A mathematical model for vaporization of explosive thin film in active detection techniques

When detecting explosive traces by optical remote methods based on recording the vapors, it is essential to know the applicability limits of these techniques. The amount of a vaporized explosive depends on the vaporization kinetics, which, in turn, relies on the physicochemical properties of the explosive, film weight and thickness, ambient air temperature, and film temperature. In active detection techniques, the explosive film temperature on the surface of objects may be higher than the air temperature due to special heating devices. In this case, the questions on how the quantity of matter available for detection is about to change and how much energy has to be consumed to heat up the film can be answered by mathematical modeling. The mathematic model is based on the Hertz–Knudsen–Langmuir equation that describes the vaporization rate of matter with mass transfer between the surface and surrounding air, which is taken into account. In an elaboration of the mathematical model, we introduced previously the temperature difference between the film and ambient air, which is now taken into consideration. The basic parameters influencing the film vaporization rate, and their variation range, were identified. The kinetic parameters of vaporization of thin films of some explosives with a quantity of matter typical of a fingerprint were estimated. The weight of matter in air during vaporization of explosive thin films in a wide range of parameters under study was calculated. Conclusions were made of the applicability limits of the developed standoff detection methods for trace explosives.