Volume Expansion and Micro-Explosion of Combusting Iron Particles Analyzed Using Magnified Holographic Imaging

Abstract

Micron-sized iron powder is a promising energy carrier for the realization of large-scale storage and transportation. In-situ characterization of the combustion behaviors of iron particles is of great importance for understanding the combustion mechanism. In this work, magnified holographic imaging is employed to investigate the transient morphology and dynamics of iron particles (~85 µm diameter) during combustion. The volume expansion behavior of combusting iron particles is observed in situ for the first time. The particle volume increases to eight times of its initial volume within 0.14 ms, indicating that a hollow structure is generated due to the generation and expansion of the gas bubbles inside the particle. In addition, the micro-explosion behavior of both expanded and unexpanded particles are resolved with both high spatial and temporal resolutions. The ratio between the overall volume of the fragments (after explosion) and the volume of the expanded particle (before explosion) is around 0.2, which further validates the existence of gas bubbles inside the particles. Finally, based on the observed evolution of particle morphology during combustion, a hypothesis of gas bubble generation and expansion within the particle is proposed to explain the comprehensive combustion behaviors of iron particles.

Keywords: Iron particle combustion, magnified digital holography, particle morphology, volume expansion, micro-explosion