Thermal self-ignition simulation of pyrotechnic composite in different conditions
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Abstract
The combustion and explosion accidents of pyrotechnic composite occur frequently. The study on the thermal hazard of large size of pyrotechnic composite by experiment method is dangerous. It would consume huge manpower and material resources. In this paper, a study was conducted to investigate the thermal hazards of pyrotechnic composite under different ambient temperature, size and packing condition by numerical simulation method. The results show that the thermal hazards of pyrotechnic composite increase with the increase in ambient temperature. The ignition temperature of pyrotechnic composite as the inherent property of pyrotechnic composite is not affected by packing condition and size. In the same conditions, the lower thermal conductivity of packing material is, the lower SADT of pyrotechnic composite is. With the increase in the size of the grain, its SADT decreases and ignition delay period shortens, and the ignition position shifts from the center to the top of the grain with lower thermal conductivity of packing material.
Keywords
Pyrotechnic composite Thermal hazard Packing Size Ambient temperatureList of symbols
- A
Pre-exponential factor (s^{−1})
- E
Activation energy (kJ mol^{−1})
- Q
Reaction heat (kJ kg^{−1})
- R
Gas constant (J mol^{−1} K^{−1})
- T
Temperature (K)
- T_{a}
Ambient temperature (K)
- f(α)
Reaction mechanism function
- f(x, y, z, t)
Known temperature function
- g(α)
Integral form of the reaction mechanism function
- g(x, y, z, t)
Heat flux function
- α
Degree of conversion (g)
- c
Specific heat (J kg^{−1} K^{−1})
- n
Reaction order
- ρ
Density (kg m^{−3})
- λ
Thermal conductivity coefficient (W m^{−1} K^{−1})
- χ
Coefficient of heat transfer (W m^{−2} K^{−1})
- \(q^{\prime\prime\prime}\)
Heat source (W m^{−3})
- Γ
Boundary of object
Introduction
In recent years, although the safety production situation of chemical industry has showed a certain improvement, the overall situation is still serious. Especially, the combustion accident of dangerous chemical warehouse in Tianjin port caused the severe personnel casualty and property loss and was a bitter, bloody lesson. It is well known that the sensitivity of energetic materials is related to the kind of energetic materials, size, ambient condition and so on. Several researches also have done a lot of work in recent years on the thermal stability and self-ignition process of energetic materials from those aspects.
Roduit [1, 2, 3, 4] carried out their study on the thermal stability for the energetic materials with multistage decomposition by finite element method. The thermal equilibrium state of the large samples was calculated. After that, he investigated the action process of a propellant at some temperature and analyzed the critical self-ignition temperature, critical size of tank and critical temperature of the propellant. The combustion mechanism and thermal runaway of hydroxyl ammonium nitrate (HAN) was studied by Liu [5]. The safe storage condition for small mass of HAN was determined by thermal explosion theory. The effects of size and natural convection on critical condition of HAN with the large size were calculated by computational fluid mechanics (CFD). Jiang et al. [6] confirmed the critical size of propellant powder at a certain temperature by simulating self-ignition process. Huang et al. [7] simulated self-accelerating decomposition temperature (SADT) of cumyl hydroperoxide (CHP) with different packing material. The results show that SADT of CHP decreased with the diameter of the tank and that it was almost unaffected by the thickness of the tank. Liu et al. [8] reported the thermal stability of fireworks. The thermal explosion model of fireworks with sphere and cylinder was built by using thermal explosion theory. Furthermore, the thermal stability of fireworks under different packing material, charge structure and charge type was simulated by advanced kinetics and technology solutions (AKTS) software. The critical temperature of pyrotechnic composite obtained by theory was excellent agreement with the numerical result. Xing [9] simulated the cook-off phenomenon of RDX (hexogen) and obtained the ignition position of RDX under different ambient temperature. Dong et al. [10] studied the deflagration to detonation transition in granular HMX (octogen) explosives under thermal ignition, and he introduced the conductive burning into the classical model during simulation. The result shows that the time to detonation increases with the decrease in particle diameter. Xu et al. [11] investigated the thermal stability of ammonium nitrate in high-temperature coal seam. They found that with temperature elevated, the organic materials were oxidized by HNO_{3}, which caused exothermic and gave rise to premature and misfire in blasting process. The effects of magnesium additive on the thermal behavior of Al/CuO thermites were verified by Sheikhpour et al. [12]. Addition of the magnesium powder did not initiate the reaction between micron-Al and nano-CuO, but this additive had a significant effect on the heat of reaction of nano-Al/nano-CuO system. Hoyani et al. [13] study finds that the thermal stability of HAN will be influenced during mixing metal ions like barium and calcium ions.
Pyrotechnic composite is dangerous and is easier to be ignited than other energetic materials by stimulation of energy during storage. How to reduce the accident probability and to improve the safety of pyrotechnic composite is one of the hot issues in the pyrotechnic composite research. The study on the self-ignition process of pyrotechnic composite is an important way to study its safety. Red pyrotechnic composite is a common stainer used in fireworks and tracer composite, in which safety would be affected by the safety of red pyrotechnic composite. In this paper, the safety of red pyrotechnic composite would be first studied, and the numerical simulation method will be used.
Self-ignition process simulation
Simulation conditions
- 1.
Effect of ambient temperature
- 2.
Effect of packing condition
- 3.
Effect of size
- 4.
Effect of heating rate
The ignition time and ignition delay period of the grain under different condition were determined. Ignition delay period is the time that the system temperature rises from ambient temperature to the ignition temperature. Ignition time includes two parts: ignition delay time and the time for the system temperature of material rises from the initial temperature to ambient temperature. The lowest ambient temperature of storage for energetic materials is an important parameter to evaluate safety of the energetic materials. According to the definition of SADT [15], SADT of energetic materials is approximately equal to its lowest ambient temperature of safety storage. Then, SADT of the red pyrotechnic composite under different condition also was calculated. The calculation time of numerical simulation is from 0 to 604,800 s.
Theoretical description
Parameters of materials
Material | ρ/kg m^{−3} | c/J kg^{−1} K^{−1} | λ/W m^{−1} K^{−1} | Q/kJ kg^{−1} |
---|---|---|---|---|
Red pyrotechnic composite | 1348 | 1423 | 0.19 | 2722 |
Low thermal conductivity packing materials | 550 | 2301 | 0.0357 | – |
High thermal conductivity packing materials | 8030 | 502 | 16.27 | – |
- 1.
Modeling and meshing the grain.
- 2.
Configuration physical properties of red pyrotechnic composition, packing material and the initial temperature of the system.
- 3.
Loading boundary conditions.
- 4.
Reaction thermokinetics.
There are three kinds of boundary conditions as follows [19].
Assuming the grain is set on the ground and directly exposed to the air. Then, there is a heat exchange between the top surface of the grain, the side of the grain and the air when heated. The boundary condition for the top surface and the side of the grain can be dealt with the third-type boundary condition. The heat transfer coefficient is about 5 W m^{−2} K^{−1}. The boundary condition for the bottom of the grain can be dealt with the first-type boundary condition.
Results and discussion
- 1.
Ambient temperature effect
Simulation results of the grain with no packing under different ambient temperatures
Ambient temperature/K | Ignition time/s | Ignition delay period/s | Ignition temperature/K | Ignition position/mm |
---|---|---|---|---|
650 | 551,487 | 5532 | 731.4 | 14 above center |
680 | 489,613 | 1809 | 730.8 | 28 above center |
700 | 331,939 | 566 | 732.3 | 54 above center |
- 2.
Packing condition effect
Simulation results for the grain at different packing conditions
Packing condition | Ignition time/s | Ignition temperature/K | SADT/K | Ignition position/mm |
---|---|---|---|---|
No packing | 331,939 | 731.1 | 647 | 54 above center |
Low thermal conductivity materials | 335,347 | 731.6 | 652 | 60 above center |
High thermal conductivity materials | 337,603 | 732.3 | 656 | 18 above center |
- 3.
Size effect
Simulation results with the lower thermal conductivity packing and different sizes
Size | Ignition delay period/s | SADT/K | Ignition position/mm |
---|---|---|---|
Φ60 × 120 mm | 855 | 661 | 32 above center |
Φ80 × 160 mm | 569 | 652 | 60 above center |
Φ100 × 200 mm | 382 | 646 | 86 above center |
- 4.
Heating rate effect
Conclusions
According to the results, the following conclusions would be obtained.
First, by the numerical simulation, the self-ignition processes of pyrotechnic composite is researched, the following parameters have been obtained, such as ignition delay period, ignition timing, ignition position and SADT, which could reflect the thermal hazards of pyrotechnic composite from different aspect.
Second, when the grain with the same size is heated at different ambient temperatures, the higher the ambient temperature is, the shorter ignition delay period of the grain is, and the more the ignition position closed to the top side of the grain. The ignition delay period and ignition position all verified that the thermal hazards of the grain increases as the ambient temperature rises. As the ambient temperature rises at a certain heating rate, the thermal hazards of the grain increase.
Third, according to SADT, it can be concluded that once pyrotechnic composite occurs as autothermic reaction, the thermal hazards of pyrotechnic composite packed by low thermal conductivity materials is higher than that packed by high thermal conductivity materials when pyrotechnic composite is accidently heated. Thus, it is necessary to keep fireworks at low ambient temperature and to avoid exposing to heat during its production, storage or transportation.
Fourth, at the same ambient temperature, once self-heating reaction of the pyrotechnic composite occurs, the grain with a big size will ignite firstly. The result shows that the thermal hazards of pyrotechnic composite packed by low thermal conductivity material increases with the increase in size. Thus, fireworks should avoid extensive stores.
Moreover, the research results are also available for guiding other pyrotechnic composition or energetic materials.
References
- 1.Roduit B, Borgeat C, Berger B, Folly P, Andres H, Schädeli U, Vogelsanger B. Up-scaling of DSC data of high energetic materials simulation of cook-off experiments. J Therm Anal Calorim. 2006;85:195–202.CrossRefGoogle Scholar
- 2.Roduit B, Borgeat C, Berger B, Folly P, Alonso B, Aebischer JN, Stoessel F. Advanced kinetic tools for the evaluation of decomposition reactions. J Therm Anal Calorim. 2005;80:229–36.CrossRefGoogle Scholar
- 3.Roduit B, Borgeat C, Berger B, Folly P, Alonso B, Aebischer JN. The prediction of thermal stability of self-reactive chemicals. J Therm Anal Calorim. 2005;80:91–102.CrossRefGoogle Scholar
- 4.Roduit B, Xia L, Folly P, Berger B, Mathieu J, Sarbach A, Andres H, Vogelsanger B. The simulation of the thermal behavior of energetic materials based on DSC and HFC signals. J Therm Anal Calorim. 2008;93:143–52.CrossRefGoogle Scholar
- 5.Liu L. The safe storage of autocatalytic reactive chemicals. Texas A&M University; 2009.Google Scholar
- 6.Jiang PX, Jiang JY, Chen MH. The numerical simulation of self-ignition for propellant. J Tsinghua Univ Nat Sci Ed. 1998;38:78–81.Google Scholar
- 7.Huang YJ, Xie CX, Cao JZ. The study on the thermal stability and thermal safety of cumyl hydroperoxide. China Saf Sci J. 2011;21:116–22.Google Scholar
- 8.Liu HY, Qian XM, Du ZM. Thermal explosion model and calculation of sphere fireworks and crackers. J Therm Anal Calorim. 2012;110:1029–36.CrossRefGoogle Scholar
- 9.Xing SJ. The study on the cook-off mechanism and 2D numerical simulation of condensed explosive. National University of Defense Technology; 2004.Google Scholar
- 10.Dong HF, Zan WT, Hong T, Zhang XL. Numerical simulation of deflagration to detonation transition in granular HMX explosives under thermal ignition. J Therm Anal Calorim. 2017;127:975–82.CrossRefGoogle Scholar
- 11.Xu ZX, Wang Q, Zhu X, Fu XQ. Thermal stability of ammonium nitrate in high-temperature coal seam. J Therm Anal Calorim. 2017;130:1171–9.CrossRefGoogle Scholar
- 12.Sheikhpour A, Hosseini SG, Tavangar S, Keshavarz MH. The influence of magnesium powder on the thermal behavior of Al–CuO thermite mixture. J Therm Anal Calorim. 2017;129:1847–54.CrossRefGoogle Scholar
- 13.Hoyani S, Patel R, Oommen C, Rajeev R. Thermal stability of hydroxyl ammonium nitrate (HAN). J Therm Anal Calorim. 2017;129:1083–93.CrossRefGoogle Scholar
- 14.Shi XJ. Study on the thermal stability and numerical simulation for series of pyrotechnic composite with strontium nitrate. Beijing: Beijing Institute of Technology; 2015.Google Scholar
- 15.Biasutti GS. History of accidents in the explosives. Private Publication; 1985.Google Scholar
- 16.Zhou GW. The study of fireworks. Beijing: Beijing Institute of Technology; 2010.Google Scholar
- 17.Liu HY. Study of fireworks storage thermal safety. Beijing: Beijing Institute of Technology; 2011.Google Scholar
- 18.Wang P. Cook-off experiment and numerical simulation. Beijing: Beijing Institute of Technology; 2009.Google Scholar
- 19.Zhang CH. Thermal analysis tutorial and examples. China Railway Publishing House; 2007.Google Scholar
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