Simulation method for membrane material pyrolysis and toxic gas concentration distribution in fire scene

Abstract

The invention discloses a simulation method for membrane material pyrolysis and toxic gas concentration distribution in a fire scene, and the method comprises the following steps: S1, determining membrane structure building data, building a CAD model, and importing the CAD model into Pyros im software; s2, establishing a calculation area, specifying a combustion product yield, and setting fire source parameters; s3, different building material models and surface types are defined and given to corresponding building components; s4, setting a temperature measuring point, visibility and toxic gas volume fraction measuring points, setting simulation parameters, and calling an FDS program for calculation; and S5, extracting a result, and obtaining a curve of temperature, toxic gas concentration and visibility change along with time near an evacuation exit. According to the invention, the membrane material pyrolysis process of a membrane structure building in a fire scene can be simulated, and the key technical problem of how to obtain and consider the toxic gas concentration distribution of the membrane material pyrolysis product in numerical simulation is solved.

Description

Technical Field

[0001] The present invention relates to the field of fire resistance of membrane structures, and more specifically to a method for simulating thermal decomposition of membrane materials and concentration distribution of toxic gases under fire scenarios. Background Art

[0002] Membrane structures have been widely used in large-span buildings due to their unique advantages of light weight, high strength and good light transmittance. However, the safety of such buildings in fires has also attracted much attention. Membrane materials, as their main constituent materials, are prone to thermal decomposition in fires, producing toxic gases, which have a serious impact on human health and personnel evacuation.

[0003] At present, numerical simulation has become one of the important means to study fire behavior. By constructing a numerical model of the fire scene, the changes in smoke temperature, gas concentration, and visibility during the fire can be simulated, providing a scientific basis for fire prevention and emergency rescue. However, when simulating fires in membrane structures, how to obtain and predict the distribution of toxic gas concentrations taking into account the thermal decomposition products of membrane materials has become a key technical problem in numerical simulation.

[0004] Therefore, providing a method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases under fire scenarios is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0006] In view of this, the present invention provides a simulation method for membrane material pyrolysis and toxic gas concentration distribution under fire scenarios, which can simulate the membrane material pyrolysis process of membrane structure buildings under fire scenarios, so as to solve the key technical problem of how to obtain the toxic gas concentration distribution considering the membrane material pyrolysis products in numerical simulation.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for simulating film material pyrolysis and toxic gas concentration distribution under fire scenarios comprises the following steps:

[0009] S1. Determine the membrane structure building data, build the CAD model, and import it into Pyros im software;

[0010] S2. Establish the calculation area, specify the combustion product yield, and set the fire source parameters;

[0011] S3. Define different building material models and surface types, and assign them to corresponding building components;

[0012] S4. Set the temperature measurement points, visibility and toxic gas volume fraction measurement points, set the simulation parameters, and call the FDS program for calculation;

[0013] S5. Extract the results to obtain the curves of the temperature, toxic gas concentration and visibility near the evacuation exit changing with time.

[0014] Furthermore, in step S1, the membrane structure building data includes the use function, basic physical parameters of building materials, geometric dimensions, ventilation conditions, the presence or absence of sprinklers, and the type and location of combustibles; wherein the fire source parameters are determined according to the use function, the presence or absence of sprinklers, and the type and location of combustibles of the membrane structure building; and a CAD model is constructed according to the geometric dimensions of the membrane structure building and imported into the Pyrosim software.

[0015] Furthermore, the fire source parameters in step S1 include fire source power, fire source growth model, speed, fire source location and the yield of combustible combustion products.

[0016] Furthermore, the basic physical parameters of building materials include the density, specific heat capacity and thermal conductivity of the material.

[0017] Furthermore, the membrane structure building data also includes pyrolysis parameters, and the pyrolysis parameters include pyrolysis rate, different pyrolysis products and their yields.

[0018] Further, step S2 includes:

[0019] S21. Establish the calculation area and determine the reasonable grid size according to the fire source power;

[0020] S22, specify the combustion reaction, specify the yield of the combustion products of the combustibles;

[0021] S23. According to the fire source parameters of step S1, a Burner type surface is established and the heat release rate per unit area and the fire source growth curve are set; a Vent type obstacle is newly created and assigned with Burner surface attributes, the Vent area is the fire source area; the product of the fire source area and the heat release rate per unit area is the fire source power.

[0022] Further, step S3 includes:

[0023] S31, according to the pyrolysis product of the film material in step S1, define the pyrolysis product by specifying the molar mass or chemical equation under the Primitive tab of the Species tab;

[0024] S32. Define the material properties of the membrane material. Create a new membrane material in the Materials tab. Specify the density, specific heat capacity, and thermal conductivity of the membrane material in the Thermal Properties tab. Create a new pyrolysis reaction in the Pyrolysis tab. In the Edit Pyrolysis Reaction window, you can obtain the pyrolysis rate by inputting the reference temperature, heating rate, pyrolysis angle, or pre-exponential factor and activation energy in the Rate tab.

[0025] S33, specifying the reaction heat absorbed during the pyrolysis of the film material under the Byproducts tab of the Edit Pyrolysis Reaction window, and inputting different pyrolysis products and corresponding yields according to the pyrolysis products and yields of the film material determined in step S1;

[0026] S34, according to the physical parameters of the building material in step S1, refer to the material property definition of the membrane material, define the building material properties, establish different surfaces based on the membrane material and the building material properties, and specify the material type and corresponding thickness under the MaterialLayers tab of the Surface tab;

[0027] S35, assigning surface properties of the membrane surface and other components to the membrane surface and other components respectively.

[0028] Further, step S4 includes:

[0029] S41. Set a measuring point for temperature, volume fraction of toxic gas including pyrolysis products, and visibility at a height of 2 m from the evacuation exit;

[0030] S42. Set simulation parameters, including air supply vents, smoke exhaust vents, sprinklers, ambient temperature, simulation duration and output parameters, and call the FDS program for calculation.

[0031] It can be seen from the above technical solution that the present invention discloses a method for simulating the pyrolysis of membrane materials and the concentration distribution of toxic gases under fire scenarios. Compared with the prior art, the present invention has the following beneficial effects: it can simulate the pyrolysis process of membrane materials in membrane structure buildings under fire scenarios, and solves the key technical problem of how to obtain the concentration distribution of toxic gases taking into account the pyrolysis products of membrane materials in numerical simulations. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0033] Figure 1 The accompanying drawing is a flow chart of a method for simulating the thermal decomposition of membrane materials and the concentration distribution of toxic gases under a fire scenario provided by the present invention.

[0034] Figure 2 The accompanying drawing is a structural schematic diagram of the membrane structure building model provided by the present invention.

[0035] Figure 3The attached drawing is a curve diagram showing the temperature variation over time at a height of 2 m of the evacuation outlet provided by the present invention.

[0036] Figure 4 The attached drawing is a graph showing the concentration of toxic gases (CO, HCl) at a height of 2 m at the evacuation outlet provided by the present invention changing with time.

[0037] Figure 5 The attached drawing is a graph showing the visibility at a height of 2m at the evacuation exit provided by the present invention changing with time.

[0038] In the figure: 1-roof; 2-wall; 3-air supply vent, 4-evacuation exit. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] like Figure 1-5 As shown, an embodiment of the present invention discloses a method for simulating the thermal decomposition of a film material and the concentration distribution of toxic gases in a fire scene, comprising the following steps:

[0041] S1. Determine the membrane structure building data, build the CAD model, and import it into Pyros im software;

[0042] The membrane structure building data includes the use function, basic physical parameters of building materials, geometric dimensions, ventilation conditions, whether there is sprinkler, and the type and location of combustibles; the fire source parameters are determined according to the use function, whether there is sprinkler, and the type and location of combustibles of the membrane structure building; according to the geometric dimensions of the membrane structure building, a CAD model is constructed and imported into the Pyrosim software;

[0043] The fire source parameters include fire source power, fire source growth model, speed, fire source location and the yield of combustible combustion products; the basic physical parameters of building materials include material density, specific heat capacity and thermal conductivity;

[0044] The membrane structure building data also includes pyrolysis parameters, which include pyrolysis rate, different pyrolysis products and their yields;

[0045] In this embodiment, the established membrane structure building model includes a roof 1 covered with PVC membrane material, a wall 2, an air supply port 3 and an evacuation outlet 4. The wall 2 is assumed to be an insulating surface during simulation. The size of the air supply port 3 is 44×2m, and the size of the evacuation outlet 4 is 4×2m. There are no fire-fighting facilities such as smoke exhaust ports and sprinklers. The combustible material is soft polyurethane foam, the combustible material is located in the center of the room, and the fire source height is 0m from the ground.

[0046] The target building is used as a store without sprinklers. With reference to the Technical Standard for Smoke and Exhaust Systems in Buildings (GB51251-2017) and the Technical Code for Fire Protection of Steel Structures in Buildings (CECS200:2006), the fire source power is set to 10MW. With reference to the Technical Standard for Smoke and Exhaust Systems in Buildings (GB51251-2017), the fire growth model shown in formula (1) is adopted. The combustible is soft polyurethane foam plastic, the fire category is fast fire, and α = 0.044kW / s 2 .

[0047] Q=α·t 2 (1)

[0048] Where Q is the fire source power (kW);

[0049] α——Fire growth coefficient (kW / s 2 );

[0050] t——time(s).

[0051] Refer to the SFPE Fire Engineering Manual to obtain the yield of combustion products (such as CO, Soot) of soft polyurethane foam under good ventilation.

[0052] S2. Establish the calculation area, specify the combustion product yield, and set the fire source parameters;

[0053] The specific steps are as follows:

[0054] S21. Establish the calculation area and determine the reasonable grid size according to the fire source power;

[0055] The characteristic diameter D of the fire source and the grid size δ generally meet the requirement of D / δ∈[4,16], where D is calculated using formula (2):

[0056]

[0057] Where Q is the fire source power (kW);

[0058] ρ ∞ ——The initial value of ambient air density is 1.2kg / m 3 ;

[0059] c ∞——The initial value of specific heat capacity is 1 kJ / (kg·K);

[0060] T ∞ ——The initial value of ambient temperature is 293K;

[0061] g——acceleration due to gravity, take 9.81m / s 2 .

[0062] S22, specify the combustion reaction, specify the yield of the combustion products of the combustibles;

[0063] S23, according to the fire source parameters of step S1, a Burner type surface is established and the heat release rate per unit area and the fire source growth curve are set; a Vent type obstacle is newly created and assigned with the Burner surface attribute, the Vent area is the fire source area; the product of the fire source area and the heat release rate per unit area is the fire source power;

[0064] S3. Define different building material models and surface types, and assign them to corresponding building components;

[0065] The specific steps are as follows:

[0066] S31, according to the pyrolysis product of the film material in step S1, define the pyrolysis product by specifying the molar mass or chemical equation under the Primitive tab of the Species tab;

[0067] S32. Define the material properties of the membrane material. Create a new membrane material in the Materials tab. Specify the density, specific heat capacity, and thermal conductivity of the membrane material in the Thermal Properties tab. Create a new pyrolysis reaction in the Pyrolysis tab. In the Edit Pyrolysis Reaction window, you can obtain the pyrolysis rate by inputting the reference temperature, heating rate, pyrolysis angle, or pre-exponential factor and activation energy in the Rate tab.

[0068] S33, specifying the reaction heat absorbed during the pyrolysis of the film material under the Byproducts tab of the Edit Pyrolysis Reaction window, and inputting different pyrolysis products and corresponding yields according to the pyrolysis products and yields of the film material determined in step S1;

[0069] S34, according to the physical parameters of the building material in step S1, refer to the material property definition of the membrane material, define the building material properties, establish different surfaces (membrane surface, other components) based on the membrane material and the building material properties, and specify the material type and corresponding thickness under the Material Layers tab of the Surface tab;

[0070] S35, assigning surface properties of the membrane surface and other components to the membrane surface and other components respectively;

[0071] In this embodiment, the pyrolysis rate of the material is measured by a thermogravimetric analyzer, and the heating rate needs to be set during the experiment. Unit K / min. When the temperature reaches a certain value, the material begins to pyrolyze, the mass fraction decreases, and the pyrolysis rate r gradually increases. The temperature at which the pyrolysis rate reaches its peak is the reference temperature in Pyrosim, unit ℃. A certain amount of heat needs to be absorbed during the pyrolysis process. The reaction heat of the material pyrolysis is specified in the Heat of Reaction parameter under the Byproducts tab.

[0072] Material mass fraction Y s is the time t and temperature T s The function is expressed as formula (3):

[0073]

[0074] Where A is the pre-exponential factor, 1 / s;

[0075] E——activation energy, kJ / kmol;

[0076] R——constant.

[0077] Although the thermal decomposition rate of a material can be calculated by the pre-exponential factor A and the activation energy E, these two values ​​are not available for most materials. Therefore, the reference temperature T p To replace the pre-exponential factor A and activation energy E, their relationship can be expressed by formulas (4) to (6).

[0078]

[0079] In the formula ——The heating rate during the thermogravimetric test is set in the "Heating Rate" parameter;

[0080] ΔT——pyrolysis angle, set in the "Pyrolysis Range" parameter, the default value is 80℃;

[0081] v s ——The solid residue content after pyrolysis, the default value is 0;

[0082] r p ——Peak value of pyrolysis rate, i.e. pyrolysis rate at reference temperature;

[0083] Y s ——Mass fraction, when a single material is pyrolyzed, it is 1;

[0084] R——ideal gas constant, 8.314 J / (mol·K);

[0085] T p ——Reference temperature, in °C, set in the “Reference Temperature” parameter.

[0086] When setting material pyrolysis parameters, the pre-exponential factor A, activation energy E and reference temperature are set separately, and the two can be converted to each other through formula calculation.

[0087] S4. Set the temperature measurement points, visibility and toxic gas volume fraction measurement points, set the simulation parameters, and call the FDS program for calculation;

[0088] The specific steps are as follows:

[0089] S41. Set a measuring point for temperature, volume fraction of toxic gas including pyrolysis products, and visibility at a height of 2 m from the evacuation exit;

[0090] S42, set simulation parameters, including air supply port, smoke exhaust port, sprinkler, ambient temperature, simulation duration and output parameters, and call FDS program for calculation;

[0091] S5. Extract the results to obtain the curves of the temperature, toxic gas concentration, and visibility near the evacuation exit over time, such as Figure 3 As shown in Figure 2, the highest temperature during the fire is around 215°C; Figure 4 As shown in Figure 2, the concentration of HCl gas is slightly higher than that of CO gas; Figure 5 As shown, visibility is less than 0.5m after 350s.

[0092] The present invention can simulate the pyrolysis process of membrane materials in membrane structure buildings under fire scenarios, and solves the key technical problem of how to obtain the concentration distribution of toxic gases taking into account the pyrolysis products of membrane materials in numerical simulation.

[0093] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0094] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases under fire scenarios, characterized in that: The following steps are involved: S1. Determine the membrane structure building data, build the CAD model, and import it into Pyrosim software; S2. Establish the calculation area, specify the combustion product yield, and set the fire source parameters; S3. Define different building material models and surface types, and assign them to corresponding building components; S4. Set the temperature measurement points, visibility and toxic gas volume fraction measurement points, set the simulation parameters, and call the FDS program for calculation; S5. Extract the results to obtain the curves of the temperature, toxic gas concentration and visibility near the evacuation exit changing with time.

2. The method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases in a fire scene according to claim 1, characterized in that: In step S1, the membrane structure building data includes the use function, basic physical parameters of building materials, geometric dimensions, ventilation conditions, the presence or absence of sprinklers, and the type and location of combustibles; wherein the fire source parameters are determined according to the use function, the presence or absence of sprinklers, and the type and location of combustibles of the membrane structure building; and a CAD model is constructed according to the geometric dimensions of the membrane structure building and imported into the Pyrosim software.

3. The method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases in a fire scene according to claim 2, characterized in that: The fire source parameters in step S1 include fire source power, fire source growth model, speed, fire source location and the yield of combustible combustion products.

4. The method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases in a fire scene according to claim 3, characterized in that: The basic physical parameters of building materials include material density, specific heat capacity and thermal conductivity.

5. The method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases in a fire scene according to claim 4, characterized in that: Membrane structure building data also include pyrolysis parameters, which include pyrolysis rate, different pyrolysis products and their yields.

6. The method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases in a fire scene according to claim 5, characterized in that: Step S2 includes: S21. Establish the calculation area and determine the reasonable grid size according to the fire source power; S22, specify the combustion reaction, specify the yield of the combustion products of the combustibles; S23. According to the fire source parameters of step S1, a Burner type surface is established and the heat release rate per unit area and the fire source growth curve are set; a Vent type obstacle is newly created and assigned with Burner surface attributes, the Vent area is the fire source area; the product of the fire source area and the heat release rate per unit area is the fire source power.

7. The method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases in a fire scene according to claim 6, characterized in that: Step S3 includes: S31, according to the pyrolysis product of the film material in step S1, define the pyrolysis product by specifying the molar mass or chemical equation under the Primitive tab of the Species tab; S32. Define the material properties of the membrane material. Create a new membrane material in the Materials tab. Specify the density, specific heat capacity, and thermal conductivity of the membrane material in the Thermal Properties tab. Create a new pyrolysis reaction in the Pyrolysis tab. In the Edit Pyrolysis Reaction window, you can obtain the pyrolysis rate by inputting the reference temperature, heating rate, pyrolysis angle, or pre-exponential factor and activation energy in the Rate tab. S33, specifying the reaction heat absorbed during the pyrolysis of the film material under the Byproducts tab of the Edit Pyrolysis Reaction window, and inputting different pyrolysis products and corresponding yields according to the pyrolysis products and yields of the film material determined in step S1; S34, according to the physical parameters of the building material in step S1, refer to the material property definition of the membrane material, define the building material properties, establish different surfaces based on the membrane material and the building material properties, and specify the material type and corresponding thickness under the Material Layers tab of the Surface tab; S35, assigning surface properties of the membrane surface and other components to the membrane surface and other components respectively.

8. The method for simulating the thermal decomposition of film materials and the concentration distribution of toxic gases in a fire scene according to claim 7, characterized in that: Step S4 includes: S41. Set a measuring point for temperature, volume fraction of toxic gas including pyrolysis products, and visibility at a height of 2 m from the evacuation exit; S42. Set simulation parameters, including air supply vents, smoke exhaust vents, sprinklers, ambient temperature, simulation duration and output parameters, and call the FDS program for calculation.

Images