Method for calculating injection time of alkyl halide fire extinguishing system

Abstract

The invention belongs to the technical field of fluid mechanics, and particularly relates to a haloalkane fire extinguishing system injection time calculation method which comprises the following steps: step 1, inputting fire extinguisher dosage, pipeline inner diameter and the number n of nozzles mounted at the downstream of a pipeline; 2, calculating the average design flow of the pipeline according to the inner diameter of the pipeline; 3, the average design flow of the nozzle is calculated; 4, theoretical fire extinguishing injection time is calculated; and 5, correcting the theoretical fire extinguishing injection time to obtain the final fire extinguishing injection time.

Description

Technical Field

[0001] The invention belongs to the technical field of fluid mechanics, and in particular relates to a method for calculating the injection time of a halon fire extinguishing system. Background Art

[0002] The injection time of the Halon 1301 fire extinguishing system is a key technical parameter for timely extinguishing fires. GB50163 defines the injection time of fire extinguishing agents as the time from when all nozzles start to spray liquid-based fire extinguishing agents to when one of the nozzles starts to spray gas, and stipulates that the injection time is no more than 10 seconds. GJB3275 and the US military standard stipulate that the injection time is no more than 1 second. The relevant Soviet standards stipulate that the injection time is no more than 3 seconds.

[0003] For the Halon 1301 fire extinguishing system, the spraying time is neither the longer the better nor the shorter the better. If the time is too long, the prescribed fire extinguishing concentration cannot be reached within a certain period of time; if the spraying time is too short, the fire extinguishing agent will leak faster and the prescribed fire extinguishing concentration cannot be reached within a certain period of time. The decomposition products of the 1301 fire extinguishing agent are related to the time of contact with the flame (that is, the toxic products are proportional to the spraying time). Shortening the spraying time can minimize the concentration of the decomposition products, thereby reducing damage. The spraying time must be an appropriate value that can achieve the fire extinguishing effect and reduce the decomposition products of the fire extinguishing agent.

[0004] When designing a fire extinguishing system, the designer needs to determine the injection time, which must meet the requirements of the corresponding specifications. If the injection time does not meet the requirements, the design parameters of the fire extinguishing system need to be adjusted.

[0005] Since the release of 1301 fire extinguishing agent is driven by the expansion of gas, the flow rate gradually decreases with time during the release process. In the process of releasing halon 1301, due to the continuous decrease in pressure, the nitrogen dissolved in the liquid halon 1301 will be partially separated, so the 1301 fire extinguishing agent presents an obvious two-phase flow state in the pipeline. It can be concluded that the calculation of the flow characteristics of the fire extinguishing agent in the pipeline is more complicated than the calculation of the fluid in the single-phase (single liquid or gas) state. For example, Li Shijiu published "Fluid Mechanics Analysis and Calculation of the Spray Time of Liquid Fire Extinguishing Agent in Automatic Fire Fighting System" in the first issue of "Journal of Northeast Polytechnic University" in 1982, analyzing and calculating the spray time of fire extinguishing agent through complex fluid mechanics. Zou Shuning analyzed the spray process in "Derivation of the Verification Formula of Halon 1211 Spray Time" in 1990 according to the design specifications of the halon 1211 fire extinguishing system and established a set of complex calculation formulas. Complex two-phase fluid calculations are very difficult for engineering and technical personnel, which is not conducive to their timely grasp of the key performance parameters of the fire extinguishing system design, and therefore they cannot determine whether the system solution is the optimal solution. Summary of the invention

[0006] Purpose of the invention: To provide a method for calculating the injection time of a halogenated fire extinguishing system, so that fire extinguishing system designers can timely understand whether the system performance parameters meet the requirements during the system design process.

[0007] Technical solution:

[0008] A method for calculating the injection time of a halon fire extinguishing system comprises the following steps:

[0009] Step 1: Input the fire extinguisher dosage, the inner diameter of the pipe, and the number of nozzles n installed downstream of the pipe;

[0010] Step 2: Calculate the average design flow rate of the pipeline based on the inner diameter of the pipeline;

[0011] Step 3: Calculate the average design flow rate of the nozzle;

[0012] Step 4: Calculate the theoretical fire extinguishing spray time;

[0013] Step 5: Correct the theoretical fire extinguishing spray time to obtain the final fire extinguishing spray time.

[0014] Furthermore, in step 2, the calculation formula of the average design flow rate Q of the pipeline is as follows:

[0015] Q=KD 2

[0016] D is the inner diameter of the pipe;

[0017] K is a coefficient, ranging from 0.31 to 0.93, and is negatively correlated with the inner diameter of the pipe.

[0018] Further, in step 3, the calculation formula of the nozzle average design flow rate qi is as follows:

[0019] qi=Q / n.

[0020] Further, in step 4, the fire extinguishing spray time Td is calculated as follows:

[0021] Td = Mass / qi;

[0022] Mass is the amount of halogenated hydrocarbons that need to be sprayed from a single nozzle;

[0023] The amount of Halon required to be discharged from a single nozzle is averaged based on the extinguisher dose and the number of nozzles.

[0024] Further, in step 5, the correction formula is as follows:

[0025] T = α * Td;

[0026] α is the correction coefficient, ranging from 0.6 to 0.95;

[0027] T is the final fire extinguishing spray time.

[0028] Further, in step 5, the correction coefficient is obtained as follows:

[0029] Carry out fire extinguishing tests on fire extinguishing systems of different configurations. After multiple tests, take the longest injection time as the measured fire extinguishing agent injection time of the fire extinguishing system of the corresponding configuration;

[0030] Calculate theoretical extinguishing agent injection time based on different configurations of fire extinguishing systems;

[0031] With the inner diameter of the pipe of the fire extinguishing system of different configurations as the X-axis and the measured fire extinguishing agent injection time as Y1, draw the measured fire extinguishing injection curve 1;

[0032] With the inner diameter of the pipe of the fire extinguishing system of different configurations as the X-axis and the theoretical fire extinguishing agent injection time as Y2, the measured fire extinguishing injection curve 2 is drawn;

[0033] Taking curve 1 as the reference curve, linear fitting is performed on curve 2 so that curve 2 coincides with curve 1. According to the slope of the linear fitting, the slope is the correction coefficient α.

[0034] Furthermore, linear fitting is performed according to the intervals of the inner diameter of the pipeline, which are divided into 0-10 mm, 11 mm-15 mm, 16 mm-20 mm, 21-40 mm, and greater than 40 mm.

[0035] Further, the method is applicable to a balanced pipe network fire extinguishing system;

[0036] The balanced pipe network means that the pipe length of each nozzle fire extinguisher is greater than 90% of the maximum pipe length and the average design flow of each nozzle is equal.

[0037] Furthermore, in step 2, if the pipeline is divided into a main pipe and a branch pipe, the average design flow of the main pipe is calculated according to the formula in step 2, and then the average design flow of the branch pipe is obtained by averaging the number of branches.

[0038] A computer-readable storage medium stores a computer program, which, when executed by a processor of a computer, enables the computer to execute the method for calculating the injection time of a halogenated fire extinguishing system.

[0039] Beneficial Effects

[0040] This method can be applied to the system design of the Halon 1301 fire extinguishing system. For example, in the system design stage, this method can enable engineering and technical personnel to timely grasp the key performance parameters of the fire extinguishing system design and determine whether the system solution is the optimal solution. For example, for a finalized system, when it is impossible to measure the injection time of the fire extinguishing system, this method can obtain the system injection time. It can be seen that this method has the advantages of improving system design efficiency, being beneficial to environmental protection (Halon 1301 fire extinguishing agent seriously damages the ozone layer, and a certain concentration of Halon 1301 fire extinguishing agent has a certain toxicity. The Montreal Protocol stipulates that such items must be stopped from use), reducing labor intensity and system development costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is the schematic diagram of the Halon 1301 fire extinguishing system;

[0042] In the figure, 1 is a fire extinguisher bottle, 2 is a release device, 3 is a fire extinguishing pipeline and its components, 4 is a fire extinguishing button, 5 is a cable, and 6 is a fire zone. DETAILED DESCRIPTION

[0043] The Halon1301 fire extinguishing system consists of a fire extinguishing bottle 1, a fire extinguishing agent release device 2, a fire extinguishing pipeline and its components 3, a fire extinguishing button 4, and a cable 5. The fire extinguishing agent bottle stores fire extinguishing agents whose storage pressure and weight meet the fire extinguishing requirements; the fire extinguishing pipeline and its components are used to transport the fire extinguishing agent to the fire area, and the fire extinguishing agent release device is used to release the fire extinguishing agent; the fire extinguishing button is used to energize the fire extinguishing agent release device, detonate the fire extinguishing agent release device, and release the fire extinguishing agent from the release device. The basic working principle of the fire extinguishing system is: the operator confirms that the fire area 6 is on fire, and presses the fire extinguishing button 4 to detonate the release device 2 on the fire extinguishing bottle 1 to release the fire extinguishing agent to the designated fire area 6 for fire extinguishing. See the system schematic diagram. Figure 1 .

[0044] The present invention is to calculate the time from when all nozzles of the fire extinguishing pipeline start to spray the liquid-based fire extinguishing agent to when one of the nozzles starts to spray gas in the longest fire extinguishing pipeline. The measurement of the spraying time is to count from when the fire extinguishing agent leaves the end of the pipeline until the total amount of the required fire extinguishing agent is sprayed. The premise of the present invention is that the fire extinguishing agent metering and filling pressure, the length and diameter of the fire extinguishing pipeline are known. The calculation method of the present invention is based on the fact that the gas and liquid two-phase fluid in the pipeline is in a turbulent state. If it is in a non-turbulent state, the method is not applicable.

[0045] The present invention provides a balanced pipe network, and the balanced pipe network should comply with the following provisions:

[0046] The length of the pipe from the fire extinguisher bottle to each nozzle should be greater than 90% of the longest pipe length; the pipe length is the equivalent length of the pipe taking into account the adapter

[0047] The average design flow rate from each nozzle should be equal.

[0048] The specific implementation steps of the present invention are as follows:

[0049] Determine known conditions: input extinguishing agent dosage, branch pipe outer diameter and branch pipe length, main pipe outer diameter and main pipe length.

[0050] Length, wall thickness, number of nozzles. If there is no branch, the relevant quantity of the branch is 0;

[0051] S102: Determine whether the designed pipe network system is balanced. If it does not meet the requirements of balanced layout, it is recommended to redesign the pipe network system.

[0052] Adjust the pipe network layout. If it is a balanced layout, do the following;

[0053] S103: Calculate the average design flow of the main pipe

[0054] The average design flow rate of Halon 1301 in the corresponding main pipeline;

[0055] Q i-j =KD 2

[0056] Q i-j The corresponding average design flow rate of halogenated hydrocarbon 1301 in the main pipeline is kg / s;

[0057] D Pipe inner diameter mm;

[0058] K coefficient ranges from 0.31 to 0.93.

[0059] S104: Calculate the average design flow rate of the branch pipe Q_branch

[0060] The average design flow rate of the branch pipe can be calculated according to the following formula

[0061] Q_branch = Qi-j / m;

[0062] m is the number of branches of the trunk;

[0063] S105: Calculate the design flow rate qi of the nozzle;

[0064]

[0065] Q_branch = n*qi;

[0066] Q_branch: S104 has been calculated;

[0067] nThe number of nozzles installed downstream of the calculation branch pipe;

[0068] The design flow rate of the i-th nozzle is kg / s.

[0069] S106: Calculate the time of fire extinguishing agent injection

[0070] Td = Mass / qi;

[0071] Td extinguishing agent injection time, Mass single nozzle needs to spray halogenated hydrocarbon 1301 (kg), this value is related to the filling dosage of the fire extinguishing bottle. If there is no branch, it is the extinguishing agent dosage of the fire extinguishing bottle. If there is a branch, the extinguishing agent dosage is averaged according to the principle of balanced pipe network;

[0072] S106: Corrected the fire extinguishing spray time of S106

[0073] In the test, the fire extinguishing agent injection test was carried out on different pipeline configurations (outer diameter, wall thickness, length, number of branches, number of nozzles) to obtain the fire extinguishing agent injection time. The specific steps for curve correction are as follows:

[0074] 1) Carry out fire extinguishing agent injection test on the fire extinguishing pipeline of the same configuration. After multiple tests, take the longest time as the measured fire extinguishing agent injection time of the configuration;

[0075] 2) Carry out fire extinguishing agent injection test on the combination of fire extinguishing pipelines of different configurations. After multiple tests, take the longest time as the measured fire extinguishing agent injection time of the configuration;

[0076] 3) Theoretically calculate the extinguishing agent injection time based on different configurations;

[0077] 4) Taking the parameters of different pipeline configurations as the X-axis (such as the inner diameter) and the measured fire extinguishing agent injection time as Y1, a measured fire extinguishing agent injection time curve 1 is formed, and curve 1 is used as a reference curve;

[0078] 5) Taking the parameters of different pipeline configurations as the X-axis (such as the inner diameter), the theoretically calculated fire extinguishing spray time is Y2, and forming a theoretically calculated fire extinguishing spray time curve 2;

[0079] 6) Take curve 1 as the reference curve (true value curve), divide it into intervals according to the inner diameter of the pipeline configuration (such as 0-10mm, 11mm-15mm, 16mm-20mm, 21-40mm, greater than 40mm), and perform linear fitting on curve 2 according to the intervals, so that curve 2 and curve 1 basically coincide. The slope α of the linear fitting ranges from 0.6 to 0.95.

[0080] T = α * Td;

[0081] Y11=αY21

[0082] This application does not require the calculation of the fluid characteristics of the complex two-phase flow in the pipeline; the filling pressure range of the fire extinguisher bottle is wide, and the typical filling pressure is 2.5MPa and 4.2MPa; the filling density range of the fire extinguisher bottle is large, and the density is 600kg / m3~1125kg / m3;

[0083] Embodiment 1

[0084] The results obtained by this method are basically consistent with the actual test data. Table 1 shows the results when other parameters of the fire extinguishing system are the same but the dosage of the fire extinguishing agent is different;

[0085] Table 1

[0086]

[0087] Take the calculation of No. 2 in Table 1 as an example. The fire extinguishing agent dosage is 1.89kg, the filling pressure of the fire extinguisher bottle is 4.2MPa, the filling density of the fire extinguisher bottle is 800kg / m3, the main pipe length of the fire extinguishing pipeline is 4 meters, the outer diameter is 18mm, the branch pipe length is 3 meters, the outer diameter is 12mm, and the wall thickness is 1mm. The pipeline system has 2 branches and a nozzle.

[0088] a) Calculate the average design flow

[0089] The average design flow rate of the main pipe is calculated by the formula to be 1.1378 kg / s. After K is taken as 0.53, the average design flow rate of the main pipe is 0.603 kg / s, and the average design flow rate of the branch pipe is 0.302 kg / s.

[0090] b) Calculate the injection time

[0091] The injection time is calculated by the formula: 3.1343s, α is taken as 0.81, and the corrected time is 2.54s.

[0092] Embodiment 2

[0093] The results obtained by this method are basically consistent with the calculation data published abroad. Table 2 shows the results when other parameters of the fire extinguishing system are the same but the outer diameter and wall thickness of the pipe are different.

[0094] Table 2

[0095]

[0096] Take the calculation of No. 3 in Table 2 as an example, the fire extinguishing agent dosage is 1.2kg, the filling pressure of the fire extinguishing bottle is 4.2MPa, the filling density of the fire extinguishing bottle is 800kg / m3, the main pipe length of the fire extinguishing pipeline is 2 meters, the outer diameter is 16mm, there is no branch pipe, the wall thickness is 1mm, and the pipeline system has one nozzle. Table 2 is the calculation result based on the same filling state of the fire extinguishing bottle.

[0097] a) Calculate the average design flow

[0098] The average design flow rate of the main pipe is calculated by the formula to be 0.8711 kg / s. After K is taken as 0.73, the average design flow rate of the main pipe is 0.6359 kg / s.

[0099] b) Calculate the injection time

[0100] The injection time is calculated by the formula: 1.887s, α is taken as 0.899, and the corrected time is 1.696s.

Claims

1. A method for calculating the injection time of a halon fire extinguishing system, characterized in that: The method comprises the following steps: Step 1: Input the fire extinguisher dosage, the inner diameter of the pipe, and the number of nozzles n installed downstream of the pipe; Step 2: Calculate the average design flow rate of the pipeline based on the inner diameter of the pipeline; Step 3: Calculate the average design flow rate of the nozzle; Step 4: Calculate the theoretical fire extinguishing spray time; Step 5: Correct the theoretical fire extinguishing spray time to obtain the final fire extinguishing spray time.

2. The method according to claim 1, characterized in that: In step 2, the calculation formula for the average design flow rate Q of the pipeline is as follows: Q=KD 2 D is the inner diameter of the pipe; K is a coefficient, ranging from 0.31 to 0.93, and is negatively correlated with the inner diameter of the pipe.

3. The method according to claim 2, characterized in that: In step 3, the calculation formula of the nozzle average design flow rate qi is as follows: qi=Q / n.

4. The method according to claim 3, characterized in that: In step 4, the fire extinguishing spray time Td is calculated as follows: Td = Mass / qi; Mass is the amount of halogenated hydrocarbons that need to be sprayed from a single nozzle; The amount of Halon required to be discharged from a single nozzle is averaged based on the extinguisher dose and the number of nozzles.

5. The method according to claim 4, characterized in that: In step 5, the correction formula is as follows: T = α * Td; α is the correction coefficient, ranging from 0.6 to 0.95; T is the final fire extinguishing spray time.

6. The method according to claim 5, characterized in that: In step 5, the correction coefficient is obtained as follows: Carry out fire extinguishing tests on fire extinguishing systems of different configurations. After multiple tests, take the longest injection time as the measured fire extinguishing agent injection time of the fire extinguishing system of the corresponding configuration; Calculate theoretical extinguishing agent injection time based on different configurations of fire extinguishing systems; With the inner diameter of the pipe of the fire extinguishing system of different configurations as the X-axis and the measured fire extinguishing agent injection time as Y1, draw the measured fire extinguishing injection curve 1; With the inner diameter of the pipe of the fire extinguishing system of different configurations as the X-axis and the theoretical fire extinguishing agent injection time as Y2, the measured fire extinguishing injection curve 2 is drawn; Taking curve 1 as the reference curve, linear fitting is performed on curve 2 so that curve 2 coincides with curve 1. According to the slope of the linear fitting, the slope is the correction coefficient α.

7. The method according to claim 6, characterized in that: When linear fitting is performed, fitting is performed according to the inner diameter of the pipe, which is divided into intervals of 0-10mm, 11mm-15mm, 16mm-20mm, 21-40mm, and greater than 40mm.

8. The method according to claim 1, characterized in that: The method is applicable to a balanced pipe network fire extinguishing system; The balanced pipe network means that the pipe length of each nozzle fire extinguisher is greater than 90% of the maximum pipe length and the average design flow of each nozzle is equal.

9. The method according to claim 2, characterized in that: In the step 2, if the pipeline is divided into a main pipe and a branch pipe, the average design flow of the main pipe is calculated according to the formula in step 2, and then the average design flow of the branch pipe is obtained by averaging the number of branches.

10. A computer-readable storage medium, characterized in that: A computer program is stored thereon, and when the computer program is executed by a processor of a computer, the computer is enabled to execute the method for calculating the injection time of a halogenated fire extinguishing system according to any one of claims 1 to 9.

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