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

Olga B Kudryashova,Sergey S Titov,Alexander B Vorozhtsov,Anatoly A Pavlenko

doi:10.1063/5.0053736

Abstract

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.

Highlights

Due to the increased threat of terrorist attacks, the issue of timely detection of explosives remains highly relevant.1 In particular, the research direction concerned with standoff detection of explosives and hazardous agents is developing
We previously introduced a mathematical model for the vaporization of an explosive thin film and discovered basic parameters influencing this process, such as ambient temperature and phase transition heat, with the film temperature considered to be equal to the ambient temperature
Analytical expressions were derived for the time courses of the vapor mass, maximum film thickness, minimum film temperature, and the time of vaporization to the specified scitation.org/journal/adv mass of vapors detectable

Summary

INTRODUCTION

Due to the increased threat of terrorist attacks, the issue of timely detection of explosives remains highly relevant. In particular, the research direction concerned with standoff detection of explosives and hazardous agents is developing. Researchers and engineers seek to develop systems that would be able to remotely detect trace amounts of an explosive, for example, when going through inspection on transport or in crowded places.4,5 In this case, it is impossible to use conventional methods for detection and identification of substances based on sampling (such as solid phase microextraction). The technique of standoff observation of objects based on optical spectral analysis and image recognition has been rapidly developed. The resulting multidimensional spatial–spectral image obtained as a result of registration is called a multi- or hyperspectral image or “hypercube” of data This is a set of data formed by the intensities of the light signal scattered (emitted) by the two-dimensional surface of the object. Based on the mathematical model, we sought to establish the conditions under which the vapors of the matter when explosive traces vaporize would suffice for their detection

Assumptions

Basic equations

Dimensionless groups

RESULTS AND DISCUSSION

CONCLUSIONS