Influence Of variable heat transfer coefficient of fireworks and crackers on thermal explosion critical ambient temperature and ttime to ignition

Aim of this study was to investigate influence of heat transfer coefficient of fireworks and crackers on thermal explosion, critical ambient temperature and ignition time. It is proposed that heat transfer coefficient is power function of temperature, mathematical model to describe thermal explosion, steady-state and unsteady-state of finite cylindrical fireworks and crackers with complex shell structures are established. Models have been based on two-dimensional steady-state thermal explosion theory. The influence of variable heat transfer coefficient on thermal explosion critical ambient temperature and time to ignition are analyzed. When heat transfer coefficient is changing with temperature and in the condition of natural convection heat transfer, critical ambient temperature lessen, thermal explosion time to ignition shorten. If ambient temperature is close to critical ambient temperature, the influence of variable heat transfer coefficient on ignition time will be large. For firework with inner barrel, the critical ambient temperature of propellant is 463.88 K and ignition time is 4054.9 s. At ambient temperature 466 K, and with constant heat transfer coefficient critical temperatue is 0.26 K lower and time to ignition 450.8 s less smaller. The calculation results show that the influence of variable heat transfer coefficient on thermal explosion time to ignition is greater in this example. Therefore, the effect of variable heat transfer coefficient should be considered into thermal safety evaluation of fireworks to reduce potential safety hazard.