protect the safety of personnel and equipment in the downstream, and instead, it may increase the risk in the downstream. For example, the paper "Thermal and fire characteristics of hydrogen jet flames in the tunnel at longitudinal ventilation strategies" compared the temperature distribution in the tunnel under different longitudinal ventilation, and proposed that with the increase of longitudinal ventilation speed, the height of the thermal layer increases, but with the further increase of longitudinal ventilation speed, the height of the thermal layer remains constant, which cannot guarantee the safety of personnel and equipment in the downstream. It did not consider the influence of the transverse ventilation system on the critical longitudinal ventilation speed. For example, Chinese invention patent CN119005041A established a method for predicting the critical longitudinal ventilation speed by analyzing the influence of the water mist system on the fire. However, for hydrogen jet fire in the tunnel, the water mist system is extremely easy to cause the fire to worsen, and its effect is far inferior to that of the transverse ventilation system.

[0007] (2) Did not consider the influence of ventilation mode on the critical longitudinal ventilation speed in multi-shaft tunnels

[0008] Transverse ventilation is a ventilation mode that can effectively reduce the distribution range of high-temperature areas in the tunnel. However, due to the mutual influence between longitudinal ventilation and transverse ventilation, the wrong ventilation mode may lead to an increase in fire hazards. For example, the paper "Hazard analysis on tunnel hydrogen jet fire based on CFD simulation of temperature field and concentration field" compared the influence of single fixed vertical shaft transverse ventilation speed on hydrogen jet fire, but it did not conduct in-depth discussion on the coupling influence of longitudinal and transverse ventilation, and ultimately only concluded that multiple groups of transverse ventilation shafts need to be established, without being able to propose an effective method to control hydrogen jet fire.

[0009] (3) Did not consider the differences between hydrogen jet fire and ordinary fire

[0010] Hydrogen jet fire belongs to turbulent diffusion combustion, with the characteristics of long flame length, extremely high temperature (more than 2000℃) and strong radiation. Due to the structural characteristics of low top wall height and narrow space, the tunnel is often regarded as a closed or nearly closed space. When hydrogen jet fire occurs in the tunnel, its danger is greater than that of conventional fire. For example, the paper "Fire characteristics of rescue station inside railway tunnel with semi transverse ventilation" discusses different transverse ventilation modes for conventional fire, which is quite different from hydrogen jet fire in terms of danger level, and the conclusions provided cannot be completely applied to hydrogen jet fire. SUMMARY

[0011] To at least overcome one of the deficiencies existing in the prior art, the present application provides a new hybrid ventilation method for tunnel hydrogen energy fire accident safety rescue.

[0012] To achieve the object of the present application, the present application provides a new hybrid ventilation method for tunnel hydrogen energy fire accident safety rescue, comprising the following steps:

[0013] According to the physical structure of the tunnel and the setting of the hybrid ventilation system in the tunnel, the basic setting parameters of the fire scene simulation in the tunnel are determined, and a multi-shaft tunnel simulation model with a hybrid ventilation system is established in a finite element software;

[0014] The different existing ventilation modes are compared, and a new hybrid ventilation mode is proposed based on the advantages and disadvantages of various existing ventilation modes; the ventilation effect of different new hybrid ventilation modes is simulated and analyzed, and the optimal ventilation mode suitable for the hydrogen jet fire in the tunnel is determined based on the influence of different new hybrid ventilation modes on the back layer length of the hydrogen jet fire and the temperature in the tunnel;

[0015] The influencing factors of the critical longitudinal ventilation speed are determined, the critical longitudinal ventilation speed, the transverse ventilation speed and the heat release rate suitable for the optimal ventilation mode of the hydrogen jet fire in the tunnel are fitted by the polynomial fitting method of the least square method, a dimensionless prediction model of the critical longitudinal ventilation speed in the tunnel is established, the critical longitudinal ventilation speed is predicted by using the prediction model, and a new hybrid ventilation method suitable for tunnel hydrogen energy fire accidents with a speed prediction model is obtained.

[0016] Further, in the multi-shaft tunnel simulation model, a plurality of groups of shafts are installed between the upstream and downstream areas of the fire source; in the tunnel simulation model, temperature detection points are arranged in the top wall area and the personnel activity area to measure the temperature change in the tunnel, and a temperature slice is arranged on the center line of the tunnel to observe the change of the temperature field inside the tunnel.

[0017] Preferably, the tunnel model adopts a multi-shaft structure, comprising:

[0018] (1) The tunnel size is 15m in length, 0.25m in width and 0.25m in height, 11 groups of shafts with a spacing of 1.25m are installed in the upstream and downstream areas of the fire source, the shaft diameter is 0.18m, and the ratio of the tunnel model to the actual tunnel size is 1:20;

[0019] (2) In the tunnel model, the top wall area and the personnel activity area (with a height of 0.25m and 0.1m respectively) are provided with temperature detection points for measuring the temperature change in the tunnel, and a temperature slice is provided on the center line of the tunnel to observe the change of the temperature field inside the tunnel.

[0020] Further, the transverse ventilation speed of the shaft, the fire source radius size, the heat release rate of the fire source, the position of the fire source and the length of the fire source from the tunnel entrance are set in the finite element software. Preferably, the transverse ventilation speed of the shaft is set to 0m / s, 1m / s, 2m / s, 3m / s, 4m / s and 5m / s, the fire source radius size is 0.106m, the heat release rate of the fire source is 5MW, 15MW, 25MW and 34MW, and the position of the fire source is set on the center line of the tunnel, 7.5m away from the tunnel entrance.

[0021] Further, the advantages and disadvantages of various existing ventilation modes are determined based on the temperature cloud map and the hydrogen jet flame diffusion range of various existing ventilation modes, comprising:

[0022] Through simulation, the temperature cloud map under single longitudinal ventilation, the temperature cloud map under single transverse ventilation and the temperature cloud map under conventional mixed ventilation are obtained;

[0023] Based on the temperature cloud map, the hydrogen jet flame diffusion range is determined;

[0024] According to the comparison of the temperature cloud map and the hydrogen jet flame diffusion range, the advantages and disadvantages of different existing ventilation modes in handling hydrogen jet fire accidents in the tunnel are determined.

[0025] Further, the new mixed ventilation mode is:

[0026] (1) A mixed ventilation mode of longitudinal ventilation combined with transverse ventilation above the leakage source in the tunnel;

[0027] (2) A mixed ventilation mode of longitudinal ventilation combined with transverse ventilation downstream of the leakage source in the tunnel.

[0028] Further, simulate different new hybrid ventilation modes in finite element software to obtain temperature slices on the center line of the tunnel under different ventilation speeds; obtain the change of critical longitudinal ventilation speed under different new hybrid ventilation modes according to the critical longitudinal ventilation speed calculation algorithm, and draw the curves of critical longitudinal ventilation speed, transverse ventilation speed and temperature in the tunnel under different ventilation conditions.

[0029] Further, the critical longitudinal ventilation speed calculation algorithm is:

[0030] (1) measure the back layer length of the flame and the corresponding ventilation speed by using the FLUENT software system;

[0031] (2) draw the curve of ventilation speed and back layer length, extend the curve of ventilation speed and back layer length outward, and derive the critical longitudinal ventilation speed when the back layer length of the flame is 0 m;

[0032] (3) use the derived critical longitudinal ventilation speed when the back layer length of the flame is 0 m to simulate, judge whether there is a backflow speed at the upstream of the tunnel and whether there is a flame back layer in the cloud chart, if not, it is proved that the longitudinal ventilation speed is the critical speed.

[0033] Further, the drawing of the curves of critical longitudinal ventilation speed, transverse ventilation speed and temperature in the tunnel under different ventilation conditions comprises:

[0034] (1) draw the curve of different ventilation modes-transverse ventilation speed-critical longitudinal ventilation speed;

[0035] (2) draw the curve of different ventilation modes-transverse ventilation speed-temperature in the personnel activity area;

[0036] (3) draw the curve of different ventilation modes-transverse ventilation speed-temperature in the top wall area.

[0037] Further, the influencing factors in the prediction method of the critical longitudinal ventilation speed are the heat release rate of the fire Q, the transverse ventilation speed V t , the tunnel height H, the tunnel cross-sectional area A, the environmental air density ρ a , the environmental air temperature Ta, the constant-pressure specific heat capacity of air C p , and the gravitational acceleration g.

[0038] Further, the tunnel height H, the tunnel cross-sectional area A, the environmental air density ρ a , the environmental air temperature T a , the constant-pressure specific heat capacity of air C p , and the gravitational acceleration g are known basic physical quantities, and the prediction model of the critical longitudinal ventilation speed in the tunnel in a dimensionless form is established according to the polynomial fitting of the least square method:

[0039]

[0040] wherein V c is the critical longitudinal ventilation velocity, V t is the transverse ventilation velocity, Q is the hydrogen heat release rate, and are the dimensionless critical longitudinal ventilation velocity, the dimensionless transverse ventilation velocity and the dimensionless hydrogen heat release rate, respectively.

[0041] Compared with the prior art, the present application has at least the following beneficial technical effects:

[0042] (1) The present application proposes a new hybrid ventilation mode for a multi-shaft tunnel model, and considers the influence of the transverse ventilation system on the critical longitudinal ventilation velocity. By comparing the simulation data of different ventilation modes, the critical longitudinal ventilation velocity, the transverse ventilation velocity and the temperature curve under different ventilation modes are obtained, the correlation between the ventilation mode, the ventilation velocity and the temperature distribution is established, a hybrid ventilation mode that can reduce the critical longitudinal ventilation velocity in the tunnel and the distribution range of the high temperature area in the tunnel is proposed, and a corresponding prediction model of the critical longitudinal ventilation velocity is proposed. The critical longitudinal ventilation velocity can be predicted by the prediction model.

[0043] (2) The present application breaks through the limitation that the prediction of the critical longitudinal ventilation velocity of hydrogen jet fire in the tunnel is confined to a single ventilation system, and lacks research on a hybrid ventilation method for a multi-shaft tunnel model. Compared with the prior art, it can better cope with hydrogen jet fire in the tunnel, reduce the critical longitudinal ventilation velocity and the distribution range of the high temperature area in the tunnel and the maximum temperature, and has important application value and economic and social benefits.

[0044] (3) The present application is based on different ventilation mode-ventilation velocity-temperature distribution to adapt to the hybrid ventilation method for handling hydrogen energy fire accidents in the tunnel. A dimensionless prediction model of the critical longitudinal ventilation velocity is established, the danger of hydrogen jet fire in the tunnel is reduced, the rapid selection of the ventilation mode and the rapid prediction of the ventilation velocity when hydrogen jet fire occurs in the tunnel are realized, the method makes up for the limitations of traditional single ventilation mode in preventing and controlling hydrogen energy fire, effectively reduces the temperature in the tunnel, reduces the distribution of high temperature area in the tunnel and the length of flame back layer, accurately and efficiently predicts the ventilation velocity of hydrogen energy fire in the tunnel, and forms a safe fire rescue and escape area in the upstream of the tunnel. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a flowchart of a new hybrid ventilation method for tunnel hydrogen energy fire accident safety rescue provided by the embodiment of the present application;

[0046] Figure 2Figure for mixed ventilation tunnel geometry model of embodiment of the present application;

[0047] Figure 3 Figure for finite element model verification of mixed ventilation tunnel of embodiment of the present application;

[0048] Figure 4 Temperature slice cloud chart for single longitudinal ventilation mode of embodiment of the present application;

[0049] Figure 5 Temperature slice cloud chart for single transverse ventilation mode of embodiment of the present application;

[0050] Figure 6 Temperature slice cloud chart for conventional mixed ventilation mode of embodiment of the present application;

[0051] Figure 7 Velocity vector chart for defect analysis of conventional mixed ventilation mode of embodiment of the present application;

[0052] Figure 8 Temperature slice cloud chart for mixed ventilation mode of longitudinal ventilation cooperating with transverse ventilation above and downstream of leakage source in tunnel of embodiment of the present application;

[0053] Figure 9 Temperature slice cloud chart for mixed ventilation mode of longitudinal ventilation cooperating with vertical shaft downstream of leakage source in tunnel of embodiment of the present application;

[0054] Figure 10 Curve chart for different ventilation modes-transverse ventilation speed-critical longitudinal ventilation speed of embodiment of the present application;

[0055] Figure 11 Curve chart for different ventilation modes-transverse ventilation speed-temperature in personnel activity area of embodiment of the present application;

[0056] Figure 12 Curve chart for different ventilation modes-transverse ventilation speed-temperature in top wall area of embodiment of the present application;

[0057] Figure 13 Model verification chart for critical longitudinal ventilation speed prediction model of embodiment of the present application. DETAILED DESCRIPTION

[0058] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application, but the embodiments of the present application are not limited to this. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0059] Please refer to Figure 1The embodiment of the application provides a new mixed ventilation method for tunnel hydrogen energy fire accident safety rescue, which comprises the following steps:

[0060] Step 1: According to the physical structure of the tunnel and the setting condition of the vertical shaft in the tunnel, the basic setting parameters of the hydrogen jet fire scene in the tunnel are determined, a multi-vertical shaft tunnel simulation model with a mixed ventilation system is established in a finite element software, the grid is divided and the boundary condition is set, and the model accuracy is verified by comparing experimental data.

[0061] This step specifically comprises the following sub-steps:

[0062] Step 1.1: Determine the tunnel size: the multi-vertical shaft tunnel simulation model adopts a multi-vertical shaft structure, the tunnel size is 15m in length, 0.25m in width and 0.25m in height, 11 groups of vertical shafts with a spacing of 1.25m are installed in the upstream and downstream areas of the fire source, the vertical shaft diameter is 0.18m, and the tunnel model and the actual tunnel size ratio is 1:20, as shown in Figure 2 The top wall area and the personnel activity area (height is 0.25m and 0.1m respectively) in the tunnel model are provided with temperature detection points for measuring the temperature change in the tunnel, and a temperature slice is arranged on the center line of the tunnel to observe the change of the temperature field in the tunnel.

[0063] Step 1.2: A multi-vertical shaft tunnel simulation model with a mixed ventilation system is established by a three-dimensional modeling software, and is introduced into a finite element software FLUENT for geometric model pretreatment, grid division, grid element type setting and selection of a turbulent flow model, a combustion model and a radiation model.

[0064] Among them, step 1.2 specifically comprises the following sub-steps:

[0065] Step 1.2.1: A multi-vertical shaft tunnel simulation model with a mixed ventilation system is established by using SOLIDWORKS software according to the size of the preset tunnel simulation model, and different areas of the tunnel simulation model are marked by SPACECLAIM software in ANSYS-WORKBENCH and are introduced into the FLUENT software.

[0066] Step 1.2.2: The grid element type is set in the FLUENT software, including the grid element type of the tunnel, the vertical shaft and the leakage source;

[0067] Step 1.2.3: The propagation process of the hydrogen jet flame is analyzed, and the problems such as fluid flow, combustion reaction and radiation heat transfer are mainly involved in the process from hydrogen leakage to hydrogen jet flame propagation.

[0068] In one embodiment of the present application, Realizable k-ε turbulent flow model is selected in FLUENT software and enhanced wall function is introduced for near-wall treatment. Meanwhile, curvature correction is made to the turbulent flow model by considering pressure gradient effect and thermal effect, and the influence of buoyancy effect is considered:

[0069]

[0070] In the formula, t is time, p is density, k is turbulent flow energy, x y is axial coordinate in y direction, u y is axial velocity component in y direction, p is molecular viscosity, p t is turbulent viscosity, G k is turbulent flow energy generated due to average velocity gradient, G b is turbulent flow energy generated by buoyancy, and e is turbulent dissipation rate, Y M is the effect of wave expansion on total dissipation rate in compressible turbulent flow, S k and S ε are user-defined source terms, and S is scalar measure of deformation tensor, p k and p ε are Prandtl constants corresponding to k and e respectively, C1, C2, C 1ε and C 3ε are all constants, and v is molecular kinematic viscosity.

[0071] In one embodiment of the present application, non-premixed combustion model is selected for the combustion model, which does not need to solve a large number of component transport equations and strictly considers the interaction between turbulent flow and chemical reaction:

[0072] ①The basis of the model is to solve the transport equation of mixing fraction f, and then calculate the temperature and component concentration in the calculation domain. The mixing fraction f is defined by the element mass fraction:

[0073]

[0074] In the formula, Z i is the mass fraction of element i, %, Z i,ox and Z i,fuel are the mass fractions of oxidizer and fuel respectively.

[0075] ②The transport equation of mixing fraction f is:

[0076]

[0077] In the formula: is the average value of mixing fraction f, is velocity vector, m.s -1 ; S mis the source term for mass transfer from liquid fuel droplets or reacting particles into the gas phase; S user is the source term for user defined source terms; is the bias mean square of the mixing fraction f; σ t , C g , C d are constants with values 0.85, 2.86, 2.0, respectively.

[0078] In one embodiment of the present application, the radiation model is selected as the DO model, which is applicable to all optical depth radiation problems, can consider scattering problems, and can calculate non-gray body radiation using a gray band model:

[0079]

[0080] In the formula: is the partial derivative of a quantity with respect to all directions in the selected coordinate system, is a position vector, is a direction vector, is a scattering direction vector, s is a path length, a is an absorption coefficient, n is a refractive index, σ s is a scattering coefficient, σ is the Stefan-Boltzmann constant, I is the radiation intensity, which is related to the position r and s, T is the local temperature, Φ is the phase function, and Ω' is the solid angle.

[0081] Step 1.3: The fire source radius in the tunnel is set to 0.106 m, the heat release rate of the fire source is set to 5 MW, 15 MW, 25 MW, and 34 MW, and the position of the fire source is set on the center line of the tunnel, 7.5 m away from the tunnel entrance. The lateral ventilation velocity is set to 0 m / s, 1 m / s, 2 m / s, 3 m / s, 4 m / s, and 5 m / s.

[0082] Step 1.4: According to the experimental data of the tunnel smoke control test using a longitudinal ventilation system [Wu Y, Bakar MZA. Control of smoke flow in tunnel fires using longitudinal ventilation systems-a study of the critical velocity [J] (Control of smoke flow in tunnel fires using longitudinal ventilation systems-a study of the critical velocity)], the critical longitudinal ventilation simulation calculation of the tunnel under the same parameters is carried out, and the obtained critical longitudinal ventilation velocity curve with the change of the heat release rate is compared with the experimental results, as shown in Figure 3 The simulation results are in good agreement with the experimental results, with a maximum error of 7.45%, which meets the engineering application range, and the accuracy of the tunnel simulation model provided by the present application with a mixed ventilation system is illustrated.

[0083] Step 2: Under the preset fire source heat release rate, the advantages and disadvantages of the single longitudinal ventilation mode, the single transverse ventilation mode and the conventional mixed ventilation mode are compared, and a new type of mixed ventilation mode is proposed; the ventilation effect of different new type of mixed ventilation modes is simulated and analyzed, and based on the influence of different new type of mixed ventilation modes on the hydrogen jet fire back layer length and the temperature in the tunnel, the optimized ventilation mode suitable for the hydrogen jet fire in the tunnel is determined.

[0084] This step includes the following steps:

[0085] Step 2.1: The temperature cloud maps under the single longitudinal ventilation mode, the single transverse ventilation mode and the conventional mixed ventilation mode are simulated and obtained, and the advantages and disadvantages of different ventilation modes in handling the hydrogen jet fire accident in the tunnel are compared according to the temperature cloud maps.

[0086] In one embodiment of the present application, Figure 4 、 Figure 5 and Figure 6 are the temperature cloud maps obtained under the single longitudinal ventilation mode, the single transverse ventilation mode and the conventional mixed ventilation mode respectively. As shown in Figure 4 , when the longitudinal ventilation reaches the critical ventilation speed threshold, the heat generated by the fire can be prevented from flowing upstream to form a safe upstream evacuation and rescue channel, but the longitudinal ventilation cannot solve the problem of thermal stratification in the downstream area of the tunnel, and with the increase of the longitudinal ventilation speed, the high-temperature distribution area in the downstream gradually expands, and the temperature in the activity range of people and vehicles in the tunnel increases; as shown in Figure 5 , the transverse ventilation significantly reduces the thickness of the high-temperature layer on the top wall of the tunnel, and the jet flame can be effectively controlled between the shaft and the leakage port, but the transverse ventilation in the upstream area of the tunnel cannot effectively control the temperature of the upstream tunnel; as shown in Figure 6 , compared with the transverse ventilation, the conventional mixed ventilation cannot effectively control the flame temperature, which increases the possibility of injury to people and vehicles in the downstream by the flame, and compared with the longitudinal ventilation, the flame back layer length becomes longer, it is more difficult to form a safe area in the upstream, and the rescue and evacuation in the downstream of the tunnel under the hydrogen jet fire are increased. As shown in Figure 7 , the velocity vector diagram of the upstream shaft of the leakage source in the conventional mixed ventilation mode can be found that the transverse ventilation at the upstream shaft will interfere with the influence of the longitudinal ventilation on the flame at the leakage source, and at the same time, it will guide the flame to spread upstream, so that the conventional mixed ventilation mode will increase the range of high-temperature area in the whole tunnel, and increase the danger of the flame.

[0087] Step 2.2: According to the disadvantages of the conventional mixed ventilation mode, the interference of the upstream transverse ventilation is excluded, and a new type of mixed ventilation mode is proposed.

[0088] The new type of mixed ventilation mode comprises:

[0089] (1) longitudinal ventilation combined with lateral ventilation above the leakage source in the tunnel;

[0090] (2) longitudinal ventilation combined with lateral ventilation downstream of the leakage source in the tunnel.

[0091] Step 2.3: simulate the two new hybrid ventilation modes in the FLUENT software to obtain the temperature slices on the center line of the tunnel under different ventilation speeds and the temperatures of each detection point, obtain the critical longitudinal ventilation speed changes under different new hybrid ventilation modes according to the critical longitudinal ventilation speed calculation algorithm, and draw the critical longitudinal ventilation speed, lateral ventilation speed and tunnel temperature relationship curves.

[0092] The critical longitudinal ventilation speed calculation algorithm is:

[0093] (1) measure the back layer length of the flame and the corresponding ventilation speed by using the FLUENT software system;

[0094] (2) draw the relationship curve of the ventilation speed and the back layer length, extend the relationship curve of the ventilation speed and the back layer length outward, and derive the critical longitudinal ventilation speed when the back layer length of the flame is 0m;

[0095] (3) use the critical longitudinal ventilation speed when the back layer length of the flame is 0m derived to simulate, judge whether there is a backflow speed at the upstream of the tunnel and whether there is a flame back layer in the temperature cloud picture, if not, it is proved that the longitudinal ventilation speed is the critical longitudinal ventilation speed.

[0096] Draw the relationship curves of different ventilation modes-lateral ventilation speed-critical longitudinal ventilation speed; draw the relationship curves of different ventilation modes-lateral ventilation speed-temperature in the personnel activity area; and draw the relationship curves of different ventilation modes-lateral ventilation speed-temperature in the top wall area.

[0097] Step 2.4: determine the new hybrid ventilation mode suitable for the tunnel based on the ventilation mode-ventilation speed-temperature distribution.

[0098] In one embodiment of the present application, the temperature slices on the center line of the tunnel under different ventilation speeds are as shown in Figure 8 and Figure 9 .

[0099] In one embodiment of the present application, the relationship curves of different ventilation modes-lateral ventilation speed-critical longitudinal ventilation speed drawn according to the simulation results are as shown in Figure 10 , the relationship curves of different ventilation modes-lateral ventilation speed-temperature in the personnel activity area are as shown in Figure 11 , and the relationship curves of different ventilation modes-lateral ventilation speed-temperature in the top wall area are as shown in Figure 12shown.

[0100] By comparison, it can be found that the two new mixed ventilation methods can effectively control the temperature in the tunnel, and the temperature in the tunnel gradually decreases with the increase of the horizontal ventilation speed. Figure 8 and Figure 9 It can be found that these two new mixed ventilation methods can effectively control the height of the thermal layer in the tunnel and reduce the temperature of the top wall area and the personnel activity area. Figure 10 It can be found that in this embodiment, the new mixed air mode 1 causes the critical longitudinal ventilation speed to increase due to the influence of the vertical shaft, making it more difficult to form a safe upstream rescue area. At the same time, the location of the leakage source in the tunnel fire appears randomly, and the new mixed ventilation mode 1 cannot solve the situation where the leakage source is not below the vertical shaft. Therefore, it is determined that the mixed ventilation mode of longitudinal ventilation combined with the vertical shaft downstream of the leakage source in the tunnel in this embodiment is the ventilation mode optimized for hydrogen fire accidents in hydrogen transportation tunnels.

[0101] Step 3: Determine the influencing factors of the critical longitudinal ventilation velocity, fit the simulation data to establish a prediction model for the critical longitudinal ventilation velocity in the tunnel, and realize the rapid prediction of the critical longitudinal ventilation velocity of hydrogen fire in the tunnel based on the new hybrid ventilation method.

[0102] Step 3.1: Determine the factors affecting the critical longitudinal ventilation speed: The factors affecting the critical longitudinal ventilation speed include the heat release rate Q of the fire source, the transverse ventilation speed V t , tunnel height H, tunnel cross-sectional area A, ambient air density ρ a , ambient air temperature Ta, constant pressure specific heat capacity of air C p , gravitational acceleration g.

[0103] Step 3.2: Combine the critical longitudinal ventilation velocity, transverse ventilation velocity and temperature data under different working conditions obtained in step 2.3, and exclude the known basic physical quantities such as tunnel height H, tunnel cross-sectional area A, and ambient air density ρ. a , ambient air temperature T a , constant pressure specific heat capacity of air C p The influence of gravitational acceleration g is considered and the polynomial fitting method of least squares method is used to fit the formula using MATLAB software.

[0104] (1) Least squares formula:

[0105] D={(x1,y1),(x2,y2),...,(x i ,y i ),...,(x N ,y N )}

[0106] xi ∈R

[0107] y i ∈R

[0108] In the formula: D is the dependent variable, x and y are independent variables, R is a real number, N is the number of independent variables, and i is an index number.

[0109] (2) Polynomial function:

[0110]

[0111] In the formula: f(x) is the dependent variable, x is the independent variable, w and b are constants, and M is the highest degree of the polynomial.

[0112] (3) Error sum of squares:

[0113]

[0114] In the formula: E(w) is the error sum of squares, x and y are independent variables, w is a constant, and m and n are the highest degrees of the polynomial.

[0115] Step 3.3: Determine the value of the unknown number of the dimensionless prediction formula by calculating the fitting, and establish the prediction model of the critical longitudinal ventilation velocity in the tunnel as:

[0116]

[0117] In the formula: V c is the critical longitudinal ventilation velocity, V t is the transverse ventilation velocity, Q is the hydrogen heat release rate, and are the dimensionless critical longitudinal ventilation velocity, the dimensionless transverse ventilation velocity, and the dimensionless hydrogen heat release rate, respectively.

[0118] In one embodiment of the present application, Figure 11 Figure 12 Figure 13 is the distribution of the simulation data around the fitting formula, as shown in the figure, the simulation data is evenly scattered around the data of the fitting formula, and the fitting effect is good.

[0119] For the step numbers in the above embodiments, they are only set for convenient explanation and description, and the order between the steps is not limited, and the execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0120] Finally, it should be noted that the contents not described in detail in the embodiments of the present application belong to the prior art known to the person skilled in the art. The above only describes the preferred embodiments of the present application and is not used to limit the present application. For the person skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A new hybrid ventilation method for safe rescue of hydrogen fire accidents in tunnels, characterized in that: The following steps are involved: Determine basic setting parameters for simulating a fire scenario in the tunnel based on the physical structure of the tunnel and the configuration of the hybrid ventilation system in the tunnel, and establish a multi-shaft tunnel simulation model with a hybrid ventilation system in finite element software; Compare different existing ventilation methods and propose a new hybrid ventilation method based on their advantages and disadvantages. Simulate and analyze the ventilation effects of different new hybrid ventilation methods. Based on their impact on the back layer length and temperature in the tunnel during hydrogen jet fires, determine the optimal ventilation method for this tunnel hydrogen jet fire. Determine the factors affecting the critical longitudinal ventilation velocity. Fit the critical longitudinal ventilation velocity, transverse ventilation velocity, and fire source heat release rate for the optimized ventilation method for hydrogen jet fires in this tunnel using a least squares polynomial fitting method. Establish a dimensionless prediction model for the critical longitudinal ventilation velocity in the tunnel. Use this prediction model to predict the critical longitudinal ventilation velocity. The novel mixed ventilation mode is any one of a mixed ventilation mode of longitudinal ventilation combined with transverse ventilation above the leakage source in the tunnel and a mixed ventilation mode of longitudinal ventilation combined with transverse ventilation downstream of the leakage source in the tunnel; Different new mixed ventilation modes were simulated in finite element software to obtain temperature slices on the tunnel centerline at different ventilation speeds. The changes in critical longitudinal ventilation speed under different new mixed ventilation modes were obtained according to the critical longitudinal ventilation speed calculation algorithm, and the critical longitudinal ventilation speed, transverse ventilation speed and tunnel temperature curves under different ventilation conditions were plotted.

2. A novel mixed ventilation method for safe rescue of hydrogen fire accidents in tunnels according to claim 1, characterized in that: In the multi-shaft tunnel simulation model, multiple groups of shafts are installed at intervals in the upstream and downstream areas of the fire source; temperature detection points are set in the top wall area and the personnel activity area to measure the temperature changes in the tunnel. At the same time, temperature slices are set on the center line of the tunnel to observe the changes in the temperature field inside the tunnel.

3. A novel mixed ventilation method for safe rescue of hydrogen fire accidents in tunnels according to claim 1, characterized in that: The model parameters are set in the finite element software, including the horizontal ventilation speed of the shaft, the radius of the fire source, the heat release rate of the fire source, the location of the fire source, and the distance between the fire source and the tunnel entrance.

4. A novel mixed ventilation method for safe rescue of hydrogen fire accidents in tunnels according to claim 1, characterized in that: The advantages and disadvantages of various existing ventilation methods are determined based on their temperature cloud maps and the spread range of hydrogen jet flames, including: Through simulation, the temperature cloud maps under single longitudinal ventilation mode, single transverse ventilation mode and conventional mixed ventilation mode are obtained; Determine the hydrogen jet flame spread range based on the temperature cloud map; Based on the comparison of temperature cloud maps and hydrogen jet flame diffusion range, the advantages and disadvantages of different existing ventilation methods in dealing with hydrogen jet fire accidents in tunnels are determined.

5. The novel mixed ventilation method for safe rescue of hydrogen fire accidents in tunnels according to claim 1 is characterized in that: The critical longitudinal ventilation velocity calculation algorithm is: Finite element software was used to measure the back layer length of the flame and its corresponding ventilation speed; Draw the relationship curve between ventilation speed and back layer length, extend the relationship curve between ventilation speed and back layer length outward, and deduce the critical longitudinal ventilation speed when the back layer length of the flame is 0m; The critical longitudinal ventilation velocity when the derived flame back layer length is 0m is used for simulation to determine whether there is a backflow velocity measured at the upstream of the tunnel and whether there is a flame back layer in the cloud map. If not, it proves that the longitudinal ventilation velocity is the critical velocity.

6. A novel mixed ventilation method for safe rescue of hydrogen fire accidents in tunnels according to claim 1, characterized in that: The drawing of the critical longitudinal ventilation velocity, transverse ventilation velocity and tunnel temperature curve under different ventilation conditions includes: Draw the relationship curve between different ventilation modes, transverse ventilation speed and critical longitudinal ventilation speed; Draw the relationship curve between different ventilation modes, horizontal ventilation speed and temperature of the personnel activity area; Draw the relationship curves of different ventilation modes-lateral ventilation speed-top wall area temperature.

7. A novel mixed ventilation method for safe rescue of hydrogen fire accidents in tunnels according to any one of claims 1 to 6, characterized in that: The factors affecting the critical longitudinal ventilation speed include: the heat release rate of the fire source , transverse ventilation speed , tunnel height H, tunnel cross-sectional area A, ambient air density , ambient air temperature Ta, constant pressure specific heat capacity of air C p and the acceleration due to gravity g.

8. A novel mixed ventilation method for safe rescue of hydrogen fire accidents in tunnels according to claim 7, characterized in that: The tunnel height H, tunnel cross-sectional area A, ambient air density , ambient air temperature Specific heat capacity of air at constant pressure and gravitational acceleration g are known basic physical quantities. Based on the polynomial fitting of the least squares method, a dimensionless prediction model for the critical longitudinal ventilation velocity in the tunnel is established, which is expressed as follows: Where, is the critical longitudinal ventilation velocity, is the transverse ventilation velocity, is the hydrogen heat release rate, 、 and are the dimensionless critical longitudinal ventilation velocity, dimensionless transverse ventilation velocity and dimensionless hydrogen heat release rate, respectively.

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