Dynamic inversion method for heat release rate of longitudinal ventilation tunnel fire source

Abstract

The invention provides a dynamic inversion method for the heat release rate of a longitudinal ventilation tunnel fire source, and belongs to the technical field of tunnel fire protection. According to the dynamic inversion method for the heat release rate of the longitudinal ventilation tunnel fire source, three situations that the highest temperature of fire smoke flow can be detected, the temperature except the highest temperature of the fire smoke flow can be detected and actually measured data of the temperature without fire are considered, and different fire scenes can be coped with. Dynamic fire information in the tunnel is established in an inversion mode according to parameters such as tunnel longitudinal distribution temperature, flue gas countercurrent mass flow rate and countercurrent layer thickness which can be obtained and easily obtained in the tunnel, data support is provided for dynamic design of an escape and rescue scheme, and firefighters and trapped persons can carry out emergency rescue according to the dynamic development condition of the fire. And rescue and self-rescue can be carried out timely and scientifically.

Description

Technical Field

[0001] The invention relates to a dynamic inversion method for heat release rate of a fire source in a longitudinal ventilation tunnel, belonging to the technical field of tunnel fire protection. Background Art

[0002] Tunnels are long and narrow structures with few external exits, relatively closed spaces, and difficulty in natural smoke exhaust. In tunnel fire conditions, in order to determine the location of the fire source as early as possible and monitor the development of the fire, fire detectors are often installed in the tunnel. Commonly used in China are point-type photosensitive detection systems and linear temperature sensing detection systems. However, the main function of fire detectors is still to alarm fires, and the fire information they provide is relatively limited. In addition, the location of the fire source is also easily affected by the tunnel environment.

[0003] After a fire occurs in a tunnel, whether it is firefighters rescuing or trapped people saving themselves, being able to quickly and accurately understand the fire information on the scene and make scientific and reasonable escape and rescue decisions in a short time is of positive significance for protecting people's lives and property safety. Fire information needs to be reconstructed through data collected at the fire scene. The key to achieving dynamic fire reconstruction lies in correctly and dynamically inverting the heat release rate at the fire source under tunnel fire conditions. Summary of the invention

[0004] The present invention relates to a dynamic inversion method for the heat release rate of a fire source in a longitudinal ventilation tunnel. The method aims to dynamically invert the heat release rate of a fire source point based on the data of the longitudinal distribution temperature of the tunnel, the smoke backflow mass flow rate, the backflow layer thickness and the like collected under fire conditions, with the aid of the functional relationship between the above data and the heat release rate of the fire source, so as to obtain the dynamic fire situation of the fire tunnel and scientifically guide the escape and rescue on site.

[0005] Technical solution of the present invention:

[0006] Due to the limitation of the tunnel vault, under fire conditions, the rising plume is blocked when it reaches the vicinity of the vault, and the floating plume is stagnant vertically, thus forming a local impact zone. In the impact zone, due to the large pressure gradient, the fire smoke plume is driven to flow both upwind and downwind. When the smoke is in a relatively stable flow state, it can be considered that a balance has been reached, and a relatively stable smoke stratification will be formed under the vault, such as Figure 1 shown.

[0007] Based on the heat transfer theory and a large number of model test results, the maximum temperature calculation formula under tunnel fire conditions is derived as follows:

[0008]

[0009] In formula (1), ΔTmax is the maximum temperature rise, in K; Q is the fire heat release rate, in kilowatts (kW); u a b is the tunnel longitudinal ventilation wind speed, in meters per second (m / s); f0 is the radius of the fire source, in meters (m); H ef is the effective tunnel calculation height, in meters (m); u a ′ is the dimensionless ventilation speed;

[0010] It can be seen from formula (1) that ΔT max There is a functional relationship with Q, and Q can be expressed as ΔT max The functional relationship is (2), so the key to inverting the fire heat release rate is to obtain ΔT under fire conditions. ΔT max .

[0011]

[0012] In formula (2), ΔT max is the maximum temperature rise, in K; Q is the fire heat release rate, in kilowatts (kW); u a b is the tunnel longitudinal ventilation wind speed, in meters per second (m / s); f0 is the radius of the fire source, in meters (m); H ef is the effective tunnel calculation height, in meters (m); u a ′ is the dimensionless ventilation speed;

[0013] The heat release rate of a fire in a longitudinal ventilation tunnel of the present invention can be inverted by the following steps:

[0014] For longitudinal ventilation tunnels, when a fire occurs, there are three types of fire data that can be collected in the tunnel:

[0015] 1. Can detect the highest temperature of fire smoke

[0016] For tunnels with temperature sensor systems arranged along the longitudinal length of the tunnel, the maximum fire smoke temperature T max When ΔT max , and the heat release rate Q of the fire is calculated by formula (2):

[0017]

[0018] In formula (2), ΔT max is the maximum temperature rise, in K; Q is the fire heat release rate, in kilowatts (kW); u a b is the tunnel longitudinal ventilation wind speed, in meters per second (m / s); f0is the radius of the fire source, in meters (m); H ef is the effective tunnel calculation height, in meters (m); u a ′ is the dimensionless ventilation speed;

[0019] 2. Can detect temperatures other than the highest temperature of fire smoke

[0020] For tunnels with temperature sensor systems along the longitudinal length of the tunnel, when the temperature sensor near the fire source is burned out and the maximum temperature cannot be obtained, but the temperature sensors at both ends of the tunnel can still work normally, or under fire conditions, the highest temperature point appears between the two sensors, and the temperature collected by the sensor is not the highest temperature, K can be obtained by fitting the longitudinal temperature data collected by the temperature sensor, and ΔT can be inverted. max , use formula (2) to calculate the heat release rate Q of the fire source,

[0021] K and ΔT max The functional relationship between them can be expressed by formula (3):

[0022]

[0023] In formula (3), T is the smoke temperature, in Kelvin (K); T max is the maximum temperature of fire smoke, in Kelvin (K); T a is the atmospheric temperature, in Kelvin (K); ΔT is the temperature rise, in Kelvin (K); x is the distance between the temperature sensor and the fire source, in meters (m);

[0024] 3. No actual fire temperature data

[0025] When the longitudinal temperature sensor is burned out or no temperature sensor is installed in the tunnel, the longitudinal temperature data in the tunnel cannot be obtained, and the smoke counterflow mass flow rate m' is expressed as ΔT max The heat release rate Q of the fire source is further calculated using formula (2);

[0026] The flue gas mass flow rate is expressed by formula (4):

[0027] m'=ρu BF H s W (4)

[0028] In formula (4), m' is the flue gas counterflow mass flow rate, in kilograms per second (kg / s), and ρ is the combustion gas density, in kilograms per cubic meter (kg / m 3 ),u BF is the average wind speed of flue gas counterflow, in meters per second (m / s), H s is the thickness of the smoke layer, in meters (m), W is the tunnel width, in meters (m),

[0029] The average counterflow velocity of the smoke counterflow layer near the fire source is expressed by formula (5):

[0030]

[0031] In formula (5), f3 is the conversion coefficient, which represents the ratio of the horizontal counterflow velocity to the maximum vertical velocity of the smoke flow. When the tunnel aspect ratio is less than 2, the value is 0.20-0.64, with an average value of 0.36. When the tunnel aspect ratio is greater than or equal to 2, the value is 0.15-0.23, with an average value of 0.18. g is the acceleration of gravity, in meters per second. 2 (m / s 2 ), H is the tunnel height in meters (m), φ n is the mixing ratio, which represents the ratio of the mass flow rate of the fire combustion products in the smoke micro-clusters to the wind flow; u0 is the speed at which the combustion-generated gas leaves the surface of the combustible material, and its unit is meter per second (m / s).

[0032] Furthermore, when the tunnel fire is in a stable flow state, when the area around the combustible is relatively dry and there is no other evaporable substance, u0→0 is approximately true. If the density change during combustion is ignored, equation (4) can be simplified to equation (6):

[0033]

[0034] The present invention has the following advantages and effects:

[0035] 1. Under fire conditions, the heat release rate of the fire source point can be dynamically inverted using the actually measurable fire data, which can realize the dynamic acquisition of fire information at the fire scene and provide data support for the dynamic design of escape and rescue plans. Firefighters and trapped people can carry out rescue and self-rescue in a timely and scientific manner according to the dynamic development of the fire situation to ensure the safety of life and property.

[0036] 2. The present invention provides a dynamic inversion method for the heat release rate of a fire source under three different data acquisition conditions. It is suitable for situations where the maximum temperature of a fire smoke flow can be detected, where temperatures other than the maximum temperature of a fire smoke flow can be detected, and where there is no actual measured data on the fire temperature. It can cope with different fire scenes and greatly improves the flexibility of the design of a disaster prevention and rescue system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of smoke flow characteristics and analysis under tunnel fire conditions.

[0038] Figure 2 It is a schematic diagram of the dynamic inversion method of the heat release rate of the fire source under the tunnel fire condition of the present invention. DETAILED DESCRIPTION

[0039] Those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be considered to limit the scope of the present invention. If no specific techniques or conditions are specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product instructions. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased.

[0040] Due to the limitation of the tunnel vault, under fire conditions, the rising plume is blocked when it reaches the vicinity of the vault, and the floating plume is stagnant vertically, thus forming a local impact zone. In the impact zone, due to the large pressure gradient, the fire smoke plume is driven to flow both upwind and downwind. When the smoke is in a relatively stable flow state, it can be considered that a balance has been reached, and a relatively stable smoke stratification will be formed under the vault, such as Figure 1 shown.

[0041] Based on the heat transfer theory and a large number of model test results, the maximum temperature calculation formula under tunnel fire conditions is derived as follows:

[0042]

[0043] In formula (1), ΔT max is the maximum temperature rise, in K; Q is the fire heat release rate, in kilowatts (kW); u a b is the tunnel longitudinal ventilation wind speed, in meters per second (m / s); f0 is the radius of the fire source, in meters (m); H ef is the effective tunnel calculation height, in meters (m); u a ′ is the dimensionless ventilation speed;

[0044] It can be seen from formula (1) that ΔT max There is a functional relationship with Q, and Q can be expressed as ΔT max The functional relationship is (2), so the key to inverting the fire heat release rate is to obtain ΔT under fire conditions.

[0045] max

[0046]

[0047] In formula (2), ΔT max is the maximum temperature rise, in K; Q is the fire heat release rate, in kilowatts (kW); u a b is the tunnel longitudinal ventilation wind speed, in meters per second (m / s); f0 is the radius of the fire source, in meters (m); H ef is the effective tunnel calculation height, in meters (m); u a′ is the dimensionless ventilation speed;

[0048] The heat release rate of a fire in a longitudinal ventilation tunnel of the present invention can be inverted by the following steps, as shown in the flow chart: Figure 2 For longitudinal ventilation tunnels, when a fire occurs, there are three types of fire data that can be collected in the tunnel:

[0049] Example 1: The highest temperature of fire smoke can be detected

[0050] For tunnels with temperature sensor systems arranged along the longitudinal length of the tunnel, the maximum fire smoke temperature T max When ΔT max , and the heat release rate Q of the fire is calculated by formula (2):

[0051]

[0052] In formula (2), ΔT max is the maximum temperature rise, in K; Q is the fire heat release rate, in kilowatts (kW); u a b is the tunnel longitudinal ventilation wind speed, in meters per second (m / s); f0 is the radius of the fire source, in meters (m); H ef is the effective tunnel calculation height, in meters (m); u a ′ is the dimensionless ventilation speed;

[0053] Example 2: Detecting temperatures other than the highest temperature of fire smoke

[0054] For tunnels with temperature sensor systems along the longitudinal length of the tunnel, when the temperature sensor near the fire source is burned out and the maximum temperature cannot be obtained, but the temperature sensors at both ends of the tunnel can still work normally, or under fire conditions, the highest temperature point appears between the two sensors, and the temperature collected by the sensor is not the highest temperature, K can be obtained by fitting the longitudinal temperature data collected by the temperature sensor, and ΔT can be inverted. max , use formula (2) to calculate the heat release rate Q of the fire source,

[0055] K and ΔT max The functional relationship between them can be expressed by formula (3), (this formula is derived by Hu Longhua et al. based on the research results of predecessors (Delichatsios, 1981; Kunsch, 1998, 2002) to show that the longitudinal temperature distribution of the tunnel under the steady flow state conforms to the exponential law, and is verified by full-scale test data.)

[0056]

[0057] In formula (3), T is the smoke temperature, in Kelvin (K); Tmax is the maximum temperature of fire smoke, in Kelvin (K); T a is the atmospheric temperature, in Kelvin (K); ΔT is the temperature rise, in Kelvin (K); x is the distance between the temperature sensor and the fire source, in meters (m);

[0058] Example 3: No fire temperature measured data

[0059] When the longitudinal temperature sensor is burned out or no temperature sensor is installed in the tunnel, the longitudinal temperature data in the tunnel cannot be obtained, and the smoke counterflow mass flow rate m' is expressed as ΔT max The heat release rate Q of the fire source is further calculated using formula (2);

[0060] The flue gas mass flow rate is expressed by formula (4):

[0061] m'=ρu BF H s W (4)

[0062] In formula (4), m' is the flue gas counterflow mass flow rate, in kilograms per second (kg / s), and ρ is the combustion gas density, in kilograms per cubic meter (kg / m 3 ),u BF is the average wind speed of flue gas counterflow, in meters per second (m / s), H s is the thickness of the smoke layer, in meters (m), W is the tunnel width, in meters (m),

[0063] The average counterflow velocity of the smoke counterflow layer near the fire source is expressed by formula (5):

[0064]

[0065] In formula (5), f3 is the conversion coefficient, which represents the ratio of the horizontal counterflow velocity to the maximum vertical velocity of the smoke flow. When the tunnel aspect ratio is less than 2, the value is 0.20-0.64, with an average value of 0.36. When the tunnel aspect ratio is greater than or equal to 2, the value is 0.15-0.23, with an average value of 0.18. g is the acceleration of gravity, in meters per second. 2 (m / s 2 ), H is the tunnel height in meters (m), φ n is the mixing ratio, which represents the ratio of the mass flow rate of the fire combustion products in the smoke micro-clusters to the wind flow; u0 is the speed at which the combustion-generated gas leaves the surface of the combustible material, and its unit is meter per second (m / s).

[0066] When the tunnel fire is burning in a stable flow state, when the area around the combustible is relatively dry and there is no other evaporable substance, it is approximately u0→0. Ignoring the density change during combustion, equation (4) can be simplified to equation (6):

[0067]

[0068] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A dynamic inversion method for heat release rate of fire source in longitudinal ventilation tunnel, characterized by: Follow these steps: For longitudinal ventilation tunnels, when a fire occurs, there are three types of fire data that can be collected in the tunnel: 1) The highest temperature of fire smoke can be detected For tunnels with temperature sensor systems distributed along the longitudinal length of the tunnel, the maximum smoke temperature T max When ΔT max , and the heat release rate Q of the fire is obtained by inversion of formula (1): In formula (1), ΔT max is the maximum temperature rise, in Kelvin; Q is the fire heat release rate, in kilowatts kW; u a b is the tunnel longitudinal ventilation wind speed, in meters per second (m / s); f0 is the radius of the fire source, in meters; H ef is the effective tunnel calculation height, in meters; u a ′ is the dimensionless ventilation speed; Express Q as ΔT max The functional relationship of is (2), In formula (2), ΔT max is the maximum temperature rise, in K; Q is the fire heat release rate, in kilowatts kW; u a b is the tunnel longitudinal ventilation wind speed, in meters per second (m / s); f0 is the radius of the fire source, in meters; H ef is the effective tunnel calculation height, in meters; u a ′ is the dimensionless ventilation speed; 2) Can detect temperatures other than the highest temperature of fire smoke For tunnels with temperature sensor systems along the longitudinal length of the tunnel, when the temperature sensor near the fire source is burned out and the maximum temperature cannot be obtained, but the temperature sensors at both ends of the tunnel can still work normally, or under fire conditions, the highest temperature point appears between the two sensors, and the temperature collected by the sensor is not the highest temperature, K can be obtained by fitting the longitudinal temperature data collected by the temperature sensor, and ΔT can be inverted. max , use formula (2) to calculate the heat release rate Q of the fire source, K and ΔT max The functional relationship between them can be expressed by formula (3): In formula (3), T is the smoke temperature, the unit is Kelvin; T max is the maximum temperature of fire smoke, in Kelvin; T a is the atmospheric temperature in Kelvin; ΔT is the temperature rise in Kelvin; x is the distance between the temperature sensor and the fire source in meters. 3) No actual fire temperature data When the longitudinal temperature sensor is burned out or no temperature sensor is installed in the tunnel, the longitudinal temperature data in the tunnel cannot be obtained, and the smoke counterflow mass flow rate m' is expressed as ΔT max The heat release rate Q of the fire source is further calculated using formula (2); The flue gas mass flow rate is expressed by formula (4): m'=ρu BF H s W (4) In formula (4), m' is the flue gas counterflow mass flow rate, in kilograms per second (kg / s), and ρ is the combustion gas density, in kilograms per cubic meter (kg / m 3 ),u BF is the average wind speed of smoke counterflow, in meters per second (m / s), H s is the thickness of the smoke layer, in meters, W is the width of the tunnel, in meters, The average counterflow velocity of the smoke counterflow layer near the fire source is expressed by formula (5): In formula (5), f3 is the conversion coefficient, which represents the ratio of the horizontal counterflow velocity to the maximum vertical velocity of the smoke flow. When the tunnel aspect ratio is less than 2, the value is 0.20-0.64, with an average value of 0.

36. When the tunnel aspect ratio is greater than or equal to 2, the value is 0.15-0.23, with an average value of 0.

18. g is the acceleration of gravity, in meters per second. 2 m / s 2 , H is the tunnel height in meters, φ n is the mixing ratio, which represents the ratio of the mass flow rate of the fire combustion products in the smoke micro-clusters to the wind flow; u0 is the speed at which the combustion-generated gas leaves the surface of the combustible material, and its unit is meter per second (m / s).

2. The dynamic inversion method for heat release rate of fire source in longitudinal ventilation tunnel according to claim 1 is characterized by: When the tunnel fire is burning in a stable flow state, when the area around the combustible is relatively dry and there is no other evaporable substance, it is approximately u0→0. Ignoring the density change during combustion, equation (4) can be simplified to equation (6):

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